UBC Theses and Dissertations

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UBC Theses and Dissertations

Comparison of the evolution and expression of life history traits in stable and fluctuating environments… Stearns, Stephen Curtis 1975

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A COMPARISON OF THE EVOLUTION AND E X P R E S S I O N OF L I F E HISTORY T R A I T S I N S T A B L E AND F L U C T U A T I N G ENVIRONMENTS: GAMBUSIA A F F I N I S I N HAWAII STEPHEN C U R T I S STEARNS B . S . , Y a l e U n i v e r s i t y , 1967 M . S . , U n i v e r s i t y o f W i s c o n s i n , 1971 A T H E S I S S U B M I T T E D IN P A R T I A L F U L F I L L M E N T OF T H E REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY We a c c e p t t h i s t h e s i s a s c o n f o r m i n g t o t h e r e q u i r e d s t a n d a r d THE U N I V E R S I T Y OF B R I T I S H COLUMBIA by i n t h e D e p a r t m e n t f l o q y o Zoo N o v e m b e r , 1 975 i In p r e s e n t i n g t h i s t h e s i s in p a r t i a l f u l f i l m e n t o f the requirements f o r an advanced degree at the U n i v e r s i t y of B r i t i s h Columbia, I agree that the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e fo r reference and study. I f u r t h e r agree t h a t permiss ion fo r e x t e n s i v e copying o f t h i s t h e s i s f o r s c h o l a r l y purposes may be granted by the Head of my Department or by h i s r e p r e s e n t a t i v e s . It i s understood that copying or p u b l i c a t i o n of t h i s t h e s i s f o r f i n a n c i a l ga in s h a l l not be a l lowed without my w r i t t e n p e r m i s s i o n . Department of Zoology The U n i v e r s i t y of B r i t i s h Columbia 2075 Wesbrook P l a c e Vancouver, Canada V6T 1W5 Date Ll AJ i A b s t r a c t How do environmental f l u c t u a t i o n s a f f e c t the e v o l u t i o n of l i f e h i s t o r y t r a i t s ? Advocates of r - and K - s e l e c t i o n c l a i m t h a t f l u c t u a t i o n s s e l e c t f o r e a r l y maturity, l a r g e r e p r o d u c t i v e e f f o r t s , and many young. Advocates of bet-hedging c l a i m t h a t they can s e l e c t f o r delayed maturation, s m a l l r e p r o d u c t i v e e f f o r t s , and few young. In t e s t i n g these i d e a s , I worked with two s p e c i e s of p o e c i l i i d f i s h i n t r o d u c e d to r e s e r v o i r s i n Hawaii: Gambusia a f f i n i s and P o e c i l i a r e t i c u l a t a . In some r e s e r v o i r s , water l e v e l s f l u c t u a t e d . In o t h e r s , they d i d not. I concluded t h a t (1) Gambusia and P o e c i l i a have undergone an e v o l u t i o n a r y experiment i n Hawaii l a s t i n g 50-70 yea r s , and t h a t (2) the experiment was f a i r l y w e l l c o n t r o l l e d . I compared f i s h from s t a b l e and f l u c t u a t i n g r e s e r v o i r s f o r t h r e e t r a i t s : s i z e at maturity, number of young, and r e p r o d u c t i v e e f f o r t s . (3) Eight of ,9 i n t r a s p e c i f i c d i f f e r e n c e s i n r e p r o d u c t i v e t r a i t s between s t a b l e and f l u c t u a t i n g r e s e r v o i r s were i n the d i r e c t i o n p r e d i c t e d by r - and K - s e l e c t i o n , but 7 of these 9 d i f f e r e n c e s were not s i g n i f i c a n t . (4) There were no i n t r a s p e c i f i c d i f f e r e n c e s i n s i z e at maturity, which r - and K-s e l e c t i o n had p r e d i c t e d should be l a r g e s t d i f f e r e n c e s of a l l . (5) P o e c i l i a had more young, s m a l l e r young, and made l a r g e r r e p r o d u c t i v e e f f o r t s i n the f l u c t u a t i n g r e s e r v o i r s , as p r e d i c t e d by r - and K - s e l e c t i o n . (6) Although P o e c i l i a has r e p r o d u c t i v e t r a i t s , r e l a t i v e to Gambusia, which would be c a l l e d r - s e l e c t e d , Gambusia, not P o e c i l i a , dominated the f l u c t u a t i n g r e s e r v o i r s , and P o e c i l i a d i d b e t t e r i n the s t a b l e r e s e r v o i r s . I suggested that Gambusia was pre-adapted f o r f l u c t u a t i n g r e s e r v o i r s . Gambusia females produce female young with a wide range i n ages at maturity (2.5-7 months). P o e c i l i a females, whose young mature at 2.3 to 3.5 months, cannot do t h i s . By i n s u r i n g that some progeny always s u r v i v e long drawdowns, t h i s t r a i t uncouples Gambusia from the water l e v e l f l u c t u a t i o n s . I concluded; (7) Reproductive t r a i t s need not be a s s o c i a t e d i n the p a r t i c u l a r groupings t h a t recent e v o l u t i o n a r y theory p r e d i c t s . P o e c i l i a , f o r example, showed l a r g e d i f f e r e n c e s i n number of young and r e p r o d u c t i v e e f f o r t s , but no d i f f e r e n c e s i n s i z e at m a t u r i t y . (8) The t r e n d s d i s c u s s e d by r - and K - s e l e c t i o n i s t s may be i n c o r p o r a t e d i n t o a r e p r o d u c t i v e l y polymorphic p o p u l a t i o n as part of a bet-hedging a d a p t a t i o n . (9) By doing m u l t i p l e r e g r e s s i o n analyses with long-term measures of water l e v e l f l u c t u a t i o n s d e r i v e d from time s e r i e s 16 to 27 years l o n g , I could e x p l a i n at best 36.6% of the v a r i a b i l i t y i n number of young. (10) When I added short-term measures, the e x p l a i n a b l e v a r i a b i l i t y i n number of young shot up to 61.8%. Short-term measures alone could account f o r 46.4% of the v a r i a b i l i t y i n number of young. (11) Therefore i abandoned the idea t h a t most of the v a r i a b i l i t y i n l i f e h i s t o r y t r a i t s observed i n the f i e l d has evolved; much of i t r e s u l t s from developmental p l a s t i c i t y . By r a i s i n g Gambusia i n the l a b under c o n t r o l l e d d e n s i t y , food, and temperature, I found: (12) S i z e of young at b i r t h , growth r a t e s , and ages at maturity d i f f e r e d s i g n i f i c a n t l y among r e s e r v o i r s . (13) By v a r y i n g food and temperature, I could produce i n a s i n g l e l a b o r a t o r y stock d i f f e r e n c e s as l a r g e as I observed between any two r e s e r v o i r s i n the f i e l d . (14) The i i i d i f f e r e n c e s among s t o c k s i n r e p r o d u c t i v e t r a i t s were, with two exc e p t i o n s , i n the same d i r e c t i o n i n the l a b as i n the f i e l d . (15) Long p e r i o d s of low water and r e s t r i c t e d food f a v o r e d l a r g e f i s h (>20 mm) i n both lab and f i e l d . Short-term f l u c t u a t i o n s i n the f i e l d seem to f a v o r s m a l l f i s h (<22 mm) . These l a b o r a t o r y r e s u l t s l e d me to the f o l l o w i n g c o n c l u s i o n s : (16) The l i f e h i s t o r y t r a i t s of Gambusia have evolved, s i n c e 1905, i n d i f f e r e n t d i r e c t i o n s i n d i f f e r e n t r e s e r v o i r s . A d e t e c t a b l e and s i g n i f i c a n t p o r t i o n of the v a r i a b i l i t y among s t o c k s had a g e n e t i c b a s i s . (17) In the f l u c t u a t i n g r e s e r v o i r s , Gambusia are undergoing o s c i l l a t i n g s e l e c t i o n pressures on age at maturity and growth r a t e . They cope with these pressures by producing young with a great range of growth r a t e s and ages at maturity. Although I d i d not f a l s i f y the o r i g i n a l p r e d i c t i o n s , I d i d demonstrate that the models l e a d i n g t o those p r e d i c t i o n s ignored d e t a i l s t h a t were demonstrably important: (a) developmental p l a s t i c i t y i n l i f e h i s t o r y t r a i t s , (b) the range of v a r i a b i l i t y of l i f e h i s t o r y t r a i t s i n a s i n g l e brood, and (c) the d i f f e r e n c e s among s e v e r a l d i f f e r e n t kinds of i n s t a b i l i t y . i v TABLE OF CONTENTS Ab s t r a c t .................................................. i Table Of Contents . . i v L i s t Of Ta b l e s . i x L i s t Of Fi g u r e s x i i i Acknowledgements x v i CHAPTER I . INTRODUCTION 1 1. The General Ideas 1 2. Deduction Of The P r e d i c t i o n s 2 2a. A B r i e f Mathematical I n t e r l u d e 3 2b. r - And K - S e l e c t i o n ..4 2c. Bet-Hedging ..14 2d. S i z e Of Young ....26 3. Summary Of The P r e d i c t i o n s ....28 4. Assessment Of Pub l i s h e d Tests Of The P r e d i c t i o n s ...29 5. Choice Of A T e s t .....31 6. Summary .. .......33 CHAPTER I I . THE BIOLOGY OF* GAMBUSIA 35 1. I n t r o d u c t i o n 35 2. Taxonomy And Zoogeography .......................... 35 3. Chromosome Number And The I n h e r i t a n c e Of Sex .......37 4. C o n t r o l Of Age And S i z e At Maturity In Males ..37 5. Pregnancy And The D e l i v e r y Of Young ................ 43 6. Fecundity And Interbrood I n t e r v a l .................. 47 7. Food Habits .....53 8. Environmental Physiology ..54 9. I n t e r a c t i o n s With Other F i s h .55 10. A Comparison Of P o e c i l i a With Gambusia..... 59 11. Summary .....60 CHAPTER I I I . THE ECOLOGY OF GAMBUSIA IN HAWAII ...62 1. I n t r o d u c t i o n ..62 2. The E c o l o g i c a l Theatre: The Texas G u l f Coast 63 3. H i s t o r y In Hawaii: Assembling The Cast ....70 4. Methods .75 5. R e s u l t s .80 5a. D e f i n i t i o n s ---81 5b. Confounding F a c t o r s ...84 5c. Demographic S t a t i s t i c s -.100 6. D i s c u s s i o n ...........115 6a. Confounding F a c t o r s ...115 6b. Demographic Comparisons ........................ 122 6c. E c o l o g i c a l I m p l i c a t i o n s Of Demographic Changes .123 7. Summary • ....124 CHAPTER IV. LIFE HISTORY PATTERNS: FIELD DATA 126 1. I n t r o d u c t i o n ..126 2. Methods ...127 3. R e s u l t s ..131 3a. Hawaii: S t a b l e Vs. F l u c t u a t i n g Environments ...131 1. Number Of Embryos X Weight ................... 132 2. Reproductive E f f o r t .-135 3. S i z e Of Young .....136 4. S i z e At M a t u r i t y ......144 5. C o n d i t i o n F a c t o r s 145 6. Summary ..152 v i 3b. Texas D e t a i l s 156 3c. Texas-Hawaii Comparisons ........162 4. D i s c u s s i o n ......................................... 165 4a. Hawaii: S t a b l e Vs. F l u c t u a t i n g Environments ...165 1. r and K - s e l e c t i o n Or Bet-hedging? .....166 4b. Texas D e t a i l s 170 4c. Texas-Hawaii Comparisons 171 5. Summary 173 CHAPTER V. DETAILED ANALYSIS OF INSTABILITY ......175 1. I n t r o d u c t i o n .........175 2. Methods ........................................ 179 2a. C o l l e c t i o n And Treatment Of Data ....179 1. A u t o c o r r e l a t i o n . ............................ 181 2. Range And Variance. ......................... 131 3. S p e c t r a l A n a l y s i s . ........182 4. Other Techniques. 184 2b. F u r t h e r Data Reduction ......................... 185 3. R e s u l t s ............................ ............ 188 3a. Measures Of I n s t a b i l i t y ......188 3b. P r i n c i p l e Components A n a l y s i s .........212 3c. . M u l t i p l e Regression A n a l y s i s ..216 4. D i s c u s s i o n .......221 5. Summary ....225 CHAPTER VI. LABORATORY RESULTS ............ ........... 227 1. I n t r o d u c t i o n ........227 1a. Purpose .......227 1b. A Warning To Those Who Would Work On Gambusia...228 2. Methods ............... .,229 2a. C o l l e c t i o n , Shipping, And Lab C u l t u r e .......... 229 2b. S i z e At B i r t h ....233 2c. S i z e At 8 Days 234 2d. Growth Experiments ..234 2e. Long-term Experiments .......................... 235 2f. E f f e c t s Of Drawdowns 238 3. R e s u l t s 239 3a. S i z e At B i r t h And 8 Days ............ ......239 3b. Growth Experiments .......243 3c. Long-term Experiments .......................... 249 3d. The E f f e c t s Of Drawdowns .261 3f. Summary Of Laboratory R e s u l t s .................. 264 4, D i s c u s s i o n ..265 4a. Growth And Maturation .......................... 265 4b. The Impact Of Changes In Water L e v e l ...268 CHAPTER VII. GENERAL DISCUSSION .......................... 270 1. P r e d i c t i o n s 270 2. I m p l i c a t i o n s .......................................271 2a. Developmental And P h y s i o l o g i c a l P l a s t i c i t y .....272 2b. I n d i v i d u a l V a r i a b i l i t y ......................... 273 2c. D i f f e r e n t Types Of I n s t a b i l i t y 274 2d. C o n c l u s i o n s 274 3. Weak Po i n t s And Strong P o i n t s 275 LITERATURE CITED .......................................... 277 APPENDIX I . OPTIMIZING REPRODUCTIVE EFFORT ANALYTICALLY ..284 APPENDIX I I . AGE AND SIZE AT MATURITY IN MALE GAMBUSIA.... 286 1. I n t r o d u c t i o n 286 2. F i e l d R e s u l t s 286 v i i i 3. F i e l d O bservations: D i s c u s s i o n ..287 4. Laboratory Methods 297 5. Laboratory R e s u l t s ................................. 298 6. D i s c u s s i o n ....309 i x L i s t O f T a b l e s Number T i t l e P a g e 1 Some Of T h e C o r r e l a t e s Of r - And K - s e l e c t i o n 15 2 r - And K - s e l e c t i o n V s . B e t - h e d g i n g 27 .3 T h e B r e e d i n g S e a s o n Of G a m b u s i a a f f i n i s I n T e m p e r a t e R e g i o n s 49 4 G e o g r a p h i c V a r i a t i o n I n F e c u n d i t y : G a m b u s i a 51 5 S p e c i e s S e i n e d A t T h e A r m a n d B a y o u E n t r a n c e , 1 9 6 1 - 6 2 68 6 F r e s h w a t e r S p e c i e s I n t r o d u c e d T o H a w a i i 72 7 Summary Of R e s e r v o i r S a m p l e s 82 8 F i s h S p e c i e s Known T o Be I n R e s e r v o i r s I n 1974 88 9 T r e a t m e n t s R e c e i v e d By G a m b u s i a And P o e c i l i a I n H a w a i i 89 10 w a t e r f o w l S i g h t e d At H a w a i i a n R e s e r v o i r s : A v e r a g e Number S i g h t e d P e r V i s i t 91 11 P l a n k t o n D e n s i t y : N u m b e r s P e r T o w , J a n u a r y , 1974 92 12 P l a n k t o n S a m p l e s : J a n u a r y 1 9 7 4 , A v e r a g e L e n g t h I n mm By R e s e r v o i r And S p e c i e s 94 13 S t o m a c h S a m p l e s , November 1 9 7 4 , Number Of I t e m s P e r R e s e r v o i r By S p e c i e s 95 14 S t o m a c h S a m p l e s , November 1 9 7 4 , A v e r a g e L e n g t h Of F o o d I t e m s I n mm 96 15 Summary Of S t o m a c h C o n t e n t A n a l y s i s 97 16 G a m b u s i a C o n d i t i o n F a c t o r s And F i s h D e n s i t i e s 99 17 C h a n g e s I n P r o p o r t i o n Of F i s h >15 mm 102 18 C h a n g e s I n S i z e S t r u c t u r e s O f P o p u l a t i o n s 103 L i s t Of Tables (cont.) Number T i t l e Paqe 19 Changes In P r o p o r t i o n s Of Females Pregnant 104 20 R e p l i c a t e d Goodness Of F i t T e s t s On Sex Ratios 105 21 A n a l y s i s Of "Variance Of Gambusia Density: Between Dates, Within R e s e r v o i r s 106 22 Summary Of Changes In Demographic S t a t i s t i c s 108 23 D i f f e r e n c e s Between G And C r i t i c a l C h i -sguare 109 24 Changes In Reproductive T r a i t s Between Dates 110 25 Matrix Of K e n d a l l Rank C o r r e l a t i o n C o e f f i c i e n t s : No C o r r e c t i o n For Water L e v e l 112 26 Matrix Of K e n d a l l Rank C o r r e l a t i o n C o e f f i c i e n t s : C o r r e c t e d For Water L e v e l On Sampling Date In Unstable R e s e r v o i r s 113 27 Summary Of S t a t i s t i c a l Procedures 129 28 A n a l y s i s Of Covariance : Number Of Embryos X Weight, Done On: A l l Pregnant Females 133 29 A n a l y s i s Of Covariance: Reproductive E f f o r t X Weight, Done On: A l l Females With NEL, EE, LE, Or VLE Embryos 134 30 Summary Of D i f f e r e n c e s In Pregnancy And S u p e r f e t a t i o n 135 31 A n a l y s i s Of V a r i a n c e : Weight Of Young 143 32 Size At M a t u r i t y , P r o b i t A n a l y s i s Of Percent Pregnant By S i z e C l a s s 151 33 A n a l y s i s Of Covariance: Length X Log Weight, Done On: A l l Adult Females 153 34 Summary Of D i f f e r e n c e s In Reproductive T r a i t s (Values Given For A 175 MG Female In Regressions) 154 L i s t Of Tables (cont.) Number T i t l e Page 35 Summary Of Hypotheses And Evidence For Females, G i v i n g The P r e d i c t i o n s For S t a b l e R e s e r v o i r s Only 155 36 Summary Of L i f e H i s t o r y T r a i t s For Gambusia C o l l e c t e d Near Seabrook, Texas 157 37 Texas Vs. Hawaii Comparisons, Sex R a t i o s , P r o p o r t i o n Pregnant, And P r o p o r t i o n S u p e r f e t a t i n g 163 38 D i f f e r e n c e s In Reproductive T r a i t s , Texas Vs. Hawaii 164 39 A u t o c o r r e l a t i o n Measures Of I n s t a b i l i t y 206 4 0 Range Measures Of I n s t a b i l i t y 207 41 Variance Measures Of I n s t a b i l i t y 209 42 Power Spectrum Measures Of I n s t a b i l i t y 210 43 M i s c e l l a n e o u s Measures Of I n s t a b i l i t y 211 44 P r i n c i p l e Components A n a l y s i s , Amount Of T o t a l Variance Accounted For By The F i r s t 6 P r i n c i p l e Components 213 45 R e s e r v o i r C o o r d i n a t e s In The 4-space Spanned By The F i r s t 4 P r i n c i p l e Components 214 46 The C o r r e l a t i o n s Of The 30 O r i g i n a l I n s t a b i l i t y Measures With The F i r s t 4 P r i n c i p l e Components 215 4 7 Summary Of Stepwise M u l t i p l e Regression A n a l y s i s 218 48 Short-term Measures Of I n s t a b i l i t y , January Samples 220 49 D e t a i l s Of Steps 4 And 5 Of The M u l t i p l e Regression A n a l y s i s 22 2 50 A n a l y s i s Of Va r i a n c e : Heights Of Newborn Young, I . Lab Data 240 51 A n a l y s i s Of V a r i a n c e : Weights Of Earl y - e y e d Young, I I . F i e l d Data 241 X X X L i s t Of T a b l e s ( c o n t . ) Number T i t l e P a g e 52 A n a l y s i s O f V a r i a n c e : W e i g h t s O f 8 Day O l d F i s h 242 53 G r o w t h E x p e r i m e n t s : E f f e c t s Of F o o d , A n a l y s i s O f V a r i a n c e : W e i g h t s Of 34 Day O l d F i s h , H a w a i i a n F i s h O n l y 244 54 G r o w t h E x p e r i m e n t s : E f f e c t s Of F o o d , A n a l y s i s O f V a r i a n c e : W e i g h t s O f 34 Day O l d F i s h , H a w a i i a n + T e x a n F i s h 250 55 Age At M a t u r i t y / I n F e m a l e s , L a b D a t a : L o n g -t e r m E x p e r i m e n t s 251 56 C o m p a r i s o n O f L a b A n d F i e l d D a t a : Number Of Y o u n g , A n a l y s i s Of C o v a r i a n c e 255 57 C o m p a r i s o n Of L a b And F i e l d D a t a : R e p r o d u c t i v e E f f o r t , A n a l y s i s O f C o v a r i a n c e 256 58 Drawdown E x p e r i m e n t : R e s u l t s 262 59 E f f e c t s Of D r a w d o w n s : F i e l d D a t a , A n a l y s i s Of V a r i a n c e I n L e n g t h 263 60 A n a l y s i s O f V a r i a n c e : L e n g t h Of M a t u r e M a l e s 294 61 M a l e Age A n d S i z e At M a t u r i t y 303 62 Age A t M a t u r i t y I n M a l e s , L a b D a t a : L o n g -t e r m E x p e r i m e n t s 306 63 M a l e Age And S i z e At M a t u r i t y , C o n t r o l l i n g F o r A d u l t M a l e S i z e 307 XXIX L i s t Of F i g u r e s Number T i t l e Page 1 The L o g i s t i c Equation and r - and K - s e l e c t i o n 6 2 The S e n s i t i v i t y Of r To Age At M a t u r i t y And Number Of Young 9 3 The Lewontin Model of a L i f e H i s t o r y 12 4 The Murphy Model Of Competing P o p u l a t i o n s 19 5 A G r a p h i c a l Model For Hedging Reproductive Bets 22 6 The S c h a f f e r Model For F l u c t u a t i n g Environments 25 7 The Main C h a r a c t e r : Gambusia a f f i n i s 39 8 The Geographical D i s t r i b u t i o n Of Gambusia a f f i n i s 41 9 Thermal Tolerance Domains Of Gambusia a f f i n i s 57 10 A Map Of The Area Near Seabrook, Texas 66 11 Maps Of The Hawaiian I s l a n d s : The F i e l d S i t e s 77 12 Stocking Dates Of E x o t i c F i s h e s In Hawaii 86 13 The Design Of The Analyses Of Variance And Covariance 131 14 Egg Development: Gambusia, January 138 15 Egg Development: Gambusia, November 140 16 Egg Development, P o e c i l i a , January 142 17 Percent Pregnant By S i z e C l a s s : Gambusia, January 146 18 Percent Pregnant By S i z e C l a s s : Gambusia, November 14 8 19 Percent Pregnant By S i z e C l a s s : P o e c i l i a , January 150 x i v L i s t of F i g u r e s (cont.) Number T i t l e Page 20 Egg Development: Gambusia, Armand Bayou, Texas 159 21 Percent Pregnant By S i z e C l a s s : Gambusia, Armand Bayou, Texas 161 22 Types Of Environmental F l u c t u a t i o n 178 23 The A u t o c o r r e l a t i o n And Range Fun c t i o n s Of A Sine Wave 190 24 The Variance And S p e c t r a l Density Function Of A Sine Wave 192 25 The A u t o c o r r e l a t i o n And Range F u n c t i o n s Of A Random S e r i e s 194 26 The Variance And S p e c t r a l Density Functions Of A Random S e r i e s 196 27 Measures Of I n s t a b i l i t y : R e s e r v o i r 25 199 28 Measures Of I n s t a b i l i t y : R e s e r v o i r 91 202 29 Measures Of I n s t a b i l i t y : R e s e r v o i r 81 205 32 Temperature C o n t r o l Data And Duration Of Experiments 232 31 Experimental Food Regimes 237 32 Growth Experiments: Hawaiian Gambusia 246 33 Growth Experiments: Texan Gambusia 248 34 Maturation Rates: Females 253 35 Summary Of Growth: S t a b l e R e s e r v o i r s 258 36 Summary Of Growth: F l u c t u a t i n g R e s e r v o i r s 260 37 Adult Male S i z e D i s t r i b u t i o n : Gambusia, January 289 38 Adult Male Si z e D i s t r i b u t i o n : Gambusia, November 291 39 Adult Male Size D i s t r i b u t i o n : P o e c i l i a , January 293 X V L i s t Of F i g u r e s (cont.) Number T i t l e Page 40 Adult Male S i z e D i s t r i b u t i o n : Gambusia, Arraand Bayou, Texas 296 41 D i s t r i b u t i o n Of Adult Male S i z e s : Gambusia, January 300 42 Length And Age At M a t u r i t y : Males, Laboratory R e s u l t s 302 4 3 Maturation Rates: Males 305 x v i A c k n o w l e d g e m e n t s I c a r r i e d o u t t h e work f o r t h i s t h e s i s i n V a n c o u v e r , on t h e i s l a n d s o f H a w a i i , M a u i , a n d O a h u , a n d a t S e a b r o o k , T e x a s . At e a c h l o c a t i o n many p e o p l e h e l p e d me. V a n c o u v e r : Con W e h r h a h n , my s u p e r v i s o r , Don M c P h a i l , a n d B i l l N e i l l s e r v e d a s s o u n d i n g b o a r d s a n d p r o v i d e d much c o n s t r u c t i v e c r i t i c i s m . A t o n e t i m e o r a n o t h e r , a l m o s t e v e r y member o f t h e I n s t i t u t e o f A n i m a l R e s o u r c e E c o l o g y e n c o u r a g e d me w i t h t h e i r i n t e r e s t i n my w o r k , a n d i n d i r e c t l y t h r o u g h t h e i r i n t e r e s t i n t h e i r own w o r k . I was f o r t u n a t e t o b e l o n g t o a g r o u p o f p e o p l e t h a t s h a r e d t h e i r common i n t e r e s t s i n a s t i m u l a t i n g a n d c o n s t r u c t i v e way. D r s . W e h r h a h n , M c P h a i l , H o l l i n g , l a r k i n , W a l t e r s , a n d W e l l i n g t o n f o r m e d a g e n e r o u s c o n s o r t i u m t h a t f i n a n c e d e v e n t h e more e x p e n s i v e o f my r e a s o n a b l e i d e a s . D r s . M c P h a i l , L i l e y , L a r k i n , a n d H o l l i n g w e r e g e n e r o u s w i t h t h e i r e g u i p m e n t . I was s u p p o r t e d f o r o n e y e a r by a n I s a a k W a l t o n K i l l a m P r e - D o c t o r a l F e l l o w s h i p , a n d f o r two y e a r s by a N a t i o n a l R e s e a r c h C o u n c i l P r e - D o c t o r a l F e l l o w s h i p . Among my f e l l o w g r a d u a t e s t u d e n t s , I am p a r t i c u l a r l y g r a t e f u l f o r c o n s t r u c t i v e d i s c u s s i o n s w i t h K i m H y a t t , J i m M a c l e a n , Daphne F a i r b a i r n , P e t e r P r e s s l e y , a n d J u d i t h A n d e r s o n . P h i l C h a n g g a v e me t h e F a s t F o u r i e r T r a n s f o r m a l g o r i t h m i n f u n c t i o n a l f o r m . N e a r t h e s t a r t o f t h i s p r o j e c t , R i c C h a r n o v s t i m u l a t e d my i n t e r e s t i n l i f e h i s t o r y t r a i t s . J o s e p h i n e J e y a k u m a r d e s e r v e s a s p e c i a l a n d p r o m i n e n t v o t e o f t h a n k s . She w o r k e d a s ray t e c h n i c i a n f o r n e a r l y a y e a r , d i s s e c t i n g , w e i g h i n g , a n d m e a s u r i n g f i s h , a n d a n a l y z i n g s t o m a c h x v i i c o n t e n t s . I r e n e A m i r a s l a n y , a t t h e U . B . C . C o m p u t i n g C e n t r e , k e y p u n c h e d o v e r h a l f a m i l l i o n n u m b e r s o f f p l a n t a t i o n d o c u m e n t s t h a t w e r e d i f f i c u l t t o r e a d , a n d made l e s s t h a n o n e m i s t a k e p e r 1 0 , 0 0 0 n u m b e r s p u n c h e d . C l y d e M u r r a y c a r e d f o r my f i s h a n d m a i n t a i n e d my e x p e r i m e n t s d u r i n g my s e c o n d t r i p t o H a w a i i a n d my t r i p t o T e x a s , * a n d r e c e i v e d s h i p m e n t s o f l i v e f i s h a t t h e a i r p o r t a t a l l h o u r s o f t h e d a y a n d n i g h t , c h e e r f u l l y e n d u r i n g B y z a n t i n e c u s t o m s p r o b l e m s . T h e h e l p g i v e n me b y S t e v e B o r d e n , B i l l Webb, D o l o r e s L a u r i e n t e , a n d R o b i n K a r d y n a l o f t h e B i o l o g y D a t a C e n t r e made t h e a n a l y s i s o f ray d a t a a n d t h e p r o d u c t i o n o f my t h e s i s much e a s i e r a n d more e n j o y a b l e . My t h a n k s t o them a l l . H a w a i i : A l a n d R u t h S t e a r n s p r o v i d e d f o o d a n d l o d g i n g o n H a w a i i , a s d i d Bob a n d J o a n G o r d o n a n d B i l l a n d P e g g y P a t y o n O a h u . Doug a n d B a r b a r a T h o m s o n p r o v i d e d a d e l i g h t f u l c a b i n f o r o u r t h r e e - w e e k s t a y a t K u l a , on M a u i . A t K o h a l a S u g a r C o . , o n H a w a i i , A l S t e a r n s p r o v i d e d me w i t h r e c o r d s a n d i n f o r m a t i o n . At H a w a i i a n C o m m e r c i a l a n d S u g a r C o . , o n M a u i , Don H u g h e s , Bob W a r z e c h a , a n d S h i g e O k u d a p r o v i d e d r e c o r d s , d i r e c t i o n s , h o s p i t a l i t y , a n d g e n e r a l a s s i s t a n c e , a s d i d Masa U e h a r a , R u s s S o w e r s , a n d Tom H i r a y a m a a t W a i a l u a S u g a r C o . , o n O a h u . M a h a l o n u i l o a t o them a l l . On my f i r s t t r i p t o H a w a i i , Bev S t e a r n s h e l p e d w i t h f i e l d c o l l e c t i o n s ; J a m i e S m i t h d i d s o on t h e s e c o n d t r i p . A l a n d R u t h S t e a r n s a n d Mary M u s g r o v e s h i p p e d l i v e f i s h t o me f r o m K o h a l a s e v e r a l t i m e s , a n d p r o v i d e d a p r e s e r v e d s a m p l e f r o m T w i n R e s e r v o i r i n A u g u s t , 1974. B i l l D e v i c k a n d R i c h a r d Y o s h i d a o f t h e D i v i s i o n o f F i s h a n d G a m e , D e p a r t m e n t o f L a n d a n d N a t u r a l x v i i i Resources, State of Hawaii, provided i n f o r m a t i o n on s t o c k i n g a c t i v i t i e s i n and many unpublished r e p o r t s on the f r e s h waters of Hawaii. Texas: Dr. C l a r k Hubbs, o f the U n i v e r s i t y of Texas at A u s t i n , d i r e c t e d me t o the Texas Parks and W i l d l i f e l a b o r a t o r y at Seabrook. There the d i r e c t o r , Roy Johnson, d i d e v e r y t h i n g he cou l d to help me, and John Key helped with f i e l d c o l l e c t i o n s . They made my v i s i t e n joyable and c o n s t r u c t i v e . F i n a l l y , t o Aikane my thanks f o r comic r e l i e f , and to my wife, Bev, my thanks f o r support and understanding. Without her, t h i s study would c e r t a i n l y have taken much longer to complete and might never have been done at a l l . 1 CHAPTER I . INTRODUCTION I i T h e G e n e r a l I d e a s Can we p r e d i c t how o r g a n i s m s w i l l c h a n g e a s t h e y e v o l v e i n d i f f e r e n t e n v i r o n m e n t s ? I b e l i e v e we c a n . To a s k a more s p e c i f i c q u e s t i o n o f m a n a g e a b l e p r o p o r t i o n s , we m u s t f i r s t f o c u s o n a p o r t i o n o f t h e t o t a l b i o l o g y o f o r g a n i s m s t h a t c a n be h a n d l e d a s a r e l a t i v e l y i s o l a t e d u n i t , t h e n r e d u c e o u r d e s c r i p t i o n o f t h e c o m p l e x i t y o f t h e e n v i r o n m e n t t o a few r e l e v a n t a n d i m p o r t a n t c h a r a c t e r i s t i c s . S e v e r a l a r e a s h a v e e m e r g e d i n t h e l i t e r a t u r e o f e v o l u t i o n a r y e c o l o g y a s p o t e n t i a l l y t r a c t a b l e s u b j e c t s . F o r e x a m p l e , o p t i m a l f o r a g i n g t h e o r i s t s t r y t o p r e d i c t how a p r e d a t o r s h o u l d b e h a v e when e n c o u n t e r i n g d i f f e r e n t d i s t r i b u t i o n s o f f o o d . E c o l o g i c a l g e n e t i c i s t s t r y t o e x p l a i n g e n e t i c v a r i a b i l i t y , a n d i t s p o s s i b l e a s s o c i a t i o n w i t h s p a t i a l a n d t e m p o r a l v a r i a b i l i t y i n t h e e n v i r o n m e n t . Many p o p u l a t i o n b i o l o g i s t s s t u d y d i s p e r s a l , a t r a i t whose b e n e f i t s a n d d i s a d v a n t a g e s a r e i n a d e q u a t e l y u n d e r s t o o d . T h e t h e o r e t i c i a n s o f c o m m u n i t y e c o l o g y t r y t o e x p l a i n t h e p a t t e r n s a n d c h a r a c t e r i s t i c s o f s p e c i e s a s s o c i a t i o n s . T h i s t h e s i s d e a l s w i t h a f i f t h a r e a , l i f e h i s t o r y t a c t i c s . H e r e b i o l o g i s t s f o c u s on how a g e a t m a t u r i t y , t h e n u m b e r o f y o u n g , t h e s i z e o f y o u n g , a n d t h e amount o f e f f o r t p u t i n t o r e p r o d u c t i o n a r e a d j u s t e d b y n a t u r a l s e l e c t i o n t o s o l v e t h e p r o b l e m s p o s e d by p a r t i c u l a r e n v i r o n m e n t a l s i t u a t i o n s . T h u s t h e p r o b l e m s a r e d e l i m i t e d by t h e r e p r o d u c t i v e c h a r a c t e r i s t i c s o f 2 organisms and the environmental f a c t o r s that a f f e c t them. Elsewhere (Stearns 1976) I have reviewed the l i t e r a t u r e on l i f e h i s t o r y theory i n d e t a i l . Here I review only papers t h a t t r e a t a s p e c i f i c problem with t e s t a b l e consequences: What i s the impact of temnora1 f l u c t u a t i o n s i n the environment on the e v o l u t i o n of r e p r o d u c t i v e t r a i t s ? I w i l l f i r s t t r a c e the development of two c o n t r a s t i n g approaches to the problem, r - and K - s e l e c t i o n and bet-hedging, then show how p r e d i c t i o n s from the two t h e o r i e s d i f f e r . A f t e r a s s e s s i n g p u b l i s h e d t e s t s of the p r e d i c t i o n s , I w i l l d e s c r i b e my c h o i c e of a t e s t s i t u a t i o n . By ending t h i s i n t r o d u c t i o n with a c a p s u l e summary of how I explored the t e s t s i t u a t i o n , I hope to g i v e you an overview t h a t w i l l keep my purpose and methods c l e a r l y i n your mind as you read. 2. Deduction Of The P r e d i c t i o n s Since l i f e h i s t o r y t r a i t s are i n t i m a t e l y i n t e r r e l a t e d , attempts to e x p l a i n v a r i a b i l i t y i n l i f e h i s t o r y t r a i t s should model the important t r a i t s and t h e i r i n t e r a c t i o n s . Two t h e o r e t i c a l approaches have shown promise. They have l e d to c o n t r a d i c t o r y p r e d i c t i o n s . One approach t r a v e l s under the name " r - and K - s e l e c t i o n " ; I c a l l the other approach "bet-hedging". Advocates of r - and K - s e l e c t i o n assume t h a t f i t n e s s c o n s i s t s of maximizing the number of young l e f t at the end of a l i f e t i m e of r e p r o d u c t i o n . Advocates of bet-hedging assume t h a t f i t n e s s c o n s i s t s of minimizing the p r o b a b i l i t y of l e a v i n g no young a t a l l . Before p r e s e n t i n g the two views, I f i r s t review two equations necessary to the argument. Those f a m i l i a r with demography may want to s k i p the next s e c t i o n . 2a. A B r i e f Mathematical I n t e r l u d e The p r e d i c t i o n s of l i f e h i s t o r y theory have been deduced from the behavior of mathematical models of p o p u l a t i o n growth, and almost a l l such work s t a r t s with Lotka's eguation. I f we d e f i n e : l x = the p r o b a b i l i t y of s u r v i v i n g to age x, and b x= the instantaneous b i r t h r a t e ; and assume t h a t : 1. the m o r t a l i t y and f e c u n d i t y schedules ( l y and b^ ) are c o n s t a n t , i . e . the environment does not change over time, and 2. the p o p u l a t i o n i s growing e x p o n e n t i a l l y , which i s e q u i v a l e n t to assuming a s t a b l e age d i s t r i b u t i o n , then. 00 1 = ) e l x b xdx. T h i s equation, d e r i v e d by Lotka (1913), r e l a t e s the growth r a t e of a p o p u l a t i o n to i t s age s t r u c t u r e and to the d i f f e r e n t p r o b a b i l i t i e s of g i v i n g b i r t h and dying at d i f f e r e n t ages. The parameter r , i n the exponent, i s c a l l e d the i n t r i n s i c r a t e of n a t u r a l i n c r e a s e , and when the assumptions of the d e r i v a t i o n are s a t i s f i e d , Nfc = e rN t-,, where N t i s the number of females i n the p o p u l a t i o n a t time t , 4 and NA_, i s the number of females at time t - 1 . The second paradigm i s embodied i n the l o g i s t i c e g u a tion. B i o l o g i s t s r e c o g n i z e d . e a r l y on that the growth of b a c t e r i a at low d e n s i t y i n f r e s h medium c o u l d be represented as a simple e x p o n e n t i a l process, = rN . But t h i s simple r e l a t i o n s h i p d i d not hold a t higher d e n s i t i e s , and was modified by the a d d i t i o n of a term, K, c a l l e d the c a r r y i n g c a p a c i t y or s a t u r a t i o n l e v e l , which represented a l i m i t i n g d e n s i t y at which the p o p u l a t i o n stopped growing. T h i s l e d t o a new equa t i o n , c a l l e d the l o g i s t i c ( V e r h u l s t 1838, P e a r l and Reed 1920): d f r N ( i r >* The l o g i s t i c equation c o n t a i n s the two parameters, r and K (or i n t r i n s i c r a t e of n a t u r a l i n c r e a s e and s a t u r a t i o n l e v e l ) , on which the comparisons of r - and K - s e l e c t i o n are based. F i g . 1a presents a graph of po p u l a t i o n growth over time as represented by the l o g i s t i c . Note t h a t the r of Lotka's equation i s only e q u i v a l e n t to the r of the e x p o n e n t i a l equation, not to r as i t i s used i n the l o g i s t i c . 2b_;_ r - And K - s e l e c t i o n The idea of r - and K - s e l e c t i o n o r i g i n a t e d with Dobzhansky (1950), who proposed t h a t n a t u r a l s e l e c t i o n operates i n a fundamentally d i f f e r e n t way i n the t r o p i c s than i t does i n temperate areas. He argued that i n temperate areas p h y s i c a l 5 FIGURE 1 The L o g i s t i c Equation and r - and K - s e l e c t i o n F i g . 1A: The l o g i s t i c equation models the growth of a po p u l a t i o n with no age s t r u c t u r e i n an environment with l i m i t e d r e s o u r c e s . K i s the c a r r y i n g c a p a c i t y , the number of organisms the environment can support when resources are f u l l y u t i l i z e d . r i s the r a t e at which the p o p u l a t i o n grows a t low d e n s i t y . F i g . 1B: Simple as i t i s , the l o g i s t i c equation models r e l a t i o n s complex enough t o express the key i d e a s of r - and K - s e l e c t i o n . Suppose t h a t organisms are so c o n s t r u c t e d t h a t types t h a t can c o n t r i b u t e to r a p i d p o p u l a t i o n growth (e.g. Po p u l a t i o n 1) cannot s u r v i v e at p o p u l a t i o n d e n s i t i e s as high as those t o l e r a t e d by other types which c o n t r i b u t e t o slower p o p u l a t i o n growth (e.g. P o p u l a t i o n 2). Then P o p u l a t i o n 1 wins when r i s f a v o r e d , and P o p u l a t i o n 2 wins when K i s favored . • — . —> T :Time (b) The r- and K-Selection Paradigm t •  1 / 7 r l > r 2 / / K, < K 2 / / Population 1 wins when r is favored / / Population 2 wins when K is favored " d T \ r < N A dN 2 dt = r 2 N ~ •  — — — K T :Time 7 f a c t o r s are most f r e q u e n t l y l i m i t i n g . These a c t i n d e n s i t y -independent f a s h i o n , s e l e c t i n g f o r e a r l i e r maturity and l a r g e r c l u t c h e s . But, he argued, i n t r o p i c a l areas b i o l o g i c a l i n t e r a c t i o n s predominate, l e a d i n g to s e l e c t i o n f o r a b i l i t y to compete and to avoid p r e d a t i o n . Skutch (1949,1967) has made s i m i l a r suggestions. MacArthur (1962) gave t h e o r e t i c a l support to these i d e a s by deducing t h a t , i n density-dependent s i t u a t i o n s , n a t u r a l s e l e c t i o n w i l l f a v o r genes that c o n f e r a higher c a r r y i n g c a p a c i t y , K, and by suggesting t h a t i n such s i t u a t i o n s K can r e p l a c e r , the Ma.lt.hu s i an parameter, as a f i t n e s s measure. l o t k a ' s equation r e l a t e s the l i f e h i s t o r y of a p o p u l a t i o n to i t s growth r a t e , r , at low d e n s i t i e s . Thus a n a l y s i s of Lotka's equation should y i e l d an a p p r e c i a t i o n f o r the kinds of l i f e h i s t o r y t r a i t s that c o n t r i b u t e t o more r a p i d p o p u l a t i o n growth. But Lotka's equation i s n o t o r i o u s l y i n t r a c t a b l e . In order to get answers to l i f e h i s t o r y problems, Cole (1954), Lewontin (1965), and Meats (1971) have used numerical a n a l y s i s to uncover the interdependence of the s e v e r a l f a c t o r s t h a t enter i n t o the equation. Cole (1954) found that r i s q u i t e s e n s i t i v e t o changes i n age at maturity ( a l p h a ) , and that r i s most s e n s i t i v e t o a given percentage change i n alpha when alpha i s low. Moreover, r i s most s e n s i t i v e to a change i n alpha when the b i r t h - r a t e i s high (see F i g . 2). Thus one could expect t o f i n d age at maturity and b i r t h - r a t e under strong s e l e c t i o n when p o p u l a t i o n s are growing r a p i d l y . Lewontin (1965) was concerned with those combinations of 8 FIGURE 2 The S e n s i t i v i t y Of r To Age At M a t u r i t y And Number Of Young Legend: b= number of young born per year to an organism r e p r o d u c i n g once a year, r= e x p o n e n t i a l r a t e at which such a p o p u l a t i o n would i n c r e a s e , alpha= age at maturity. The growth r a t e of a p o p u l a t i o n i s more s e n s i t i v e to age at maturity than to number of young over most o f the range of these parameters. The s e n s i t i v i t y of r to alpha i n c r e a s e s as alpha decreases, and i n c r e a s e s as b i n c r e a s e s ( a f t e r Cole 1954). 6 10 l i f e h i s t o r y t r a i t s t h a t produced i n d i v i d u a l s f i t f o r c o l o n i z a t i o n . He assumed e x p o n e n t i a l p o p u l a t i o n growth, a s t a b l e age d i s t r i b u t i o n , and o v e r l a p p i n g g e n e r a t i o n s , and took r as h i s f i t n e s s measure. He then modeled a l i f e h i s t o r y using V(x)= lxmx as a t r i a n g u l a r f u n c t i o n of age (see F i g . 3), and d e f i n e d A,T, and W as age at f i r s t r e p r o d u c t i o n , peak r e p r o d u c t i o n , and l a s t r e p r o d u c t i o n , r e s p e c t i v e l y . To d e r i v e an exp r e s s i o n f o r r i n terms of these parameters, Lewontin noted from the geometry of F i g . 3 t h a t 2SJW_ z_xl V(x)= (» - T) (M - A) f o r x > T, and 2SJx_-_Al V(x)= (T - A) (W - A) f o r x < T. He then s u b s t i t u t e d these expressions i n o© i n t e g r a t e d , and obt a i n e d a complicated i m p l i c i t e x p r e s s i o n f o r r th a t c o u l d be eval u a t e d n u m e r i c a l l y . He took as h i s b a s e l i n e the case where A=12 (age at m a t u r i t y ) , T=23 (age at peak r e p r o d u c t i o n ) , W=55 (age a t l a s t r e p r o d u c t i o n ) , r=0.30, and S=780 ( t o t a l eggs expected per female over her l i f e t i m e ) . These values are a p p r o p r i a t e f o r a D r o s o 2 h i l a p o p u l a t i o n d u r i n g i t s e x p o n e n t i a l growth phase. The change i n S r e q u i r e d to change r from 0.30 to 0.33 i s +670, n e a r l y a doubling to 1350 eggs. The changes i n the other parameters that would be e q u i v a l e n t i n e f f e c t on r to t h i s change i n f e c u n d i t y are a 1.55 u n i t r i g i d t r a n s l a t i o n of the V(x) t r i a n g l e to the l e f t , a 2.20 u n i t decrease i n age at mat u r i t y , a 5.55 u n i t decrease i n age at peak r e p r o d u c t i o n , and 1 = 11 FIGURE 3 The Lewontin Model of a L i f e H i s t o r y Legend: V(x) = the a g e - s p e c i f i c c o n t r i b u t i o n to r e p r o d u c t i o n , A= age at maturity, T= the turnover point i n the V(x) f u n c t i o n , i . e . the age a t which net r e p r o d u c t i v e output s t a r t s t o d e c l i n e , W = age a t l a s t r e p r o d u c t i o n , and S = Ro = the area under the V(x) t r i a n g l e — the f i n i t e r a t e of p o p u l a t i o n i n c r e a s e . Lewontin used t h i s model i n a computer s i m u l a t i o n aimed at f i n d i n g combinations of l i f e h i s t o r y t r a i t s t h a t produce i n d i v i d u a l s f i t f o r c o l o n i z a t i o n ( a f t e r Lewontin 1965). 0 A T 13 a 21.00 u n i t decrease i n age at l a s t r e p r o d u c t i o n . r was most s e n s i t i v e to a given change i n time u n i t s when f e r t i l i t y i s high and age at maturity low, and l e a s t s e n s i t i v e when f e r t i l i t y i s low and age at maturity high, as Cole found. But i n gene r a l r was most s e n s i t i v e t o changes i n age at maturi t y . From t h i s , l e w o n t i n p r e d i c t e d t h a t c o l o n i z i n g s p e c i e s should show much l e s s g e n e t i c v a r i a n c e i n age at mat u r i t y , which i s under strong s e l e c t i o n pressure, than they show f o r f e c u n d i t y . (The same c o n c l u s i o n can be drawn f o r a more r e s t r i c t e d case with a n a l y t i c t e c h n i q u e s . See Appendix I.) Heats (1971) extended Lewontin's a n a l y s i s t o a wider range of v a l u e s of r and examined the separate e f f e c t s of changes i n m o r t a l i t y and n a t a l i t y f o r both d i s c r e t e and o v e r l a p p i n g g e n e r a t i o n s . His important r e s u l t s were these: (1) When pre-r e p r o d u c t i v e m o r t a l i t y i s high (ca. 0.80-0.99), then the growth r a t e of an annual p o p u l a t i o n (Ro) i s much more s e n s i t i v e to changes i n m o r t a l i t y than n a t a l i t y ; when p r e - r e p r o d u c t i v e m o r t a l i t y i s low (ca. 0.01-0.60) then the e f f e c t s of a given percentage change i n m o r t a l i t y or n a t a l i t y are n e a r l y e q u i v a l e n t . (2) Bsing Lewontin's example as a b a s e l i n e , he found that as r d e c l i n e s below 0.05, i t becomes l e s s s e n s i t i v e to changes i n age at maturity (A), peak r e p r o d u c t i o n ( T ) , and l a s t r e p r o d u c t i o n (W). When r drops below about 0.025 i n Heats's model i t becomes more s e n s i t i v e to changes i n b i r t h - r a t e than to age at mat u r i t y . Thus at low values of r , Lewontin's r e s u l t s don't h o l d . MacArthur and Wilson (1967) drew these i d e a s together and coin e d the terms " r - s e l e c t i o n " f o r s e l e c t i o n i n environments f a v o r i n g r a p i d 'population growth, and " K - s e l e c t i o n " f o r s e l e c t i o n i n s a t u r a t e d environments, f a v o r i n g a b i l i t y t o compete and to a v o i d p r e d a t i o n . F i g . 1b s e t s f o r t h the r - and K-s e l e c t i o n argument i n i t s s i m p l e s t form. Table 1 summarizes the c o r r e l a t e s of r and K - s e l e c t i o n i n the environment and i n the organism {modified a f t e r Pianka 1970). Most of the r e l a t i o n s h i p s f o l l o w i n a s t r a i g h t f o r w a r d f a s h i o n from the arguments given by Schmaulhausen and Dobzhansky, C o l e , and Lewontin. The theory i s q u a l i t a t i v e , not q u a n t i t a t i v e , and admits comparisons only w i t h i n l i m i t e d , groupings. But i t does p r e d i c t the a s s o c i a t i o n of the b i o l o g i c a l t r a i t s c o n s t i t u t i n g l i f e h i s t o r y t a c t i c s i n t o two groups: (a) r - s e l e c t i o n _ : e a r l y maturity, l a r g e c l u t c h s i z e , s e m e l p a r i t y , no p a r e n t a l c a r e , a l a r g e r e p r o d u c t i v e e f f o r t , s m a l l , numerous, o f f s p r i n g , and a s h o r t l i f e ; (b) K - s e l e c t i o n : delayed maturity, i t e r o p a r i t y , s m a l l c l u t c h e s , p a r e n t a l c a r e , s m a l l e r r e p r o d u c t i v e e f f o r t , a few, l a r g e o f f s p r i n g , and a long l i f e . 2c.. Bet-Hedging Markedly d i f f e r e n t p r e d i c t i o n s were generated by Murphy (1968) and S c h a f f e r (1974b), who examined the same tr e n d s from the bet-hedging viewpoint. Murphy compared two p o p u l a t i o n s i n a computer s i m u l a t i o n . P o p u l a t i o n 1 (r=.3188, alpha=3) had l a t e r maturation, b e t t e r a d u l t s u r v i v a l r a t e s , lower f e c u n d i t y , and a higher c a r r y i n g c a p a c i t y than p o p u l a t i o n 2 (r=.5472, alpha=2). The two p o p u l a t i o n s were l i n k e d by R i c k e r ' s (1954) r e p r o d u c t i v e eguations. When the i n t e r a c t i o n c o e f f i c i e n t s were equal and there was Some Of Tho C o r r e l a t e s o f r ; And K z £ £ l * £ t i o n ' I M o J i f i ^ d A f t e r P i a n k a J. £70]_ ~ ~ 1——— — — —i —— T , I r - S e l e c t i o n 1 K - S e l e c t i o n 1 R e f e r e n c e 1 C l i m a t e I V a r i a b l e a n d / o r I u n p r e d i c t a b l e | C o n s t a n t a n d / o r I p r e d i c t a b l e | D o b z h a n s k y ( 1 9 5 0 ) I S k u t c h ( 1 9 ( » 9 , 1 9 6 ? ) | P i a n k a ( 1 9 7 0 ) 1 M a c A r t h u r and I i ' i l s o n ( 1 9 6 7 ) 1 M o r t a l i t y | D e n s i t y - i n d e p e n d e n t I U n c e r t a i n a d u l t I s u r v i v a l I D e n s i t y - d e p e n d e n t I U n c e r t a i n j u v e n i l e 1 s u r v i v a l | P i a n k a ( 1 9 7 0 ) I M u r p h y ( 1 9 6 8 ) I Cody ( 1 9 7 1 ) I S u r v i v o r s h i p | O f t e n T y p e I I I | D e e v e y ( 1 9 4 7 ) . | U s u a l l y T y p e I a n d I I | D e e v e y ( 1 9 4 7 ) 1 P i a n k a ( 1 9 7 0 ) | 1 P o p u l a t i o n s i z e I V a r i a b l e i n t i m e , I n o n e q u i l i b r i u a ; I u s u a l l y b e l o w 1 c a r r y i n g c a p a c i t y ; | f r e q u e n t r e c o l o n -1 i z a t i o n n e c e s s a r y I C o n s t a n t i n t i n e I e q u i l i b r i u m ; I a t o r n e a r I c a r r y i n g c a p a c i t y ; I no r e c o l o n i z a t i o n I n e c e s s a r y I M a c A r t h u r a n d | I W i l s o n ( 1 9 6 7 ) | I P i a n k a ( 1 9 7 0 ) | 1 C o m p e t i t i o n 1 O f t e n l a x I U s u a l l y k e e n j D o b z h a n s k y ( 1 9 5 0 ) | I S k u t c h { 1 9 6 7 ) | M a c A r t h u r a n d | . W i l s o n ( 1 9 6 7 ) | 1 S e l e c t i o n f a v o r s I 1 . R a p i d d e v e l o p m e n t I 2 . H i g h r - m a x 1 3 . E a r l y r e p r o d u c t i o n 1 <*. H i g h r e s o u r c e I t h r e s h o l d s I 1 . S l o w d e v e l o p m e n t 1 2 . C o m p e t i t i v e a b i l i t y I 3 . D e l a y e d r e p r o d u c t i o n I 4 . Low r e s o u r c e I t h r e s h o l d s D o b z h a n s K y ( 1 9 5 0 ) | C o l e ( 1 9 5 4 ) | L e w o n t i n ( 1 9 6 5 ) | K a c A r t h u r & W i l s o n 1 9 6 7 ) | 5 . S m a l l b o d y s i z e 6 . S e m e l p a r i t y 7 . I n c r e a s e d b i r t h r a t e 5 . L a r g e body s i z e 6 . I t e r o p a r i t y 7 . D e c r e a s e d d e a t h r a t e G a d g i l S B o s s e r t ( 1 9 7 0 ) P i a n k a ( 1 9 7 0 ) M e a t s ( 1 9 / 1 ) T a b l e J. J c o n t ^ l Some Of T h e C o r r e l a t e s Of r - And K - S e l e c t i o n t~. I i r - s a l e c t i o n r •"' | K - s e l e c t i o n i 1 1 I R e f e r e n c e | I L e n g t h o f l i f e I S h o r t , <1 y e a r i | L o n g , >1 y e a r | P i a n n a (1970) | | L e a d s t o | P r o d u c t i v i t y I E f f i c i e n c y I M a c A r t h u r a n d | | W i l s o n (1967) | I P r o p o r t i o n o f e n e r g y | a l l o c a t e d t o | r e p r o d u c t i o n : | 1. Mass o f o f f s p r i n g I p e r p a r e n t p e r b r o o d I 2. Mass o f o f f s p r i n g l / p a r e n t / l i f e t i m e | 3. S i z e o f o f f s p r i n g I 1. P a r e n t a l c a r e I R e l a t i v e l y l a r g e I L a r g e r I L a r g e r | S m a l l e r | L e s s • | R e l a t i v e l y s m a l l | S m a l l e r i S m a l l e r | L a r g e r I H o r e t | G a d g i l a n d | I S o l b r i g (1972) | | C o a r s e - g r a i n e d s e a s o n a l e n v i r o n m e n t s l e a d I s t a b l e p o l y m o r p h i s m b e t w e e n h i g h r - a n d 1 L-t o a h i g h K- g e n e s | R o u g h g a r d e n (1971) | | Number o f b r e e d i n g 1 p e r i o d s p e r s e a s o n a l 1 c y c l e | Fewer I More | K i n g a n d | | A n d e r s o n (1971) ( | T o l e r a n c e t o n i c h e | o v e r l a p | L a r g e r | S m a l l e r I P i a n k a (1972) | 1 D e g r e e o f p o l y m o r p h i s m | o f g e n e s d e t e r m i n i n g j c a r r y i n g c a p a c i t y | a n d n i c h e b r e a d t h t | L e s s 1 G r e a t e r • I C l a r k e (1972) | X . . 1 17 no environmental v a r i a b i l i t y , the s i m u l a t i o n model behaved r e a l i s t i c a l l y . P o p u l a t i o n 2 ( s h o r t - l i v e d , high r) i n c r e a s e d more r a p i d l y than p o p u l a t i o n 1 ( l o n g - l i v e d , lower r ) , then went e x t i n c t as p o p u l a t i o n 1 grew past the c a r r y i n g c a p a c i t y of p o p u l a t i o n 2. Next Murphy a l t e r e d the i n t e r a c t i o n c o e f f i c i e n t s so t h a t the two p o p u l a t i o n s c o e x i s t e d i n a s t a b l e environment (pop. 1 = 2364 i n d i v i d u a l s , pop. 2 = 6757 i n d i v i d u a l s ) . He s t a r t e d both p o p u l a t i o n s with 1000 i n d i v i d u a l s . Then a f t e r 26 time u n i t s , when they had almost reached e q u i l i b r i u m , he i n t r o d u c e d uniform random temporal v a r i a t i o n i n r e p r o d u c t i v e success. In a l l c a s e s , p o p u l a t i o n 1 ( l o n g - l i v e d , lower r) i n c r e a s e d i n numbers and dominated, while p o p u l a t i o n 2 (s h o r t -l i v e d , higher r) decreased i n numbers, but d i d not go e x t i n c t ( F i g . 4). T h i s r e s u l t goes counter to the r - s e l e c t i o n argument, but seems to be supported by data on h e r r i n g - l i k e f i s h , where r e p r o d u c t i v e span i s s t r o n g l y c o r r e l a t e d with v a r i a t i o n i n spawning success (Murphy 1967). Murphy's i d e a s are q u i t e s i m i l a r to those suggested by Cohen (1967) and Boer (1968), which i n v o l v e hedging bets i n the f a c e of u n c e r t a i n t y . Suppose environmental c o n d i t i o n s vary from year to year, and that the organism cannot be c e r t a i n , at the time of r e p r o d u c t i o n , what c o n d i t i o n s w i l l be l i k e f o r the r e s t of the year. Since making too l a r g e a r e p r o d u c t i v e e f f o r t may r e s u l t i n d i s a s t e r (with a l l the young and perhaps the parents dying) whereas l a y i n g a s m a l l e r c l u t c h at l e a s t r e s u l t s i n some young, the organism should always hedge i t s bet on the s i d e of a s m a l l e r c l u t c h , r a t h e r than i n the other d i r e c t i o n ( F i g . 5). 18 FIGURE 4 T h e M u r p h y M o d e l O f C o m p e t i n g P o p u l a t i o n s M u r p h y c o m p a r e d two p o p u l a t i o n s . T h e f i r s t ( r e p r e s e n t e d by t h e d i a g r a m i n t h e u p p e r l e f t c o r n e r ) , w i t h l a t e m a t u r i t y , g o o d s u r v i v a l , s l o w p o p u l a t i o n g r o w t h , l o n g l i f e , a n d low b i r t h r a t e s , w o u l d be c a l l e d K - s e l e c t e d . T h e s e c o n d ( r e p r e s e n t e d by t h e d i a g r a m i n t h e u p p e r r i g h t c o r n e r ) , w i t h e a r l y m a t u r i t y , p o o r s u r v i v a l , h i g h b i r t h r a t e s , a n d s h o r t l i f e w o u l d be c a l l e d r - s e l e c t e d . 8 h e n M u r p h y i n t r o d u c e d t e m p o r a l v a r i a b i l i t y i n j u v e n i l e s u r v i v a l r a t e s t o a s i m u l a t i o n m o d e l i n w h i c h t h e t w o p o p u l a t i o n s w e r e c o e x i s t i n g a t c o m p e t i t i v e e g u i l i b r i u m , t h e f i r s t , l o n g - l i v e d p o p u l a t i o n i n v a r i a b l y i n c r e a s e d , r e v e r s i n g t h e p r e v i o u s d o m i n a n c e r e l a t i o n s h i p . T h i s r e s u l t was t h e f i r s t s u b s t a n t i a l c h a l l e n g e t o r ~ a n d K - s e l e c t i o n ( a f t e r M u r p h y 1 9 6 8 ) . SUMMARY OF MURPHY'S MODEL POPULATION 1: long lived POPULATION 2: short lived TIME INTERVAL SIMULATION (average of 20 iterations) 20 S c h a f f e r (1974b) e x t e n d e d a n d r e i n f o r c e d M u r p h y ' s c o n c l u s i o n s w i t h a s i m p l e p o p u l a t i o n m o d e l . C o n s i d e r a p o p u l a t i o n w i t h o u t a g e s t r u c t u r e . T h e n w h e r e B i s t h e number o f o f f s p r i n g t h a t s u r v i v e f r o m t i m e t t o t i m e t + 1 , a n d P i s t h e p r o b a b i l i t y t h a t t h e f e m a l e h e r s e l f s u r v i v e s t o b r e e d a g a i n . B o t h B a n d P a r e f u n c t i o n s o f r e p r o d u c t i v e e f f o r t , E . I n a f l u c t u a t i n g e n v i r o n m e n t , b r e e d i n g s u c c e s s a n d a d u l t s u r v i v a l v a r y f r o m y e a r t o y e a r . I n s u c h c i r c u m s t a n c e s , t h e l o n g - t e r m r a t e a t w h i c h a p o p u l a t i o n i n c r e a s e s , ^ , i s t h e p r o d u c t o f t h e v a r i o u s r a t e s o f i n c r e a s e i n d i f f e r e n t e n v i r o n m e n t s ( e 1 , e 2 , . . . . . e n ) , r a i s e d t o a p o w e r g i e q u a l t o t h e f r e q u e n c y o f t h e e n v i r o n m e n t . T h e r e f o r e , S c h a f f e r c o n s i d e r e d t h e s i m p l e s t c a s e , w h e r e two e n v i r o n m e n t a l s t a t e s , g o o d a n d b a d , a r e r a n d o m l y d i s t r i b u t e d a n d o c c u r w i t h e q u a l f r e q u e n c y : L e t s m e a s u r e t h e d e p a r t u r e o f q o o d a n d b a d y e a r s f r o m t h e mean. B + P a n d , ( L e v i n s 1 9 6 8 ) . T h e n , 21 FIGURE 5 A G r a p h i c a l M o d e l F o r H e d g i n g R e p r o d u c t i v e B e t s L e g e n d : b= n u m b e r o f y o u n g , S= j u v e n i l e s u r v i v a l r a t e , b x S = n u m b e r o f y o u n g t h a t s u r v i v e t o r e p r o d u c e , q = a d u l t m o r t a l i t y r a t e . C o n s i d e r t h e r e p r o d u c t i o n c u r v e r e p r e s e n t e d by b x S1 f i r s t . T h e o p t i m a l c l u t c h s i z e i s t h e o n e t h a t m a x i m i z e s n u m b e r o f y o u n g t h a t s u r v i v e t o r e p r o d u c e w h i l e m i n i m i z i n g a d u l t m o r t a l i t y . I t i s f o u n d by c o n s t r u c t i n g t h e a d u l t m o r t a l i t y f u n c t i o n , q , t a n g e n t t o t h e b x S1 c u r v e , w h i c h r e s u l t s i n b o a s t h e o p t i m a l c l u t c h s i z e . Now s u p p o s e t h a t t h e e n v i r o n m e n t v a r i e s f r o m y e a r t o y e a r r e s u l t i n g i n d i f f e r e n t j u v e n i l e s u r v i v a l r a t e s S , a n d t h a t t h e o r g a n i s m d o e s n o t know, a t t h e s t a r t o f a r e p r o d u c t i v e s e a s o n , w h e t h e r i t w i l l e n c o u n t e r c o n d i t i o n s r e s u l t i n g i n s u r v i v a l r a t e S2 f o r i t s y o u n g , w i t h 1 a n o p t i m a l c l u t c h s i z e a t b 1 , o r i n s u r v i v a l r a t e S 1 , w i t h an o p t i m a l c l u t c h s i z e a t b o . I f i t g a m b l e s , p r o d u c i n g c l u t c h s i z e b 3 , a n d s u r v i v a l r a t e S2 p r e v a i l s , t h e n n o n e o f t h e y o u n g s u r v i v e . E v e n c l u t c h s i z e b 2 , t h e most p r o d u c t i v e c l u t c h s i z e when s u r v i v a l r a t e S1 p r e v a i l s , r e s u l t s i n h e a v y l o s s e s when s u r v i v a l r a t e S2 p r e v a i l s . T h e r e f o r e , i n a t e m p o r a l l y v a r y i n g a n d u n p r e d i c t a b l e e n v i r o n m e n t , w h e r e a d u l t m o r t a l i t y i n c r e a s e s w i t h r e p r o d u c t i v e e f f o r t , w h e r e t h e o r g a n i s m c a n s u r v i v e t o r e p r o d u c e a g a i n , a n d w h e r e t h e most y o u n g s u r v i v e t o r e p r o d u c e a t a n i n t e r m e d i a t e c l u t c h s i z e , t h e o r g a n i s m s h o u l d a l w a y s h e d g e i t s b e t s w i t h s m a l l e r c l u t c h e s ( a f t e r S t e a r n s 1 9 7 6 ) . 23 B(1+s) + P, ~\ L- B (1-s) + P, and - 2 = ^ ^ l , = (B+P) 2 - s 2 B « . For the optimum E, = 0, and = - < 1-(s 2B/(B + P ) ) * f . Since 0<{1-(s 2B/ (B+P)}<1 f o r s 2<P/B +1, optimal e f f o r t , E, v a r i e s i n v e r s e l y with s ( F i g . 6a). On the other hand, i f environmental v a r i a b i l i t y a f f e c t s a d u l t , r a t h e r than j u v e n i l e , s u r v i v a l . *A =^ B + P (1 + S) , V B +P(1-s), and ^ 2 = (B+P) 2 - s 2 P 2 . Thus, ~ = - ( 1 - s 2 P / ( B + P ) ) ^ . Now so long as 0<(1-s 2P/(B+P))<1, or s 2>B/P +1, i n c r e a s e d s f a v o r s i n c r e a s e d r e p r o d u c t i v e e f f o r t ( F i g . 6b). To summarize S c h a f f e r ' s argument, a f l u c t u a t i n g environment 24 FIGURE 6 The S c h a f f e r Model For F l u c t u a t i n g Environments Legend: E = r e p r o d u c t i v e e f f o r t , B = number of o f f s p r i n g t h a t s u r v i v e to reproduce, P - the p r o b a b i l i t y t h a t the female s u r v i v e s t o breed again, S = the departure of good and bad years from the mean. F i g . 6A: Where environmental f l u c t u a t i o n s r e s u l t i n v a r i a b l e j u v e n i l e s u r v i v a l , B, the optimal r e p r o d u c t i v e e f f o r t , i n the f l u c t u a t i n g environment, E f , i s l e s s than the optimal r e p r o d u c t i v e e f f o r t i n the s t a b l e environment, E. Moreover, Ef decreases as the amplitude, s, of the f l u c t u a t i o n s i n c r e a s e s . F i g . 6B: Where environmental f l u c t u a t i o n s r e s u l t i n v a r i a b l e a d u l t s u r v i v a l , P, the optimal r e p r o d u c t i v e e f f o r t , Ef, i s g r e a t e r than the optimal r e p r o d u c t i v e e f f o r t i n the s t a b l e environment, E. Moreover, Ef i n c r e a s e s as the amplitude, s, of the f l u c t u a t i o n s i n c r e a s e s . The case represented i n F i g . 6A l e a d s t o Murphy's p r e d i c t i o n s (cf, F i g . 4 ) ; the case r e p r e s e n t e d i n F i g . 6B l e a d s to the same p r e d i c t i o n s as r - and K - s e l e c t i o n ( c f . Table 2) . 26 that has i t s impact on j u v e n i l e m o r t a l i t y f a v o r s reduced r e p r o d u c t i v e e f f o r t , s m a l l e r c l u t c h e s , and. l o n g e r - l i v e d organisms. But environmental v a r i a b i l i t y t h a t a f f e c t s a d u l t s u r v i v a l f a v o r s i n c r e a s e d r e p r o d u c t i v e e f f o r t , l a r g e r c l u t c h e s , and s h o r t - l i v e d organisms. Table 2 c o n t r a s t s the bet-hedging p r e d i c t i o n s with those made by r - and K - s e l e c t i o n . 2(U S i z e Of You 113 D i s c u s s i o n s of the s e l e c t i o n pressures o p e r a t i n g on s i z e of young have u s u a l l y considered b i o t i c , r a t h e r than p h y s i c a l , f a c t o r s , and have not been couched i n terms of a s t a b l e -f l u c t u a t i n g d i s t i n c t i o n . One approach c o n s i d e r s the resources a v a i l a b l e t o newborn progeny and the r i s k they encounter from p r e d a t i o n . We s t a r t with the assumption t h a t eggs should be l a i d at a s i z e which y i e l d s the maximum growth r a t e on the p a r e n t a l investment. The e f f e c t i v e growth i s the average growth r a t e of i n d i v i d u a l s towards r e p r o d u c t i v e maturity minus the l o s s t o m o r t a l i t y . In a po p u l a t i o n t h a t i s not growing r a p i d l y , the number of o f f s p r i n g decreases over time owing t o m o r t a l i t y , and unless the growth r a t e of the s u r v i v i n g o f f s p r i n g more than makes up f o r the l o s s , net y i e l d on rep r o d u c t i v e e f f o r t w i l l be ne g a t i v e . I f progeny can grow f a s t e r as l a r v a e o u t s i d e the parent (resources f o r young abundant, p r e d a t i o n pressure low), then many sm a l l progeny w i l l be f a v o r e d . I f resources f o r young are s c a r c e , or p r e d a t i o n r i s k to smal l s i z e c l a s s e s i s high, then the parent w i l l tend t o produce a few l a r g e progeny. In such circumstances, l i v e - b e a r i n g w i l l be f a v o r e d over e g g - l a y i n g i f T a b l e 2 r - And K - S e l e c t i o n V s . B e t - H e d g i n g r • 1. R And B e t - H e d g i n g W i t h K - S e l e c t i o n And A d u l t M o r t a l i t y V a r i a b l e —-, S t a b l e E n v i r o n m e n t s T F l u c t u a t i n g E n v i r o n m e n t s S l o w D e v e l o p m e n t And l a t e M a t u r i t y I t e r o p a r i t y S m a l l e r R e p r o d u c t i v e E f f o r t F e w e r Y o u n g L o n g L i f e • R a p i d D e v e l o p m e n t And e a r l y M a t u r i t y S e m e l p a r i t y L a r g e r R e p r o d u c t i v e E f f o r t M o r e Y o u n g S h o r t L i f e j 2. B e t - H e d g i n g W i t h J u v e n i l e M o r t a l i t y V a r i a b l e 1 E a r l y M a t u r i t y I t e r o p a r i t y ? L a r g e r R e p r o d u c t i v e E f f o r t S h o r t e r L i f e M o r e Y o u n g P e r B r o o d F e w e r B r o o d s T L a t e M a t u r i t y I t e r o p a r i t y S m a l l e r R e p r o d u c t i v e E f f o r t L o n g e r L i f e F e w e r Y o u n g P e r B r o o d M o r e B r o o d s 28 i n t e r n a l f e r t i l i z a t i o n i s p o s s i b l e , b e c a u s e l i v e y o u n g d o n o t e x p e r i e n c e t h e s t a r t - u p t i m e o f e g g s t h a t h a v e t o d e v e l o p b e f o r e t h e y c a n b e g i n a s s i m i l a t i n g e n e r g y a n d g r o w . ( T h i s i s a n a b s t r a c t o f an a r g u m e n t g i v e n by W i l l i a m s , 1 9 6 6 a , C h a p t e r 6 ) . 3_. Summary Of T h e P r e d i c t i o n s We a r e f a c e d w i t h c o n t r a d i c t o r y p r e d i c t i o n s o n t h e d i r e c t i o n s s e l e c t i o n s h o u l d p u s h l i f e h i s t o r y t r a i t s a s e n v i r o n m e n t a l f l u c t u a t i o n s i n c r e a s e . On t h e one h a n d , C o l e ( 1 9 5 4 ) , L e w o n t i n ( 1 9 6 5 ) , a n d M e a t s (1971) showed t h a t when p o p u l a t i o n s a r e g r o w i n g r a p i d l y , s e l e c t i o n f a v o r s e a r l i e r m a t u r a t i o n , many y o u n g p e r b r o o d , a n d l a r g e r e p r o d u c t i v e e f f o r t s . I d o u b t t h a t f l u c t u a t i n g e n v i r o n m e n t s n e c e s s a r i l y f a v o r o r g a n i s m s w i t h h i g h r a t e s o f i n c r e a s e . A f t e r a l l , p o p u l a t i o n s f l u c t u a t i n g i n n u m b e r s must d e c r e a s e a s f r e q u e n t l y a s t h e y i n c r e a s e . B u t i f o n e i s w i l l i n g t o c o n c e d e t h a t s t e p , a s w e r e M a c A r t h u r a n d W i l s o n ( 1 9 6 7 ) , t h e n t h e p r e d i c t i o n i s c l e a r . On t h e o t h e r h a n d . M u r p h y (1968) a n d S c h a f f e r (1974) h a v e shown t h a t when f l u c t u a t i o n s a f f e c t r e p r o d u c t i v e s u c c e s s ( j u v e n i l e s u r v i v a l ) , s e l e c t i o n f a v o r s l a t e r m a t u r a t i o n , f e w e r y o u n g , a n d s m a l l e r r e p r o d u c t i v e e f f o r t s . When t h e f l u c t u a t i o n s a f f e c t a d u l t i n s t e a d o f j u v e n i l e s u r v i v a l , S c h a f f e r c o n c l u d e d t h a t t h e t r e n d s p r e d i c t e d b y r - a n d K - s e l e c t i o n i s t s s h o u l d h o l d . F o r s i z e o f y o u n g , t h e s i t u a t i o n i s s i m p l e r . Where r e s o u r c e s f o r y o u n g a r e s c a r c e , y o u n g s h o u l d b e l a r g e r ( W i l l i a m s 1 9 6 6 a ) . I a s s u m e d a t t h e o u t s e t t h a t s c a r c e r e s o u r c e s c h a r a c t e r i z e , s t a b l e e n v i r o n m e n t s , r a t h e r t h a n u n s t a b l e o n e s , a n d p r e d i c t e d t h a t y o u n g s h o u l d be l a r g e r a t b i r t h i n s t a b l e 29 environments. i i i Assessment Of P u b l i s h e d Tests Of The P r e d i c t i o n s Cody (1966, 1971) argued that b i r d s l i v i n g i n s t a b l e environments should have reduced c l u t c h s i z e , l a t e r maturation, and l o n g e r l i f e s p a n s , s i n c e they must a l l o c a t e more of t h e i r energy to c o m p e t i t i o n and to a v o i d p r e d a t i o n . Then he s a i d t h a t the t r o p i c s , i s l a n d s , and c o a s t l i n e s are more s t a b l e than higher l a t i t u d e s , c o n t i n e n t s , and the i n t e r i o r of c o n t i n e n t s , and produced evidence t o show that c l u t c h s i z e s v a r i e d i n the manner p r e d i c t e d . He may w e l l have the c o r r e c t e x p l a n a t i o n , but there i s no way to assess the v a l i d i t y of h i s p r e d i c t i o n s from the evidence he o f f e r s . F i r s t , i t i s not at a l l c l e a r t h a t r e p r o d u c t i o n , c o m p e t i t i v e a b i l i t y , and c a p a c i t y f o r predator avoidance are a l l bought i n the same u n i t s of energy curre n c y . E v o l u t i o n a r y changes i n design, r a t h e r than energy a l l o c a t i o n , may s o l v e problems with c o m p e t i t o r s and p r e d a t o r s more f r e q u e n t l y than s h i f t s i n energy a l l o c a t i o n ( except where the s o l u t i o n s i n v o l v e changes i n growth r a t e s ) . Secondly, without an independent measure of s t a b i l i t y , Cody's argument i s c i r c u l a r ; he c o u l d j u s t as w e l l p r e d i c t i n c r e a s e d c l u t c h s i z e i n g e o g r a p h i c a l areas t h a t harbor b i r d s with l a r g e r c l u t c h e s . T h i r d l y , he o f f e r s no evidence on the a g e - s p e c i f i c i t y of m o r t a l i t y f a c t o r s i n s t a b l e and unstable environments. Thus we cannot use h i s evidence to check S c h a f f e r ' s (1974) and Murphy's (1968) c o n t e n t i o n t h a t i t i s the a g e - s p e c i f i c impact of f l u c t u a t i o n s , r a t h e r then j u s t t h e i r presence or absence, which i s the c r i t i c a l f a c t o r to 30 measure. F o u r t h l y , he d i d not r a i s e the b i r d s i n s i m i l a r environments t o see i f the d i f f e r e n c e s were simply due to phenotypic p l a s t i c i t y r a t h e r than to g e n e t i c a d a p t a t i o n . G a d g i l and S o l b r i g (1972) managed to i d e n t i f y a probable m o r t a l i t y source In t h e i r study of dandelions. They showed t h a t dandelion p o p u l a t i o n s c o n s i s t of a mixture of f o u r parthenogenetic b i o t y p e s . In environments d i s t u r b e d by the passage of people and eguipment, and mowed once a week, the dominant biotype has higher seed output, a l a r g e r biomass devoted to r e p r o d u c t i o n , and lower c o m p e t i t i v e a b i l i t y than the b i o t y p e dominating a l e s s d i s t u r b e d s i t e . . They d i d r e a r the f o u r b i o t y p e s i n s i m i l a r environments, and demonstrated t h a t the d i f f e r e n c e s were g e n e t i c . But, they d i d not measure the f l u c t u a t i o n s i n d i s t u r b a n c e , nor d i d they d e t a i l the age-s p e c i f i c i t y of the m o r t a l i t y caused by the d i s t u r b a n c e . Menge (1974) examined the e f f e c t of wave shock (a d e n s i t y -independent f a c t o r ) and competition (a density-dependent f a c t o r ) on two measures of r e p r o d u c t i v e e f f o r t , f e c u n d i t y and energy a l l o c a t e d at a p o i n t i n time t o r e p r o d u c t i o n , i n a s t a r f i s h , L e p t a s t e r i a s h e x a c t i s , that broods i t s young. He found t h a t brooding s t a r f i s h exposed t o wave shock made s m a l l e r r e p r o d u c t i v e e f f o r t s than those l i v i n g i n q u i e t areas where co m p e t i t i o n with another s t a r f i s h , P i s a s t e r o c h r a c e u s A could be demonstrated. Moreover, c o m p e t i t i o n appeared to have no e f f e c t on r e p r o d u c t i v e e f f o r t . Wave shock operated by a f f e c t i n g the number of young a s t a r f i s h c o u l d brood: the l a r g e r the brood, the more l i k e l y the parent would be t o r n from the rock, thus l o s i n g the whole brood. Menge's data run counter to r - and K-31 s e l e c t i o n , but support Murphy and S c h a f f e r ' s idea t h a t f l u c t u a t i o n i n r e p r o d u c t i v e success should lead to reduced ( r e p r o d u c t i v e e f f o r t . In only one p u b l i s h e d study has the author managed to measure r e p r o d u c t i v e e f f o r t f a i r l y r i g o r o u s l y . I l e s (1974) measured the r a t i o of annual somatic growth to annual gonad growth i n North Sea h e r r i n g , and showed that measure of r e p r o d u c t i v e e f f o r t i n c r e a s e d d r a m a t i c a l l y with age, thus u n d e r l i n i n g the f a c t t h a t an i n s t a n t a n e o u s measure of r e p r o d u c t i v e biomass i s inadequate without knowledge of the time taken to form i t . In only one study have the authors demonstrated that the d i f f e r e n c e s observed i n the f i e l d had a g e n e t i c b a s i s . In no study have the authors measured a d u l t and j u v e n i l e m o r t a l i t y a c c u r a t e l y . And i n no study have the authors measured the environmental f l u c t u a t i o n s they l a t e r invoke to e x p l a i n the d i f f e r e n c e s observed. 5^ Choice Of A Test The i d e a l experimental design f o r a t e s t of the p r e d i c t i o n s presented i n Table 2 would i n v o l v e t a k i n g a number of p o p u l a t i o n s with the same v a r i a b i l i t y i n l i f e h i s t o r i e s w i t h i n each p o p u l a t i o n , a l l derived from a s i n g l e p a r e n t a l s t o c k , and i n t r o d u c i n g them i n t o a s e r i e s of r e p l i c a t e environments. In one s e t of r e p l i c a t e s a l l environmental f a c t o r s would be s t a b l e . In the other s e t , some c r i t i c a l f a c t o r s would f l u c t u a t e . I d e a l l y , a l l other d i f f e r e n c e s ( temperature, food, other species) would be c o n t r o l l e d . A f t e r many ge n e r a t i o n s , we could assess the r e s u l t s of the experiment by r a i s i n g organisms from 32 both s e t s of environments under i d e n t i c a l c o n d i t i o n s i n the l a b o r a t o r y f o r two ge n e r a t i o n s (to e l i m i n a t e maternal e f f e c t s ) . I f the second l a b - r a i s e d generation maintained c o n s i s t e n t and s i g n i f i c a n t d i f f e r e n c e s i n l i f e h i s t o r y t r a i t s , then we would have s a t i s f a c t o r i l y t e s t e d the p r e d i c t i o n s of Table 2. By chance, I happened upon a s i t u a t i o n that approximates the i d e a l design. In 1905, about 150 m o s g u i t o f i s h , Gambusia a f f i n i s , were in t r o d u c e d t o Hawaii from Texas f o r mosquito c o n t r o l . They m u l t i p l i e d and were spread i n t o a s e r i e s of sugar p l a n t a t i o n r e s e r v o i r s . Some r e s e r v o i r s f l u c t u a t e d , some d i d not. Men on the p l a n t a t i o n s recorded the water l e v e l i n the f l u c t u a t i n g r e s e r v o i r s every day f o r the l a s t 15-27 years, and made t h e i r records a v a i l a b l e t o me. Thus I was a b l e t o e s t a b l i s h an independent measure of the f l u c t u a t i o n s i n a c r i t i c a l environmental f a c t o r , r e s e r v o i r water l e v e l . In 1974, 67 years a f t e r the experiment s t a r t e d , I v i s i t e d 27 Hawaiian r e s e r v o i r s , 6 of them t w i c e . I c o l l e c t e d and preserved over 250 f i s h from each. A n a l y s i s of these f i s h produced d e s c r i p t i o n s of the p a t t e r n of v a r i a b i l i t y i n l i f e h i s t o r i e s t h a t e x i s t e d i n the f i e l d i n 1974. I a l s o shipped f i s h from 5 r e s e r v o i r s back t o Vancouver, where I managed to r a i s e the progeny through a s i n g l e g e n e r a t i o n . In Chapter I I I have reviewed the b i o l o g y of i Gambusia a f f i n i s , to place the a b s t r a c t i o n s of l i f e h i s t o r y theory i n a concrete b i o l o g i c a l c o n t e x t . In Chapter I I I , I have d e s c r i b e d the i n t r o d u c t i o n of Gambusia to Hawaii and examined the assumptions made i n c a l l i n g i t an e v o l u t i o n a r y experiment. Chapter IV d e a l s with the l i f e h i s t o r y p a t t e r n s I found i n the 33 preserved f i e l d c o l l e c t i o n s . Chapter V, with the d e t a i l e d impact of r e s e r v o i r f l u c t u a t i o n s on Gambusia, and Chapter VI with the r e s u l t s of the l a b o r a t o r y experiments. Chapter VII i s a gen e r a l d i s c u s s i o n and overview o f the meaning t h i s t e s t has f o r l i f e h i s t o r y theory. I f you are i n t e r e s t e d i n the d e t a i l s of Gambusia*s b i o l o g y and need to be convinced that the experiment was not confounded, then continue d i r e c t l y on, reading Chapters I I and I I I next. Otherwise, I suggest you t u r n to Chapter IV and examine the r e s u l t s of f i e l d t e s t s of the p r e d i c t i o n s I j u s t reviewed. 6.. Summary At the beginning of t h i s chapter, I asked a gu e s t i o n : What i s the impact of temporal f l u c t u a t i o n s i n the environment on the e v o l u t i o n of r e p r o d u c t i v e t r a i t s ? A review of t h e o r e t i c a l work r e v e a l e d two c o n f l i c t i n g p r e d i c t i o n s . On the one hand, f o r r -s e l e c t i o n , temporal f l u c t u a t i o n s are thought to s e l e c t f o r e a r l y maturation, l a r g e r e p r o d u c t i v e e f f o r t s , and many young (Cole 1954, Lewontin 1965, MacArthur and Wilson 1967, Pianka 1970, Meats 1971). On the other hand, f o r bet-hedging, where the temporal f l u c t u a t i o n s a f f e c t r e p r o d u c t i v e success r a t h e r than a d u l t m o r t a l i t y , they are thought to s e l e c t delayed maturation, low r e p r o d u c t i v e e f f o r t , and fewer young (Murphy 1968, S c h a f f e r 1974). The few e m p i r i c a l t e s t s p u b l i s h e d s u f f e r from inadequate measurement of a g e - s p e c i f i c m o r t a l i t y , r e p r o d u c t i v e e f f o r t , and environmental f l u c t u a t i o n s . Evidence from b i r d s (Cody 1966,1971) and dandelions (Gadgil and S o l b r i g 1972) supports the r - s e l e c t i o n view, while evidence from a s t a r f i s h that broods i t s 34 young (Mange 1974) and from h e r r i n g - l i k e f i s h (Murphy 1967) show tha t a g e - s p e c i f i c m o r t a l i t y may be important. But none of the evidence i s s o l i d enough, i n i t s e l f , to r e f u t e one hypothesis or the other. We need a t e s t i n which the f l u c t u a t i o n s of the environment are documented and measured f o r q u a n t i t a t i v e comparison, i n which t h e i r impact on a g e - s p e c i f i c m o r t a l i t y i s d e s c r i b e d , and i n which the organism i s r a i s e d under constant c o n d i t i o n s i n the l a b o r a t o r y t o uncover the g e n e t i c p o r t i o n of the d i f f e r e n c e s observed i n the f i e l d . 35 CHAPTER I I . THE BIOLOGY OF GAMBUSIA IA I n t r o d u c t i o n T h i s c h a p t e r r e v i e w s t h e b i o l o g y o f G a m b u s i a t o g i v e t h e t h e s i s a c o n c r e t e f o u n d a t i o n . I h a v e b r o u g h t t o g e t h e r t h o s e a s p e c t s o f G a m b u s i a 1 s b i o l o g y t h a t a f f e c t i t s r e p r o d u c t i o n , t o g e t h e r w i t h e n o u g h g e n e r a l b a c k g r o u n d i n f o r m a t i o n t o g i v e t h e r e a d e r some u n d e r s t a n d i n g o f what t h e o r g a n i s m i s a n d what i t d o e s . I h a v e n o t r e v i e w e d t h e b i o l o g y o f P o e c i l i a r e t i c u l a t a i n d e t a i l , s i n c e S e g h e r s (1973) p r o v i d e d an e x c e l l e n t e n t r y t o t h e l i t e r a t u r e o n P o e c i l i a . I h a v e p r e s e n t e d e n o u g h o f i t s n a t u r a l h i s t o r y t o p e r m i t a c o m p a r i s o n w i t h G a m b u s i a . F o r G a m b u s i a , I h a v e b r o u g h t t o g e t h e r much o f what i s known a b o u t t h e s p e c i e s . 2i Taxonomy. And Z o o g e o g r a p h y . B o t h G a m b u s i a a f f i n i s , t h e m o s g u i t o f i s h , a n d P o e c i l i a r e t i c u l a t a , t h e g u p p y , b e l o n g t o t h e s u b f a m i l y P o e c i l i i n a e , o f t h e P o e c i l i i d a e , a f a m i l y o f c y p r i n o d o n t i f o r m f i s h e s r e s t r i c t e d t o t h e New l o r l d . T h e f a m i l y p r o b a b l y h a d i t s o r i g i n i n C e n t r a l A m e r i c a , a n d h a s s p r e a d n o r t h t o New J e r s e y a n d s o u t h t o B u e n o s A i r e s . T h i s b r o a d g e o g r a p h i c d i s t r i b u t i o n may s t e m f r o m t h e t o l e r a n c e t o s a l i n i t y t h a t c h a r a c t e r i z e s t h e w h o l e f a m i l y . T h e p o e c i l i i d s a r e s m a l l f i s h , n o n e e x c e e d i n g 20 cm i n l e n g t h , a n d a t t h e c e n t e r o f t h e i r r a n g e , i n C e n t r a l A m e r i c a a n d t h e B e s t I n d i e s , t h e y f o r m a d o m i n a n t f r e s h w a t e r 36 group. The f a m i l y i s d i s t i n g u i s h e d by s t r i k i n g sexual dimorphism, the anal f i n and p e l v i c suspension of the male being modified t o form an i n t r o m i t t e n t organ, the gonopodium. Hales are g e n e r a l l y s m a l l e r than females, and stop growing at matu r i t y , while females continue t o grow throughout most of t h e i r l i v e s . A l l p o e c i l i i d s p e c i e s but one, Tomeurus g r a c i l i s , are o v o v i v i p a r o u s (Rosen and B a i l e y 1963), and some (e.g. He t e r a n d r i a formosa, g o e c i l i o g s i s e l o n g a t a , Scrimshaw 1945) no u r i s h t h e i r d e v e l o p i n g o f f s p r i n g i n t e r n a l l y . The genus Gambusia shares with the other members of i t s t r i b e a p r i m a r i l y c a r n i v o r o u s h a b i t t h a t , i n Gambusia a f f i n i s , grades i n t o omnivorousness when food i s s c a r c e . The genus i s d i s t i n g u i s h e d by the upswept, and sometimes notched, p e c t o r a l f i n of the males, a morphological m o d i f i c a t i o n r e l a t e d t o mating behavior. The n a t i v e range of Gambusia a f f i n i s extends from Veracruz, Mexico, northward to Indiana, and along the Gulf Coast and up the A t l a n t i c Seaboard to New J e r s e y . There are two sub s p e c i e s , G^ a f f i n i s a f f i n i s and G. a f f i n i s h o l b r o o k i , d i s t i n g u i s h e d by gonopodial c h a r a c t e r s , the f i r s t found from Veracruz t o Alabama, the second from Alabama to New Jersey (Rosen and B a i l e y 1963). Gambusia a f f i n i s a f f i n i s , the subspecies I s t u d i e d i n Hawaii, has been i n t r o d u c e d to many p a r t s o f the world f o r mosquito c o n t r o l and i s now one of the most widespread of freshwater f i s h e s . F i g . 7 presents the f i s h , showing an a d u l t female and male. Note the sexual dimorphism, the r e l a t i v e s i z e s of the two sexes, the f l a t t e n e d d o r s a l s u r f a c e (probably an ad a p t a t i o n f o r f e e d i n g at the s u r f a c e ) , and the a b s o l u t e s i z e 37 from the s c a l e i n the f i g u r e . F i g . 8 shows the g e o g r a p h i c a l d i s t i b u t i o n of G.. a f f i n i s as summarized i n Krumholz (1948). Undoubtedly, the s p e c i e s has extended i t range s i n c e then. 3. Chromosome Number find The I n h e r i t a n c e Of Sex Roberts (1965) recorded a d i p l o i d chromosome number of 48 f o r G_j_ a f f i n i s h o l b r o o k i from North C a r o l i n a . Chen and E b e l i n g (1968) confirmed 48 as the d i p l o i d number f o r a f f i n i s from C a l i f o r n i a and Texas, and f u r t h e r e s t a b l i s h e d t h a t i n Gambusia a f f i n i s the female i s the heterogametic sex (female W2, male ZZ). i t i C o n t r o l Of Acje And S i z e At Maturity. In Males Nothing i s known about the f a c t o r s c o n t r o l l i n g the i n h e r i t a n c e of age and s i z e at maturity i n female p o e c i l i i d s , but the c o n t r o l of maturation i n males of the genus Xi£k°Eliorus ( t r i b e P o e c i l i i n i , Family P o e c i l i i d a e ) i s p a r t i a l l y understood. Both g e n e t i c and s o c i a l f a c t o r s have been i m p l i c a t e d . In a l l p o e c i l i i d s s t u d i e d , males v i r t u a l l y stop growing at maturity, whereas females c o n t i n u e to grow throughout t h e i r l i f e . Since growth r a t e s of j u v e n i l e s are roughly comparable, the s i z e of mature males r e f l e c t s the age at which they matured. Kallman and Schreibman (1973) i n v e s t i g a t e d the g e n e t i c s of male maturation i n Xiphoghorus maculatus, a s p e c i e s with polymorphic sex chromosomes. Three female types (XX,WX,WY) and two male types (XY,YY) may occur i n the same n a t u r a l p o p u l a t i o n . Kallman and Schreibman l o c a t e d a maturation gene l i n k e d t o a 38 FIGURE 7 The Main Character; Gambusia a f f i n i s As i n most p o e c i l i i d s , Gambusia a f f i n i s females are f r e q u e n t l y l a r g e r than the males, because females continue to grow a f t e r maturing. Males v i r t u a l l y stop growing a t m a t u r i t y . Note the s t r i k i n g s e x u a l dimorphism: the male's a n a l f i n i s modified i n t o an i n t r o m i t t e n t organ, the gonopodium, and h i s p e c t o r a l f i n has an upswept notch which i s used d u r i n g c o p u l a t i o n to brace the gonopodium. The f l a t t e n e d d o r s a l s u r f a c e and the upturned mouth are probably a d a p t a t i o n s f o r f e e d i n g at the water s u r f a c e . 40 FIGUBE 8 The Geographical D i s t r i b u t i o n Of Gambusia a f f i n i s The n a t i v e range of Gambusia a f f i n i s extended from Veracruz, Mexico, along the A t l a n t i c seaboard t o New J e r s e y , and up the r i v e r s of Texas and the M i s s i s s i p p i drainage, where i t reached southern I l l i n o i s . Since 1905, i t has been spread around the world f o r mosguito c o n t r o l . T h i s map represents i t s d i s t r i b u t i o n i n the mid-1940*s; i t has undoubtedly i n c r e a s e d i t s range s i n c e then ( a f t e r Krumholz 1948). WORLD DISTRIBUTION OF GAMBUSIA AFFINIS 42 c o l o r marker l o c a t e d on the Y chromosome. Males homozygous f o r one a l l e l e matured e a r l y (10-16 weeks), heterozygous males matured a t i n t e r m e d i a t e ages (18-24 weeks), and p r e l i m i n a r y evidence showed t h a t males homozygous f o r the other a l l e l e matured l a t e (20-32 weeks). They were able to demonstrate d i f f e r e n c e s i n the development of the p i t u i t a r y gland corresponding to d i f f e r e n c e s observed i n age at maturation. Thus, i n one p o e c i l i i d s p e c i e s age and s i z e a t maturation i n males i s a t l e a s t p a r t i a l l y under the c o n t r o l of a s e x - l i n k e d gene t h a t i s expressed through p i t u i t a r y a c t i o n . On the other hand, Borowsky (1973) has shown th a t i n H£h°Rhj3£uj-> v a r i a t u s , a c l o s e l y r e l a t e d s p e c i e s , s i z e and age at maturation are at l e a s t p a r t i a l l y under s o c i a l c o n t r o l . The presence of l a r g e r or more r a p i d l y growing j u v e n i l e males, or l a r g e r a d u l t males, delays the i n i t i a t i o n of maturation i n s m a l l e r j u v e n i l e s . Only one other male need be present to produce the e f f e c t , which i s more pronounced when the two i n d i v i d u a l s are s i m i l a r i n l e n g t h . The e f f e c t d i s a p p e a r s when males are reared i n i s o l a t i o n . Furthermore, these i n t e r a c t i o n s determine the i n t e n s i t y of e x p r e s s i o n of yellow-red (YB) c o l o r a t i o n i n the d o r s a l and caudal f i n s of some males. Borowsky s t a t e d t h a t "YR c o l o r a t i o n develops i n the l a r g e s t a d u l t male i n the group at any time s t a r t i n g at maturity and stopping when the male i s exceeded i n s i z e by a newly matured male." Males holding the dominant p o s i t i o n the l o n g e s t develop the most v i v i d c o l o r , which l e a d s to advantages i n male-male a g g r e s s i v e i n t e r a c t i o n s . M c A l i s t e r (1958) found that male Gambusia h u r t a d o i 43 e s t a b l i s h a f a i r l y r i g i d s o c i a l h i e r a r c h y i n l a b o r a t o r y a q u a r i a , the top-ranked f i s h having a b r i g h t yellow d o r s a l f i n , c a udal f i n base, and v e n t r a l s i d e of the caudal peduncle, and a conspicuous black outer border on the d o r s a l f i n . However, the dominance h i e r a r c h y broke down i f f i s h d e n s i t y was too high or too low, and may have been a l a b o r a t o r y a r t i f a c t . M c A l i s t e r s p e c u l a t e d that the dominant male does most of the mating, but o f f e r e d no evidence to support t h i s a s s e r t i o n . In Chapter VI, I have shown t h a t age and s i z e at maturation i n male G.. a f f i n i s i s a t l e a s t p a r t i a l l y under s o c i a l c o n t r o l . 5^ Pregnancy And The D e l i v e r y Of Young Three processes make p o e c i l i i d r e p r o d u c t i o n remarkable. (1) Females can r e t a i n l i v e sperm i n t h e i r o v a r i e s f o r s e v e r a l months, as demonstrated by microscopic examination of the o v a r i e s of females kept i n i s o l a t i o n and by the s e r i a l p r o d u c t i o n of s e v e r a l v i a b l e broods by i s o l a t e d females (Hildebrand 1917). (2) Females can n o u r i s h embryos during development, as demonstrated by o b s e r v a t i o n s showing no d e c l i n e , and i n some cases, an i n c r e a s e i n dry weight of the embryo as i t progresses from f e r t i l i z a t i o n to b i r t h {Scrimshaw 1945). And (3) females may have two or more broods i n d i f f e r e n t stages of development i n t h e i r o v a r i e s at the same time (Scrimshaw 1944, Turner 1947). T h i s process can shorten i n t e r b r o o d i n t e r v a l s and reduce peak r e p r o d u c t i v e e f f o r t , and i s c a l l e d s u p e r f e t a t i o n . Both embryonic nourishment (Scrimshaw 1945) and s u p e r f e t a t i o n (Scrimshaw 1944) have been demonstrated i n Gambusia a f f i n i s . The weight gains experienced by developing 44 embryos are not l a r g e ; embryos e i t h e r maintain t h e i r dry weight or i n c r e a s e i t by a few percent p r i o r t o b i r t h . In t h i s c o n n e c t i o n , Sanders and Soret (1954) s u c c e s s f u l l y r e a r e d embryos °f 5L. a f f i n i s i n s t e r i l e t i s s u e c u l t u r e s o l u t i o n s , showing t h a t e x t e r n a l nourishment may be necessary, but i n t i m a t e c o n t a c t with the mother i s not. Nor i s s u p e r f e t a t i o n o b l i g a t e i n G a f f i n i s . A v a r i a b l e percentage of females i n a p o p u l a t i o n (0-271 i n Hawaiian f i s h ) may have two (Scrimshaw 1944) or more r a r e l y , t h r e e (my observations) broods present, but many mature females have e i t h e r one brood or no maturing eggs at a l l i n t h e i r o v a r i e s . Krumholtz (1948) found no s u p e r f e t a t i n g females i n I l l i n o i s , and Hubbs (1971), only a few i n Texas. These p o e c i l i i d p e c u l i a r i t i e s have important consequences. F i r s t , i t i s hard to e s t a b l i s h the parentage of broods because females r e t a i n sperm. Females may be m u l t i p l y inseminated; we do not know i f they a r e . Thus care must be taken t o use v i r g i n females i n g e n e t i c work. Secondly, p o e c i l i i d s have a v a i l a b l e s e v e r a l r e p r o d u c t i v e o p t i o n s that most other organisms l a c k . Consider a p o e c i l i i d p o p u l a t i o n under s e l e c t i o n f a v o r i n g i n c r e a s e d s i z e of young a t b i r t h . The mechanism used t o produce t h a t change i n s i z e could i n v o l v e production of a l a r g e r egg, i n c r e a s e d nourishment of the embryo, or both. S e l e c t i o n f o r i n c r e a s e d numbers of young co u l d change e i t h e r the numbers of young per brood, t h e i r developmental time and through i t the i n t e r b r o o d i n t e r v a l (both o p t i o n s open to most organisms), or the s u p e r f e t a t i o n r a t e , b r i n g i n g more e n t i r e broods i n t o development at the same time. My o b s e r v a t i o n s i n d i c a t e t h a t females l i v i n g i n a densely 45 populated h o l d i n g tank may r e t a i n mature embryos f o r up to a week past t h e i r normal spawning date, d e l i v e r i n g immediately when i s o l a t e d . That a d u l t p o e c i l i i d s eat t h e i r newborn i s w e l l -known to most a q u a r i s t s , and has l e d to the p r o d u c t i o n of s p e c i a l breeding t r a p s that allow the newborn to escape t h e i r mother immediately a f t e r d e l i v e r y . But i n the w i l d I suspect females u s u a l l y d e l i v e r a t night or i n the weeds f o r reasons t h a t the f o l l o w i n g s t o r y should make c l e a r . One day I observed a l a r g e female d e l i v e r i n g her brood i n a h o l d i n g tank. She remained near the aquarium f l o o r , i n one c o r n e r , b r e a t h i n g r a p i d l y , with caudal and d o r s a l f i n s e r e c t and p e c t o r a l f i n s f a n n i n g . S e v e r a l of the f i s h i n the aquarium swam by her every 15-20 seconds, and appeared to be aware of what she was doing. As the young moved down the b i r t h c a n a l and a head or a t a i l would appear, the other Gambusia i n c r e a s e d the frequency of t h e i r approaches, and when the young f i s h was about halfway out, one of the other f i s h would d a r t i n , r i p the h a l f -d e l i v e r e d young f i s h from the b i r t h c a n a l , and eat i t . T h i s continued u n t i l a l l the young were born, a process i n v o l v i n g about 20 young and l a s t i n g three or f o u r hours. None s u r v i v e d . In Hawaiian r e s e r v o i r s , very s m a l l , one to three day o l d young stay c o n t i n u o u s l y i n the weeds, i f weeds are a v a i l a b l e , while l a r g e r j u v e n i l e s move out of the weeds and mingle with a d u l t s i n the s u r f a c e waters near shore. That o b s e r v a t i o n , coupled with o b s e r v a t i o n s on l a b o r a t o r y a q u a r i a , suggests to me t h a t s u s c e p t i b i l i t y t o c a n n i b a l i s m peaks during and immediately a f t e r b i r t h , and d e c l i n e s to i n s i g n i f i c a n c e w i t h i n the f i r s t week of l i f e , except when t r u l y s t a r v e d a d u l t s are present ( c f . the drawdown experiments i n Chapter V I ) . Another o b s e r v a t i o n u n d e r l i n e s the importance to G.. a f f i n i s of submerged v e g e t a t i o n . Barney and Anson (1920) found t h a t ponds with submerged v e g e t a t i o n produced more Gambusia than ponds with no v e g e t a t i o n or a dense s u r f a c e mat of weeds. They s p e c u l a t e d that d i f f e r e n c e s i n d i s s o l v e d oxygen c o n c e n t r a t i o n caused the d i f f e r e n c e s i n p r o d u c t i v i t y , but t h e i r r e s u l t s suggest another e x p l a n a t i o n to me. Sub-surface v e g e t a t i o n o f f e r s r e f u g i a to newborn Gambusia where they can escape p r e d a t i o n and c a n n i b a l i s m . Gambusia l i v i n g i n ponds with more sub-surface v e g e t a t i o n experience l e s s j u v e n i l e m o r t a l i t y . Thus more a d u l t Gambusia are produced. K r i s t e n s e n (1970) s t u d i e d a r e l a t e d s p e c i e s , P o e c i l i a s£henop_s y a n d e p o l l i , t h a t occupies the same h a b i t a t as Gj. a f f i n i s over a more s o u t h e r l y range: from n o r t h e a s t e r n Mexico to the Netherlands A n t i l l e s . He observed t h a t P.. S£henop.s r a r e l y moved i n t o open water, u s u a l l y congregating near submerged v e g e t a t i o n . To t e s t the hypothesis t h a t submerged v e g e t a t i o n promotes j u v e n i l e s u r v i v a l , he set up a g u a r i a with and without algae and maintained 2 males and 4 females i n each f o r 10 weeks. In the tank without algae a t o t a l of 11 broods were produced, but no young s u r v i v e d . In the tank with a l g a e , 10 broods were produced and 6 j u v e n i l e s (about 1%) s u r v i v e d . His evidence does not convince me t h a t P.. s.phenops can only reproduce where there i s a q u a t i c v e g e t a t i o n , but i t does at l e a s t support that c o n c l u s i o n . A requirement f o r access to s h e l t e r s u i t a b l e f o r j u v e n i l e s probably c h a r a c t e r i z e s a l l p o e c i l i i d s t h a t l i v e i n ponds or s l o w l y moving waters. Stream 47 d w e l l e r s , such as j e o h e t e r a n d r i a t r i d e n t i c j e r , which do not have access to aq u a t i c v e g e t a t i o n , have evolved c o l o r p a t t e r n s i n the young t h a t seem to e l i c i t r e c o g n i t i o n by a d u l t s and prevent c a n n i b a l i s m (McPhail, pers. comm.). fix Fecundity and Interbrood I n t e r v a l The main q u e s t i o n I ask i n t h i s study i s , d i d the r e p r o d u c t i v e t r a i t s of Gambusia evolve i n d i f f e r e n t d i r e c t i o n s i n s t a b l e and f l u c t u a t i n g r e s e r v o i r s i n Hawaii? Of course, phenotypic d i f f e r e n c e s e s t a b l i s h e d from f i e l d c o l l e c t i o n s need not r e f l e c t e v o l u t i o n a r y changes i n the g e n e t i c makeup of a p o p u l a t i o n . They c o u l d r e s u l t from the d i f f e r e n t developmental responses of a s e r i e s of p o p u l a t i o n s , a l l of which have the same g e n e t i c c o n s t i t u t i o n , but which encounter d i f f e r e n t l o c a l c o n d i t i o n s d u r i n g t h e i r growth and development. Here I review those environmental f a c t o r s known to a f f e c t growth and r e p r o d u c t i o n i n Gambusia a f f i n i s , p r o v i d i n g some of the background needed t o decide whether the s t a b l e - f l u c t u a t i n g d i s t i n c t i o n , which l i e s at the core of t h i s t h e s i s , was s e r i o u s l y confounded. The f e c u n d i t y of f i s h l i k e Gambusia a f f i n i s i s known t o depend on food, s i z e , age, and season, and i s suspected of being l i n k e d to f l u c t u a t i o n s i n temperature and the brood sequence i t s e l f . Hester (1964) r a i s e d guppies ( P o e c i l i a r e t i c u l a t a ) on th r e e d i f f e r e n t food r a t i o n s over t h r e e c o n s e c u t i v e r e p r o d u c t i v e p e r i o d s . He found t h a t the l a r g e r the female, and the l a r g e r her d a i l y food r a t i o n , the more young she bore. Furthermore, he demonstrated t h a t the number of young born i n the second brood 48 was i n p a r t dependent on the food r a t i o n r e c e i v e d d u r i n g the development of the f i r s t brood - a c l e a r l a g e f f e c t t h a t may be due to s u p e r f e t a t i o n . Food l e v e l had no e f f e c t on the s i z e of young or the l e n g t h of the g e s t a t i o n p e r i o d . In temperate, seasonal environments, G.. a f f i n i s s t a r t r e p r o d u c i n g i n the e a r l y summer and stop by e a r l y f a l l . Table 3 presents i n f o r m a t i o n on the breeding season over a broad g e o g r a p h i c a l range. C l e a r l y , the number of embryos found i n females from temperate regions depends s t r o n g l y on the date of c o l l e c t i o n . But s i n c e Hawaii i s very n e a r l y aseasonal i n photoperiod (11 hours of d a y l i g h t on December 21, 13 hours on June 21) and temperature (a mean of 20.6°C i n January and 26.2°C i n August at K a h u l u i , Maui i n 197 2), G.. a f f i n i s reproduce there throughout the year. In Chapter I I I , I have presented evidence demonstrating year-round r e p r o d u c t i o n , and some evidence of a seasonal c y c l e with r e p r o d u c t i o n d e c r e a s i n g , but not sto p p i n g completely, d u r i n g the dry season. As f o r g e s t a t i o n p e r i o d , Hildebrand (1917) observed i n t e r b r o o d i n t e r v a l s ranging from 16 t o 42 days f o r a s i n g l e female over the course of one summer, with a mean of 27.4 (5 i n t e r b r o o d i n t e r v a l s ) . He was working i n a l a b o r a t o r y at Bea u f o r t , North C a r o l i n a . Krumholtz (1948) observed i n t e r b r o o d i n t e r v a l s ranging from 21 to 27 days, with a mean of 23.0 (4 f i s h , 3 i n t e r b r o o d i n t e r v a l s each), near Chicago, I l l i n o i s , Hubbs (1971) i s o l a t e d females caught i n l a t e May i n C e n t r a l Texas and maintained them at 10, 15, 20, 25, 30, and 35QC. At 10°C, females produced dead young, and at 35°C females d i e d w i t h i n two weeks. At 20°C, the mean time t o the f i r s t brood was Table 3 Gambusia's Breeding Season In Temperate Regions Lo c a t i o n Breeding Season |Reference ! -+ Menard County, Texas Mound, Lousiana Be a u f o r t , North C a r o l i n a Chicago, I l l i n o i s Long I s l a n d , New York . March - Sept March - Oct A p r i l - Oct June ,- Sept May - Aug JHubbs (1971) I I Barney and |Anson (1921b) I IHildebrand (1917) I jKrumholz (1948) I JMaglio and | Rosen (1969) 50 60 days (81 f e m a l e s ) , at 25<>c, 34 days (48 f e m a l e s ) , and at 30°C, 24 days (33 f e m a l e s ) . Thus g e s t a t i o n p e r i o d decreases as temperatures r i s e , and at extreme temperatures r e p r o d u c t i o n f a i l s e n t i r e l y . At i n t e r m e d i a t e temperatures, the number of embryos per female i s probably not a f f e c t e d by temperature. Krumholtz (1948), Hubbs (1971), and Wu, Hoy, and Anderson (1974) a l l estimated the r e l a t i o n s h i p between numbers of young and s i z e of mother. T h e i r data c l e a r l y show that f e c u n d i t y i n c r e a s e s with s i z e , but t h e r e are f u r t h e r c o m p l i c a t i o n s . F i r s t , both Wu et a l . and Krumholtz showed that the r a t e of i n c r e a s e of f e c u n d i t y with s i z e decreases e i t h e r as females age or as the season progresses. Very o l d females have much reduced brood s i z e s , and a p e r i o d of s t e r i l e s e n i l i t y p r i o r to death. Secondly, Krumholz noted that females t h a t produced broods i n the f i r s t summer of t h e i r l i f e became p h y s i o l o g i c a l l y s e n i l e at a much e a r l i e r age than females which waited t o reproduce u n t i l the next s p r i n g . Thus a female's f e c u n d i t y i s i n part a f u n c t i o n of her past r e p r o d u c t i v e h i s t o r y . Remember that p o i n t . I t becomes important i n Chapter IV. T h i r d l y , I took the data from the three papers, c o r r e c t e d f o r d i f f e r e n t methods of measuring length (standard l e n g t h = 0.8 x t o t a l l e n g t h , Hubbs 1971), estimated the f e c u n d i t y of a 30 mm female (standard l e n g t h ) , and found the r e s u l t s presented i n Table 4. C l e a r l y , f e c u n d i t y v a r i e s from place to p l a c e . T h i s v a r i a t i o n could be s t r i c t l y the r e s u l t of v a r i a t i o n i n l o c a l c o n d i t i o n s : Krumholz's I l l i n o i s data suggest t h i s p o s s i b i l i t y most s t r o n g l y , f o r G.. a f f i n i s had been i n t r o d u c e d to h i s study ponds on l y 3-5 years before he sampled them, and probably could Table 4 Geographic V a r i a t i o n In Fec u n d i t y : Gambusia L o c a t i o n |Yng Menard County, Texas -+ C l e a r Creek, J u l y , 1969 | 21. 0 J 300 S u t t e r County, C a l i f o r n i a | Rice F i e l d , J u l y , 1971 | 67. 3 J 30 Rice F i e l d , Aug., 1971 ] 41. 7 | 30 Stock Pond, J u l y , 1971 | 25. 7 | 30 Stock Pond, Aug., 1971 | 27. 8 J 30 Cook County, I l l i n o i s ] Argonne Woods Pond, | J u l y 1939 | 47. 6 I 43 S a n i t a r y D i s t r i c t Lake, j J u l y 1939 I 19. 8 I 25 Pond 2, F o r e s t Preserve ) D i s t r i c t , August 1938 I 39. 1 I 9 Pond 3, F o r e s t Preserve | D i s t r i c t , August 1938 | 72. 0 I 4 Macon County, I l l i n o i s | P a r r ' s Pond, J u l y , 1940 ! 75. 2 | 20 Mound, L o u i s i a n a 1 June - J u l y , 1917,-19,-21 129.0 | 32 J Reference -+ Hubbs (1969) Wu, Hoy, And Anderson (1974) Krumholz (1948) Barney and Anson (1921b) 52 n o t h a v e e v o l v e d s u c h l a r g e d i f f e r e n c e s i n s o s h o r t a p e r i o d . Two o t h e r f a c t o r s c a n be s u s p e c t e d o f i n f l u e n c i n g f e c u n d i t y , b u t t h e d a t a s u g g e s t i n g t h e s e s u s p i c i o n s a r e n o t e x t e n s i v e . H u b b s (1971) d i f f e r e n t i a t e d h i s s t u d y a r e a i n t o t h e r m a l l y s t a b l e a n d t h e r m a l l y f l u c t u a t i n g e n v i r o n m e n t s , a n d s h o w e d t h a t G a m b u s i a a f f i n i s f r o m t h e t h e r m a l l y f l u c t u a t i n g e n v i r o n m e n t h a d h i g h e r f e c u n d i t y t h a n t h o s e f r o m t h e t h e r m a l l y s t a b l e e n v i r o n m e n t . B u t h i s t h e r m a l d i s t i n c t i o n was c o n f o u n d e d b y c h a n g e s i n b i o t a a n d p r e s u m a b l y f o o d s u p p l y . S i n c e h e d i d n o t p r o v i d e s e p a r a t e l e n g t h - f e c u n d i t y d a t a f o r t h e s t a b l e a n d u n s t a b l e e n v i r o n m e n t s , I c a n n o t a s s e s s H u b b s ' s c o n t e n t i o n t h a t t e m p e r a t u r e f l u c t u a t i o n s , n o t some o t h e r f a c t o r , c a u s e d t h e f e c u n d i t y d i f f e r e n c e s o b s e r v e d . B o t h R o s e n t h a l (1952) a n d H e s t e r (1964) h a v e s u g g e s t e d t h a t P o e c i l i a r e t i c u l a t a r e g u l a r l y a l t e r n a t e l a r g e w i t h s m a l l b r o o d s , t h e s t r e s s o f p r o d u c i n g t h e l a r g e b r o o d s o d e p l e t i n g m e t a b o l i c r e s o u r c e s t h a t t h e s u b s e q u e n t b r o o d i s s m a l l . B o t h M c P h a i l ( p e r s . comm.) a n d I h a v e some e v i d e n c e t h a t t h e same p a t t e r n may be f o u n d i n N e o h e t e r a n d r i a t £ i d e n t j . c [ e r , a p o e c i l i i d n a t i v e t o P a n a m a . B u t no o n e h a s u n e q u i v o c a l l y d e m o n s t r a t e d a c y c l i c a l t e r n a t i o n o f l a r g e w i t h s m a l l b r o o d s i n a n y p o e c i l i i d . I n s u m m a r y , t h e e s t i m a t e d n u m b e r s o f e m b r y o s p e r f e m a l e i n a f i e l d s a m p l e o f G a m b u s i a i n c r e a s e s w i t h t h e s i z e o f t h e f e m a l e a n d t h e a m o u n t o f f o o d a v a i l a b l e t o h e r ; t h e v a r i a n c e o f t h e r e l a t i o n s h i p o f f e c u n d i t y a n d s i z e i s i n c r e a s e d by v a r i a t i o n s i n t h e a g e s o f f e m a l e s o f a g i v e n s i z e , by v a r i a t i o n s i n t h e s i z e s o f t h e i r p r e v i o u s b r o o d s , by v a r i a t i o n s i n f o o d i n t a k e d u e t o m i c r o h a b i t a t d i f f e r e n c e s , a n d p o s s i b l y by 53 v a r i a t i o n s i n t e m p e r a t u r e a n d b r o o d s e q u e n c e . Z-. f o o d H a b i t s G a m b u s i a a f f i n i s i s an o p p o r t u n i s t i c c a r n i v o r e t h a t c a n e a t a l m o s t a n y t h i n g i t e n c o u n t e r s i n t h e s i z e r a n g e i t c a n h a n d l e , w h i c h p r o b a b l y s p a n s 0 . 2 - 5 . 0 mm, d e p e n d i n g o n t h e s i z e o f f i s h a n d t h e t y p e o f f o o d i t e m . I t d o e s f e e d s e l e c t i v e l y . F o r e x a m p l e , B a r n e y a n d A n s o n (1920) f o u n d c l a d o c e r a n s , d i p t e r a n l a r v a e , r o t i f e r s , p r o t o z o a , a n d b l u e - g r e e n f i l a m e n t o u s a l g a e i n t h e s t o m a c h s o f 105 G^ a f f i n i s f r o m M o u n d , L o u i s i a n a . H e s s a n d T a r z w e l l (1941) e x a m i n e d t h e s t o m a c h c o n t e n t s o f 1018 G_. a f f i n i s f r o m W h e e l e r R e s e r v o i r , T e n n e s s e e , a n d , by c o m p a r i n g s t o m a c h c o n t e n t s w i t h a v a i l a b l e f o o d , c a l c u l a t e d f o r a g e r a t i o s {% i t e m i n s t o m a c h / % i t e m i n e n v i r o n m e n t , e x p r e s s e d i n n u m b e r s o f i t e m s ) . G a m b u s i a f e d o n a d u l t i n s e c t s , i n s e c t l a r v a e , a n d c r u s t a c e a , a n d r a r e l y on a n n e l i d s . T h e y a c t i v e l y s e l e c t e d a q u a t i c d i p t e r a n l a r v a e ( m o s q u i t o e s a n d m i d g e s ) , t h e i r p r e f e r e n c e f o r m o s q u i t o l a r v a e i n c r e a s i n g a s l a r v a l d e n s i t y i n c r e a s e d , a n d a v o i d e d e a t i n g d r a g o n f l y l a r v a e , a l t h o u g h t h e y w o u l d t a k e t h e m o c c a s i o n a l l y . H u b b s (1971) f o u n d a m p h i p o d s a n d i n s e c t s i n t h e s t o m a c h s o f l a r g e f e m a l e G a m b u s i a (>26 mm) f r o m C e n t r a l T e x a s , w h i l e M a g l i o a n d R o s e n (1969) f o u n d p r i m a r i l y p l a n k t o n i c c r u s t a c e a a n d m i d g e l a r v a e , a n d f e w e r b e n t h i c c r u s t a c e a a n d i n s e c t s . T h e y f o l l o w e d G a m b u s i a a s t h e y moved a r o u n d t h e p o n d , i n a n d o u t o f d e e p w a t e r , a n d d e c i d e d t h a t t h e d i e t o f G a m b u s i a c h a n g e s t h r o u g h t h e d a y a s t h e y f e e d a d v e n t i t i o u s l y o n t h e d i f f e r e n t t y p e s o f c r u s t a c e a t h e y e n c o u n t e r i n d i f f e r e n t m i c r o h a b i t a t s . T h e i r 54 c o n t e n t i o n t h a t Gambusia i s an u n s e l e c t i v e feeder i s c o n t r a d i c t e d by Hess and T a r z w e l l ' s c a r e f u l documentation of s e l e c t i v e f e e d i n g i n Gambusia i n Tennessee. The range of items found i n Gambusia stomachs depends on the food items present i n the m i c r o h a b i t a t s i n which the f i s h were f e e d i n g , but w i t h i n t h a t range of food items Gambusia does feed s e l e c t i v e l y , c o n c e n t r a t i n g on mosquito and midge l a r v a e i f they are present. 8.. Environmental £hisioloqjy_ The p o e c i l i i d s are known as a fa m i l y f o r t h e i r broad s a l i n i t y t o l e r a n c e , s e v e r a l s p e c i e s i n h a b i t i n g the b r a c k i s h i n t e r f a c e between f r e s h and s a l t water (Bosen and B a i l e y 1963), and Gambusia shares t h i s t r a i t . Benf.ro (1959) found i n a c c l i m a t i o n experiments t h a t the l e t h a l s a l i n i t y f o r Gambusia l i e s between 15 and 24 ppt, but i n the f i e l d he u s u a l l y found Gambusia i n waters of l e s s than 1.1 ppt (Benfro 1960). Ahuja (196 4) a c c l i m a t e d G.. a f f i n i s to i n c r e a s i n g c o n c e n t r a t i o n s of NaCl (0.2% per day over 37 to 41 days), and found t h a t although m o r t a l i t y i n c r e a s e d with s a l i n i t y (30% m o r t a l i t y at 30 ppt) , some f i s h were ab l e to s u r v i v e at 80 ppt (95% m o r t a l i t y ) . During a c c l i m a t i o n , Gambusia developed c h l o r i d e - s e c r e t i n g c e l l s i n t h e i r g i l l s . Ahuja's experiment was confounded by oxygen c o n c e n t r a t i o n , which f e l l below 1 ppm as s a l i n i t y exceeded 10 PPt. Among the p o e c i l i i d s , Gambusia a f f i n i s had the l a r g e s t n a t u r a l l a t i t u d i n a l range (Bosen and B a i l e y 1963). Thus, i t i s no s u r p r i s e t o f i n d t h a t G, a f f i n i s has broad temperature t o l e r a n c e . Otto (1973) s t u d i e d the c a p a c i t i e s of a warm-adapted 55 G A a f f i n i s p o p u l a t i o n from the Sonoran Desert, and a c o l d -adapted p o p u l a t i o n from northern Utah, to a d j u s t to temperature s t r e s s . The two p o p u l a t i o n s had almost the same thermal t o l e r a n c e domains, as presented i n F i g . 9. F i s h from Utah were s l i g h t l y more t o l e r a n t of c o l d , those from A r i z o n a , s l i g h t l y more t o l e r a n t of heat. (Both p o p u l a t i o n s are i n t r o d u c e d , the Utah stock coming from Tennessee i n 1931 ; nothing i s known of the o r i g i n of the A r i z o n a stock.) Absolute upper and lower temperatures f o r permanent oc c u p a t i o n were near 38°C and 3°C, and f i s h a c c l i m a t e d a t 20°C could r a p i d l y a d j u s t to temperatures ranging from 4 to 35°C. Otto found that the areas of the zones of temperature t o l e r a n c e were 1033°C 2 f o r the Utah p o p u l a t i o n and 1065°C 2 f o r the A r i z o n a p o p u l a t i o n , comparable t o the f i g u r e of 1110°C 2 f o r ^ a f f i n i s r eported i n B r e t t (1956). Thus G._ a f f i n i s has much broader temperature t o l e r a n c e than, f o r example, salmonids (450-5300C 2), and i s comparable to c a t f i s h (970-1162°C 2) and g o l d f i s h (1220°C 2), which had the g r e a t e s t thermal t o l e r a n c e of any f i s h i n c l u d e d i n B r e t t ' s review. Maglio and Rosen (1969) found that Gambusia a f f i n i s s e l e c t e d the highest temperature a v a i l a b l e up t o 33°C. They would not enter water h o t t e r than 33°C, but f o l l o w e d areas of water as warm as 33°C around the pond as the sun heated d i f f e r e n t areas over the course of a day. 9-. I n t e r a c t i o n s With Other F i s h At the c e n t e r of t h e i r n a t i v e range, on the Texas G u l f Coast, G. a f f i n i s i n h a b i t shallow, b r a c k i s h waters i n bayous 56 FIGURE 9 Thermal T o l e r a n c e Domains Of Gambusia a f f i n i s Gambusia can t o l e r a t e as wide a range of temperatures as almost any f i s h . F i s h from Utah ( s t i p p l e d area) were s l i g h t l y more t o l e r a n t of c o l d , f i s h from A r i z o n a ( c l e a r area) were s l i g h t l y more t o l e r a n t of heat. The Utah stock o r i g i n a t e d i n Tennessee; the o r i g i n of the A r i z o n a stock i s unknown ( a f t e r Otto 1973). 57 Acclimation temperature (°C) 58 and e s t u a r i e s , and penetrate f a r i n l a n d i n freshwater c r e e k s and ponds. In the b r a c k i s h , e s t u a r i n e h a b i t a t they are not dominant, and are found only on the shallow p e r i p h e r y of bayous. S a i l f i n m o l l i e s , P o e c i l i a 1 a t i p_ inn a, are the dominant p o e c i l i i d , v e n t u r i n g i n t o deeper and more s a l i n e waters than G.. a f f i n i s . On the other hand, Gambusia are much more l o c a l l y abundant i n f r e s h water, and seem to exclude other p o e c i l i i d s from much of t h e i r freshwater range. In both b r a c k i s h and freshwater h a b i t a t s , G._ a f f i n i s evolved i n a complex b i o t i c c o n t e x t , encountering many p o t e n t i a l predators and competitors. In c e r t a i n circumstances, G. a f f i n i s can be q u i t e d e s t r u c t i v e , c a u s i n g major p e r t u r b a t i o n s to the s p e c i e s composition of the communities to which i t i s i n t r o d u c e d p a r t i c u l a r l y i f those communities l i e o u t s i d e i t s n a t i v e range and are made up of organisms which have not evolved with f i s h l i k e Gambusia. H u r l b e r t , Z e d l e r , and Fairbanks (1972) found t h a t Gambusia a f f i n i s completely e l i m i n a t e d Dap_hnia x Chydorus, copepod n a u p l i i , and chironomid l a r v a e from s m a l l , a r t i f i c i a l ponds, and s e v e r e l y depressed the numbers of r o t i f e r s . On C o r f u , Stephanides (1964) noted t h a t i n t r o d u c e d Gambusia had s e r i o u s l y depleted the n a t i v e a q u a t i c c r u s t a c e a n fauna, and i n Hawaii Gambusia may be r e s p o n s i b l e f o r the e x t i n c t i o n of s e v e r a l endemic crustacean s p e c i e s (Maciolek, pers. comm.). Introduced Gambusia can have a s i m i l a r e f f e c t on n a t i v e f i s h . Hyers (1965) noted c o r r e l a t i o n s between the a r r i v a l of Gambusia a f f i n i s and the disappearance or s e r i o u s r e d u c t i o n i n numbers of P o e c i l i o p s i s i n the American Southwest, Phaenocostethus and A g l o c h e i l u s i n Bangkok, Gulap_hallus i n the 59 P h i l l i p p i n e s , a n d ^%.oro2dLiachax i n t h e l o w e r N i l e , ( A l l a r e s m a l l f i s h ) , Nakagawa a n d I k e d a (1970) n o t e d t h a t i n H a w a i i , G a m b u s i a t e n d s t o o c c u p y t h e l o w e r , s l o w e r - m o v i n g p o r t i o n s o f s t r e a m s a n d l e s s p o l l u t e d w a t e r , w h i l e P o e c i l i a r e t i c u l a t a p e n e t r a t e t h e h e a d w a t e r s o f s t r e a m s a n d c a n l i v e i n e x t r e m e l y p o l l u t e d d a i r y p o n d s . I n a n y g i v e n l o c a l i t y , o n e o r t h e o t h e r w i l l u s u a l l y d o m i n a t e . D e v i c k (1971) f o u n d t h a t t u c u n a r e ( C i c h l a o c e l l a r i s ) a n d l a r g e m o u t h b a s s ( M i c r o j a t e r u s s a l m o i d e s ) p r e y o n G a m b u s i a i n H a w a i i a n r e s e r v o i r s managed f o r s p o r t f i s h i n g . A l l t h r e e s p e c i e s a r e i n t r o d u c e d t o H a w a i i , b u t G a m b u s i a d o e s o v e r l a p w i t h l a r g e m o u t h b a s s i n i t s n a t i v e r a n g e . A s H i l d e b r a n d (1917) o b s e r v e d , G a m b u s i a i s f a i r l y s l o w - m o v i n g a n d c a n e a s i l y be c a u g h t b y f i s h p r e d a t o r s i n o p e n w a t e r . IO.*. A C o m p a r i s o n Of P o e c i l i a W i t h G a m b u s i a P o e c i l i a r e t i c u l a t a a n d G a m b u s i a a f f i n i s r e s e m b l e e a c h o t h e r m o r e t h a n t h e y d i f f e r . T h e s i z e r a n g e s o f b o t h s e x e s o v e r l a p c o n s i d e r a b l y : m a l e P o e c i l i a r a n g e d f r o m 16 t o 30 mm i n T r i n i d a d ( S e g h e r s 1 9 7 3 ) , a n d m a l e G a m b u s i a r a n g e d f r o m 17 t o 32 mm i n I l l i n o i s ( K r u m h o l z 1 9 4 8 ) . F e m a l e P o e c i l i a r a n g e d f r o m 18 t o 47 mm i n T r i n i d a d ( S e g h e r s 1 9 7 3 ) , a n d f e m a l e G a m b u s i a r a n g e d f r o m 14 t o 57 mm i n I l l i n o i s ( K r u m h o l z 1 9 4 8 ) . B o t h s p e c i e s a r e c a r n i v o r o u s , f e e d i n g p r i m a r i l y o n a g u a t i c i n v e r t e b r a t e s , b u t P o e c i l i a , l i k e G a m b u s i a , p r o b a b l y w i l l e a t a l g a e when o t h e r f o o d i s s c a r c e . P o e c i l i a a n d G a m b u s i a r e s e m b l e o t h e r members o f t h e i r t r i b e s , a n d d i f f e r f r o m o t h e r t r i b e s o f p o e c i l i i d s , i n h a v i n g s h o r t g o n o p o d i a , some a u x i l i a r y m e c h a n i s m t o a s s i s t 60 gonopodial a c t i o n (a modified p e c t o r a l f i n i n Gambusia, a modified p e l v i c f i n i n P o e c i l i a ) , and r e l a t i v e l y e l a b o r a t e c o u r t s h i p behavior (Rosen and B a i l e y 1963). P o e c i l i a r e t i c u l a t a dwells p r i m a r i l y i n streams and r i v e r s (Seghers 1973), r a t h e r than the q u i e t e r water of pools, ponds, and e s t u a r i e s t h a t Gambusia i n h a b i t s . Neither i s s t r i c t i n i t s h a b i t a t p r e f e r e n c e s , and w i l l move i n t o q u i e t e r or more r a p i d l y moving water. But on the whole, Gambusia a f f i n i s l i v e s i n q u i e t water, and P o e c i l i a r e t i c u l a t a i n moving water. lis. Summary Gambusia a f f i n i s i s a s m a l l , s e x u a l l y dimorphic, p o e c i l i i d f i s h n a t i v e t o the Gu l f Coast, lower M i s s i s s i p p i drainage, and A t l a n t i c seaboard of Mexico and the United S t a t e s . The female i s the heterogametic sex. Both g e n e t i c and s o c i a l f a c t o r s have been i m p l i c a t e d i n the c o n t r o l of age and s i z e a t maturity of male p o e c i l i i d s , which stop growing when they mature. F e r t i l i z a t i o n i s i n t e r n a l , accomplished a f t e r a f a i r l y simple c o u r t s h i p , and young are born a l i v e a f t e r a g e s t a t i o n p e r i o d , i n Gambusia, of 20 t o 60 days, depending on temperature, season, and the l o c a l p o p u l a t i o n c h a r a c t e r i s t i c s . Females can r e t a i n v i a b l e sperm i n t h e i r o v a r i e s f o r s e v e r a l months, n o u r i s h the developing embryos duri n g g e s t a t i o n , and at times c a r r y two broods i n d i f f e r e n t stages of development ( s u p e r f e t a t i o n ) . Fecundity i n c r e a s e s with food i n t a k e and s i z e of female, decreases with age of female, changes over the year i n a seasonal environment, and may vary with temperature and the s i z e of previous broods, as well as with g e n e t i c a d a p t a t i o n t o l o c a l 61 c o n d i t i o n s . Gambusia i s an o p p o r t u n i s t i c c a r n i v o r e whose d i e t c o n s i s t s l a r g e l y of p l a n k t o n i c and benthic c r u s t a c e a and i n s e c t l a r v a e , supplemented by i n s e c t s t h a t f a l l on the s u r f a c e o f the water and, i n times of food s t r e s s , by algae. Gambusia has broad s a l i n i t y and thermal t o l e r a n c e s , i t s thermal t o l e r a n c e being near the maximum known f o r f i s h . Since 1905, i t has been spread around the world f o r mosquito c o n t r o l , and now i n h a b i t s freshwater and b r a c k i s h areas i n Europe, A s i a , A f r i c a , South America, and Oceania. 62 CHAPTER I I I . THE ECOLOGY OF GAMBUSIA IN HAWAII I n t r o duct ion In t h i s study, I have t e s t e d two models that c o n t r a s t the e v o l u t i o n of r e p r o d u c t i v e t r a i t s i n s t a b l e and f l u c t u a t i n g environments. In Chapter I, I presented the models, d e t a i l i n g t h e i r assumptions and p r e d i c t i o n s . T h i s chapter provides the background needed to e v a l u a t e , f i r s t , how w e l l the experimental design was c o n t r o l l e d , and secondly, how we l l the organism and f i e l d s i t u a t i o n s e l e c t e d f o r the t e s t s a t i s f i e d the assumptions u n d e r l y i n g the models t e s t e d . I have f i r s t summarized the e c o l o g i c a l t h e a t r e i n which Gambusia evolved i n Texas, and the h i s t o r y of i t s i n t r o d u c t i o n and spread i n Hawaii, Then, a f t e r d e s c r i b i n g the methods used i n the f i e l d , I have used f i e l d data to answer these g u e s t i o n s : How we l l c o n t r o l l e d was the experiment? Am I j u s t i f i e d i n c a l l i n g i t an experiment at a l l ? I have c o n f i d e n t l y d i f f e r e n t i a t e d between s t a b l e and f l u c t u a t i n g r e s e r v o i r s as though such terms have meaning to the f i s h p o p u l a t i o n s l i v i n g i n the r e s e r v o i r s . But i f I c o n s i d e r the demographic c h a r a c t e r i s t i c s of f i s h from s t a b l e and f l u c t u a t i n g r e s e r v o i r s at two p o i n t s i n time, can I f i n d evidence o r i g i n a t i n g i n the f i s h p o p u l a t i o n s themselves which i n d i c a t e s t h a t the s t a b l e -f l u c t u a t i n g d i s t i n c t i o n i s a r e a l one? Moreover, can I uncover, by a c r i t i c a l look at the c h a r a c t e r i s t i c s o f the r e s e r v o i r s and f i s h p o p u l a t i o n s , f a c t o r s which I can c o n f i d e n t l y c a l l confounding agents? 63 Thus the purpose of t h i s chapter i s twofold: f i r s t to d e s c r i b e the arena i n which c e r t a i n t e s t s of e v o l u t i o n a r y theory were c a r r i e d out, and secondly to c r i t i c a l l y review e m p i r i c a l evidence that could i n v a l i d a t e any of the assumptions made i n c a l l i n g the s i t u a t i o n "an e v o l u t i o n a r y experiment". Zs. The E c o l o g i c a l T h e a t r e ^ The Texas Gulf Coast The remainder of t h i s t h e s i s t e l l s the s t o r y of the c o n d i t i o n s G._ a f f i n i s encountered i n Hawaii, and of the l i f e h i s t o r y responses t h a t those c o n d i t i o n s e l i c i t e d . Before proceeding with t h a t s t o r y , I c o n s i d e r i n t h i s s e c t i o n the e c o l o g i c a l t h e a t r e - the Texas Gulf Coast - i n which G.. a f f i n i s e v o l v e d , i n order to assess the scope of i t s e v o l u t i o n a r y experience p r i o r to a r r i v a l i n Hawaii. Rosen and B a i l e y (1963) b e l i e v e d t h a t Gambusia and P o e c i l i a are the two most r e c e n t l y evolved (and r a p i d l y evolving) genera of the P o e c i l i i d a e , because of the l a r g e number of s p e c i e s i n each genus and t h e i r numerous s p e c i a l i z a t i o n s . Gambusia a f f i n i s probably s p e c i a t e d on the G u l f Coast somewhere between Texas and F l o r i d a d u r i n g t h e P l e i s t o c e n e or Holocene. During the P l e i s t o c e n e , g l a c i e r s advanced and r e t r e a t e d at l e a s t f o u r times, c a u s i n g the sea l e v e l along the G u l f Coast t o r i s e and f a l l as much as 150 meters. Since the Texas p l a i n s slope very g r a d u a l l y i n t o the G u l f , such l a r g e s h i f t s i n sea l e v e l imply the advance and r e c e s s i o n of the s h o r e l i n e a c r o s s a broad, f l a t p l a i n spanning 300-450 k i l o m e t e r s . During t h i s p e r i o d , r i v e r s s h i f t e d t h e i r courses (the Brazos emptied i n t o Galveston 64 Bay i n t h e l a t e P l e i s t o c e n e , f o r e x a m p l e ) , b a r r i e r i s l a n d s f o r m e d a n d were w a s h e d a w a y , a n d l a r g e b r a c k i s h b a y s f o r m e d , w e r e r e a r r a n g e d , a n d d i s a p p e a r e d ( F i s h e r , McGowen, B r o w n , a n d G r o u t 1 9 7 2 ) . T h u s , when s e e n i n g e o l o g i c a l t i m e , t h e G u l f C o a s t i s a h i g h l y d y n a m i c , u n s t a b l e e n v i r o n m e n t w i t h c o n t i n u a l l y s h i f t i n g t o p o g r a p h y . On s h o r t e r t i m e s c a l e s , t h e h a b i t a t i n w h i c h G.. a f f i n i s l i v e s i s j u s t a s u n s t a b l e a s t h e w h o l e c o a s t l i n e i s o v e r l o n g e r t i m e p e r i o d s . A l o n g t h e G u l f C o a s t , t i d e w a t e r r e a c h e s 5 - 1 5 m i l e s i n l a n d f r o m t h e l a r g e , b r a c k i s h b a y s a n d e s t u a r i e s t h a t p o c k t h e G u l f m a r g i n . Gambusj.a i s f o u n d i n f r e s h w a t e r a n d a l o n g t h e b r a c k i s h - f r e s h w a t e r i n t e r f a c e , w i t h o n l y a few s t r a g g l e r s p e n e t r a t i n g i n t o t h e o p e n w a t e r s o f t h e b a y s a n d b a y o u s . A t A r m a n d B a y o u , an a r e a p r e s e r v e d f o r n a t u r e s t u d y , I made r e p e a t e d s e i n e h a u l s on 28 A p r i l 1 9 7 5 , w o r k i n g f r o m o p e n w a t e r 50 cm d e e p i n t o s h o r e . F i g . 10 p r e s e n t s a map o f t h e a r e a . I n t h e o p e n w a t e r . G u l f menhaden ( B r e v o o r t i a p a t r o n u s ) a n d t h e t i d e w a t e r s i l v e r s i d e , ( M e n i d i a b e r y l l i n a ) were t h e o n l y s p e c i e s I c a u g h t . I n w e e d - f i l l e d w a t e r a b o u t 20 cm d e e p , I c a u g h t s t r i p e d m u l l e t ( M u g i l c e j p j i a l u s ) , t i d e w a t e r s i l v e r s i d e s , a n d a few s a i l f i n m o l l i e s ( P.. l a t i £ i n j i a ) . I n s h a l l o w , weedy w a t e r , 1 0 - 1 5 cm d e e p n e x t t o s h o r e , I c a u g h t s a i l f i n m o l l i e s , g u l f k i l l i f i s h ( F u n d u l u s g r a n d i s ) , b a y o u k i l l i f i s h ( F u n d u l u s p u l v e r e u s ) , s h e e p s h e a d m i n n o w s ( , C i £ r i n o d o n v a r i e g a t u s ) , w a r m o u t h s u n f i s h ( L e p o m i s g u l o s u s ) , a n d m o s g u i t o f i s h , G a m b u s i a a f f i n i s . A s e i n e h a u l i n v e r y s h a l l o w w a t e r , 2 - 5 cm d e e p , p r o d u c e d m a n y , a n d n o t h i n g b u t , y o u n g p o e c i l i i d s 8-12 mm l o n g . I n t h e N e t h e r l a n d s A n t i l l e s , K r i s t e n s e n (1970) n o t e d a 65 FIGUBE 10 A Map Of The Area Near Seabrook, Texas The stock of Gambusia a f f i n i s taken to Hawaii i n 1905 came from drainage d i t c h e s i n Seabrook. In May, 1975, I sampled Gambusia a f f i n i s i n Armand Bayou Park, 4-5 miles from the 1905 c o l l e c t i o n . The Armand Bayou Park and Nature Center i s a r e l a t i v e l y u n disturbed, oak-covered bottomland d i s s e c t e d by meandering streams and a b r a c k i s h - f r e s h estuary. 67 s i m i l a r p a t t e r n , with Cyprinodon de a r p o r n i i n h a b i t i n g the open, b r a c k i s h water (as s a i l f i n m o l l i e s do i n Texas), and P o e c i l i a sphenops v a n d e p o l l i shallower and l e s s s a l i n e water (as ^ a f f i n i s does i n Texas). Thus I found G.. a f f i n i s r a r e i n the bayou, c o n f i n e d t o the shallow, w e e d - f i l l e d margins. In c o n t r a s t , Gambusia dominated a s e r i e s of s m a l l , vegetation-choked pools that l a y along a dried-up streambed f e e d i n g the bayou. There I found Gambusia a s s o c i a t e d with the golden topminnow, Fundulus chry_sotus, and the golden s h i n e r , Notemigonus c h r y s o l e u c a s , as w e l l as l a r g e , predatory a q u a t i c b e e t l e s and d r a g o n f l y l a r v a e . In a d d i t i o n t o the few f i s h s p e c i e s I caught i n ten or twenty s e i n e hauls on a s i n g l e day, there are many other s p e c i e s known to occur i n armand Bayou. Table 5 l i s t s the s p e c i e s caught i n a year-long s e r i e s of semi-monthly se i n e hauls taken a t the mouth of Armand Bayou, where i t flows i n t o Mud Lake, by personnel of Texas Parks and W i l d l i f e . An a d d i t i o n a l 30-50 s p e c i e s of f i s h and l a r g e c r u s t a c e a probably occur i n the bayou and would t u r n up i f the area were sampled i n t e n s i v e l y . These s p e c i e s are not n e c e s s a r i l y permanent r e s i d e n t s . The e s t u a r i e s serve as n u r s e r i e s f o r many s p e c i e s which spend t h e i r a d u l t l i v e s i n the sea, e.g. g u l f menhaden ( B r e y o o r t i a patronus), brown shrimp (Penaeus a z t e c u s ) , and spotted sea t r o u t (Cynoscion nebulosus), among ten or f i f t e e n o t h e r s . These f i s h and shrimp move i n t o the e s t u a r i e s to spawn i n the s p r i n g , r e l e a s i n g b i l l i o n s of young which dominate the e s t u a r i n e food c h a i n during the summer and e a r l y f a l l , moving i n t o the bays l a t e r i n the year. Thus G.. a f f i n i s encounters a complex, Table 5 Species Seined At The Armand Bayou Entrance, 1961-62 r T ~ 1 • " - -J Higher Taxon | Common Name I S c i e n t i f i c Name 1 |Crustacea | Blue Crab 1 C a l l i l l ^ c t e s sapidus | | Mud crab 1Rhithropanopeus h a r r i s s i I | Brown shrimp 1Penaeus aztecus | | White shrimp IPenaeus s e t i f e r u s I ) Grass shrimp 1Pliaemonetes | IT e l e o s t F i s h I 1 1 |Clupeidae | G u l f menhaden 1Brevoortia patronus I | G i z z a r d Shad 1Dorosoma ce£edianum | | T h r e a d f i n Shad 1 Dorosoma p.etenense | IEngraulidae | Bay Anchovy 1Anchoa m i t c h e l l i | |Mugilidae | S t r i p e d M u l l e t 1Mugil cephalus j |Gobiidae | Clown goby 1Microgobius gulosus | | Naked goby 15obiosoma b o s c i | I Da r t e r goby 1Gobionellus boleosoma | | Marked Goby 1 G o b i o n e l l u s s t i g m a t i c u s | I T r i g l i d a e | Bighead se a r o b i n IPrianotus t r i b u l u s I I A r i i d a e I Sea c a t f i s h 1Arius f e l i s | |Sciaenidae | Spotted sea t r o u t |Cy.noscion nebulosus | | Sand sea t r o u t ICynoscion a r e n a r i u s | | Star drum j S t e l l i f e r l a n c e o l a t u s | | A t l a n t i c Croaker 1 Mlcrop_ogon undulatus \ j Spot JLeiostomus xanthurus I | A c h i r i d a e | Hogchoaker I T r i n e c t e s maculatus I IS o l e i d a e \ L i n e d s o l e |Achirus l i n e a t u s | |Ple u r o n e c t i d a e | Bay whiff 1 C i t h a r i c h t h y e s s p i l g p t e r u s | | Southern f l o u n d e r 1 £arj.lichthy_es lethostigma j L . , „ . j . J „. . _ i 69 s e a s o n a l l y s h i f t i n g s p e c i e s assemblage t h a t seems to prevent i t from moving i n t o the deeper waters of the e s t u a r y . Rapid, hou r l y changes c h a r a c t e r i z e the physico-chemical environment of the shallow e s t u a r i n e margins. Because the water i s so shallow, i t can be heated r a p i d l y , and changes from 24°C at 0800 hrs to 34°C at 1400 hrs are common i n the summer months. S e a s o n a l l y , the temperatures i n deeper water at the center of Armand Bayou ranged from 14.3<>C (16 March 1962) to 32.3°C (15 August 1961, Texas Parks and W i l d l i f e r e c o r d s ) . During the passage of winter c o l d f r o n t s , temperatures i n shallow water probably reach 3-4°C, s i n c e they r e g u l a r l y reach 7~8°C i n 2m of water i n Galveston Bay at such times. S a l i n i t i e s can f l u c t u a t e hourly due to t i d a l changes. Over 24 biweekly sampling p e r i o d s at the i n t e r s e c t i o n of Armand Bayou and Mud Lake i n 1961-62, s a l i n i t i e s ranged from 0.1 to 12.8 ppt (Texas Parks and W i l d l i f e r e c o r d s ) . The t i d a l range along the G u l f Coast i s only 0.2-0.75 m, but s i n c e the bayous and bays have low r e l i e f , t h i s range exposes l a r g e areas at low t i d e , causing c o n s i d e r a b l e mixing o f the f r e s h and s a l t waters. In summary, those p o p u l a t i o n s of Gambusia a f f i n i s which l i v e along the margins of e s t u a r i e s on the Gulf Coast encounter b i o l o g i c a l , p h y s i c a l , and chemical f a c t o r s t h a t vary on time s c a l e s from hours to eons. The f i s h t h a t Seale took to Hawaii i n 1905 came from such a p o p u l a t i o n . In many ways, the environment they entered i n Hawaii represented a r a d i c a l s i m p l i f i c a t i o n : s m a l l e r seasonal temperature ranges (ca. 19-26°C), no s a l i n i t y changes i n f r e s h water, a much l e s s d i v e r s e s p e c i e s assemblage, and no seasonal s h i f t s i n that assemblage. 70 Any e v o l u t i o n a r y c h a n g e s t h e y h a v e u n d e r g o n e i n H a w a i i may r e p r e s e n t s p e c i a l i z a t i o n f o r t h e p a r t i c u l a r c i r c u m s t a n c e s e n c o u n t e r e d - a n a r r o w i n g o f t h e o v e r a l l a d a p t i v e r a n g e o f t h e p o p u l a t i o n - r a t h e r t h a n an e v o l u t i o n a r y e x t e n s i o n p r o d u c i n g t r a i t s l y i n g b e y o n d t h e r a n g e o f n a t i v e T e x a n s . 3_;_ H i s t o r y I n H a w a i i : A s s e m b l i n g T h e C a s t B e f o r e t h e a r r i v a l o f E u r o p e a n s , H a w a i i h a d no n a t i v e m o s q u i t o e s . T h e f i r s t i n a d v e r t a n t i n t r o d u c t i o n o c c u r r e d i n 1826 a t L a h a i n a , M a u i , when t h e n i g h t - b i t i n g m o s q u i t o , C u l e x fiipiens f a t i g a n s , a r r i v e d i n f r e s h w a t e r k e g s c a r r i e d f r o m t h e w e s t c o a s t o f M e x i c o by t h e s h i p W e l l i n g t o n . T h e W e l l i n g t o n ' s w a t e r i n g p a r t y e m p t i e d t h e i r d r e g s i n t o a s t r e a m n e a r L a h a i n a . E a r l y i n 1 8 2 7 , a few m o n t h s l a t e r , H a w a i i a n s l i v i n g i n t h e a r e a b e g a n c o m i n g i n t o s e e D r . J u d d , a m i s s i o n a r y d o c t o r , w i t h c o m p l a i n t s o f a n o v e l i t c h i n f l i c t e d by a k i n d o f n a l o ( f l y ) d e s c r i b e d a s " s i n g i n g i n t h e e a r " ( H a l f o r d 1 9 5 4 : 9 9 ) . S o m e t i m e b e f o r e t h e 1 8 9 0 ' s , two s p e c i e s o f d a y - b i t i n g m o s g u i t o s , A e d e s a e g y p t i a n d h±. - g - l b o p i c t u s , a r r i v e d i n H a w a i i ( B e r g e r 1 9 7 2 ) , a n d i n 1962 a f o u r t h s p e c i e s , A e d e s y e x a n s n o c t u r n u s , t u r n e d up o n O a h u a n d K a u a i ( J o y c e a n d Nakagawa 1963) . By t h e t u r n o f t h e c e n t u r y , t h e f i r s t t h r e e m o s g u i t o s t o a r r i v e w e r e w e l l e n o u g h e s t a b l i s h e d a t l o w e l e v a t i o n s o n a l l t h e i n h a b i t e d i s l a n d s t o c o n s t i t u t e a m a j o r n u i s a n c e a n d h e a l t h t h r e a t . T h e r e were n o n a t i v e H a w a i i a n , p r i m a r y f r e s h w a t e r f i s h e s . T h e o n l y n a t i v e f i s h c a p a b l e o f p e n e t r a t i n g f r e s h w a t e r a r e s t r e a m - d w e l l i n g g o b i e s w h i c h h a v e r e t a i n e d a r e q u i r e m e n t f o r l a r v a l d e v e l o p m e n t i n s e a w a t e r . N e i t h e r t h e g o b i e s , n o r a n y o f 71 the freshwater s p e c i e s i n t r o d u c e d p r i o r t o 1900 (carp, Chinese c a t f i s h , Japanese w e a t h e r f i s h , g o l d f i s h , largemouth bass, r i c e f i e l d e e l s , or snakeheads, c f . Table 6) were capable of c o n t r o l l i n g mosquitos. Faced with a s e r i o u s mosquito problem, D.L. Van Dine, the entomologist at the U.S. Experiment S t a t i o n i n Honolulu, decided i n 1902 or 1903 to t r y to import f i s h to c o n t r o l mosquitos i n Hawaii, Through correspondence with P r o f e s s o r D. S. Jordan a t S t a n f o r d U n i v e r s i t y , he determined that p o e c i l i i d s would be the best c a n d i d a t e s . In 1905, he persuaded the T e r r i t o r i a l L e g i s l a t u r e to a p p r o p r i a t e $1500 to f i n a n c e the a c q u i s i t i o n of the f i s h , and sent a $500 advance to A l v i n Seale at S t a n f o r d , the man Jordan had chosen f o r the work (Ann. Rept. Haw. A g r i c . Expt. S t a . 1905). Seale went to the Gulf Coast t o c o l l e c t and t r a n s p o r t to Hawaii f i s h f o r mosquito c o n t r o l . Near Seabrook, Texas he "found the f a m i l y of top-minnows, P o e c i l i i d a e , i n l a r g e numbers. They were swarming i n a l l the stagnant waters at s e a - l e v e l as w e l l as i n v a r i o u s d i t c h e s , ponds and standing p o o l s . " He c o l l e c t e d about 150 each o f Gambusia a f f i n i s , the m o s g u i t o f i s h , P o e c i l i a l a t i p i n n a , the s a i l f i n molly, and Fundulus g r a n d i s , the Gulf k i l l i f i s h , and took them to Honolulu i n s i x 10 g a l l o n milk cans, by r a i l and steamship. Having departed Seabrook on 4 September 1905, he a r r i v e d i n Honolulu on 15 September 1905. Twenty-seven f i s h d i e d i n t r a n s i t (Seale 1905). In Hawaii, Fundulus died out (Brock 1960), l a t i p i n n a p e r s i s t e d i n low numbers, and G.. a f f i n i s m u l t i p l i e d and spread i n t o freshwater streams and r e s e r v o i r s throughout the s t a t e . By 1907, 72 Table 6* Freshwater Species Introduced To Hawaii 1 jCommon Name i r - — ~ I S c i e n t i f i c Name i T | Date j O r i g i n i \ • i f 1. E s t a b l i s h e d Species + 1 Crustaceans C r a y f i s h G i ant shrimp Giant prawn F i s h C e n t r a r c h i d s ££2£§.mbrus c l a r k i i l a c r o b r a c h i u m l a r Macrobrachium r o s e n b e r g j B l u e g i l l JLepomis macrochirus 1946 C e n t r a l U.S Largemouth bass IMicropterus salmoides | 1897 C e n t r a l O.S. Smallmouth bass IMicropterus dolomieu 1953 C e n t r a l U.S. C i c h l i d s : T i l a p i a | T i l a p i a macrochir 1957 Congo T i l a p i a ( T i l a p i a melanopleura 1956 Congo T i l a p i a | T i l a p i a mossambica 1951 j East A f r i c a T i l a p i a I 1 i l a p i a z i l l i 1955 N i l e Tucunare I C i c h l a o c e l l a r i s J 1957 Amazon Oscar llst£°S2iJis o c e l l a t u s 1951 Amazon Firemouth JCichlasoma meeki 1940 Amazon C y p r i n i d s : Carp ICyprinus c a r p i o <1900 East Asia G o l d f i s h fjCarassius auratus <1900 East Asia Half-banded barb IS§£bus s e m i f a s c i o l a t u s 1940 South Asia P o e c i l i i d s : M o s g u i t o f i s h |Gambusia a f f i n i s 1905 Gulf Coast S a i l f i n molly | P o e c i l i a l a t i p i n n a 1905 Gulf Coast Guppy I P o e c i l i a r e t i c u l a t a 1922 Guyana Southern p l a t y f i s h JXiphophorus maculatus 1922 Yucatan Green s w o r d t a i l IXiphophorus h e l l e r i 1922 Yucatan Topminnow J P o e c i l i a v i t t a t a 2 Cuba Salmonids: Rainbow t r o u t | Salmo g a i r d n e r i 1920 P a c i f i c NW I c t a l u r i d s Channel c a t f i s h l l c t a l u r u s punctatus 1953 C e n t r a l U.S. C l a r i i d s : Chinese c a t f i s h f C l a r i u s f u s c u s <1900 South China O p h i c e p h a l i d s : Snakehead 1Ophicephalus s t r i a t u s <1900 S.E. A s i a C l u p e i d s : T h r e a d f i n shad \ Dorosoma petenense 1958 Gulf Coast C o b i t i d s : Japanese weatherfish JMisgurnis a n g u i l l i c a u d a t u s <1900 Japan A n g u i l l i d s : B i c e f i e l d e e l }Fluta a l b a <1900 South As i a 192 3 1956 1964 U.S. South Oceania Oceania * Revised a f t e r Bro ** T e l e o s t f a m i l i e s Myers (1966). B a i l e y (1963). ck (1960) and Kanayama (1967). checked i n Greenwood, Bosen, Weitzman, and P o e c i l i i d genera checked i n Rosen and 7 3 Table 6 Icont Common Name | S c i e n t i f i c Name | Date |Origin Species That May Be Established , +-Cyprinodonts: "Annual f i s h " Argentine pearl INothobranchius guentheri fish|Cynolebias b e l l o t t i i Introductions Known To Have Failed j. 1967 1967 A f r i c a S. America Ephemeroptera: Mayfly Mayfly Salmonids: Brook trout Brown trout King salmon Cyprinodontids: Gulf k i l l i f i s h Oryziatids: Medaka I c t a l u r i d s : Brown bullhead Anabantids: Giant gourami Pearl gourami Plecoglossids: Ayu I IS£Etagenia rubroventrig |iron lagunitas I I JSalyelinus fontenalis I Salmo t r u t t a IQnchorhynchus tschawytscha I \ |Fundulus grandis I I IQSI^ias l a t i p e s Ictalurus nebulosus IOsphronemus gouraray JTrichogaster l e u i I El§£23i2§sus a 1 t i y e 1 i s 1961 1961 1876 1935 1876 1905 1922 1893 1950 1940 1925 C a l i f o r n i a C a l i f o r n i a Eastern D. S, Europe N. P a c i f i c Gulf Coast East Asia Central 0. S. South Asia South Asia Japan 74 Gambusia a f f i n i s had been d i s t r i b u t e d to the f o l l o w i n g l o c a t i o n s : " I s l a n d of Oahu - Honolulu and v i c i n i t y g e n e r a l l y , A i e a , P e a r l C i t y , Waialua, Maunawai, Wahiawa, and Waimanalo; i s l a n d of Hawaii - H i l o and v i c i n i t y , and Paauhau; i s l a n d of Maui - K a h u l u i , Wailuku, and Lahaina; i s l a n d of Kauai - L i h u e , E l e e l e , and waimea; and i s l a n d of Molokai - Kalaupapa" (Ann. Rept. Hawn. A g r i c . Expt. Sta. 1907). Thus G.J. a f f i n i s were r a p i d l y spread to a l l the major i s l a n d s , and I have assumed t h a t w i t h i n a few years, t h r e e to f i v e at most, they had been i n t r o d u c e d to most standing bodies of f r e s h water on the f o u r main i n h a b i t e d i s l a n d s . Between 1905 and 1950, there were few i n t r o d u c t i o n s of freshwater f i s h t o Hawaii. Then s t o c k i n g e f f o r t s i n c r e a s e d , and today many s p e c i e s are e s t a b l i s h e d i n Hawaii. Table 6 l i s t s the freshwater s p e c i e s known or suspected o f being e s t a b l i s h e d i n the S t a t e , adapted from Brock (1960) and Kanazawa (1967). L a t e r i n t h i s chapter I w i l l l i s t the s p e c i e s a c t u a l l y documented as o c c u r r i n g i n the same bodies of water that I sampled f o r Gambusia. Although the s p e c i e s l i s t i n Tahle 6 i s l o n g , i t i s a summary l i s t f o r the whole S t a t e . In a g i v e n r e s e r v o i r , i t i s unusual to f i n d more than t h r e e or f o u r s p e c i e s of f i s h . Having d e s c r i b e d the c o n d i t i o n s under which Gambusia evolved i n Texas, summarized the circumstances that l e d to i t s i n t r o d u c t i o n to Hawaii f o r mosguito c o n t r o l , and documented i t s r a p i d spread to a l l major i s l a n d s , I w i l l now d e s c r i b e the c o n d i t i o n s Gambusia encountered, and t h e i r impact on m o s g u i t o f i s h p o p u l a t i o n s . 75 *U Methods I v i s i t e d Hawaii twi c e , the f i r s t t r i p spanning 30 December 1973 t o 6 February 1974, and the second, 21 November to 5 December 1974. In a d d i t i o n , preserved samples from one r e s e r v o i r were taken i n August 1974 by f r i e n d s i n Hawaii and mailed to me. On the f i r s t t r i p I v i s i t e d t hree i s l a n d s , sampling 4 r e s e r v o i r s on Hawaii, 23 on Maui, and 7 on Oahu. Three r e s e r v o i r s on Maui and two r e s e r v o i r s on Oahu had n e i t h e r G, a f f i n i s nor P.. r e t i c u l a t a , which I c o l l e c t e d to check the trends observed i n Gambusia. On the second t r i p , I v i s i t e d Maui and Hawaii, t a k i n g samples from 5 r e s e r v o i r s on Maui and 2 r e s e r v o i r s on Hawaii. Of these, one Maui r e s e r v o i r had no Gambusia, the p o p u l a t i o n having died out s i n c e January. Thus I analyzed preserved f i s h from 29 r e s e r v o i r s sampled on the f i r s t t r i p , and from 6 r e s e r v o i r s sampled again on the second t r i p . F i g . 11 presents the f i e l d s i t e s , showing the l o c a t i o n of the r e s e r v o i r s sampled. At each r e s e r v o i r v i s i t e d on the f i r s t t r i p , I took one 15 m plankton haul with a #20 c o n i c a l plankton net (25 cm diameter, 153 micrometer mesh), and a s e r i e s of temperature r e a d i n g s at the s u r f a c e , 15, 30, 45, 60, 75, and 90 cm. In November, I took t h r e e 15 m plankton hauls with the same net and a s i n g l e temperature reading at 45 cm. F i s h were caught i n a two-man beach s e i n e 3 m l o n g , 1.2 m high, with a mesh s i z e of 2.2-2.8 mm. I took 5 f i s h samples at a l l r e s e r v o i r s except 4 of the r e s e r v o i r s sampled i n November, at which I took 3 samples. I t r i e d to space the samples out around the r e s e r v o i r margin and to get samples from d i f f e r e n t h a b i t a t s . Each sample c o n s i s t e d 76 FIGURE 11 Maps Of The Hawaiian I s l a n d s : The F i e l d S i t e s Gambusia were introduced to Hawaii i n 1905 at Moanalua Gardens i n Honolulu, and by 1907 were i n p l a n t a t i o n r e s e r v o i r s on a l l fou r sugar-producing i s l a n d s : Kauai, Oahu, Maui, and Hawaii. I found Gambusia, P o e c i l i a , or both i n 1974 i n the r e s e r v o i r s and pump sumps i n c l u d e d i n these maps. They al'so i n h a b i t many other bodies of water. These impoundments were c l a s s e d as s t a b l e i n my study: Pump 4 (Haialua, Oahu), Kaihue Booster Pump, Camp 17, Twin, and Kay R e s e r v o i r s (Kohala, Hawaii), and U n i v e r s i t y Quarry Pond (Oahu, not shown). The other r e s e r v o i r s shown ( a l l of those on Maui, and 3 on Oahu) were c l a s s e d as f l u c t u a t i n g . Waialua Sugar Company \^ * MILES , . ~~~~ > '~- - -~-^_~"^VVS5L^ | . \ ^ ^ ^ w ^ ^ ^ j ^ ' ' upper Helefnano * \ Res. ':• Schof:old *'Bzrrazki\^_^?y/0%y^ ^ ^ / ^ ^ ^ ^ ^ ^ ^ ^ ^ . v ^ h i a w a Res. £ K A U A I L E G E N D RCCcnvoiR •«» TCWN o <Q> PLVP • STATE HIGHWAY NUV3E3 (ST) BORDER OF SUGAR COMPANY LAND Hawaiian Islands 50 MIL£S \ Oahu . ^ / ^ l Hawaii Ha'.vaiian Commercial and Sugar Company ~/^ ,r 2 MILES . p^y f j / ' ^ ^ ^ L W ^ ^ ^ / > O p a ; a ^ Nv-^^^"^ ^ ^ S p r e c W e s v i l l e Kar\j!ui / \ ©.Res.25 "• V y ^ r V X ^CL— \ "Res.21 C-i „ \ ^ ' »Res .22 / tOctjPuLner.e Res. 34 / / ^ - V „ 3< Bes.35 ft'Rcs-32^ / / Res^-X - Res.33 ^ s _ 3 . „ • / / Res. 80 \ • / • / -Res. 41 \ •Res. 91 J »F.es. 9 0 *Res.42 \ Q9 .Res.SI _ „ „ „ \ M «>Res.40 y \ Ttes.82 Moat, y °Kaihue B< A CN. 5 • -A c ^v— -C Kohala Sugar Company point poster Pump^i •> *Camp f7 Res. ^ \ . \ \ • • 1 \ \ _ , 'Kay'' fi.es. & j .Twin Res. 78 of enough sweeps to c o l l e c t at l e a s t 100 f i s h , or to exhaust the f i s h i n the area, whichever happened f i r s t . In t a k i n g a sweep, my a s s i s t a n t and I would u s u a l l y wade i n t o water about 0.5 m deep, spread the s e i n e , and move d i r e c t l y onto the s h o r e l i n e , being c a r e f u l to drag the s e i n e , as much as p o s s i b l e , through the weeds as well as open water. When the bottom dropped o f f q u i c k l y , we o c c a s i o n a l l y had to swim the se i n e i n t o shore. Seine hauls v a r i e d i n l e n g t h from about 3 t o 15 m, depending on c o n d i t i o n s . Host were 8 t o 10 m l o n g . Thus the u n i t of e f f o r t t h a t went i n t o each c a t c h was q u i t e v a r i a b l e . While at the p l a n t a t i o n s , I examined o l d maps and annual r e p o r t s to determine the c o n s t r u c t i o n dates of r e s e r v o i r s . I f a r e s e r v o i r appeared on a map dated 1907, I assumed i t had been c o n s t r u c t e d before 1907. The c o n s t r u c t i o n dates f o r Twin, Kay, and Camp 17 r e s e r v o i r s were i n f e r r e d from h i s t o r i c a l accounts of the development of the sugar i n d u s t r y i n Kohala. I found exact dates f o r the c o n s t r u c t i o n of s i x impoundments i n p l a n t a t i o n or municipal r e c o r d s . In p r e s e r v i n g the f i s h , I was c a r e f u l to take f i s h of a l l s p e c i e s , sexes, and s i z e s to get a r e p r e s e n t a t i v e sample. I u s u a l l y preserved e v e r y t h i n g i n the net. When l i v i n g f i s h were returned t o the r e s e r v o i r (e.g. P l a t i p i n n a , Xiphophprus, T i l a p i a ) , they were counted and the numbers recorded. I f we caught more f i s h than I wanted to pre s e r v e , we would d i v i d e the ca t c h i n t o halves o r gu a r t e r s , preserve one p o r t i o n and r e t u r n the r e s t to the r e s e r v o i r . The f r a c t i o n preserved on s i n g l e -sweep samples, and the number of sweeps made f o r multiple-sweep samples, were recorded at the time the sample was taken. As 79 samples were c o l l e c t e d , they were l a b e l l e d and preserved i n f o r m a l i n . In Vancouver, they were washed, t r a n s f e r r e d to 70% e t h a n o l , and permanently l a b e l l e d . In a n a l y z i n g the f i s h samples, a t e c h n i c i a n s e l e c t e d 50 f i s h at random from the preserved sample, or fewer i f there were l e s s than 50 i n the sample. On each f i s h , she measured the standard l e n g t h (from the edge of the upper l i p to the t i p of the caudal peduncle) to the nearest 0.1 mm, c l a s s i f i e d the f i s h as one of 5 types (adult female, j u v e n i l e female, a d u l t male, j u v e n i l e male, or unsexed j u v e n i l e ) , and i f i t was a female she d i s s e c t e d i t and counted the embryos. The embryos were c l a s s i f i e d as one of f i v e t y pes: no-eyed s m a l l (NES), no-eyed l a r g e (NEL), e a r l y - e y e d (EE), l a t e - e y e d (LE), and very l a t e - e y e d (VLE). The NES eggs were l e s s than 0.5 mm i n diameter and w h i t i s h . NEL eggs were about 1.5-2 mm i n diameter, as l a r g e as more advanced stages, and y e l l o w i s h , but with no v i s i b l e d i f f e r e n t i a t i o n other than a s m a l l , white d i s c on the s u r f a c e . EE eggs had an embryo v i s i b l e on the s u r f a c e of the y o l k mass with an eye formed, but the y o l k mass was s t i l l c l e a r l y l a r g e r than the embryo. LE eggs had embryos l a r g e r than the yolk mass, with w e l l developed f i n s and mouth. VLE embryos were ready f o r b i r t h , with the yolk mass v i r t u a l l y gone. A f t e r c l a s s i f y i n g the embryos, she d r i e d a l l the f i s h and embryos i n an oven at 100°C f o r 6 hours, s t o r e d them i n a d e s i c c a t o r , and weighed each f i s h and each c l a s s of embryos s e p a r a t e l y to the n e a r e s t 0.1 mg on a M e t t l e r H16 balance. Lengths, weights, and codes were entered d i r e c t l y on keypunching forms, keypunched, v e r i f i e d , and input to the computer, where 80 the data was s t o r e d on disk and tape f i l e s . I e d i t e d the f i s h data with a program t h a t checked f o r i n c o r r e c t codes and f o r numbers, l e n g t h s , and weights o u t s i d e a reasonable range, then spot-checked the data manually. In p r o c e s s i n g the plankton samples, the t e c h n i c i a n f i r s t removed a l l d e b r i s from the sample, then resuspended i t i n 70% et h a n o l with 10 drops of g l y c e r i n . A f t e r making i t up to 5 ml with water, she s t i r r e d the sample and took three 1 ml subsamples, i n which she i d e n t i f i e d and counted each organism and measured i t s l e n g t h under a d i s s e c t i n g microscope with an o p t i c a l micrometer. Stomach samples were handled d i f f e r e n t l y . She d i s s e c t e d the f i s h , t r a n s f e r r e d the stomach c o n t e n t s t o a l c o h o l , and c l a s s i f i e d and measured up to 50 i n d i v i d u a l s of each s p e c i e s . She measured only those items which were s t i l l complete enough t o allow measurement of a h e a d - t o - t a i l l e n g t h . The r e s t of the items i n the stomach were c l a s s i f i e d and counted. 5 X R e s u l t s T h i s s e c t i o n presents a l l the data I could develop t o t e s t the assumptions made i n c a l l i n g the i n t r o d u c t i o n of Gambusia to Hawaiian r e s e r v o i r s an e v o l u t i o n a r y experiment. I have t h e r e f o r e organized the r e s u l t s as answers to a s e r i e s of que s t i o n s t h a t probe, from d i f f e r e n t angles, the v a l i d i t y of my c l a i m t h a t some G.. a f f i n i s p o p u l a t i o n s i n Hawaii encountered s t a b l e environments, o t h e r s , f l u c t u a t i n g ones. Therefore, I f i r s t d e f i n e what I mean by " s t a b l e " and " f l u c t u a t i n g " , then look f o r environmental f a c t o r s which c o u l d have confounded the 81 s t a b l e - f l u c t u a t i n g d i s t i n c t i o n . By examining p o t e n t i a l confounding f a c t o r s , I a l s o r e f i n e the d e f i n i t i o n of the treatments t h a t d i f f e r e n t f i s h s t o c k s r e c e i v e d . Then I examine evidence from the preserved f i s h samples to see i f f i s h p o p u l a t i o n s i n s o - c a l l e d " s t a b l e " r e s e r v o i r s are a c t u a l l y more demographically s t a b l e than those from " f l u c t u a t i n g " r e s e r v o i r s . 5 a D e f i n i t i o n s I d e f i n e s t a b i l i t y s o l e l y i n terms of water l e v e l i n the r e s e r v o i r s . Table 7 l i s t s the impoundments sampled and i n d i c a t e s the s t a b l e - f l u c t u a t i n g s p l i t . The r e s e r v o i r s I c l a s s e d as s t a b l e a re f e d by s p r i n g s , w e l l s , or d i t c h e s , and have dams with c o n c r e t e l i p s o r c u l v e r t s that put a p r e c i s e upper l i m i t on the water l e v e l . The s t a b l e r e s e r v o i r s are almost always f u l l . Of the s t a b l e impoundments. Twin R e s e r v o i r and Kaihue Booster Pump Sump i n Kohala and the a r t e s i a n w e l l at Pump #4 at Waialua have probably not v a r i e d i n depth by more than a few ce n t i m e t e r s s i n c e they became s t a b l e s h o r t l y a f t e r c o n s t r u c t i o n . They are fed by water sources that continue to flow i n the d r i e s t summers. Camp 17 R e s e r v o i r at Kohala i s f e d by the Kohala Ditch and i s kept f u l l as a form of insurance f o r the sugar m i l l . ( I t has never been used f o r that purpose). However, every two or thre e years the water l e v e l i s lowered to allow maintenance work on the o u t l e t , an op e r a t i o n t h a t drops the r e s e r v o i r to about 70% f u l l . Kay Reservor i n Kohala i s q u i t e s i m i l a r i n aspect to Twin, but i s fed by a s p r i n g that does stop f l o w i n g during unusually 82 Table 7 Summary Of Re s e r v o i r Samples T T ! "1 Elevation|Constructed!Sampled 1 Temp (meters) \ | I 45cm 1 1 1 R e s e r v o i r , 1 S/U }Veg|WC*} I I I i i J 1. Kohala Twin Kay Camp 17 Kaihue Pump 564 503 251 73 j. h ! i Before 1910|3lDec73 |20°C }27Nov74 |21« Before 1910} 5Feb74 |20o |27Nov74 |230 Before 1910} 2Jan74 |21o 1934 | 5Feb74 |220 4 -S s I 5 | 2 I \ I 5 | 2 S I 3 | 2 S f 1 | 4 i x Oahu Univ. Quarry | 6 I 1927 | 3Uan74 I 210 J S I 2 i 2 Pump #4 | 6 I 1900 | 2Feb74 | 210 I s I 1 i 1 Wahiawa | 256 j 1906 \ 1Feb74 I 220 t o I 4 I 3 Opaeula #1 | 320 I 1914 | 2Feb74 |21o 1 o I 2 I 4 Upper Belemanol 314 | 1909 J 2Feb74 L . I 230 I o I _ i 2 i 4 .j 3. Maui R e s e r v o i r 21 I 256 |Before 1907| 14Jan74 j 20 0 1 u 1 3 | 3 R e s e r v o i r 22 | 258 |Before 1907 10Jan74 |21« 1 o 1 3 3 R e s e r v o i r 25 | 117 | Before 1907| 15Jan74 I 2 2 . 5 0 \ o 1 4 | 3 R e s e r v o i r 31 l 246 |Before 19071 12Jan74 j 200 1 u } 4 ; 3 R e s e r v o i r 32 | 248 | Before 1907) 14Jan74 I 2 0.5OJ u 1 4 3 R e s e r v o i r 33 | 246 J Before 1907 14Jan74 22Nov74 |21 . 5 0 j rj I 1 9 . 5 0 } 1 3 3 R e s e r v o i r 35 j 165 I Before 1917J 1Uan74 | 2 1 0 1 u 1 5 5 R e s e r v o i r 40 | 317 I Before 1926| 16Jan74 | 2 1 0 1 u" 1 2 j 3 R e s e r v o i r 41 I 195 I Before 1907! 11Jan74 5Dec74 | 220 } 240 1 o \ 4 | 3 R e s e r v o i r 42 | 23 5 I Before 1917i 16Jan74 | 220 1 o 1 u 3 R e s e r v o i r 50 | 133 |Before 1907; 10Jan74 5Dec74 1210 I 2 1 0 1 o 1 3 3 R e s e r v o i r 51 | 133 i Before 1910! 8Jan74 |210 1 o } 3 ) 3 R e s e r v o i r 60 I 34 |Before 19101 21Jan74 121.50} o 1 2 | 3 R e s e r v o i r 61 I 50 j Before 1910| 2Uan74 | 240 I o 1 2 | 4 Res e r v o i r 80 | 122 I Before 1910) 17Jan74 122 .50} U 1 3 | 4 Re s e r v o i r 81 I 73 I Before 1910 16Jan74 23Nov74 | 230 j 230 1 o 1 ^ 2 R e s e r v o i r 84 | 90 | Before 1910! 8Jan74 1 230 J u 1 3 3 R e s e r v o i r 90 | 40 j Before 1910| 17Jan74 \ 250 1 u 1 4 3 R e s e r v o i r 91 | 53 I Before 19101 21 Jan74 I 250 1 o 1 4 1 2 * V e g e t a t i o n : 1=none; 5=dense Water C l a r i t y : 1=clear; 5=murky 83 dry summers (e.g. 1974), The water l e v e l i n Kay dropped t o about 20% f u l l i n August-October 1974, one of the two or three d r i e s t summers s i n c e the p l a n t a t i o n s t a r t e d keeping records i n the ISSO's. , The summer of 1974 was the only time i n the memories o f the men who run the p l a n t a t i o n (spanning 30-40 years) that Kay had v a r i e d i n water l e v e l at a l l . U n i v e r s i t y Quarry Pond, on the U n i v e r s i t y of Hawaii campus i n Honolulu, c o n s i s t s of a freshwater l e n s f l o a t i n g on s a l t water t h a t l i e s below the pond bottom. During t o r r e n t i a l winter storms i t o c c a s i o n a l l y o v erflows. In summary, of the s i x r e s e r v o i r s c l a s s e d as s t a b l e , three vary i n depth hardly at a l l , two experience s m a l l changes i n water l e v e l (ca. 10%) every two or three y e a r s , and one, Kay, may go through severe drawdowns every 30-50 ye a r s . By any standard, the r e s e r v o i r s c l a s s e d as f l u c t u a t i n g vary w i l d l y i n depth. A l l can and do go empty o c c a s i o n a l l y , l e a v i n g only a s m a l l pool lower than the o u t l e t p i p e . The f l u c t u a t i n g r e s e r v o i r s are i n a c t i v e use i n p l a n t a t i o n i r r i g a t i o n systems, and are fed by w e l l s or d i t c h e s that channel r a i n f a l l r u n o f f from the windward mountains onto the leeward p l a i n s . Thus they are d r i v e n by an i n t e r a c t i o n of r a i n f a l l r u n o f f , which i s randomly d i s t r i b u t e d over s h o r t p e r i o d s , and i r r i g a t i o n p r a c t i c e , which i s s y s t e m a t i c . Small f l u c t u a t i n g r e s e r v o i r s can go from f u l l t o empty i n e i g h t hours; the l a r g e s t takes months to empty. A l l vary from near f u l l t o near empty every year, and some do so every week. In Chapter V I d e s c r i b e the f l u c t u a t i o n s i n d e t a i l , c l a s s i f y them i n t o a few p a t t e r n s , and examine t h e i r impact on the f i s h p o p u l a t i o n s . For present purposes, I simply 84 n o t e t h a t H a w a i i a n r e s e r v o i r s f a l l c l e a r l y i n t o two c l a s s e s : s t a b l e r e s e r v o i r s t h a t v a r y i n w a t e r l e v e l r a r e l y i f a t a l l , a n d f l u c t u a t i n g r e s e r v o i r s t h a t v a r y i n w a t e r l e v e l o v e r t h e i r f u l l r a n g e on p e r i o d s r a n g i n g f r o m d a y s t o o n e y e a r . 5b.. C o n f o u n d i n g f a c t o r s O t h e r s p e c i e s ^ The s t a b l e - f l u c t u a t i n g d i s t i n c t i o n , c o u c h e d s i m p l y i n t e r m s o f w a t e r d e p t h , i s c l e a r e n o u g h . B u t d o o t h e r f a c t o r s v a r y a l o n g w i t h w a t e r l e v e l ? F i r s t , do s t a b l e r e s e r v o i r s s h a r e a c h a r a c t e r i s t i c s p e c i e s a s s e m b l a g e d i f f e r e n t f r o m t h a t s h a r e d by u n s t a b l e r e s e r v o i r s ? I f t h e y d o , t h e G . a f f i n i s l i v i n g i n them h a v e b e e n e x p o s e d t o d i f f e r e n t p r e d a t o r s , c o m p e t i t o r s , a n d f o o d r e s o u r c e s , a n d t h e s e d i f f e r e n c e s c o u l d e a s i l y c o n f o u n d t h e s t a b i l i t y c l a s s i f i c a t i o n . I n e x a m i n i n g t h i s p r o b l e m , I h a v e a v a i l a b l e t h e f o l l o w i n g d a t a : t h e s t o c k i n g r e c o r d s o f t h e S t a t e o f H a w a i i D e p a r t m e n t o f F i s h a n d Game, t h e r e c o r d s o f s p e c i e s c a u g h t o r s i g h t e d on my two f i e l d t r i p s , a n d t h e a n a l y s i s o f t h e p l a n k t o n s a m p l e s . T h e s e s o u r c e s a l l o w t h e c o n s t r u c t i o n o f a f a i r l y c o m p l e t e l i s t o f t h e i n h a b i t a n t s o f e a c h r e s e r v o i r . F i g . 12 p r e s e n t s t h e r e s e r v o i r s t o c k i n g d a t e s f o r a l l r e s e r v o i r s t h a t I s a m p l e d w h i c h a l s o a p p e a r e d i n t h e D e p a r t m e n t o f F i s h a n d G a m e ' s s t o c k i n g r e c o r d s . I h a v e i n c l u d e d summary s t o c k i n g r e c o r d s f o r o t h e r r e s e r v o i r s on M a u i a n d i n K o h a l a , s i n c e t h o s e r e s e r v o i r s p r o v i d e d p o o l s f r o m w h i c h s p e c i e s c o u l d be d r a w n f o r l a t e r , u n r e c o r d e d i n t r o d u c t i o n s . One f e a t u r e s t a n d s o u t i n F i g . 12: b e f o r e 1 9 5 0 , t h e r e was v e r y l i t t l e s t o c k i n g a c t i v i t y i n H a w a i i . G^. a f f i n i s i n h a b i t e d r e s e r v o i r s 85 FIGURE 12 S t o c k i n g Dates Of E x o t i c F i s h e s In Hawaii I compiled t h i s f i g u r e from s t o c k i n g r e c o r d s i n the D i v i s i o n of F i s h and Game, Department of Land and N a t u r a l Resources, S t a t e of Hawaii, Honolulu, Hawaii. I have i n c l u d e d a l l r e s e r v o i r s t h a t I sampled t h a t a l s o appeared i n the s t o c k i n g r e c o r d s , as w e l l as nearby r e s e r v o i r s that could have served as pools from which l a t e r , unrecorded i n t r o d u c t i o n s might have o r i g i n a t e d . Note t h a t Gambusia and P o e c i l i a l i v e d f o r 30-40 years i n r e s e r v o i r s i n which they were u s u a l l y the only f i s h p resent. 86 87 f o r 40 y e a r s i n w h i c h t h e o n l y c o h a b i t a n t s w e r e c a r p , C h i n e s e c a t f i s h , g u p p i e s , a n d s a i l f i n m o l l i e s , a n d t h o s e p r o b a b l y n o t i n a l l r e s e r v o i r s a n d f r e q u e n t l y i n l o w n u m b e r s i f p r e s e n t p a t t e r n s h e l d t r u e i n t h e p a s t . O n l y o n e r e s e r v o i r , W a h i a w a , h a d a p o t e n t i a l G a m b u s i a p r e d a t o r , t h e s n a k e h e a d ( Q p h i c e p h a l u s ) , b e f o r e 1 9 5 0 . a f t e r 1 9 5 0 , b l u e g i l l s , l a r g e m o u t h b a s s , s m a l l m o u t h b a s s , o s c a r s , a n d t u c u n a r e , a l l p o t e n t i a l G a m b u s i a p r e d a t o r s , were s t o c k e d f o r s p o r t f i s h i n g i n c e r t a i n r e s e r v o i r s , w h i l e p o t e n t i a l c o m p e t i t o r s , s u c h a s t h r e a d f i n s h a d a n d v a r i o u s t i l a p i a s p e c i e s , w e r e s t o c k e d f o r b a i t f i s h a n d weed c o n t r o l . B l u e g i l l s , w h i c h a r e p l a n k t i v o r o u s , a r e a l s o p o t e n t i a l G a m b u s i a c o m p e t i t o r s , a s a r e P.. l a t i p i n n a a n d P.. r e t i c u l a t a . S t o c k i n g r e c o r d s c a n n o t p r o v i d e a c o m p l e t e s p e c i e s l i s t f o r a r e s e r v o i r f o r two r e a s o n s . P e o p l e o t h e r t h a n F i s h a n d Game o f f i c i a l s p u t f i s h i n t o r e s e r v o i r s a n d l e a v e no r e c o r d s , a n d some o f t h e s t o c k s p l a n t e d d i e o u t . T a b l e 8 p r e s e n t s a m o r e a c c u r a t e p i c t u r e : t h e f i s h s p e c i e s a c t u a l l y c a u g h t by me i n 1974 ( n o t e d a s S C S ) , o r r e p o r t e d a s b e i n g c a u g h t i n F i s h a n d Game r e c o r d s ( n o t e d a s F G ) . H o s t r e s e r v o i r s h a v e G a m b u s i a a n d o n e o r two o t h e r s p e c i e s , u s u a l l y T i l a p i a o r a n o t h e r p o e c i l i i d , i n l o w e r n u m b e r s . One r e s e r v o i r , W a h i a w a , h a s an a s s e m b l a g e o f 1 4 -16 s p e c i e s . No o t h e r r e s e r v o i r h a s m o r e t h a n 4 s p e c i e s . P r e d a t o r s o c c u r i n W a h i a w a a n d Ku T r e e , a n d p o s s i b l y i n T w i n a n d O p a e u l a #1. P r e d a t o r s t o c k s p l a n t e d by F i s h a n d Game o f f i c i a l s d i d n o t s u r v i v e o n M a u i o r i n Camp 17 r e s e r v o i r ( p l a n t a t i o n o f f i c i a l s , p e r s , c o m m . ) . I n T a b l e 9 I p r e s e n t t h e t r e a t m e n t s r e c e i v e d b y G._ a f f i n i s , a n d i n a few r e s e r v o i r s , b y P.. r e t i c u l a t a , o v e r t h e l a s t 5 0 - 7 0 88 T a b l e 8 F i s h S p e c i e s Known To Be I n R e s e r v o i r s I n 1974 R e s e r v o i r I G a m b u s i a j J _ a f f i n i s J P o e c i l i a r e t i c u l a t a P o e c i l i a | X i f i h o p h o r u s | T i l a p i a | O t h e r Aa^ifiiJlfla.I k § l i § E i I s p p . I F i s h _ Z _ Z Z Z J Z a j . K o h a l a T w i n Kay Camp 17 K a i h u e SCS SCS SCS SCS * 2 SCS SCS Oahu D . Q u a r r Pump #4 Wahiawa O p a e u l a H e l e m a n o Ku T r e e Yl SCS | SCS | SCS | SCS | SCS i SCS SCS SCS SCS SCS SCS FG SCS SCS FG SCS * 3 * 4 * 5 3 . M a u i -+ H S e s . 21 R e s . 22 R e s . 25 R e s . 31 R e s . 32 R e s . 33 R e s . 35 R e s . 40 R e s . 41 R e s . 42 R e s . 50 R e s , R e s , R e s . 61 R e s . 80 R e s . 81 R e s . 84 R e s . 90 R e s . 91 51 60 SCS SCS SCS SCS SCS SCS SCS SCS SCS SCS SCS SCS SCS SCS SCS SCS SCS SCS SCS SCS SCS SCS SCS SCS SCS SCS SCS SCS SCS SCS SCS SCS SCS SCS SCS ' ? ? ?? SCS ?? SCS ? ? ?? ?? SCS ? ? SCS SCS ?? SCS SCS ?? ?? SCS SCS * 4 * 2 • O t h e r f i s h : 1 = b l u e g i l l s , C h i n e s e c a t f i s h 2 = c a r p 3 = c a r p , b l u e g i l l s , s m a l l m o u t h b a s s , l a r g e m o u t h b a s s , t u c u n a r e , o s c a r s , c h a n n e l c a t f i s h , t h r e a d f i n s h a d , s n a k e h e a d s , g o b i e s , a n d C h i n e s e c a t f i s h . 4 = J a p a n e s e w e a t h e r f i s h 5 = b l u e g i l l s , l a r g e m o u t h b a s s , a n d t u c u n a r e Table 9 Treatments Received By Gambusia and P o e c i l i a In Hawaii •T 1 1 T 1 I I I I I | I n t r o . | S t a b l e jDnstable |Comp. |Pred. R e s e r v o i r Const, + 1. Kohala +• I I 164 y r s | |64 y r s | |64 y r s j |40 yrs | Twin Kay Camp 17 Kaihue 1910 1910 1910 1934 11910 11910 | 1910 | 1935 I I |22 y r s | I I I ? I i ? i 2. Oahu | U n i v e r s i t y | 1927 | 1927 |47 yr s ! ? I IPump #4 | 1900 | 1 907 I67 y r s 1 | ? I 1Bahiawa | 1906 | 1907 I |67 yrs J 23 yrs|22 yrs | JOpaeula #1) 1914 \ 1914 I |60 y r s 125 y r s | JHelemano | 1909 11909 I I 65 yr s | I |Ku Tree \ 1935 11935 I 39 yr s 1 |23 y r s | 6 yrs j i i i i „ J • V3. Maui , i „ • • • 1 - J l JRes.21 | 1907 11907 j 1 67 yr s 7 1 |Res.22 ) 1907 | 1907 j J 67 y r s | 7 1 |Res.25 | 1907 I 1 907 | |67 yrs 1 17 yrs | JRes.31 | 1907 | 1907 J | 67 y r s | 7 i |Res.32 | 1907 | 1907 | | 67 yrs |17 y r s | |Res.33 I 1907 | 1907 | |67 y r s |Res.35 | 1917 | 1917 j |57 y r s I 7 1 |Res.40 | 1926 | 1926 | |48 y r s j •> 1 |Res.41 | 1907 | 1907 | 1 67 yrs I 17 y r s | |Res.4 2 | 1917 | 1917 J | 57 y r s j ? i |Res.50 | 1907 I 1907 J 167 y r s I 17 y r s j JRes.51 | 1910 11910 | | 64 y r s I 17 y r s j |Res.60 | 1910 | 1910 j |64 y r s | 7 j |Res.61 | 1910 |1910 1 | 64 y r s 117 y r s | |Res.80 | 1910 J1910 | j 64 yr s 1 17 y r s | JRes.81 j 1910 11^10 | ]64 yr s | ? | |Res.84 j 1910 11910 | |64 yrs | 7 1 |Res.90 j 1910 11910 | |64 y r s I 17 yrs | |Res.91 | 1910 | 1910 I | 64 yr s I 17 yr s | 90 years, as I r e c o n s t r u c t e d them from Tables 7 and 8. I have assumed that i f a game f i s h was stocked i n the 1950's and 1960's, but died out, t h a t i t has had no s i g n i f i c a n t impact on the p o e c i l i i d p o p u l a t i o n s i n the r e s e r v o i r and d i d not f i g u r e i n the d e f i n i t i o n of the treatment r e c e i v e d . Other f i s h s p e c i e s are important members of Gambusia *s community, but not the only ones. Table 10 summarizes the b i r d s s i g h t e d at the r e s e r v o i r s during 40 v i s i t s to d i f f e r e n t r e s e r v o i r s . C l e a r l y , there are more s h o r e b i r d s and ducks on Maui than on Oahu or Hawaii. Hawaiian s t i l t s and ducks probably have l i t t l e impact on Gambusia, but the black-crowned n i g h t heron almost c e r t a i n l y eats Gambusia whenever i t can. The composition of the plankton communities of 10 r e s e r v o i r s sampled with a s i n g l e tow i n January 1974 i s shown i n Table 11. Both p l a n k t o n i c forms and the b e n t h i c s p e c i e s caught i n the plankton tow were counted. There were from 2 t o 7 t o t a l s p e c i e s per r e s e r v o i r , and from 1 to 4 p l a n k t o n i c s p e c i e s per r e s e r v o i r . U s u a l l y one s p e c i e s was dominant, making up 50-90% of the number of animals present, and the two most common s p e c i e s accounted f o r 80-100% of the animals present. There were no c l e a r d i f f e r e n c e s between s t a b l e and unstable r e s e r v o i r s i n d e n s i t y or s p e c i e s composition of the plankton communities. Of course, these samples merely r e p r e s e n t an estimate of s t a n d i n g crop at a s i n g l e p o i n t i n time, and give no i n f o r m a t i o n on the r a t e of production of plankton, or changes over time. Food.. I f there were c o n s i s t e n t d i f f e r e n c e s i n mean p r o d u c t i v i t y or food a v a i l a b i l i t y between s t a b l e and unstable r e s e r v o i r s , 91 Table 10 Waterfowl Sighted At Hawaiian R e s e r v o i r s ; Average Number Sighted Per V i s i t r-Kohala R e s e r v o i r s Maui R e s e r v o i r s * Waialua R e s e r v o i r s Herons 0.0 1.5 0.0 Hawn S t i l t s 0.0 0.5 0.0 -+-P i n t a i l Ducks 0.0 10.9 0.0 # V i s i t s 8 28 4 *0ther b i r d s s i g h t e d : numerous golden p l o v e r , wandering t a t t l e r s , ruddy t u r n s f o n e s , and an u n i d e n t i f i e d scaup. Table j .2 Plankton Density: Numbers Per Tow January 1 9 7 4 1 T T— i • r T 1 r T— 4 I Twin | J i Kay | Ku Treo | Opaeula |H elemano.| Res 2 5 1 1 Res 5 1 1 I Res 8 0 | Res 8 1 | Res 9 1 j J 1 . D e t a i l s 1 P l a n k t o n i c Species • i 1 1 1 1 1 j j - -)— j [ 1 3 0 1 . 6 7 | 3 . 3 3 | 1 . 6 7 1 1 - 6 7 | 8 5 . 0 0 | 2 1 . 6 7 1 3 . 3 3 1 8 . 3 3 | 1 7 5 . 0 0 | 1 . 6 7 1 2i§2liaa2sonia | 5 . 0 0 | 1 . 6 7 | 3 . 3 3 I 3 5 3 . 3 3 | - 3 . 3 3 | . 1 9 8 . 3 3 | I I 3 . 3 3 | 3 . 3 3 | Cerioda£hnia I I | 3 . 3 3 1 1 I | 1 • I R o t i f e r s I I 9 6 . 6 7 | 1 1 7 0 8 . 3 3 | 2 6 . 6 7 I 1 I 1 0 . 0 0 | 2 0 1 . 6 7 I Chironomids 1 1 1 1 1 I 1 1 1 1 . 6 7 | I S u b t o t a l | | 1 3 0 6 . 6 7 | • • 1 0 1 . 6 7 | 8 . 3 3 I 3 5 5 . 0 0 | 7 9 6 . 6 7 | 2 4 6 . 6 7 i 1 3 . 3 3 | 8 . 3 3 | 1 9 0 . 0 0 | 2 0 6 . 6 7 | | B e n t h o - l i t t o r a l s p e c i e s 1 1 L_ 1 1 i | A1 o n a 1 1 3 . 3 3 | 1 1 1 1 j T 1 } 1— 6 . 6 7 | | Chvdorus 1 1 . 6 7 | | 1 1 3 5 . 0 0 | 1 1 i I Sida 1 I | 1 1 - 6 7 | I I I • I H a r p a c t i c o i d cop. 1 1 j I I | 1 1 3 . 3 3 | 5 . 0 0 | I Ostracods 1 1 - 6 7 | | I I | 1 2 3 . 3 3 | 4 5 . 0 0 | I O l i g o c h a e t e s 1 3 . 3 3 | 1 . 6 7 | 1 1 j ( 1 • | Nematodes 1 1 - 6 7 | 1 1 I | • • • J Hydra | 6 . 6 7 I | 1 I I I 1 1 1 ] I l y o c r y p t u s I I I 1 1 i i I 1 1 0 . 0 0 | 1 i | S u b t o t a l j j | 1 5 . 0 0 1 1 1 | - .. | 5 . 0 0 | 1 1 1 1 - 6 7 | 1 1 3 5 . 0 0 | 1 1 1 3 3 . 3 3 | 3 . 3 3 | 5 6 . 6 7 | | T o t a l Numbers 1 3 2 1 . 6 7 | • • 1 0 6 . 6 7 | 8 . 3 3 | J I 3 5 6 . 6 7 | » ' 8 3 1 . 6 7 | 2 4 6 . 6 7 •1 1 1 4 6 . 6 7 |. 1 . 1 . 6 7 | 2 4 6 . 6 7 | 8 8 0 . 0 0 | 1 2 . Suranary 1 i 1 i J i J_ i , . . | Number of Species 1 1 1 5 | 3 1 1 1 3 | *» I 3 T 1 3 J 2 | 7 | 4 | j Number.of P l a n k t e r s 1 2 | 3 | 3 1 2 I 3 | 3 I 1 • 1 | 3 | 4 | | % Dominant Form 1 94 | 91 I 4 0 1 9 9 | 8 5 I 8 0 1 5 0 I 71 I 7 1 1 7 7 | | % 2 Dominant Forms 1 96 | 9 4 | 8 0 1 9 9 . 5 | 9 5 | 91 I - 7 9 I 1 0 0 | 8 9 | 9 9 . 9 | j X P l a n k t o n i c Forms 1 9 5 | 9 5 | 1 0 0 1 9 9 . 5 | 9 6 | 1 0 0 1 2 9 | 7 1 I 7 6 | 1 0 0 | • j - _ ... _ ... . i i " • '. i i i 1 93 then the f i e l d data would be s e r i o u s l y confounded, f o r n u t r i t i o n has a d i r e c t impact on growth r a t e s , f e c u n d i t y , and p o s s i b l y s i z e of young. I have a v a i l a b l e analyses of plankton samples, stomach c o n t e n t s , and c o n d i t i o n f a c t o r s f o r use i n comparing the n u t r i t i o n a l s t a t e of animals i n s t a b l e and unstable r e s e r v o i r s . Table 12 presents the average l e n g t h s of a l l s p e c i e s found i n plankton hauls from 10 r e s e r v o i r s sampled i n January-February 1974, with the numbers of i n d i v i d u a l s per s p e c i e s i n parentheses. Cyclops was the l a r g e s t common p l a n k t o n i c s p e c i e s , with a few (ca, 1-3%) i n d i v i d u a l s r e a c h i n g 1.5-1.8 mm, but most Cyclops were l e s s than 1 mm l o n g . The other three common p l a n k t o n i c types, Diaphanosoma, Ceriodaphnia, and v a r i o u s r o t i f e r s were not only small (0.3-0.7 mm); Diaphanosoma and Cerio d a p h n i a were s m a l l i n comparison to other s t o c k s of the same genera. Table 13 d i s p l a y s the numerical d i s t r i b u t i o n s of types of food items found i n the stomachs of 24 f i s h from each of 5 r e s e r v o i r s sampled i n November 1974. Table 14 presents the average lengths of the food items, and Table 15 summarizes the a n a l y s i s of the stomach samples. As the data presented i n Table 15 i n d i c a t e , Gambusia eats p l a n k t o n i c c r u s t a c e a , benthic and l i t t o r a l a q u a t i c i n v e r t e b r a t e s , and windblown i n s e c t s and s p i d e r s i n a l l r e s e r v o i r s . In only one r e s e r v o i r , Twin, d i d p l a n k t o n i c s p e c i e s dominate the d i e t n u m e r i c a l l y . In Kay, Re s e r v o i r 33, and Re s e r v o i r 81, windblown i n s e c t s formed the p r i n c i p l e food c l a s s , and i n Re s e r v o i r 22 Gambusia had been f e e d i n q f a i r l y e q u a l l y on a l l food c l a s s e s . The r e s e r v o i r s vary widely i n both number of food items per f i s h and the p r o p o r t i o n s Table 12 Plankton Samples: January 1974 Average Length In mm By R e s e r v o i r And Species 1 — i r I Twin | t i Kay — i 1 1 r t Ku Tree | Opaeula |Helemano | i i i t 1 1 1 1 1 Res 25 | Res 51 | Res 80 | Res 81 |- Res 91 | i I I i i 1 P l a n k t o n i c Species —+ r -H + 4- h + 1 + + -i Cyclops | Diaphanosoma 1 Ceriodaphnia | R o t i f e r s I Chironomids I 1 - 0 8 | (181) I 0 - 4 6 | (3) I 0 . 8 3 | (2) I 0 . 5 5 | ( D I 0 . 3 1 | (58) | < 0 . 9 9 | ( D I 0 . 3 3 | (2) I 0 . 4 7 | (2) I t 1 . 4 2 | (1) 1 0 . 3 8 | (212) | • 0 - 7 7 | (51) | 0 . 5 1 | (2) I 0 . 4 8 | (425) | 0 . 8 2 | (13) I 0 . 5 7 | (119) | 0 . 3 4 | (16) | 0 . 9 3 - | (8) I 0 . 9 4 | (5) I 0 . 8 1 | (105) | 0 . 6 4 | (2) I l ' 0 . 4 1 | (6) I 1 . 9 2 | ( D I 0 . 9 1 (1) 0 . 3 9 (2) 0 . 3 3 (404) 0 . 3 1 (121) B e n t h o - l i t t o r a l Species • t Alona | Chydorus 1 0 . 3 1 | 0 . 4 9 | (2) I 1 I 0 . 3 2 | ! I i 0 . 5 3 | (4) I (1) I l y o c r y p t u s Sida H a r p a c t i c o i d Copepods Ostracods O l i g o c h a e t e s Nematodes Hydra 0 . 6 3 ( D 0 . 8 5 (2) 0 . 7 9 d ) 0 . 6 1 2 . 7 6 0 . 3 9 (1) (21) 0 . 4 8 (6) 0 - 5 3 (14) 0 . 7 5 (2) 0 . 7 5 (3) 0 . 5 7 (27) Taule 13 Stomach Samples November 1974 Number Of Items Per Re s e r v o i r By Species 1 1 ITime Of Day I I Twin -+ I Kay -+-13-14 114-15 | P l a n k t o n i c Species I | Cyclops I Diaphanosoma • | Ceriodaphnia | R o t i f e r s IChironomids I N a u p l i i | S u b t o t a l I 724 551 8 2 1285 | B e n t h o - l i t t o r a l Species | (Alona | 50 IChydorus | 13 J l l y o c r y p t u s | | i i a r p a c t i c o i d Copepods j 4 (Ostracoda | 30 JAmphipoda | |Mites | 3 j o l i g o c h a e t a I ( K i r u d i n s a I JGastropod Molluscs | 3 | S u b t o t a l (103 IWindblown Arthropods |Spiders |Diptera I Hymenoptera | Thysanoptera | Kemiptera | Or thoptera ] Homop t e r a |Coleoptera | Deraoptera |Collembola ( M i l l i p e d e s 1 . S u b t o t a l 1 I 1 I I 21 I 47 | U n i d e n t i f i e d | Seeds I 27 |218 7 17 27 12 47 1 14 j T o t a l Items Counted I ; 1680 123 Bits 22 8-10 185 1 60 246-12 32 10 22 77 3 2 158 Res 33 | Res 81 13-14 | 9-10 17 1 17 80 263 3 42 13 2 15 1 13 5 5 20 124 12 540 6 3 3 15 2 320 13 6 368 1 645 131 1 250 4 1 1 388 12 4 34 3 1 1 4 - 1 1 4 86 2 1 937 1338 * Counted 1086 17 1 551 152 2 1809 193 49 10 32 359 8 6 1 "i 3 664 32 62 76 55 40 5 334 20 9 956 1 1590 50 4331 Table JN» Stomach Samples November 1974 Average Length of Food I t e n s i n MM (Twin I P l a n k t o n i c Species 1-I Cyclops I Diaphanosorca ICeriodaphnia I R o t i f e r s I Chironoraids I N a u p l i i I 0 . 6 1 I I 0 . 1 5 1 . 8 7 I 0 . 3 0 I Alona I Ch.ydorus I I l y o c r y p t u s | H a r p a c t i c o i d Copepods | Ostracoda | Anphipoda IMites (Oligochaetea JHirudinea IGastropod Molluscs I I 0 . 3 5 I 0 . 3 2 I I 0 . 5 4 I 0 . 4 1 I I 0 . 5 3 I 1 . 8 1 I Windblown Arthropods |Spiders j Diptera I Hymenoptera 1Th ysanoptera | Hera i p t e ra |Orthoptera | Honoptera |Coleoptora |Dernoptera I C o l l e s b o l a M i l l i p e d e s I U P . i d e n t i f i e d I T o t a l Items Measured 1 . 3 3 1 . 9 9 1 . 6 3 1 . 0 1 3 . 2 0 1 . 4 2 0 . 4 7 591 I Kay I Hes 22 i Res 33 | Res 81 |* Measure -J : 1 : i i 2 . 8 0 I S e n t h o - l i t t o r a l Species 3 . 6 0 0 . 26 0. 6 5 2 . 59 1. 60 0. 73 1. 83 0. 77 f I 77 0.64 0 . 3 9 2 . 0 0 1 . 2 5 4 . 1 5 1 . 9 8 0 . 7 3 2 . 2 2 1 . 8 2 1 . 2 2 6 . 8 0 0 . 4 3 1.5c! 43 8 | 0 . 9 0 0 . 4 1 1 . 6 3 1 . 3 8 2 . 0 6 2 . 0 9 1 . 0 8 2 . 89 1 . 7 3 1 . 0 6 0 . 3 3 0 . 5 2 | 1 . 3 8 714 I 17 I 1 I 51 I 94 I 2 0 . 3 6 | 0 . 3 5 | 159 0 . 2 8 | 0 . 3 1 1 49 0 . 3 4 | 1 10 0 . 4 5 | 0 . 2 8 0 . 5 1 | 25 0 . 5 9 | 0 . 5 5 | 0 . 3 9 | 3 37 1 . 9 9 | 3 . 8 0 | 7 0 . 3 2 | 0 . 4 7 t 1 4 . 9 6 | 1 7 . 6 8 | 1 8 1 1 3 2 8 4 . 4 0 2 . 14 0 . 7 9 2 . 30 4 . 8 0 8 . 2 4 0 . 5 1 8 . 6 4 0 . 3 7 2 5 . 6 4 0 . 7 9 497 | 32 47 66 51 24 2 219 19 5 389 1 13 744 | 2 3 4 7 97 Table 15 Summary Of Stomach Content A n a l y s i s Twin Kay Res 22 Res 33 Res 81 T o t a l Number Of F i s h 24 24 24 24 24 120 Number Of Food Items Measured Counted 591 1472 77 128 438 540 497 645 744 1338 2347 4113 | Food Items/Fish -+ + | 6 0 , 9 2 ) 5 . 331 i 2 2 . 5 0 H-| 2 6 . 8 8 -+ | 5 5 . 7 5 1 3 4 . 2 8 | i i J 1 j 1 I I D i e t Composition, Percent: I I ! \ I 1 1 P l a n k t o n i c Species | 8 7 . 9 J 0 . 8 1 4 5 . 6 i 4 1 . 6 I 0 . 7 | 4 4 . 0 J B e n t h o - l i t t o r a l Spp. I 7 . 0 | 5 . 5 J 2 9 . 3 I 1 . 2 | 2 9 . 0 1 1 6 . 1 I Windblown I n s e c t s I 3 . 2 | 8 9 . 1 | 2 3 . 0 J 5 7 . 1 | 7 0 . 0 J 3 8 . 7 J U n i d e n t i f i e d I 1 . 2 | 4 . 6 | 2 . 1 | 0 . 1 | 0 . 3 I 1 . 2 J T o t a l | 1 0 0 . 0 j 1 0 0 . 0 1 1 0 0 . 0 I 1 0 0 . 0 I 1 0 0 . 0 I 1 0 0 . 0 | Average S i z e Of Item (mm) 0.58 1.32 1.11 1.33 0. 68 0.89 Average S i z e Of F i s h (mm) 20.7 27.7 31.3 19. 1 20. 9 22.6 A n a l y s i s Of Covariance Length Of Food Item Vs. Length Of F i s h , Among R e s e r v o i r s : F = 85.63, P<0.0001 !§3E£ssionj_ Length Of Food Item = -0.38 + 0.056 X Length Of F i s h , P<0.001 98 of v a r i o u s types eaten. Larger f i s h tend to eat l a r g e r food items (r=0,34, p<. 0001), but the r e l a t i o n s h i p i s not t i g h t . A n a l y s i s of c o v a r i a n c e shows that the r e g r e s s i o n of l e n g t h of food item on l e n g t h of f i s h v a r i e s s i g n i f i c a n t l y among r e s e r v o i r s (F=85.63, p<.0001), a r e s u l t t h a t probably stems from the d i f f e r e n t abundances of l a r g e and s m a l l food items i n d i f f e r e n t r e s e r v o i r s . Tables 13 and 14 combine to demonstrate t h a t Gambusia can eat l a r g e numbers of very s m a l l food items. For example, the 51 r o t i f e r s i n the stomachs of Gambusia from Twin R e s e r v o i r averaged 0.15 mm; the 159 Alona from Twin, 22, and 81 averaged 0.36 mm; and the 337 o s t r a c o d s from a l l r e s e r v o i r s averaged 0.39-0.59 mm. F i s h e r i e s workers accept t h e c o e f f i c i e n t of the r e g r e s s i o n of l e n g t h of l o g weight as an index of the c o n d i t i o n of f i s h . Stocks with f a t f i s h y i e l d high c o n d i t i o n f a c t o r s ; those with t h i n f i s h y i e l d low c o n d i t i o n f a c t o r s . Thus the c o n d i t i o n f a c t o r r e f l e c t s the o v e r a l l n u t r i t i o n a l s t a t e of the s t o c k . In the r e g r e s s i o n e q u a t i o n , l e n g t h = a + b l o g weight, b i s the c o n d i t i o n f a c t o r . In Table 16, I present the c o n d i t i o n f a c t o r s of a d u l t females from a l l r e s e r v o i r s analyzed, together with a rough estimate of the d e n s i t y of f i s h d e r i v e d from data on c a t c h - p e r - u n i t - e f f o r t . A n a l y s i s of the c o v a r i a n c e of l e n g t h with l o g weight shows t h a t f i s h from s t a b l e r e s e r v o i r s are s i g n i f i c a n t l y t h i n n e r than f i s h from unstable r e s e r v o i r s (F=33.83, p<0.0001). However, the f i s h d e n s i t y data i s e g u i v o c a l . A Mann-Whitney U t e s t on the raw c a t c h - p e r - u n i t -e f f o r t data showed t h a t f i s h d e n s i t y was lower i n s t a b l e than i n T a b l e 1.6 G a m b u s i a C o n d i t i o n F a c t o r s And F i s h D e n s i t i e s R e s e r v o i r I I I C o n d t n | G a m b u s i a 1 A d j u s t e d | P o e c i l i a F a c t o r } I G a m b u s i a | 1 1 i I O t h e r l l i l § £ i § . P o e c i l i i d s | S t a b l e R e s e r v o i r s L -I I T w i n J a n I 8-21 | 58 .6 1 58.6 1 j I T w i n Nov | 7.75 i 5 8 . 3 \ 58.3 ! | I Kay J a n | 8.68 | 3 9 . 5 1 39.5 1 | I Kay Nov | 8.80 | 60 .5 ! 60 .5 1 j I Camp 17 I | 0.6 1 |325.6 J I K a i h u e | 7. 89 | 43.9 1 43.9 | 19.3 | I U n i v e r s i t y | 6 .70 | 50 .5 1 50 .5 | 63.0 i 3.9 I Pump #4 | | 5.0 1 | 117.6 I 31 .2 ( i. > ....x .... , X F l u c t u a t i n g R e s e r v o i r s -+ 1- +-Wahiawa 8.56 1 51 .3 | 35-9 I \ 3 .7 O p a e u l a #1 8 . 54 } 45.8 | 32. 1 I o. 9 | J 17.6 H e l e m a n o | | j | 374. I 4 | | R e s . 21 8.93 |171.8 | 60 .0 | 0 .8 j R e s . 22 10. 17 | 91.3 | 50.7 I o. 1 | 0 .2 | R e s . 25 10. 57 1113.2 | 83.9 | 188. 4 j I 1.0 R e s . 31 10. 15 |103.8 J 53.9 I | | R e s . 32 9.67 I 24 .8 1 17.2 I o. 1 | 1.3 I 0 . 5 R e s . 33 J a n ! 10.28 | 44.9 | 29. 1 I 1. 2 j 0 .2 | R e s . 33 Nov] 6.76 | 13.8 i 8 .9 I 7 . 4 1 0 .8 R e s . 35 9.10 I 36.6 ! 23.9 I | 0 . 3 | R e s . 40 9.25 i 88 .3 | 52.6 I | 0 . 1 | R e s . 41 J a n | 7.05 1 66 .2 | 41,6 » | I 0 . 5 R e s . 41 Nov 8.58 1223.3 I 102.9 I j | R e s . 42 7.96 | 73 .0 | 51.2 1 { 0 .2 \ R e s . 50 J a n | 7.71 \285.6 j 285.6 1 | | 3 . 1 R e s . 50 Nov• 7.49 | 82.7 | 38.4 1 j | 0.6 R e s . 51 7 .35 I 135.0 |135.0 1 | | R e s . 60 9.30 | 85.4 | 15.3 \ 4 . 9 | R e s . 61 10.00 J 165.0 | 22.4 | 0. 3 | 1.0 | 10.0 R e s . 80 9.78 J434.4 |151.2 1 j j R e s . 81 J a n 10.33 | 281.7 |173.5 1 | I R e s . 81 Nov] 7.06 | 118.2 I 33.2 1 J I R e s . 84 8.44 |315.2 I19 3 .2 1 j I R e s . 90 8.54 |251.6 |181.2 1 1- 3 | j R e s . 91 10. 11 |162.0 |144.5 I j 25 .0 100 unstable r e s e r v o i r s (U=121, z=2.30, p=.0107). When I c o r r e c t e d the c a t c h - p e r - u n i t - e f f o r t data by accounting f o r the water l e v e l i n u n s t a b l e r e s e r v o i r s on the sampling date, and assumed t h a t lower water l e v e l s concentrated f i s h by an amount p r o p o r t i o n a l to the r e d u c t i o n i n r e s e r v o i r volume, I got the o p p o s i t e r e s u l t : f i s h d e n s i t y was higher i n s t a b l e than i n unstable r e s e r v o i r s (U=30, z=-2.25, p=.0158). 5c. J ^ i o g r a j j h i c S t a t i s t i c s S t a b i l i t y , oyer time.. Having e r e c t e d a s t a b l e - f l u c t u a t i n g r e s e r v o i r c l a s s i f i c a t i o n , and having examined f a c t o r s that might have confounded that d i s t i n c t i o n , I have asked three q u e s t i o n s i n t h i s s e c t i o n . I sampled two s t a b l e and four f l u c t u a t i n g r e s e r v o i r s over two p e r i o d s , which f o r convenience I lumped as January and November, 1974 ( c f . Table 7). The f i r s t q u e s t i o n i s t h i s : Did the f i s h p o p u l a t i o n s i n the s t a b l e r e s e r v o i r s remain more s i m i l a r over time than those i n the f l u c t u a t i n g r e s e r v o i r s ? I c o n s i d e r e d f i v e demographic s t a t i s t i c s : the p r o p o r t i o n of young f i s h (those l e s s than 15 mm), the o v e r a l l s i z e d i s t r i b u t i o n , the p r o p o r t i o n of a d u l t females that were pregnant, the sex r a t i o , and d e n s i t y expressed as catch-per-u n i t - e f f o r t . Table 17 e x h i b i t s changes i n the f r e q u e n c i e s of f i s h l e s s than 15 mm between January and November, 1974. In a l l s i x r e s e r v o i r s , the p r o p o r t i o n of younq f i s h i n the p o p u l a t i o n d e c l i n e d between the two samplinq dates. In f o u r of the r e s e r v o i r s . Twin, 41, 50, and 81, the d e c l i n e was s i g n i f i c a n t . 101 Table 18 d i s p l a y s changes i n the o v e r a l l s i z e s t r u c t u r e of the same stock s between January and November. In a l l s i x cases, there were s i g n i f i c a n t changes i n s i z e s t r u c t u r e . In November, t h e r e were fewer very s m a l l or very l a r g e f i s h , with more f i s h c o n centrated between 15 and 30 mm than i n January. Table 19 s e t s f o r t h changes i n the p r o p o r t i o n of females pregnant between the two sampling dates. In f i v e out of s i x cases, the p r o p o r t i o n of females pregnant d e c l i n e d . F i v e of the s i x changes were s i g n i f i c a n t , with one r e s e r v o i r , 41, showing a s i g n i f i c a n t i n c r e a s e , and one, 81, showing a decrease t h a t was not s i g n i f i c a n t . Table 20 p r e s e n t s changes i n sex r a t i o s between January and November. In three r e s e r v o i r s , Kay, 33, and 4 1, t h e r e were s i g n i f i c a n t changes, and i n t h r e e t h e r e were not. In r e s e r v o i r s 33 and 81 i n January, and r e s e r v o i r 41 i n November, the a d u l t sex r a t i o s were not s i g n i f i c a n t l y d i f f e r e n t from 1:1. In a l l other samples but one, males s i g n i f i c a n t l y outnumbered females. The sample taken from Kay R e s e r v o i r i n January had 280 females and 9 males. Table 21 e x h i b i t s changes i n f i s h d e n s i t y , expressed as c a t c h - p e r - u n i t - e f f o r t , between January and November. I c a l c u l a t e d the d i f f e r e n c e s two d i f f e r e n t ways: f i r s t with the raw data, and secondly a f t e r c o r r e c t i n g the numbers caught i n the unstable r e s e r v o i r s f o r the e f f e c t s of drawdowns. In making th a t c a l c u l a t i o n , I assumed that i f , f o r example, the r e s e r v o i r was h a l f f u l l on the sample date, the f i s h were twice as dense as they would have been i n the f u l l r e s e r v o i r . In only one case was the change i n d e n s i t y s i g n i f i c a n t ; the c o r r e c t e d data f o r Table 17 Comparison Of Frequencies Of F i s h <15 Mm With F i s h >15 Mm Over Time | R e s e r v o i r | i t Date | <15mm |>15nn | T o t a l S t a t i s t i c s i ....... ^  |Twin Re s e r v o i r | Jan I Nov I 23 . 7 . j , , . , , „ , . j_ I 215 | I 1«3 | 238 150 Chi-square= 3. 8410 | T o t a l | ! 30 1 35 8 | 388 G = 4. 2707 |Kay R e s e r v o i r | Jan | Nov | 2 0 I 311 | I 1 4 5 | 313 145 Chi-square= 3. 8410 1 • Total'l ! 2 1 "56 | 458 • G = 1. 9152 ] R e s e r v o i r 33 | Jan | Nov j 52 30 1 198 | 1 159 | 250 189 Chi-square= 3. 8410 I T o t a l | I 82 1 357 | 439 G= 2. 0875 I R e s e r v o i r 41 | Jan | Nov | 1 1 0 1 23 9 | 1 1 " | 250 147 Chi-square= 3. 8410 I T o t a l | I 11 1 386 | 397 G= 10. 8672 I R e s e r v o i r 50 | Jan | Nov | 43 8 1 181 | 1 1«2 | 224 150 Chi-square= 3. 8410 I T o t a l | I 51 | 323 | 374 G = 17. 8507 I R e s e r v o i r 81 | Jan | Nov | 87 21 I 163 | I 229 | 250 250 Chi-square= 3. 8410 I T o t a l | ! 108 I 392 | 500 G= 56. 26 16 I 1 1 1 1 I J TaDle ! 8 Comparison Of S i z e S t r u c t u r e s Of P o p u l a t i o n s Over Time R e s e r v o i r Date T T T -5-10|10-15|15-20|. ITwin R e s e r v o i r | Jan | Nov | 0| 01 1 i 23| 7| + -90| 4 1 | 63J 56| I 27 | 30 | T 25| HI + — 10| 21 1 +— 0| 01 i -i 0! 0| + -01 01 +— 23 3 | 150 I Chi--square= 16.9190 | 1 T o t a l | I 0| —\— 30 ; 131| 119| I . 57 | | 39| 1 12| 1 0| 1 01 1 01 389 | G= 17.1776 | |Kay R e s e r v o i r | Jan | Nov | 0| 01 1 2| 0| 20| 18| 29 | 65| 47 | 31 I 134 | 9| j 66 I 16| 10| 5| -)— 5| 11 (--0| 0| 313 | 145 | Chi-•square= 16.9190 | 1 T o t a l | 0| 1— 2| 38| | 1 73 J j 143| 1 | 82| I 15| I 6| 1 0| 458 | G = 125.6216 | IR e s e r v o i r 33 | Jan | Nov | 10| 0| 1 42| 30 | 103 | 7 81 52| 55| | 15| 16 | 8| 91 j 31 11 i + 111 01 1 4| 01 4— 21 0| 250 | 189 | Chi- square= 16.9190 | 1 T o t a l | I 10| -1— 72) 181| 107 | . I 31 | | 1 7 | 1 1 4 | 1 111 i 1 "I 1 2| 439 | G = 35.6216 | IRe s e r v o i r 41 | Jan | Nov | 0| 0| 1 1 1 I 0| 6 0 J 1 | 123| 50 | 1 46 | 58 | 1 9! 24 | -j 01 12| 1 1 11 21 i 0| 0| 1— 0| 01 250 | 147 | Ch i - square= 16.9190 | T o t a l | 0| 1-_ 11 I 61| 173| I 104| | 331 I 121 1 31 i 1 01 1 0| 397 | G= 119.8044 | R e s e r v o i r 50 | Jan | Nov | 21 0| 1 4 1 | 8| 1 14| 48! 58| 79| I 5| 10 | 1 2| 21 1 . . . . | . . 11 31 1 j 11 o r i ~ 1 — 01 01 1 H— 0| 01 224 | 150 | C h i - square= 16.9190 | T o t a l | I 21 49 | 162| 137| _ _^ 15|  "1  1 11 1 0| 1 01 374 | G = 47.3983 | Re s e r v o i r 81 | Jan | Nov | 11 01 1 86| 21 | 99| 132| 41| 66 | | 12| 25 | 1 3| 51 | 1 1 — * 3| 0| 1 h 0| 1 1 11 11 1 H— 0| 0| 250 | 250 | C h i - square= 16.9190 | T o t a l | . _ J _ i 11 1 107| — . . . i 231| i.. 107 | j 37 | —i 81 i I 3 1 I "1 1 21 1 0| 1 500 |. G= 69.2539 | Table J.9 Comparison Of Frequencies Of Pregnant And Non-pregnant Females Over Time i : 1 Res e r v o i r I' T I Date | Not - •• i Preg ( i Pregl T o t a l I S t a t i c t i c s ITwin R e s e r v o i r 1 Jan | 53 | 7 | 60 —1 J 1 Nov | 46 | 0 | 46 1 Chi-square= 3.8410 1 1 T o t a l 1 1 99 | 7 | 106 1 G = 4.8943 | |Kay R e s e r v o i r I Jan | 10 | 24 1 ( 25 1 J I Nov | 46 | 15 | 6 1 ( Chi-sguare= 3.8410 I 1 T o t a l 56 | 256 | 312 1 G = 137.3049 ! I R e s e r v o i r 33 I Jan | 8 | 29 ( 37 J I Nov | 22 | 3 | 25 I Chi-sguare= 3.8410 i 1 T o t a l « 1 30 | 32 | 62 1 G = 25.7553 i I R e s e r v o i r 41 1 Jan | 35 | 9 | 44 J •j I Nov ( 33 | 41 | 79 I Chi-square= 3.8410 i 1 T o t a l 1 73 | 50 | 123 1 G= 13.6826 ! |Reservoir 50 Jan | 3 | 5 | 8 j 1 Nov | 11 I 1 | 12 |. Chi-square= 3.8410 i 1 T o t a l • 14 | 6 | 20 1 G = 4.4271 ! ( R e s e r v o i r 81 Jan | 3 | 16 |. 19 j j Nov | 11 I 20 | 31 1 Chi-square= 3.8410 i I T o t a l 1 14 | 36 | 50 j G= 1.4511 I Table 20 R e p l i c a t e d Goodness of F i t Tests on Sex R a t i o s Between Dates, Within R e s e r v o i r s - T T -i : 1 -I . , . . I R e s e r v o i r | Date Males j Females Row j S t a t i s t i c s | C o n c l u s i o n | | t o t a l | 1 I Twin I Jan 70 | 28 . 93 | Gh= 0. 329 | Accept; No Change between Dates | I Nov 8 1 | 25 106 | Gp = 49. 030 | R e j e c t ; Males outnumber females 1 I Column T o t a l 1 | Gj = 17. 692 I Reject ; Males outnumber f c a a l e s j 1 151 1 53 204 | Gn = 29. 980 I Reject ; Males outnumber females | 1 Kay I Jan 9 I 280 289 | Gh = 279. 63 4 | R e j e c t ; January and November D i f f e r | | Nov 10 1 | 23 124 l Gp = 46. 900 I R e j e c t ; Females outnumber males | I Column T o t a l 1 | Gj = 317. 070 | R e j e c t ; Females outnumber males | ] 110 |. 303 413 | Gn = 25. 475 | R e j e c t ; Males outnumber females | I R e s e r v o i r 33 1 Jan 58 1 69 127 | Gh = 37. 770 | R e j e c t ; January and November D i f f e r j | Nov 116 1 27 143 | Gp= 11. 429 I R e j e c t ; K a l e s outnumber females | j Column T o t a l 1 | Gj = 0. 788 | Accept; Sex r a t i o 1:1 | | ] 174. 1 96 270 | Gn = 58. 223 1 R e j e c t ; Males outnumber females | | R e s e r v o i r 41 I Jan ! 83 1 39 122 | Gh = 6. 836 | Reje c t ; January and November D i f f e r | | Nov | 77 1 70 147 | Gp = 9. 72 9 I R e j e c t ; Kales outnumber females | I Column T o t a l 1 1 ( Gj = 15. 486 | R e j e c t ; Males outnumber femaes | 1 ' 160 1 1 0 9 | 269 | Gn= 0. 250 | Accept; Sex r a t i o 1:1 | | R e s e r v o i r 50 | Jan | 65 I 26 91 | Gh= 2. 598 i Accept; no change between dates | | Nov | 61 I 40 101 | Gp= 1 9. 069 | R e j e c t ; Males outnumber r e s a l e s | 1 I | Gj = 37. 550 I R e j e c t ; Hales outnumber fe&ales | I Column T o t a l 1 | 126 66 | 192 | j Gn= 3. 987 I R e j e c t ; Males outnumber females | 1 R e s e r v o i r 80 I Jan | . 37 I 26 | 1 63 | Gh= 0. 636 | Accept; No change between dates | | NOV | 85 46 i 131 | Gp= 1 3. 035 | R e j e c t ; Males outnumber females | I Column T o t a l 1 I | Gj = 1. 594 | Accept; Sex r a t i o s 1:1 | 1 1 122 72 | 194 | Gn = 11. 183 I R e j e c t ; Males outnumber females | J L T a b l e 21 A n a l y s i s Of Variance Of Gambusia D e n s i t y : Between Dates, Within R e s e r v o i r s 1. Uncorrected D e n s i t i e s R e s e r v o i r D a t e N Density -+-Prob. Twin Jan 58.6 0.0.144 0.8744 | Nov I 3 | 58.3 1 Kay I Jan | Nov I 5 I 3 | 39.5 | 60.5 | 1.9214 I o. 2138 Res. 33 I Jan j Nov I 5 I 5 I 44.9 I 13.8 | 2.4866 I o . 1511 Res. 41 j Jan | Nov I 5 I 3 | 66.2 | 223.3 | 1.7225 I o. 2365 Res. 50 | Jan I Nov » 5 | 3 I 285.6 | 82.7 | 2.3998 I o. 1705 Res. 81 \ Jan | Nov \ 5 I 5 1 281.6 | 118.2 | 2.6891 I o . 1372 2. C o r r e c t e d D e n s i t i e s R e s . 33 | J a n I 5 ! 29. 1 | 2.4866 I o . 1511 | Nov 1 5 8.9 J R e s . 41 I J a n 1 5 41.6 j 0.6330 I 0. 4609 I Nov 1 3 102.9 j R e s . 50 I J a n 1 5 285.6 | 3.6092 I o. 1043 I Nov 1 3 38.4 j R e s . 81 | J a n 1 5 173.5 | 9.6592 I o . 0142 | Nov I 5 33.2 ! 107 R e s e r v o i r 81 showed a s i g n i f i c a n t d e c l i n e . Table 22 summarizes the changes i n demographic s t a t i s t i c s between January and November. 60 per cent of the s t a t i s t i c s changed s i g n i f i c a n t l y i n the s t a b l e r e s e r v o i r s , and 60 per cent of the s t a t i s t i c s changed s i g n i f i c a n t l y i n the unstable r e s e r v o i r s . Table 23 d i s p l a y s the magnitude of tha changes i n s t a t i s t i c a l l y comparable form f o r a l l s t a t i s t i c s but d e n s i t y , f o r which I used a n a l y s i s of v a r i a n c e i n s t e a d of the G-test. The numbers d i s p l a y e d are the d i f f e r e n c e s between the value of G c a l c u l a t e d from the data, and the c r i t i c a l c h i - s g u a r e value 3.841 (p=0.05,d.f.=1). a l l f o u r of the u n s t a b l e r e s e r v o i r s , 33, 41, 50, and 81, and Kay R e s e r v o i r , had o v e r a l l changes i n p o p u l a t i o n s t a t i s t i c s t h a t were very l a r g e . The changes i n Twin, while s i g n i f i c a n t , were g u i t e s m a l l . Kay, a s t a b l e r e s e r v o i r , showed the l a r g e s t changes of a l l . There were a l s o s i g n i f i c a n t changes between sampling dates i n r e p r o d u c t i v e t r a i t s . Table 24 s e t s f o r t h a comparison of the changes i n c o n d i t i o n f a c t o r s , numbers of young, and r e p r o d u c t i v e e f f o r t s between sampling dates. The comparisons are based on data from Twin R e s e r v o i r f o r January and August, and f o r Kay, 33, 41, and 81 f o r January and November. I used the August samples from Twin because there were no pregnant females i n the November sample. There were too few pregnant females i n e i t h e r sample from R e s e r v o i r 50 to make i t worth i n c l u d i n g . The r e g r e s s i o n c o n s t a n t s given are based on the pooled samples from the two sampling dates, but the a n a l y s i s of c o v a r i a n c e t h a t y i e l d e d the F-values was done with a nested design: r e s e r v o i r s w i t h i n s t a b i l i t y c l a s s i f i c a t i o n w i t h i n sample dates. Thus the 1 0 8 Table 22 Summary Of Changes In Demographic S t a t i s t i c s I Twin| Kay 1 H 1 i i 1 1 H 1 1 1 1 1 I S i g . | • i j P r o p o r t i o n Of Young F i s h 1 S i g , 1 j N. S. ! I S i g . 1 I S i g . • I N.S. 1 S i g . I S i g . 1 O v e r a l l S i z e S t r u c t u r e 1 S i g . 1 S i g . I S i g . I S i g . 1 1 I S i g . | 1 1 JN.S. | 1 1 |N.S. \ 1 1 I S i g . | • i I P r o p o r t i o n Pregnant 1 S i g . I S i g . j S i g . 1 S i g . |Sex E a t i o | N.S. ! J S i g . t 1 S i g . | S i g . | N.S. JCorrected Density I N.S. I jN.S. 1 i I N.S. JN.S. ] N.S. » _ i .. -i . i .„.. , i 1 1 j . J 33 41 5 0 81 109 Table 23 D i f f e r e n c e s Between G And C r i t i c a l Chi-sguare 1 ... T "T •T T T — r -| Twin j Kay fRes. 33 } Res. 41 | Res. 50 | Res ..81| i (Number < 15 Mil 1 0. 430 I -1 - 926 1 - 1 . 754 I 7. 026 I 14. 010 | 52. i 421 | | S i z e D i s t . | 0. 259 | 108, 703 | 18. 703 | 102. 885 | 30. 479 j 52. 335 | |% Pregnant 1 1- 053 | 133. 464 | 21. 914 | 9. 842 I o« 586 | -2 . 390 | |Sex R a t i o i | -3 . 512 | 275. 793 ! 33. 929 \ 2. 995 I -1 . .243 I - 3 . 155 ] r J T o t a l 1-1. 7 70 1520. 034 I 72. 792 I 122. 748 | 43. '832 | 99. 210 | L._ ._ i . i. _ i _ .j i j 110 Table 24 Changes In Reproductive T r a i t s Between Dates 1. Nested A n a l y s i s Of Covariance On Pregnant Females Model: Y = A + BX 1 + T r a i t Y Dep. Var. X January A B Aug.+ Nov, A B Prob, l e n g t h JLn Wgt I Num. Young {Weight I Rep. E f f o r t | W e i g h t I Wgt NEL Yng| I Wgt EE Yng | -! 52.24 9.439 •29.02 358.7 0.196 0.187 1.81 MG 1.67 MG 52.79 9.351 3.979 68.16 0.144 -0.185 1.40 MG 1.58 MG 37.64 6.87 108.99 59.53 4.60 <0.0001 0.0088 <0.0001 <0.0001 0.0314 2. T r a i t s Compared For A 175 Mg Female T r a i t Length Of A 175 Mg Female (mm) Number Of Young In A 175 Mg Female Reproductive E f f o r t . Of A 175 Mg Female Weight Of NEL Young Weight Of EE Young Jan 35.79 MM 33.75 0. 229 1.81 MG 1.67 MG Nov 36.49 MM 15.91 0.112 1.40 MG 1.58 HG 111 F-value given t e s t s the hypothesis t h a t t h e r e i s a s i g n i f i c a n t remaining d i f f e r e n c e between January and August-November samples a f t e r t a k i n g account of the v a r i a n c e due to d i f f e r e n c e s between i n d i v i d u a l r e s e r v o i r s and the s t a b l e - f l u c t u a t i n g dichotomy. There were s i g n i f i c a n t changes i n c o n d i t i o n f a c t o r s , numbers of young a t a given weight, and r e p r o d u c t i v e e f f o r t s . But, as the second part of the t a b l e shows, the change i n c o n d i t i o n f a c t o r was s m a l l . Numbers of young and r e p r o d u c t i v e e f f o r t s showed l a r g e d e c l i n e s . Demographic s t a t i s t i c s and recent f l u c t u a t i o n s ^ In the p r e v i o u s s e c t i o n , I presented data on the r e l a t i v e s t a b i l i t y of f i s h p o p u l a t i o n s i n s t a b l e and f l u c t u a t i n g r e s e r v o i r s . In t h i s s e c t i o n , I examine the r e l a t i o n s h i p s among the demographic s t a t i s t i c s , and between the demographic s t a t i s t i c s and the r e c e n t h i s t o r y of the r e s e r v o i r s sampled. My purpose i s to answer two q u e s t i o n s . F i r s t , does the f i e l d data suggest r e l a t i o n s h i p s t h a t allow us to e r e c t hypotheses about the processes causing the p a t t e r n s observed? Secondly, and more s i g n i f i c a n t l y , are t h e r e any s t r o n g r e l a t i o n s h i p s between the demographic s t a t i s t i c s and the recent h i s t o r y of the unstable r e s e r v o i r s t h a t permit comments on the probable impact of r e s e r v o i r f l u c t u a t i o n s on the f i s h ? T able 25 d i s p l a y s f o u r matrices of Kendall's rank-c o r r e l a t i o n c o e f f i c i e n t s , tau, c a l c u l a t e d f i r s t on the demographic s t a t i s t i c s from a l l 31 samples, next f o r j u s t the s t a b l e and unstable r e s e r v o i r s , and f i n a l l y f o r the Maui r e s e r v o i r s where I c o u l d represent r e c e n t r e s e r v o i r h i s t o r y n u m e r i c a l l y . In Table 25 I d i d not c o r r e c t f i s h d e n s i t i e s f o r Table 25 Matrix Of Ke n d a l l Rank C o r r e l a t i o n C o e f f i c i e n t s : No C o r r e c t i o n For Water L e v e l I . A l l R e s e r v o i r s -+- + Pet Preg, JPct |<15mm ICond, | Fact, JGamb. | Dens. I +-Pet. Pregnant Pet. <15 Mm Cond. F a c t . Gamb. Dens. Oth. Fsh Dens. Sex R a t i o 1.000 10.028 11.000 H |0.313**|0.015 |0.093 jO.140 |1.000 I JO.127 |1.000 I I Other |Sex F i s h |Ratio Dens. | 0.195+1-0.593** 0.050 | 0.075 0.023 1-0.265* -0.248*1-0.028 1.000 1-0.192+ I 1.000 I I . S t a b l e R e s e r v o i r s — I 1-Pc t . Pregnant Pet. <15 Mm Cond. F a c t . Gamb. Ens. Oth. Fsh Dens, Sex Ratio 11.000 I -0.467+ 1.000 0.200 j-0.333 -0.467+I 0.333 1.000 | 0.200 I 1.000 I 1 0.414 I-0.467+ |-0.276 |-0.067 j-0.138 | 0.067 1-0.138 | 0.600* 1 1.000 J-0.257 J 1 1.000 I I I . Unstable R e s e r v o i r s -+- + Pet. Pregnant Pet. <15 Mm Cond. F a c t . Gamb. Dens Oth. Fsh Dens, Sex R a t i o J 1.000 0.043 10.347**1-0.006 | 0.178 (-0.507** 1.000 J0.127 | 0.080 | 0.108 | 0.140 11.000 1 0.073 } 0.080 1-0.280* 1 J 1.000 |-0.295*| 0.060 J | | 1.000 J-0.201 | I I I 1.000 -+-IV. Maui R e s e r v o i r s H 1 h 60d Mn }60d Cv J180d Mn|180d Cv\% F u l l \ + +-Pet. Pregnant Pet. <15 Mm Cond. F a c t . Gamb. Dens Oth. Fsh Dens, Sex R a t i o 0.004 J-0.028 1-0.059 | 0.087 J-0.075 0.146 0.123 0.123 0. 104 •0.129 •0.028 1 0.067 1 0.040 •0.162 J 0.059 1 0.008 -0.051 1 0.091 1-0. 119 0.179 I 0.154 1-0.125 0.193+1-0.170 | 0.194+ 0.051 -0.067 -0.099 0. 196 0.091 +: P<.10; *:p<.05; **:p<.01 113 Table 26 Matrix Of K e n d a l l R a n k - c o r r e l a t i o n C o e f f i c i e n t s : Cor r e c t e d For l a t e r L e v e l On Sampling Date In Unstable R e s e r v o i r s I. A l l R e s e r v o i r s + Pet Preg. Pet |Cond. |Gamb, <15mm |Fact. jDesn, I I Other F i s h Dens. Sex Ratio j Pet. I Pet. |Cond. | Gamb, | Oth. Pregnant <15 Mm Fa c t . Dens. Fsh Dens. I-0.097 j 0.028 I 0.041 0. 164+ 0.061 •0.029 •0.249* 0.092 -0. 145 I I . Unstable R e s e r v o i r s \ | Pet. f Pet. |Cond« |Gamb. | Oth. H + I -0 .067 | 0.114 I 0.047 | 0.156 j 0.027 j 0.010 | j - 0 . 2 9 4 * Pregnant <15 Mm Fa c t . Dens. Fsh Dens. 0.080 -0. 138 II I . Maui R e s e r v o i r s H + I |60d Mn |60d Cv |180d Mn|180d Cv\% F u l l | | Gamb. | Oth. ! Dens. Fsh Dens 10.296* 1-0.178 I0.233+ | - 0 . 1 8 2 |0.218+ | 10.169 j - 0 . 2 1 1 J0.219+ 1-0.141 |0.327* | I - X -i I +: P<.10;*: P<.05; **: P<.01 1 14 the e f f e c t s of drawdowns. Table 26 presents those c o e f f i c i e n t s a f f e c t e d by t h a t c o r r e c t i o n . Only a few of the c o r r e l a t i o n c o e f f i c i e n t s were s i g n i f i c a n t . The p r o p o r t i o n of a d u l t females that were pregnant i n c r e a s e d s i g n i f i c a n t l y with the c o n d i t i o n f a c t o r of the f i s h . Gambusia d e n s i t y decreased s i g n i f i c a n t l y as the d e n s i t y of other f i s h i n c r e a s e d . These t r e n d s were h e a v i l y weighted by the l a r g e sample of f i s h from unstable r e s e r v o i r s (25, versus 6 s t a b l e r e s e r v o i r samples). In t r y i n g to r e p r e s e n t the recent h i s t o r y of unstable r e s e r v o i r s i n numerical measures, I c a l c u l a t e d the mean water l e v e l during the 60 and 180 day p e r i o d s p r i o r to the sample date, the c o e f f i c i e n t of v a r i a t i o n over those p e r i o d s , and the water l e v e l on the sample date i t s e l f , a l l expressed as percent f u l l . The d e n s i t i e s of Gambusia and other f i s h were both higher i n r e s e r v o i r s that had tended to be f u l l d u r i n g the pre v i o u s two to s i x months. D e n s i t i e s were n e g a t i v e l y c o r r e l a t e d with c o e f f i c i e n t s of v a r i a t i o n , but not s i g n i f i c a n t l y so. C o n d i t i o n f a c t o r s and the p r o p o r t i o n of young f i s h i n the p o p u l a t i o n were both p o s i t i v e l y c o r r e l a t e d with high mean water l e v e l s i n the two months before the sample, but again , not s i g n i f i c a n t l y so. Sex r a t i o s (number of males/number of females) were p o s i t i v e l y c o r r e l a t e d with the 60 and 180 day c o e f f i c i e n t s of v a r i a t i o n i n water l e v e l , and n e g a t i v e l y c o r r e l a t e d with the d e n s i t y of other f i s h , the per cent of females pregnant, and i n the u n s t a b l e r e s e r v o i r s , with c o n d i t i o n f a c t o r s . Making the c o r r e c t i o n f o r the water l e v e l s on the sampling date made a 115 d i f f e r e n c e t o the c o r r e l a t i o n water l e v e l s on the sampling date s i x months, but d i d not change other c o r r e l a t i o n s of f i s h d e n s i t y with the mean and over the p r e v i o u s two and the s i g n i f i c a n c e of any of the 6.r d i s c u s s i o n I have sketched the e v o l u t i o n of Gambusia i n Texas, r e l a t e d the h i s t o r y of i t s i n t r o d u c t i o n to Hawaii i n 1905 f o r mosquito c o n t r o l , d e s c r i b e d the d i f f e r e n t types of c o n d i t i o n s i t encountered i n d i f f e r e n t r e s e r v o i r s , and c h a r a c t e r i z e d the f i s h p o p u l a t i o n s as I found them i n 1974. I s e t out to t e s t c e r t a i n e v o l u t i o n a r y hypotheses based on a d i s t i n c t i o n between s t a b l e and f l u c t u a t i n g environments. I s e l e c t e d Gambusia i n Hawaii because I thought the s t a b l e - f l u c t u a t i n g d i s t i n c t i o n was c l e a r -cut and because the uniguely documented h i s t o r y of the r e s e r v o i r s allowed me to check assumptions. In t h i s chapter, I have summarized a l l the i n f o r m a t i o n I could assemble t o check those assumptions. Now I c o n s i d e r three q u e s t i o n s : Was the experimental design confounded? Did the p o p u l a t i o n s i n s t a b l e r e s e r v o i r s f l u c t u a t e l e s s than those i n unstable r e s e r v o i r s ? Were there c o n s i s t e n t changes between January and November, 1974, that t e l l us something about the ecology of Gambusia? 6a. Confounding! F a c t o r s Other fish_j_ As Table 9 i n d i c a t e s , most r e s e r v o i r s e i t h e r had other f i s h s p e c i e s that c o u l d p o t e n t i a l l y compete with Gambusia, or may 116 have had such s p e c i e s at some point i n the past. Camp 17 and Helemano r e s e r v o i r s o n l y had P.. r e t i c u l a t a , I w i l l use P o e c i l i a i n the next chapter to check c o n c l u s i o n s drawn from data on Gambusia. Of the unstable r e s e r v o i r s , only Wahiawa has predators (tucunare, largemouth bass, snakeheads). Ku Tree, which i s s t a b l e , a l s o has tucunare and largemouth bass. There were so few Gambusia i n Ku Tree that we were unable t o catch enough to analyze (8 sweeps y i e l d e d 11 s m a l l Gambusia). Ku Tree c l o s e l y resembles Twin and Kay i n ge n e r a l appearance and apparent p r o d u c t i v i t y . The tucunare i n Ku Tree have only Gambusia i n t h e i r stomachs, and are i n poor c o n d i t i o n (Devick, pers. comm.). Thus i t seems l i k e l y t h a t predatory f i s h are capable of reducing Gambusia to extremely low d e n s i t i e s i n s t a b l e , o l i g o t r o p h i c r e s e r v o i r s . U n f o r t u n a t e l y , I co u l d not d e s c r i b e the l i f e h i s t o r y t r a i t s of Gambusia from Ku Tree because I caught so few. The major p o t e n t i a l competitors of Gambusia are other p o e c i l i i d s (guppies, green s w o r d t a i l s , and s a i l f i n m o l l i e s ) and t i l a p i a . ftll the r e s e r v o i r s on Maui have probably had t i l a p i a i n them at some time. We caught or s i g h t e d t i l a p i a i n only 9 of 19 of them. For purposes of a n a l y s i s , I have c l a s s i f i e d only those 9 Maui r e s e r v o i r s , Opaeula 1, and Wahiawa as c o n t a i n i n g t i l a p i a . In most cases, the d e n s i t y of the p o e c i l i i d s was so low r e l a t i v e to Gambusia (Table 9) t h a t I have dismissed them as p o t e n t i a l c o m p e t i t o r s . The e x c e p t i o n s are Kaihue Pump, Pump #4, and U n i v e r s i t y Quarry among the s t a b l e r e s e r v o i r s , and Re s e r v o i r 25 among the unstable r e s e r v o i r s . In the unstable r e s e r v o i r s , Gambusia i s the dominant p o e c i l i i d , a p a t t e r n 117 c o n s i s t e n t with i t s a g g r e s s i v e r e p u t a t i o n i n other p a r t s of the world ( c f . Chapter I I ) . Both Twin R e s e r v o i r and Wahiawa support b l u e g i l l s , which probably compete with a l l s i z e s of Gambusia and eat j u v e n i l e s . However, the b l u e g i l l p o p u l a t i o n i n Twin i s stunted and sparse. The r e s e r v o i r has never supported a s p o r t f i s h e r y , and I am i n c l i n e d to d i scount the impact t h a t b l u e g i l l s may have had on Gambusia. However, I do c l a s s i f y Twin as c o n t a i n i n g c o m p e t i t o r s . In Wahiawa, b l u e g i l l s form one of a complex assemblage of 14-16 s p e c i e s with which Gambusia must d e a l . From the d e t a i l s presented i n the p r e v i o u s two paragraphs, I conclude t h a t there are r e s e r v o i r s with competitors and r e s e r v o i r s without competitors i n both the s t a b l e and f l u c t u a t i n g c l a s s e s . I f one i s w i l l i n g t o lump t i l a p i a , b l u e g i l l s , and p o e c i l i i d s together and c a l l them a l l p o t e n t i a l c o m p e t i t o r s of Gambusia, then I have d e s c r i b e d an experimental design with a competition-no c o m p e t i t i o n dichotomy nested w i t h i n the s t a b l e - f l u c t u a t i n g s p l i t . I d i s c a r d e d Wahiawa, with i t s 14-16 f i s h s p e c i e s , from the a n a l y s i s . Thus other s p e c i e s do not confound the s t a b l e - f l u c t u a t i n g s p l i t ; they represent a second l e v e l i n the experimental h i e r a r c h y . Herons. In 28 v i s i t s to r e s e r v o i r s on Haui, I s i g h t e d 42 b l a c k -crowned n i g h t herons (MYcticorax n y c t i c o r a x h o a c t l i ) , p a r t i c u l a r l y around R e s e r v o i r 81, where I suspect there i s a heronry near the i n l e t channel. I never saw a heron near the r e s e r v o i r s I sampled on Hawaii and Oahu. Since herons feed on f i s h , c r a y f i s h , a g u a t i c i n s e c t s , f r o g s , mice, and n e s t l i n g s 118 (Berger 1972), i t i s p o s s i b l e that they eat Gambusia and have an e v o l u t i o n a r y impact on them. Since herons are common on Maui, where most (19) of the unstable r e s e r v o i r s are, and r a r e i n those p a r t s of Hawaii and Oahu where the s t a b l e r e s e r v o i r s are l o c a t e d , heron predation c o u l d confound the s t a b l e -f l u c t u a t i n g dichotomy. I have l i t t l e data on which t o base a judgement. Ny£ticorax feeds at night as well as du r i n g the day, making o b s e r v a t i o n s d i f f i c u l t . In s e v e r a l hours of o b s e r v a t i o n during the day, I never saw a heron s t r i k e at a Gambusia. I d i d see s e v e r a l c r a y f i s h and one carp on which herons had been f e e d i n g , and I a l s o noted t h a t herons tended to assemble at r e s e r v o i r s with dense p o p u l a t i o n s of Gambusia, e s p e c i a l l y i f the r e s e r v o i r had been drawn down. When such r e s e r v o i r s s t a r t to f i l l , the Gambusia congregate near the entrance channel, along which the herons s t a t i o n themselves (e.g. R e s e r v o i r 80, 16 January 1974, 2 herons, r e s e r v o i r 62% f u l l and r i s i n g ) . In such s i t u a t i o n s , herons probably eat a f a i r number of the l a r g e r Gambusia. But the number taken cannot exceed 10 2 or 10 3 d u r i n g the day or two tha t the Gambusia remain congregated. The numbers of Gambusia i n r e s e r v o i r s that have dense enough p o p u l a t i o n s t o a t t r a c t herons i s probably on the order of 10 7 to 10 8. When a r e s e r v o i r with a dense p o p u l a t i o n o f Gambusia i s emptied, l e a v i n g only a s m a l l pool of water lower than the o u t l e t p i p e , most of the Gambusia are swept out, c a r r i e d through i r r i g a t i o n channels, and d e p o s i t e d on the s o i l of the sugar cane f i e l d s , where they die i n huge numbers ( s e v e r a l p l a n t a t i o n i r r i g a t o r s , pers. comm.). Thus I discount herons as a s e l e c t i v e f a c t o r , 119 e s p e c i a l l y when t h e i r maximum p o t e n t i a l impact i s compared to the c a t a s t r o p h i c m o r t a l i t i e s caused by a major drawdown i n water l e v e l . Temperature.. I have not presented any data on water temperature, other than the readings l i s t e d i n Table 7, because I could not f i n d any t h a t I f e l t were r e p r e s e n t a t i v e . Hawaii has a moderate, oceanic c l i m a t e . The temperature range from 19.5°C to 25°C t h a t I recorded at 45 cm spans the normal annual range of monthly mean temperatures i n the lowlands. During the warm part o f the day i n a l l r e s e r v o i r s , there i s u s u a l l y a three to f i v e degree drop i n temperature from the s u r f a c e to the bottom, unless the r e s e r v o i r has been drawn down to l e s s than 0.5 m. Thus w i t h i n a r e s e r v o i r on a s i n g l e day Gambusia can sample a range of temperatures almost as broad as those a v a i l a b l e w i t h i n the e n t i r e s e t of r e s e r v o i r s . Temperatures probably f l u c t u a t e more f r e q u e n t l y i n the unst a b l e r e s e r v o i r s . The incoming water i s gathered i n mountain streams and d i v e r t e d i n t o d i t c h e s t h a t c a r r y i t t o the r e s e r v o i r s . The temperature i n the d i t c h e s runs from 19°C to 20°C, whereas the normal r e s e r v o i r temperature a t 45 cm i s 21°C to 22°C. Thus the water temperature i n an unstable r e s e r v o i r depends i n part on how r e c e n t l y the r e s e r v o i r f i l l e d . Over the course o f a year, a l l r e s e r v o i r s probably vary from 20°C to 25°C at 45 cm, and many r e s e r v o i r s span t h a t range between the e a r l y morning and the afternoon at the s u r f a c e . Thus the temperature f l u c t u a t i o n s are too s m a l l , and too r a p i d , t o analyze without e x t e n s i v e r e c o r d s , which are not a v a i l a b l e . 120 Temperature d i f f e r e n c e s complicate the experimental design by adding noise to the system, but I have no method of determining whether or not they confound the s t a b l e - f l u c t u a t i n g d i s t i n c t i o n . In any case, the v a r i a b i l i t y i n temperature between r e s e r v o i r s i s c e r t a i n l y of the same magnitude as the v a r i a b i l i t y i n temperature w i t h i n r e s e r v o i r s , and the d i f f e r e n c e s between the annual mean temperatures of d i f f e r e n t r e s e r v o i r s probably do not exceed 2-3°. Food. Of the p o t e n t i a l confounding f a c t o r s , I have argued t h a t other f i s h can be i n c o r p o r a t e d as a second l e v e l i n the experimental design, herons can be dismissed by numerical arguments, and temperature c o n t r i b u t e s n o i s e but not i n a confounding manner. However, there i s s u f f i c i e n t evidence to conclude that food was probably a confounding f a c t o r . F i r s t , n e i t h e r the plankton samples nor the stomach analyses c o n t a i n s u f f i c i e n t evidence to show t h a t the kind and amount of food might d i f f e r between s t a b l e and unstable r e s e r v o i r s . Table 11 shows t h a t the d i f f e r e n c e s among r e s e r v o i r s i n numbers of p l a n k t o n i c s p e c i e s are s m a l l , and both the s t a b l e and u n s t a b l e r e s e r v o i r s span a wide range of plankton d e n s i t i e s and a s m a l l e r range of s p e c i e s composition. In a l l r e s e r v o i r s the plankton are s m a l l , as would be expected from the stomach analyses summarized i n Table 14, which shows t h a t Gambusia can eat very s m a l l food p a r t i c l e s . One of the main p o i n t s of the stomach a n a l y s i s i s that Gambusia are o p p o r t u n i s t i c f e e d e r s , u t i l i z i n g b e n t h i c , l i t t o r a l , and wind-blown s p e c i e s as w e l l as plankton. That alone r u l e s out the use 121 of plankton samples to e s t a b l i s h d i f f e r e n c e s i n food a v a i l a b l e to Gajibusia. i t a l s o p o i n t s out the f u t i l i t y of t r y i n g to measure the p r o d u c t i v i t y of the food resources t h a t Gambusia does u t i l i z e . while i t might be p o s s i b l e f o r one person to estimate the p r o d u c t i v i t y of the plankton, to estimate the p r o d u c t i v i t y of the b e n t h i c , l i t t o r a l , and wind-blown components of the mosquitofish's d i e t would i n v o l v e enormous e f f o r t by a team of r e s e a r c h e r s . D i f f e r e n c e s i n c o n d i t i o n f a c t o r s provide t e l l i n g evidence t h a t n u t r i t i o n a f f e c t s the l i f e h i s t o r y t r a i t s of Gambusia i n the f i e l d and confounds the s t a b l e - f l u c t u a t i n g d i s t i n c t i o n . Not only were f i s h from s t a b l e r e s e r v o i r s s i g n i f i c a n t l y t h i n n e r than those from unstable r e s e r v o i r s {cf. Table 16); the pregnancy r a t e decreased s i g n i f i c a n t l y i n t h i n n e r f i s h ( c f . Table 25). Since the c o n d i t i o n f a c t o r i s a d i r e c t measure of the n u t r i t i o n a l s t a t e of the f i s h , I regard the r e s u l t s presented i n Tables 16 and 25 as r e l i a b l e enough to conclude that there are o v e r a l l d i f f e r e n c e s between s t a b l e and u n s t a b l e r e s e r v o i r s i n the amount of food a v a i l a b l e to Gambusia, ..and t h a t these d i f f e r e n c e s i n a v a i l a b l e food, r e f l e c t e d i n c o n d i t i o n f a c t o r s , made some d i f f e r e n c e to the e x p r e s s i o n of l i f e h i s t o r y t r a i t s . Thus food was a confounding f a c t o r . The c r i t i c a l q u e s t i o n now becomes, were the d i f f e r e n c e s i n c o n d i t i o n f a c t o r s , and the degree of dependence of given t r a i t s on c o n d i t i o n f a c t o r s , l a r g e enough to account f o r the a c t u a l d i f f e r e n c e s observed? Or was there a s i g n i f i c a n t r e s i d u a l component to the vari a n c e of c e r t a i n t r a i t s only e x p l a i n a b l e by the s t a b l e - f l u c t u a t i n g d i s t i n c t i o n ? I have approached t h a t q u e s t i o n i n Chapter IV and 122 V. 6b. Demographic Comparisons Did the p o p u l a t i o n s i n s t a b l e r e s e r v o i r s f l u c t u a t e l e s s than those i n unstable r e s e r v o i r s ? On the b a s i s of the summary i n Table 22, I would have to say no, s i n c e i n both c l a s s e s 60 per cent of the demographic s t a t i s t i c s changed s i g n i f i c a n t l y between January and November. But a c l o s e r look at the r e s u l t s , i n Table 23, r e v e r s e s t h a t c o n c l u s i o n . The changes i n Twin were q u i t e s m a l l , while the changes i n a l l the f l u c t u a t i n g r e s e r v o i r s (33, 41, 50, and 81) were r e l a t i v e l y q u i t e l a r g e . Kay showed the l a r g e s t changes of a l l : i t i s the exception t h a t proves the r u l e . R e c a l l that i n the summer of 1974, between the two sample dates, Kay experienced i t s only s e r i o u s drawdown i n at l e a s t 30 years. The e f f e c t s of that drawdown were r e f l e c t e d i n changes i n the demographic s t a t i s t i c s many times l a r g e r than the changes o c c u r r i n g i n the f o u r unstable r e s e r v o i r s , a l l of which went through a s e r i e s of s e v e r a l drawdowns t h a t summer, each one of which was as s e r i o u s as the one Kay experienced. I suggest that the f i s h i n Kay were not adapted to drawdowns, and when they d i d encounter one i t presented a much more s e r i o u s p e r t u r b a t i o n to the p o p u l a t i o n than s i m i l a r drawdowns do to f i s h t h a t have l i v e d i n f l u c t u a t i n g r e s e r v o i r s f o r many ge n e r a t i o n s . Thus I have concluded t h a t , on balance, the f i s h p o p u l a t i o n s l i v i n g i n r e s e r v o i r s with s t a b l e water l e v e l s d i f f e r l e s s over time i n t h e i r demographic s t a t i s t i c s than f i s h l i v i n g i n r e s e r v o i r s where the water l e v e l f l u c t u a t e s . 1 2 3 6c._ E c o l o g i c a l I m p l i c a t i o n s O f D e m o g r a p h i c C h a n g e s N o t o n l y d i d t h e c h a n g e s i n d e m o g r a p h i c s t a t i s t i c s p e r m i t a c h e c k on t h e d e f i n i t i o n o f some r e s e r v o i r s a s f l u c t u a t i n g a n d o t h e r s a s s t a b l e . T h e y a l s o c o n t a i n e d some i n t e r e s t i n g e c o l o g i c a l i n f o r m a t i o n . I n a l l r e s e r v o i r s , t h e p r o p o r t i o n o f y o u n g f i s h i n t h e p o p u l a t i o n s d e c l i n e d b e t w e e n J a n u a r y a n d N o v e m b e r ( c f . T a b l e 1 7 ) . I n f i v e o u t o f s i x o f t h e r e s e r v o i r s , t h e p r o p o r t i o n o f f e m a l e s p r e g n a n t d e c l i n e d ( c f . T a b l e 1 9 ) . I n t h e one r e s e r v o i r t h a t s h o w e d a s i g n i f i c a n t c h a n g e i n d e n s i t y , d e n s i t y d e c l i n e d ( c f . T a b l e 2 1 ) . I n a l l r e s e r v o i r s , t h e o v e r a l l s i z e s t r u c t u r e n a r r o w e d t o w a r d s t h e b r o a d c e n t e r o f t h e s i z e d i s t r i b u t i o n a t 1 5 - 3 0 mm ( c f . T a b l e 1 8 ) . I n N o v e m b e r , p r e g n a n t f i s h w e r e s l i g h t l y t h i n n e r , h a d s l i g h t l y s m a l l e r y o u n g , many f e w e r y o u n g , a n d made much s m a l l e r r e p r o d u c t i v e e f f o r t s ( T a b l e 2 4 ) . T h i s s y n d r o m e o f p o p u l a t i o n c h a n g e s makes s e n s e when o n e c o n s i d e r s t h e t i m i n g o f wet a n d d r y s e a s o n s i n H a w a i i . T h e wet s e a s o n r u n s f r o m N o v e m b e r t o A p r i l , a n d t h e d r y s e a s o n f r o m May t o O c t o b e r . D u r i n g t h e d r y s e a s o n , t e r r e s t r i a l p r i m a r y p r o d u c t i o n d e c l i n e s . T h u s t h e i n p u t t o r e s e r v o i r s o f w i n d b l o w n i n s e c t s p r o b a b l y d e c l i n e s d u r i n g t h e s u m m e r . W a t e r t e m p e r a t u r e s i n c r e a s e f r o m 2 1 - 2 2 ° C t o 2 3 - 2 4 ° C , w h i c h w o u l d n o t g r e a t l y i n c r e a s e t h e r a t e o f p r o d u c t i o n o f a q u a t i c c r u s t a c e a . T h e n e t e f f e c t i s a d e c l i n e i n a v a i l a b l e f o o d d u r i n g t h e s u m m e r . T h e J a n u a r y s a m p l e s came two m o n t h s i n t o t h e wet s e a s o n ; t h e N o v e m b e r s a m p l e s came two weeks a f t e r t h e e n d o f o n e o f t h e d r i e s t summers on r e c o r d . T h a t t h e c h a n q e s i n a l l s i x f i s h p o p u l a t i o n s , on two d i f f e r e n t i s l a n d s , w e r e c o n s i s t e n t l y i n t h e 124 same d i r e c t i o n argues f o r a broad geographic e f f e c t l i k e s e a s o n a l i t y . The d i r e c t i o n the changes took argues t h a t the proximal cause was a decrease i n the supply of food. Thus c i r c u m s t a n t i a l evidence i n d i c a t e s t h at both s t a b l e and f l u c t u a t i n g r e s e r v o i r s experience seasonal changes i n food supply t h a t a f f e c t the ex p r e s s i o n of r e p r o d u c t i v e t r a i t s i n f i s h . F i n a l l y , a n a l y s i s of the recent h i s t o r y of water l e v e l f l u c t u a t i o n s (during the 60 and 180 days before the sample date) shows t h a t the d e n s i t y of both Gambusia and other f i s h was higher i n r e s e r v o i r s that tended to be f u l l and have sma l l f l u c t u a t i o n s ( c f . Table 26). Co r r e c t e d f i s h d e n s i t i e s were p o s i t i v e l y c o r r e l a t e d with the l e v e l of water i n the r e s e r v o i r on the day of the sample, and with the mean water l e v e l d u r i n g the 60 and 180 days p r i o r to the sample. C o r r e c t e d f i s h d e n s i t i e s were n e g a t i v e l y c o r r e l a t e d with the c o e f f i c i e n t s of v a r i a t i o n i n water l e v e l f o r the 60 and 180 days p r i o r t o the sample. T h i s i s s t r o n g evidence t h a t f l u c t u a t i o n s i n water l e v e l reduce f i s h d e n s i t i e s i n r e s e r v o i r s , and i s strengthened by the r e p o r t s of p l a n t a t i o n workers t h a t r e s e r v o i r drawdowns f r e g u e n t l y f l u s h l a r g e numbers of f i s h i n t o the cane f i e l d s . 2i Summary, 5i a f f i n i s evolved i n a complex physico-chemical and b i o l o g i c a l environment on the Gulf Coast, probably d u r i n g the P l e i s t o c e n e . In 1905, about 150 Gambusia were i n t r o d u c e d to Hawaii f o r mosguito c o n t r o l . They m u l t i p l i e d and spread i n t o most of the freshwater impoundments i n the St a t e . In some C5 125 r e s e r v o i r s , they encountered a s t a b l e p h y s i c a l environment; i n ot h e r s , water l e v e l s f l u c t u a t e d w i l d l y and the f i s h p o p u l a t i o n s f l u c t u a t e d with them. In some s t a b l e and unstable r e s e r v o i r s , they encountered other f i s h t h a t were p o t e n t i a l c o m p e t i t o r s . In o t h e r s , they d i d not. The d i s t i n c t i o n between s t a b l e and f l u c t u a t i n g r e s e r v o i r s was p a r t i a l l y confounded by food a v a i l a b i l i t y : there was l e s s food a v a i l a b l e i n s t a b l e r e s e r v o i r s . T h i s chapter d e s c r i b e d the h i s t o r y of Gambusia i n Hawaiian r e s e r v o i r s and e s t a b l i s h e d the v a l i d i t y of c a l l i n g the s t o r y an experiment. The next chapter w i l l assess the r e s u l t s of the experiment as expressed i n the r e p r o d u c t i v e t r a i t s of preserved Gambusia caught i n the f i e l d . 126 CHAPTER IV. LIFE HISTORY PATTERNS: FIELD DATA l * . I f i t r o d u c t i o n To r e c a p i t u l a t e b r i e f l y : In Chapter I, I c o n t r a s t e d two s e t s of p r e d i c t i o n s . Advocates of r - and K - s e l e c t i o n c l a i m t h a t f l u c t u a t i n g environments s e l e c t f o r e a r l y maturation, l a r g e r e p r o d u c t i v e e f f o r t s , and many young. On the other hand, advocates of bet-hedging c l a i m that where f l u c t u a t i o n s a f f e c t j u v e n i l e r a t h e r than a d u l t m o r t a l i t y , they s e l e c t f o r delayed maturation, lower r e p r o d u c t i v e e f f o r t , and fewer young. In Chapter I I , I reviewed the b i o l o g y of Gambusia a f f i n i s and P o e c i l i a r e t i c u l a t a , the two main c h a r a c t e r s i n t h i s s t o r y . In Chapter I I I , a f t e r m a r s h a l l i n g the a v a i l a b l e evidence, I concluded that Gambusia and P o e c i l i a have undergone an e v o l u t i o n a r y experiment i n Hawaii, the r e s u l t s of which c o u l d be used to assess the c o n t r a s t i n g p r e d i c t i o n s of r - and K - s e l e c t i o n and bet-hedging. In t h i s c h a p t e r , I have used f i e l d data from preserved specimens to t e s t the p r e d i c t i o n s reviewed i n Chapter I . I f i r s t compared f i s h from s t a b l e and unstable r e s e r v o i r s i n Hawaii. Since I found s i g n i f i c a n t d i f f e r e n c e s between Gambusia c o l l e c t e d i n January and November, I t r e a t e d the January and November samples s e p a r a t e l y . That gave me a s e t of i n t r a s p e c i f i c comparisons f o r Gambusia on two dates. I a l s o compared P o e c i l i a from f o u r s t a b l e r e s e r v o i r s with P o e c i l i a from two f l u c t u a t i n g r e s e r v o i r s . That allowed me t o make the i n t e r s p e c i f i c comparison between Gambusia and P o e c i l i a . The 127 h i s t o r y of P o e c i l i a i n Hawaii i s not as we l l documented as Gambusia's. We cannot be sure of the date i t a r r i v e d i n the s t a t e and was in t r o d u c e d to the r e s e r v o i r s . Brock (1960) s a i d i t a r r i v e d i n 1922, but he d i d not document h i s c l a i m . And because P o e c i l i a i s a popular aquarium f i s h , people are much more l i k e l y to move i t around from r e s e r v o i r to r e s e r v o i r . Although my data are not as r e l i a b l e f o r P o e c i l i a as they are f o r Gambusia, they make a u s e f u l supplement. A f t e r having compared the r e p r o d u c t i v e t r a i t s of Gambusia and P o e c i l i a from s t a b l e and f l u c t u a t i n g r e s e r v o i r s i n Hawaii, I have d e s c r i b e d the r e p r o d u c t i v e t r a i t s of Gambusia c o l l e c t e d at Armand Bayou, Texas. Armand Bayou i s an area s e t a s i d e as a nature r e s e r v e , and was the only spot I c o u l d f i n d t h a t was both near Seabrook, where the Hawaiian stock o f Gambusia o r i g i n a t e d , and r e l a t i v e l y undisturbed. F i n a l l y , I have compared the r e p r o d u c t i v e t r a i t s of the Texan and Hawaiian f i s h to see how Gambusia has evolved i n Hawaii s i n c e i t s i n t r o d u c t i o n . 2^ Methods In Chapter I I I , I des c r i b e d the methods used to c o l l e c t and analyze f i s h from Hawaii. I used the same techniques i n Texas i n A p r i l , 1975, s e i n i n g with the same s e i n e and t a k i n g s e v e r a l samples, s c a t t e r e d among the a v a i l a b l e types of h a b i t a t , from each l o c a t i o n . But the C l e a r Creek sample was c o l l e c t e d f o r me by Texas Parks and W i l d l i f e personnel with a dip n e t , not a s e i n e , on 1 August 1974. I have i n c l u d e d i t i n the d e s c r i p t i o n °f Gambusia from Texas, but d i s c a r d e d i t when making comparisons between Texas and, Hawaii. 128 In Table 27, I have summarized the types of s t a t i s t i c a l a n a l y s e s I performed, the s e t s of f i s h I performed them on, and the names of the computer f i l e s t h a t c o n t a i n those s e t s of f i s h . F i g . 13 d e s c r i b e s the nested, t h r e e - l e v e l design I used f o r a n a l y s e s of v a r i a n c e and c o v a r i a n c e . I generated the design through a c o n s i d e r a t i o n of the treatments the f i s h r e c e i v e d s i n c e 1905, as r e c o n s t r u c t e d i n Chapter I I I . For the Texas-Hawaii comparisons, I simply added a f o u r t h , higher l e v e l : the Texas-Hawaii dichotomy. Note that I t r e a t e d each r e s e r v o i r as a separate sample nested w i t h i n a no c o m p e t i t o r - p o t e n t i a l competitor dichotomy, i t s e l f nested w i t h i n a s t a b l e - f l u c t u a t i n g c l a s s i f i c a t i o n . In order to summarize the data i n compact form, my r e p o r t s of the r e s u l t s i n c l u d e the F v a l u e s and a s s o c i a t e d p r o b a b i l i t i e s only f o r the f i r s t two l e v e l s o f the anova and ancova t a b l e s . F v a l u e s were c a l c u l a t e d using the mean square f o r the t h i r d l e v e l , i n d i v i d u a l r e s e r v o i r s , as the denominator. I used these package programs i n making the s t a t i s t i c a l a n a l y s i s : UBC ANOVAR f o r a n a l y s i s of v a r i a n c e and c o v a r i a n c e , UBC TRIP f o r l i n e a r r e g r e s s i o n s , and the GTEST program (A3.15) from Sokal and Rohlf (1969). 3_. R e s u l t s 3a._ Hawaii:. S t a b l e Vs.. F l u c t u a t i n g Environments 1. Number of Embryos x Weight 129 Table 27 Summary Of S t a t i s t i c a l Procedures " T T ~ T ••• i V a r i a b l e s Involved I A n a l y s i s i ( Done On ( F i l e Name ( i 1 1. Number Of Embryos X Weight |Ancova And (Linear Reg. ( A l l Pregnant }Females ( F i s h . f empl 2. Reproductive E f f o r t X Weight (Ancova And |Linear Reg. ( A l l Females (With NEL, EE, |LE, Or VLE Yng j F i s h . feme ( 3. Weight Of NEL Embryos (Anova ( A l l Females |With NEL Yng 1 F i s h . NEL J 4. Weight Of EE Embryos |Anova ( A l l Females (With EE Yng | F i s h . EE ( 5. Length At M a t u r i t y , Females j P r o b i t (Adult (Females ( F i s h , i f emt ( 6. C o n d i t i o n F a c t o r s , Females (Ancova And (Linear Reg. |Adult |Females r ( F i s h . f emt ( 7. Length At M a t u r i t y , Males | Anova 1 Adult (Males ( F i s h . mala | 8. P r o p o r t i o n Pregnant I Mann-Whitney |U-test i.. .,„ ( A l l Females ( F i s h . femt | 1 • 9. P r o p o r t i o n S u p e r f e t a t i n g (Mann-Whitney (U-test ( A l l Pregnant |Females i j F i s h . f emp ( l i 10 . Sex R a t i o s (G-test i _ |A11 Ad u l t s • * j F i s h . i o | i 1 3 0 FIGDBE 13 The Design Of The Analyses Of Variance And Covariance For the analyses of Hawaiian f i s h , I used a three l e v e l , nested (or hierarchical) design for analysis of variance and covariance. In making comparisons with Texan f i s h I simply added a fourth l e v e l , on top, representing the Texas-Hawaii dichotomy. 131 NESTED ANALYSIS OF VARIANCE/COVARIANCE DESIGN LEVEL 1 LEVEL 2 LEVEL 3 l; CAMBUSIA, JANUARY STABLE I HO COMPETITORS L i POTENTIAL COMPETITORS I NO COMPETITORS FLUCTUATING I Kay R e s e r v o i r Twin R e s e r v o i r f-Kaihuo Pump U n i v e r s i t y Quarry t R e s e r v o i r 31 R e s e r v o i r 40 R e s e r v o i r 51 R e s e r v o i r 81 • — R e s e r v o i r 84 1 POTENTIAL COMPETITORS j-Opaeula 01 • R e s e r v o i r 21 - R e s e r v o i r 22 — R e s e r v o i r 25. - R e s e r v o i r 32 - R e s e r v o i r 33 — R e s e r v o i r 35 — R e s e r v o i r 41 — R e s e r v o i r 42 " " R e s e r v o i r 50 • R e s e r v o i r 60 R e s e r v o i r 61 - R e s e r v o i r 80 _ R e s c r v o i r 90 - R e s e r v o i r 91 LEVEL 1 LEVEL 2 LEVEL 3 LEVEL 1 LEVEL 2 LEVEL 3 2. CAMBUSIA, UOVHTOER STABLE FLUCTUATING 1 NO COMPETITORS L POTENTIAL COMPETITORS Kay R e s e r v o i r Twin R e s e r v o i r , August L - T v i n R e s e r v o i r . November i 1 NO COMPETITORS POTENTIAL COMPETITORS L • R e s e r v o i r 81 I - R e s e r v o i r 33 f - R e s e r v o i r 41 R e s e r v o i r 50 3. POECILIA, JANUARY STABLE FLUCTUATING I 1 NO COMPETITORS POTENTIAL COMPETITORS L 'Camp 17 R e s e r v o i r Kalhuc Pump U n i v e r s i t y Quarry '-Pump ( 4 NO COMPETITORS L Upper Helemano R e s e r v o i r POTENTIAL COMPETITORS L. • R e s e r v o i r 25 132 Table 28 d i s p l a y s the s t a t i s t i c a l r e s u l t s of comparing f i s h from s t a b l e and f l u c t u a t i n g r e s e r v o i r s f o r number of young. I d i d the a n a l y s i s on a l l pregnant females. In a l l t h r e e c o l l e c t i o n s , f i s h from f l u c t u a t i n g r e s e r v o i r s had more young, and the d i f f e r e n c e s were l a r g e : 15% f o r Gambusia c o l l e c t e d i n January, 182% f o r Gambusia c o l l e c t e d i n November, and 318% f o r P o e c i l i a . However, the d i f f e r e n c e was only s i g n i f i c a n t f o r P o e c i l i a . (Here and below, I have repo r t e d percentage d i f f e r e n c e s i n r e p r o d u c t i v e t r a i t s f o r a 175 mg f i s h . ) i n a l l t h r e e c o l l e c t i o n s , a good d e a l of the v a r i a n c e c o u l d be accounted f o r at L e v e l 3 by v a r i a t i o n among i n d i v i d u a l r e s e r v o i r s , but not i n any c o n s i s t e n t p a t t e r n . 2. Reproductive e f f o r t Table 29 presents s i m i l a r l y d e r i v e d r e s u l t s f o r r e p r o d u c t i v e e f f o r t . I d i d the a n a l y s i s on a l l pregnant females that had NEL, EE, LE, or VLE eggs. In a l l three cases, f i s h from f l u c t u a t i n g r e s e r v o i r s made l a r g e r r e p r o d u c t i v e e f f o r t s . Again, the d i f f e r e n c e was only s i g n i f i c a n t f o r P o e c i l i a . In two c a s e s , the d i f f e r e n c e was l a r g e : Q0% f o r Gambusia c o l l e c t e d i n November, and 117% f o r P o e c i l i a . For Gambusia c o l l e c t e d i n January, the d i f f e r e n c e was only 7%. In f i v e out of s i x cases at L e v e l 2, r e p r o d u c t i v e e f f o r t d e c l i n e d with s i z e , and presumably age. In a l l three c o l l e c t i o n s , much of the v a r i a n c e c o u l d be e x p l a i n e d at L e v e l 3, but again, not i n any c o n s i s t e n t p a t t e r n . Table 30a e x h i b i t s a summary of the d i f f e r e n c e s between s t a b l e and f l u c t u a t i n g r e s e r v o i r s f o r pregnancy and 133 T a b l e 28 A n a l y s i s Of C o v a r i a n c e : Number O f E m b r y o s X W e i g h t Done On : A l l P r e g n a n t F e m a l e s T T Mean Num. E m b r y o s ' "i I P r o b , S a m p l e N | Y = A + BX 1 A B i JLs. G a m b u s i a , J a n u a r y -I 290 | 7.143 66.49 1330 | 3.997 101.00 H A . S t a b l e F l u c t u a t i n g 17. 11 23.46 0 . 0 9 3 4 | > 0 . 7 5 I B . S t a b l e No Comp S t a b l e Comp F l u c t . No Comp F l u c t . Comp 18. 34 11.08 32. 20 22.78 2 4 1 | 7 . 2 2 6 7 2 . 5 3 4 9 | 6 . 9 6 9 3 0 . 7 5 9 5 I 2 4 . 4 8 0 2 3 . 5 2 1 2 3 5 | 0 . 0 5 1 1 2 4 . 8 0 I I 0.0458|>0.75 I G a m b u s i a , N o v e m b e r j A . S t a b l e F l u c t u a t i n g 7. 90 17.59 139 J 4.346 32.45 73 | 2.096 149.60 _| 5.099 >0. 10 B . S t a b l e No Comp S t a b l e Comp F l u c t . No Comp F l u c t . Comp 8.40 7.84 10.25 22. 16 15 |-0.935 38. 39 124 | 0.025 83.72 28 | 3.159 87.50 45 | 3.387 159.60 1.7149 >0.25 i P o e c i l i a , J a n u a r y ^ I 5.74 | 294 | 1. 146 42. 29 24.49 | 138 {12.910 138.80 A . S t a b l e F l u c t u a t i n g 95.3500 <0.0250 9 J-0.820 114.50 285 | 1. 520 42. 14 107 | 0.330 360.20 31 | 9.555 52.93 B . S t a b l e No Comp S t a b l e Comp F l u c t . No Comp F l u c t . Comp 2.44 5.84 26. 86 15.42 6.4856 >0.10 134 Table 29 A n a l y s i s Of Covariance: Reproductive E f f o r t X Weight Done On: A l l Females With NEL, EE, LE, Or VLE Embryos Sample •T r I Mean | | Repro. | | E f f o r t | N J Y = A + BX | I A B | Prob, 1. Gambusia, January ..j- L L A. S t a b l e F l u c t u a t i n g | 0.224 | 246 | 0.270 -0.302| j 0.229 |1108 | 0.264 -0.178| 4 + j f-0.3256 >0.50 S t a b l e No Comp S t a b l e Comp F l u c t . No Comp F l u c t . Comp 1 0.237 | 0.159 | 0.227 f 0.229 | 205 | 0.275 | 41 | 0.249 | 73 | 0.370 11035 | 0.257 I •0.246 | •0.649J •0.4101 •0.149| 0.9515 >0.50-2. Gambusia, November —Z_I+_ ^ A. S t a b l e F l u c t u a t i n g 0.112 | 105 | 0.126 -0.1301 0.200 | 64 | 0.221 -0.205| 7.2551 >0.10 S t a b l e No Comp S t a b l e Comp F l u c t . No Comp F l u c t . Comp 0.067 j 0.117 | 0.174 | 0.215 | 11 I 94 | 24 j 40 | 0.088 0. 094 0. 170 0.282 •0.084| 0.259| 0.055| •0.584 | 0.4669 >0.50 i P o e c i l i a , January +-+ +  i I •0.021|141.3856|<0.005 •0.1771 1 j ^ A. S t a b l e F l u c t u a t i n g S t a b l e No Comp S t a b l e Comp F l u c t . No Comp F l u c t . Comp 0. 105 0.240 I | 226 | 0.107 | 134 | 0.254 0.065 0. 106 0.254 0. 182 I -+ -I I 3 | 22 3 I 107 j I 27 1 | 0.081 | 0.109 0.253 0. 190 I •0.627J •0.031 | 0.019| •0.0781 5.6167|>0.10 135 Table 30 Summary Of Differences In Pregnancy And Superfetation ~! I I u _J Sample |Mean Var, •T I IProb 1. Percent Pregnant: Mann-Whitney U-test On Stable-fluctuating Diff, Gambusia, January Gambusia, November P o e c i l i a , January 25 5 6 I 37 2 5 | 42 13.49 | -.371 2. Percent Superfetating, Mann-Whitney U-test Gambusia, January Gambusia, November P o e c i l i a , January 25 5 6 I 40.5| 3 I 3 I L. 42 13.49 | -.111 .456 .600 .400 B. Kendall Rank Correlation C o e f f i c i e n t s Correlation Tau Prob 1. Gambusia, January H I |<0.0427 |<0.0571 | 0.0951 % Preg X % Superfet % Preg X Repro. E f f. % Superfet. X Repro. E f f . I 0.2646 0.2430 0.2012 1.724 1.583 1.310 Gambusia, November 1—Z H I j<0.2206 |<0.3121 % Preg X % Superfet. % Preg. X Repro. E f f . % Superfet. X Repro. E f f . 0.3162 0.2000 0.775 0.490 3« P o e c i l i a , January +  I I<0.2206 |<0.0951 I<0.1660 % Preg. X % Superfet. % Preg. X Repro. E f f . % Superfet. X Repro. Eff, -0.2760 0.4667 0.3450 •0.778 1.315 0.972 136 s u p e r f e t a t i o n r a t e s . I used a l l females over 16 mm S.L. i n c a l c u l a t i n g percent pregnant, and a l l females with a t l e a s t one NEL, EE, LE, or VLE brood i n c a l c u l a t i n g s u p e r f e t a t i o n r a t e . I d e f i n e d s u p e r f e t a t i o n as having two broods i n d i s t i n c t l y d i f f e r e n t stages of development (e.g. EE and I E ) , not counting NES eggs. A s e r i e s of Mann-Whitney U t e s t s on the ranks of r e s e r v o i r s f o r percent pregnant and percent s u p e r f e t a t i n g d i d not t u r n up any s i g n i f i c a n t d i f f e r e n c e s . Table 30b s e t s f o r t h the c o r r e l a t i o n s among pregnancy r a t e s , s u p e r f e t a t i o n r a t e s , and r e p r o d u c t i v e e f f o r t s . I used K e n d a l l ' s r a n k - c o r r e l a t i o n c o e f f i c i e n t , t a u . The only s i g n i f i c a n t c o r r e l a t i o n s were i n the sample of Gambusia c o l l e c t e d i n January, where a l l three s t a t i s t i c s were p o s i t i v e l y c o r r e l a t e d with each other. In a l l samples but one, the c o r r e l a t i o n s were at l e a s t p o s i t i v e , i f not s i g n i f i c a n t . Since I only had 5 r e s e r v o i r s to rank f o r Gambusia c o l l e c t e d i n November, and 6 f o r P o e c i l i a , I suspect t h a t a l l c o r r e l a t i o n s would have become s i g n i f i c a n t with l a r g e r sample s i z e s . 3. S i z e of Young F i g u r e s 14, 15, and 16 present the p a t t e r n of weight change i n the embryos as they develop. I found r e l a t i v e l y few females with LE and VLE embryos, i n d i c a t i n g that these stages are passed through r a p i d l y . For purposes of s t a t i s t i c a l a n a l y s i s , I i s o l a t e d a l l females with an NEL brood and a l l females with an EE brood, and performed a nested a n a l y s i s of v a r i a n c e on the average weight of NEL or EE young from each female. Table 31 d i s p l a y s the r e s u l t s . In a l l cases but one, the embryos were 137 FIGURE 14 Egg Development: Gambusia, January Legend: Egg stages - 1 = no eyes, s m a l l ; 2 = no eyes, l a r g e ; 3 = e a r l y - e y e d ; 4 = l a t e - e y e d ; 5 = very l a t e -eyed . The eggs are probably inseminated with s t o r e d sperm a t Stage 2. That they do not l o s e much weight d u r i n g development i s an i n d i c a t i o n t h a t they r e c e i v e nourishment from the mother. There was no s i g n i f i c a n t d i f f e r e n c e between the weights of f i s h a t Stages 3 and 4 from s t a b l e and f l u c t u a t i n g r e s e r v o i r s . m CD ci CO —I ID CD WEIGHT IN MG CD ro — i — f N J CO co x - m < UD — i ZD CD r~ rn cz CD CZ ZD CD CD ZD CD CD CD CO a r—i rn Z D CD ZD 'TD ZD ^ TO —\ -< 139 FIGURE 15 Egg Development: Gambusia, November Legend: Egg stages - 1 = no eyes, s m a l l ; 2 = no eyes, l a r g e ; 3 = e a r l y - e y e d ; 4 = l a t e - e y e d ; 5 = very l a t e -eyed. The eggs are probably inseminated with s t o r e d sperm at Stage 2. That they do not l o s e much weight dur i n g development i s an i n d i c a t i o n t h a t they r e c e i v e nourishment from the mother. There was no s i g n i f i c a n t d i f f e r e n c e between the weights of f i s h a t Stages 3 and 4 from s t a b l e and f l u c t u a t i n g r e s e r v o i r s . O H CO —I ID CD r~ m c: i — i ZD 3 CD d CO I—I ID < m ~n CD ~73 141 FIGURE 16 Egg Development, P o e c i l i a , January Legend: Egg stages - 1 = no eyes, s m a l l ; 2 = no eyes, l a r g e ; 3 = e a r l y - e y e d ; 4 = l a t e - e y e d ; 5 = very l a t e -eyed. The eggs are probably inseminated with s t o r e d sperm at Stage 2. That they do not l o s e much weight d u r i n g development i s an i n d i c a t i o n t h at they r e c e i v e nourishment from the mother. Note t h a t P o e c i l i a young from f l u c t u a t i n g r e s e r v o i r s were s i g n i f i c a n t l y s m a l l e r at Stages 2, 3, and 4 than t h e i r c o u n t e r p a r t s from s t a b l e r e s e r v o i r s . 143 T a b l e 31 A n a l y s i s Of V a r i a n c e : W e i g h t Of Y o u n g S a m p l e -+-JMean | N -J ; t NEL - + -I I — I •T-1 E E -+-1. G a m b u s i a , J a n u a r y P r o b . JMean | N j I P r o b . A . S t a b l e F l u c t u a t i n g S t a b l e No Comp Comp F l u c t u a t i n g No Comp Comp 1 . 8 9 1.81 +-1.94 1 . 6 8 1 .70 1 .94 142 470 114 28 41 429 0 . 4 7 9 0 >.25 | 1 . 8 1 | 1 . 9 1 0 . 7 4 8 9 >.25 I | 1 . 7 8 I 2 . 0 2 ! | 1 .97 | 1 . 9 1 112 506 101 11 26 480 0 . 7 1 5 7 >. 25 0 . 2 2 5 5 >.75 S t a b l e 1. 59 48 F l u c t u a t i n g 1. 09 35 S t a b l e No Comp 1. 67 3 Comp 1. 59 45 F l u c t u a t i n g No Comp 1. 24 13 Comp 1. 00 22 2. G a m b u s i a , N o v e m b e r j B. 5 . 3 7 8 6 >.25 0 . 2 5 7 2 >.75 1.61 1 .50 51 22 0 . 2 5 1 1 >.50 3. P o e c i l i a , J a n u a r y - + + +— A . S t a b l e F l u c t u a t i n g 1 . 8 9 0 . 9 1 133 78 B. S t a b l e No Comp Comp F l u c t u a t i n g No Comp Comp 1 . 9 0 1 .89 0 . 7 5 1 .46 1 132 61 17 5 . 2 3 0 7 0 . 3 6 3 8 >. 10 >.50 2 . 0 1 0 . 7 6 91 64 9 . 1 5 9 3 2 . 0 1 0 . 6 8 1 . 2 0 91 54 10 0 . 3 5 3 7 >.05 >. 50 — j 144 s m a l l e r i n the females from f l u c t u a t i n g r e s e r v o i r s . (The EE embryos from Gambusia c o l l e c t e d i n January sere s m a l l e r i n females from s t a b l e r e s e r v o i r s . ) i n none of the samples were the d i f f e r e n c e s s i g n i f i c a n t , most of the v a r i a n c e being absorbed at L e v e l .3 by i n d i v i d u a l r e s e r v o i r s . The d i f f e r e n c e s i n embryo weight f o r P o e c i l i a were e s p e c i a l l y s t r i k i n g : 108% f o r NEL embryos and 164% f o r EE embryos. 4. S i z e at Maturity I estimated s i z e at maturity from the f i e l d data using a s t a t i s t i c a l technique, p r o b i t a n a l y s i s , employed by t o x i c o l o g i s t s to e s t a b l i s h the dose of a drug at which 50% of t h e i r t e s t animals d i e . I took a l l the females f o r each sample (Gambusia c o l l e c t e d i n January, Gambusia c o l l e c t e d i n November, and P o e c i l i a ) , d i v i d e d them i n t o 2 mm l e n g t h c l a s s e s , and c a l c u l a t e d the percent pregnant i n each c l a s s . I then di d a weighted l i n e a r r e g r e s s i o n of the log of the midpoint of the l e n g t h c l a s s e s on the p r o b i t t r a n s f o r m a t i o n of the percent pregnant i n the l e n g t h c l a s s . The e f f e c t was simply to l i n e a r i z e the data and estimate the length at which one could expect 50% of the females to be pregnant. F i g u r e s 17, 18, and 19 set f o r t h the d i s t r i b u t i o n of percent pregnant over l e n g t h c l a s s e s f o r the t h r e e samples, and T able 32 presents the r e s u l t s of the p r o b i t a n a l y s i s . In no case was there a s i g n i f i c a n t d i f f e r e n c e i n s i z e at maturity between s t a b l e and f l u c t u a t i n g r e s e r v o i r s f o r females. 5. C o n d i t i o n F a c t o r s 145 FIGURE 17 Percent Pregnant By S i z e C l a s s : Gambusia, January The p r o p o r t i o n of Gambusia females t h a t are pregnant i n c r e a s e s with s i z e . There was no s i g n i f i c a n t d i f f e r e n c e i n the l e n g t h s at which 50% of the females were pregnant between s t a b l e and f l u c t u a t i n g r e s e r v o i r s . 146 PERCENT PREGNANT BY SIZE CLASS GAMBITS I A. JANUARY STABLE 100 T 80 { 5 0 * POINT-29.! 1 60 f ^ 40 -20 0 0 8 16 24 32 40 MM FLUCTUATING i 100 T 80 60 40 I 20 0 50,? P0INT=--28.33. N"149C 0 8 16 243240 MM 147 FIGURE 18 Percent Pregnant Ey S i z e C l a s s : Gambasia, November The p r o p o r t i o n o f Gambusia females that are pregnant i n c r e a s e s with s i z e . There was no s i g n i f i c a n t d i f f e r e n c e i n the le n g t h s at which 50% of the females were pregnant between s t a b l e and f l u c t u a t i n g r e s e r v o i r s . 148 PERCENT:PREGNRNT BY SIZE CLASS GRMB'JSIR. NOVEMBER S'TRBLE 100 80 60 --. 40 -20 •-0-50X P O I N T S . 25 0 8 16 24 32 4Q' MM FLUCTURTING 100 80 60 40 20 0 502 P3INT=3Q.4fi 0 8 16 2432 40 MM 149 FIGURE 19 Percent Pregnant By S i z e C l a s s : P o e c i l i a , January The p r o p o r t i o n of P o e c i l i a females that are pregnant i n c r e a s e s with s i z e . There was no s i g n i f i c a n t d i f f e r e n c e i n the l e n g t h s a t which 50% of the females were pregnant between s t a b l e and f l u c t u a t i n g r e s e r v o i r s . However, note that Gambusia females matured, on the average, at 28-30 mm, while P o e c i l i a females matured, on the average, at 20 mm. I estimate t h a t P o e c i l i a females mature at 60-80 days, and t h a t Gambusia females mature a t 120-150 days ( c f . Chapter V I ) . 150 ERCENT PREGNANT BY SIZE CLASS POECII IR. . I Q N i l Q P Y 100 80 60 40 20 I 0 STABLE 50.? P3JNT-20.51 H=382 ru 0 8 16 2432 40 MM 7 100 80 60 40 20 0 FLUCTUATING 50? POINT: 20.23 M N::]44 ^ 0 8 16 2^32 40 MM 151 Table 32 S i z e At Maturity P r o b i t A n a l y s i s Of Percent Pregnant By S i z e C l a s s —T 1 1 |Mean Length]Log Length j 95% I At 50% Preg jAt 50% PregI C.I. — i 1 1 1. Gambusia, January —H — + 1 H I I 1 | 2 9.11 | 3.371 i ± .178 | 28,33 | 3.344 | ± .567 — i 1 1 2. Gambusia, November -+ Z j — I I I I I | 29.25 | 3.376 J ± .388 | 30.48 | 3.417 | ± .375 —i 1 j 3. P o e c i l i a , January - H 1 1- + i I t | 20.51 J 3.021 | ± .827 | 20.23 | 3.007 | ± .410 — i 1 j Sample St a b l e F l u c t u a t i n g S t a b l e F l u c t u a t i n g Prob. >.05 >.05 Stab l e F l u c t u a t i n g >.05 The c o n d i t i o n f a c t o r - the c o e f f i c i e n t term i n the r e g r e s s i o n of le n g t h on l o g weight - i s g e n e r a l l y taken to be a measure of a f i s h ' s p h y s i o l o g i c a l c o n d i t i o n , of i t s b u i l d - u p of energy r e s e r v e s . In chapter I I I , I showed that Gambusia from s t a b l e r e s e r v o i r s had lower c o n d i t i o n f a c t o r s than those from f l u c t u a t i n g r e s e r v o i r s . Here I repeat the a n a l y s i s f o r the January and November Gambusia c o l l e c t i o n s s e p a r a t e l y , and f o r P o e c i l i a . Table 33 s e t s f o r t h the s t a t i s t i c a l a n a l y s i s of c o n d i t i o n f a c t o r s . In the January sample of Gambusia and i n P o e c i l i a , f i s h from f l u c t u a t i n g r e s e r v o i r s were i n b e t t e r c o n d i t i o n . The d i f f e r e n c e s were moderately l a r g e : 11% f o r Gambusia c o l l e c t e d i n January, 16% f o r P o e c i l i a . For Gambusia c o l l e c t e d i n November, the f i s h from s t a b l e r e s e r v o i r s were i n b e t t e r c o n d i t i o n . Again, the d i f f e r e n c e was moderately l a r g e : 17%. But i n no case was the s t a b l e - f l u c t u a t i n g d i f f e r e n c e s i g n i f i c a n t , most of the v a r i a b i l i t y being absorbed at l e v e l 3 by i n d i v i d u a l r e s e r v o i r s . 6. Summary Tables 34 and 35 present a summary of the f i e l d evidence t h a t bears on the c o n t r a s t i n g p r e d i c t i o n s of r - and K - s e l e c t i o n and bet-hedging. In every case where there was a l a r g e d i f f e r e n c e i n a r e p r o d u c t i v e t r a i t between s t a b l e and f l u c t u a t i n g r e s e r v o i r s , the d i f f e r e n c e was i n the d i r e c t i o n p r e d i c t e d by advocates of r - and K - s e l e c t i o n . In every case where there was a l a r g e d i f f e r e n c e , the d i f f e r e n c e was l a r g e r i n the November c o l l e c t i o n of Gambusia than i n the January 153 Table 33 A n a l y s i s Of Covariance: Length X Log Weight Done On: A l l Adult Females Sample Mean Length Gambusia, January -I T r~ N | Y = A + BX | I a B j 1 1_. T 1 \ Prob. A. S t a b l e F l u c t u a t i n g 31.30 32.99 477 | 49.92 8.361 | 1.0951 | >0.-25 1932 | 51.66 9.293 \ | -j j. ^ B. S t a b l e No Comp S t a b l e Comp F l u c t . No Comp F l u c t . Comp 33.77 28.51 32.61 33.05 253 | 50.86 8.680 | 224 | 47.75 7.642 | 260 | 50.82 8.947 j 1672 | 51.90 9.402 | 1 SL. I 0.3431|>0.50 I Gambusia, November -+- +-A. S t a b l e F l u c t u a t i n g 28.79 25. 12 324 | 51.12 8.675 311 | 46.94 7.412 3.7051 >0. 10 S t a b l e No Comp St a b l e Comp F l u c t . No Comp F l u c t . Comp 29.49 28.53 23. 13 25.96 88 j 50.84 8.804 236 | 51.53 8.747 92 | 46.00 7.063 219 | 47.36 7.586 0.9202 >0.25 3_j_ P o e c i l i a , January +  I 419 | 44.27 6,778 155 I 48.20 7.848 A. S t a b l e F l u c t u a t i n g 25. 12 26.60 0.3764 >0.50 B. S t a b l e No Comp St a b l e Comp F l u c t . No Comp F l u c t . Comp 16.29 26.68 26.85 25.84 63 | 39.16 5.322 356 | 46.07 7.561 111 | 48.11 7.673 45 | 47.98 8.114 1 0.5194 >0.50 154 Table 34 Summary Of D i f f e r e n c e s In Reproductive T r a i t s (Values Given For A 175 MG Female In Regressions ) Sample T — T " | Number Of | Repro, {Emb. Wgt< H +-| Embryos | E f f o r t |NEL |EE 1. Gambusia, January A. S t a b l e F l u c t u a t i n g S t a b l e No Comp St a b l e Comp F l u c t u a t i n g No Comp F l u c t u a t i n g Comp 18.78 21.67 I I I 0.217 0.233 I i 1.89 11.81 19.92 12.35 28.60 21.89 0.232 0.135 0.298 0.231 I 1.94 | 1.68 |1.70 | 1.94 .j 1.81 1.91 1.78 2.02 1.97 1.91 Lngth. .{Lngth + 50%prg|175MG + 29.11 135.35 28.33 {35.46 j_ I Gambusia, November Z ., -+ I | 1.59 I 1.09 1 36.00 34.02 A. S t a b l e F l u c t u a t i n g 10.02 28. 28 0.103 0.185 1.61 1.50 29.25 30.48 ..j 1 | 1 .67 I 1.59 11.24 11.00 S t a b l e No Comp St a b l e Comp F l u c t u a t i n g No Comp F l u c t u a t i n g Comp 5.78 14.68 19.47 31.32 0.073 0.139 0.180 0.180 1.96 1.53 1.60 1.45 . P o e c i l i a , January +-A. S t a b l e F l u c t u a t i n g 8.90 37.20 0,103 0.223 1.89 0. 91 2.01 0.76 20.51 20. 23 S t a b l e , No Comp S t a b l e , Comp F l u c t u a t i n g No Comp F l u c t u a t i n g Comp 19.22 8.89 63. 37 18.82 -0.029 0.104 0.256 0.175 i I 11.90 11.89 | 0.75 I 1.46 2.01 0.68 1.20 32.46 34.52 JL. 155 T a b l e 35 Summary O f H y p o t h e s e s And E v i d e n c e F o r F e m a l e s , G i v i n g T h e P r e d i c t i o n s F o r S t a b l e R e s e r v o i r s O n l y T r a i t T " I P r e d i c t i o n 1. Number Of Y o u n g 2. S i z e Of Y o u n g 3 . R e p r o d u c t i v e E f f o r t RSK B e t - H e d g i n g O t h e r F e w e r M o r e -+ L a r g e r L e s s G r e a t e r 4. S i z e A t M a t u r i t y G r e a t e r L e s s T r a i t E v i d e n c e G a m b u s i a , J a n u a r y G a m b u s i a N o v e m b e r P o e c i l i a J a n u a r y 1. Number Of Y o u n g 15% F e w e r NS 182% F e w e r NS 318% F e w e r S i g 2. S i z e O f Y o u n g NEL E E L a r g e r NS S m a l l e r NS 46% L a r g e r NS 1% L a r g e r NS 108% L a r g e r NS 164% L a r g e r * 3 . R e p r o d u c t i v e E f f o r t 7% L e s s NS 80% L e s s NS 116% L e s s S i g 4. S i z e A t M a t u r i t y No D i f f e r e n c e No D i f f e r e n c e No D i f f e r e n c e * 0 . 0 5 < p < 0 . 1 0 156 c o l l e c t i o n , and l a r g e r yet f o r P o e c i l i a . However, only P o e c i l i a females showed any s i g n i f i c a n t d i f f e r e n c e i n number of young or r e p r o d u c t i v e e f f o r t , and there was no s i g n i f i c a n t d i f f e r e n c e i n any of the three samples analyzed i n s i z e at maturity i n females. Note that P o e c i l i a has a l e n g t h a t maturity 8-10 mm l e s s than Gambusia. P o e c i l i a makes a r e p r o d u c t i v e e f f o r t i n f l u c t u a t i n g r e s e r v o i r s as l a r g e as Gambusia's, and produces more, but s m a l l e r young. 3b. Texas D e t a i l s Table 36 pre s e n t s a summary of l i f e h i s t o r y t r a i t s f o r three samples of Gambusia c o l l e c t e d near Seabrook, Texas. The C l e a r Creek sample was small and c o l l e c t e d i n August 1974 by d i p n e t . I d i d not analyze i t i n as much d e t a i l as the two samples from Armand Bayou, one from a freshwater pond and the other from the e s t u a r y , which were c o l l e c t e d on 28 A p r i l 1975 with the same s e i n e as the Hawaii samples. The most s t r i k i n g d i f f e r e n c e s are those between the freshwater pond and the e s t u a r y at Armand Bayou, c o l l e c t e d on the same day not more than 200 m a p a r t . F i s h from the e s t u a r y had more young, made l a r g e r r e p r o d u c t i v e e f f o r t s , and h e l d s m a l l e r embryos than f i s h from the freshwater pond ( c f . F i g . 20) . V i r t u a l l y a l l females caught were pregnant (95.9%, F i g . 21) . The s m a l l e s t pregnant female from the freshwater pond was between 18 and 20 mm long (n=157); the s m a l l e s t pregnant female from the e s t u a r y was between 22 and 24 mm long (n=76). D i f f e r e n c e s i n c o n d i t i o n f a c t o r s were s m a l l but s i g n i f i c a n t . The f i s h from C l e a r Creek had about as many young and made 157 T a b l e 36 Summary O f L i f e H i s t o r y T r a i t s F o r G a m b u s i a C o l l e c t e d N e a r S e a b r o o k , T e x a s A . D e t a i l s 1. Number O f E m b r y o s X W e i g h t +• L o c a t i o n C l e a r C r e e k F r e s h w a t e r E s t u a r y Mean I N Y = A + BX x. -+-| 11.41 | 17 1 15.46 |157 | 35.79 | 76 I i A •5.349 •1.012 3.088 I \ P r o b . 2. R e p r o d u c t i v e E f f o r t X W e i g h t -I H -i C l e a r C r e e k F r e s h w a t e r E s t u a r y 0. 137 0.274 0.353 I 12 | 144 I 68 | 0.061 | 0.274 | 0.330 3 . L e n g t h X L o g W e i g h t ~ H i i C l e a r C r e e k F r e s h w a t e r E s t u a r y | 25.23 | 26 | 27.17 1166 I 30.97 J 77 1 48.47 1 49.82 | 51.81 —I 4. W e i g h t Of Y o u n g II EL E E Mean • 1 H 1 I P r o b . | M e a n J N -+- + 1 P r o b . C l e a r C r e e k F r e s h w a t e r E s t u a r y 1 1 1. 22 153 110. 1478 0.99 J 32 | 1 i T r— 1 11.00 | 4 I0.0022 J1.29 J 68 I 11.11 I 36 J j i T 14.4831 <0.0001 B . Summary C l e a r C r e e k ^ , — Number O f Y o u n g I n A 175 Mg F e m a l e W e i g h t Of .An A v e r a g e E m b r y o , Mg R e p r o d u c t i v e E f f o r t O f A 175 Mg F e m a l e L e n g t h O f A 175 Mg F e m a l e F r e s h W a t e r E s t u a r y 44.94 0.95 0.292 34.99 40.32 1.28 0.275 3 5 . 23 53. 17 1.10 0. 367 36. 14 158 FIGDRE 20 Egg Development: Gambusia, Armand Bayou, Texas Legend: Egg stages - 1 = no eyes, s m a l l ; 2 = no eyes, l a r g e ; 3 = e a r l y - e y e d ; 4 = l a t e - e y e d ; 5 = very l a t e -eyed. The eggs are probably inseminated with s t o r e d sperm at Stage 2. That they do not l o s e much weight during development i s an i n d i c a t i o n t h a t they r e c e i v e nourishment from the mother. The weights of f i s h a t Stages 2 and 3 from the freshwater pond were s i g n i f i c a n t l y g r e a t e r than those from the estuary (cf. Table 37). 160 FIGURE 21 Percent Pregnant By S i z e C l a s s : Gambusia, Armand Bayou, Texas There was no s i g n i f i c a n t d i f f e r e n c e i n the l e n g t h s at which 50% of the females were pregnant between the es t u a r y and the freshwater pond. A l l females caught were pregnant. 161 PERCENT PREGNRNT BY SIZE CLRSS GRMBUSIR. RRMRND BRYQU, TEXAS FRESHWRTER X 100 80' 60 -40 -20 -.- 0 100 T 80 -60 40 I 20 0 0 8 16 24 32 40 MM ESTURRY 0 8 16 2432 40' MM 162 r e p r o d u c t i v e e f f o r t s a b o u t a s l a r g e a s t h o s e f r o m t h e f r e s h w a t e r p o n d a t A r m a n d B a y o u . T h e i r e m b r y o s w e r e s m a l l e r . T h u s t h e r e i s c o n s i d e r a b l e m i c r o g e o g r a p h i c v a r i a b i l i t y i n l i f e h i s t o r y t r a i t s o f G a m b u s i a i n t h e i r n a t i v e r a n g e n e a r S e a b r o o k , T e x a s . T h e m a j o r d i f f e r e n c e s I o b s e r v e d w e r e c o r r e l a t e d w i t h d i f f e r e n c e s b e t w e e n a f r e s h w a t e r p o n d a n d t h e b r a c k i s h e s t u a r y . 3 c . T e x a s ^ H a w a i i C o m p a r i s o n s T a b l e s 37 a n d 38 p r e s e n t a c o m p a r i s o n o f t h e r e p r o d u c t i v e t r a i t s o f G a m b u s i a c o l l e c t e d i n T e x a s on 28 A p r i l 1975 a n d i n H a w a i i i n J a n u a r y 1974. T h e r e was a much l o w e r p r o p o r t i o n o f m a l e s i n T e x a s (4.1%) t h a n i n H a w a i i ( 3 1 . 9 % ) , a n d t h e d i f f e r e n c e was s i g n i f i c a n t ( G = 1 0 8 . 4 9 ; 3 . 8 4 1 w o u l d h a v e b e e n s i g n i f i c a n t ) . A h i g h e r p r o p o r t i o n o f f e m a l e s w e r e p r e g n a n t i n T e x a s (95.9%) t h a n i n H a w a i i ( 6 2 . 4 % ) , a n d a g a i n t h e d i f f e r e n c e was s i g n i f i c a n t ( G = 1 4 4 . 8 3 ) . S i g n i f i c a n t l y more p r e g n a n t f e m a l e s w e r e s u p e r f e t a t i n g i n T e x a s (12.3%) t h a n i n H a w a i i ( 5 . 5 ^ ; G = 1 2 . 7 2 ) . G a m b u s i a f r o m T e x a s h a d more y o u n g , s m a l l e r y o u n g , a n d make l a r g e r r e p r o d u c t i v e e f f o r t s t h a n G a m b u s i a f r o m H a w a i i , b u t o n l y t h e d i f f e r e n c e i n s i z e o f y o u n g was s i g n i f i c a n t . I n a l l c a s e s a l l T e x a s s a m p l e s h a d more y o u n g , s m a l l e r y o u n g , a n d made l a r g e r r e p r o d u c t i v e e f f o r t s t h a n e i t h e r t h e s t a b l e o r f l u c t u a t i n g H a w a i i a n s a m p l e s . H o w e v e r , a t a f i n e r l e v e l o f d e t a i l , l o o k i n g a t t h e H a w a i i a n r e s e r v o i r s a m p l e s i n d i v i d u a l l y , I f o u n d two i n w h i c h G a m b u s i a a p p r o a c h e d o r e x c e e d e d t h e r e p r o d u c t i v e e f f o r t s o f T e x a s G a m b u s i a : R e s e r v o i r 33 ( 0 . 3 6 1 ) a n d R e s e r v o i r 81 ( 0 . 4 4 0 ) . By c o m p a r i n g T a b l e 32 a n d F i g . 17 w i t h 163 Table 37 Texas Vs. Hawaii Comparisons Sex R a t i o s , P r o p o r t i o n Pregnant, And P r o p o r t i o n S u p e r f e t a t i n g 1. Sex R a t i o s : Adults Only j i Males Females T I J T o t a l rexas Freshwater Estuary T o t a l 1 9 1 10 T 1 157 76 233 T-L— 166 77 243 Hawaii S t a b l e F l u c t u a t i n g T o t a l i . 184 599 783 t • 293 1375 1668 I 477 1974 245T 2. I n c l u d i n g i P r o p o r t i o n Pregnant: J u v e n i l e Females Over 16 MM 1 1 1 i Pregnant 1 1 Not Pregnant 1 1 I T o t a l Texas Freshwater E s t u a r y T o t a l i i 157 76 232 9 1 10 T 166 75 242 Hawaii S t a b l e F l u c t u a t i n g T o t a l I • 265 971 1236 1 180 564 744 1__ 445 1535 1980 I n c l u d e s 3. P r o p o r t i o n S u p e r f e t a t i n g : Pregnant Females With NEL, EE, LE, Or VLE ™ - i . Broods i 1 i S u p e r f e t a t i n g | Not Superfet T • ] T o t a l Texas •Freshwater Estuary T o t a l 1 19 7 26 ] 125 61 186 j 144 68 212 Hawaii S t a b l e F l u c t u a t i n g T o t a l . i, „ 26 48 74 t 220 1060 1280 _ J. 246 1108 1354 • 164 T a b l e 38 D i f f e r e n c e s I n R e p r o d u c t i v e T r a i t s T e x a s v s . H a w a i i S a m p l e Mean 175 Mg F e m a l e 1 I Y = A + BX | F A B i P r o b , 1 . Number Of Y o u n g X w e i g h t -+-A . T e x a s H a w a i i I 53.66 250| - 6 . 8 4 2 345.70 21.33 1620f 3.921 99.48 + 0.5700 >0.25 B. F r e s h w a t e r E s t u a r y S t a b l e F l u c t u a t i n g 39.31 157| - 1 . 0 1 2 230.40 56.25 76 < 3.088 303. 80 18.78 290| 7.143 66.49 21.67 1330| 3.997 101.00 0.29 90 >0.75 2. H e i g h t O f NEL A n d EE B r o o d s NEL I E E 1 Mean I N I F | P r o b I Mean I N | F | P r o b | A. T e x a s I 1. 13 | 85 I 26. 2717 ! K 0 . 0 0 0 1 M .22 1108 | 31. 8715 |<0.0001| H a w a i i | 1. 83 |612 J j I 1 .89 |618 | | j B. F r e s h w a t e r j 1. 22 I 53 J I I 1 .29 | 68 | j | E s t u a r y I 0. 99 I 32 I o. 4850 |>0.50 i 1 . 11 I 36 J 0. 7703 |>.25 | S t a b l e | 1. 89 1142 | j i 1 .81 |112 | I | F l u c t u a t i n g | 1. 81 | 470 | | I 1 .91 1506 | | | • i 1 i i < 3 . R e p r o d u c t i v e E f f o r t X W e i g h t H- . j — ~ j — A. T e x a s H a w a i i 0.366 224J 0.224 0.8126 0.230 1354) 0 . 2 6 2 - 0 . 1 8 1 3 0.9512 >0.25 B. F r e s h w a t e r E s t u a r y S t a b l e F l u c t u a t i n g 0.275 0 . 367 0.217 0.233 I 144| 681 246| 1 108| 0 , 2 7 4 - 0 . 0 0 3 0 0.330 0.2138 0 . 2 7 0 - 0 . 3 0 1 7 0 . 2 6 4 - 0 . 1 7 7 5 1.3817 >0.25 165 F i g . 21, I found t h a t although the minimum s i z e a t which Gambusia become pregnant was about the same i n both l o c a l e s (18 mm), the average s i z e at maturity was lower i n Texas (19-23 mm) than i n Hawaii (28-29 mm). In summary, there i s c o n s i d e r a b l e l o c a l v a r i a t i o n i n the l i f e h i s t o r y t r a i t s o f Gambusia i n both Texas and Hawaii, On the whole, the Texan f i s h reach maturity at a s m a l l e r s i z e , have more, s m a l l e r young, and make l a r g e r r e p r o d u c t i v e e f f o r t s than those from Hawaii. But there i s enough v a r i a b i l i t y among samples from both l o c a t i o n s to make most of these d i f f e r e n c e s i n s i g n i f i c a n t . Only embryo weights d i f f e r e d s i g n i f i c a n t l y . i i i D i s c u s s i o n 4a.. Hawaii:. S t a b l e Vs.. F l u c t u a t i n g Environments I emphasize two p o i n t s at the o u t s e t . F i r s t , I have a v a i l a b l e both i n t r a s p e c i f i c and i n t e r s p e c i f i c comparisons of r e p r o d u c t i v e t r a i t s . Considered alone, the two types of comparisons l e a d t o q u i t e d i f f e r e n t c o n c l u s i o n s , but considered together they complement each other i n forming a coherent s t o r y . Secondly, a l l the data presented i n t h i s chapter i s f i e l d data; i t a l l d e a l s with phenotypes, not genotypes. I t i s c o n c e i v a b l e that a l l the v a r i a b i l i t y i n l i f e h i s t o r y t r a i t s r eported i n the preceding pages c o u l d , at l e a s t f o r each s p e c i e s considered s e p a r a t e l y , have been produced by a s e r i e s o f g e n e t i c a l l y i d e n t i c a l s t o c k s with c o n s i d e r a b l e developmental p l a s t i c i t y . I thought t h a t e x p l a n a t i o n u n l i k e l y , and w i l l present evidence i n 166 Chapter VI to r e f u t e i t , but at t h i s stage i t remains a p o s s i b i l i t y . One could s t i l l argue t h a t although e v o l u t i o n occurs through changes i n gene f r e q u e n c i e s , t h a t i t i s the phenotype, not the genotype, upon which s e l e c t i o n a c t s , and that f i t n e s s i s t h e r e f o r e a f u n c t i o n of both the g e n e t i c i n f o r m a t i o n contained i n the nucleus and the developmental p l a s t i c i t y with which t h a t i n f o r m a t i o n i s expressed. Thus while i t i s s t i l l necessary to show g e n e t i c d i f f e r e n c e s between two st o c k s i n order to cla i m t h a t they possess d i f f e r e n t a d a p t a t i o n s , i t i s not necessary to demonstrate t h a t the ad a p t a t i o n s p r e d i c t e d , f o r example, by l i f e h i s t o r y theory are r e f l e c t e d i n s t r i c t l y g e n e t i c d i f f e r e n c e s . A l l the theory p r e d i c t s i s phenotypic d i f f e r e n c e s that have some g e n e t i c b a s i s . 1. r and K - s e l e c t i o n or Bet-hedging? The summary of i n t r a s p e c i f i c comparisons presented i n Tab l e s 34 and 35 c o n t a i n s some evidence c o r r o b o r a t i n g the p r e d i c t i o n s of r - and K- s e l e c t i o n . The i n t r a s p e c i f i c t r e n d s i n number of young and r e p r o d u c t i v e e f f o r t were both i n the d i r e c t i o n p r e d i c t e d by r - and K - s e l e c t i o n : more young and l a r g e r e f f o r t s i n f l u c t u a t i n g environments. However, I found no d i f f e r e n c e s i n s i z e at maturity i n any of the three samples. T h i s i s a heterodox r e s u l t , e s p e c i a l l y when you r e c a l l Lewontin's (1965) s e n s i t i v i t y a n a l y s i s of Lotka's c h a r a c t e r i s t i c equation: r - s e l e c t i o n i s supposed to push age (and presumably s i z e ) at f i r s t r e p r o d u c t i o n to a minimum, and the s e l e c t i o n pressure i s supposed to be much s t r o n g e r on age a t maturity than 167 o n number o f y o u n g o r t o t a l r e p r o d u c t i v e e f f o r t . M o r e o v e r , i t c a n n o t be a r g u e d t h a t t h e r e was no v a r i a b i l i t y i n a g e a t m a t u r i t y on w h i c h s e l e c t i o n c o u l d w o r k , b e c a u s e f e m a l e s f r o m f l u c t u a t i n g r e s e r v o i r s h a v e a g e s a t m a t u r i t y t h a t do v a r y f r o m 76 t o o v e r 207 d a y s i n t h e l a b o r a t o r y ( c f . C h a p t e r 7 1 ) . Now l o o k a t t h e i n t e r s p e c i f i c c o m p a r i s o n s . P o e c i l i a h a s a l e n g t h a t m a t u r i t y 8 - 1 0 mm s h o r t e r t h a n G a m b u s i a ' s i n b o t h s t a b l e a n d f l u c t u a t i n g r e s e r v o i r s . T h a t d i f f e r e n c e i n l e n g t h c o r r e s p o n d s t o a d i f f e r e n c e o f a b o u t a m o n t h i n a g e - p e r h a p s 80 d a y s a t a v e r a g e m a t u r i t y f o r P o e c i l i a v s . 110 d a y s a t a v e r a g e m a t u r i t y f o r G a m b u s i a . P o e c i l i a p r o d u c e m o r e , s m a l l e r y o u n g t h a n G a m b u s i a , a n d make a r e p r o d u c t i v e e f f o r t a l m o s t a s l a r g e a s G a m b u s i a . An a d v o c a t e o f r - a n d K - s e l e c t i o n w o u l d p r e d i c t t h a t P o e c i l i a s h o u l d d o m i n a t e t h e f l u c t u a t i n g r e s e r v o i r s , a n d G a m b u s i a t h e s t a b l e o n e s . T h e a c t u a l s i t u a t i o n i s j u s t t h e o p p o s i t e . T a b l e 16 p r e s e n t s t h e d e n s i t i e s o f G a m b u s i a , P o e c i l i a , a n d o t h e r f i s h i n a l l r e s e r v o i r s s a m p l e d . G a m b u s i a was f o u n d i n 27 o f t h e 28 r e s e r v o i r s s a m p l e d , P o e c i l i a i n o n l y 14. I n o n l y 1 o f t h e 9 f l u c t u a t i n g r e s e r v o i r s i n w h i c h P o e c i l i a c o - o c c u r r e d w i t h G a m b u s i a ( R e s e r v o i r 25) d i d i t a c h i e v e d e n s i t i e s c o m p a r a b l e t o G a m b u s i a 1 s . I n t h e o t h e r f l u c t u a t i n g r e s e r v o i r ( U p p e r H e l e m a n o ) w i t h h i g h P o e c i l i a d e n s i t y , G a m b u s i a d i d n o t o c c u r . On t h e o t h e r h a n d , P o e c i l i a d o m i n a t e d two o f t h e s t a b l e i m p o u n d m e n t s i n w h i c h G a m b u s i a c o - o c c u r r e d : Camp 17 a n d Pump #4. I n t h e o t h e r two s t a b l e i m p o u n d m e n t s i t a c h i e v e d m o d e r a t e d e n s i t i e s . I f we i g n o r e s i g n i f i c a n c e , a n d j u s t c o n s i d e r t h e d i r e c t i o n o f i n t r a s p e c i f i c d i f f e r e n c e s , t h e n 8 o f 9 c o r r o b o r a t e t h e r - a n d 168 K - s e l e c t i o n p r e d i c t i o n s . But the i n t e r s p e c i f i c d i f f e r e n c e s v i o l a t e those p r e d i c t i o n s , and s i z e s a t maturity d i d not d i f f e r s i g n i f i c a n t l y when they should have. What i s going on? I have an e x p l a n a t i o n to o f f e r which I f i n d p l a u s i b l e , but I o f f e r i t only as a s p e c u l a t i o n , s i n c e I do not have enough data to t e s t i t d i r e c t l y . I t a t l e a s t does not c o n f l i c t with any of my r e s u l t s . F i r s t , r e c a l l t h a t Gambusia evolved i n a seasonal environment i n Texas and along the Gulf Coast, but P o e c i l i a evolved i n a much l e s s seasonal environment along the no r t h - e a s t co a s t of South America and i n T r i n i d a d . Krumholtz (1948) noted that Gambusia females produce two kinds of female o f f s p r i n g : those t h a t mature g u i c k l y and reproduce d u r i n g the l a t e summer and f a l l of the year i n which they were born, and those which wait, grow to a l a r g e s i z e , and do not reproduce u n t i l the s p r i n g of the next year. Thus each parent female i s hedging her bets on which type of young w i l l be most l i k e l y to succeed i n a seas o n a l environment. I know of no evidence t h a t P o e c i l i a females can produce a s i m i l a r d i s t r i b u t i o n of maturation times i n t h e i r o f f s p r i n g . Now c o n s i d e r Gambusia i n f l u c t u a t i n g r e s e r v o i r s i n Hawaii. The same t r a i t s t h a t adapted them to s e a s o n a l i t y i n Texas served them j u s t as w e l l i n d e a l i n g with u n p r e d i c t a b l e f l u c t u a t i o n s i n Hawaii. I w i l l r e p o r t evidence i n Chapter VI t h a t Gambusia from f l u c t u a t i n g Hawaiian r e s e r v o i r s produce a d i s t r i b u t i o n of maturation times i n t h e i r progeny, v a r y i n g from 76 to 207 days, a range of 4.3 months. In c a s u a l o b s e r v a t i o n s , I recorded maturation times i n P o e c i l i a females ranging from 6 9 to 104 169 days, a range of 1.2 months. In Chapter V I w i l l present evidence that l a r g e f i s h s u r v i v e long drawdowns b e t t e r than smal l f i s h . I f you w i l l accept those p o i n t s f o r the time b e i n g , then I can s k e t c h the e s s e n t i a l f e a t u r e s of Gambusia* s a d a p t a t i o n to f l u c t u a t i n g r e s e r v o i r s , and e x p l a i n why P o e c i l i a does not dominate the f l u c t u a t i n g r e s e r v o i r s . The c r i t i c a l t r a i t i s the c a p a c i t y t o produce both e a r l y and l a t e maturing female o f f s p r i n g . The e a r l y - m a t u r i n g o f f s p r i n g can p a r t i c i p a t e i n the r a p i d p r o d u c t i o n of l a r g e numbers of progeny. But they are s m a l l , as are t h e i r newborn young, and o c c a s i o n a l l y a severe drawdown w i l l k i l l them a l l . The l a t e - m a t u r i n g o f f s p r i n g have i n the meantime been growing to a l a r g e s i z e , r a t h e r than reproducing, and have a much b e t t e r chance of s u r v i v i n g a s e r i o u s drawdown. P o e c i l i a does not have t h i s c a p a c i t y , and although i t may outcompete Gambusia i n the production of l a r g e numbers of young, i t i s a l s o more f r e g u e n t l y pushed t o very low p o p u l a t i o n d e n s i t i e s by f l u c t u a t i o n s . On balance, Gambusia does b e t t e r i n f l u c t u a t i n g r e s e r v o i r s . T h i s s t o r y holds two l e s s o n s . (1) Reproductive t a c t i c s are not immutable assemblages of coadapted t r a i t s t h a t must always be found together. I t i s q u i t e p o s s i b l e to produce many young, make a l a r g e r e p r o d u c t i v e e f f o r t , but have the same age and s i z e at maturity as other p o p u l a t i o n s of the same s p e c i e s which make small r e p r o d u c t i v e e f f o r t s and have few young. The elements of a t a c t i c can become d i s s o c i a t e d as the balance of s e l e c t i o n f o r c e s i n the environments s h i f t s . (2) P o p u l a t i o n s can e x h i b i t r - and K - s e l e c t e d a d a p t a t i o n with some t r a i t s ( i n t h i s case, number of young and r e p r o d u c t i v e e f f o r t ) , and bet-170 hedging adapt a t i o n with others ( i n t h i s case, v a r i a b i l i t y i n age at m a t u r i t y ) . The c a p a c i t y to adapt to both s i t u a t i o n s i s i t s e l f a form of bet hedging. , F i n a l l y , r e c a l l t h a t when the v a r i a b i l i t y i n m o r t a l i t y f a l l s p r i m a r i l y on a d u l t s , the advocates of bet-hedging p r e d i c t a r e p r o d u c t i v e p a t t e r n i d e n t i c a l t o t h a t p r e d i c t e d by advocates of r - and K - s e l e c t i o n . I have not performed a c r i t i c a l t e s t of the c o n t r a s t i n g p r e d i c t i o n s of r - and K - s e l e c t i o n and bet-hedging, because I was not able t o measure j u v e n i l e and a d u l t m o r t a l i t i e s i n the f i e l d . However, I b e l i e v e I have expl o r e d the s i t u a t i o n thoroughly enough to demonstrate that i n t h i s s p e c i e s the e v o l u t i o n of r e p r o d u c t i v e t r a i t s i s more complex than e i t h e r t h e o r e t i c a l p o i n t of view would l e a d one t o b e l i e v e . T h e r e f o r e I doubt the adequacy of e i t h e r theory as a d e s c r i p t i o n of the e v o l u t i o n of r e p r o d u c t i v e t r a i t s , and have some reason to c a l l f o r a more comprehensive and r e a l i s t i c t h e o r e t i c a l apparatus. i i i Texas D e t a i l s The most s t r i k i n g d i f f e r e n c e s i n the Texas sample were between f i s h c o l l e c t e d i n the b r a c k i s h e s t u a r y at Armand Bayou and f i s h c o l l e c t e d i n a s m a l l , freshwater pond on the same day not more than 200 m away. The pond was connected to the e s t u a r y by a drainage channel t h a t was reduced to a t r i c k l e i n l a t e A p r i l , but had almost c e r t a i n l y o f f e r e d f r e e passage to f i s h a few months e a r l i e r d u r i n g the winter. Thus I f i n d i t d i f f i c u l t t o a s s i g n the phenotypic d i f f e r e n c e s found to g e n e t i c d i f f e r e n c e s between the s t o c k s . I suspect they are due to 171 developmental p l a s t i c i t y , and suggest t h a t Gambusia has a developmental switch t r i g g e r e d by s a l i n i t y changes. I p r e d i c t t h a t one c o u l d take newborn young from a s i n g l e brood of a female Gambusia from Texas, from e i t h e r f r e s h or b r a c k i s h water, r a i s e some of them i n f r e s h and others i n b r a c k i s h water, and r e g a i n both phenotypes, the freshwater phenotype having fewer young, a s m a l l e r r e p r o d u c t i v e e f f o r t , and a s m a l l e r s i z e at maturity than the b r a c k i s h phenotype. No one has done such an experiment on Gambusia, but Feltkamp and K r i s t e n s e n (1970) performed a growth experiment on P o e c i l i a §£henojgs y a n d e p o l l i , i n which morphological d i f f e r e n c e s are known to e x i s t among f r e s h and s a l t water p o p u l a t i o n s . They r a i s e d f i s h from s i n g l e broods i n both f r e s h and s a l t water, and found t h a t the morphological d i f f e r e n c e s , which are s t r i k i n g enough to have r e s u l t e d i n d i f f e r e n t s u b s p e c i f i c names f o r the two forms, were due s t r i c t l y t o developmental p l a s t i c i t y . I t makes good s t r a t e g i c sense f o r an organism l i v i n g at the f r e s h -s a l t w a t e r boundary, where the chances of progeny developing i n e i t h e r f r e s h or s a l t water are both high, t o make that kind of a d e c i s i o n a developmental r a t h e r than a g e n e t i c one. ifSJL Texas-Hawaii Comparisons I argued i n Chapter I I I that the changes experienced by Gambusia i n moving from Texas to Hawaii i n 1905 i n many ways represented a r a d i c a l s i m p l i f i c a t i o n of t h e i r environment. The range of temperature f l u c t u a t i o n s dropped from 5-30°C to 19-27°C; they no longer encountered, i n most cases, any b r a c k i s h or s a l t water; they encountered many fewer s p e c i e s of other f i s h . 172 e s p e c i a l l y fewer f i s h predators. Thus even the w i l d l y f l u c t u a t i n g Hawaiian r e s e r v o i r s may re p r e s e n t a s t a b l e r , and c e r t a i n l y a s i m p l e r * environment, than the Texas e s t u a r i e s . The Texas f i s h mature at a s m a l l e r s i z e (19-23 mm) than the Hawaii f i s h (28-29 mm), have more young (53.66 vs. 21.33 f o r a 175 mg female), commit a l a r g e r p r o p o r t i o n o f t h e i r weight to r e p r o d u c t i o n (0.366 vs. 0.230 f o r a 175 mg female), are more f r e q u e n t l y pregnant (95.9% vs. 62.4%), and produce s m a l l e r young (1.22 mg vs. 1.89 mg f o r e a r l y - e y e d young). Those are p r e c i s e l y the d i f f e r e n c e s an advocate of r - and K - s e l e c t i o n would p r e d i c t f o r an animal moving from a f l u c t u a t i n g to a s t a b l e environment. I am somewhat s u s p i c i o u s of r e f e r r i n g the r e p r o d u c t i v e d i f f e r e n c e s to r - and K - s e l e c t i o n , because I have not been a b l e to d e f i n e p r e c i s e l y how Hawaii d i f f e r s from Texas, or by how much. Without a b e t t e r d e f i n i t i o n of the two environments, and without some technique f o r s e p a r a t i n g the e f f e c t s of the complex set of environmental agents at work i n Texas, the r e p r o d u c t i v e d i f f e r e n c e s must remain an i n t r i g u i n g o b s e r v a t i o n . I do not c o n s i d e r the comparison w e l l enough understood to admit i t as evidence i n an argument about e v o l u t i o n a r y causes. To do otherwise would admit c i r c u l a r i t y t o the argument. Furthermore, the o v e r a l l d i f f e r e n c e s i n r e p r o d u c t i v e t r a i t s between Texas and Hawaii could be as e a s i l y a t t r i b u t e d to d i f f e r e n c e s i n predation pressure as to d i f f e r e n c e s i n environmental s t a b i l i t y . Both e x p l a n a t i o n s are p l a u s i b l e , and n e i t h e r can be f a l s i f i e d with the a v a i l a b l e evidence. 173 5^ . Summary In 1905, Gambusia were i n t r o d u c e d t o Hawaii from Texas f o r mosguito c o n t r o l . They spread i n t o a s e r i e s o f sugar p l a n t a t i o n r e s e r v o i r s . Some r e s e r v o i r s remained s t a b l e , o t hers f l u c t u a t e d . Some contained p o t e n t i a l competitors, others d i d not. Sometime a f t e r 1922 P o e c i l i a were in t r o d u c e d to Hawaii and encountered s i m i l a r s i t u a t i o n s . In 1974 and 1975 I v i s i t e d Hawaii and Texas, c o l l e c t e d f i s h , analyzed t h e i r r e p r o d u c t i v e t r a i t s , and te s t e d two s e t s of c o n t r a s t i n g p r e d i c t i o n s . advocates of r - and K - s e l e c t i o n c l a i m t h a t f l u c t u a t i n g environments s e l e c t f o r e a r l y maturation, l a r g e r r e p r o d u c t i v e e f f o r t s , and many young, advocates of bet-hedging p r e d i c t t h a t where f l u c t u a t i o n s , a f f e c t j u v e n i l e r a t h e r than a d u l t m o r t a l i t y , f l u c t u a t i n g environments should s e l e c t f o r delayed maturation, s m a l l e r r e p r o d u c t i v e e f f o r t s , and fewer young. I a l s o p r e d i c t e d t h a t young should be l a r g e r a t b i r t h i n s t a b l e r e s e r v o i r s . In t e s t i n g the p r e d i c t i o n s , I used data on samples of Gambusia c o l l e c t e d i n January and November of 1974, and of P o e c i l i a c o l l e c t e d i n January 1974. Ei g h t o f 9 i n t r a s p e c i f i c d i f f e r e n c e s i n r e p r o d u c t i v e t r a i t s between s t a b l e and f l u c t u a t i n g r e s e r v o i r s were i n the d i r e c t i o n p r e d i c t e d by advocates of r - and K - s e l e c t i o n , but 7 of those 9 d i f f e r e n c e s were not s i g n i f i c a n t . There were no i n t r a s p e c i f i c d i f f e r e n c e s i n s i z e at maturity; but r - and K - s e l e c t i o n p r e d i c t e d t h a t t h i s should be the l a r g e s t d i f f e r e n c e of a l l . furthermore, the i n t e r s p e c i f i c P o e c i l i a - Gambusia comparison showed t h a t P o e c i l i a has r e p r o d u c t i v e t r a i t s , r e l a t i v e to Gambusia, which would be c a l l e d r - s e l e c t e d . But i t was Gambusia, not P o e c i l i a , 174 which dominated the f l u c t u a t i n g r e s e r v o i r s . To account f o r these heterodox r e s u l t s , I suggested t h a t Gambusia was pre-adapted, by e v o l v i n g i n a s e a s o n a l environment, f o r f l u c t u a t i n g r e s e r v o i r s . I t has p r e c i s e l y t h a t t r a i t - the c a p a c i t y of a s i n g l e female to produce young with a wide range of maturation ages - needed to uncouple i t from f l u c t u a t i o n s and to guarantee p e r s i s t e n c e . P o e c i l i a , l a c k i n g t h i s t r a i t , was t i g h t l y l i n k e d to the w i l d f l u c t u a t i o n s of the unstable r e s e r v o i r s , where i t was s u b j e c t e d t o repeated p o p u l a t i o n crashes that kept i t s numbers well below those a t t a i n e d by Gambusia. The Hawaiian Gambusia make s m a l l e r r e p r o d u c t i v e e f f o r t s , mature at a l a r g e r s i z e , and have fewer young than the Texas Gambusia. I f Gambusia encountered s t a b l e r environments i n Hawaii than Texas, a l l these changes would be p r e d i c t e d by an r -and K - s e l e c t i o n i s t . My r e s u l t s hold two l e s s o n s . (1) Reproductive t r a i t s are not n e c e s s a r i l y a s s o c i a t e d i n the p a r t i c u l a r ways t h a t r e c e n t e v o l u t i o n a r y theory p r e d i c t s . More young and l a r g e r r e p r o d u c t i v e e f f o r t s may be a s s o c i a t e d with no d i f f e r e n c e a t a l l i n s i z e a t maturity. (2) The bet-hedging viewpoint does not n e c e s s a r i l y c o n t r a d i c t the r - and K - s e l e c t i o n viewpoint. My data suggest t h a t the t r e n d s d i s c u s s e d by r - and K - s e l e c t i o n i s t s may be i n c o r p o r a t e d i n t o a r e p r o d u c t i v e l y polymorphic p o p u l a t i o n as part of a bet-hedging a d a p t a t i o n . 175 CHAPTER V. DETAILED ANALYSIS OF INSTABILITY 1. I n t r o d u c t i o n In Chapter IV, I presented the r e s u l t s of a f i e l d t e s t of the c o n t r a s t i n g p r e d i c t i o n s of r - and K - s e l e c t i o n and bet-hedging. P o e c i l i a showed those d i f f e r e n c e s between s t a b l e and f l u c t u a t i n g r e s e r v o i r s t h a t r - and K- s e l e c t i o n i s t s would p r e d i c t , but Gambusia d i d not. N e v e r t h e l e s s , Gambusia dominated the f l u c t u a t i n g r e s e r v o i r s , and P o e c i l i a a t t a i n e d higher d e n s i t i e s i n s t a b l e r e s e r v o i r s than i t d i d i n f l u c t u a t i n g ones. To see i f I c o u l d uncover su g g e s t i v e c o r r e l a t i o n s between Gambusia * s r e p r o d u c t i v e t r a i t s and the d e t a i l s of the f l u c t u a t i o n p a t t e r n s of i n d i v i d u a l r e s e r v o i r s , I have undertaken, i n Chapter V, an i n t e n s i v e a n a l y s i s of the long-term f l u c t u a t i o n p a t t e r n s of 20 r e s e r v o i r s . Because environmental f l u c t u a t i o n s are r a r e l y measured, many d i f f e r e n t types of f l u c t u a t i o n p a t t e r n s are f r e q u e n t l y lumped under the g e n e r i c term " u n s t a b l e " . I have q u a n t i t a t i v e measures of f l u c t u a t i n g environments, and have been ab l e to av o i d t h i s widespread source of c o n f u s i o n . In the process of a n a l y z i n g r e s e r v o i r f l u c t u a t i o n s , I have a l s o r e c e i v e d the b e n e f i t s of a s i d e - e f f e c t : a n o n - c i r c u l a r d e f i n i t i o n of " i n s t a b i l i t y " through measurement of a q u a n t i t a t i v e v a r i a b l e that i s q u i t e independent of the r e p r o d u c t i v e t r a i t s o f the f i s h . I had c e r t a i n e x p e c t a t i o n s , at the o u t s e t , concerning the d e t a i l e d impact of f l u c t u a t i o n s on the r e p r o d u c t i v e t r a i t s of 176 organisms. F i g . 22 sketches the r e l a t i o n s h i p between the gene r a t i o n time of an organism l i v i n g i n a f l u c t u a t i n g environment, and f i v e d i f f e r e n t combinations of the p e r i o d of a p r e d i c t a b l e f l u c t u a t i o n and d i f f e r e n t l e v e l s of u n c e r t a i n t y about the amplitude of the f l u c t u a t i o n (the shaded area on the graphs). The s i x t h environment, Type 3, i s random, or dependably u n p r e d i c t a b l e . When the p e r i o d o f f l u c t u a t i o n i s about egual to or l e s s than the ge n e r a t i o n time of the organism, when the amplitude of the f l u c t u a t i o n i s u n p r e d i c t a b l e , and when there i s some u n c e r t a i n t y i n the p e r i o d i t s e l f , I expected the f o l l o w i n g a d a p t a t i o n s t o evolve: polymorphisms i n age at mat u r i t y , r e p r o d u c t i v e e f f o r t , and numbers of young. Such environmental c o n d i t i o n s c h a r a c t e r i z e the f l u c t u a t i n g r e s e r v o i r s . R i t h these i d e a s i n mind, I have organized Chapter V acco r d i n g t o the f o l l o w i n g p l a n : F i r s t , measure the r e s e r v o i r f l u c t u a t i o n s . Secondly, reduce the measurements to a manageable set t h a t preserves most of the o r i g i n a l i n f o r m a t i o n . T h i r d l y , undertake p r i n c i p l e components a n a l y s i s on the reduced s e t of measures t o produce a s m a l l number of u n c o r r e l a t e d p r i n c i p l e components that account f o r most of the v a r i a b i l i t y i n f l u c t u a t i o n p a t t e r n s . F o u r t h l y , do a stepwise m u l t i p l e r e g r e s s i o n of r e p r o d u c t i v e t r a i t s on the p r i n c i p l e components d e r i v e d from the f l u c t u a t i o n p a t t e r n s , p l u s a few other important r e s e r v o i r c h a r a c t e r i s t i c s . F i f t h l y , do a s i m i l a r m u l t i p l e r e g r e s s i o n using the recent h i s t o r y of each r e s e r v o i r , as w e l l as the long-term p a t t e r n s , t o see how much of the v a r i a b i l i t y i n r e p r o d u c t i v e t r a i t s c o u l d be accounted f o r by 177 FIGURE 22 Types Of Environmental F l u c t u a t i o n Legend: T = g e n e r a t i o n l e n g t h , shaded area = r e g i o n of u n c e r t a i n t y . In Type 1 environments, the p e r i o d and amplitude of environmental f l u c t u a t i o n s are c o n s t a n t , and the p e r i o d i s longer than the g e n e r a t i o n time of the organism. In a l l Type 2 environments, the g e n e r a t i o n time of the organism i s g r e a t e r than or about equal t o the p e r i o d of the f l u c t u a t i o n s . Types 2b, 2c, and 2d are d i s t i n g u i s h e d by d i f f e r e n t degrees of u n c e r t a i n t y i n the amplitude of the f l u c t u a t i o n s . Type 3 i s a randomly f l u c t u a t i n g environment; i t s s p e c t r a l d e n s i t y p l o t would show equal power at a l l f r e q u e n c i e s . T h i s f i g u r e r e p r e s e n t s a p r e l i m i n a r y way of t h i n k i n g about environmental f l u c t u a t i o n s . As a r e s u l t of the work presented i n t h i s chapter, I have rethought the problem, and present my new c o n c l u s i o n s i n the d i s c u s s i o n ( a f t e r Stearns 1976). 178 Type 1 I 1 T= generation length o 179 events i n the recent p a s t . Throughout Chapter V, I have used a reduced s e t of the f i s h I analyzed i n Chapter IV. I have worked only with the January, 1974 c o l l e c t i o n of Gambusia from Opaeula 1 R e s e r v o i r on Oahu and the 19 unstable r e s e r v o i r s on Maui. Within t h a t c o l l e c t i o n , I have analyzed only pregnant females. 2*. Methods 2a. C o l l e c t i o n And Treatment Of Data I obtained d a i l y r e c o r d s of the water l e v e l i n Opaeula 1 R e s e r v o i r from Waialua Sugar Company, Waialua, Hawaii, and of the 19 r e s e r v o i r s on Maui from Hawaiian Commercial and Sugar Company, Puunene, Maui. Water i s a c o n t r o l l a b l e l i m i t i n g f a c t o r to cane growth on i r r i g a t e d p l a n t a t i o n s , and these two p l a n t a t i o n s i n p a r t i c u l a r keep d a i l y r e c o r d s of the water l e v e l i n c e r t a i n r e s e r v o i r s as an a i d to budgeting water s u p p l i e s and planning i r r i g a t i o n p r a c t i c e s . At both p l a n t a t i o n s , the depth of water i n the r e s e r v o i r s i s measured both i n the morning (at about 0700 hrs) and i n the afternoon (at about 1600 h r s ) . I s e l e c t e d j u s t the morning l e v e l s f o r a n a l y s i s , s i n c e using both would double the a l r e a d y massive keypunching l o a d . P l a n t a t i o n o f f i c i a l s estimated the accuracy of the i r r i g a t i o n foremen a t r e c o r d i n g water l e v e l s at about ± 0.5 f o o t . For Opaeula 1, I obtained records from November 1943 to January 1971. For the Maui r e s e r v o i r s , I o b t a i n e d r e c o r d s from January 1959 to 5 December 1974. T h i s amounted to 9950 days' data f o r Opaeula 1 180 and 5818 days* data f o r the 19 Maui r e s e r v o i r s . I c o n s i d e r e d t h i s a r e p r e s e n t a t i v e sample of the f l u c t u a t i o n p a t t e r n s encountered by Gambusia i n these r e s e r v o i r s over t h e i r e n t i r e p e r i o d of r e s i d e n c e i n Hawaii s i n c e 1907. There were no days' data missing f o r Opaeula 1, but i n 1965 HC&S stopped r e c o r d i n g water l e v e l s on weekends and h o l i d a y s . Between 1965 and 1974 t h i s r e s u l t e d i n 1154 days' data t h a t were missing, which amounted to 31.5% of the data over t h a t p e r i o d , or 19.8% of the data from 1959 to 1974. I t r e a t e d the missing days' data by assuming that the r e s e r v o i r s remained a t the l a s t recorded l e v e l u n t i l the night b e f o r e the next recorded l e v e l . I encountered f u r t h e r problems i n o b t a i n i n g a c l e a n set of data. E i g h t of the 19 Maui r e s e r v o i r s were remodeled, on d i f f e r e n t dates, between 1959 and 1974, r e s u l t i n g i n a change i n c a p a c i t y . I had to allow f o r such changes i n c a p a c i t y i n e d i t i n g and manipulating the water l e v e l i n p u t . The r e s e r v o i r f l u c t u a t i o n data were keypunched by the s t a f f at the UBC Computer Centre d i r e c t l y o f f the p l a n t a t i o n r e cords, not v e r i f i e d , and loaded onto computer f i l e s . I e d i t e d the data with a program that checked each item t o be sure i t l a y w i t h i n reasonable bounds f o r t h a t r e s e r v o i r , checked each card f o r sequencing t o be sure no days' data were missing, and i n s e r t e d the l a s t recorded water l e v e l where days were l e g i t i m a t e l y m i ssing. A f t e r making r e v i s i o n s , I p r i n t e d the data out and spot-checked about 1% of i t manually. I found no e r r o r s . I then used c o n v e r s i o n t a b l e s obtained from the c i v i l e n gineers at the sugar p l a n t a t i o n s to convert the water l e v e l s t o volume, measured i n m i l l i o n g a l l o n s . F i n a l l y , I converted 181 volume to percent f u l l , u s i n g the p a r t i c u l a r c a p a c i t y of each i n d i v i d u a l r e s e r v o i r as the denominator, and changing i t f o r the 8 r e s e r v o i r s mentioned on the date that they were remodeled. I had no i d e a what the f i s h found important about the f l u c t u a t i o n s , so I a p p l i e d a b a t t e r y of d i f f e r e n t t e c h n i q u e s : a n a l y s i s of a u t o c o r r e l a t i o n , of the range and v a r i a n c e c a l c u l a t e d over d i f f e r e n t time s t e p s , average weekly and y e a r l y maximum ranges, and s p e c t r a l a n a l y s i s . To c l a r i f y the meaning of these measures, I c o n s t r u c t e d two a r t i f i c i a l time s e r i e s , one a s i n e wave with a p e r i o d of a year, a mean of 50%, and an amplitude of 100%, t h e other a uniform random s e r i e s with the same mean and amplitude. 1. A u t o c o r r e l a t i o n . To c a l c u l a t e the a u t o c o r r e l a t i o n f u n c t i o n of a time s e r i e s , one f i r s t c a l c u l a t e s the mean of the whole s e r i e s and s u b t r a c t s i t from each day's datum to normalize the s e r i e s . For a s e r i e s of time steps t , one then c a l c u l a t e s the c o r r e l a t i o n of the value at time x with the value at time x+t, over a l l a v a i l a b l e v a l u e s . , I used a time increment of 5 days, and c a l c u l a t e d a l l a u t o c o r r e l a t i o n c o e f f i c i e n t s f o r time steps from 0 to 1000 days. 2. Bange and v a r i a n c e . I c a l c u l a t e d the average range of f l u c t u a t i o n s over d i f f e r e n t time s t e p s varying from 0 t o 1000 days i n increments of 5 days i n the f o l l o w i n g f a s h i o n . For a given time s t e p , say 15 days, I s e l e c t e d a s t a r t i n g p o i n t a t random from the f i r s t 182 300 clays of the r e c o r d . I then c a l c u l a t e d the range a t t a i n e d i n each subsequent 15 day i n t e r v a l as the maximum minus the minimum value, and averaged a l l such values over the e n t i r e time s e r i e s . For each time s t e p , I repeated the procedure 20 times, s e l e c t i n g a d i f f e r e n t s t a r t i n g point from w i t h i n the f i r s t 300 days each time, and f i n a l l y averaged the r e s u l t i n g 20 v a l u e s . I used p r e c i s e l y the same procedure i n c a l c u l a t i n g v a r i a n c e s over d i f f e r e n t time s t e p s , s u b s t i t u t i n g the formula f o r the v a r i a n c e f o r the formula f o r the range. 3. S p e c t r a l a n a l y s i s . Any time s e r i e s can be represented as some l i n e a r combination of s i n e and c o s i n e f u n c t i o n s of d i f f e r e n t f r e q u e n c i e s and amplitudes, o r , e g u i v a l e n t l y , as the sum of a s e r i e s of complex e x p o n e n t i a l s . The mathematical technique used i n o b t a i n i n g t h i s r e p r e s e n t a t i o n i s c a l l e d the F o u r i e r Transform, and the u s u a l method of p r e s e n t i n g the r e s u l t s o f the t r a n s f o r m a t i o n i s c a l l e d the s p e c t r a l d e n s i t y p l o t . The transform uses a n o n - a r b i t r a r y s et of f r e q u e n c i e s . The lowest frequency corresponds to a p e r i o d e x a c t l y h a l f the l e n g t h of the time s e r i e s . The next lowest freguency corresponds to a pe r i o d 2/3 the l e n g t h of the time s e r i e s , and so f o r t h up to the h i g h e s t frequency, which corresponds to the p e r i o d between two data p o i n t s . In my case, the lowest frequency f o r the Maui r e s e r v o i r s corresponded to a p e r i o d of about 8 ye a r s , and the hi g h e s t corresponded to a p e r i o d of 1 day. In computing the F o u r i e r Transform, I used an a l g o r i t h m w r i t t e n i n F o r t r a n by S i n g l e t o n (1969) t h a t u t i l i z e s a very 1 8 3 e f f i c i e n t method c a l l e d the Fast F o u r i e r Transform, proposed by Cooley and Tukey (1965). Since the time r e q u i r e d t o compute the transform i n c r e a s e s very r a p i d l y with the l a r g e s t prime f a c t o r of h a l f the l e n g t h of the s e r i e s , I t r u n c a t e d my time s e r i e s i n t o m u l t i p l e s of 2x364 days f o r the purposes of t h i s p a r t i c u l a r a n a l y s i s . (364 = 2 2 x 7 x 13; 365 = 5 x 73.) as a r e s u l t , the time s e r i e s f o r Opaeula 1 was reduced from 9950 to 9464 days (95.12% of i t s o r i g i n a l l e n g t h ) , and the time s e r i e s f o r the 19 Maui r e s e r v o i r s were reduced from 5818 to 5096 days (87.59% of t h e i r o r i g i n a l l e n g t h ) . The Fast F o u r i e r Transform a l g o r i t h m takes the o r i g i n a l time s e r i e s and r e t u r n s the c o e f f i c i e n t s of the s i n e and c o s i n e (imaginary and r e a l ) terms f o r each frequency. The i n t e r e s t i n g and u s e f u l part of F o u r i e r a n a l y s i s i s generated from these two c o e f f i c i e n t s , A and B, r e p r e s e n t i n g the amplitude of the s i n e and c o s i n e waves at each frequency. A f t e r s c a l i n g the c o e f f i c i e n t s by m u l t i p l y i n g them by the fundamental frequency of the s e r i e s , 1/2T (T = h a l f the l e n g t h of the o r i g i n a l s e r i e s ) , one computes the power at each frequency by squaring and adding the s c a l e d c o e f f i c i e n t s : Power = A 2 + 8 2. Thus one can compute the power at each frequency d e f i n e d by the transform. The power at a given frequency can be thought of as the amount of v a r i a b i l i t y i n the o r i g i n a l s e r i e s t h a t i s absorbed at t h a t frequency by the F o u r i e r Transform. Graphing the l o g of the power a g a i n s t freguency generates the s p e c t r a l d e n s i t y p l o t . One l a s t manipulation i s customary: averaging the 184 power over a s m a l l range of f r e q u e n c i e s t o reduce n o i s e . In computing t h a t average, one o b t a i n s an estimate of the 95% confi d e n c e i n t e r v a l s f o r s i g n i f i c a n t d e v i a t i o n s from the background n o i s e . The broader the freguency range, or bandwidth, used i n computing the average, the s m a l l e r the con f i d e n c e i n t e r v a l . Since i n f o r m a t i o n i s l o s t by smoothing the spectrum i n t h i s f a s h i o n , I compromised on a bandwidth of 10 frequency i n t e r v a l s . When presented i n t h i s f a s h i o n , with the l o g of the power on the o r d i n a t e and a band-averaged freguency on the a b s c i s s a , the s p e c t r a l d e n s i t y p l o t has a convenient property: the same c o n f i d e n c e i n t e r v a l a p p l i e s over the e n t i r e frequency range (Bendat and P i e r s a l 1971). In i n t e r p r e t i n g s p e c t r a l d e n s i t y p l o t s , remember t h a t long p e r i o d s have low f r e q u e n c i e s and are found at the l e f t of the p l o t , while s h o r t e r p e r i o d s , and higher f r e q u e n c i e s , are a t the r i g h t . I have i n d i c a t e d on my p l o t s the l o c a t i o n s of f r e q u e n c i e s c o r r e s p o n d i n g t o p e r i o d s o f one year and one week. 4. Other techniques. I c a l c u l a t e d t h r e e other values f o r each time s e r i e s : the weekly average range, the y e a r l y average range, and the average d a i l y r a t e of change. To compute the weekly average range I arranged the time s e r i e s as a s e r i e s o f columns 7 days long, c a l c u l a t e d the average value f o r each day a c r o s s the rows (about 831 rows f o r the Maui r e s e r v o i r s ) , then took the weekly average range as the maximum minus the minimum value over the seven days of the averaged column. I c a l c u l a t e d y e a r l y average range the same way, using 16 columns 365 days l o n g f o r the Maui 185 r e s e r v o i r s . The average d a i l y r a t e of change was c a l c u l a t e d as the average of the absolute value of the d i f f e r e n c e between one day's value and the next. Remember th a t a l l c a l c u l a t i o n s were done on r e s e r v o i r volume expressed as percent f u l l . 2b. F u r t h e r Data Reduction The s e r i e s of analyses d e s c r i b e d above gave me a s e t of f o u r graphs f o r each r e s e r v o i r , one each f o r a u t o c o r r e l a t i o n , range, v a r i a n c e , and power spectrum, plus three numbers: weekly and y e a r l y average range, and average d a i l y r a t e of change. In order t o reduce the complexity of the f o u r graphs t o a s m a l l s e t of numbers which s t i l l c ontained most of the u s e f u l i n f o r m a t i o n , I made the f o l l o w i n g measurements f o r each r e s e r v o i r : (a) A u t o c o r r e l a t i o n : the number of days t o reach .50, .10, .05, and the f i r s t minimum a u t o c o r r e l a t i o n , plus the d i f f e r e n c e between the second maximum and the f i r s t minimum. 5 numbers per r e s e r v o i r . (b) Range: the number of days to reach a range of 25, 50, 75, and 90%, the average range over a 10 day time step, and the average range over a 1000 day time step. 6 numbers per r e s e r v o i r . (c) V a r i a n c e : the number of days to reach 25, 50, 75, and 90% of the asymptotic v a r i a n c e , the average v a r i a n c e c a l c u l a t e d over a 10 day time s t e p , and the average v a r i a n c e c a l c u l a t e d over a 1000 day time s t e p . 6 numbers per r e s e r v o i r . (d) Power spectrum: the percent of t o t a l power 186 c o n t a i n e d a t medium f r e q u e n c i e s (corresponding t o p e r i o d s between 91 and 182 days), the r a t i o of low frequency power (periods g r e a t e r than 182 days) t o medium frequency power, the r a t i o of high frequency power (periods l e s s than 91 days) to medium frequency power, the percent of t o t a l power l o c a t e d under s i g n i f i c a n t peaks i n the spectrum, the percent of t o t a l power c o n t a i n e d i n background n o i s e , the r a t i o of weekly t o y e a r l y power, the r a t i o of weekly power to power not contained i n s i g n i f i c a n t peaks (background n o i s e ) , and the r a t i o of y e a r l y power t o background n o i s e . 8 numbers per r e s e r v o i r . That gave me 25 numbers with which to d e s c r i b e the f l u c t u a t i o n s of each r e s e r v o i r . I added to t h a t s e t f i v e more numbers: the weekly and y e a r l y average ranges, the average d a i l y r a t e of change, the volume o f the r e s e r v o i r i n m i l l i o n g a l l o n s , and the average volume of the r e s e r v o i r over the e n t i r e p e r i o d i n percent f u l l . Thus I ended up with a s e t of 30 numbers t h a t I thought adequately d e s c r i b e d the f l u c t u a t i o n p a t t e r n s of the r e s e r v o i r s . To f u r t h e r reduce the complexity of the data, and t o o b t a i n a more p r e c i s e , c o n c i s e measure of f l u c t u a t i o n , I used a program w r i t t e n by C F . Wehrhahn to perform a p r i n c i p l e components a n a l y s i s of the s e t of 30 measures I had f o r each of 20 r e s e r v o i r s . The program f i r s t normalized a l l the measures, t r a n s f o r m i n g them to p o s i t i o n s on a uniform 0 to 1 s c a l e , then c a l c u l a t e d the p r i n c i p l e components. The f i r s t f o u r p r i n c i p l e components accounted f o r 85.4% of the v a r i a b i l i t y i n the 187 o r i g i n a l s e t o f f l u c t u a t i o n m e a s u r e s , w h i c h I c o n s i d e r e d e n c o u r a g i n g . F u r t h e r m o r e , t h e p r o g r a m p l o t t e d t h e l o c a t i o n o f e a c h r e s e r v o i r on t h e a x e s o f t h e f i r s t t h r e e c o m p o n e n t s , t h u s g e n e r a t i n g r o u g h c l u s t e r s o f r e s e r v o i r s . F i n a l l y , I e x a m i n e d t h e c o r r e l a t i o n s b e t w e e n t h e f i r s t f o u r p r i n c i p l e c o m p o n e n t s a n d t h e 30 o r i g i n a l m e a s u r e s , a n d d i s c o v e r e d t h a t I c o u l d a p p l y i n t e r p r e t a t i o n s t o t h e f i r s t t w o c o m p o n e n t s . I d e c i d e d t h a t l o c a t i n g t h e r e s e r v o i r s a l o n g t h e f o u r p r i n c i p l e a x e s was a m o r e a c c u r a t e way o f p r e s e r v i n g t h e v a r i a b i l i t y .. i n f l u c t u a t i o n p a t t e r n s t h a n a n y c l a s s i f i c a t i o n s c h e m e . I t h e n u s e d s t e p w i s e m u l t i p l e r e g r e s s i o n t o s e e how much o f t h e v a r i a b i l i t y i n number o f y o u n g a n d r e p r o d u c t i v e e f f o r t c o u l d be e x p l a i n e d by t h e p a r t i c u l a r p a t t e r n s o f f l u c t u a t i o n i n t h e u n s t a b l e r e s e r v o i r s . S i n c e t h e s e q u e n c e o f s t e p s t a k e n i n t h a t a n a l y s i s d e p e n d e d h e a v i l y o n i n t e r m e d i a t e r e s u l t s , I h a v e e x p l a i n e d how I went a b o u t i t i n t h e r e s u l t s s e c t i o n b e l o w . T h e g e n e r a l i d e a was t h i s : f i r s t r e g r e s s n u m b e r s o f y o u n g a n d r e p r o d u c t i v e e f f o r t o n w e i g h t , c o m p e t i t i o n c o d e , a n d t h e f i r s t f o u r p r i n c i p l e c o m p o n e n t s , t h e i r s q u a r e s a n d c r o s s p r o d u c t s . T h e n i s o l a t e f r o m t h i s s e t t h e s m a l l e s t number o f i n d e p e n d e n t v a r i a b l e s t h a t e x p l a i n e d t h e most v a r i a b i l i t y i n t h e d a t a . S e c o n d l y , a u g m e n t t h e f i r s t s e t o f i n d e p e n d e n t v a r i a b l e s w i t h f o u r s h o r t - t e r m m e a s u r e s o f i n s t a b i l i t y : t h e mean w a t e r l e v e l a n d c o e f f i c i e n t o f v a r i a t i o n o f w a t e r l e v e l f o r t h e 60 a n d 180 d a y s p r i o r t o t h e d a t e s t h e c o l l e c t i o n s were m a d e . I n c l u d e t h e s q u a r e s a n d c r o s s p r o d u c t s f o r t h i s s e t o f f o u r t e r m s . R e p e a t t h e a n a l y s i s . T h i s p r o c e d u r e g i v e s some i n d i c a t i o n o f t h e r e l a t i v e i m p o r t a n c e o f s h o r t a n d l o n g - t e r m f l u c t u a t i o n s i n 188 determining the reproductive t r a i t s of Gambusia. 3_i R e s u l t s 3a. Measures Of I n s t a b i l i t y Before proceeding to the d e t a i l s of the p r i n c i p l e components and m u l t i p l e r e g r e s s i o n a n a l y s e s , I have presented here a comparison of the f o u r p r i n c i p l e measures of i n s t a b i l i t y f o r two a r t i f i c i a l l y generated time s e r i e s and a r e p r e s e n t a t i v e s e l e c t i o n of three r e a l time s e r i e s of r e s e r v o i r water l e v e l s . F i g u r e s 23 and 24 present the f o u r main i n s t a b i l i t y measures f o r the a r t i f i c i a l s i n e wave. The a u t o c o r r e l a t i o n f u n c t i o n of a s i n e wave i s a c o s i n e wave with the same p e r i o d , a mean of 0, and an amplitude of 2. (The s l i g h t decay shown i n the s i n e wave correlogram i s due to rounding e r r o r s i n the computer induced by my d e c i s i o n t o s t o r e the time s e r i e s as i n t e g e r values accurate to f o u r decimal places.) The range f u n c t i o n r i s e s s l o w l y from a very low v a l u e to 100% range a t 1 year. The v a r i a n c e f u n c t i o n behaves q u i t e s i m i l a r l y , r i s i n g from near 0 to a very high v a r i a n c e at 1 year, followed by a s l i g h t d i p d u r i n g the second year, then back t o an asymptotic value equal to the v a r i a n c e a t one year. The power spectrum of a s i n e wave has almost a l l the power co n c e n t r a t e d under the y e a r l y peak at the l e f t of the graph. By way of comparison. F i g u r e s 25 and 26 present the same measures c a l c u l a t e d on the random time s e r i e s . The a u t o c o r r e l a t i o n f u n c t i o n of a random s e r i e s drops r a p i d l y to 0 189 FIGURE 23 The A u t o c o r r e l a t i o n And Range Functions Of A Sine Have I have presented F i g s . 27-30 t o g i v e you a f e e l f o r the c h a r a c t e r i s t i c s of two time s e r i e s t h a t stand at the opposite ends of the spectrum of p r e d i c t a b i l i t y : a sin e wave and a random s e r i e s . I c o n s t r u c t e d the two s e r i e s so t h a t the numbers re p r e s e n t e d , i n the f i r s t case, a r e s e r v o i r that o s c i l l a t e d smoothly up and down with a p e r i o d of 1 year, and i n the second case, of a r e s e r v o i r t h a t f l u c t u a t e d at random. A s i n e wave with a p e r i o d of 1 year models an i d e a l i z e d s e a s o n a l environment. I t s a u t o c o r r e l a t i o n f u n c t i o n i s a c o s i n e wave with a p e r i o d of 1 year. The range f u n c t i o n of a s i n e wave r i s e s smoothly and slow l y from a very low value t o 100% range, a t t a i n e d at 1 year. SINE WAVE. PERIOD - 1 YEAR TIME STEPS SINE WAVE. PERIOD =.1 YEAR °0 100 200 300 400 500 600 700 BOO^OoToOO TIME STEPS 191 FIGURE 24 The Variance And S p e c t r a l Density Function Of A Sine Wave The v a r i a n c e f u n c t i o n of a s i n e wave behaves much l i k e the range f u n c t i o n . I t r i s e s s l o w l y from zero t o a very high value at 1 year, then d i p s s l i g h t l y before a t t a i n i n g the asymptotic v a r i a n c e at 2 years. The s p e c t r a l d e n s i t y f u n c t i o n of a s i n e wave has almost a l l i t s power co n c e n t r a t e d at the frequency corresponding to the n a t u r a l p e r i o d of 1 year. Because of t e c h n i c a l d e t a i l s of the Fast F o u r i e r Transform, the s p e c t r a l p l o t would be even more d r a m a t i c a l l y single-peaked i f the s i n e wave had had a p e r i o d with s m a l l prime f a c t o r s (e.g. 364 i n s t e a d of 365). SINE WRVE. PERIOD =• 1 YERR TIME STEPS . S INE WAVE. PER IOD = 1 YEAR G.-12 T 193 FIGURE 25 The A u t o c o r r e l a t i o n And Range Functions Of A Random S e r i e s I have presented F i g s . 27-30 to g i v e you a f e e l f o r the c h a r a c t e r i s t i c s of two time s e r i e s t h a t stand at the opposite ends of the spectrum of p r e d i c t a b i l i t y : a s i n e save and a random s e r i e s . I c o n s t r u c t e d the two s e r i e s so that the numbers repres e n t e d , i n the f i r s t case, a r e s e r v o i r t h a t o s c i l l a t e d smoothly up and down with a p e r i o d of 1 year, and i n the second case, of a r e s e r v o i r t h a t f l u c t u a t e d at random. Since by d e f i n i t i o n two p o i n t s i n a random s e r i e s are u n c o r r e l a t e d , the a u t o c o r r e l a t i o n f u n c t i o n drops immediately t o 0 and f l u c t u a t e s around 0 with s m a l l amplitude. The range f u n c t i o n of a random s e r i e s r i s e s r a p i d l y from a high l e v e l t o v i r t u a l l y 100% i n 100-200 days. RRNDOM SERIES TIME STEPS' i — i — i — i 7 D O 8 0 0 9 0 0 1 0 0 0 U J CD CE 100 T 90 80 70 60 50 40 30 20 10 0 RANDOM SERIES — i — i — i — i — i — i 1 H: 1 I 0 100 200 300 400 500 600 700 800 900 1000 TIME STEPS 195 FIGURE 26 The Variance And S p e c t r a l Density F u n c t i o n s Of A Random S e r i e s L i k e the range f u n c t i o n , the variance f u n c t i o n of a random s e r i e s r i s e s r a p i d l y from a high i n i t i a l l e v e l t o an asymptote reached i n 100-200 days. Note t h a t the asymptotic v a r i a n c e of a random s e r i e s (about 800 i n t h i s case) i s much lower than t h a t of a s i n e wave (asymptotic v a r i a n c e = 1250) with the same amplitude. The s p e c t r a l d e n s i t y p l o t of a random s e r i e s i s a d e f i n i t i o n of white n o i s e : moderately high power spread evenly a c r o s s the e n t i r e spectrum of f r e q u e n c i e s c o r r e s p o n d i n g to p e r i o d s ranging from years to days. RANDOM SERIES 820 738 656 574 LU <_> 492 •z. CE i—i .410 or cr 328 > 24S 164 62 0 r 4-1—y- ^ 1 r-100 200 300 400 500 600 700 800 900 1000 TIME STEPS POWER RANDOM SERIES 6.13 197 and f l u c t u a t e s around 0 with a s m a l l amplitude. The range f u n c t i o n s t a r t s out at a high l e v e l (around 80% range at 5 days), and climbs r a p i d l y to 100% (at about 100 d a y s ) . The variance f u n c t i o n behaves s i m i l a r l y , s t a r t i n g out at an even lower l e v e l and r e a c h i n g i t s asymptote more r a p i d l y . However, the asymptotic v a r i a n c e of the random s e r i e s was only about 65% t h a t of the s i n e wave. The power spectrum of a random s e r i e s i s a d e f i n i t i o n of white n o i s e : r e l a t i v e l y high power with no s i g n i f i c a n t peaks, d i s t r i b u t e d evenly r i g h t a c r o s s the freguency spectrum. The s i n e wave and random s e r i e s r e p r e s e n t two poles of a spectrum of types of i n s t a b i l i t y between which f a l l most of the 20 r e a l f l u c t u a t i o n p a t t e r n s I s t u d i e d . For example, F i g . 27 d i s p l a y s a s e c t i o n of the time s e r i e s f o r R e s e r v o i r 25, i t s a u t o c o r r e l a t i o n f u n c t i o n , range f u n c t i o n , and power spectrum. Notice f i r s t , i n the a c t u a l time s e r i e s , t h a t the f l u c t u a t i o n s approximate a n o i s y , skewed s i n e wave with a p e r i o d of about a year. There are many shorter-term f l u c t u a t i o n s , but they have v a r i o u s amplitudes and p e r i o d s , and do not form a s t r i k i n g p a t t e r n . F i n a l l y , note a f e a t u r e t h a t c h a r a c t e r i z e s many of the Maui r e s e r v o i r s : they present two types of environment to the f i s h i n h a b i t i n g them. For a long p e r i o d the r e s e r v o i r never went dry, o s c i l l a t i n g up and down with i r r i g a t i o n demands and the a l t e r n a t i o n of wet and dry seasons. But i n very dry years, such as 1974 (others were 1962, 1953, and 1951), the r e s e r v o i r d r i e d up f o r almost two months, with only a s m a l l puddle l e f t below the l e v e l of the o u t l e t p i p e . Gambusia can s u r v i v e such c o n d i t i o n s , but the s e l e c t i o n pressures on them duri n g lengthy 198 FIGURE 27 Measures Of I n s t a b i l i t y ; R e s e r v o i r 25 T h i s f i g u r e p r e s e n t s a p o r t i o n of the a c t u a l time s e r i e s of r e s e r v o i r volumes (in percent f u l l ) at the top, f o l l o w e d by three i n s t a b i l i t y measures: the a u t o c o r r e l a t i o n f u n c t i o n , the range f u n c t i o n , and the s p e c t r a l d e n s i t y p l o t . On the a u t o c o r r e l a t i o n p l o t , I have i n d i c a t e d with v e r t i c a l l i n e s 1- and 2-year l a g times. On the s p e c t r a l d e n s i t y p l o t , I have i n d i c a t e d the f r e q u e n c i e s corresponding to p e r i o d s of 1 year and 1 week, and the 95% confidence i n t e r v a l . The y - a x i s r e p r e s e n t s the l o g of the power at a given frequency, and the x - a x i s ranges over a l l f r e q u e n c i e s i n i n t e g r a l s u b m u l t i p l e s of the whole l e n g t h of the time s e r i e s , with long p e r i o d s (years) at the l e f t , and s h o r t p e r i o d s (days) at the r i g h t . The curve has been smoothed by averaging over groups of 10 p o i n t s . R e s e r v o i r 25 i s a s t r o n g l y seasonal r e s e r v o i r with a s m a l l but s i g n i f i c a n t weekly component to i t s f l u c t u a t i o n s . The s e a s o n a l i t y can be i n f e r r e d from the strong y e a r l y peaks i n the a u t o c o r r e l a t i o n f u n c t i o n and the s p e c t r a l d e n s i t y p l o t . Consider a f i s h l i k e Gambusia, with an age at maturity of 75-210 days, l i v i n g i n such a r e s e r v o i r . I t can expect water l e v e l s to be high i n the winter and low i n the summer, but on the average i t w i l l encounter f l u c t u a t i o n s i n water l e v e l over 50-85% of the volume of the r e s e r v o i r before i t matures, and the c o r r e l a t i o n of c o n d i t i o n s at the time i t matures with c o n d i t i o n s at the time i t i s born w i l l be low (.05^.20). RESERVOIR 25 1973 JOO.O 1974 199 JflN f£B ' KflR ' fiPR ' MR* ' JUN ' JUL to I-Z UJ RESERVOIR 25. HCiS. MRUI. Hqwflll .i c. -.3 -.6 -.8 ] 1 • ti tftfl •»- ! Inn RESERVOIR 25."HCiS. MflUI. HAWAII TIME STEPS 10O BOO 900 1C03 0 100 200 300 400 500 600 700 600 900 1000 TIME STEPS POWER RESERVOIR 25. HC&S. MRUI. HRWRII * WEEKLY 31 95X CONFIDENCE INTERVAL • / ~ " V * V — 0 .023 .05 .5/5 .1 :;r, .15 .175 .2 W .23 .2/5 .3 .325 .31 .375 .4 ^ An .5 FREQUENCY: RON'OV/nTH" 1 0 200 drawdowns are q u i t e d i f f e r e n t from those o p e r a t i n g during high-water f l u c t u a t i o n s ( c f . Chapter VI) . The c o r r e l a t i o n f u n c t i o n f o r R e s e r v o i r 25 r e v e a l s the dominance of the seasonal c y c l e . There i s j u s t a h i n t of high-frequency f l u c t u a t i o n s that might be weekly. The ranqe f u n c t i o n s t a r t s o f f at a f a i r l y low l e v e l , climbs r a p i d l y at f i r s t , then c o n t i n u e s a slow climb from one year up t o 1000 days. The power spectrum i s dominated by low-frequency c y c l e s of about a year's p e r i o d , with a s i g n i f i c a n t , but low, weekly peak two orders of magnitude lower than the y e a r l y peak. On the spectrum between a random s e r i e s and a s i n e wave, R e s e r v o i r 25 l i e s much c l o s e r t o the s i n e wave than t o the random s e r i e s . F i g . 28 presents the same f l u c t u a t i o n i n f o r m a t i o n f o r Re s e r v o i r 91, which l i e s near the opp o s i t e end of the spectrum. The a u t o c o r r e l a t i o n f u n c t i o n f o r R e s e r v o i r 91 f a l l s o f f r a p i d l y , but not as r a p i d l y as a random s e r i e s , to near 0, then f l u c t u a t e s around a long-term mean s l i g h t l y above 0. The range f u n c t i o n i s r a t h e r s i m i l a r to R e s e r v o i r 25's. although R e s e r v o i r 91 i s f l u c t u a t i n g w i l d l y and almost randomly, i t i s doing so over a s m a l l e r amplitude than the a r t i f i c i a l random s e r i e s . R e s e r v o i r 91 has a high mean water l e v e l and r a r e l y goes dry f o r an extended p e r i o d . The power spectrum r e v e a l s a n e a r l y random p a t t e r n . There i s some low frequency power, but not n e a r l y as much as R e s e r v o i r 25 had, and no s i g n i f i c a n t weekly peak. From about h a l f a year on out to periods of a day, the spectrum i s low and f l a t , r e p r e s e n t i n g background noise t h a t c h a r a c t e r i z e s random f l u c t u a t i o n s with s m a l l amplitudes. R e s e r v o i r 81 belongs to an i n t e r e s t i n g i n t e r m e d i a t e c l a s s 201 FIGURE 28 Measures Of I n s t a b i l i t y ; R e s e r v o i r 91 T h i s f i g u r e presents a p o r t i o n of the a c t u a l time s e r i e s of r e s e r v o i r volumes (in percent f u l l ) at the top, f o l l o w e d by t h r e e i n s t a b i l i t y measures: the a u t o c o r r e l a t i o n f u n c t i o n , the range f u n c t i o n , and the s p e c t r a l d e n s i t y p l o t . On the a u t o c o r r e l a t i o n p l o t , I have i n d i c a t e d with v e r t i c a l l i n e s 1- and 2-year l a g times. On the s p e c t r a l d e n s i t y p l o t , I have i n d i c a t e d the f r e q u e n c i e s corresponding t o p e r i o d s of 1 year and 1 week, and the 95% c o n f i d e n c e i n t e r v a l . The y - a x i s r e p r e s e n t s the l o g of the power at a given frequency, and the x-axis ranges over a l l f r e q u e n c i e s i n i n t e g r a l s u b m u l t i p l e s of the whole l e n g t h of the time s e r i e s , with long p e r i o d s (years) at the l e f t , and s h o r t p e r i o d s (days) at the r i g h t . The curve has been smoothed by averaging over groups of 10 p o i n t s . R e s e r v o i r 91's f l u c t u a t i o n p a t t e r n i s more s i m i l a r to a random s e r i e s than any other r e s e r v o i r ' s . R e s e r v o i r 91 i s s m a l l , tends to be kept f u l l , and because of i t s s m a l l s i z e can r a p i d l y r e f l e c t short-term changes i n i n f l o w s . I t s a u t o c o r r e l a t i o n f u n c t i o n f a l l s o f f f a i r l y r a p i d l y t o a low l e v e l (about ,2 at 50 days), then decays to z e r o . U n l i k e the range f u n c t i o n of a u n i f o r m l y d i s t r i b u t e d random s e r i e s , the range f u n c t i o n of R e s e r v o i r 91 r i s e s s l o w l y from a low l e v e l , not a t t a i n i n g i t s asymptote f o r more than 2 y e a r s . I t s power spectrum r e p r e s e n t s a low l e v e l of white noise with no s i g n i f i c a n t peaks except f o r one at a very low frequency (corresponding to a p e r i o d of s e v e r a l y e a r s ) . R e s e r v o i r 91 has a higher mean, a s m a l l e r v a r i a n c e , and more short-term a u t o c o r r e l a t i o n than the u n i f o r m l y d i s t r i b u t e d random s e r i e s I used f o r comparison, but i n other r e s p e c t s i t i s q u i t e random. RESERVOIR 91 JOO.O 1973 JOO.O 202 1974 JfW • FEB • WW 1 RPR ' rflt • JUN ' JUL ' B U 5 SEP OCT ' NOV ' OEC ' JSN ' fE9 ' MR ' RPR ' MKT ' JUN ' JUL RESERVOIR 91. HCLS. MflUI. HAWAII RESERVOIR 91. HC&S. MflUI. HAWAII 3 I M 250 »00 <3 s ; c KO 750 Kid 330 1000 TIME STEPS 0 100 200 300 400 500 600 700 800 200 1000 TIME STEPS 12 9 . 2 6.4 3.6 kYEARLY RESERVOIR 91 . HCkS. MflUI. HAWAII * WEEKLY £ 95X CONFIDENCE INTERVAL 0 .025 .05 .075 .1 .125 ,15 .173 .2 .22') .25 25 .2)5 .3 .325 .35 .375 .1 .423 .45 .<w; FREQUENCY: BANDWOTH-10 203 of r e s e r v o i r s t h a t had strong seasonal and weekly f l u c t u a t i o n s . F i g . 29 s e t s f o r t h the f l u c t u a t i o n p a t t e r n s f o r R e s e r v o i r 81. At f i r s t g l ance, the time s e r i e s does not look much d i f f e r e n t from R e s e r v o i r 25's, but i n f a c t the high freguency peaks have more p r e d i c t a b l e p e r i o d s . T h i s shows up i n the a u t o c o r r e l a t i o n f u n c t i o n , where the high-freguency f l u c t u a t i o n s present themselves as a secondary s i n e wave superimposed on the s e a s o n a l c y c l e , and i n the power s p e c t r a , where the high frequency f l u c t u a t i o n s can be i d e n t i f i e d as weekly. Furthermore, the amount of power contained i n the weekly peak i s much higher r e l a t i v e t o the s e a s o n a l peak than i t was i n R e s e r v o i r 25: only an order of magnitude lower. Those were the three main c l a s s e s i n t o which I had placed almost a l l the f l u c t u a t i n g r e s e r v o i r s before I d i d the p r i n c i p l e components a n a l y s i s : s e a s o n a l , random, and seasonal with a s t r o n g weekly element. I then took from each f l u c t u a t i o n f u n c t i o n a s e r i e s of numbers that I f e l t were s u f f i c i e n t t o r e p r e s e n t the e s s e n t i a l p a t t e r n d e p i c t e d by the f u n c t i o n . Table 39 presents the f i v e numbers I took from the a u t o c o r r e l a t i o n f u n c t i o n : the number of days to reach .50, .10, .05, and the f i r s t minimum a u t o c o r r e l a t i o n , and the d i f f e r e n c e between the second maximum and the f i r s t minimum (which i s l a r g e f o r seasonal c y c l e s and s m a l l f o r random f l u c t u a t i o n s ) . Most of the v a r i a b i l i t y among r e s e r v o i r s f o r t h i s measure l a y i n the r a p i d i t y with which the a u t o c o r r e l a t i o n f u n c t i o n f e l l o f f towards zero, and i n the s i z e of the seasonal component. Table 40 d i s p l a y s the s i x numbers I took from the range f u n c t i o n : the number of days to reach 25%, 50%, 75%, and 90% 204 FIGURE 29 Measures Of I n s t a b i l i t y : R e s e r v o i r 81 T h i s f i g u r e presents a p o r t i o n of the a c t u a l time s e r i e s of r e s e r v o i r volumes (in percent f u l l ) a t the top, f o l l o w e d by three i n s t a b i l i t y measures: the a u t o c o r r e l a t i o n f u n c t i o n , the range f u n c t i o n , and the s p e c t r a l d e n s i t y p l o t . On the a u t o c o r r e l a t i o n p l o t , I have i n d i c a t e d with v e r t i c a l l i n e s 1- and 2-year l a g times. On the s p e c t r a l d e n s i t y p l o t , I have i n d i c a t e d the f r e q u e n c i e s corresponding to p e r i o d s of 1 year and 1 week, and the 95% c o n f i d e n c e i n t e r v a l . The y - a x i s r e p r e s e n t s the l o g of the power at a given freguency, and the x-axis ranges over a l l f r e g u e n c i e s i n i n t e g r a l s u b m u l t i p l e s of the whole l e n g t h of the time s e r i e s , with long p e r i o d s (years) at the l e f t , and short p e r i o d s (days) a t the r i g h t . The curve has been smoothed by averaging over groups of 10 p o i n t s . R e s e r v o i r 81 i s s t r o n g l y s e a s o n a l , but i t a l s o has very strong weekly f l u c t u a t i o n s r e v e a l e d i n the s h o r t -term o s c i l l a t i o n s of the a u t o c o r r e l a t i o n c o e f f i c i e n t and the dramatic weekly peak on the s p e c t r a l d e n s i t y p l o t . (The other two high-freguency peaks are a r t i f a c t u a l "echoes" of the weekly peak i n t r o d u c e d by the method of a n a l y s i s . ) the range f u n c t i o n of R e s e r v o i r 81 s t a r t s higher and r i s e s f a s t e r than the range f u n c t i o n of R e s e r v o i r 25. T h i s i m p l i e s t h a t a f i s h l i v i n g i n R e s e r v o i r 81 can expect to encounter l a r g e v a r i a t i o n s i n volume (40-60%) over s h o r t p e r i o d s of time (5-50 days). RESERVOIR 81 J33.0, J.7.S R l 1973 "jS ' FE3 ' ttRR ' S?R ' MT ' .ON ' JUL ' RUG ll/v JOO.O SEP OCt. NOV OEC M.O 17.5 J2.5 205 1974 V .«W FEB MAS RPR KRT .OJN JUL I i .4 .? C. - . 3 -.< - . 6 RESERVOIR 8 1 . KCIS. M3UI. HRVHII RESERVOIR 8 1 . HCLS. MflUI. HflWRIl' 5 i:o JCO JOO «oc MO r o TOO KO SOO I:OO TIME STEPS c r o r 100 90 80 70 ,60 50 40 30 20 10 0 0 100 200 300 <S00 500 600 700 800 900 1000 TIME STEPS 9.2 6.4 3.6 .733 YEARLY -2 RESERVOIR 81. HC&S. MAUI. HAWAII * WEEKLY Z 95J CONFIDENCE INTERVAL 0 .025 .05 .573 .1 .125 .15 .173 .2 ?23 .23 .273 .3 .325 .33 .373 .4 .425 .45 .4; : FREQUENCY: fjANDWDTH" 10 206 Table 39 A u t o c o r r e l a t i o n Measures Of I n s t a b i l i t y T r i R e s e r v o i r | Number Of Days To Reach | 2nd Max-1st Min | ! . 50 .10 .05 F i r s t | Minimum | Sine Wave I 61 86 89 180 I 1.9050 l Random S e r i e s | 3 5 5 25 | .0789 | Opaeula 1 ! 20 99 142 190 | .1680 | Res e r v o i r 21 | 9 110 139 180 | .3814 | Res e r v o i r 22 | 25 164 531 185 | .3093 | Res e r v o i r 25 | 36 161 177 185 I .3872 J Reservoir 31 I 5 178 427 185 J .0276 | Reservoir 32 | 10 1.37 143 180 J .2808 | Reservoir 33 I 18 127 140 185 | .3500 | Res e r v o i r 35 | 16 457 635 220 1 .0120 | Reservoir 40 | 10 135 143 180 \ .3330 | Reservoir 41 | 10 142 158 185 | .1899 | Reservoir 42 \ 8 148 890 180 | .1161 | Reservoir 50 | 7 52 60 200 | .1587 | Reservoir 51 | 9 74 144 185 I .3316 J Reservoir 60 | 37 147 165 185 J .2986 J Reservoir 61 | 39 163 531 185 | .3123 | Reservoir 80 J 22 112 128 185 | .3469 J Reservoir 81 | 21 128 144 185 | .4370 | Reservoir 84 | 21 114 142 185 | .5038 | Reservoir 90 | 5 95 148 150 j .2163 { Reservoir 91 | .. . . i . 4 89 132 135 | — ._. i _ .0578 I j 207 T a b l e 40 R a n g e M e a s u r e s O f I n s t a b i l i t y — r i R e s e r v o i r | Number O f D a y s T o R e a c h | A v e r a g e R a n g e O v e r | ! 25% 50% 75% Range 90% ! 10 D a y s 1000 D a y s J S i n e H a v e ; 47 97 163 222 I 4 . 9 9 9 . 9 | Random S e r i e s ! 3 6 9 22 • 8 1 . 6 9 9 . 8 | O p a e u l a 1 ] 15 48 174 736 T 2 0 . 1 • - - ~1 9 2 . 0 J R e s e r v o i r 21 ! 6 16 48 145 | 4 2 . 1 9 6 . 9 | R e s e r v o i r 22 J 7 22 68 153 | 3 4 . 4 9 8 . 7 } R e s e r v o i r 25 | 8 34 125 558 | 3 0 . 1 9 4 . 5 j R e s e r v o i r 31 | 6 21 98 304 | 3 9 . 0 9 6 , 9 | R e s e r v o i r 32 J 6 16 52 141 J 4 2 . 1 9 7 . 4 | R e s e r v o i r 33 ! 6 19 57 129 ! 3 9 . 1 9 9 , 3 | R e s e r v o i r 35 ! 7 23 99 361 1 3 5 . 7 9 8 . 0 ! R e s e r v o i r 40 | 6 18 56 148 I 3 8 . 6 9 7 . 0 | R e s e r v o i r 41 J 7 21 89 706 I 3 6 . 9 9 2 . 1 | R e s e r v o i r 42 | 7 25 100 303 j 3 4 . 3 9 9 . 0 | R e s e r v o i r 50 | 7 26 106 300 j 3 3 . 9 9 7 . 3 | R e s e r v o i r 51 | 7 21 77 272 ! 3 8 . 3 9 7 . 0 J R e s e r v o i r 60 | 10 65 791 1 2 5 . 8 7 8 . 0 | R e s e r v o i r 61 J 8 29 119 420 1 3 3 . 0 9 7 . 0 | R e s e r v o i r 80 J 7 25 92 256 ! 3 3 . 4 9 7 . 1 | R e s e r v o i r 81 ! 6 17 66 190 1 4 2 . 6 9 9 . 7 | R e s e r v o i r 84 J 8 32 122 282 1 3 0 . 9 9 8 . 7 | R e s e r v o i r 90 | 7 27 114 400 1 3 4 , 9 9 4 . 7 | R e s e r v o i r 91 ! ..,. J. 7 26 104 329 L. 3 4 . 6 9 7 . 0 | . i 208 range, and the average range encountered over 10 days and 1000 days. Most the the v a r i a b i l i t y l a y i n the r a t e at which r e s e r v o i r s reached f u l l range. They almost a l l s t a r t e d with about 30-35% range over 5-10 days and reached 95-100% range over 1000 days, but they reached i t at q u i t e d i f f e r e n t r a t e s , as the f i r s t f o u r columns of numbers show. Table 41 s e t s f o r t h s i m i l a r numbers taken from the vari a n c e f u n c t i o n . They p a i n t a r a t h e r d i f f e r e n t p i c t u r e . There was c o n s i d e r a b l e v a r i a b i l i t y among r e s e r v o i r s i n the average v a r i a n c e over both 10 and 1000 day p e r i o d s , more so than i n the 10 and 1000 day ranges. T h i s d i f f e r e n c e probably r e f l e c t s d i f f e r e n c e s among r e s e r v o i r s i n mean water l e v e l s . There was a l s o c o n s i d e r a b l e v a r i a b i l i t y among r e s e r v o i r s i n the numbers of days taken to reach 50% and 75% of the asymptotic (1000 day) v a r i a n c e . Table 42 e x h i b i t s the numbers I took from the power s p e c t r a : the percent of the t o t a l power at medium f r e q u e n c i e s (91-182 day p e r i o d s ) , the r a t i o of low to medium and high to medium freguency power, the percent of t o t a l power contained i n s i g n i f i c a n t peaks, the percent of t o t a l power t h a t was background n o i s e , and the r a t i o s of weekly t o y e a r l y , weekly t o background, and y e a r l y to background power. The s t r o n g l y seasonal r e s e r v o i r s stand out i n columns 2 and 4, with low frequency power more than 10 times as l a r g e as medium frequency power, and over 50% of t o t a l power co n t a i n e d i n s i g n i f i c a n t peaks. The seasonal r e s e r v o i r s with s t r o n g weekly c y c l e s (e.g. 51, 81, and 90) stand out i n column 6, with weekly power exceeding 10% of seasonal power, and i n column 7, with weekly power more than 10 times higher than background n o i s e . The more 209 Table 41. Variance Measures Of I n s t a b i l i t y T r -i R e s e r v o i r | Number Of Days To Reach I Average Variance | ] 25% 50% Of The 75% Asymptotic 90% Variance | 10 Days • 1000 Days | Sine Wave j 106 162 221 270 — f | 3.0 1245. 8 | Random S e r i e s | 3 6 8 10 I 737.3 i . 815.5 | Opaeulua 1 | 23 65 170 360 — 1 — \ 92.2 746.7 | Re s e r v o i r 21 | 9 37 137 307 | 268.4 921.2 | Re s e r v o i r 22 | 15 65 235 674 | 190.7 901.2 | Re s e r v o i r 25 | 12 61 19.1 347 | 152.6 662.7 | Re s e r v o i r 31 | 6 18 114 479 | 250.3 575.7 | Re s e r v o i r 32 | 8 35 126 301 I 273.0 881.0 | Re s e r v o i r 33 1 10 47 155 304 | 217.3 848.4 | Re s e r v o i r 35 | 7 33 139 364 | 180.2 527.0 | Re s e r v o i r 40 f 10 41 145 320 | 222.2 857.7 | Re s e r v o i r 41 | 8 34 128 377 | 201.7 630.0 | Re s e r v o i r 42 f 6 19 94 226 | 161.6 374.0 \ Re s e r v o i r 50 j 6 23 83 182 I 198.3 511.5 | Re s e r v o i r 51 I 7 33 130 284 | 218.0 641.4 | Re s e r v o i r 60 | 8 45 157 287 | 95.1 317.3 | Re s e r v o i r 61 I 8 51 199 468 | 154.0 520.8 ) Re s e r v o i r 80 | 8 50 180 319 | 158.7 532.2 | Re s e r v o i r 81 1 7 42 172 320 | 270.2 799.5 | Res e r v o i r 84 J 9 43 137 232 | 156.7 554.4 | Re s e r v o i r 90 | 5 14 92 249 | 192,2 409.5 | Res e r v o i r 91 | .,...... J 5 10 78 308 f 179.7 i 341.7 | _ , i 210 Table 42 Power Spectrum Measures Of I n s t a b i l i t y T T ~ T T T —r r r T R e s e r v o i r |%fled |Low/ | Hgh/ | % S i g j %Bck | Wkly/ | Wkly/ I Y r l y / | j Freq I Hed Frg | Medfrq} Peaks j Grnd | Y r l y | Bckgrnd } Bckgrnd J Sine Wave | .0000 | 999.999} 3 . T 544| .99951 .0005} .0000} • 3333 | 999-999 J Random S e r i e s |.0525 \ m 906 | 17. 142j •0171| .9829} 1.4112} • 96 87 J 1.030} Opaeula 1 |.1283 I 5 . 768 | 1. 026| .2399} .7601} .0084| • 4114 I 48.724} R e s e r v o i r 21 I.1059 1 6 . 248) 2. 199j .3744| .62561 .0526| 2. 4810 j 70 .790| R e s e r v o i r 22 1.0751 | 10. 559 | 1. 762| .5566} .4434} .03181 3 . 2090 |151.470} R e s e r v o i r 25 j .0681 I 11- 573 | 2. 106| .59781 .4022} .0474} 5 . 5769 } 176.661} R e s e r v o i r 31 f .0998 I 5 . 450| 3 . 570| .39851 .6015} .0688} 3 . 5424 I 77.186} R e s e r v o i r 32 |.0975 I 6 . 770 | 2. 488 | .3686} .6314} .0685} 3 . 1074 } 68.033} R e s e r v o i r 33 1.0971 I 7 . 333 | 1. 965| .46 39} .5361} .0759} 5 . 0688 | 100.134} R e s e r v o i r 35 }.0868 I 7 . 760J 2. 765| .4591| .5409} .0251| 1. 7255 }103.089| R e s e r v o i r 40 |. 1065 ! 6 . 545| 1. 8411 .4087| .5913} .0772} 4. 1114 1 79.897} R e s e r v o i r 41 }.0923 i 6 . 906 | 2. 933| .3867J .6133} .1125} 5 . 2927 } 70.564 1 R e s e r v o i r 42 | .0786 I 7. 558 | 4. 163| .4267} .5733} .07171 4. 1319 } 86.4751 R e s e r v o i r 50 I .0728 I 8 . 171J 4 . 5711 .2845} .7155} .1117} 3 . 3170 } 44.527} R e s e r v o i r 51 I .0696 I 8 . 877 | 4. 5011 .4068) .5932} .2043} 9. 6535 } 70.883| R e s e r v o i r 60 | .0611 | 12. 085} 3 . 281 | .6481} .3519} .1219} 16. 6131 1204.393} R e s e r v o i r 61 | .0563 I 13. 068j 3 . 695} .6671} .3329} .1139} 16. 9983 1223.9481 R e s e r v o i r 80 |.0635 I 10. 575 J 4. 1701 .5394} .4606} .1706} 14. 1657 1 124.535} R e s e r v o i r 81 |.0567 | 10. 789 | 5 . 878 J .5524} .44761 .3439} 26. 2172 1114.337} R e s e r v o i r 84 ! .0728 I 9 . 9181 2. 829| .5464} .4536} .09921 9 . 0248 } 136.433} R e s e r v o i r 90 | .0631 | 8 . 631 | 6. 211| .4712} .5288} .2543} 14. 9926 | 88.436} R e s e r v o i r 91 | .1069 | 4 . 121 | 4. 234| .3044} .6956| .0970} 3 . 2106 | 49.666} • x X i ... ... J. j- . . J . x 1 Table 43 M i s c e l l a n e o u s Measures Of I n s t a b i l i t y R e s e r v o i r — i r - •— Avg. Max Wkly Rnge T 1 1 1 - " • r Avg. YrlyAvg D a i l y Max Rnge j dv/dt T— | Volume 1 (mg) | Mean | | % F u l l | Sine Wave Random S e r i e s 0. 1. 01 97 1 1 99 99 .9 .3 0.55 33. 12 I _ | 49.95 | I 53.12 | Opaeula 1 1. 32 1 98, .3 j 3. 36 | 84, .0 | 55, .24 | R e s e r v o i r 21 7. 25 j 93, .6 | 9. 18 I 18, .5 \ 38. .29 I R e s e r v o i r 22 | 7. 92 j 100. .0 | 7. 30 i 38. .2 | 37. 36 | R e s e r v o i r 25 | 8. 61 j 85. .7 | 6. 49 I 42. .0 I 23, .73 | R e s e r v o i r 31 | 5. 12 | 96. .3 J 10. 30 I 5. .4 | 61. 48 | R e s e r v o i r 32 | 8. 63 100. .0 | 9. 74 f 10. .2 | 50. 86 | Re s e r v o i r 33 | 10. 08 | 97. .9 8. 56 I 41-.5 | 48, 47 | R e s e r v o i r 35 | 3. 63 | 80. 3 8. 77 I 12, 2 I 38. .86 | R e s e r v o i r 40 8. 81 ] 96. .0 | 8. 14 | 65. 4 | 41, .42 { R e s e r v o i r 41 ! 8. 24 | 87. .2 | 8. 66 | 10. 2 | 44. 02 I R e s e r v o i r 42 | 4. 91 J 79. 3 9. 01 ! 9. . 1 | 52. 89 | R e s e r v o i r 50 j 6. 49 88. .9 | 9. 10 ! 7, 8 I 65, 08 | Re s e r v o i r 51 | 12. 97 | 91, .5 9. 63 | 14. 1 I 62. .00 | Re s e r v o i r 60 | 10. 54 | 100. 0 | 5. 72 I 96, 0 | 24, 44 | Re s e r v o i r 61 | 12. 92 | 57. 0 | 7. 56 I 50. 2 I 28. 78 | Re s e r v o i r 80 I 11. 95 1 89. .2 j 7. 96 | 38. 1 I 60, 15 | R e s e r v o i r 81 | 20. 15 | 94. 6 j 10. 44 I 24. 8 i 66. 39 | Re s e r v o i r 84 1 11. 78 94. 0 j 6. 96 I 35. 1 J 49. 17 | Res e r v o i r 90 | 9. 23 83. 9 | 8. 76 I 42, 4 | 63, 98 | Res e r v o i r 91 ! 3. 01 | 85. 5 | 9. 39 I 11. 8 I 68. 57 | i J. j — j. i 212 n e a r l y random r e s e r v o i r s (e.g. 31, 41, 50, and 91) stand out i n column 5, with more than 60% of t h e i r t o t a l power contained i n background n o i s e . T able 43 presents the remaining, m i s c e l l a n e o u s measures of i n s t a b i l i t y : average weekly range, average seasonal range, average d a i l y r a t e o f change, volume, and mean percent f u l l . The weekly and sea s o n a l ranges were w e l l c o r r e l a t e d with the s i z e of the weekly and seasonal peaks i n the power s p e c t r a . The average d a i l y r a t e of change was high f o r r e s e r v o i r s with high-freguency f l u c t u a t i o n s , whether weekly or random. R e s e r v o i r volume i n pa r t determined the f l u c t u a t i o n p a t t e r n s , because s m a l l r e s e r v o i r s can f l u c t u a t e much f a s t e r than l a r g e ones. The mean water l e v e l i n r e s e r v o i r s was a l s o roughly c o r r e l a t e d with the f l u c t u a t i o n p a t t e r n . l a r g e r e s e r v o i r s tend to be dominated by s e a s o n a l c y c l e s and have lower mean water l e v e l s , while s m a l l r e s e r v o i r s are dominated by high-frequency f l u c t u a t i o n s and have higher mean water l e v e l s . 3b. P r i n c i p i e Components A n a l y s i s Table 44 d i s p l a y s the i n i t i a l r e s u l t s of the p r i n c i p l e components a n a l y s i s of the 30 numbers I took o f f the i n s t a b i l i t y measures, and the i n t e r p r e t a t i o n s I placed on the f i r s t two i n s t a b i l i t y measures. Since the f i r s t 4 p r i n c i p l e components accounted f o r 85.4% of the t o t a l v a r i a n c e , I s e l e c t e d them f o r the m u l t i p l e r e g r e s s i o n a n a l y s i s . Table 45 s e t s f o r t h the p o s i t i o n s of each r e s e r v o i r i n the 4-space spanned by the f i r s t 4 p r i n c i p l e components ( i . e . the c o o r d i n a t e s of each r e s e r v o i r given i n terms of the dominant 4 e i g e n v e c t o r s of the normalized 213 Table 44 P r i n c i p l e Components A n a l y s i s Amount Of T o t a l Variance Accounted For By The F i r s t 6 P r i n c i p l e Components 1 T T 1 P r i n c i p l e I Corresponding|Proportion Of | I n t e r p r e t a t i o n } Component | Eigenvalue | T o t a l V ariance| I | |By Item Summed| | h h H 1 I I I I 1 | 0.423 |0.361 0.361 | Seasonal | 2 | 0.264 |0.225 0.586 | weekly | 3 | 0.175 |0. 150 0.736 | ? | 4 | 0.138 |0. 118 0.854 | ? | 5 I 0.055 |0.047 0.901 | - | 6 | 0.035 10.030 0.931 J - j 1 1 i i Table 45 R e s e r v o i r Coordinates In The 4-space Spanned By The F i r s t 4 P r i n c i p l e Components T i T i R e s e r v o i r I Axis 1 1 Axis 2 I Axis 3 i Axis 4 j Opaeula 1 j 0, 257 j -1. 312 j -0. 090 j -0. 720 R e s e r v o i r 21 | -0. 392 | -0. 185 j 0. 519 i -0. 118 R e s e r v o i r 22 | 0. 541 j -0. 466 j 0. 561 i 0. 448 R e s e r v o i r 25 j 0. 864 J -0. 265 J 0. 250 j 0. 164 R e s e r v o i r 31 | -0. 793 j -0. 103 | -0. 194 i 0. 330 R e s e r v o i r 32 I -0. 507 j -0. 070 | 0. 403 i -0. 061 R e s e r v o i r 33 | 0. 018 j -0. 138 | 0. 446 -0. 129 R e s e r v o i r 35 1 -0. 299 j -0. 443 -0. 286 i 0. 815 R e s e r v o i r 40 I -0. 103 j -0. 273 j 0. 380 i -0. 250 R e s e r v o i r 41 J -0. 375 | -0. 067 j 0, 031 i -0. 003 R e s e r v o i r 42 J -0. 535 -0. 053 J -0. 517 i 0. 54 4 R e s e r v o i r 50 | -0. 701 | 0. 124 j -0. 271 i -0. 272 R e s e r v o i r 51 I -0. 303 | 0. 506 | 0. 123 i -0. 207 R e s e r v o i r 60 j 1. 54 3 -0. 001 | -1. 005 i -0. 299 R e s e r v o i r 61 I 1. 031 | 0. 281 j 0. 001 i 0. 593 R e s e r v o i r 80 J 0. 359 0. 400 | 0. 079 i -0. 104 R e s e r v o i r 81 | 0. 254 | 1. 272 j 0. 419 i -0. 143 R e s e r v o i r 84 | 0. 402 j 0. 149 | 0. 138 i -0. 178 R e s e r v o i r 90 I -0. 319 | 0. 709 J -0. 456 j -0. 241 R e s e r v o i r 91 | -0. 942 | -0. 063 J -0. 528 i -0. 169 . .. i._.„ j . . . _ , . i , ,. ± - i 2 1 5 Table 46 T h e C o r r e l a t i o n s Of T h e 30 O r i g i n a l I n s t a b i l i t y M e a s u r e s W i t h T h e F i r s t 4 P r i n c i p l e C o m p o n e n t s , , r T " i r - i M e a s u r e I PC1 i PC2 | PC3 | PC4 | 1. A v g # D a y s T o 25% R a n g e | 0 . 417 J - 0 . 5 4 5 | - 0 . 3 2 8 | - 0 . 3 9 7 | 2 . Avg # D a y s To 50% R a n g e | 0 . 633 | - 0 . 290 | - 0 . 6 3 0 | - 0 . 3 0 3 | 3 . Avg # D a y s T o 75% R a n g e | 0 . 588 | - 0 . 0 6 1 | - 0 . 6 4 7 | - 0 . 2 0 8 | 4 . A v g # D a y s T o 90% R a n g e I 0 . 568 { - 0 . 0 3 0 | - 0 . 5 9 3 | - 0 . 1 9 8 | 5 . Avg # D a y s To 25% V a r . | 0 . 378 | - 0 . 7 0 2 | 0 . 3 2 3 | - 0 . 2 9 4 | 6 . Avg # D a y s To 50% V a r . f 0 . 7 5 5 | - 0 . 3 5 4 j 0 . 4 8 8 | - 0 . 0 6 7 | 7. Avg # D a y s TO 75% V a r . | 0 . 766 I - 0 . 1 5 5 | 0 . 4 9 8 | 0 . 1 8 9 \ 8 . Avg # D a y s T o 90% V a r . | 0 . 254 | - 0 . 2 9 6 | 0 . 3 2 8 | 0 . 4 6 7 | 9 . Avg # D a y s To . 5 0 E | 0 . 956 | - 0 . 0 5 0 J 0 . 0 4 0 | 0 . 1 6 3 1 1 0 . Avg # D a y s To . 10 R | 0 . 059 | - 0 . 2 4 8 | - 0 . 0 9 1 | 0 . 7 0 6 | 11. Avg # D a y s T o . 0 5 R j - 0 . 015 | - 0 . 1 7 4 | - 0 . 2 0 1 | 0 . 8 4 9 | 12. Avg # D a y s T o 1 s t M i n R \ 0 . 227 I - 0 . 242 | 0 . 1 8 2 | 0 . 3 1 9 1 13. V o l u m e | 0 . 759 | - 0 . 2 7 9 | - 0 . 1 5 4 j - 0 . 4 0 7 | 1 4 . Mean % F u l l - 0 . 680 | 0 . 3 6 5 | - 0 . 0 9 0 | - 0 . 3 5 4 | 15 . Avg 10 Day V a r i a n c e j - 0 . 566 | 0 . 3 9 0 | 0 . 5 6 7 | 0 . 0 9 1 | 16. Avg 1000 Day V a r i a n c e | - 0 . 017 | - 0 . 2 1 1 | 0 . 9 1 5 | - 0 . 1 2 6 | 17. Avg 10 Day R a n g e \ - 0 . 517 | 0 . 4 8 9 j 0 . 4 9 5 | 0 . 2 4 6 J 1 8 . Avg 1000 Day Range | - 0 . 506 | 0 . 1 7 5 | 0 . 5 8 4 | 0 . 3 3 1 | 1 9 . 2nd Max - 1 s t M i n R | 0 . 561 \ 0 . 3 5 2 | 0 . 5 8 1 | - 0 . 3 0 3 | 2 0 . Avg W e e k l y Max Range | 0 . 435 j 0 . 8 0 2 | 0 . 3 4 8 | - 0 . 0 8 3 | 2 1 . Avg S e a s o n a l Max Range | - 0 . 064 | - 0 . 2 1 0 | 0 . 2 5 4 | - 0 . 5 4 7 | 2 2 . Avg D a i l y D v / d t | - 0 . 656 l 0 . 6 0 2 | 0 . 1 5 5 | 0 . 3 0 0 | 2 3 . ,% P o w e r At Med F r e g | - 0 . 492 | - 0 . 7 2 2 | 0 . 1 5 1 | 0 . 2 7 2 | 2 4 . Low/med F r e g P o w e r | 0 . 835 | 0 . 4 0 5 | 0 . 0 2 1 | 0 . 2 2 5 | 2 5 . H i g h / m e d F r e g Power | - 0 . 221 \ 0 . 8 5 3 | - 0 . 3 8 9 | 0 . 0 0 0 J 2 6 . % P o w e r I n s i g P e a k s | 0 , 802 | 0 . 3 8 9 | 0 . 0 2 5 | 0 . 3 9 2 | 2 7 . % P o w e r I n B c k g r n d N o i s e | - 0 . 802 | - 0 . 3 8 9 | - 0 . 0 2 5 \ - 0 . 3 9 2 \ 2 8 . W e e k l y / y e a r l y P o w e r i 0 . 037 | 0 . 9 1 6 | - 0 . 0 4 7 | - 0 . 2 5 3 | 2 9 . W e e k l y / b c k g r n d Power | 0 . 500 | 0 . 807 | - 0 . 0 9 7 | - 0 . 0 8 6 | 3 0 . Y e a r l y / b c k g r n d P o w e r | 0 . 888 | 0 . 1 6 4 | - 0 . 0 5 3 | 0 . 3 7 3 | • < i . . . X i 216 s p a c e ) . Table 46 e x h i b i t s the c o r r e l a t i o n s of the 30 i n s t a b i l i t y measures with each of the f i r s t 4 p r i n c i p l e components. I based my i n t e r p r e t a t i o n of the components on these c o r r e l a t i o n s . For example. P r i n c i p l e Component 1 was p o s i t i v e l y c o r r e l a t e d with the number of days i t took to reach a given range or v a r i a n c e , with volume, with the percent of t o t a l power i n s i g n i f i c a n t peaks, and with the r a t i o of y e a r l y power to background n o i s e . I t was n e g a t i v e l y c o r r e l a t e d with the average v a r i a n c e and range over given p e r i o d s , with the average d a i l y r a t e of change, and with the r a t i o of high to medium freguency power. I t h e r e f o r e concluded that r e s e r v o i r s with a high value f o r P r i n c i p l e Component 1 should be c h a r a c t e r i z e d by p r e d i c t a b l e , s t r o n g seasonal f l u c t u a t i o n s , and have l a r g e volumes and s m a l l to moderate weekly f l u c t u a t i o n s . R e s e r v o i r s 60, 61, and 25 ranked highest f o r PC 1, and a l l met those c r i t e r i a . R e s e r v o i r s 91, 31, and 50 ranked lowest f o r PC 1. A l l were c h a r a c t e r i z e d by s m a l l s i z e and r e l a t i v e l y random f l u c t u a t i o n s . In s i m i l a r f a s h i o n , I decided that P r i n c i p l e Component 2 r e p r e s e n t e d the s t r e n g t h of weekly f l u c t u a t i o n s . I had d i f f i c u l t y i n t e r p r e t i n g p r i n c i p l e components 3 and 4. 3c^ M u l t i p l e Regression A n a l y s i s To generate the data r e c o r d s used i n the m u l t i p l e r e g r e s s i o n a n a l y s i s , I s e l e c t e d the c o m p e t i t i o n code, weight, number of young, and r e p r o d u c t i v e e f f o r t o f f " the r e c o r d s of every pregnant female Gambusia caught i n January 1974, then added to each r e c o r d the f o u r a p p r o p r i a t e p r i n c i p l e components 217 corresponding to the r e s e r v o i r i n which the f i s h were caught. T a b l e 47 presents a summary of the r e s u l t s of the m u l t i p l e r e g r e s s i o n a n a l y s e s , which I d i d i n a s e r i e s of s t e p s designed to maximize the p r o p o r t i o n of t o t a l v a r i a b i l i t y e x p l a i n e d by the r e g r e s s i o n , and minimize the number of independent v a r i a b l e s r e q u i r e d to e x p l a i n i t . In Step 1, I simply r e g r e s s e d number of young and r e p r o d u c t i v e e f f o r t on weight, c o m p e t i t i o n code (a dummy v a r i a b l e t a k i n g the value 1 f o r no competitors present and 2 f o r p o t e n t i a l c o m p e t i t o r s p r e s e n t ) , and the f i r s t 4 p r i n c i p l e components. Only 26.3% of the v a r i a n c e i n number of young and 15.6% of the v a r i a n c e i n r e p r o d u c t i v e e f f o r t was e x p l a i n e d . A l l independent v a r i a b l e s f i g u r e d s i g n i f i c a n t l y i n the r e g r e s s i o n . In Step 2, I added the squares and c r o s s p r o d u c t s of the f i r s t 4 p r i n c i p l e components to allow f o r n o n l i n e a r i n t e r a c t i o n s . The i n c r e a s e i n variance e x p l a i n e d was d i s a p p o i n t i n g l y s m a l l : to 36.6% f o r number of young and 23.4% f o r r e p r o d u c t i v e e f f o r t . Twelve independent v a r i a b l e s f i g u r e d s i g n i f i c a n t l y f o r number of young, 9 f o r r e p r o d u c t i v e e f f o r t . The most important terms were weight and the squares and c r o s s p r o d u c t s of the p r i n c i p l e components. By s e l e c t i n g o n l y the dominant terms, i n Step 3, I found I could e x p l a i n 29.6% of the v a r i a n c e i n number of young with 6 terms, 4 of them n o n l i n e a r , and 20.7% of the v a r i a n c e i n r e p r o d u c t i v e e f f o r t with 5 terms, 4 of them n o n l i n e a r . That seemed u n s a t i s f a c t o r y . According t o my p r e c o n c e p t i o n s , the long-term f l u c t u a t i o n p a t t e r n s , which d i f f e r e d s i g n i f i c a n t l y among r e s e r v o i r s , should have been w e l l c o r r e l a t e d with d i f f e r e n c e s i n r e p r o d u c t i v e t r a i t s (which a l s o 218 Table 47 Summary Of Stepwise M u l t i p l e Regression A n a l y s i s < Dependent V a r i a b l e ) Ind. V a r i a b l e s \ A v a i l a b l e i Ind. V a r i a b l e s Used R 2 1. Step 1 N= 108 Number Of Young {Weight, Comp Code Repro. E f f o r t JAnd The 1st 4 PCs A l l A l l 2. Step 2 N = 108 Number Of Young Repfo. E f f o r t I |As In Step 1,plus |The Squares And |Crossproducts Of |The PCs Weight,Compcode,PC1 PC4,Wgt 2,Pd 2,PC2 2, P C 3 2 , P C 4 2 , P C 1 X P C 3 , PdxPC4,PC2xPC3 Wgt,Compcode,PC2, PC4,PC1 2,PC3 2,PC4 2, PCTxPC4,PC2xPC3 3. Step 3 N = 108 Number Of Young Repro. E f f o r t I !Wgt,Compcode,PC1 2, |PC3 2,PC1xPC4,PC2xPC3 I |Wgt,PCl 2,PC3 2, |PC4 2,PC2xPC3 A l l Wgt,PCl 2,PC4 2, PC2xPC3 4. Step 4 N = 953 Number Of Young I As In Step 2, P l u s I The 6 0 And 180 Day |Means S CVs, T h e i r jSquares And j Crossproducts 16 Of The 35 0.263 0. 156 0.366 0.234 0.296 0.207 0.618 5. Step 5 N = 953 -+ I IWgt, 60 Day CV 2, |180 Day CV 2, |60x180 Day CV Number Of Young A l l 0.464 219 d i f f e r e d s i g n i f i c a n t l y among r e s e r v o i r s , c f . Chapter I V ) , because I saw those long-term p a t t e r n s as the p r i n c i p l e s e l e c t i v e agents c a u s i n g e v o l u t i o n a r y changes i n r e p r o d u c t i v e t r a i t s . In an a s s a u l t on that p r e c o n c e p t i o n , I decided to i n c l u d e s e v e r a l measures of short-term f l u c t u a t i o n s i n the a n a l y s i s . Simply because the measures had to be c a l c u l a t e d over s h o r t time p e r i o d s , I could not r e l i a b l y use a u t o c o r r e l a t i o n , range, and v a r i a n c e f u n c t i o n s , or s p e c t r a l a n a l y s i s . I s e t t l e d on the means and c o e f f i c i e n t s of v a r i a t i o n i n water l e v e l f o r the 60 and 180 days p r i o r to the sample dates as a p p r o p r i a t e measures, and added them to the f i s h r e c o r d s . I a l s o added the c o n d i t i o n f a c t o r s c a l c u l a t e d f o r the female p o p u l a t i o n of each r e s e r v o i r . Table 48 s e t s f o r t h the short-term i n s t a b i l i t y measures f o r the 19 Maui r e s e r v o i r s (I d i d not have the necessary data f o r Opaeula 1, whose records ended i n 1971, t h r e e years before my v i s i t ) . In Step 4 of the m u l t i p l e r e g r e s s i o n a n a l y s i s , I regressed number of young on weight, c o m p e t i t i o n code, the f o u r p r i n c i p l e components with t h e i r squares and c r o s s p r o d u c t s , and the f o u r short-term measures of i n s t a b i l i t y with t h e i r sguares and c r o s s -products. The amount of v a r i a b i l i t y I c o u l d e x p l a i n shot up from 36.6%, the best I c o u l d do with j u s t the long-term measures, to 61.8%. But 16 of the 35 v a r i a b l e s f i g u r e d s i g n i f i c a n t l y i n the r e g r e s s i o n , making the r e l a t i o n s h i p i m p o s s i b l e t o i n t e r p r e t . Since I c o u l d not s i g n i f i c a n t l y i n c r e a s e the amount of e x p l a i n a b l e variance i n r e p r o d u c t i v e e f f o r t by adding short-term 220 Table 48 Short-term Measures Of I n s t a b i l i t y January Samples R e s e r v o i r | S t a t i s t i c s Computed On I n t e r v a l s Before I Sample Date | | 60 Day Mean | 60 Day C V . | i i 180 Day Mean J 180 Day C.V.J 21 | 3 6 . 98 i j | 0 . 6 8 8 | 2 2 . 84 } 0 . 8 7 3 | 22 | 4 6 . 3 7 | 0 . 4 9 4 | 3 1 . 3 6 | 0 . 6 0 5 | 25 | 6 3 . 25 J 0 . 2 2 8 | 3 8 . 1 3 | 0 . 5 6 7 | 31 J 6 2 . 97 | 0 . 2 4 8 | 4 4 . 3 8 | 0 . 4 8 3 | 32 | 6 4 . 5 5 I 0 . 4 2 2 | 3 5 . 4 3 I 0 . 9 0 6 | 33 | 5 5 . 12 I 0 . 4 6 6 | 2 6 . 6 6 | 1 . 0 9 2 | 35 | 5 5 . 38 I 0 . 3 4 3 J 4 2 . 1 1 | 0 . 4 8 3 | 40 | 4 8 . 3 5 I 0 . 5 5 5 | 2 6 . 1 9 | 1 . 0 0 3 J 41 | 4 5 . 25 I 0 . 4 6 2 | 2 3 . 6 1 | 1 . 0 5 9 | 42 | 8 0 . 6 7 | 0 . 1 6 3 J 6 6 . 7 7 ) 0 . 3 3 6 | 50 | 8 6 . 5 7 | 0 . 2 3 8 | 6 2 . 5 5 | 0 . 4 8 1 I 51 I 7 3 . 5 0 J 0 . 2 8 4 < 5 1 . 4 9 J 0 . 4 7 8 | 60 I 5 5 . 20 | 0 . 3 5 5 | 3 3 . 9 7 f 0 . 6 2 9 j 61 | 5 3 . 42 I 0 . 3 7 0 | 3 4 . 3 4 | 0 . 5 4 6 \ 80 | 7 1 . 8 2 I 0 . 3 1 9 | 4 4 . 3 2 | 0 . 6 0 7 J 81 | 5 8 . 4 5 I 0 . 4 3 6 | 2 8 . 6 7 | 0 . 9 6 0 | 84 | 5 1 . 8 7 | 0 . 5 8 1 | 3 4 . 6 7 | 0 . 6 8 3 | 90 | 8 9 . 6 5 I 0 . 1 8 3 | 6 8 . 9 9 \ 0 . 3 0 9 | 91 J 6 8 . 5 7 | 0 . 2 6 2 | 6 9 . 4 2 | 0 . 1 9 5 | - JL x _ _ 1 1 ... _.. i 221 measures (the best I could do was 29.7%), I d i d not take the a n a l y s i s of r e p r o d u c t i v e e f f o r t any f u r t h e r . t h e r e f o r e , I s e l e c t e d only the most dominant terms i n the r e g r e s s i o n run i n Step 4 f o r Step 5. Table 49 d i s p l a y s the d e t a i l e d r e s u l t s of Steps 4 and 5. When I used on l y the dominant terms from Step 4, I c o u l d e x p l a i n 46.4% of the v a r i a n c e i n number of young. The four most important terms were weight and the squares and c r o s s p r o d u c t s of the 60 and 180 day c o e f f i c i e n t s of v a r i a t i o n . To summarize: t o the extent t h a t f l u c t u a t i o n s i n water l e v e l had any impact at a l l on the r e p r o d u c t i v e t r a i t s of Gambusia, short-term f l u c t u a t i o n s i n the immediate past could e x p l a i n more of the v a r i a b i l i t y i n number of younq than f l u c t u a t i o n s over a p e r i o d long enough f o r e v o l u t i o n t o have taken pl a c e . N o n l i n e a r i n t e r a c t i o n s were more important than l i n e a r i n t e r a c t i o n s . The c o m p e t i t i o n code used i n the nested analyses of c o v a r i a n c e i n Chapter IV f i g u r e d s i g n i f i c a n t l y , but was r e l a t i v e l y unimportant when compared to any number of s h o r t -term and long-term measures of i n s t a b i l i t y . The c o n d i t i o n f a c t o r s of the p o p u l a t i o n s from which the f i s h were drawn d i d not c o n t r i b u t e t o an e x p l a n a t i o n of v a r i a b i l i t y i n numbers of young. i i i D i s c u s s i o n By p r e s e n t i n g a d e t a i l e d a n a l y s i s of the f l u c t u a t i o n s of 20 d i f f e r e n t r e s e r v o i r s , t h i s chapter has provided me with the m a t e r i a l t o make three main p o i n t s . The f i r s t , and the most important i n terms of l o g i c , emphasizes the importance of using 222 Table 49 D e t a i l s Of Steps 4 And 5 Of The M u l t i p l e Regression A n a l y s i s 1. Step 4 N= 953 R 2 = 0.618, Dependent V a r i a b l e = Number Of Young V a r i a b l e 1- +_ { C o e f f i c i e n t | F I Prob | Constant J 345. 47 | ] Weight ! 77. 81 | 136. 97 I o . 0000 1 Competition Code | -64. 39 j 104. 14 I o . 0000 j PC 2 | 88. 60 | 126. 22 I o. 0000 | PC 3 I 193. 06 | 174. 66 I o. 0000 | PC 4 | -199. 72 | 159. 96 i o . 0000 | PC 12 I -81. 60 j 137. 21 I o. 0000 | PC 2 2 I -176. 07 | 193. 03 I o. 0000 J PC 3 2 | 263. 78 \ 243. 47 I o. 0000 | PC4 2 i 519. 10 | 220. 00 I o . 0000 f PCTxpC2 | 255. 12 | 114. 42 1 o. 0000 | PC3xpC4 J 240. 28 | 78. 49 1 o . 0000 | 60 Day CV 2 j 3750. 85 | 278. 13 1 o. 0000 j 180 Day CV 2 } 1406. 22 | 427. 68 | 0. 0000 | 60 Day Mean X 60 Day CV \ -15. 44 j 136. 48 1 o . 0000 | 60 Day Mean X 180 Day CV I 2. 63 | 38. 18 1 o. 0000 J 60 Day CVx 180 Day CV | -4861. 76 | 345. 93 I o. 0000 | i - . J . J 2. Step 5 N =953, R 2= 0.464, Dependent V a r i a b l e = Number Of Young x_ , Constant Weight 60 Day CV 2 180 Day CV 2 60 Day CV X 180 Day CV -1.7 69.81 1224.45 554.64 -1651.77 109.39 213.48 307.63 250.39 0.0000 0.0000 0.0000 0.000 0 223 data to avoid c i r c u l a r arguments. Whenever an e v o l u t i o n a r y b i o l o g i s t i n v e s t i g a t e s an h y p o t h e t i c a l r e l a t i o n s h i p between an environmental p a t t e r n and the b i o l o g i c a l t r a i t s of organisms, he must measure both the p a t t e r n and the t r a i t s . Not measuring the environmental p a t t e r n s does not make c i r c u l a r i t y i n e v i t a b l e , but i t does make c i r c u l a r i t y much e a s i e r to f a l l i n t o . By i n h e r i t i n g the r e s e r v o i r water l e v e l records from two sugar p l a n t a t i o n s , I have measured environmental f l u c t u a t i o n s independently of the r e p r o d u c t i v e t r a i t s of the f i s h l i v i n g i n the r e s e r v o i r s . As one important s i d e e f f e c t , I have a l s o e s t a b l i s h e d that the r e s e r v o i r s I c a l l e d " f l u c t u a t i n g " d i d indeed f l u c t u a t e , and f l u c t u a t e d so much more markedly than the r e s e r v o i r s I c a l l e d " s t a b l e " t h a t the s t a b l e - f l u c t u a t i n g d i s t i n c t i o n upon which t h i s t h e s i s i s based was c l e a r and i n c o n t e s t a b l e . Secondly, t h e r e are many d i f f e r e n t k i n d s of environmental i n s t a b i l i t y . I can t h i n k of no reason to suppose that they a l l have the same impact, and many reasons to argue t h a t i t i s important to d i s t i n g u i s h among the d i f f e r e n t kinds of i n s t a b i l i t y i n attempting to understand t h e i r e f f e c t s . The s t a b l e - f l u c t u a t i n g d i s t i n c t i o n i s r e a l , but s i m p l i s t i c . An adeguate b i o l o g i c a l c h a r a c t e r i z a t i o n of f l u c t u a t i n g environments c o u l d be achieved by l o c a t i n g the environment i n q u e s t i o n i n a space spanned by measures of frequency ( = p e r i o d i c i t y ) , power ( = r e l a t i v e dominance of f l u c t u a t i o n s a t t h a t f r e q u e n c y ) , and p r e d i c t a b i l i t y (~the r a t i o of power i n s i g n i f i c a n t peaks to background noise) f o r each environmental v a r i a b l e f e l t t o have a s i g n i f i c a n t impact on the p o p u l a t i o n under study. I expect 224 e v o l u t i o n a r y q u e s t i o n s about the impact of f l u c t u a t i n g environments to be answered at t h i s , or an even f i n e r , l e v e l of r e s o l u t i o n , r a t h e r than through broad arguments about f l u c t u a t i n g environments i n g e n e r a l . T h i r d l y , the data I presented i n t h i s chapter (together with the r e s u l t s of Chapters I I I and IV) have f o r c e d me to d i s c a r d my preconception that most of the v a r i a b i l i t y observed i n l i f e h i s t o r y t r a i t s i n the f i e l d has evolved and r e p r e s e n t s a r i g i d l y encoded g e n e t i c response to e v o l u t i o n a r y c h a l l e n g e s . The r e s u l t i n Chapter V that s u r p r i s e d me most was the do u b l i n g of e x p l a i n a b l e v a r i a n c e i n number of young when I i n c l u d e d short-term measures o f i n s t a b i l i t y i n the m u l t i p l e r e g r e s s i o n . Both long-term measures (the fou r p r i n c i p l e components) and short-term measures (the 60 and 180 day c o e f f i c i e n t s of v a r i a t i o n ) f i g u r e d s i g n i f i c a n t l y i n accounting f o r v a r i a b i l i t y i n numbers of young. I see no reason t o d i s c a r d completely the idea t h a t some of the v a r i a b i l i t y I observed i n l i f e h i s t o r y t r a i t s r e p resented an e v o l u t i o n a r y response t o d i f f e r e n t environments. But i t i s a l s o c e r t a i n that the major p a r t of the o v e r a l l v a r i a b i l i t y i n numbers of young was generated by p l a s t i c developmental and p h y s i o l o g i c a l adjustments by the f i s h t o short-term f l u c t u a t i o n s . Such responses can be adap t i v e , and most probably a r e , but they may not represent e v o l u t i o n a r y changes among p o p u l a t i o n s l i v i n g i n d i f f e r e n t environments. They do repr e s e n t the c a p a c i t y of a s i n g l e p o p u l a t i o n to handle the c h a l l e n g e s posed by many d i f f e r e n t s i t u a t i o n s without e v o l u t i o n a r y change. Thus they serve t o f u r t h e r uncouple the p o p u l a t i o n from the 225 environment. I regard developmental and p h y s i o l o g i c a l p l a s t i c i t y i n l i f e h i s t o r y t r a i t s , and g e n e t i c v a r i a b i l i t y i n progeny maturation times, as b u f f e r s a g a i n s t environmental v a g a r i e s t h a t have themselves evolved, but which make f u r t h e r e v o l u t i o n much l e s s necessary. They serve to maintain the constancy of the coadapted gene complex that c h a r a c t e r i z e s p o p u l a t i o n s of s e x u a l organisms by minimizing the need f o r g e n e t i c changes. In H o l l i n g ' s s t r a t e g i c j a r g o n , they serve t o broaden the domain of r e s i l i e n c e of the p o p u l a t i o n , w i t h i n which i n d i v i d u a l organisms can f u n c t i o n without having t o s u f f e r heavy s e l e c t i o n l o a d s on t h e i r progeny. 5_. Summary Through a d e t a i l e d a n a l y s i s of r e s e r v o i r f l u c t u a t i o n p a t t e r n s , I t r i e d to e s t a b l i s h s uggestive c o r r e l a t i o n s between the d e t a i l s of r e s e r v o i r f l u c t u a t i o n s and the r e p r o d u c t i v e t r a i t s of Gambusia l i v i n g i n those r e s e r v o i r s . I measured long-term f l u c t u a t i o n s by s e r i a l a u t o c o r r e l a t i o n , range and v a r i a n c e f u n c t i o n s , s p e c t r a l d e n s i t y p l o t s , volume, mean percent f u l l , average weekly and y e a r l y ranges, and average d a i l y r a t e of change. I reduced these f u n c t i o n s to a set of 30 numbers f o r each of the 20 f l u c t u a t i n g r e s e r v o i r s analyzed, and d i d a p r i n c i p l e components a n a l y s i s on them. The f i r s t 4 p r i n c i p l e components accounted f o r 85.4% of the v a r i a b i l i t y i n f l u c t u a t i o n measures. I then added the f i r s t 4 p r i n c i p l e components t o the f i s h r e cords, and undertook a stepwise m u l t i p l e r e g r e s s i o n a n a l y s i s using weight, competition code, the f i r s t 4 p r i n c i p l e 226 components, and t h e i r squares and c r o s s p r o d u c t s as the set of independent v a r i a b l e s . At best, I c o u l d e x p l a i n 36.6% of the v a r i a b i l i t y i n number of young, and 23.4% of the v a r i a b i l i t y i n r e p r o d u c t i v e e f f o r t . I then added 4 measures of short-term i n s t a b i l i t y : the mean and c o e f f i c i e n t s of v a r i a t i o n i n water l e v e l 60 and 180 days p r i o r to the date t h a t the c o l l e c t i o n s were made. The e x p l a i n a b l e v a r i a b i l i t y i n number of young shot up to 61.8%. I co u l d e x p l a i n 46.4% of the v a r i a b i l i t y i n number of young using only weight and the squares and c r o s s p r o d u c t of the,60 and 180 day c o e f f i c i e n t s of v a r i a t i o n . I concluded t h a t , f i r s t , d e t a i l e d analyses of environmental f l u c t u a t i o n s are e s s e n t i a l to e v o l u t i o n a r y arguments because they a v o i d c i r c u l a r i t y and because t h e r e are, demonstrably, many g u i t e d i f f e r e n t kinds of i n s t a b i l i t y . Secondly, both long-term and short-term f l u c t u a t i o n s f i g u r e d s i g n i f i c a n t l y i n e x p l a i n i n g v a r i a b i l i t y i n numbers of young. I t h e r e f o r e argued t h a t much of the a d a p t a t i o n Gambusia e x h i b i t s i n i t s l i f e h i s t o r y t r a i t s i s contained i n the p l a s t i c i t y of i t s developmental and p h y s i o l o g i c a l responses to the environment. I t has a l s o undergone an adaptive r a d i a t i o n i n l i f e h i s t o r y t r a i t s i n environments c h a r a c t e r i z e d by d i f f e r e n t f l u c t u a t i o n p a t t e r n s , but i t s developmental p l a s t i c i t y has g r e a t l y reduced the amount of e v o l u t i o n a r y change necessary f o r i t t o p e r s i s t . 227 CHAPTER VI. LABORATORY RESULTS 1*. I n t r o d u c t i o n Ii* . Purpose Did Gambusia evolve i n Hawaii, or were the d i f f e r e n c e s observed i n the f i e l d phenotypic responses of g e n e t i c a l l y s i m i l a r s t o c k s ? To measure the g e n e t i c component u n d e r l y i n g the d i v e r s i t y of l i f e h i s t o r y p a t t e r n s observed i n the f i e l d , I brought f i s h i n t o the l a b and r a i s e d them under constant c o n d i t i o n s of temperature, food, and d e n s i t y . To e s t i m a t e the range of developmental p l a s t i c i t y i n l i f e h i s t o r y t r a i t s , I a l s o r a i s e d f i s h under d i f f e r e n t temperature and food c o n d i t i o n s because I wanted to see i f I could produce p o p u l a t i o n s of Gambusia i n the l a b , d e r i v e d from a s i n g l e r e s e r v o i r , t h a t d i f f e r e d as much i n t h e i r l i f e h i s t o r y t r a i t s as the two s t o c k s that d i f f e r e d most i n the f i e l d . I d e a l l y , I would have done the experiments on both Gambusia and P o e c i l i a from a l l s t a b l e r e s e r v o i r s and an equal number of u n s t a b l e r e s e r v o i r s . In p r a c t i c e , due to l i m i t a t i o n s on number of a q u a r i a , I used only Gambusia from two s t a b l e and two u n s t a b l e r e s e r v o i r s . I d e a l l y , I would have r a i s e d the f i s h throuqh two complete generations to check f o r maternal e f f e c t s . In p r a c t i c e , I found t h a t Gambusia s u f f e r e d high a b o r t i o n r a t e s under my l a b o r a t o r y c o n d i t i o n s , and I was unable t o gather enough l a b - r a i s e d young from l a b - r a i s e d females t o do any ) 228 experiments on the second g e n e r a t i o n . Because I wanted i n s i g h t i n t o the d e t a i l e d impact of water l e v e l f l u c t u a t i o n s on Gambusia p o p u l a t i o n s , I a l s o d i d an experiment on the e f f e c t s of crowding and s t a r v a t i o n on p o p u l a t i o n s t r u c t u r e . I then compared these l a b o r a t o r y r e s u l t s t o f i e l d o b s e r v a t i o n s on long-term drawdowns, and c o n t r a s t e d them with the e f f e c t s of r a p i d , short-term f l u c t u a t i o n s . Thus the l a b o r a t o r y work had three g o a l s : (1) to measure the g e n e t i c component of the d i f f e r e n c e s i n l i f e h i s t o r y t r a i t s observed i n the f i e l d , (2) to measure the scope of developmental response to d i f f e r e n t food and temperature treatments, and (3) t o measure the impact of crowding and s t a r v a t i o n on p o p u l a t i o n s t r u c t u r e . I k i . A Warning To Those Who Would Work On Gambusia I Gathered l i v e f i s h i n the f i e l d on both the January and the November 1974 f i e l d t r i p s to Hawaii. In January, I shipped both P o e c i l i a and Gambusia from R e s e r v o i r 25 on Maui, Gambusia from Twin R e s e r v o i r on Hawaii, and P o e c i l i a from Camp 17 R e s e r v o i r on Hawaii to Vancouver. I then experienced numerous d i f f i c u l t i e s t r y i n g t o r a i s e Gambusia i n the l a b . An attempt to r e a r i n d i v i d u a l s i n j a r s f a i l e d . An attempt to estimate h e r i t a b i l i t i e s of l i f e h i s t o r y t r a i t s f a i l e d when a l l the l a b -r a i s e d females aborted t h e i r f i r s t broods. Disease reduced the sample s i z e s on my f i r s t attempt to rear Gambusia and P o e c i l i a through t h e i r e n t i r e l i f e c y c l e s , and I got l i t t l e or no u s e f u l data from that experiment. The only r e l i a b l e i n f o r m a t i o n I got from the f i r s t 8 months 229 of l a b o r a t o r y work c o n s i s t e d of estimates of the age and s i z e a t maturity of male Gambusia from R e s e r v o i r 25 and Twin R e s e r v o i r . By October my s t o c k s were too depleted to generate enough young f o r new experiments, and I returned to Hawaii i n November 1974 t o gather more f i s h . I shipped Gambusia from R e s e r v o i r s 81 and 90 on Maui and Twin and Kay R e s e r v o i r s on Hawaii to Vancouver duri n g the l a s t week i n November. They provided the young born i n the l a b which I used i n most of the experiments reported i n t h i s chapter. 2^ Methods 2a.. C o l l e c t i o n ^ S h i p p i n g ^ And Lab C u l t u r e I c o l l e c t e d l i v e f i s h using the same s e i n i n g techniques d e s c r i b e d i n Chapter I I I . From each r e s e r v o i r , I s e l e c t e d 30 to 40 l a r g e , pregnant females and 10 to 20 a d u l t males and placed them i n 5 to 10 cm of r e s e r v o i r water i n two l a r g e p l a s t i c garbage bags (about 20 to 30 f i s h / b a g ) . I then placed the bags i n styrofoam p i c n i c c o o l e r s , aerated the water with i n d u s t r i a l oxygen from a welding r i g , f i l l e d the bags as f u l l of oxygen as I c o u l d , then s e a l e d the bags and the styrofoam c o o l e r s . The f i s h were shipped by a i r to Vancouver, and were u s u a l l y unpacked and i n t o l a b o r a t o r y a g u a r i a w i t h i n 24 hrs of t h e i r c o l l e c t i o n i n Hawaii, There was l i t t l e m o r t a l i t y due to s h i p p i n g ; i n a few cases where f i s h d i d d i e , I a t t r i b u t e d the m o r t a l i t y t o rough hand l i n g at the time of c o l l e c t i o n . In Vancouver, I had a v a i l a b l e a c o n t r o l l e d temperature room, which I maintained at 27°C, and a water t a b l e through which I could pump r e f r i g e r a t e d water, which I maintained at 17°C. Temperatures i n both the room and the water t a b l e f l u c t u a t e d around t h e i r means with amplitudes of ± 0.5-1.0°C. F i g . 30 d i s p l a y s the a c t u a l temperatures I recorded once a day during the course of the experiment. I used a g u a r i a with bottom f i l t e r s , and placed a mixture of coarse i n d u s t r i a l sand and o y s t e r s h e l l s (mixed at about 10:1) 2-3 cm deep over the bottom f i l t e r s . In a l l a g u a r i a , I used aged, d e c h l o r i n a t e d water t r e a t e d with Black Water Tonic (0.25 cup/30 g a l l o n s ) and A g u a r i s o l (an a n t i f u n g a l agent, 20 drops/30 g a l l o n s ) . Before p u t t i n g any f i s h i n the a g u a r i a , I f i l l e d them with water and l e t them s i t f o r n e a r l y 4 months (October 1973-January 1974). The i n c i d e n c e of d i s e a s e i n my l a b o r a t o r y d e c l i n e d as the experiments progressed. I a t t r i b u t e d the d e c l i n e to continuous treatments with low l e v e l s of Black Water Ton i c and A g u a r i s o l , and to my p r a c t i c e of d i s c a r d i n g the f i s h , water, and sand from a l l i n f e c t e d aguaria w e l l away from the l a b , then s t e r i l i z i n g the aguaria by soaking them completely under water i n a s o l u t i o n of P i n e - S o l and soap. P r i o r to each experiment, I gathered the aged water and sand from a l l a g u a r i a to be used i n the experiment and pooled them s e p a r a t e l y i n two l a r g e c o n t a i n e r s . I washed the sand thoroughly, d i s t r i b u t e d i t among the a q u a r i a , placed the a g u a r i a i n p o s i t i o n s chosen at random, and f i l l e d them a l l from the common pool of aged water. As the aquaria aged, algae grew on the s i d e s and bottom. Once every week or two I scraped the growth of algae o f f the f r o n t of the a q u a r i a so that I c o u l d see 231 FIGURE 30 Temperature C o n t r o l Data and Duration Of Experiments F i g . 34A presents the a c t u a l temperatures recorded once a day i n the high {27°C) and low (17°C) temperature areas. Temperatures were f a i r l y w e l l c o n t r o l l e d , with o c c a s i o n a l f l u c t u a t i o n s of ± 1-2°C. F i g . 34B d i s p l a y s the d u r a t i o n of the experiments run between December, 1974 and June, 1975. 30 A. TEMPERATURE CONTROL DATA w 2 5 T ce | 20 + U J 15 4 10 A A A DEC JAN FEB MAR APR MAY JUNE B. DURATION OE EXPERIMENTS RESERVOIRS 81 AND 90: LONGTERM 81&90 GROWTH HF 3 : • KAY RESERVOIR: LONGTERM -O -a TWIN&KAY:GROWTH HF • H 90 GROWTH HF • : • KAY GROWTH LF B — • TWIN RESERVOIR: LONGTERM • Q TEXAS GROWTH LF&HF • : ••—• KAY GROWTH HF 90 GROWTH LF • • • • TWIN GROWTH LF • • DEC JAN FEB MAR APR MAY JUNE O-l to 233 the f i s h , but I made no attempt to c o n t r o l the algae growing on the bottom and the other three s i d e s . Once a week I added aged, t r e a t e d water t o b r i n g a l l a g u a r i a up to the same water l e v e l . E v a p o r a t i o n l o s s e s never exceeded 2 cm/week. A l l a q u a r i a were covered with c l e a r p l e x i g l a s sheets to reduce e v a p o r a t i o n and keep f i s h from jumping out. In a l l experiments, I randomized the p o s i t i o n s of r e p l i c a t e s w i t h i n the s h e l f space set a s i d e f o r each experiment. A l l f i s h were fed T e t r a - H l n f l a k e s , e i t h e r whole f l a k e s f o r a d u l t s , or f l a k e s ground to powder i n a blender f o r s m a l l e r f i s h . I used f l o u r e s c e n t overhead l i g h t s on a 12 hr l i g h t : 12 hr dark c y c l e . The aguaria f o r the long-term experiment were on lower shelves or i n the water t a b l e . I mounted banks of f l o u r e s c e n t l i g h t s over them, a l l the same d i s t a n c e from the tops of the a q u a r i a . The aquaria f o r the growth, drawdown, and male maturation experiments were on top shelves d i r e c t l y under the overhead l i g h t s . 2b. S i z e At B i r t h To document s i z e a t b i r t h , I i s o l a t e d f i e l d - c a u g h t pregnant females i n p o e c i l i i d breeding t r a p s and f e d them once a day u n t i l they gave b i r t h , I then gathered the young and preserved about 1/3 to 1/2 of each brood i n 10% f o r m a l i n , r e s e r v i n g the r e s t f o r l a t e r experiments. The preserved newborn young were l a t e r measured (standard l e n g t h s ) , d r i e d at 100°C f o r 1 h r , and weighed to the nearest 0.1 mg. 234 2c.. S i z e At 8 Days I placed the l i v e newborn young from each r e s e r v o i r i n separate 20 l i t e r a q u a r ia at d e n s i t i e s t h a t v a r i e d from 10 to 60 young per aquarium. I accumulated young i n t h i s manner f o r up t o 7 days, then computed the mean b i r t h date of the young i n each aguarium as the weighted average of t h e i r b i r t h dates. A f t e r g a t h e r i n g young f o r a week, I continued to feed them generously once a day f o r 8 more days before d i s t r i b u t i n g them among ag u a r i a f o r v a r i o u s experiments. I d i d t h i s t o reduce m o r t a l i t y l o s s e s d u r i n g the experiments, reasoning that most of the weak and d e f e c t i v e f i s h would d i e w i t h i n the f i r s t 8 days. In p r a c t i c e , most of the young from the f i e l d - c a u g h t females were healthy, and few f i s h d i e d . When the young f i s h were an average of 8 days o l d (at the time t h a t I d i s t r i b u t e d them among the v a r i o u s experiments) I took a sample of 15 to 40 e i g h t day o l d young and preserved them to document the s i z e at which f i s h s t a r t e d the experiments. These samples were l a t e r weighed and measured i n the same f a s h i o n as the newborn young. 2d.. Growth Experiments For the growth experiments, I d i v i d e d the 8 day o l d young at random i n t o r e p l i c a t e s of 10 f i s h , placed the f i s h i n 13.25 l i t e r a q u a r i a , fed them qenerously t h a t day and the next, then fed them weighed food p o r t i o n s f o r the next 25 days. At the end of 25 days of c o n t r o l l e d f e e d i n g , I k i l l e d and preserved the f i s h , which were then an average of 34 days o l d . They were measured, d r i e d , and weighed l a t e r . F i g . 31a presents the 235 f e e d i n g schedule f o r the growth experiments. I used both high and low food treatments, but I was not able to get enough f i s h from R e s e r v o i r 81 f o r the low food treatments- F i s h g e t t i n g high food treatments were f e d every day; f i s h g e t t i n g low food treatments were f e d every other day. 2e. Long-term Experiments For the long-term experiments, I gathered and a s s o r t e d groups of 15 e i g h t day o l d young among treatments l o c a t e d a t random over the a v a i l a b l e s h e l f space. I was able to r e a r f i s h from R e s e r v o i r s 81 and 90 a t both high and low food l e v e l s and high and low temperatures f o r 207 days. I reared f i s h from Kay R e s e r v o i r at high and low food l e v e l s , at 27°C only, f o r 148 days. I had d i f f i c u l t y with my stock females from Twin R e s e r v o i r ( s t a b l e ) , which got pregnant l e s s f r e q u e n t l y than the o t h e r s . In consequence, an adequate supply of young was l a t e i n coming, and I c o u l d only r e a r one r e p l i c a t e a t high food and 27°C f o r 74 days. I checked each aquarium at l e a s t once every three days, f r e q u e n t l y more o f t e n . On the day that a male matured, I removed him, measured h i s standard l e n g t h , and returned him t o the aquarium. I judged a male mature when h i s gonopodium changed from a narrow blade to a t r a n s l u c e n t s p i k e with a s e t of c h a r a c t e r i s t i c hooks on i t s t i p . The f i n a l change i n the gonopodium, from a s t r a i g h t t h i n blade with no v i s i b l e hooks to the mature form, took p l a c e w i t h i n a p e r i o d of 24-48 hours. I estimated my accuracy a t measuring age at maturation i n males a t ± 1-2 days. 236 FIGURE 31 Experimental Food Regimes The growth experiments ( F i g . 35A) were s t a r t e d when the f i s h were 10 days o l d . Food l e v e l s s t a r t e d a t 10 mg/day, and were incremented by 5 mg/day every f i f t h day i n the high-food r e p l i c a t e s , and by 5 mg/day every t e n t h day i n the low-food r e p l i c a t e s . The f i s h on high-food r a t i o n s were f e d once a day; the f i s h on low-food r a t i o n s were f e d once every other day. In the long-term experiments ( F i g . 35B), food l e v e l s were incremented by 5 mg/day every f i f t h day u n t i l the f i s h were 50 days o l d , then every t e n t h day u n t i l the f i s h were 150 days o l d . A f t e r that I f e d them a constant amount: 100 mg/aguarium/day. The f i s h on high-food r a t i o n s were f e d once a day; the f i s h on low-food r a t i o n s were f e d once every other day. 238 When a p r e g n a n t f e m a l e was n e a r t e r m , I i s o l a t e d h e r i n a b r e e d i n g t r a p i n a s e p a r a t e a g u a r i u m a n d f e d h e r g e n e r o u s l y o n c e a d a y u n t i l s h e g a v e b i r t h . When y o u n g a p p e a r e d i n t h e b r e e d i n g t r a p , I k i l l e d a n d p r e s e r v e d b o t h m o t h e r a n d y o u n g a n d r e c o r d e d t h e d a t e a n d number o f y o u n g . L a t e r , t h e f e m a l e was m e a s u r e d a n d d i s s e c t e d , t h e n u m b e r o f e m b r y o s i n s i d e w e r e c o u n t e d , a n d m o t h e r a n d y o u n g w e r e d r i e d a n d w e i g h e d . F i g . 31b p r e s e n t s t h e f e e d i n g s c h e d u l e f o r t h e l o n g - t e r m e x p e r i m e n t s . I d i d n o t a d j u s t f o o d l e v e l s t o a c c o u n t f o r c h a n g e s i n d e n s i t y due t o m o r t a l i t y o r r e m o v a l o f m a t u r e f e m a l e s . E a c h r e p l i c a t e r e c e i v e d i t s a s s i g n e d f o o d l e v e l n o m a t t e r how many f i s h were r e m a i n i n g i n i t . T h i s p r a c t i c e o n l y h a d a s i g n i f i c a n t e f f e c t on t h e l o w f o o d r e p l i c a t e s f o r Kay R e s e r v o i r , w h i c h s u f f e r e d h e a v y m o r t a l i t i e s i n t h e f i r s t 60 d a y s o f t h e e x p e r i m e n t . I n a l l o t h e r r e p l i c a t e s , m o r t a l i t i e s were l o w (1 o r 2 f i s h d i e d p e r t a n k ) , a n d t h e o n l y d e n s i t y c h a n g e s w e r e c a u s e d b y r e m o v a l o f f e m a l e s a s t h e y m a t u r e d . I b e g a n t h e e x p e r i m e n t on 10 D e c e m b e r 1974 a n d c o n t i n u e d i t f o r 197 d a y s , t o 26 J u n e 1975. At t h a t t i m e o n l y t h e two r e p l i c a t e s o f t h e h i g h t e m p e r a t u r e , h i g h f o o d t r e a t m e n t f o r R e s e r v o i r 81 w e r e c o m p l e t e , w i t h a l l f i s h h a v i n g r e a c h e d m a t u r i t y . F o r t h e r e m a i n i n g r e p l i c a t e s my r e s u l t s a r e i n c o m p l e t e . 2 f . E f f e c t s O f Drawdowns To a s s e s s t h e i m p a c t o f c r o w d i n g a n d l o w f o o d l e v e l s on p o p u l a t i o n s t r u c t u r e , I t o o k two 40 1 a q u a r i a a n d p l a c e d 69 f i s h 239 i n each, having matched the s i z e s and sexes of the f i s h so t h a t the two a g u a r i a contained p o p u l a t i o n s of f i s h with i d e n t i c a l s i z e and sex d i s t r i b u t i o n s . I then l e t the water l e v e l drop s l o w l y , at the same r a t e i n both a q u a r i a , from a depth of 17 cm at the s t a r t of the experiment to a depth of 8 cm at the end. The food r a t i o n was 50 mg/aguarium every other day. The experiment ran 36 days, from 24 A p r i l 1975 t o 30 May 1975. At the end of the experiment I c o l l e c t e d the f i s h and measured them. I intended t h i s experiment t o model p o p u l a t i o n processes i n the f i e l d d u r i n g the summer i n f l u c t u a t i n g r e s e r v o i r s , when r e s e r v o i r s o c c a s i o n a l l y drop to 0-10% f u l l and remain low f o r 1-3 months. I checked the impact of r a p i d water l e v e l f l u c t u a t i o n i n the f i e l d at R e s e r v o i r 50 on 5 December 1974. I sampled i n the r e s e r v o i r and i n the o u t l e t channel at 11:30 am, when the r e s e r v o i r was 1.8 m deep, and at 2:00 pm, when i t had f a l l e n as low as i t could go and only a s m a l l pool of water about 10-30 cm deep was l e f t . A l l f i s h were preserved and measured l a t e r . 3_. R e s u l t s 3a. S i z e At B i r t h And 8 Days Table 50a pr e s e n t s the r e s u l t s of an a n a l y s i s of v a r i a n c e on b i r t h weights. Young were born a t s i g n i f i c a n t l y d i f f e r e n t average s i z e s i n each r e s e r v o i r , but the v a r i a b i l i t y among r e s e r v o i r s was so great that the s t a b l e - f l u c t u a t i n g d i f f e r e n c e was i n s i g n i f i c a n t . Table 50b presents a s i m i l a r a n a l y s i s of 240 l a ^ l e 50 A n a l y s i s Of Variance: Heights Of Newborn Young I. Lab Data - T -I Sample I I I Mean »gt| Prob 1. Hawaiian F i s h Only S t a b l e F l u c t u a t i n g 129 244 1.536 1.445 0.0829 >0.75 Twin B e s e r v o i r Kay B e s e r v o i r B e s e r v o i r 81 B e s e r v o i r 90 96 33 112 132 1.741 0.939 1.372 1.506 101.2947 I 0.0001 Hawaiian + Texan F i s h 1 _, -+-Hawaii Texas 373 66 1.476 1. 153 0.6949 >0. 25 Twin B e s e r v o i r Kay B e s e r v o i r B e s e r v o i r 81 B e s e r v o i r 90 Armand Bayou 96 33 112 132 66 1.741 0. 939 1.372 1.506 1. 153 108.0658 <0.0001 * Denominator Mean Square = R e s e r v o i r s ** Denominator Mean Square = I n d i v i d u a l F i s h 241 Table 5! A n a l y s i s Of Var i a n c e : Heights Of Ea r l y - e y e d Young I I . F i e l d Data Sample n j Mean Wgt| I 1. January, 1974 Sample Only -+ 1 \-Prob S t a b l e F l u c t u a t i n g I 101 13 i 1.784 1.662 0.0557* Twin R e s e r v o i r Kay R e s e r v o i r R e s e r v o i r 81 R e s e r v o i r 90 101 6 7 1.784 1. 133 2. 114 | 30.1211** I >0.75 <0.0001 2. November, 1974 Sample Only S t a b l e F l u c t u a t i n g 51 7 1.608 I 1.600 | 0.0002* Twin R e s e r v o i r Kay R e s e r v o i r R e s e r v o i r 81 Re s e r v o i r 90 42 | 9 I 7 I 1.533 1.956 1.600 I I 16.6086** I >0.95 0.0002 3. January + S t a b l e F l u c t u a t i n g I 152 20 November Samples + 1.725 1.640 t 0.0561* >0,75 Twin R e s e r v o i r Kay R e s e r v o i r R e s e r v o i r 81 R e s e r v o i r 90 I 42 110 13 7 I I 1.533 1.789 1. 385 2. 114 | 22.8019** t January + November + Texas Samples j. + 1- •+-<0.0001 Hawaii Texas 172 68 1.715 1. 285 3.9536* >0. 10 Twin R e s e r v o i r Kay R e s e r v o i r R e s e r v o i r 81 R e s e r v o i r 90 Armand Bayou 42 110 13 7 68 1. 583 1.789 1.385 2. 114 1. 285 27. 5517 <0.0001 * Denominator Mean Square = R e s e r v o i r s ** Denominator Mean Square = I n d i v i d u a l F i s h 242 Table 52 A n a l y s i s Of Var i a n c e : Weights Of 8 Day Old F i s h Sample i I | Mean Wgtj Prob S t a b l e F l u c t u a t i n g Twin R e s e r v o i r Kay R e s e r v o i r R e s e r v o i r 81 R e s e r v o i r 90 Hawaii Texas Twin R e s e r v o i r Kay R e s e r v o i r R e s e r v o i r 81 R e s e r v o i r 9 0 Armand Bayou 1. Hawaiian F i s h Only + (-79 93 2.800 | 0.5761* | 2.214 | j 36 43 23 70 3.333 2. 353 3. 239 1.877 I ! 2. Hawaiian + Texas F i s h , _ 172 17 2.483 | 0.0735* 2.135 | 1 36 43 23 70 17 3.333 2. 353 3. 239 1.877 2. 135 I | 29.2419** >0.50 J 28.0578**| <0.0001 I I >0.75 <0.0001 * Denominator Mean Sguare = R e s e r v o i r s ** Denominator Mean Sguare = I n d i v i d u a l F i s h 243 v a r i a n c e , i n c l u d i n g the Texas f i s h . Newborn Gambusia from Armand Bayou were s m a l l e r than newborn Gambusia from 3 of 4 Hawaiian r e s e r v o i r s , but the d i f f e r e n c e was not s i g n i f i c a n t . Table 51 d i s p l a y s s i m i l a r comparisons from the f i e l d data. Note t h a t i n the f i e l d data the v a r i a t i o n among r e s e r v o i r s again rendered the s t a b l e - f l u c t u a t i n g d i s t i n c t i o n i n s i g n i f i c a n t . S e v e r a l of the rankings were d i f f e r e n t i n the f i e l d than i n the l a b . In the f i e l d d ata, R e s e r v o i r 90 ranked h i g h e s t of a l l . In the l a b , i t ranked behind Twin. In the f i e l d data, Kay R e s e r v o i r e a r l y - e y e d embryos ranked second l a r g e s t i n January, and l a r g e s t i n November when there was no sample from R e s e r v o i r 90. In the l a b , Kay R e s e r v o i r newborn were the s m a l l e s t of the newborn from any r e s e r v o i r . Table 52 shows t h a t at 8 days, the young f i s h from Kay had grown r a p i d l y enough to outrank the young from R e s e r v o i r 90, but they were s t i l l s m a l l e r than 8 day o l d f i s h from R e s e r v o i r 81 or Twin. The Texas Gambusia grew s l o w l y , and by 8 days were s m a l l e r than Kay, Twin, or 81. I suspect the slow growth of the R e s e r v o i r 90 young d u r i n g the f i r s t 8 days of t h e i r l i f e was due to crowding. Because of the l a r g e number of young born to R e s e r v o i r 90 females, I was f o r c e d i n t o r e a r i n g them at higher d e n s i t i e s than f i s h from the other r e s e r v o i r s . When placed i n t o growth experiments at lower d e n s i t i e s , they recovered and outgrew the R e s e r v o i r 81 f i s h . 3b.. Growth Experiments Tables 53 and F i g u r e s 32 and 33 d i s p l a y the r e s u l t s of the growth experiments. F i s h from Kay, Twin, and R e s e r v o i r 90 grew 244 T a b l e 53 G r o w t h E x p e r i m e n t s : E f f e c t s O f F o o d a n a l y s i s O f V a r i a n c e : W e i g h t s O f 34 Day O l d F i s h H a w a i i a n F i s h O n l y S a m p l e -+ Number R p l c t s Mean Wgt (mg) P r o b S t a b l e F l u c t u a t i n g 99 127 11 13 6 . 9 7 6 5 . 2 2 4 3.9683 05<p<.10 +-T w i n R e s e r v o i r K a y R e s e r v o i r R e s e r v o i r 81 R e s e r v o i r 90 43 56 30 97 5 6 3 10 8 . 7 6 5 5 . 6 0 2 6 . 2 9 3 4 . 8 9 7 3.3423 .05<p<. 10 T w i n R e s e r v o i r H i g h F o o d l o w F o o d Kay R e s e r v o i r H i g h F o o d Low F o o d R e s e r v o i r 81 H i g h F o o d Low F o o d R e s e r v o i r 90 H i g h F o o d Low F o o d 25 18 28 28 30 58 39 3 2 3 3 5 5 1 1 . 2 5 2 5 . 3 1 1 7 . 8 8 9 3 . 3 1 4 6 . 2 8 3 6 . 4 8 8 2 . 5 3 1 7 , 9 6 5 5 < 0 . 0 0 5 * D e n o m i n a t o r Mean S q u a r e = R e p l i c a t e s 245 FIGURE 32 Growth Experiments: Hawaiian Gambusia Legend: S o l i d l i n e s = high food treatments, dashed l i n e s = low food treatments ( c f . F i g . 35), v e r t i c a l bars = 95% c o n f i d e n c e l i m i t s . F i s h from a l l f o u r r e s e r v o i r s d i f f e r e d s i g n i f i c a n t l y from each other i n b i r t h weights. During the peri o d of c o n t r o l l e d f e e d i n g (from 10 to 34 d a y s ) , f i s h from Kay, Twin, and R e s e r v o i r 90 grew e q u a l l y r a p i d l y . Any d i f f e r e n c e s among them were due to d i f f e r e n c e s i n b i r t h weights or weights at 8 days. F i s h from R e s e r v o i r 81 grew more s l o w l y than any of the others on the high-food treatment. C o n c l u s i o n s : There was s i g n i f i c a n t v a r i a b i l i t y among st o c k s from d i f f e r e n t r e s e r v o i r s i n (1) weight at b i r t h and (2) growth r a t e s at c o n t r o l l e d d e n s i t y , temperature, and food l e v e l s . (3) Gambusia have a very p l a s t i c growth response to changes i n food l e v e l s e a r l y i n l i f e . (4) F i s h from one f l u c t u a t i n g r e s e r v o i r , 90, were more s i m i l a r to f i s h from two s t a b l e r e s e r v o i r s , Twin and Kay, than t o f i s h from the other f l u c t u a t i n g r e s e r v o i r , 81. 247 FIGURE 33 Growth Experiments: Texan Gambusia Legend: S o l i d l i n e s = high food treatments, dashed l i n e s = low food treatments (cf. F i g . , 35), v e r t i c a l bars = 35% c o n f i d e n c e l i m i t s . Texan f i s h were s m a l l e r at b i r t h than the f i s h from 3 of 4 Hawaiian s t o c k s r a i s e d i n the l a b o r a t o r y ( b i r t h weights of f i s h from Kay R e s e r v o i r were l o w e r ) , and they grew more s l o w l y than 3 of 4 Hawaiian s t o c k s . T h e i r growth r a t e s were p r a c t i c a l l y i d e n t i c a l to f i s h from R e s e r v o i r 81. Co n c l u s i o n s : the b i r t h weights and growth r a t e s of the a n c e s t r a l Texan stoc k s f e l l w i t h i n the range of v a r i a b i l i t y i n those t r a i t s t h a t has evolved i n the Hawaiian s t o c k s . The Hawaiian f i s h tend t o be l a r g e r at b i r t h and to grow more r a p i d l y . 248 GROWTH EXPERIMENTS ' TEXAS 2.5 j 5.1.9-. ' -1 • 3 t CD y j . 7 -.5 TEX 0 8 34 DAYS OLD 249 e q u a l l y r a p i d l y u n d e r h i g h f o o d c o n d i t i o n s , a n d any d i f f e r e n c e s among them i n w e i g h t m e a s u r e d a t t h e e n d o f t h e e x p e r i m e n t were d u e t o d i f f e r e n c e s i n w e i g h t s a t t h e s t a r t o f t h e e x p e r i m e n t . F i s h f r o m R e s e r v o i r 81 a n d A r m a n d B a y o u grew e q u a l l y r a p i d l y u n d e r h i g h f o o d c o n d i t i o n s , a n d b o t h grew more s l o w l y t h a n f i s h f r o m a n y o f t h e o t h e r t h r e e r e s e r v o i r s ( c f . F i g s . 32 a n d 33) . F i s h i n a l l r e p l i c a t e s g r o w n u n d e r l o w f o o d c o n d i t i o n s g r e w a b o u t e q u a l l y r a p i d l y , and a l l grew s i g n i f i c a n t l y more s l o w l y t h a n a n y r e p l i c a t e g r o w n u n d e r h i g h f o o d c o n d i t i o n s . 3 c . L o n g - t e r m E x p e r i m e n t s T a b l e 5 5 a e x h i b i t s t h e r e s u l t s o f an a n a l y s i s o f v a r i a n c e o f a g e a t m a t u r i t y f o r f e m a l e s f r o m R e s e r v o i r s 81 a n d 90 g r o w n a t h i g h f o o d a n d h i g h t e m p e r a t u r e , a n d f o r m a l e s f r o m R e s e r v o i r s 8 1 , 9 0 , a n d K a y R e s e r v o i r g r o w n a t h i g h t e m p e r a t u r e s a n d b o t h h i g h a n d l o w f o o d t r e a t m e n t s . O n l y t h e R e s e r v o i r 81 r e p l i c a t e s a t h i g h f o o d l e v e l s were c o m p l e t e ; t h e r e f o r e t h e mean a g e s a t m a t u r i t y f o r a l l o t h e r r e p l i c a t e s were u n d e r e s t i m a t e s . F e m a l e s f r o m R e s e r v o i r 81 m a t u r e d s i g n i f i c a n t l y e a r l i e r t h a n t h o s e f r o m R e s e r v o i r 90 ( b o t h a r e u n s t a b l e r e s e r v o i r s ) . M o s t o f t h e v a r i a b i l i t y i n m a l e a g e a t m a t u r i t y was a t t h e l e v e l o f r e p l i c a t e s , a n d e v e n d i f f e r e n c e s among r e p l i c a t e s were n o t s i g n i f i c a n t . My s a m p l e s i z e s were q u i t e s m a l l . F i q . 34 p r e s e n t s t h e c u m u l a t i v e number o f f e m a l e s m a t u r e , p l o t t e d a g a i n s t a g e . T a b l e 55b e x h i b i t s K o l m o g o r o f f - S m i r n o f f o n e - t a i l e d t e s t s f o r d i f f e r e n c e s i n t h e a g e s a t m a t u r i t y p r e s e n t e d i n F i g . 3 4 . F e m a l e s f r o m R e s e r v o i r 81 ( h i g h f o o d ) m a t u r e d s i g n i f i c a n t l y e a r l i e r t h a n f e m a l e s f r o m Kay ( h i g h f o o d ) 250 Table 54 Growth Experiments: E f f e c t s Of Food a n a l y s i s Of V a r i a n c e : Weights Of 34 Day Old F i s h Hawaiian + Texan F i s h T T -T- r 1 Sample | n I Number J Mean j |Prob | 1 I | E p l c t s J wgt (mg) { { | i 1 t I I r ~+ n Hawaii | 226 | 24 ! 5.992 | 3.5499 |.05<p<.10| 1 Texas h J 34 1 4 3.821 j Twin J 43 1 5 j 8.765 | 4.3y486 |0.05 J Kay | 56 1 6 i 5.602 | | | 81 | 30 1 3 i 6.293 J I j 90 | 97 J 10 i 4.897 | I | Armand Bayou 1 34 I 4 « 3.821 ( ! I armand Bayou 1 i ] { { High Food | 18 I 2 i 4.617 | I | Low Food | 16 I 2 2.925 | I | J i - J L - . , i . i .. J * Denominator Mean Sguare = E e p l i c a t e s 251 Table 55 Age At Maturity In Females Lab Data: Longterm Experiments 1. A n a l y s i s Of Variance, R e s e r v o i r s 81 And 90 High Temperature - High Food Only + + _ + -Sample R e s e r v o i r 81 R e s e r v o i r 90 11 7 Number R p l c t s 2 2 Mean Age 122.9 147. 3 I |Prob I 18.7208**|<0.05 2. Kolmogoroff-Smirnoff O n e - t a i l e d T e s t s Of D i f f e r e n c e s In Age At Maturity 1 Samples h 81-90 High Food 81-Kay High Food 90-Kay High Food 293 370 120 81-90 Low Food 077 81-81 H-L Food 90-90 H-L Food 43 3 16 9 N1 N2 Chi-sqr Prob +-27 27 25 25 25 25 4.4575 7. 1083 0.7200 .10<p<.20 <0.05 >0.50 21 14 0. 1992 >0. 90 27 25 21 14 8.8588 1.0253 <0. 02 >0.50 * Denominator Mean Square = Food Treatments ** Denominator Mean Square = I n d i v i d u a l F i s h \ 252 FIGURE 34 Maturation Rates: Females From a quick inspection of the graphs, i t appears that female f i s h from Reservoirs 81 and 90 (fluctuating) mature e a r l i e r than do f i s h from Kay Reservoir (stable) at both high and low food l e v e l s . In f a c t , because sample sizes were small and the experiments were cut short, only the differences between Reservoir 81 and Kay Reservoir at high food l e v e l s , and the differences between Reservoir 81 f i s h raised under high and low food treatments, were s i g n i f i c a n t . A l l data shown raised at 27°C at i n t h i s figure were taken from f i s h densities of 0.75 f i s h / l i t e r . 253 MATURATION- RATES: FEMALES HIGH F O O D L O W F O O D 1 5 T 1 0 - -5 -0 - -L U - 5 - -UR 0 cc 1 5 T . 1 0 -QC 5 •-LiJ 0 - - ' m ^ ~ — \ - 5 +-0 1 L L J 1 5 T > 1 0 -1—1 1 — 5 - -cr 0 i - 5 - -ZD 0 CU 1 5 T I 1 I I I I I I I 1 I I I I I [ I I I I I 3 0 6 0 9 0 1 2 0 1 5 0 1 8 0 2 1 0 9 0 -) i i i i i i i i i i i i i i i i i i i i 3 0 6 0 9 0 1 2 0 1 5 0 1 8 0 2 1 0 KAY -a 1 0 + 5 0 - 5 I I I I I I I I I I I I I I I I I I I M 3 0 6 0 9 0 1 2 0 1 5 0 1 8 0 2 1 0 TWIN -a i i i i i i i i i i i i i i i i i i i i i 0 3 0 6 0 9 0 1 2 0 1 5 0 1 8 0 2 1 0 A G E IN D A Y S 1 5 T 1 0 •-5 - -0 81 - 5 l i i i i i i I I I I I I I I I I ! I I I I 0 3 0 6 0 9 0 1 2 0 1 5 0 1 8 0 2 1 0 1 5 T 1 0 -• 5 -0 - 5 9 0 - f - i - M - l - H I 1 I I I I | | | | | | | | 0 3 0 6 0 9 0 1 2 0 1 5 0 1 8 0 2 1 0 1 5 T 1 0 5 + 0 KAY -a - 5 I i i i i i i i ) i i i i i i i i i i i i i 3 3 0 6 0 9 0 1 2 0 1 5 0 1 8 0 2 1 0 1 5 T 1 0 - -5 - -0---E3 - 5 TWIN i i i I i i i i i i i i i i i i i i i i i 0 3 0 6 0 9 0 1 2 0 1 5 0 1 8 0 2 1 0 A G E IN D A Y S 254 and from R e s e r v o i r 81 (low fo o d ) . None of the other d i f f e r e n c e s were s i g n i f i c a n t . T a b l e s 56 and 57 compare the numbers of young produced and the r e p r o d u c t i v e e f f o r t s made by females bearing t h e i r f i r s t broods i n the l a b with numbers of young and r e p r o d u c t i v e e f f o r t s from the f i e l d . For the l a b data I used age as the c o v a r i a t e ; f o r the f i e l d data I used weight. In the l a b , females from Kay B e s e r v o i r bore fewer young and made s m a l l e r r e p r o d u c t i v e e f f o r t s than females from R e s e r v o i r s 81 or 90. In the f i e l d , females from Kay bore fewer young and made s m a l l e r e f f o r t s than females from R e s e r v o i r 81 i n both January and November samples, but they bore more young and made l a r g e r e f f o r t s than females from R e s e r v o i r 90 i n the January samples. F i g u r e s 35 and 36 summarize the growth of Gambusia from b i r t h to the end of the long-term experiments. F i r s t , f i s h from the two s t a b l e r e s e r v o i r s ( F i g . 35) grew f a s t e r than f i s h from e i t h e r of the two uns t a b l e r e s e r v o i r s ( F i g , 36). Secondly, f i s h from Kay r a i s e d on low food c o n d i t i o n s a c t u a l l y grew f a s t e r than those r a i s e d under high food c o n d i t i o n s . That e f f e c t was probably due to lowered d e n s i t i e s i n the low-food r e p l i c a t e s caused by high m o r t a l i t y r a t e s e a r l y i n the experiment. In F i g . 36 I have a l s o p l o t t e d the weights and ages of females as they matured. No matter what t h e i r age at mat u r i t y , females from both R e s e r v o i r s 81 and 90 matured at about the same weight: 55 mg. The two s e t s of two l i n e s i n F i g . 36 r e p r e s e n t h i g h and low food treatments (upper and lower p a i r s of l i n e s ) and high and low temperature treatments (upper and lower l i n e of each p a i r ) . Although food and temperature l e v e l s had l a r g e e f f e c t s 255 Table 56 Comparison Of Lab And F i e l d Data: Number Of Young Analysis Of Covariance Sample Number Rplcts I Adj. Mean| # Yng | I | Prob I _J 1. Lab Data: Number Of Young j L In F i r s t Brood X Age + •—H + I Stable I Fluctuating I I 6 37 Kay Reservoir Reservoir 81 Reservoir 90 6 23 14 4 7 3.34 10.05 4 4 3 3. 34 9.01 11.77 4.6247 1.3247* .05<p<. 10 >0.25 Kay Reservoir HF Kay Reservoir Lf Reservoir 81 HF Reservoir 81 Lf Reservoir 90 HF Reservoir 90 Lf I 3 3 15 8 1 1 3 2 2 2 2 2 1 4.00 2.67 9. 64 7. 83 12.86 7.79 0.4902* >0. 50 Field Data: Number Of Young f. j (- X Weight, January f-Stable Fluctuating 24 1 54 1 2 18.60 | 0.0941* 27.88 I + >0. 90 Kay Reservoir Reservoir 81 Reservoir 90 24 1 16 38 I 18.60 |256.4473 70.17 | ** 10.07 | 1 <0.0001 3. Field Data: Number Of Young Kay Reservoir Reservoir 81 X Weight, November j. +. 15 28 I 1.013 | 28.0642 |<0.0001 14.21 | ** | * Denominator Mean Sguare = Replicates Or Reservoirs ** Denominator Mean Sguare = Individual Fish 256 Table 57 Comparison Of Lab And F i e l d Data: Reproductive E f f o r t A n a l y s i s Of Covariance Sample I 1 I Number |Adj. Mean) R p l c t s | Rep.eff. I I Prob 1. Lab Data 1-Reproductive E f f o r t X Age j , S t a b l e F l u c t u a t i n g I 6 37 4 7 0.055 0.181 -+-Kay R e s e r v o i r R e s e r v o i r 81 Re s e r v o i r 90 6 23 14 4 4 3 0.055 0. 184 0.177 Kay R e s e r v o i r HF Kay R e s e r v o i r Lf Res e r v o i r 81 HF R e s e r v o i r 81 Lf R e s e r v o i r 90 HF Re s e r v o i r 90 Lf 3 3 15 8 11 3 2 2 2 2 2 1 0.056 0.053 0.182 0.186 0.181 0.163 6.6218* <0.05 0.0281 >0.90 0.0238 >0. 90 2. F i e l d Data: Reproductive E f f o r t X Weight, January , , + . St a b l e F l u c t u a t i n g f* 241 54 I 1 2 0.213 0.200 | 0.0087 1>0.90 Kay R e s e r v o i r R e s e r v o i r 81 R e s e r v o i r 90 241 16 38 0.213 0.398 0.116 i I |84.1135**j<0.000 3. F i e l d Data: T ~ Reproductive E f f o r t + _ +  X Weight, November —f- +— Kay R e s e r v o i r R e s e r v o i r 81 15 28 I I 0.034 0. 164 I I |14.4074**10.0006 * Denominator Mean Square = R e p l i c a t e s Or R e s e r v o i r s ** Denominator Mean Square = I n d i v i d u a l F i s h 257 FIGURE 35 Summary Of Growth: S t a b l e R e s e r v o i r s Legend: V e r t i c a l l i n e s i n d i c a t e 95% con f i d e n c e l i m i t s ; the lower of the two groups of f i s h at 34 days were those r a i s e d under low-food c o n d i t i o n s , a l l data shown i n t h i s f i g u r e were taken from f i s h r a i s e d at 27<>c at d e n s i t i e s of 0.75 f i s h / l i t e r . F i s h from the two s t a b l e r e s e r v o i r s grew more r a p i d l y than those from e i t h e r f l u c t u a t i n g r e s e r v o i r {cf. F i g . 41). F i s h from Kay R e s e r v o i r r a i s e d under low-food c o n d i t i o n s a c t u a l l y outgrew those r a i s e d under h i g h -food c o n d i t i o n s . That probably r e s u l t e d from high e a r l y m o r t a l i t i e s i n the low-food tanks, which l e d to lower d e n s i t i e s and more food per f i s h than i n the high-food tanks. Only the high-temperature, low-food r e p l i c a t e s f o r Kay Reservoir experienced high e a r l y m o r t a l i t i e s . 258 5 T CD 1— 3 -• [GH' -• • — i L J J i -C D O - -r H—h SUMMARY OF GROWTH TWIN RESERVOIR 0 8. 34 74 KAY RESERVOIR AGE IN DAYS 148 259 FIGURE 36 Summary O f G r o w t h : F l u c t u a t i n g R e s e r v o i r s L e g e n d : V e r t i c a l l i n e s i n d i c a t e 95% c o n f i d e n c e l i m i t s ; t h e l o w e r o f t h e two g r o u p s o f f i s h a t 34 d a y s were t h o s e r a i s e d u n d e r l o w - f o o d c o n d i t i o n s . A l l d a t a shown i n t h i s f i g u r e w e r e t a k e n f r o m f i s h r a i s e d a t 2 7 ° C a t d e n s i t i e s o f 0 . 7 5 f i s h / l i t e r . I n t h i s f i g u r e , t w o l i n e s a r e d r a w n f r o m e a c h g r o u p o f 34 d a y o l d f i s h . T h e s e i n d i c a t e t h e d i v e r g e n c e i n g r o w t h r a t e s b e t w e e n h i g h ( 2 7 ° C ) a n d l o w ( 1 7 ° C ) t e m p e r a t u r e r e p l i c a t e s . G a m b u s i a f r o m f l u c t u a t i n g r e s e r v o i r s grew more s l o w l y a t 170C t h a n a t 2 7 ° C , b u t t h e d i f f e r e n c e s i n g r o w t h r a t e s were s u r p r i s i n g l y s m a l l . F i s h f e d o n c e a d a y m a t u r e d e a r l i e r a n d grew f a s t e r t h a n f i s h f e d e v e r y o t h e r d a y . The l i n e s d r a w n i n t h i s f i g u r e make t h e h i g h - a n d l o w - f o o d f i s h a p p e a r more n e a r l y a l i k e t h a n t h e y a c t u a l l y w e r e , b e c a u s e t h e l a r g e , e a r l y - m a t u r i n g f e m a l e s were n o t i n c l u d e d i n t h e c a l c u l a t i o n s o f w e i g h t a t 207 d a y s . N o t e t h a t a l l f e m a l e s f r o m b o t h r e s e r v o i r s a n d b o t h h i g h - a n d l o w - f o o d t r e a t m e n t s m a t u r e d a t a f a i r l y c o n s t a n t s i z e ( 4 5 - 6 0 mg) no m a t t e r what t h e i r a g e . T h e v a r i a n c e i n s i z e a t m a t u r i t y may b a g r e a t e r i n R e s e r v o i r 81 t h a n R e s e r v o i r 9 0 , b u t my s a m p l e s i z e s were t o o s m a l l t o t e l l . 260 5 T CD 1— 3 -[ GH' --WE] i -CD O I --r - i --5 T CD SUMMARY OF GROWTH RESERVOIR 81. X * x xx x gkX 0 8 3 4 0 8 34 BIRTHS: X HTHF • HTLF 207 RESERVOIR 90 x Xx XD X X BIRTHS: X HTHF • HTLF AGE IN DAYS 207 261 on age at maturity i n females, they had s m a l l e r e f f e c t s on growth r a t e s . The v a r i a b i l i t y among f i s h and r e p l i c a t e s was too l a r g e to make p o s s i b l e accurate e s t i m a t e s of the e f f e c t s of food and temperature. Under high food and temperature c o n d i t i o n s , I measured female ages at f i r s t r e p r o d u c t i o n t h a t ranged from 76 to 169 days f o r R e s e r v o i r 81, and from 117 t o more than 207 days f o r R e s e r v o i r 90. 3d.. The E f f e c t s Of Drawdowns Table 58 presents the r e s u l t s of the l a b o r a t o r y drawdown experiment. Table 58a compares o v e r a l l s i z e d i s t r i b u t i o n s , and T able 58b compares d i f f e r e n c e s i n mean l e n g t h s . The o v e r a l l s i z e d i s t r i b u t i o n of R e p l i c a t e 1 changed s i g n i f i c a n t l y from the s t a r t to the f i n i s h . of the experiment, as d i d the summed d i s t r i b u t i o n s of R e p l i c a t e s 1 and 2. The changes i n mean l e n g t h , presented i n Table 58b, were q u i t e s i g n i f i c a n t . Large f i s h s u r v i v e d the drawdown, and s m a l l f i s h d i d not. M o r t a l i t i e s f e l l most h e a v i l y on the 5-10 and 10-15 mm s i z e c l a s s e s . Table 59a presents f i e l d data on the impact of a s i n g l e r a p i d f l u c t u a t i o n : the emptying o f R e s e r v o i r 50 between 11:30 am and 2:00 pm on 5 December 1974. At both 11:00 am and 2:00 pm the f i s h being swept out of the r e s e r v o i r were s i g n i f i c a n t l y l a r g e r than the f i s h remaining i n the r e s e r v o i r . But t here was no change i n the s i z e of f i s h i n the r e s e r v o i r between 11:30 am and 2:00 pm, a r e s u l t I a t t r i b u t e t o the l a r g e number of f i s h i n the r e s e r v o i r , on which the drawdown had l i t t l e impact because i t swept away only a s m a l l p r o p o r t i o n of the f i s h , and to the d i f f e r e n t s p a t i a l d i s t r i b u t i o n of f i s h i n the h a l f - f u l l 262 Table 58 Drawdown Experiment: R e s u l t s A* Siz e D i s t r i b u t i o n s " i 1 1 I G |Prob | Sample S i z e C l a s s 1~30-35|35-40~r + 5-10 10-15 15-20 20-25{25-30 1-S t a r t 1 F i n i s h 1 13 0 7 0 25 4 16 11 3 4 3 2 2 2 21.866 <0.005 S t a r t 2 F i n i s h 2 1 3 0 7 1 25 13 16 4 3 3 3 1 2 1 11.966 >0. 05 S t a r t T o t a l F i n i s h T o t a l 26 0 14 1 50 17 32 15 6 7 6 3 4 3 25.866 <0.005 F i n i s h 1 F i n i s h 2 0 0 0 1 4 13 11 4 4 3 2 1 2 1 10.623 >0. 10 B. A n a l y s i s Of Variance 1 T " Sample n Mean Length Prob S t a r t F i n i s h 138 46 17.94 22. 83 10.5106* .05<p<.10 S t a r t 1 F i n i s h 1 S t a r t 2 F i n i s h 2 69 23 69 23 17.94 24.67 17.94 20.98 1.6087** 0.2011 * Denominator Mean Square = R e p l i c a t e s ** Denominator Mean Square = I n d i v i d u a l F i s h 26 3 Table 59 E f f e c t s Of Drawdowns : F i e l d Data A n a l y s i s Of Variance In Length A. R e s e r v o i r 50: 5 December 1974 r • • '•• | Sample i — n — , — Mean Length — J ~ 1 - ._ T F J Prob • J 11:30 am I R e s e r v o i r J O u t l e t j 150 50 L 21,00 24.39 1 18 .8441** | <0.0001 1 | 2:00 pm I R e s e r v o i r I o u t l e t j 50 26 r 21.41 26.91 | 11 .1273** \ 0.0015 I In R e s e r v o i r \ 11:30 am j 2:00 pm i i . „ 150 50 ... i 21.00 21.41 A . 0 .2936** j 0.5954 J B. January Vs. November Samples: R e s e r v o i r s 33, 41, 50, And 81 r ~T' ••• - - "T • - T •••• i Sample \ n | Mean i | Length | i i F | Pro b | i January November | 1000 I 736 I I | 19.93 | I 21.71 | 0.8385* ) >0,25 | January 33 November 33 January 41 November 41 January 50 November 50 January 81 November 81 | 250 \ 189 | 250 \ 147 | 250 | 150 | 250 | 250 | 20.57 | | 19.90 | | 22.28 | I 27.79 j | 18.95 | | 21.00 | | 17.92 | | 19.94 | i i 54.8892** | <0.0001 | • * Denominator ** Denominator Mean Sguare = Mean Sguare R e p l i c a t e s = I n d i v i d u a l F i s h 7 264 r e s e r v o i r at 11:30 am and the puddle t h a t remained at 2:00 pm. Table 59b s e t s f o r t h f i e l d data on s i z e changes i n f o u r f l u c t u a t i n g r e s e r v o i r s between January and November. On the whole, f i s h were s l i g h t l y l a r g e r i n November (21.71 mm) than January (19.93 mm), but the v a r i a b i l i t y among i n d i v i d u a l samples was so l a r g e t h a t the d i f f e r e n c e between dates was i n s i g n i f i c a n t . But i n 3 of 4 r e s e r v o i r s (41, 50, and 81) f i s h were l a r g e r i n November than January. R e s e r v o i r 33 had gone almost completely dry f o r 2 months d u r i n g the summer, and the f i s h we caught i n November were probably i n p a r t c o l o n i z e r s . Thus short-term f l u c t u a t i o n s i n the f i e l d f a v o r s m a l l e r f i s h , while low water l e v e l s during the summer dry season seem to f a v o r l a r g e r f i s h . 3f. Summary, O f L a b o r a t o r y . R e s u l t s T h e r e i s s i g n i f i c a n t v a r i a b i l i t y among r e s e r v o i r s i n s i z e o f y o u n g a t b i r t h a n d g r o w t h r a t e s . At h i g h f o o d l e v e l s , G a m b u s i a f r o m T w i n ( s t a b l e ) , Kay ( s t a b l e ) , a n d 90 ( f l u c t u a t i n g ) grew more r a p i d l y t h a n G a m b u s i a f r o m 81 ( f l u c t u a t i n g ) a n d A r m a n d B a y o u ( T e x a s ) . A t l o w f o o d l e v e l s , a l l f i s h grew a t a b o u t t h e same r e d u c e d r a t e . I n l o n g - t e r m e x p e r i m e n t s a t h i g h a n d low f o o d l e v e l s , f e m a l e s f r o m R e s e r v o i r 81 ( f l u c t u a t i n g ) m a t u r e d e a r l i e r t h a n f e m a l e s f r o m K a y R e s e r v o i r ( s t a b l e ) . Low f o o d t r e a t m e n t s s l o w e d g r o w t h s l i g h t l y a n d h a d a l a r g e r i m p a c t on a g e a t m a t u r i t y . A l l f e m a l e s f r o m R e s e r v o i r 81 a n d 90 m a t u r e d a t a b o u t 55 mg d r y w e i g h t , no m a t t e r what t h e i r a g e s , w h i c h r a n g e d f r o m 76 t o 169 d a y s f o r f e m a l e s f r o m R e s e r v o i r 81 a n d f r o m 117 t o o v e r 207 d a y s 265 f o r females from R e s e r v o i r 90. Long p e r i o d s of low water l e v e l s and r e s t r i c t e d food s u p p l i e s f a v o r e d l a r g e f i s h (over 20 mm) i n both l a b and f i e l d . Short-term f l u c t u a t i o n s i n the f i e l d seem to f a v o r s m a l l f i s h ( l e s s than 22 mm). H± D i s c u s s i o n Ua. Growth And Maturation On the whole, my l a b o r a t o r y data on s i z e at b i r t h , number of young, and r e p r o d u c t i v e e f f o r t c o r r o b o r a t e the f i e l d data. The d i f f e r e n c e s I observed i n the l a b o r a t o r y were i n the same d i r e c t i o n (with the exce p t i o n s of the newborn young from Kay and the male ages at maturity i n the long-term experiment) as the d i f f e r e n c e s I observed i n the f i e l d . Females from R e s e r v o i r 81 had s i g n i f i c a n t l y d i f f e r e n t ages at maturity than females from Kay R e s e r v o i r . Since I observed a l l these d i f f e r e n c e s among f i s h r a i s e d under s i m i l a r c o n d i t i o n s i n the l a b o r a t o r y , I have concluded t h a t the l i f e h i s t o r y t r a i t s of Gambusia have evolved i n Hawaii s i n c e 1907 i n d i f f e r e n t d i r e c t i o n s f o r d i f f e r e n t r e s e r v o i r s . That i s , s i n c e I observed d i f f e r e n c e s among 4 s t o c k s of Gambusia i n the l a b o r a t o r y t h a t were i n the same d i r e c t i o n as the / d i f f e r e n c e s observed i n those 4 s t o c k s i n the f i e l d , I have concluded t h a t a t l e a s t the d i r e c t i o n of most of the d i f f e r e n c e s observed i n the f i e l d among a l l 24 stock s of Gambusia and 6 st o c k s of P o e c i l i a would have he l d up i n the l a b o r a t o r y . T h i s 266 e v o l u t i o n a r y process has produced some f a i r l y s t r i k i n g d i f f e r e n c e s . I have not e l i m i n a t e d the p o s s i b i l i t y t h a t the d i f f e r e n c e s I observed i n the l a b o r a t o r y were due to maternal e f f e c t s . But I f i n d t h a t argument i m p l a u s i b l e because i n many cases the f i e l d - c a u g h t females had been i n the l a b f o r 1-2 months before g i v i n g b i r t h . My major c o n c l u s i o n from the l a b o r a t o r y work i s t h i s : s i g n i f i c a n t , g e n e t i c a l l y based d i f f e r e n c e s have evolved i n l o c a l s t o c k s of Gambusia i n Hawaii s i n c e 1905. That does not c o n t r a d i c t ray previous c o n c l u s i o n (Chapter V) that most of the v a r i a b i l i t y i n l i f e h i s t o r y t r a i t s observed i n the f i e l d was a p l a s t i c phenotypic response to events i n the rec e n t past. A d e t e c t a b l e and s i g n i f i c a n t p o r t i o n of the v a r i a b i l i t y among sto c k s had a g e n e t i c b a s i s , but most of the v a r i a b i l i t y among sto c k s r e s u l t e d from developmental p l a s t i c i t y . L i l e y (pers. comm.), having done growth experiments on two stocks of E o e c i l i a r e t i c u l a t a c o l l e c t e d i n d i f f e r e n t streams i n T r i n i d a d , concluded that "the d i f f e r e n c e s i n s i z e of a d u l t guppies, p a r t i c u l a r l y the males, taken from Upper Ar i p o and Guayamare pop u l a t i o n s i n T r i n i d a d are p a r t l y determined by g e n e t i c d i f f e r e n c e s , and are i n p a r t a phenotypic response to environmental temperatures." Thus i t seems l i k e l y t h a t the pa t t e r n I have documented f o r Gambusia i n Hawaii w i l l a l s o h o l d t r u e f o r P o e c i l i a i n Hawaii. The d i r e c t i o n of the d i f f e r e n c e s between females t h a t I observed i n the l a b o r a t o r y f o r R e s e r v o i r s 81, 90, and Kay c o r r o b o r a t e s the p r e d i c t i o n s of r - and K - s e l e c t i o n : more young, e a r l i e r m a t u r i t y , and l a r g e r r e p r o d u c t i v e e f f o r t s i n f l u c t u a t i n g 267 r e s e r v o i r s . But my sample s i z e s were s m a l l , and I was not a b l e to deal with the f u l l range of r e s e r v o i r s i n the l a b o r a t o r y . I c o n s i d e r i t j u s t as s i g n i f i c a n t t h a t i n many r e s p e c t s (e.g. s i z e at b i r t h , growth rates) R e s e r v o i r 90 f i s h resembled those from Kay and Twin more than they d i d those from R e s e r v o i r 81. . I take that as an i n d i c a t i o n t h at I am f a r from understanding the d e t a i l e d impact of e c o l o g i c a l c o n d i t i o n s on the e v o l u t i o n of l i f e h i s t o r y t r a i t s . Females from R e s e r v o i r 81 matured at a remarkably constant s i z e (55 mg). The g r e a t v a r i a b i l i t y i n t h e i r ages at maturity, over a range of at l e a s t 90 days f o r females from both r e s e r v o i r s , was due to d i f f e r e n c e s i n growth r a t e s . I have clai m e d , i n Chapters IV and V, that t h i s v a r i a b i l i t y i n the age of female maturity i s a c r i t i c a l f a c t o r t h a t adapts Gambusia t o f l u c t u a t i n g environments. Are the d i f f e r e n c e s i n growth r a t e that cause d i f f e r e n c e s i n age at maturity mediated by s o c i a l i n t e r a c t i o n s , or are they s t r a i g h t f o r w a r d l y g e n etic? I f they are mediated by s o c i a l i n t e r a c t i o n s , does s o c i a l dominance have a g e n e t i c or maternal component? Answers t o these g u e s t i o n s would throw l i g h t on the coadaptation o f l i f e h i s t o r y t r a i t s and s o c i a l behavior. When I d i d the high food growth experiments, I thought I had d i s c o v e r e d a d i f f e r e n c e i n food a s s i m i l a t i o n e f f i c i e n c y between s t a b l e and f l u c t u a t i n g r e s e r v o i r s . But when I repeated the experiments at low food l e v e l s , I c o u l d not f i n d any d i f f e r e n c e s between s t a b l e and f l u c t u a t i n g r e s e r v o i r s , and I d i d not have enough young from R e s e r v o i r 81 t o run the low food growth experiments f o r that r e s e r v o i r . I t was the one which had 268 d i f f e r e d most from the others i n the high food experiments. I conclude t h a t t h e r e are d i f f e r e n c e s i n growth r a t e s of young Gambusia among r e s e r v o i r s , and that Gambusia from three Hawaiian r e s e r v o i r s can grow f a s t e r than Gambusia from Texas at both high and low food l e v e l s , but I do not know how to e x p l a i n those d i f f e r e n c e s i n terms of the e c o l o g i c a l s i t u a t i o n s i n which the f i s h have evolved. 4 b. The Impact Of Changes In Water L e v e l Drawdowns seem to have d i f f e r e n t e f f e c t s on p o p u l a t i o n s t r u c t u r e , depending on whether they are r a p i d f l u c t u a t i o n s or long-term seasonal drawdowns. Short-term drops i n water l e v e l f a v o r f i s h under 20 mm, f o r l a r g e f i s h are p r e f e r e n t i a l l y drawn out of the r e s e r v o i r and deposited i n the sugar cane f i e l d s , where they d i e . Long-term drawdowns, i n both l a b o r a t o r y and f i e l d , favored l a r g e r f i s h . In the l a b o r a t o r y , almost no f i s h under 15 mm long s u r v i v e d the drawdown experiment. I suspect the l a r g e f i s h ate them because a l l the f i s h l e s s than 10 mm had disappeared from the aquaria w i t h i n the f i r s t day of the experiment. I f the same mechanism i s at work i n the f i e l d , as the d i f f e r e n c e s i n average s i z e between January and November i n R e s e r v o i r s 41, 50, and 81 suggest, then Gambusia are undergoing o s c i l l a t i n g s e l e c t i o n pressures on s i z e a t maturity and growth r a t e s . I suggested i n Chapter IV that they handle the problem by producing a mixture of types of young, some of which grow r a p i d l y and mature e a r l y . H o p e f u l l y t h e i r young would not encounter a s e a s o n a l drawdown and would s u r v i v e to reproduce. 269 But i f they were caught i n a drawdown and e l i m i n a t e d , then the slower growing young, which would have to be over 15 or 20 ram long by the time the summer drawdown a r r i v e d , could make i t through the drawdown to reproduce l a t e r . 270 CHAPTER VII. GENERAL DISCUSSION 1. P r e d i c t i o n s I r e j e c t e d n e i t h e r the r - and K - s e l e c t i o n model, nor the bet-hedging model. Because the models only make d i f f e r e n t p r e d i c t i o n s when j u v e n i l e m o r t a l i t y v a r i e s more than a d u l t m o r t a l i t y , and because I c o u l d not q u a n t i f y a g e - s p e c i f i c m o r t a l i t y r a t e s as averages, much l e s s measure t h e i r v a r i a b i l i t y , I could not r e j e c t e i t h e r model. But, s i n c e a l l the d i f f e r e n c e s I d i d observe i n r e p r o d u c t i v e t r a i t s between s t a b l e and f l u c t u a t i n g r e s e r v o i r s were i n the d i r e c t i o n p r e d i c t e d by S c h a f f e r ' s (1974) model with high v a r i a b i l i t y i n a d u l t m o r t a l i t y , I can s t a t e t h a t i f S c h a f f e r ' s model a p p l i e s , a d u l t m o r t a l i t y v a r i e s more than j u v e n i l e m o r t a l i t y i n the f l u c t u a t i n g r e s e r v o i r s I do not t h i n k t h a t t e s t i n g and attempting t o r e j e c t t h e o r e t i c a l models i s the only rewarding a c t i v i t y i n s c i e n c e . Mathematical a n a l y s i s of the k i n d t h a t l e d t o the p r e d i c t i o n s of r - and K - s e l e c t i o n and bet-hedging can suggest problems t h a t organisms f a c e by d e f i n i n g the demographic l i m i t s w i t h i n which they must operate. But only e m p i r i c a l evidence can show us how organisms a c t u a l l y s o l v e those problems, and d i f f e r e n t s p e c i e s a r r i v e at d i f f e r e n t s o l u t i o n s . I have no doubts about the g e n e r a l a p p l i c a b i l i t y of the p r e d i c t i o n s of Table 2 as d e f i n i t i o n s of b i o l o g i c a l problems that demand e v o l u t i o n a r y s o l u t i o n s . But we have no assurance that the s o l u t i o n s achieved w i l l be c a s t i n the terms we might 271 expect from the d e f i n i t i o n s of the problems. A f t e r a l l , the problems are d e f i n e d by b i o l o g i s t s , and the s o l u t i o n s are achieved by organisms. The two groups can, and f r e q u e n t l y do, view the world i n d i f f e r e n t terms. One e x c e l l e n t s o l u t i o n t o most problems, when i t can be achieved, a l t e r s the nature of the s i t u a t i o n to e l i m i n a t e the problem or blunt i t s f o r c e . That i s what I think Gambusia has done with l i f e h i s t o r y problems. At some p o i n t i n the past, i t s ancestors may have had to d e a l with problems i n the con t e x t of r - and K - s e l e c t i o n . But i t s subsequent e v o l u t i o n i n the s p a t i a l l y and temporally v a r i a b l e environment of the estu a r y - f r e s h w a t e r i n t e r f a c e l e d to the a c q u i s i t i o n of t r a i t s that e f f e c t i v e l y r e d e f i n e d the e v o l u t i o n a r y problems t h a t the organism f a c e d . I do not, by any means, have a complete l i s t of the ad a p t a t i o n s which enabled Gambusia t o r e d e f i n e i t s e v o l u t i o n a r y s i t u a t i o n . I am f a i r l y sure t h a t both developmental p l a s t i c i t y and v a r i a b i l i t y i n female age a t maturity have played a r o l e , a c t i n g as b u f f e r s t h a t uncouple Gambusia from the impact of environmental f l u c t u a t i o n s , but other f a c t o r s may a l s o have been important. 2i I m p l i c a t i o n s Where does t h i s l e a v e the o r i g i n a l p r e d i c t i o n s ? Although I d i d not perform a c r i t i c a l t e s t t h a t r e j e c t e d one or more of them, I n e v e r t h e l e s s f e e l t h a t I have some reason t o c a l l f o r a r e c o n s i d e r a t i o n of the terms i n which our t h e o r e t i c a l models are c a s t . I have suggestions t o make i n f o u r areas, but f i r s t I w i l l b r i e f l y review the evidence that l e a d s me to those 272 sug g e s t i o n s . 2 a i Developmental And P h y s i o l o g i c a l P l a s t i c i t y At the time of b i r t h , Gambusia young have the p o t e n t i a l t o develop i n t o q u i t e d i f f e r e n t kinds of animals, depending on the c o n d i t i o n s they encounter. Late r i n l i f e , what they do r e p r o d u c t i v e l y depends c o n s i d e r a b l y on what has happened i n the recent past. Here i s the evidence on which I base t h a t d e s c r i p t i o n : (a) In Texas, I found two p o p u l a t i o n s of Gambusia only 200 m a p a r t , one i n a freshwater pond and the other i n the b r a c k i s h estuary, t h a t d i f f e r e d as much i n some of t h e i r l i f e h i s t o r y t r a i t s as any two p o p u l a t i o n s i n Hawaiian r e s e r v o i r s . I suggested t h a t Gambusia may possess a developmental s w i t c h , a c t i v a t e d by the s a l i n i t y encountered e i t h e r by the newborn young or by the mother, which can s h i f t the development of an i n d i v i d u a l i n t o e i t h e r a freshwater or a b r a c k i s h phenotype. (b) In Hawaii, I observed l a r g e changes i n r e p r o d u c t i v e t r a i t s between samples taken at the end of the dry season and two months i n t o the wet season. The d i f f e r e n c e i n any one r e s e r v o i r between January and November 1974 was as l a r g e as the d i f f e r e n c e s between most p a i r s of r e s e r v o i r s at e i t h e r date. (c) In Chapter V, I d i s c o v e r e d t h a t short-term measures of i n s t a b i l i t y c o u l d e x p l a i n more of the v a r i a b i l i t y i n numbers of young i n f l u c t u a t i n g r e s e r v o i r s (46.4%) than l o n g -term measures c o u l d (36.6%). I concluded t h a t events i n the recent past, w i t h i n the l i f e t i m e of the animals c o l l e c t e d , had a 273 l a r g e r impact on the l i f e h i s t o r y t r a i t s I measured than e v o l u t i o n a r y changes caused by the long-term f l u c t u a t i o n p a t t e r n s of the r e s e r v o i r s . (d) In Chapter VI, I e s t a b l i s h e d that temperature made a l a r g e d i f f e r e n c e t o Gambusia 1 s r a t e of -growth and development. F i s h grown at 17°C matured, on the average, at l e a s t 100 days l a t e r than f i s h grown at 27°C. Food l e v e l s d i d not make ne a r l y as much d i f f e r e n c e , but there were c o n s i s t e n t , i f not s i g n i f i c a n t , d e l ays i n maturation and r e d u c t i o n s i n numbers of young under low food regimes. The impact of food l e v e l s on f i s h from a s i n g l e r e s e r v o i r d i d not cause d i f f e r e n c e s i n l i f e h i s t o r y t r a i t s as l a r g e as I observed between most p a i r s of r e s e r v o i r s i n the l a b . To summarize: Gambusia possess c o n s i d e r a b l e developmental p l a s t i c i t y i n t h e i r l i f e h i s t o r y t r a i t s . The scope of p o s s i b l e developmental response i s so l a r g e t h a t i t o v e r l a p s the e n t i r e range of any e v o l u t i o n a r y changes i n l i f e h i s t o r y t r a i t s t h a t may have occurred i n Hawaii s i n c e 1905. 2b. I n d i v i d u a 1 V a r i a b i l i t y A f t e r having spent most of t h i s t h e s i s t a l k i n g about averages (e.g. average number of young i n a female of given length i n a c e r t a i n r e s e r v o i r , average s i z e a t maturity i n s t a b l e r e s e r v o i r s ) , I have decided t h a t I was f o c u s i n g on an i n a p p r o p r i a t e measure. The p r e d i c t i o n s I was t e s t i n g were couched i n terms of averages, but I am now convinced that much of the adaptedness of Gambusia p o p u l a t i o n s l i e s i n v a r i a b i l i t y among i n d i v i d u a l s i n t h e i r l i f e h i s t o r y t r a i t s . I have not done 274 e x t e n s i v e s t a t i s t i c a l t e s t s to look f o r d i f f e r e n c e s i n v a r i a n c e s or c o e f f i c i e n t s of v a r i a t i o n r a t h e r than averages, but I can p o i n t to evidence t h a t i n d i c a t e s i n d i v i d u a l v a r i a b i l i t y i s p e r v a s i v e : I found i n Chapter VI t h a t female ages at maturity v a r i e d i n the l a b from 76 days to over 207 days. I used t h a t v a r i a b i l i t y i n age a t maturation i n both Chapters IV and V as the cornerstone of my argument that Gambusia have r e d e f i n e d t h e i r e v o l u t i o n a r y problems i n such a way th a t the f o r c e s of r -and K - s e l e c t i o n are no longer important. 20^ D i f f e r e n t Types Of I n s t a b i l i t y In Chapter V, I showed t h a t the f l u c t u a t i o n p a t t e r n s of 20 Hawaiian r e s e r v o i r s v a r i e d across a spectrum of types c h a r a c t e r i z e d by s h i f t s i n p e r i o d i c i t y , power, and p r e d i c t a b i l i t y . I was only able t o make d i s t i n c t i o n s at t h a t l e v e l of d e t a i l because I happened to i n h e r i t r e c o r d s of the environmental v a r i a b l e t h a t other people had w r i t t e n down over the l a s t 30 years. I concluded t h a t the s t a b l e - f l u c t u a t i n g d i s t i n c t i o n was s i m p l i s t i c , both because I found many d i f f e r e n t types of f l u c t u a t i o n p a t t e r n s , and because I found d i f f e r e n c e s between the l i f e h i s t o r y t r a i t s of f i s h from p a i r s of f l u c t u a t i n g r e s e r v o i r s t h a t were as l a r g e as the d i f f e r e n c e s between p a i r s of s t a b l e and f l u c t u a t i n g r e s e r v o i r s . 2d. C o n c l u s i o n s Thus I found f o u r areas i n which d e t a i l s not normally c o n s i d e r e d were important, and made a c o n s i d e r a b l e d i f f e r e n c e t o 275 the e v o l u t i o n and e x p r e s s i o n of l i f e h i s t o r y t r a i t s . Current theory does not take any of them i n t o s a t i s f a c t o r y account. Based on my experience with Gambusia, I make the f o l l o w i n g s u g g e s t i o n s f o r f u r t h e r t h e o r e t i c a l e x p l o r a t i o n . (a) What determines the scope of developmental p l a s t i c i t y of a s p e c i e s ? What kind of i n f o r m a t i o n should be r i g i d l y encoded i n the genome? In a developmental apparatus c o n t r o l l e d by the genome? In the c h a r a c t e r i s t i c s of the m a t e r i a l s out of which the organism i s b u i l t ? (b) What f o r c e s a c t to shape, not the means, but the s t a t i s t i c a l d i s t r i b u t i o n s of l i f e h i s t o r y t r a i t s ? T h i s question should be con s i d e r e d as a p p l y i n g to both the proqeny of a s i n g l e mating, and to the c h a r a c t e r i s t i c s of a p o p u l a t i o n which may r e s u l t from many such s i n g l e matings. The answers t o the two questi o n s are l i k e l y t o be q u i t e d i f f e r e n t . (c) How do our p r e d i c t i o n s change when we examine a s e r i e s of d i f f e r e n t g eneral types of f l u c t u a t i n g environments? There i s l i t t l e p oint i n t a l k i n g about s t a b l e - f l u c t u a t i n g d i f f e r e n c e s without s p e c i f y i n g the kind o f i n s t a b i l i t y . The c r i t i c a l d i s t i n c t i o n i s between the age at which r e p r o d u c t i v e events occur i n organisms, and the times of environmental events. 3. Weak Poi n t s And Strong P o i n t s The s t o r y of Gambusia i n Hawaii i s by no means completely t o l d . I have based much of my argument on comparisons with P o e c i l i a , but I do not have some of the c r i t i c a l i n f o r m a t i o n f o r P o e c i l i a , e.g. the d i s t r i b u t i o n of ages at maturity f o r females. Because of problems i n the l a b o r a t o r y , I co u l d not 276 r a i s e Gambusia through two complete l i f e c y c l e s , and was unable t o a s s ess the magnitude of maternal e f f e c t s . My experiments were too shor t to provide a s a t i s f a c t o r y comparison among the l i f e h i s t o r i e s of f i s h from Twin and Kay Re s e r v o i r and R e s e r v o i r s 81 and 90. In the f i e l d , I was not able t o measure d i f f e r e n c e s between j u v e n i l e and a d u l t m o r t a l i t y . Nor co u l d I q u a n t i f y d i f f e r e n c e s i n food between r e s e r v o i r s that could have confounded the e v o l u t i o n a r y experiment. In sum, the evidence I have gathered, and the c o n c l u s i o n s I have drawn from i t , p a i n t a p i c t u r e which i s p l a u s i b l e but not i r r e f u t a b l e . I have d i s c o v e r e d some s e r i o u s weaknesses i n the framework w i t h i n which l i f e h i s t o r y t h e o r e t i c i a n s c u r r e n t l y operate. I have shown that the l i f e h i s t o r y t r a i t s of Gambusia have evolved i n Hawaii over the course of 60-70 y e a r s , l e a d i n g to c o n s i d e r a b l e i n t e r p o p u l a t i o n a l v a r i a b i l i t y . I have been able to e x p l a i n only p a r t of what caused t h a t v a r i a b i l i t y , and I have r a i s e d many more guestions than I s e t t l e d . Given the nature of e v o l u t i o n a r y phenomena, I would be s u r p r i s e d had t h i n g s turned out d i f f e r e n t l y . 277 LITERATURE CITED Ahuja, S.K. 1964. S a l i n i t y t o l e r a n c e of Gambusia a f f i n i s . I ndian J . Exp. B i o l . 2: 9-11. Barney, R.L., and B.J. Anson. 1920. 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The r e l a t i o n s h i p between l e n g t h , weight, and brood s i z e of the m o s g u i t o f i s h , Gambusia a f f i n i s . (Baird and Girard) (Cyprinodontiformes: P o e c i l i i d a e ) . C a l . Vec. Views 21: 29-44. 284 APPENDIX I. OPTIMIZING REPRODUCTIVE EFFORT ANALYTICALLY We s t a r t with Lotka's equation, where *X = e^, lxmx = 1, and ask, how s e n s i t i v e i s the growth r a t e , r , of a p o p u l a t i o n i n s t a b l e age d i s t r i b u t i o n to a change i n f e c u n d i t y , dm^, f o r one age c l a s s , a? We f i n d oo j ~ [.^ L 'X lxmx] =0 , and l^-'xk Ixmxfj^ * * l a = 0 ' 0 1 > K i ; x * l x m x = A i a . Since ="•'*, and xA lxmx = W = g e n e r a t i o n time. 3 V * l a / B -(This d e r i v a t i o n i s modified from Hamilton 1966). Now s i n c e l i > l j and ^ y ^ 4 f o r i < j , *X>1, dr- ^ dr-7 "H^ J f o r i < j , A > 1. Thus r i s more s e n s i t i v e t o a given change i n f e c u n d i t y f o r a f i x e d age c l a s s than i t i s f o r any o l d e r age c l a s s , so long as the p o p u l a t i o n i s growing. I f we compare two p o p u l a t i o n s , one of which experiences freguent episodes of r a p i d growth, the other of which i s r e l a t i v e l y s t a b l e , we p r e d i c t t h a t the f i r s t 285 should have e a r l i e r m a t u r i t y . Note t h a t t o make t h i s p r e d i c t i o n we have had to assume that a change i n f e c u n d i t y a t a given age i s independent of the r e s t of the l i f e h i s t o r y . But t h i s i s i m p l a u s i b l e , s i n c e the m a t e r i a l s and energy which would go i n t o the e x t r a f e r t i l i t y would have to be taken away from m a t e r i a l s and energy t h a t c o u l d have gone i n t o previous b i r t h s or subseguent growth. We have assumed t h a t r e p r o d u c t i o n e n t a i l s no c o s t to parents. We have a l s o assumed t h a t the f l u c t u a t i o n s a f f e c t a l l age and s i z e c l a s s e s e q u a l l y . i 286 APPENDIX I I . AGE AND S I Z E AT MATURITY IN MALE GAMBUSIA l i I n t r o d u c t i o n B e c a u s e s o c i a l forces have been c l e a r l y i m p l i c a t e d i n the c o n t r o l of age and s i z e at maturity i n male p o e c i l i i d s ( B o r o w s k y 1 9 7 3 , and c f . C h a p t e r I I ) , male p o e c i l i i d s v i o l a t e one of the unstated assumptions of l i f e h i s t o r y theory: that s o c i a l i n t e r a c t i o n s can be u s e f u l l y ignored. I have t h e r e f o r e gathered the data on age and s i z e at maturation i n male G a m b u s i a a f f i n i s i n t h i s appendix, r a t h e r than d i v e r t a t t e n t i o n from the main points of the t h e s i s by p u t t i n g i t i n the t e x t proper. 2. F i e l d R e s u l t s T h e r e are at l e a s t two ways to estimate s i z e at maturity from f i e l d data f o r p o e c i l i i d males. One i s to perform a p r o b i t a n a l y s i s on the a d u l t and j u v e n i l e males, determining the percent mature by s i z e c l a s s and estimating the length at which 50% of the males are mature. I decided against performing the p r o b i t a n a l y s i s because both January and N o v e m b e r c o l l e c t i o n s of G a m b u s i a c l e a r l y v i o l a t e d one assumption of p r o b i t a n a l y s i s : that the d i s t r i b u t i o n s of the untransformed data be at l e a s t approximately sigmoid. T h e second method takes advantage of the f a c t that G a m b u s i a males stop growing when they mature. T h u s s i z e measured at any time a f t e r maturity i s a good estimate of s i z e at maturity. F i g u r e s 3 7 , 3 8 , and 39 d i s p l a y the freguency d i s t r i b u t i o n s of 287 a d u l t males by s i z e c l a s s , and Table 60 s e t s f o r t h the a n a l y s i s of v a r i a n c e of len g t h of mature males. In a l l three cases males were lon g e r at maturity, on average, i n the f l u c t u a t i n g r e s e r v o i r s . But i n a l l three samples the d i f f e r e n c e was s m a l l (8% f o r Gambusia c o l l e c t e d i n January, 3% f o r Gambusia c o l l e c t e d i n November, and \% f o r P o e c i l i a ) , and only s i g n i f i c a n t f o r Gambusia c o l l e c t e d i n January. In both Texan samples a l l a d u l t males were between 18 and 24 mm long with a mode at 21 mm ( F i g . 40). In both Texan samples and Gambusia c o l l e c t e d i n Hawaii i n January, the mode of the a d u l t male s i z e d i s t r i b u t i o n was 21 mm, and the shapes of the d i s t r i b u t i o n s were a l l f a i r l y s i m i l a r . 3± F i e l d Observations,: D i s c u s s i o n Males were s l i g h t l y l a r g e r , on t h e average, i n f l u c t u a t i n g r e s e r v o i r s than i n s t a b l e ones. The d i f f e r e n c e s were s m a l l , but on the fa c e of i t they c o n t r a d i c t the r - and K - s e l e c t i o n p r e d i c t i o n . However, t h i s evidence i s not a p p r o p r i a t e f o r t e s t i n g p r e d i c t i o n s d e r i v e d with females i n mind. The s e l e c t i o n f o r c e s o p e r a t i n g on male l i f e h i s t o r i e s i n Gambusia are q u i t e d i f f e r e n t from those o p e r a t i n g on female l i f e h i s t o r i e s . As Borowsky . (1973) showed f o r Xiphophorus y a r i a t u s , s o c i a l i n t e r a c t i o n s with a d u l t males can s t r o n g l y a f f e c t the age and s i z e at which male p o e c i l i i d s mature. Below I present some evidence i n d i c a t i n g t h a t t h i s i s a l s o the case f o r Gambusia, with j u v e n i l e s w a i t i n g to mature u n t i l they have grown as l a r g e or l a r g e r than the l a r g e s t of the a d u l t males present. 288 FIGURE 37 Adult Male S i z e D i s t r i b u t i o n : Gambusia, January Adult males were s i g n i f i c a n t l y l o n g e r i n January i n the f l u c t u a t i n g r e s e r v o i r s {cf. Table 33). 2 89 ADULT MALE SIZE DISTRIBUTION GRMBUSIR. JRNURRr STABLE cr. LU DO ZD 65 52 39 26 + 13 0 Ll 0 8 16 2432 40 MM FLUCTUATING 40 0 T ^240 I =)160 I 80 \ 0 TJ tL 0 8 16 2432 40 MM 290 FIGURE 38 Adult Hale S i z e D i s t r i b u t i o n : Gambusia, November In November, th e r e was no s i g n i f i c a n t d i f f e r e n c e i n l e n g t h s of a d u l t males from s t a b l e and f l u c t u a t i n g r e s e r v o i r s ( c f . Table 33) . 2 9 1 RDULT MRLE S IZE DISTRIBUTION GRMBUSIft. NOVEMBER an UJ CQ L±J CQ 2Z ZD STABLE 25 T 20 15 -• 10 -5 0 0 8 16 24 32 40 MM FLUCTUATING 40 j 32 -2 4 -16 -8 0 0 8 16 2 4 3 2 4 0 MM 292 FIGURE 39 Adult Male S i z e D i s t r i b u t i o n : P o e c i l i a , January In January, t h e r e was no s i g n i f i c a n t d i f f e r e n c e i n le n g t h s of a d u l t males from s t a b l e and f l u c t u a t i n g r e s e r v o i r s ( c f . Table 33) . 293 ADULT MALE SIZE DISTRIBUTION POECILIA. JRNURRY STABLE cn U J cn ZD 120 T 96-72 -48 241 0 cn L U C Q I tu 0 8 16 2432 40 MM FLUCTUATING 60 481 36 24 12 0 0 8 16 2432 40 MM 294 Table 60 A n a l y s i s Of Variance: Length Of Mature Males Sample Mean Length! i ~ N I | Prob. Gambusia, January J-A. S t a b l e F l u c t u a t i n g 21.20 | 192 22. 85 J 1206 + 4.5271 | <0.05 B. S t a b l e No Comp S t a b l e Comp F l u c t . No Comp F l u c t . Comp 24. 16 20.52 23.32 22. 66 I 36 156 347 859 I 2.4952 | >0.10 I I 1 Gambusia, November — - + A. S t a b l e F l u c t u a t i n g 21. 24 21. 88 51 110 0.1769 >0.50 B. S t a b l e No Comp S t a b l e Comp F l u c t No Comp F l u c t Comp 20. 82 21.31 21. 13 22. 03 8 43 18 92 0.0841 >0.75 3. P o e c i l i a , -+  Z- January A. S t a b l e F l u c t u a t i n g 19.00 19.21 244 119 0.0606 H->0.75 B. S t a b l e No Comp St a b l e Comp F l u c t No Comp F l u c t Comp 16. 10 19.33 18. 45 20. 15 25 219 66 53 2.8290 >0. 25 295 FIGURE 40 Ad u l t Male S i z e D i s t r i b u t i o n : Gambusia, ftrmand Bayou, Texas There was no s i g n i f i c a n t d i f f e r e n c e i n l e n g t h s of a d u l t males from the estuary and the freshwater pond. 296 ADULT MALE SIZE DISTRIBUTION GRMBUSIR. TEXRS CT L U cn FRESHWATER 30 T 24 • 18-12 -6 -0 0 8 16 24 32 40 MM cr L U CD ZD 15 12 : 9 -6-3-0 ESTUARY MM 0 8 16 2432 40 297 U_j_ Laboratory Methods From my January 1974 s t o c k s f o r Twin R e s e r v o i r and R e s e r v o i r 25, I r a i s e d i n d i v i d u a l broods of f i s h , a t the d e n s i t y of the number of young i n the brood, i n 25 l i t e r a g u a r i a , g i v i n g them one unweighed f e e d i n g per day. As each male matured I removed him, recorded h i s age and l e n g t h , and t r a n s f e r r e d him t o a h o l d i n g aguarium. Thus the j u v e n i l e males never encountered a d u l t males as they matured, and d e n s i t y and food were not c o n t r o l l e d . I then took the a d u l t males from R e s e r v o i r 25, measured them a l l , and s e l e c t e d 15. In one 13.25 l i t e r aquarium I placed only the l a r g e s t males, 2 3 t o 25 mm l o n g . In the second aquarium I placed a spectrum of males ranging from 18 to 23 mm. In the t h i r d aguarium I placed only s m a l l males, from 16 to 20 mm l o n g . I then gathered a l l the young f o r R e s e r v o i r 81 born between 14 and 21 December 1974 (mean b i r t h date 17 December), and r a i s e d them f o r 46 days i n f o u r 25 l i t e r a q u a r i a . At t h a t time a s i g n i f i c a n t number of males had s t a r t e d to mature, and c o u l d be d i s t i n g u i s h e d from the females. I s e l e c t e d 15 j u v e n i l e males, with a n a l f i n s t h a t had s t a r t e d to elongate but were f a r from being mature gonopodia, and a s s o r t e d them at random i n t o 3 r e p l i c a t e s of 5 j u v e n i l e s each. I then placed each r e p l i c a t e i n t o one of the 3 aquaria with d i f f e r e n t a d u l t male s i z e d i s t r i b u t i o n s , and f e d them 50 mg of powdered Tetramin each day f o r 145 days. I checked the aguaria at l e a s t once every three days, and recorded the s i z e and age of the j u v e n i l e s as they matured. 298 5_;_ Laboratory R e s u l t s F i g . 41 d i s p l a y s the s i z e d i s t r i b u t i o n of a d u l t males i n s t a b l e and f l u c t u a t i n g r e s e r v o i r s i n January, 1974. R e c a l l t h a t p o e c i l i i d males stop growing at mat u r i t y , so t h a t s i z e of an a d u l t male i s a good estimate of s i z e at ma t u r i t y . Table 61a presents an a n a l y s i s of va r i a n c e of the data d i s p l a y e d i n F i g . 41. The males from s t a b l e r e s e r v o i r s were about 1.5 mm s h o r t e r on the average, and the d i f f e r e n c e was s i g n i f i c a n t . Table 61b presents the r e s u l t s of a G t e s t on the o v e r a l l d i s t r i b u t i o n s , which were s i g n i f i c a n t l y d i f f e r e n t . The s i z e d i s t r i b u t i o n s f o r males from s t a b l e r e s e r v o i r s was skewed toward s m a l l e r s i z e c l a s s e s , with a mode at 18 mm; that f o r f l u c t u a t i n g r e s e r v o i r s was skewed towards l a r g e r s i z e c l a s s e s with a mode a t 23 mm. These r e s u l t s stood i n c o n t r a d i c t i o n t o the ideas of r - and K - s e l e c t i o n , which p r e d i c t e d s m a l l e r males i n f l u c t u a t i n g r e s e r v o i r s . But Borowsky (1973) had demonstrated t h a t s o c i a l i n t e r a c t i o n s among males i n f l u e n c e d age and s i z e at maturity i n Xiphophorus maculatus. T h e r e f o r e , I r a i s e d male Gambusia under constant c o n d i t i o n s to see i f the f i e l d p a t t e r n s held up. Table 61c p r e s e n t s the r e s u l t s of an a n a l y s i s of the c o v a r i a n c e of le n g t h and l o g age a t maturity f o r Twin R e s e r v o i r and R e s e r v o i r 25 males. Males from Twin matured at s i g n i f i c a n t l y s m a l l e r l e n g t h s and younger ages than those from R e s e r v o i r 25, c o r r o b o r a t i n g the f i e l d data. F i g . 42 pr e s e n t s the r e g r e s s i o n l i n e s . Males from R e s e r v o i r 25 matured almost 30 days l a t e r than males from Twin. In t h i s experiment, males were removed as they matured. In the long-term experiment, I l e f t the males i n the. tanks 299 FIGURE 41 D i s t r i b u t i o n Of a d u l t Male S i z e s : Gambusia, January In the f i e l d , a d u l t males were sm a l l e r (mean = 21.2 mm) i n the s t a b l e r e s e r v o i r s than they were {mean = 22.8 mm) i n the f l u c t u a t i n g r e s e r v o i r s . Moreover, the shapes of the d i s t r i b u t i o n s were skewed i n op p o s i t e d i r e c t i o n s : towards s m a l l e r f i s h i n s t a b l e r e s e r v o i r s (mode = 18-19 mm), and towards l a r g e r f i s h i n f l u c t u a t i n g r e s e r v o i r s (mode = 22-23 mm) . DISTRIBUTION STABLE OF MALES FLUCTUATING 301 FIGURE 4 2 Length and age At M a t u r i t y : Males, Laboratory R e s u l t s In the l a b o r a t o r y , males from a s t a b l e r e s e r v o i r (Twin) were younger (41 vs 69 days) and s m a l l e r (18.8 vs. 20.2 mm) at maturity than males from a f l u c t u a t i n g r e s e r v o i r ( R e s e r v o i r 25). Thus the p a t t e r n observed i n the f i e l d ( c f . F i g . 42) held up i n the l a b o r a t o r y f o r t h i s p a i r of r e s e r v o i r s , but not f o r others ( c f . F i g . 3 9) . LENGTH VS TWIN RES. (S) 30 • r Y = 4 . 8 1 4 X + 1 . 3 3 0 N" ~ 95 25- MEAN ALPHA = 4 0 . 9 0 20 • 15-10 -i . __H LN[MALE ALPHA) LOG ALPHA RES. 25 (U) T Y =' 3 . 8 7 4 X + 4 . 2 6 5 LN(MALE ALPHA) o to 30 3 Table 6J_ Hale Age And S i z e At Matu r i t y A. A n a l y s i s Of Variance, Male S i z e , January FIELD DATA j j +. Sample n | Mean | Length I Prob S t a b l e F l u c t u a t i n g 201 1335 21.19 22.76 71.2399 <0.0001 B. G T e s t , Male S i z e D i s t r i b u t i o n , January FIELD DATA G = 100.37, Prob < 0.005 S i z e C l a s s (mm) 14 15 16 17 18 19 20 21 22 23 24 25 26 St a b l e 0 0 22 45 43 25 18 12 16 F l u c t u a t i n g 7 27 44 89 160 185 210 212 154 117 12 C. A n a l y s i s Of Covariance, Length X Log Age At Maturity Twin R e s e r v o i r And R e s e r v o i r 25 LAB DATA + -h I Mean Age At | Matur i t y I . x. Sample J n Mean Length At Maturity Prob Twin 25 I i 95 I 83 40.90 69.33 18.78 20. 19 4.8345 0.0276 304 FIGORE 43 Maturation Sates: Males Male Gambusia from R e s e r v o i r 90 matured e a r l i e r under high food treatments than male Gambusia from R e s e r v o i r 81 and Kay R e s e r v o i r . No other d i f f e r e n c e s i n age at maturity were s i g n i f i c a n t . These r e s u l t s c o n t r a d i c t other experiments c o n t r a s t i n g age at maturity i n males from a s t a b l e r e s e r v o i r (Twin) and a f l u c t u a t i n g r e s e r v o i r (Reservoir 25, c f . F i g . 43). Thus there appears to be a s i g n i f i c a n t amount of l o c a l a d a p t a t i o n i n t r a i t s l i k e age at maturity, but i n many s p e c i f i c cases i t i s not c l e a r l y a s s o c i a t e d with the s t a b i l i t y of the r e s e r v o i r . A l l data shown i n t h i s f i g u r e were taken from f i s h r a i s e d a t 27°C at d e n s i t i e s of 0.75 f i s h / l i t e r . 305 MATURATION RATES: MALES HIGH FOOD LOW FOOD -5 4 I I I I I I I I I I I I I M I I I I 1 I 0 30 60 90 120 150 180210 15 10 5 0 81 -5 l I I I I I I I 1 I I I I I I I I I I I H 0 30 60 90 120 150 180 210 - H I I I I I I I I I I I I 1 I I I l 30 60 90 120 150 180 210 15 T 10 -5 -0 90 •-5 i i i i I I I I I I M I I I I I 1 I I I I 0 30 60 90 120 150 180 210 15 T 10 •• 5 •-0 -KAY -5 I i i i i i i i i i i i i i i i i i i i i i 0 30 60 90 120150180 210 1 5 T 10 5 0 KflY -5 l i i i i i i i i i i i i i i i i i i i i i 0 30 60 90 120150 180 210 151 0 TWIN -5 l i i i i i i i i i i i i i i i i i i i i i 0 30 60 90 120 150 180 210 15 T 10 -5 •-• o • • • TWIN -5 I i i i i i i i i i i i i i i i i i i i i i 0 30 60 90 120 150 180 210 AGE IN DAYS AGE IN DAYS 306 Table 62 Age At Maturity In Males Lab Data: Longterm Experiments r - ' • - , , . , , J 1. A n a l y s i s Of Variance, R e s e r v o i r s 81, 90, And Kay j | High Temperature, High And Low Food Treatments I |Sample ! n T Number | B p l c t s | Mean Age ! F T 1 |Prob | j S t a b l e j F l u c t u a t i n g ] 9 38 I 2 I 4 ! 80.56 85.14 ! 0.0657* |>0.75 | |Kay |Reservoir 81 J R e s e r v o i r 90 9 16 22 j 2 1 2 1 2 1 80.56 98.50 75.50 | 2.0659* |>0.10 | I Kay HF jKay Lf |81 HF | 81 Lf | 90 HF | 90 L f T * 5 4 7 9 14 8 i i 83.40 77.00 76. 14 1 15.89 70.93 83.50 • 2.1178** 10.1114 | i j I 2. Kolmogoroff-Smirnoff O n e - t a i l e d T e s t s Of D i f f e r e n c e s In Age At Ma t u r i t y I Samples D T N1 | N2 | Ch i - s g r I Prob | |81-90 High Food | j81-Kay High Food | J 90-Kay High Food J |90-Twin High Food | i ,, i . . 375 .145 .400 .400 27 | 27 j 25 | 25 J 25 25 25 10 I 7.3017 1.0917 8.0000 4.5714 |<0.05 | |>0.50 | |<0.02 | |. 10<p<.20j |81-90 Low Food |81-Kay Low Food |90-Kay Low Food • . 357 .124 .304 j 21 I 21 | 14 | 14 15 15 j 4.2823 0.5382 2.6769 |. 10<p<.20| |>0.50 | |>0.20 | 1 J81-81 H-L Food |90-90 H-L Food |Kay-Kay H-L Food i . J . . .170 . 186 .107 27 | 25 | 25 | 21 14 15 _ J _ 1.3655 1.2419 0.4 293 j>0.50 | |>0.50 | |>0.80 | . X - 1 * Denominator Mean Square = Food Treatments ** Denominator Mean Square = I n d i v i d u a l F i s h Table 63 Male Age And S i z e At M a t u r i t y , C o n t r o l l i n g For Adult Male S i z e A. Ages And S i z e s 1 ••" - T j - T 1 |Experiment |Adult Male |Juv. Age j Min. , J Juv. S i z e I Min. | | Si z e (mm ) |At M a t u r i t y I Mean |At Maturity (Mean | i i | 1. Large | 22.9 | 128 j 23.35 i t | a d u l t s J 24.3 | 199 | 175. 251 22.60 |23.26J I | 22.6 \ >191 j | >23. 5 1 | | | 24.2 J > 19 1 | J >23.6 | | | 24.7 1 • j 2. Broad | 17.7 j 104 j j 22.0 ] j | d i s t r i b . | 21.8 | 128 | 148. * t 23. 1 |23.35| I of a d u l t s | 22.0 I 128 J } 25.6 | | j | 21.9 I >191 | | 22.2 ] | | i 23.2 | >191 J J >24.4 | j i .„ • • , i i i i i I j J I i j 3. Small | 16.8 | 55 ] j 20.2 I | | a d u l t s | 17.9 | 104 |111. 3 1 20.6 |21.45| I | 19.0 ! 104 | 22.2 | | | \ 19.5 | 128 | 22.6 j | | | 19.8 | 168 | | 21.8 | j • • i • * B. Mann-Shitney U-T e s t s • I |Comparison | T r a i t | D Prob j • i - • In • J — T 1 | 1x2 | Age | 9 | .452 j | 1x3 1 Age j 1 .008 | | 2x3 J Age | 4 .048 1 J 1x2 | S i z e | 7 J .278 ] | 1x3 | Size | 0 | .004 | | 2x3 j Si z e j 3 J .028 i . . . .... i . X _ J 3 0 8 a f t e r they had matured. F i g . 43 presents the cumulative number of males mature, p l o t t e d a g a i n s t age. Table 62a pr e s e n t s the r e s u l t s of an a n a l y s i s of v a r i a n c e i n age at m a t u r i t y , and t a b l e 62b e x h i b i t s Kolmogoroff-Smirnoff o n e - t a i l e d t e s t s f o r d i f f e r e n c e s i n the ages a t maturity presented i n F i g . 43. Hales from both R e s e r v o i r 81 (high food) and Re s e r v o i r 90 (high food) matured e a r l i e r than males from Kay Res e r v o i r (high f o o d ) . None of the other d i f f e r e n c e s were s i g n i f i c a n t . Thus the f i e l d and l a b o r a t o r y comparisons of male age and s i z e a t maturity are at l e a s t p a r t i a l l y c o n t r a d i c t o r y . The t r a i t s measured are g u i t e s e n s i t i v e t o c e r t a i n c o n d i t i o n s , p a r t i c u l a r l y d e n s i t y and the presence of a d u l t males, and t h i s s e n s i t i v i t y may d i f f e r from r e s e r v o i r to r e s e r v o i r . Table 63 presents the r e s u l t s of the experiment i n which I c o n t r o l l e d the s i z e d i s t r i b u t i o n of a d u l t males i n the environments of maturing j u v e n i l e males. When j u v e n i l e males were r a i s e d i n the presence of l a r g e a d u l t s , they remained j u v e n i l e s f o r a long time, maturing a t an average of more than 175 days and a l e n g t h of at l e a s t 23.3 mm. When r a i s e d i n an aguarium with a broad d i s t r i b u t i o n of a d u l t s , they grew more r a p i d l y , maturing at an average age of at l e a s t 150 days, and an even l a r g e r s i z e , 23.4 mm. When r a i s e d with s m a l l a d u l t s , they matured e a r l i e r , at an average of 112 days, and at an average of only 21.5 mm. I d i d Hann-Whitney U-Tests f o r s i g n i f i c a n t d i f f e r e n c e s i n the ranks of age and s i z e at matur i t y . Table 63b presents the r e s u l t s . There were no s i g n i f i c a n t d i f f e r e n c e s between the f i r s t two groups, but both were s i g n i f i c a n t l y d i f f e r e n t from the t h i r d . Thus the s i z e d i s t r i b u t i o n of a d u l t 309 males i n the environment does a f f e c t the age and s i z e at maturity of maturing j u v e n i l e males. That there were no s i g n i f i c a n t d i f f e r e n c e s i n the impact of the d i f f e r e n t a d u l t male s i z e d i s t r i b u t i o n s i n the f i r s t two groups suggests that i t was not the average s i z e of a d u l t males, or the range of s i z e s of a d u l t males, that a f f e c t e d the j u v e n i l e s , but the s i z e of the l a r g e s t male present. In the f i e l d , males matured a t s m a l l e r average s i z e s i n s t a b l e than f l u c t u a t i n g r e s e r v o i r s . T h i s d i f f e r e n c e held up i n the l a b f o r a t l e a s t one s t a b l e - f l u c t u a t i n g p a i r of r e s e r v o i r s when males were removed from a q u a r i a as they matured. The s i z e d i s t r i b u t i o n of a d u l t males i n the environment has an impact on the age and s i z e at maturity of j u v e n i l e males, which are r a t h e r p l a s t i c i n t h e i r development. They appear to f o l l o w the f o l l o w i n g r u l e : grow as l a r g e or l a r g e r than the l a r g e s t male present before maturing. 6*. D i s c u s s i o n That males mature, on the average, at a l a r g e r s i z e i n f l u c t u a t i n g r e s e r v o i r s c o u l d be a t t r i b u t e d e i t h e r to e v o l u t i o n a r y changes i n s o c i a l s t r u c t u r e , to s e l e c t i o n f o r l a r g e r males by dry season drawdowns i n f l u c t u a t i n g r e s e r v o i r s , to h i g h e r food l e v e l s i n f l u c t u a t i n g r e s e r v o i r s , or to a l l t h r e e . I have shown, i n a p r e l i m i n a r y f a s h i o n , that j u v e n i l e males reared i n the presence of l a r g e a d u l t males grow up t o be l a r g e , and that j u v e n i l e males reared i n the presence of small a d u l t males grow up t o be s m a l l . T h i s demonstrates that some of the same s o c i a l f o r c e s that Borowsky (1973) observed i n 3 1 0 Xiphophprus maculatus are at work i n Gambusia p o p u l a t i o n s . The e v o l u t i o n a r y f o r c e s on males are q u i t e d i f f e r e n t from those on females. A l l p o e c i l i i d males stop growing at maturity, while females c o n t i n u e to grow u n t i l they reach s e n i l i t y . That i s a major, and unexplained, d i f f e r e n c e i n a l i f e h i s t o r y t r a i t . I found the f o l l o w i n g f u r t h e r evidence of d i f f e r e n c e s between males and females. (a) In the f i e l d , I c o u l d f i n d no d i f f e r e n c e s i n s i z e a t maturity i n females between s t a b l e and f l u c t u a t i n g r e s e r v o i r s . Males from s t a b l e r e s e r v o i r s were s i g n i f i c a n t l y s m a l l e r at maturity than males from f l u c t u a t i n g r e s e r v o i r s . (b) S o c i a l i n t e r a c t i o n s appear to have a much st r o n g e r e f f e c t on the age and s i z e at which males mature than they do on maturation i n females. But t h a t statement cannot be made with c o n f i d e n c e u n t i l the male maturation experiments I r e p o r t e d here have been done f o r both males and females with more r e p l i c a t e s . No one has shown why, i n an e v o l u t i o n a r y sense, some males should mature at s i z e s and ages d i f f e r e n t from o t h e r s . One could r e a r j u v e n i l e s from s t a b l e and f l u c t u a t i n g r e s e r v o i r s with a d u l t males of d i f f e r e n t s i z e d i s t r i b u t i o n s from both s t a b l e and f l u c t u a t i n g r e s e r v o i r s , to see i f the e f f e c t was due to the r e a c t i o n of the j u v e n i l e s , the dominance of the a d u l t s , or to s t r i c t l y the i n t e r a c t i o n between the two. On the b a s i s of the f i e l d data, I p r e d i c t t h a t a d u l t males from s t a b l e r e s e r v o i r s w i l l not r e t a r d maturity i n j u v e n i l e s from f l u c t u a t i n g r e s e r v o i r s to the same extent t h a t a d u l t males from f l u c t u a t i n g r e s e r v o i r s do. Why should the l i f e h i s t o r y t r a i t s of p o e c i l i i d males 311 d i f f e r from those of females? Since f e r t i l i z a t i o n i s i n t e r n a l , only a s m a l l amount of sperm i s necessary f o r impregnation, and there i s no p o i n t i n growing past a c e r t a i n s i z e i n order to produce more sperm. Secondly, t h e r e i s a high premium on being the f i r s t male t o inseminate a female, because she can r e t a i n sperm i n her o v a r i e s and use i t to inseminate s e v e r a l broods i n s u c c e s s i o n . I t i s p o s s i b l e t h a t p o e c i l i i d females are o n l y e f f e c t i v e l y inseminated once i n t h e i r l i v e s . I suggest t h a t s i z e at maturation i n male p o e c i l i i d s i s determined by a compromise between manoeuverability, a s s o c i a t e d with s m a l l s i z e , and s o c i a l dominance, a s s o c i a t e d with l a r g e s i z e . 

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