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Growth and regulation of springtail populations, with special reference to predation by pseudoscorpions Johnson, Dan Lloyd 1980

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cl GROWTH AND REGULATION OF SPRINGTAIL POPULATIONS, WITH SPECIAL .REFERENCE TO PREDATION BY PSEUDOSCORPIONS by Dan L l o y d Johnson B . S c , The U n i v e r s i t y of Saskatchewan, 1978 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n THE FACULTY OF GRADUATE STUDIES (Department of P l a n t S c i e n c e and The I n s t i t u t e of Animal Resource Ecology) We a c c e p t t h i s t h e s i s as co n f o r m i n g t o t h e r e g u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA (5} Dan L l o y d Johnson, 1980 In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f t h e r e q u i r e m e n t s f o r an a d v a n c e d d e g r e e a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e t h a t t h e 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 f o r r e f e r e n c e and s t u d y . I f u r t h e r a g r e e t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by t h e Head o f my D e p a r t m e n t o r by h i s r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l n o t be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . D e p a r t m e n t o f P 1 a r y K c , M . n . 0 The U n i v e r s i t y o f B r i t i s h C o l u m b i a 2075 Wesbrook P l a c e Vancouver, Canada V6T 1WS D a t e August 29, 1980 ABSTRACT The e f f e c t s of p r e d a t i o n by a p s e u d o s c o r p i o n , Apo chthonius minimus, on growing p o p u l a t i o n s - of s p r i n g t a i l s , F o l s o m i a C a n d i d a , were s t u d i e d e x p e r i m e n t a l l y . A n a l y s i s of i n d i v i d u a l s p r i n g t a i l growth over time p r o v i d e d a t e c h n i q u e f o r d e t e r m i n i n g prey age. P r e d a t i o n r a t e s and t h e degree o f s i z e - s e l e c t i o n by t h e p r e d a t o r were measured. I t was shown t h a t t h e p r e d a t o r s p r e f e r o l d e r prey i n d i v i d u a l s and t h a t t h i s p r e f e r e n c e may r e s u l t i n h i g h e r d e n s i t i e s of prey j u v e n i l e s . B a s e l i n e d a t a on p o p u l a t i o n dynamics, p o p u l a t i o n d i s t r i b u -t i o n s , d i s p e r s a l , s p e c i e s c o m p o s i t i o n of t h e m i c r o a r t h r o p o d community i n t h e s t u d y a r e a , s o i l m o i s t u r e and weather were p r o v i d e d . TABLE OF CONTENT'S ABSTRACT i i LIST OF TABLES . . v i LIST OF FIGURES . . . i x ACKNOWLEDGEMENTS x i i i INTRODUCTION 1 G e n e r a l B i o l o g y . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 CHAPTER ONE: A COMMUNITY SETTING FOR POPULATION STUDIES.... 8 I n t r o d u c t i o n .....9 Methods 9 R e s u l t s and D i s c u s s i o n . . . . . 11 D e n s i t i e s and dynamics.. ............................. 11 D i s t r i b u t i o n s . ...........................13 CHAPTER TWO: POST-EMBRYONIC GROWTH OF THE COLLEMBOLANS, FOLSOMIA CANDIDA AND XMXi±I.A G RISE A, AT THREE TEMPERATURES ..r, . . . , i 6 I n t r o d u c t i o n . ... 17 Methods . . . ... 18 R e s u l t s and D i s c u s s i o n . . . . . . . . . . . . . . . 20 Le n g t h and age 20 Comparison of l e n g t h - a g e r e g r e s s i o n l i n e s . . . . . . . . . . . . 27 T e s t s of s l o p e s : do t h e growth parameters d i f f e r ? . . . . 2 8 T e s t s of i n t e r c e p t s : do t h e l e n g t h s a t h a t c h i n g d i f f e r ? 30 Head w i d t h 30 L i n e a r and n o n - l i n e a r e f f e c t s of temperature 34 Development of an a g i n g t e c h n i g u e .......36 CHAPTER THREE: PREDATION OF AP0CHTH0NI0S M I N I M S (PSEUDOSCORPIONIDA: CHTHONIIDAE) ON FOLSOMIA CANDIDA (C0LLEM50L A: ISOTOMIDAE) . . I . . PREDATION AND SIZE-SELECTION 38 I n t r o d u c t i o n . • . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 9 B i o l o g y o f t h e prey and p r e d a t o r . . . . . . . . . . . . . . . . . . . . . 41 F p l s o m i a Candida 41 Ap o c h t h g n i u s minimus. ... 43 Methods . 44 I . . P r e d a t i o n r a t e s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 I I . S i z e - s e l e c t i o n . . . . . . . . . . . . . . ...47 R e s u l t s and D i s c u s s i o n . . 43 I . . P r e d a t i o n r a t e s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 I I . . S i z e - s e l e c t i o n by t h e p r e d a t o r s . . . . . . . . . . . .57 CHAPTER FOUR: PREDATION OF APOCHTHONIUS MINIMUS (PSEUDOSCORPIONIDA: CHTHONIIDAE) ON FOLSOMIA CANDIDA (COLLEM BOL A: ISOTOMIDAE).. I I . . EFFECTS OF PREDATION ON PREY POPULATIONS 64 I n t r o d u c t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 5 Methods. ......66 R e s u l t s and D i s c u s s i o n . ......68 V U n c o n t r o l l e d e n v i r o n m e n t a l v a r i a b l e s . . . . . . . . . . . . . . . . . 68 I n t e r p r e t a t i o n of l e n g t h - f r e g u e n c y d i s t r i b u t i o n s . . . . . 70 SUMMARY 8 3 LIT ER AT UR E CITED. ......85 APPENDIX A: C a l i b r a t i o n o f the E x t r a c t o r 102 APPENDIX B: Abundance and D i s t r i b u t i o n of S o i l M i c r o a r t h r o p o d s a t t h e UBC Research F o r e s t , 1979 ... 104 P a r t I . . P o p u l a t i o n d e n s i t i e s . .104 P a r t I I . _ D i s t r i b u t i o n s . . . . . ........................... 120 APPENDIX C: S o i l M o i s t u r e a t t h e Study S i t e D u r i n g 1979..135 APPENDIX D: R a i n f a l l and D a i l y Mean Temperatures a t t h e Study S i t e D u r i n g 1979 .. 139 APPENDIX E: O r t h o g o n a l C o n t r a s t C o e f f i c i e n t s 142 APPENDIX F: D i s p e r s a l of F. C a n d i d a ..........144 v i LIST OF TABLES T a b l e 1. R e g r e s s i o n s of l n ( l e n g t h ) and l n (age) c o r r e s p o n d i n g t o F i g u r e s 5 and 6............... 25 Table 2a.. Slope comparisons w i t h i n s p e c i e s f o r a l l p a i r s of t e m p e r a t u r e s ..29 Ta b l e 2b.. Slope comparisons between s p e c i e s a t each...... 2 9 t e m p e r a t u r e . T a b l e 3a. I n t e r c e p t comparisons w i t h i n s p e c i e s f o r a l l p a i r s of t e m p e r a t u r e s . . . . . . . . ...31 T a b l e 3b.. I n t e r c e p t comparisons between s p e c i e s 31 Table 4a. R e g r e s s i o n f o r F. C a n d i d a 35 Ta b l e 4b. R e g r e s s i o n f o r X. g r i s e a . . . . . . . . . . . . ...35 Table 5.. A n a l y s i s of v a r i a n c e of the number o f prey e a t e n . i n t h e f u n c t i o n a l r e s p o n s e experiment ...51 Tabl e 6.. O r t h o g o n a l c o n t r a s t s ( i n d i v i d u a l degree of freedom t e s t s ) 52 711 Table 7. Estimates of h a n d l i n g time (Th) and a t t a c k r a t e (a) f o r d i f f e r e n t prey s i z e and temperature treatments ...................53 Table 8. S e l e c t i v i t y s t a t i s t i c s f o r length c l a s s e s of prey. 6 0 Table 9. D e s c r i p t i o n of the f i n a l p o p u l a t i o n s and contents of the c o n t a i n e r s at the end of the experiment...69 Table 10. R e l a t i v e f r e q u e n c i e s (% of t o t a l ) o f the d i f f e r e n t s i z e s of F. Candida i n the 16 p o p u l a t i o n s . . 75 Table B1. D i s t r i b u t i o n of Folsomia sp 121 Tabl e B2. D i s t r i b u t i o n of Afiochthonius minimus a d u l t s . . . . 122 Table B3. D i s t r i b u t i o n of Apochthonius minimus nymphs.... 123 Table B4. D i s t r i b u t i o n of Isotomids other than Folsomia. ..124 spp. Table B5. . D i s t r i b u t i o n of Hypogasturids.................. 125 Table B6. . D i s t r i b u t i o n of O n y c h i u r i d s (other than T u l l b e r g i a sp.) 126 v i i i T a b l e B7. . D i s t r i b u t i o n o f T u l l b e r q i a s p . . . . . . 127 Table B8. D i s t r i b u t i o n of Entomobryids. .128 T a b l e B9. D i s t r i b u t i o n o f L e p i d o c y r t u s spp................ 129 Table B10._ D i s t r i b u t i o n of Tomocerus spp .....130 Tab l e B11.. D i s t r i b u t i o n o f Neanura 131 T a b l e B12. D i s t r i b u t i o n o f S m i n t h u r i d s . . 132 Table B13. D i s t r i b u t i o n o f Mesostigmata 133 T a b l e B14.. D i s t r i b u t i o n o f C h i l o p o d s 134 Table C I . . S o i l m o i s t u r e a t t h r e e depths from May to September 1979. Water l o s s i s from 2.5 cm x 5.0 cm d i a c o r e s 1 36 Table C2. Mean w e i g h t s o f s o i l samples. M l samples were 2.5 cm x 5.0 cm d i a c o r e s 138 T a b l e E1.. O r t h o g o n a l c o n t r a s t c o e f f i c i e n t s . . .....143 i x LIST OF FIGURES F i g u r e 1. The harmony of the pedosphere 2 F i g u r e 2a. R e p r e s e n t a t i v e s p r i n g t a i l s s i m i l a r t o t h o s e c o l l e c t e d i n t h e su r v e y p a r t o f t h i s s t u d y ( l e n g t h s 1-3 mm)..... 5 F i g u r e 2b. More r e p r e s e n t a t i v e s p r i n g t a i l s s i m i l a r t o t h o s e c o l l e c t e d i n t h e s u r v e y p a r t o f t h i s s t u d y ( l e n g t h s 1-2 mm). ...........6 F i g u r e 3.. The U n i v e r s i t y o f B r i t i s h Columbia Research F o r e s t , Maple R i d g e , B.C 10 F i g u r e 4. A h i g h - g r a d i e n t Macfadyen e x t r a c t o r s i m i l a r t o t h e one used i n t h i s s t u d y . 12 F i g u r e 5. Le.ngth-age r e l a t i o n s h i p s f o r F. C a n d i d a r e a r e d under t h r e e t e m p e r a t u r e r e g i m e s . . . . . . . 22 F i g u r e 6. Length-age r e l a t i o n s h i p s f o r X. g r i s e a r e a r e d under t h r e e t e m p e r a t u r e r e g i m e s . . . ......24 F i g u r e 7.. The de c r e a s e w i t h age i n t h e head w i d t h / body l e n g t h r a t i o s o f F . . C a n d i d a (a) and X . . g r i s e a (b) 33 X F i g u r e 8.. Scanning e l e c t r o n m i c r o g r a p h o f an A- minimus a d u l t 40 F i g u r e 9. The h i n g e d , s e r r a t e d c h e l i c e r a e o f A. minimus. ..45 F i g u r e 10..Type I I f u n c t i o n a l r e s p o n s e c u r v e s f o r the two t e m p e r a t u r e s and two prey s i z e s 55 F i g u r e 11. Changes i n the number eaten per 12 h o u r s w i t h changes i n prey d e n s i t y , prey s i z e and time.....56 F i g u r e 12. S i z e f r e q u e n c y d i s t r i b u t i o n o f prey p o p u l a t i o n a v a i l a b l e t o A. minimus and t h e prey e a t e n . . . . . . 58 F i g u r e 1 3 . . T a c t i l e s e t a e of the " p i n c e r " ( p a l p a l o r c h e l a l hand) of A. minimus 61 F i g u r e 14. The l e n g t h - f r e q u e n c y d i s t r i b u t i o n s o f t h e f o u r p o p u l a t i o n s t h a t s u r v i v e d the p r e d a t i o n t r e a t m e n t ................71 F i g u r e 15. The l e n g t h - f r e q u e n c y d i s t r i b u t i o n o f t h e e i g h t c o n t r o l p o p u l a t i o n s ..72 F i g u r e B1. T o t a l C o l l e m b o l a , ...105 x i F i g u r e B2. Folsomia n i v a l i s , F. q u a d r i o c u l a t a , F. Candida {Family Isotomidae) . . . . 1 0 6 F i g u r e B3. Appchthonius minimus,, a d u l t s 107 Figu r e B4. Apochthonius minimus, nymphs.................. 108 Figu r e B5..Isotomurus p a l u s t r i s , Isotoma t r i s p i n a t a , I * o l i v a c e a , I . v i r i d i s (Family Isotomidae).... 109 F i g u r e B6. Family Hypogastruridae. I n c l u d e s Hypoqastrura pseudarmata, H . . v u l g a r i s , H. y i r g o , X e n y l l a g r i s e a and X..sp............................... 110 Figu r e B7.,Onychiurus f l a y e s c e n s , 0 . armatus, Lophognathella ghoreutes (rare) (Family Onychiuridae, Subfamily Onychiurinae) 111 F i g u r e B8. T u l l b e r g i a sp. (Family Onychiuridae, Subfamily T u l l b e r g i i n a e ) ..112 F i g u r e B9. Entomgbrya g u a d r a l i n e a t a , E. m u l t i f a s c i a t a , E. comjoarata, E. i n t e r m e d i a and E. n i v a l i s (Family Entomobryidae) 113 F i g u r e B10. L e p i d o c y r t u s c i n e r e u s , L . liqnorum and L. sp. (Family Entomobryidae)........................ 114 x i i F i g u r e B11• Tofflocerus e e l s u s , T. sp. (Family Entomobryidae, Subfamily Tomocerinae) 115 Fi g u r e B12. . Neanura p e r s i m i l i s (Family Neanuridae) 116 Figure B13. Family Sminthuridae .....................117 Figu r e B14. . U n i d e n t i f i e d mesostigmatid mites....- ....118 Figu r e B15.. U n i d e n t i f i e d Chilopoda (>2mm width)... 119 Fi g u r e D1. R a i n f a l l a t the study s i t e during the sampling p e r i o d , May to September, 1979 140 Fi g u r e D2. D a i l y mean temperature at the study s i t e . 141 Fi g u r e F1. The d i s p e r s a l t r a y used i n the experiments d e s c r i b e d i n Appendix F. (top view).... 145 Figu r e F2. D i s p e r s a l over two hours; no food i n area 1...148 Fi g u r e F3. D i s p e r s a l over two hours; food i n area 1 149 Figu r e F4. D i s p e r s a l over twenty-four hours; nc food.....150 ACKNOWLEDGEMENTS I am g r a t e f u l f o r Dr. W.G. W e l l i n g t o n ' s s u p e r v i s i o n d u r i n g my master's program. H i s co n c e r n , g e n e r o s i t y and p h i l o s o p h i c a l g u i d a n c e were e s p e c i a l l y a p p r e c i a t e d . I thank Dr. V.G. M a r s h a l l f o r h i s h e l p f u l s u g g e s t i o n s and f o r p r o v i d i n g me w i t h my o r i g i n a l s t o c k of F. Candida. Dr. A. C a r t e r k i n d l y l e a n e d me e x t r a c t i o n equipment. Dr. G.W. Eaton c a l c u l a t e d t h e c o n t r a s t c o e f f i c i e n t s f o r t h e u n e g u a l l y spaced d e n s i t i e s i n Chapter Three. The s c a n n i n g e l e c t r o n m i crographs i n the same c h a p t e r a r e t h e work of D. Henderson. . Dr. E . J 3 . B e n e d i c t p r o v i d e d a copy o f her PhD. t h e s i s and o f f e r e d h e l p i n i d e n t i f y i n g p s e u d o s c o r p i o n s . A s s i s t a n c e w i t h C o l l e m b o l a taxonomy was p r o v i d e d by Dr. K. C h r i s t i a n s e n . The w i l l i n g t e c h n i c a l a s s i s t a n c e o f Stev e Gormican was both i n v a l u a b l e and e n j o y a b l e . I am g r a t e f u l t o the s t a f f o f t h e OBC Research F o r e s t f o r t h e i r f r i e n d l y s e r v i c e and p e r m i s s i o n t o e s t a b l i s h a s t u d y s i t e . I e s p e c i a l l y want t o thank my w i f e , Cathy Johnson, f o r h er h e l p , encouragement and u n d e r s t a n d i n g . Computer funds were p r o v i d e d by a NSERC g r a n t t o Dr. . W e l l i n g t o n and, i n p a r t , by t h e I n s t i t u t e o f Animal Resource E c o l o g y . I was sup p o r t e d by a g r a n t t o Dr. W e l l i n g t o n , a U n i v e r s i t y of B r i t i s h Columbia Graduate F e l l o w s h i p and a Department of P l a n t S c i e n c e T e a c h i n g A s s i s t a n t s h i p . 1 INTRODUCTION For at l e a s t a c e n t u r y , e n t o m o l o g i s t s have been t r y i n g t o d i s c o v e r what p r e v e n t s t h e u n l i m i t e d growth of i n s e c t p o p u l a t i o n s . In more r e c e n t decades the same g u e s t has been d i r e c t e d toward a l l manner of c r e a t u r e s t h a t i n h a b i t t h e e a r t h , from mice t o whales. T h e o r i e s , a c r i m o n i o u s d e b a t e s and v i o l e n t c o n t r o v e r s i e s have ebbed and f l o w e d over t h e i m p o r t a n c e of p a r a s i t i s m , p r e d a t i o n , weather, g e n e t i c feed-back mechanisms, polymorphism, b e h a v i o r , d i s p e r s a l , food a v a i l a b i l i t y , pathogens, c o m p e t i t i o n and a h o s t o f o t h e r f a c t o r s and i n t e r a c t i o n s ( t h e t h e o r i e s a r e r e v i e w e d i n a r e a d a b l e way by Andrewartha and B i r c h , 1973 and P r i c e , 1975). With such a m u l t i t u d e o f t h e o r i e s , and an even g r e a t e r a c c u m u l a t i o n of e v i d e n c e f o r we know not what, a new i d e a seems t o be a l m o s t i m m e d i a t e l y c r u s h e d by the l o a d of f a v o r i t e hypotheses t h a t has b u i l t up. In such c i r c u m s t a n c e s , f i n d i n g a r e l a t i v e l y untouched system t h a t o f f e r s i n t e r e s t i n g new p o s s i b i l i t i e s seems an almost i m p o s s i b l e dream. N e v e r t h e l e s s , I b e l i e v e t h a t t h e system d e s c r i b e d h e r e i s worth a second l o o k . The bulk of t h i s t h e s i s c o n c e r n s the p o p u l a t i o n r e l a t i o n s h i p s between a s p r i n g t a i l s p e c i e s and i t s p r e d a t o r ( F i g u r e 1 ) . In t h e f o l l o w i n g pages I have: ( i ) assembled a community s e t t i n g f o r t h e s t u d y (Chapter One and Appendix B ) ; ( i i ) s t u d i e d the growth o f i n d i v i d u a l s p r i n g t a i l s and i n so d o i n g developed a t e c h n i q u e t o determine t h e i r ages (Chapter Two); ( i i i ) q u a n t i t a t i v e l y and q u a l i t a t i v e l y c h a r a c t e r i z e d s i z e - s e l e c t i v e p r e d a t i o n o f the s p r i n g t a i l s by F i g u r e 1. The harmony o f the pedosphere. T h i s s t u d y f o c u s e s on the r e l a t i o n s h i p between the s p r i n g t a i l ( p l a y i n g the oboe) and the p s e u d o s c o r p i o n (on c e l l o ) . (From S a t c h e . l l , 1 9 7 7 ) 3 pseudo-scorpions (Chapter Three) , and ( i v ) e x p e r i m e n t a l l y demonstrated t h e e f f e c t o f t h i s p r e d a t i o n on growing s p r i n g t a i l p o p u l a t i o n s c o n f i n e d i n c o n t a i n e r s i n t h e f i e l d (Chapter F o u r ) . I n s t e a d o f s l i p p i n g i n t o a K e p l e r i a n d i s c o u r s e on e v e r y t w i s t and t u r n or e v e r y f a i l u r e and t r i u m p h of my r e s e a r c h , I s h a l l l e t t h e c h a p t e r s which f o l l o w speak f o r t h e m s e l v e s . . 4 G e n e r a l B i o l o g y S p r i n g t a i l s a r e s m a l l , w i n g l e s s i n s e c t s ( a l t h o u g h they may soon l o s e . t h i s taxonomic s t a t u s and move i n t o t h e i r own s u b c l a s s ) t h a t i n h a b i t s o i l and l i t t e r . . N e a r l y any ecosystem w i l l y i e l d from a few hundred t o 1/2 m i l l i o n per square meter of s o i l s u r f a c e . . They feed on v a r i o u s m i c r o o r g a n i s m s , mainly f u n g i , t h a t i n h a b i t d e t r i t u s . . S p r i n g t a i l s i n t u r n a r e f e d upon by a v a r i e t y of m i t e s , p s e u d o s c o r p i o n s , c e n t i p e d e s and some i n s e c t l a r v a e i A l t h o u g h they occur i n h i g h d e n s i t i e s , C o l l e m b o l a are o f t e n o v e r l o o k e d because of t h e i r c r y p t i c h a b i t s and a v e r s i o n t o b r i g h t s u n l i g h t and open a i r . T h e i r confinement i n t h e s o i l and l i t t e r has r e d u c e d the i n t e n s i t y of n a t u r a l s e l e c t i o n on s p r i n g t a i l s . They a r e sometimes r e f e r r e d t o as t h e most p r i m i t i v e i n s e c t o r d e r s i n c e t h e y c l o s e l y resemble t h e i r Devonian a n c e s t o r s . They have changed so l i t t l e , i n f a c t , t h a t a l l they have t o show f o r n e a r l y 300 m i l l i o n y e a r s o f e v o l u t i o n i s the a d d i t i o n of two a n t e n n a l segments ( K u h n e l t , 1 9 6 1 ) . . S p r i n g t a i l s d i f f e r from more l ,advanced" i n s e c t s i n development* p h y s i o l o g y and morphology. One such d i f f e r e n c e i n the c u t i c l e i s i m p o r t a n t because c u t i c l e i s t h e i n s e c t ' s i n t e r f a c e w i t h t h e e n v i r o n m e n t , and i t s q u a l i t i e s determine r e l a t i v e r e s i s t a n c e or s u s c e p t i b i l i t y t o e n v i r o n m e n t a l o n s l a u g h t s . Except f o r t h e more h i g h l y e v o l v e d S m i n t h u r i d a e , s p r i n g t a i l s have no t r a c h a e l system and t h e r e f o r e must r e s p i r e c u t a n e o u s l y . T h i s t y p e o f r e s p i r a t i o n demands c u t i c l e p e r m e a b i l i t y , a h i g h s u r f a c e t o volume r a t i o , and an absence o f Figure 2a. Representative springtails similar to those collected i n the survey part of this study. (lengths 1 - 3 mm) a. ) Isotomurus palustris (Muller) 1776 ( i l l u s t r a t i o n from Folsom, 1937) b. ) Isotoma andrei M i l l s , 193*1-( I l l u s t r a t i o n from Mi l l s , 1934) c. ) Isotoma v i r i d i s Bourlet, I839 ("Illustration from Wade, 1954) d. ) Entomobrya niva l i s (Linne) 1758 ( i l l u s t r a t i o n from Maynard, 1951) e. ) Entomobrya comparata Folsom, 1919 ( i l l u s t r a t i o n from Folsom, 1919) Figure 2b. More representative springtails similar to those collected i n the survey part of this study, (lengths 1 - 2 mm) a. ) Onychiurus armatus Folsom, 1917 ( i l l u s t r a t i o n from Folsom, 1917) b. ) Folsomia C a n d i d a Willem, 1902 [= F. fimetaria (Linnaeus)] ( i l l u s t r a t i o n from Wade, 195*0 c. ) Lepidiocyrtus cyaneus Tullberg, I87I ( i l l u s t r a t i o n from Maynard, 1951) d. ) Sminthurus purpurescens (MacGillivray) 1894 ( i l l u s t r a t i o n from Maynard, 1951) e. ) Bourletiella rustica Maynard, 1951 ( i l l u s t r a t i o n from Maynard, 1951) 7 & -impermeable e p i c u t i c l e and a near absence o f e x o c u t i c l e (Chapman, 1975). To s u r v i v e , t h e r e f o r e s p r i n g t a i l s ' m u s t be surrounded by h i g h h u m i d i t y . Many s p r i n g t a i l s ( e s p e c i a l l y t h e I s o t o m i d a e t o which F o l s o m i a C a n d i d a belongs) are g u i c k l y k i l l e d by a r e l a t i v e h u m i d i t y below 90% a t normal f i e l d t e m p e r a t u r e s ( B e l l i n g e r , 1954). They a r e a l s o k i l l e d by moderately h i g h t e m p e r a t u r e s , even when net water l o s s i s net a p p r e c i a b l e . C o n s i d e r i n g t h e l a r g e numbers t h a t are l o s t t o p r e d a t i o n , t h e number t h a t p e r i s h d u r i n g t h e i r f r e g u e n t m o l t s , and t h e narrow range o f e n v i r o n m e n t a l c o n d i t i o n s t h e y can t o l e r a t e , i t i s s u r p r i s i n g t h a t t h e y s u r v i v e i n n a t u r e at a l l . . But they do s u r v i v e , and w i t h g r e a t s u c c e s s . I n a r e a s around Vancouver, I commonly f i n d them at d e n s i t i e s of 5,000 t o 50,000 per m2. They a l s o f l o u r i s h i n h a r s h e n v i r o n m e n t s , such as t h e High A r c t i c I s l a n d s and on mountaintops, where few a n i m a l s of any k i n d a re a b l e t o s u r v i v e . At 6800 m i n the H i m a l a y a s , o n l y s p r i n g t a i l s and m i t e s a r e common (Mani, 1968).. In t h e f o l l o w i n g c h a p t e r s , o t h e r a s p e c t s and d e t a i l s of s p r i n g t a i l b i o l o g y and e c o l o g y are d i s c u s s e d as r e g u i r e d . CHAPTER ONE COMMUNITY SETTING FOR POPULATION STUDIES. 9 INTRODUCTION S i n c e l i t t l e i s known about th e i n v e r t e b r a t e s i n t h e s o i l community i n t h i s a r e a , s t u d y must be p r e f a c e d w i t h a g e n e r a l s u r v e y of what s p e c i e s a r e p r e s e n t and how they change t h e i r r e l a t i v e s e a s o n a l i m p o r t a n c e i n t h e community. I n o r d e r t o p r o v i d e t h i s background i n f o r m a t i o n f o r my s t u d y s i t e a t t h e UBC R e s e a r c h F o r e s t , I m onitored s o i l m i c r o a r t h r o p o d p o p u l a t i o n s d u r i n g 1979. . S p e c i f i c f e a t u r e s of o t h e r s i t e c h a r a c t e r i s t i c s , such as v e g e t a t i o n and weather, are noted i n f o l l o w i n g c h a p t e r s where r e l e v a n t . . METHODS O b j e c t i v e s : t o c h a r a c t e r i z e t h e s o i l m i c r o a r t h r o p o d community i n a n a t u r a l s i t e and t o g u a n t i f y t h e d e n s i t i e s , d i s t r i b u t i o n s and dynamics of the major s p e c i e s i n o r d e r t o c r e a t e a s e t t i n g i n which m e a n i n g f u l p o p u l a t i o n s t u d i e s c o u l d be d e v e l o p e d . . The s i t e i s a square c o n s i s t i n g of 12 9' X 9* b l o c k s , each w i t h a c o r n e r t r e e , i n a 19 59 D o u g l a s - f i r (Pseudotsuqa m e n z i e s i i (Mirb.) Franco) p l a n t i n g ( F i g u r e 3 ) . The s o i l t y p e i n the a r e a i s d y s t r i c b r u n i s o l . I sampled the s i t e i n a s t r a t i f i e d random sampling p l a n . On THE UNIVERSITY OF BRITISH COLUMBIA R E S E A R C H FOREST MAPLE RIDGE, B.C. F i g u r e 3 . 11 each s a m p l i n g date t w e l v e c o r e s , each c o n s i s t i n g o f t h r e e l a y e r s , were removed.. S i x c o r e s were t a k e n from the n o r t h e r n h a l f of t h e s i t e and s i x from the southern h a l f . The p o s i t i o n s of the c o r e s were d e t e r m i n e d by a s e t o f random numbers computed f o r t h e purpose. A t o t a l o f 36 2.5 X 5 cm s o i l c o r e s was c o l l e c t e d a t each of s i x s a m p l i n g d a t e s . Data from e a r l i e r sample d a t e s were d i s c a r d e d because of changes i n t e c h n i g u e and l o c a t i o n . . The c o r e s were t r a n s p o r t e d t o the l a b i n an i n s u l a t e d c o o l e r and e x t r a c t e d f o r s i x days i n a Macfadyen h i g h - g r a d i e n t e x t r a c t o r ( F i g u r e 4 ) . The c a l i b r a t i o n and o p e r a t i o n of t h i s e x t r a c t o r a r e d e t a i l e d i n Appendix A. I i d e n t i f i e d the e x t r a c t e d specimens under a d i s s e c t i n g m i croscope and p r e p a r e d s l i d e s of about 1000 specimens f o r f u r t h e r taxonomic work. The i d e n t i f i c a t i o n s of some of t h e s e were checked and c o r r e c t e d where n e c e s s a r y by Dr.. K.. C h r i s t i a n s e n , a well-known C o l l e m b o l a t a x o n o m i s t and e c o l o g i s t . RESULTS AND DISCUSSION D e n s i t i e s and dynamics Because of an unforeseen d e l a y i n t h e p u b l i c a t i o n of a comprehensive key t o t h e C o l l e m b o l a of North America by Dr. C h r i s t i a n s e n and Dr..P. B e l l i n g e r , I was n o t a b l e t o i n d e n t i f y a l l the specimens t o s p e c i e s . C o n s e q u e n t l y , I grouped them i n t o c l a s s e s of s e v e r a l s i m i l a r s p e c i e s , u s u a l l y i n one genus o r s u b f a m i l y . The abundance of each of 11 such groups of 12 a. Upper surface of heater assembly; b. Chimney; c. Ceramic insulator for heating element; d. Lower surface of heater assembly; e. Supporting rail for sample rack; f. Sample of soil; g. Bakelite cylinder containing soil; h. Sample rack containing twelve samples in cir-cular holes staggered in two rows: i. Aluminium canister; j . Cold water bath in raised position; k. Cold water bath in lowered position. F i g u r e A h i g h - g r a d i e n t Macfadyen e x t r a c t o r s i m i l a r to the one used i n t h i s study. ( I l l u s t r a t i o n from Macfadyen, 1961.) 13 C o l l e m b o l a and t h e i r p r e d a t o r s a t t h r e e depths and s i x s a m p l i n g d a t e s are shown i n Appendix B, F i g u r e s B1 to B14. I i n c l u d e t h e s e d a t a as an appendix because, a l t h o u g h t h e survey took a major p a r t of my t i m e , i t does not c o n s t i t u t e a major p a r t o f t h i s t h e s i s . Surveys have g e n e r a l l y lower i n f e r e n c e v a l u e t h a n e x p e r i m e n t s . S o i l m o i s t u r e was c a l c u l a t e d f o r t h e 216 s o i l samples and i s shown f o r the t h r e e depths and s i x d a t e s i n Appendix C. Comparisons of t h e s e data and t h e weather data i n Appendix D w i t h t h e d e n s i t y h i s t o g r a m s (Appendix B) show t h e e f f e c t of the summer drought o f 1979 on the s o i l m i c r o f a u n a . R e l a t i v e l y few C o l l e m b o l a were p r e s e n t i n the upper l a y e r a t the August 8 s a m p l i n g d a t e . . Somes s p e c i e s , l i k e F o l s o m i a spp. ( F i g u r e B 2 ) , O l l l S k i i i i i J s SPP« ( F i g u r e B7) , and Neanura ( F i g u r e B12) d i s a p p e a r e d d u r i n g t h e dry p e r i o d , p r o b a b l y due t o v e r t i c a l m i g r a t i o n and/or heavy m o r t a l i t y . I t would of c o u r s e be r i s k y t o base e x t e n s i v e i n t e r p r e t a t i o n s on mere c o r r e l a t i o n s (whether s i g n i f i c a n t or not) between d e n s i t i e s and m o i s t u r e , or p r e d a t o r and prey d e n s i t i e s (e.g. F i g u r e s B2, B3 and B4). These d a t a a r e , however, u s e f u l background f o r the p o p u l a t i o n s t u d i e s t o f o l l o w . D i s t r i b u t i o n P a r t of t h e problem o f i n t e r p r e t i n g d ata such as t h e s e l i e s i n the h i g h e s t i m a t e v a r i a n c e s caused by uneven s p a t i a l d i s t r i b u t i o n s . I n o r d e r t o c h a r a c t e r i z e the s p a t i a l d i s t r i b u t i o n s of the groups whose d e n s i t i e s a r e shown i n F i g u r e B1 t o B14 (Appendix B) , I i n c l u d e d mean v a r i a n c e r a t i o s f o r each s p e c i e s group a t each depth and each s a m p l i n g d a t e i n T a b l e s B1 t o B14. The sample mean t o sample v a r i a n c e r a t i o i s a good i n d e x of d i s p e r s i o n s i n c e i t can be used as a q u i c k t e s t of agreement w i t h a P o i s s o n d i s t r i b u t i o n . Agreement w i t h a P o i s s o n would i n d i c a t e an i n a b i l i t y ~to r e j e c t t h e h y p o t h e s i s of a random d i s t r i b u t i o n . Myers (1978) has demonstrated t h a t s 2 / x i s r e l a t i v e l y i n d e p e n d e n t of d e n s i t y and i s t h u s a u s e f u l i n d e x . A r a t i o l e s s t h a n 1 i n d i c a t e s a r e g u l a r d i s t r i b u t i o n , whereas a r a t i o g r e a t e r t h a n 1 i n d i c a t e s a g g r e g a t i o n . T h i s s t a t i s t i c can be used i n t e s t s i n c o n j u n c t i o n w i t h X 2 s i n c e J ( s 2 / x ) , where 0 = n-1 f o r sample s i z e n, i s an a p p r o x i m a t i o n t o ~ ) ( 2 w i t h \) degrees of freedom., A low ~X 2 i n d i c a t e s a r e g u l a r , o r u n i f o r m , d i s t r i b u t i o n . A h i g h "X 2 i n d i c a t e s a c o n t a g i o u s , or a g g r e g a t e d , d i s t r i b u t i o n . E l l i o t (1977) p r e s e n t s a u s e f u l graph f o r g u i c k i y making t h e s e t e s t s . T a b l e s B1 t o B14 show s 2 / x r a t i o s , p( 2 v a l u e s ( w i t h 11 df) and t h e t y p e o f d i s t r i b u t i o n i n d i c a t e d (at <*S. = .05) . As e x p e c t e d , most of the t a x o n - l e v e l - d a t e c o m b i n a t i o n s show a c o n t a g i o u s d i s t r i b u t i o n . Such d a t a a r e o f t e n f i t t e d t o t h e u b i g u i t o u s n e g a t i v e b i n o m i a l d i s t r i b u t i o n , but i n t h i s case t h e r e a r e t o o few d a t a t o do so with adeguate c o n f i d e n c e . I n t e r p r e t a t i o n s of s p a t i a l d i s t r i b u t i o n s r e q u i r e g r e a t c a r e . I n some c a s e s , as w i t h Apochthonius minimus nymphs and a d u l t s ( T a b l e s B2 and B3), we may i n t e r p r e t a change from c o n t a g i o u s t o random d i s t r i b u t i o n i n an e c o l o g i c a l s e n s e : i n t h i s case as an i n d i c a t i o n t h a t t h e a n i m a l s a r e d i s p e r s i n g from o r i g i n a l s i b l i n g groups and " t h i n n i n g o u t " as t h e y age. However, as G i l b e r t (1973) makes c l e a r , t h e r e a r e many ways t o a r r i v e a t a c e r t a i n d i s t r i b u t i o n . Rather than make unsupported i n f e r e n c e s h e r e , I p r e s e n t t h e s e d a t a as background i n f o r m a t i o n , and move t o more s o l i d ground i n t h e next t h r e e c h a p t e r s . 16 CHAPTER TWO POST-EMBRYONIC GROWTH OF THE COLLEMBOLANS, FOLSOMIA CANDIDA AND JLENILLA GRISEA, AT THREE TEMPERATURES 17 INTRODUCTION In a s s e s s i n g f a c t o r s a f f e c t i n g t h e s i z e and c h a r a c t e r i s t i c s of an i n s e c t p o p u l a t i o n , i t i s o f t e n d e s i r a b l e t o know the age d i s t r i b u t i o n . T h i s i n f o r m a t i o n i s p a r t i c u l a r l y u s e f u l when p o p u l a t i o n s have o v e r l a p p i n g g e n e r a t i o n s (Southwood, 1978). I wished t o e s t a b l i s h r e l a t i o n s h i p s between age, s i z e and te m p e r a t u r e f o r two s p e c i e s of C o l l e m b o l a ( s p r i n g t a i l s ) i n o r d e r t o p r o v i d e a g i n g t e c h n i q u e s u s e f u l i n o t h e r e x p e r i m e n t s and p r e d i c t i v e models. The two s p e c i e s , F o l s p m i a C a n d i d a Willem 1902 and X e n y l l a q r i s e a A x e l s o n 1900, a r e common i n h a b i t a n t s o f s o i l and l i t t e r i n many p a r t s o f t h e w o r l d . A c c u r a t e age-grouping i s alw a y s d i f f i c u l t and o f t e n i m p o s s i b l e f o r many k i n d s o f i n s e c t s . However, r e l i a b l e e s t i m a t e s of age can be made f o r i n s e c t s , such as C o l l e m b o l a , which c o n t i n u e t o grow a f t e r t h e y become mature. The ametabolous, monophasic l i f e c y c l e of C o l l e m b o l a , and t h e i r l a r g e number of i n s t a r s (up t o 50, C h r i s t i a n s e n , 1964) a l l o w s comparison of dimensions over time and, c o n s e q u e n t l y , o f f e r s a method of d e t e r m i n i n g age. Many l i f e h i s t o r y parameters o f i n s e c t s have been shown t o be f u n c t i o n s o f te m p e r a t u r e ( s e e , e.g., M o r r i s and F u l t o n , 1970). The i n f l u e n c e of temp e r a t u r e on the f e c u n d i t y , d e v e l o p m e n t a l p e r i o d , and m o r t a l i t y of F. C a n d i d a , f o r example, i s w e l l -18 documented ( M a r s h a l l and Kevan, 1962; Green, 1964a; S n i d e r and B u t c h e r , 1973; Hutson, 1978b). The c l a s s i c s t u d y of A g r e l l (1949) d e a l t w i t h a l l o m e t r i c g rowth, number o f ecdy s e s , and o t h e r l i f e h i s t o r y c h a r a c t e r i s t i c s o f r e l a t e d s p e c i e s . Research on t h e growth of i n d i v i d u a l s has been concerned w i t h the r a t e of development (the r e c i p r o c a l o f d e v e l o p m e n t a l time f o r the v a r i o u s s t a d i a ) as l i n e a r ( e.g., G i l b e r t e t a l . , 1976; Johnson e t a l . , 1979) o r i n h e r e n t l y n o n l i n e a r (e.g.. B a i l e y , 1976; Guppy and H a r c o u r t , 1978; T a y l o r and H a r c o u r t , 1978; T a n i g o s h i and Logan, 1979) f u n c t i o n s of t e m p e r a t u r e s n o r m a l l y e x p e r i e n c e d . R e c e n t l y , models f o r d e s c r i b i n g and p r e d i c t i n g t h i s r e l a t i o n s h i p have been produced, n o t a b l y by S t i n n e r e t a l . , 1976; Logan e t a l . , 1976; and C u r r y et a l . , 1978. S i m i l a r models o f the f u n c t i o n a l r e l a t i o n s h i p of te m p e r a t u r e w i t h t h e growth of i n d i v i d u a l i n s e c t s have been used i n s i m u l a t i o n models t o p r e d i c t the growth of p o p u l a t i o n s under f i e l d c o n d i t i o n s (e.g. Gage e t a l . , 1976; Dover e t a l . , 1979; Herne and Lund, 1979). I designed t h i s p o r t i o n of my st u d y t o s e r v e t h e d u a l purpose o f d e t e r m i n i n g growth r a t e s and d e v e l o p i n g an a g i n g t e c h n i g u e t o be used i n t h e i n t e r p r e t a t i o n o f o t h e r e x p e r i m e n t s . METHODS F. C a n d i d a and X. g r i s e a were r e a r e d i n d i v i d u a l l y i n s m a l l v i a l s (2 cm X 4 cm) embedded i n p l a s t e r - f i l l e d t r a y s s i m i l a r t o thos e used by M a r s h a l l and Kevan (1962), m a i n t a i n e d i n t h r e e d i f f e r e n t t e m p e r a t u r e regimes: 12 h r s a t 6" C / 12 h r s a t 10° C; 19 12 hrs 140 c / 12 h r s 180 c, and 12 h r s 22<> c / 12 h r s 260 c _ (These t r e a t m e n t s w i l l be r e f e r r e d t o by t h e i r mean t e m p e r a t u r e s , 8°, 16° and 240 c , r e s p e c t i v e l y , t h r o u g h o u t t h i s c h a p t e r . ) The range o f v a r i a t i o n of the a i r t e m p e r a t u r e was < 0. 5° C i n t h e i n c u b a t o r s , but was even l e s s i n t h e c o n t a i n e r s , s i n c e t h e i r t e m p e r a t u r e s were moderated by moistened p l a s t e r bottoms.. Eggs f o r each t r e a t m e n t were o b t a i n e d from c u l t u r e s kept i n t h e i n c u b a t o r s used i n the e x p e r i m e n t . The moist p l a s t e r a l l o w e d maintenance o f r e l a t i v e h u m i d i t y near 100%, a r e g u i r e m e n t f o r normal s u r v i v a l of s p r i n g t a i l s . The F. Candida c u l t u r e s descended from i n d i v i d u a l s r e c e i v e d from Dr. V. G. M a r s h a l l and t h e X. g r i s e a s t o c k o r i g i n a t e d w i t h i n d i v i d u a l s c o l l e c t e d from t h e U n i v e r s i t y c f B r i t i s h Columbia Endowment Lands, Vancouver, B.C., e i g h t months (about 10 g e n e r a t i o n s ) b e f o r e the e x p e r i m e n t . . Y e a s t , a minor component of t h e n a t u r a l d i e t of C o l l e m b o l a and commonly used f o r r a i s i n g C o l l e m b o l a under l a b o r a t o r y c o n d i t i o n s (e.g.. Usher and Stoneman, 1977), was used i n powder form as f o o d . The s p r i n g t a i l s were r e a r e d i n d i v i d u a l l y i n s t o p p e r e d p l e x i g l a s s v i a l s s i n c e Green (1964b) found t h a t t h e r e was no d i f f e r e n c e i n t h e growth r a t e s of grouped and i s o l a t e d F. -Candida. F o u r t e e n v i a l s were used f o r each of the s i x s p e c i e s - t e m p e r a t u r e c o m b i n a t i o n s . The body l e n g t h ( a n t e r i o r o f head t o p o s t e r i o r o f a n a l segment) and head w i d t h were measured each morning d u r i n g t h e e a r l y s t a g e s o f growth, and a t i n t e r v a l s of two t o f i v e days towards t h e end o f t h e s t u d y . . V i a l s i n which i n d i v i d u a l s d i e d were r e s t a r t e d w i t h the a d d i t i o n of f r e s h eggs; c o n s e g u e n t l y t h e data c o l l e c t e d f o r each s p e c i e s - t e m p e r a t u r e 20 c o m b i n a t i o n r e p r e s e n t from 15 t o 31 i n d i v i d u a l s . Measurements were ta k e n f o r 75 days. RESULTS AND DISCUSSION Length and Age I n a l l c a s e s , t h e r a t e of growth d e c l i n e d g r a d u a l l y w i t h age. The v a r i a n c e o f the l e n g t h s i n c r e a s e d w i t h age. Log t r a n s f o r m a t i o n s of both dependent and independent v a r i a b l e s y i e l d e d homogeneous v a r i a n c e and a l l o w e d parameters t o be e s t i m a t e d by s i m p l e l i n e a r r e g r e s s i o n . The r e g r e s s i o n e q u a t i o n used i s a l i n e a r i z e d form of t h e power f u n c t i o n : b l e n g t h = a (age) where a = the mean body l e n g t h a t t i m e of h a t c h i n g and b = t h e e s t i m a t e d growth power parameter. L e a s t s q u a r e s f i t s a r e shown i n F i g u r e s 5 and 6 . . The l e t t e r "m" on the time s c a l e i n these F i g u r e s i n d i c a t e s t h e age at which i n d i v i d u a l s become mature and begin t o o v i p o s i t . The e s t i m a t e s o f l n (a) and b a r e l i s t e d i n T a b l e 1 w i t h a s s o c i a t e d s t a t i s t i c s . The a c t u a l r a t e of change i n l e n g t h L a t a g i v e n age A i s : b-1 dL/dA = abA A l t h o u g h power f u n c t i o n s a re commonly used t o d e s c r i b e 21 F i g u r e 5- Length-age r e l a t i o n s h i p s f o r F. Candida r e a r e d under three temperature regimes (mean temperature f o r each case i s shown). Each r e g r e s s i o n l i n e i s bounded by the 99$ confidence i n t e r v a l s f o r the estimated mean l n ( l e n g t h ) . The "m" i n d i c a t e s the approximate age a t which i n d i v i d u a l s became mature and began to o v i p o s i t . 22 1500h • • • • • • 1 2 4 8 16 32 64 < 1 2 4 8 16 32 64 1500F 1000 8 700h AGE (DAYS. L O G E S C A L E ) 23 F i g u r e 6 . Length-age r e l a t i o n s h i p s f o r X. g r i s e a r e a r e d under three temperature regimes (mean temperature f o r each case i s shown). Each r e g r e s s i o n l i n e i s bounded by the 99$ confidence i n t e r v a l s f o r the estimated mean l n ( l e n g t h ) . The "m" i n d i c a t e s the approximate age at which i n d i v i d u a l s became mature and began to o v i p o s i t . 1500 1000 700 500 400 300 2 4 1 2 4 8 16 32 64 1500 1000 1500 1000 8 16 32 64 AGE ( D A Y S , L O G E S C A L E ) 25 l a b l e 1. Begressions of ln(length) and ln(age) corresponding to F i g ures 5 and 6 . Species Teap ( C) Begression a, the s i z e Eguation at ha'tch 8 l n L=5.652 + . 118 (ln A) 285 p. .613 <.0001 F. C a n d i d a 16 l n L=5.853 • .27 1 ( l n A) 348 jx .749 <-00 01 24° l n L=5.787 • .288 ( l n 4) 326 /i. .749 <.0001 8° ln L=5.682 • .098 (ln 4) 294 ju. .791 <.0001 gr i s e a 16° l n L=5.487 • .331 (ln &) 242 . 880 <.0001 24° l n L=5.629 .275 ( l n A) 278 JUL . 77o <.0001 26 r e l a t i v e r a t e s of growth of d i f f e r e n t body p a r t s i n a l l o m e t r i c s t u d i e s (Choudhuri and B h a t t a c h a r y y a (1978) have done t h i s w i t h a c o l l e m b o l a n s p e c i e s , and P e t e r s e n (1975) has used power f u n c t i o n s t o d e s c r i b e t h e l e n g t h - d r y weight r e l a t i o n s h i p s o f a number of C o l l e m b o l a ) , they are r a r e l y used t o d e s c r i b e a b s o l u t e growth over t i m e most c l a s s i c growth and development e q u a t i o n s a r e forms of e x p o n e n t i a l or l o g i s t i c e q u a t i o n s (Medawar, 1945; D a v i d s o n , 1944; N a i r , 1964). Welch's work (1 970) i s an e x c e p t i o n i n which a s i m p l e power f u n c t i o n was used t o p r o v i d e a r e l a t i o n s h i p between h e i g h t and age f o r c h i l d r e n . Welch used t h i s e q u a t i o n t o c o n s t r u c t o r t h o g o n a l p o l y n o m i a l s . The d a t a i l l u s t r a t e d i n F i g u r e s 5 and 6 do not e x h i b i t a l o g i s t i c form. M a r s h a l l and Kevan (1962) and M i l n e (1960) r e p o r t s i z e s of F. C a n d i d a w i t h i n c r e a s i n g age which are c o n s i s t e n t w i t h t h e r e s u l t s shewn h e r e . A n a l y s i s o f M a r s h a l l ' s and Kevan's d a t a g i v e s the r e g r e s s i o n e g u a t i o n , l n ( l e n q t h ) = 5.80 + . 232 ( l n (age) ) , ( f i t on 25 means f o r a n i m a l s r a i s e d a t 24° C ) , s i m i l a r t o t h e growth c u r v e a r r i v e d a t from my data t a k e n a t the same te m p e r a t u r e (Table 1) . The d a t a of G r e g o i r e - W i b o • s (1974) study o f t h e m o r p h o l o g i c a l development of F o l s o m i a g u a d r i o c u l a t a appear t o f o l l o w a s i m i l a r p a t t e r n . Joose and Veltkamp (1970) s t u d i e d t h e growth and m o l t i n g of f i v e l a r g e r s p e c i e s of C o l l e m b o l a . Most of t h e s e had growth p a t t e r n s s i m i l a r t o the s p e c i e s I used, but i n two c a s e s tended toward a l o g i s t i c form. 27 Comparison o f l e n g t h - a g e r e g r e s s i o n l i n e s There a r e a number of ways i n which s l o p e s o f r e g r e s s i o n l i n e s may be compared. Zar (1974) s u g g e s t s t h a t two s l o p e s can be compared w i t h t - t e s t s , w h i l e more than two s l o p e s may be compared w i t h m u l t i p l e range t e s t s . A b e t t e r , but o f t e n o v e r l o o k e d , method of comparing s l o p e s i n v o l v e s t h e use of dummy v a r i a b l e s . C u n i a (1973), K e r l i n g e r and Pedhazur ( 1973) and Neter and Wasserman (1974) d i s c u s s t h e d e t a i l s o f s i m i l a r t e c h n i q u e s . To make t h e comparisons by t h i s t e c h n i g u e , t h e s i x d a t a s e t s were combined and s i x dummy v a r i a b l e s were c o n s t r u c t e d which a l l o w e d t e s t s of t h e i n t e r c e p t s (1's f o r t h e da t a s e t of i n t e r e s t , O's f o r a l l e t h e r s ) and c o n s t r u c t i o n of s i x new ind e p e n d e n t v a r i a b l e s (ln (age) o b s e r v a t i o n s f o r t h e da t a s e t o f i n t e r e s t , O's f o r a l l o t h e r s ) . F i t t i n g a m u l t i p l e r e g r e s s i o n e q u a t i o n (Cunia's (1973) " g i a n t s i z e r e g r e s s i o n " ) t o t h e r e s u l t i n g t w e l v e v a r i a b l e s gave the r e s i d u a l sum of sguares f o r the s i x g r o u p s , t o g e t h e r w i t h t h e i r s e p a r a t e s l o p e s and i n t e r c e p t s . These new independent (dummy) v a r i a b l e s a r e v e c t o r s t h a t can be added t o combine the s l o p e s or i n t e r c e p t s of two or more groups. By combining the v e c t o r s o f i n t e r e s t ( i . e . , t h o s e c o r r e s p o n d i n g t o t h e s l o p e s or i n t e r c e p t s b e i n g compared), f i t t i n g a new m u l t i p l e r e g r e s s i o n e g u a t i o n and o b t a i n i n g a new r e s i d u a l sum o f s g u a r e s f o r comparison w i t h the o r i g i n a l , we can then t e s t whether the s l o p e s (or i n t e r c e p t s ) a r e e q u a l ; i . e . , whether t h e r e i s no s i g n i f i c a n t change i n the r e s i d u a l sum of sg u a r e s . For example, t o t e s t f o r a d i f f e r e n c e among a l l s i x s l o p e s , I f i t : 28 1. ) l n ( l e n g t h ) = b„ X „ + b Z ) X 2 1 + b 3 l X „ + b v i X S I + b s l X s , + bfcl X 6 ) + b I Z XIZ *• b , z X 2 Z + b 3 z X 3 z + b v t X V l + b 5 z X f l + b«.t X 6 z , (with D1 r e s i d u a l degrees of freedom) 2. ) l n ( l e n g t h ) = b„ X „ * b Z l X t l + b3, X 3 , + bv, X v , + b s i Xs, + + b« ( X , z + X zz + X 3 Z + X v z + X F i • X 6 l ) , ( w i t h D2 r e s i d u a l degrees of freedom) where X „ , X l ( X f c , a r e dummy v a r i a b l e s used f o r t e s t s o f i n t e r c e p t s ; X ) z , X z z X f e i a r e t h e l n (age) v a l u e s f o r each of the s i x groups and a r e used f o r comparing s l o p e s , and b' i s t h e common s l o p e . The s i g n i f i c a n c e of the d i f f e r e n c e i n r e s i d u a l s can be determined by an F - t e s t where F = [SS d i f f e r e n c e / (D2 - D1) ] / MS 1 w i t h (D2 - D1) and D1 degrees of freedom. T h i s t e c h n i g u e can e a s i l y be a p p l i e d t o moderately l a r g e data s e t s w i t h t h e a i d o f any r e l i a b l e m u l t i p l e r e g r e s s i o n package. T e s t s o f s l o p e s : do the growth parameters d i f f e r ? U s i n g t h e t e c h n i q u e d e s c r i b e d above, the s l o p e s were compared between t e m p e r a t u r e s f o r each s p e c i e s and between s p e c i e s a t c o r r e s p o n d i n g t e m p e r a t u r e s . The r e s u l t s a r e summarized i n Table 2. F o r F. ..Candida t h e s l o p e s f o r the groups r e a r e d at mean t e m p e r a t u r e s of 16° and 20° C d i d not d i f f e r . Both v a l u e s were s i g n i f i c a n t l y l a r g e r than the s l o p e f o r t h e 8« 2a. Slope comparisons within s p e c i e s f or a l l p a i r s of temperatures. Species Comparison F df P 0 8 vs 0 16 70.70 1, 58 9 <.0001 F. C a n d i d a 8° vs 24° 9 1.62 1. 589 <.0001 a 16 V S 24° 0.98 1, 58 9 =.6756 (n.s.; 0 8 V S o 16 111.78 1. 58 9 <.0001 ?, qrisea 8° vs 24° 52. 18 1. 58» <• 000 1 0 16 vs 0 24 7.33 1. 58 a =.0069 Table 2b. Slope comparisons betneen species at each temperature. Temperature df i l l temperatures 4.01 8° C 0.75 16° C 11.32 24° C 0.44 1, 589 1, 589 1. 589 1. 589 .0431 .6106 (n. s.) .0009 .5128 (n.s.) (n.s.) = not s i g n i f i c a n t l y d i f f e r e n t . 30 group. The l a r g e s t s l o p e f o r X. g r i s e a o c c u r r e d i n t h e 16° C t r e a t m e n t . . Those f o r the 8° and 24° C t r e a t m e n t s were both s m a l l e r f o r t h i s s p e c i e s . Between s p e c i e s , t h e t r e a t m e n t s a t 16° C produced d i f f e r e n t s l o p e s ; i . e . , the growth parameters d i f f e r e d f o r t h e two s p e c i e s i n t h a t regime. T e s t s of i n t e r c e p t s : do t h e l e n g t h s a t h a t c h i n g d i f f e r ? The i n t e r c e p t s f o r t h e r e g r e s s i o n e g u a t i o n s shown i n T a b l e 1 were compared w i t h the same m u l t i p l e r e g r e s s i o n t e c h n i g u e . . The r e s u l t s i n Table 3 show t h a t t h e i n t e r c e p t s ( l n ( s i z e a t h a t c h ) ) tend t o f o l l o w o p p o s i t e q u a d r a t i c f u n c t i o n s of temperature f o r the two s p e c i e s . . F. Candida has a maximum body l e n g t h a t h a t c h a t 16» c, or between 16° and 24° C, whereas X. g r i s e a has i t s minimal h a t c h i n g s i z e w i t h i n t h i s t e m p e r a t u r e range. Head w i d t h Head w i d t h i s l i n e a r l y r e l a t e d t o body l e n g t h and age (p < .001, r e s i d u a l s unbiased) f o r a l l s i x s p e c i e s - t e m p e r a t u r e c o m b i n a t i o n s . . B r i t t (1951) p r e s e n t e d t h e only comparable work on H y p o g a s t r u r i d s t h a t I c o u l d f i n d ; h i s data on head width and age, f o r a s p e c i e s s i m i l a r t o X. g r i s e a d e v e l o p i n g a t 24° C, show a comparable r e l a t i o n s h i p . The r a t i o of head w i d t h t o body l e n g t h d e c r e a s e d w i t h i n c r e a s i n g age ( F i g u r e 7). T h i s r e l a t i o n s h i p i s common i n v e r t e b r a t e s but i s not u s u a l l y d i s c e r n a b l e i n i n s e c t s because of t h e i r d i s c r e t e development and metamorphosis. In both c o l l e m b o l a n s , t h i s change seemed t o o c c u r more s l o w l y a t t h e Table 3a . Intercept comparisons within species f o r a l l p a i r s of teaperatures. 31 Species Coaparison F df P 6* vs 16" 16.30 1. 589 =.0001 Im Candida 8° vs 24° 7.8b 1, 589 =.0053 16° vs 24° 1. 42 1, 589 =.2317 (n. s.) O 8 vs O 16 16. 57 1, 589 <.000 1 8° vs 24° 1.29 1, 58 9 =.2557 16' vs 24° 10. 17 1, 589 = .00 17 t a b l e 3b. Intercept coaparisons bet Teaperature ween s p e c i e s . df 111 temperatures 8- C 16° C 24° C 42. 16 0.40 51.25 10.53 1, 589 1, 589 <.0001 .5349 (n.s.) 1. 589 <.0001 ' r 589 =.0014 (n.s.) = not s i g n i f i c a n t l y d i f f e r e n t . 3 2 F i g u r e 7* The decrease with age i n the head width/body l e n g t h r a t i o s of F. Candida (a) and X« g r i s e a ( b ) . Although p h y s i o l o g i c a l time i s not a p u r e l y l i n e a r f u n c t i o n o f temperature and c h r o n o l o g i c a l time, age i s re p r e s e n t e d here by degree-days to make the r e s u l t s more comparable. The r e g r e s s i o n equations are: For F. Candida : HW/BL = . 2 9 8 6 - . 0 1 l 6 2 ( l n Degdays) For X. g r i s e a : HW/BL = . 3 6 3 2 - . 0 2 3 6 3 ( l n Degdays) SE = . 0 3 6 3 5 2 .185 p < .0001 n = 2 3 4 r SE = .03284 2 .400 p < .0001 n = 244 r .45 .35 .15 4 " " # • • • • • • • « l •"•iter* •* 4»l • • • • . . . . * • • • • • • • • • • • • , • ; ' 1 • • • • I. • • • • 400 800 1200 1600 A G E (degree-days) .45 .35 .25 .15 • » L : P * * * • •••••• 11 • • • • —i ——i 1 1— 400 800 1200 1600 A G E (degree-days) 34 l o w e s t t e m p e r a t u r e , as might be e x p e c t e d . However, no h i g h l y s i g n i f i c a n t d i f f e r e n c e i n t h e r e l a t i o n s h i p o c c u r r e d between t h e s p e c i e s a t any t e m p e r a t u r e . These data do not s u p p o r t the f i n d i n g s o f M a r s h a l l and Kevan (1962) ; t h e i r o b s e r v a t i o n s on t h e f i r s t s i x i n s t a r s (up to about 30 days i n age) of F. Candida suggest t h a t t h e r a t i o i s a c o n s t a n t . L e a s t sguares f i t s a r e shown i n F i g u r e 7.. The l a r g e amount of v a r i a b i l i t y unaccounted f o r by age i s p r o b a b l y due t o s w e l l i n g and s h r i n k a g e o f t h e head and p r o t h o r a x b e f o r e , d u r i n g and a f t e r e c d y s i s . E r r o r s of measurement may a l s o be h i g h e r f o r t h e head w i d t h s t h a n f o r body l e n g t h s , because o f t h e s m a l l s i z e and h i g h degree of a c t i v i t y of some i n d i v i d u a l s . L i n e a r and n o n - l i n e a r e f f e c t s of temperature The r e s u l t s i n T a b l e 1 show t h a t t h e e f f e c t of t e m p e r a t u r e on t h e growth r a t e of these i n s e c t s i s c l e a r l y n o n - l i n e a r over th e range of t e m p e r a t u r e s t e s t e d . These t e m p e r a t u r e s are w e l l w i t h i n the range n o r m a l l y e x p e r i e n c e d by both s p e c i e s . F. C a n d i d a ' s r a t e of growth i s low a t 8° C and appears t o be a p p r o a c h i n g a maximum at 20" C. X. g r i s e a has i t s maximal growth r a t e near 16° C, and s l o w e r r a t e s o f growth at 8° and 24° C. . M u l t i p l e r e g r e s s i o n s were performed f o r each s p e c i e s t o t e s t t h e s i g n i f i c a n c e o f t h e s e n o n - l i n e a r e f f e c t s of t e m p e r a t u r e . L i n e a r e f f e c t s o f l n (age) and t e m p e r a t u r e , the g u a d r a t i c e f f e c t o f t e m p e r a t u r e , and t h e i r i n t e r a c t i o n s a r e shown i n T a b l e 4. In a d d i t i o n t o l n (age), t e m p e r a t u r e , t h e sguare of t e m p e r a t u r e , and the i n t e r a c t i o n of t h e s e a s p e c t s of t e m p e r a t u r e w i t h l n ( a g e ) a r e 35 Table 4a. Begression f o r F. Candida 3 * 1B length = f (ln (age), teap, teap, l n (age) X tenp, l n (age) X tenp ) F = 496.7 H u l t i p l e B p < .0001 , 8775 SE= . 16774 T a r i a b l e C o e f f i c i e n t Standard Error i n t e r c e p t 5.18630 l a (age) -.17188 teaperatare .07484 tenp* -.00208 (ln (age)) X tenp .04476 (In (age) ) X temp1 -.00 107 . 171830 .062567 .025644 .000815 .008729 .000267 p < .000 I p = .0063 p = .0040 p = .0113 p < .0001 p = .0001 Table 4b. Begression f o r £. qrisea l n l e n g t h = f (ln (age) , (ln(age)) l n (age) X teap ) teap, teap , ln(age) X teap, F = 380.5 p < .0001 H u l t i p l e 2. B = . 8977 SE= . 16774 T a r i a b l e C o e f f i c i e n t Standard Error P i n t e r c e p t 5.93560 . 115810 P < .000 1 l n (age) z -.37772 .051463 P < .000 1 (ln(age)) -.04402 .005788 P < . 0001 teaperature -.03069 .016905 P = . 0706 teap 2 -.00092 .000514 P = .074 1 (In (age)) x teap .05271 .007885 P < . 0001 (In (age)) X teap. -.00 134 .000239 P < .000 1 36 s i g n i f i c a n t terms i n t h e r e g r e s s i o n e q u a t i o n s . The i n f l u e n c e of t e m p e r a t u r e on c o l l e m b o l a n growth t h u s appears to i n c l u d e both l i n e a r and n o n - l i n e a r e f f e c t s which may vary w i t h age. Under n a t u r a l c o n d i t i o n s , n o n - l i n e a r e f f e c t s of t e m p e r a t u r e changes would a l l o w t h e s e c o l l e m b o l a n s t o undergo d i s p r o p o r t i o n a t e l y r a p i d growth whenever p e r i o d s o f f a v o r a b l e t e m p e r a t u r e and h u m i d i t y o c c u r r e d . In l e s s f a v o r a b l e e n v i r o n m e n t s , growth wculd be r e t a r d e d and t h e onset o f m a t u r i t y would be d e l a y e d u n t i l c o n d i t i o n s became more c o n d u c i v e t o r e p r o d u c t i o n . Development of an a g i n g t e c h n i g u e The r e g r e s s i o n s above were performed i n o r d e r to i l l u s t r a t e the changes i n post-embryonic growth r a t e over time and t o i s o l a t e and t e s t t h e e f f e c t s of s p e c i f i c terms i n t h e growth model., I t i s p o s s i b l e t o use t h e same d a t a t o p r e d i c t age from l e n g t h . Some r e s e a r c h e r s and s t a t i s t i c i a n s have o b j e c t e d t o r e g r e s s i o n s i n v o l v i n g independent v a r i a b l e s t h a t a r e s u b j e c t t o s a m p l i n g o r measurement e r r o r ( i . e . , not f i x e d a t s p e c i f i e d l e v e l s as i s p o s s i b l e i n many e x p e r i m e n t a l s i t u a t i o n s ) . Zar (1974) f o r i n s t a n c e recommends " i n v e r s e p r e d i c t i o n " i n which a r e g r e s s i o n e q u a t i o n and i t s p r e c i s i o n e s t i m a t e s a r e r e a r r a n g e d t o p r e d i c t X from Y, a l t h o u g h i t seems t o me t h a t such e s t i m a t e s would not be l e a s t s quares e s t i m a t e s . The reason f o r the o b j e c t i o n t o "dependent" and " i n d e p e n d e n t " v a r i a b l e s t h a t both have a s s o c i a t e d random e r r o r s i s t h a t t h e s l o p e b; i s 37 u n d e r e s t i m a t e d because t h e d i v i s o r used t o c a l c u l a t e the s l o p e i s i n c r e a s e d by t h e g u a n t i t y (n-1) Ox,- , where X,- i s t h e indep e n d e n t v a r i a b l e . The f l a w i n the argument i s the u n d e r l y i n g assumption t h a t we a r e t r y i n g t o f i n d an e s t i m a t e of the t r u e f u n c t i o n a l r e l a t i o n s h i p between two v a r i a b l e s when we perfo r m a r e g r e s s i o n . R e g r e s s i o n t e c h n i q u e s are not d e s i g n e d f o r t h i s p u rpose, however. R e g r e s s i o n e g u a t i o n s are meant t o f a c i l i t a t e p r e d i c t i o n and i n t e r p o l a t i o n o n l y . . As G i l b e r t (1973) p o i n t s o u t , i n a c t u a l p r a c t i c e i t does not matter i f t h e o b s e r v a t i o n s o f t h e in d e p e n d e n t v a r i a b l e i n c l u d e random e r r o r s of measurement. F u t u r e v a l u e s w i l l i n c l u d e the same e r r o r s and hence t h e p r e d i c t i v e v a l u e of t h e r e g r e s s i o n i s not changed. I r e v e r s e d the r e g r e s s i o n s d i s c u s s e d i n t h i s c h a p t e r and used t h e r e s u l t i n g s l o p e and i n t e r c e p t e s t i m a t e s t o e s t i m a t e t h e age of F . . C a n d i d a i n d i v i d u a l s i n o t h e r work (Chapters Three and Four as w e l l as a number of s i m u l a t i o n s ) . Although my l a t e r work does not depend on p r e c i s e e s t i m a t e s of age, t h e d a t a p r e s e n t e d i n t h i s c h a p t e r not o n l y d e s c r i b e t h e growth o f t h e s e two c o l l e m b o l a n s , but a l l o w r e l a t i v e l y p r e c i s e p r e d i c t i o n as can be seen i n F i g u r e s 5 and 6. CHAPTER THREE PREDATION OF APOCHTHONIUS MINIMUS (PSEUDOSCORPIONIDA: CHTHONIIDAE) ON FOLSOMIA CANDIDA {COLLEMBOLA: ISOTOMIDAE) I . . PREDATION RATE AND SIZE-SELECTION 39 INTRODUCTION Apo c h t h o n i u s minimus (Schuster 1966) i s a s m a l l ( a d u l t l e n g t h 1.9 - 2.3 mm) h e t e r o s p h yr o n i d pseudoscor p i on common i n l e a f l i t t e r , bark and b r y o p h y t e s of a v a r i e t y of f o r e s t s of western B r i t i s h Columbia, Washington and Oregon ( B e n e d i c t , 1978) ( F i g u r e 8 ) . P s e u d o s c o r p i o n s of t h i s t y p e are known t o p r e f e r C o l l e m b o l a ( s p r i n g t a i l s ) as f o o d (Weygoldt, 1969) . T h i s i s c e r t a i n l y the case f o r A. minimus; of n e a r l y 150 i n d i v i d u a l s c o l l e c t e d from my s t u d y s i t e n e a r l y a l l f e d on I s o t o m i d and E n t o m o b r y i d C o l l e m b o l a w h i l e none a c c e p t e d food of any o t h e r k i n d . A. minimus i s found i n r e l a t i v e l y h i g h d e n s i t i e s a t my s t u d y s i t e ; up t o s e v e r a l hundred per m2 i s not uncommon. I t i s by f a r t h e most common of t h r e e p s e u d o s c o r p i o n s p e c i e s I found i n t h e s i t e l e a f l i t t e r ( only a few specimens of the o t h e r two s p e c i e s have been c o l l e c t e d from my s t u d y s i t e ) . These p s e u d o s c o r p i o n s , a l o n g w i t h m e s o s t i g m a t i d m i t e s , are t h e major p r e d a t o r s of s p r i n g t a i l s i n the a r e a . Weygoldt (1969) s t a t e s t h a t " p s e u d o s c o r p i o n s p r o b a b l y r e g u l a t e t h e d e n s i t i e s of s m a l l e d a p h i c a n i m a l s , e s p e c i a l l y C o l l e m b o l a " . Edwards et a l . . (1967) found t h a t c o l l e m b o l a n d e n s i t i e s s i g n i f i c a n t l y i n c r e a s e d under DDT t r e a t m e n t , a p p a r e n t l y , they s u g g e s t , because t h e i r p r e d a t o r s , i n t h i s case m i t e s , were reduced. S i m i l a r c o n c o m i t a n t i n c r e a s e s i n c o l l e m b o l a n d e n s i t i e s and decreases i n p r e d a t o r d e n s i t i e s were r e p o r t e d by O l i v i e r and Ryke (1969). As p a r t o f a study o f f a c t o r s l i m i t i n g the d e n s i t i e s of s p r i n g t a i l s , the f o l l o w i n g q u e s t i o n s were of i n t e r e s t to me: how many s p r i n g t a i l s might th e F i g u r e 8 . Scanning e l e c t r o n micrograph of an A. minimus a d u l t . (Mag.: 57 X) 41 p s e u d o s c o r p i o n s e a t , what f a c t o r s i n f l u e n c e the p r e d a t i o n r a t e s and what a r e t h e e f f e c t s o f t h i s p r e d a t i o n on the growth of prey p o p u l a t i o n s under c o n t r o l l e d f i e l d c o n d i t i o n s ? The l a s t o f t h e s e g u e s t i o n s and i t s a s s o c i a t e d hypotheses a r e examined i n t h e next c h a p t e r . . B i o l o g y of t h e Prey and P r e d a t o r L i t t l e i s known about the l i v e s o f p s e u d o s c o r p i o n s because, as Muchmore (1973) p o i n t s out, t h e i r r e t i r i n g h a b i t s and i n o f f e n s i v e n e s s t o man make them " i n v i s i b l e " . . S p r i n g t a i l s , however, have caught t h e i n t e r e s t o f a r e l a t i v e l y l a r g e number of r e s e a r c h e r s , i n p a r t because o f t h e i r h i g h n a t u r a l d e n s i t i e s and presence i n a wide range of h a b i t a t s . In my s t u d y s i t e , F p l s o m i a n i v a l i s , F o l s o m i a Candida, F p l s o m i a q u a d r i o c u l a t a and o t h e r s i m i l a r I s o t o m i d s o c c u r a t d e n s i t i e s as h i g h as 30,000, and commonly 5000 t o 10,000, per m2. F o l s o m i a C a n d i d a The s p r i n g t a i l used i n t h i s s t u d y i s a s m a l l ( l e n g t h 0.2 -2.0 mm) c r y p t i c a p t e r y g o t e ( F i g u r e 2b) t h a t i n h a b i t s moist spaces between l i t t e r and s o i l p a r t i c l e s i n a v a r i e t y of ecosystems. F. C a n d i d a i s found throughout Europe and North America i n f o r e s t s and g r a s s l a n d s , wherever t h e h i g h r e l a t i v e h u m i d i t y and 42 f u n g a l food i t r e q u i r e s occur. The s p e c i e s i s p a r t h e n o g e n e t i c , and has an ametabolous-monophasic developmental seguence i n which p e r i o d i c moults throughout l i f e produce up to 30 i n s t a r s . , I t i s sof t-bo.died, b l i n d , and f o r locomotion i s eguipped with s i x clawed l e g s and a s h o r t s p r i n g ( f u r c u l a ) a r i s i n g from the ventrum of the f o u r t h abdominal segment. D e t a i l e d o b s e r v a t i o n s on the l i f e h i s t o r y and b i o l c g y of F. Candida have been made by Milne (1960), M a r s h a l l and Kevan (1962), Green (1964a,b), Snider (1971), Snider and Butcher (1973), Gregoire-Wibo and Snider (1977) and Hutson (1978b).. E c o l o g i c a l experiments with t h i s s p e c i e s have been conducted by C h r i s t i a n s e n (1970) , Usher et a l . (1971), Torne (1974), Usher and Hider (1975) and Usher and Stoneman {1977). Regarding the behavior of the prey, I noted t h a t when cont a c t e d by the sensory setae of a pseudoscorpion p a l p a l hand, F. Candida u s u a l l y runs 1 t c 20 mm, seemingly a t random, be f o r e c o n t i n u i n g f e e d i n g or r e s t i n g . T h i s response i s very b r i e f ; the apparent e f f e c t s of such c o n t a c t l a s t only a few seconds, and f o l l o w the same sequence t h a t occurs when one collembolan j o s t l e s another while s e a r c h i n g f o r food or a moister r e s t i n g place. My o b s e r v a t i o n s show t h a t " s p r i n g i n g " away from predators i n arenas, c u l t u r e pots or i n t a c t l i t t e r and s o i l samples i s r a r e . T h i s method of emergency locomotion (accomplished by l o c k i n g the f u r c u l a with the tenaculum, t e n s i n g manubrial and abdominal muscles and then r e l e a s i n g the f u r c u l a ) seems to be employed more as a means of changing p o s i t i o n i n r e l a t i o n t o p h y s i c a l c o n d i t i o n s than i n escaping from p r e d a t o r s . 43 A p o c h t h o n i u s minimus A. minimus a d u l t s are a c t i v e i n my study s i t e from l a t e March t o October. They a r e found p r i m a r i l y i n the l i t t e r l a y e r and a l s o a r e common i n l a r g e r p i e c e s of d e t r i t u s , t w i g s and moss on the f o r e s t f l o o r o r on f a l l e n l o g s . I t i s d o u b t f u l t h a t t h e p s e u d o s c o r p i o n s perform d a i l y v e r t i c a l m i g r a t i o n s w i t h i n t h e top 5 - 15 cm of s o i l , as some s p r i n g t a i l s a r e b e l i e v e d t o do. The i« linims i n d i v i d u a l s from my s o i l and l i t t e r e x t r a c t i o n s were i n a lmost a l l c a s e s found i n t h e t o p few c e n t i m e t e r s of s o i l and l i t t e r . Samples c o l l e c t e d a t 3 a.mi. and a t 3 p.m. d i d not show d i f f e r e n c e s i n depth s e l e c t i o n by t h e p s e u d o s c o r p i o n s . R e p r o d u c t i o n p r o b a b l y i s not r e s t r i c t e d t o one b r i e f p e r i o d , s i n c e nymphs a r e p r e s e n t t h r o u g h o u t the summer (Appendix B: F i g u r e s B3 and B4). A s i m i l a r p a t t e r n i n o c c u r r e n c e o f C h t h g n i u s i s c h n o c h e l e s has been r e p o r t e d by Jones (1970). G i l b e r t (1951) has d e s c r i b e d the f e e d i n g b e h a v i o r of s e v e r a l p s e u d o s c o r p i o n s , i n c l u d i n g the C h t h o n i o i d e a . H i s d e s c r i p t i o n of the a c t o f f e e d i n g i n C h t h o n i u s i s c h n o c h e l u s i s n e a r l y i d e n t i c a l t o what I have observed f o r A. minimus. A. minimus a c t i v e l y hunts f o r prey (mainly by t o u c h ; i t i s d o u b t f u l t h a t i t s f o u r o c e l l i a r e image-forming) but r e t a i n s i t s c h a r a c t e r i s t i c a l l y t i m i d , c a u t i o u s approach even when prey i s encoun t e r e d . The p r e d a t o r s o f t e n run backward i n a t y p i c a l escape attempt when the y f i r s t c o n t a c t prey or an o t h e r p r e d a t o r . When c a p t u r e i s a c h i e v e d t h e prey i s g u i c k i y p i n c h e d w i t h the p e d i p a l p s and t r a n s f e r r e d t o t h e p o w e r f u l c h e l i c e r a e . The c a p t o r then moves t o a g u i e t s p o t where, w i t h the c h e l i c e r a e a l o n e , i t k i l l s and chews 44 the p r e y . . D u r i n g f e e d i n g , the c h e l i c e r a e j o i n t l y h o l d the prey , but o f t e n g r a s p and chew i n d e p e n d e n t l y , s i n c e each c h e l i c e r a has i t s own s e r r a t e d , movable s e c t i o n ( F i g u r e 9 ) . A f t e r t h e f o o d i s macerated, t h e l i g u i d p o r t i o n , i n c l u d i n g t h e p s e u d o s c o r p i o n ' s d i g e s t i v e j u i c e s , i s a p p a r e n t l y i n g e s t e d , and the r e m a i n i n g c u t i c l e i s d i s c a r d e d by s c r a p i n g and w i p i n g the mouthparts on the s u b s t r a t e . . A g u i c k d e f e c a t i o n and c l e a n i n g of the mouthparts, and a l e n g t h y r e s t p e r i o d f o l l o w . The p r e d a t o r may spend s e v e r a l hours s l o w l y e x p l o r i n g b e f o r e making a n o t h e r c a p t u r e . D u r i n g t h i s p e r i o d , i t i s common f o r t h e p r e d a t o r t o approach a v u l n e r a b l e prey i n d i v i d u a l , t o u c h i t , and then move on w i t h o u t a t t a c k i n g . S u r p r i s i n g l y , t h e r e have been no s t u d i e s of p r e d a t i o n by C h t h o n i i d p s e u d o s c o r p i o n s . The l a r g e r p s e u d o s c o r p i o n , Neobisium muscorum ( L e a c h ) , has a t t r a c t e d some a t t e n t i o n as a p r e d a t o r o f s p r i n g t a i l s (Simon, 1966, 1969).. E r n s t i n g and Joose (1974) ex p e r i m e n t e d w i t h N. muscorum and o t h e r p r e d a t o r s of l a r g e r s p r i n g t a i l s , and suggested on the b a s i s of i n d i r e c t o b s e r v a t i o n s t h a t t h i s p s e u d o s c o r p i o n might account f o r a s i g n i f i c a n t p o r t i o n of the m o r t a l i t y of th e s e c o l l e m b o l a n s . METHODS I . P r e d a t i o n Rates O b j e c t i v e s : t o g u a n t i f y t h e f u n c t i o n a l response (as d e s c r i b e d by H o l l i n g , 1959) o f A. minimus t o F. Candida prey and F i g u r e 9. The h i n g e d , s e r r a t e d c h e l i c e r a e o f A . m i n i m u s . The c h e l i c e r a e o f t h i s s p e c i e s a r e much l a r g e r and more p o w e r f u l ( i n p r o -p o r t i o n t o s i z e ) t h a n those o f o t h e r p s e u d o -s c o r p i o n s . ( M a g n i f i c a t i o n : 120 X) 46 t o t e s t t h e h y p o t h e s i s t h a t t h i s r e l a t i o n s h i p does not change w i t h p r e y s i z e or w i t h ambient t e m p e r a t u r e . A d u l t A. minimus (body l e n g t h 1.9 - 2.4 mm from c h e l i c e r a e t o anus; p a l p a l hand ( p i n c e r ) 0.7 - 0.8 mm long) were a s p i r a t e d from l a r g e bags of l i t t e r [ r o u g h l y h a l f f e a t h e r moss ( p r i m a r i l y Hylocomium s p l e n d e n s (Hedw.) BSG.) and h a l f n e e d l e s from Douglas-f i r (Pseudotsuga m e n z i e s i i (Mirb.) Franco) and western hemlock (Tsucja h e t e r o p h y l l a (Eaf.y Sarg.) ] c o l l e c t e d from the s t u d y s i t e a t t h e . U n i v e r s i t y o f B r i t i s h Columbia Research F o r e s t . The sex and e x a c t age of t h e p r e d a t o r s were not d e t e r m i n e d . I n d i v i d u a l p s e u d o s c o r p i o n s were t r a n s f e r r e d t o s e p a r a t e a r e n a s and a l l o w e d 24 h o u r s t o e v a c u a t e t h e i r g u t s t o reduce v a r i a b i l i t y i n hunger b e f o r e the e x p e r i m e n t . The a r e n a s were 150 ml p l a s t i c specimen v i a l s (pots) w i t h screw-top l i d s . Each pot had a f l o o r 1.0 - 1.5 cm deep (area 18 cm 2) of t e c h n i c a l p l a s t e r of p a r i s mixed w i t h c h a r c o a l (40 t o 1 ) . . The c h a r c o a l i n t u r n was a m i x t u r e of 2 p a r t s powdered a c t i v a t e d c h a r c o a l t o 3 p a r t s powdered a n i m a l c h a r c o a l , which p r o v i d e s a dark s u b s t r a t e w i t h a pH of 5.5 - 6.0 (Hatson, 1978a).. The f l o o r was k e p t s a t u r a t e d , b u t not v i s i b l y wet, w i t h d i s t i l l e d w ater. About 10 washed D o u g l a s - f i r n e e d l e s were added t o each pot t o p r o v i d e a more n a t u r a l e n v i r o n m e n t a l t e x t u r e . Prey d e n s i t y , t e m p e r a t u r e , prey s i z e and t i m e were m a n i p u l a t e d t o c h a r a c t e r i z e t h e f u n c t i o n a l r e s p o n s e . Prey d e n s i t i e s were 2, 4, 8, 12 and 20 i n d i v i d u a l s per 18 cm 2 a r e a . Prey were c l a s s i f i e d as " s m a l l " (0.5 - 0.7 mm long) and " l a r g e " (1.0 - 1.2 mm long) w i t h l e n g t h s measured from the mouth t o the p o s t e r i o r of t h e a n a l segment. These l e n g t h c l a s s e s were used 47 i n s t e a d o f s t a d i a because o f F. Candida's ametabolous growth: moults occur f r e q u e n t l y (every 4-10 days) th r o u g h o u t l i f e , a l t h o u g h t h e g e n e r a l body plan does not change markedly from t h e f i r s t i n s t a r t o t h e l a s t (see Chapter Two). a l l F. Candida f o r the e x p e r i m e n t s d e s c r i b e d here were o b t a i n e d from s t o c k l a b o r a t o r y c u l t u r e s . The p o t s were d i v i d e d e q u a l l y between two i d e n t i c a l i n c u b a t o r s , one a t a c o n s t a n t Q°C and t h e o t h e r a t a c o n s t a n t 16° C, and t h e exp e r i m e n t was c a r r i e d out i n c o n t i n u o u s dim l i g h t . . S i n c e t h e p r e d a t o r s and prey were e n c l o s e d i n t i g h t l y c o v e r e d p o t s , t h e r e was no need t o c o n s i d e r " i n c u b a t o r e f f e c t s " o t h e r than t e m p e r a t u r e . To a v o i d a t r e a t m e n t sequence e f f e c t and t o account f o r v a r i a b i l i t y among p r e d a t o r s , no i n d i v i d u a l p s e u d o s c o r p i o n was s u b j e c t e d t o more than one d e n s i t y - s i z e - t e m p e r a t u r e c o m b i n a t i o n d u r i n g t h e c o u r s e of the e x p e r i m e n t . There were f o u r p s e u d o s c o r p i o n s p e r t r e a t m e n t c o m b i n a t i o n . . I n a l l , 80 p s e u d o s c o r p i o n s were used i n 80 p o t s , 40 per i n c u b a t o r . The measured v a r i a b l e was t h e number o f o f f e r e d prey t h a t were eaten by i n d i v i d u a l p s e u d o s c o r p i o n s ; t h i s number was r e c o r d e d e v e r y 12 h o u r s , when t h e prey t h a t had been eaten were r e p l a c e d . The experiment was t e r m i n a t e d a f t e r 48 hours. The p s e u d o s c o r p i o n s were observed f o r 3 days f o l l o w i n g t h e experiment t o ensure t h a t none s u f f e r e d any o b v i o u s i l l e f f e c t s o r d r a m a t i c changes i n b e h a v i o r . I I . . S i z e - s e l e c t i o n O b j e c t i v e s : t o e s t i m a t e t h e p r o b a b i l i t y of c a p t u r e of t h e 48 d i f f e r e n t s i z e c l a s s e s of prey and t o t e s t t h e h y p o t h e s i s t h a t t h e s e p r o b a b i l i t i e s a r e e q u a l . . 4 - minimus a d u l t s were c o l l e c t e d as d e s c r i b e d f o r the e x p e r i m e n t on f u n c t i o n a l r e s p o n s e . Three s i m i l a r l y - s i z e d a d u l t s were i n t r o d u c e d t o each o f 2 p o t s o f the t y p e d e s c r i b e d above. A f t e r 24 h o u r s , a p o p u l a t i o n c o n s i s t i n g of a l l s t a g e s of prey ( i n c l u d i n g eggs) was added to each p o t . The p r e d a t o r s were a l l o w e d 6 hours t o become f a m i l i a r w i t h t h e prey a v a i l a b l e . T h i s c o n d i t i o n i n g p e r i o d was r e q u i r e d because of t h e p o s s i b i l i t y t h a t s t a r v e d p s e u d o s c o r p i o n s might f e e d on prey t h a t t h e y would not n o r m a l l y p r e f e r . T h i s p e r i o d a l s o a l l o w e d the t i m i d p s e u d o s c o r p i o n s t o a d j u s t t o t h e i r s u r r o u n d i n g s . A l l p r e d a t o r y a c t i v i t y d u r i n g the f o l l o w i n g 48 h o u r s was noted and t h e l e n g t h s of c a p t u r e d i n d i v i d u a l s were a l s o r e c o r d e d . At t h e end of 48 h o u r s , t h e r e m a i n i n g prey were c o u n t e d , measured, and grouped i n t o s i z e c l a s s e s w i t h t h e f o l l o w i n g mean body l e n g t h s : 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1 . 1 , 1.2, 1.3, 1.4 and 1.5 mm. Prey e a t e n d u r i n g t h e experiment were not r e p l a c e d . RESULTS AND DISCUSSION I . P r e d a t i o n Rates Table 5 shows the 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 of number of prey e a t e n . S e l e c t e d main e f f e c t s and i n t e r a c t i o n s are 49 shown i n Table 6, w i t h i n d i v i d u a l degree of freedom t e s t s of d i f f e r e n c e s i n f u n c t i o n a l response means and shapes. F i g u r e 10 shows f i t s o f t h e o b s e r v a t i o n s {pooled over t h e f o u r p e r i o d s f o r i l l u s t r a t i o n ) t o B o i l i n g ' s d i s c e g u a t i o n ( H o l l i n g , 1961), Na = aTN / 1 + aThN where Na = number a t t a c k e d a = a t t a c k r a t e T = t o t a l t i m e a v a i l a b l e Th = h a n d l i n g time N = prey d e n s i t y . I found t h a t e s t i m a t i n g a and Th by f i t t i n g the e g u a t i o n Na/N = aT - aThNa w i t h s i m p l e l i n e a r l e a s t s g u a r e s r e g r e s s i o n gave u n r e l i a b l e and o c c a s i o n a l l y u n r e a s o n a b l e e s t i m a t e s . More r e a l i s t i c v a l u e s and lower s t a n d a r d e r r o r s of e s t i m a t e were o b t a i n e d by n o n - l i n e a r l e a s t s g u a r e s f i t s . For s i m p l i c i t y , t h e M i c h a e l i s - M e n t o n form, Na = cN / d '+ N where c = the maximum (a s y m p t o t i c ) number eaten = T/Th 50 d = the h a l f s a t u r a t i o n d e n s i t y = 1/aTh T = t o t a l t i me (2 days i n t h i s c a s e ) , N = prey d e n s i t y , was used f o r t h e s e f i t s . E s t i m a t e s of h a n d l i n g time and a t t a c k r a t e f o r t h e two t e m p e r a t u r e s and two t y p e s of prey a r e shown i n T a b l e 7.. H a n d l i n g time i s h i g h e r and a t t a c k r a t e l o w e r f o r the l a r g e r p r e y . Both h a n d l i n g time and a t t a c k r a t e are somewhat h i g h e r a t t h e h i g h e r t e m p e r a t u r e . E v i d e n c e t h a t t h e response t o prey d e n s i t y i s not merely a l i n e a r i n c r e a s e i s shown i n T a b l e 6a. Both t h e l i n e a r and g u a d r a t i c components of o r t h o g o n a l c o n t r a s t t e s t s a r e h i g h l y s i g n i f i c a n t . . The c u r v e s are a l l t y p i c a l Type I I f u n c t i o n a l r e s p o n s e s ; h i g h e r o r d e r components acc o u n t f o r l i t t l e o r none of the v a r i a t i o n {Appendix E c o n t a i n s t h e . c o n t r a s t c o e f f i c i e n t s u s e d ) . There was no h i g h l y s i g n i f i c a n t e f f e c t of temperature on f u n c t i o n a l r e s p o n s e . . The d i f f e r e n c e i n number eaten as a f u n c t i o n o f s i z e was o n l y weakly a l t e r e d by t e m p e r a t u r e (Table 5; T a b l e 6b) . . T h i s r e s u l t i s u n l i k e t h o s e of Thompson (1978) and Everson (1980) who found t h a t f u n c t i o n a l response parameters seemed to be s e n s i t i v e t o t e m p e r a t u r e . . T h i s d i f f e r e n c e i n r e s u l t s may have a r i s e n merely because 8 and 16° C are w e l l w i t h i n the range n o r m a l l y e n c o u n t e r e d by h u n t i n g p s e u d o s c o r p i o n s . Higher or lower t e m p e r a t u r e s might a l t e r a t t a c k r a t e and h a n d l i n g t i m e . P r e l i m i n a r y r e s u l t s from an e a r l i e r e x periment not r e p o r t e d here i n f a c t suggest t h a t both a t t a c k r a t e and h a n d l i n g t i m e a r e lower a t 24<> C than a t 8 o r 16° c . . A 24° C t r e a t m e n t was not i n c l u d e d i n t h i s experiment because of the u n n a t u r a l l y Table 5- A n a l y s i s of v a r i a n c e of the number of prey eaten i n the f u n c t i o n a l response experiment. A n a l y s i s of v a r i a n c e - Numbers eaten Source df SS MS F 2 Temperature 1 0.050 0.050 0.061 0.8168 Prey s i z e 1 56.113 56.113 68.447 < 0.0001 S i z e X Temp 1 0 .200 0 .200 0 .244 0.6323 D e n s i t y 4 35.519 8.880 10.832 < 0.0001 Dens X Temp 4 10.294 2.573 3.139 0.0261 Dens X S i z e 4 12.981 3.245 3.959 0.0086 Dens X Temp X Sz 4 5.956 1.489 1.722 0.1569 Pseudoscorpions 60 51.875 0.865 Time (hrs) 3 104 .463 34.821 35.790 < 0.0001 Time X Temp 3 2.575 0.858 0.882 0.4515 Time X Dens 12 10.381 0 .865 0.889 0.5597 Time X S i z e 3 25.662 8.554 8.792 < 0.0001 Time X Tmp X Den 12 10.956 0 .913 0.938 0.5104 Time X Tmp X Sz 3 1.725 0.575 0.591 0.6217 Time X Den X Sz 12 I8 . 369 1.531 1.573 0.1024 Tm X D X S X Tmp 12 17.744 1.479 1.520 0.1200 R e s i d u a l 180 175.126 0.973 T o t a l 319 539-998 52 Table 6. O r t h o g o n a l c o n t r a s t s <i B O U T c e of v a r i a t i o n a. ) P r e y D e n s i t y L i n e a r component Q u a d r a t i c component C u b i c component H i g h e r o r d e r components b. ) D e n s i t y X T e m p e r a t u r e D i f f e r e n c e s i n : L i n e a T components Q u a d r a t i c components C u b i c components Higr.er o r d e r components c. > D e n s i t y X P r e y S i z e D i f f e r e n c es i n : L i n e a r components Q u a d r a t i c components C u b i c components Higr.er- o r d e r components d ) Time L i n e a r component Q u a d r a t i c component H i g h e r o r d e r components e ) Time X P r e y S i z e D i f fe f e r, c e s i n : L i n e a r components Quedr-etic components H i g h e r o r d e r components i v i d u a l d e g r e e of fr e e d o m t e s t s ) 1/ 4 10.270 0. 0001 1 29.115 < 0 0001 1 11. 357 0 0013 1 0. 400 0 5293 1 0.212 0.6469 4 2.977 0.0261 1 5. 392 0 0236 1 2. 230 0 1406 1 3. 636 0. 0613 1 0. 650 0. 4234] 4 3. 754 0. 0083 1 5. 049 0 02S3 1 6. 412 0. 0140 1 2. 565 0. 1145 1 0. 987 0. 3244 4 35 790 < 0. 0001 1 B4.182 < 0.0001 1 20.557 0.0007 1 2. 631 0 1065 4 B. 792 < 0 0001 1 24.177 0 0007 1 0 463 0. 4973 1 1. 737 O . 1 B 9 2 1 / F o r main e f f e c t s <parts a and d) p ( t h e p r o b a b i l i t y of ar, F - v a l u e as l a r g e or l a r g e r ) i n d i c a t e s s i g n i f i c a n c e of t h e the c o n t r i b u t i o n by a component to t h e shape of the f u n c t i o n a l response. For i n t e r a c t i o n s (parts b,c and e), p i n d i c a t e s s i g n i f i c a n c e of the change i n a component due to the i n t e r — ac t i on. T a b l e 7. E s t i m a t e s o f h a n d l i n g t i m e (Th) and a t t a c k r a t e (a) f o r d i f f e r e n t p r e y s i z e and t e m p e r a t u r e t r e a t m e n t s . Each e s t i m a t e i s b a s e d on 4 measurements t a k e n on each of 20 p s e u d o s c o r p i o n s . TEHPEfiATOBE 8°C 16° C £M1 SIZE body l e n g t h 1.0 - 1. 2 mm body l e n g t h 0.5 - 0.7 am Th = . 45 1 Th = .59 a = .38 1 a = .47 Th = . 14 i Th = .24 a = .68 1 a = 1.72 54 h i g h m o r t a l i t y of t h e both the p r e d a t o r and prey a t t h i s t e m p e r a t u r e . Of t h e f o u r main e f f e c t s s t u d i e d i n t h e e x p e r i m e n t , prey s i z e a c c o u n t e d f o r most of the v a r i a b i l i t y i n g r o s s numbers e a t e n , s u g g e s t i n g t h a t a w e l l - d e f i n e d f u n c t i o n a l response t o prey s i z e d i s t r i b u t i o n may e x i s t . T h i s e f f e c t was shown i n d e t a i l by Thompson (1975) f o r I s c h n u r a e l e q a n s and by McArdle and Lawton (1979) f o r Notonecta g l a u c a . The r e s u l t s of i n d i v i d u a l degree of freedom t e s t s on prey s i z e r e l a t i o n s h i p s a r e shown i n T a b l e 6c. The l i n e a r components ( o v e r a l l r i s e s ) of t h e f u n c t i o n a l response t o s m a l l prey and t h e f u n c t i o n a l response t o l a r g e prey d i f f e r (p=0.Q245). The q u a d r a t i c components (shapes) of t h e c u r v e s a l s o d i f f e r (p=0.0 117). These d i f f e r e n c e s are m a i n l y due t o t h e h i g h e r s a t u r a t i o n l e v e l (T/Th) and a t t a c k r a t e (a) f o r s m a l l prey. More s m a l l a n i m a l s are r e q u i r e d t o s a t i s f y t h e p r e d a t o r s 1 needs, and t h e y a r e a t t a c k e d a t a h i g h e r r a t e . F i g u r e 10 r e p r e s e n t s the c u m u l a t i v e number o f c a p t u r e s over a 48-hour p e r i o d . . There were, however, s t r o n g d i f f e r e n c e s i n t h e f u n c t i o n a l r e s p o n s e s o f i n d i v i d u a l p r e d a t o r s over t i m e . The changes t h r o u g h 48 hours i n t h e numbers of prey e a t e n f o r t h e 5 prey d e n s i t i e s and 2 prey s i z e s a r e shown i n F i g u r e 11. R e c a l l t h a t each p s e u d o s c o r p i o n was s u b j e c t e d t o o n l y one c o m b i n a t i o n o f the t e m p e r a t u r e - d e n s i t y - s i z e t r e a t m e n t s but t h a t a l l were ob s e r v e d over the f o u r t i m e i n t e r v a l s . F i g u r e 11 shows t h a t c a p t u r e s were r e l a t i v e l y high d u r i n g t h e f i r s t 12 hours f o r most of the t r e a t m e n t c o m b i n a t i o n s . . W i t h i n t h e f i r s t 24 t o 36 hours. F i g u r e 10. Type II f u n c t i o n a l response curves f o r the two temperatures and two prey s i z e s . E s t i m a t e s o f the d i s c e quation parameters are shown i n Table 7. n u m b e r e a t e n (l.0-1.2mm prey) 5 4 3 2 1 ol P r e y d e n s i t y 4 8 j . t * 12 n u m b e r e a t e n (0.5-0.7mm prey) 12 24 36 48 12 24 36 48 12 24 36 48 12 24 36 48 T i m e p e r i o d ( h o u r s ) F i g u r e 11. Changes i n the number e a t e n p e r 12 hours w i t h changes i n p r e y d e n s i t y , p r e y s i z e and t i m e . S t a n d a r d e r r o r b a r s are shown. Each p o i n t i s the mean o f 8 o b s e r v a t i o n s (on 8 d i f f e r e n t p r e d a t o r s ) . 57 the number of c a p t u r e s per 12 hours i n most c a s e s l e v e l l e d o f f at a minimum. . A number o f p s e u d o s c o r p i o n s were obse r v e d f o r f u r t h e r p e r i o d s up t o 84 h o u r s , but i n no case was any d r a m a t i c i n c r e a s e or d e c r e a s e i n c a p t u r e s observed i n the l a t e r i n t e r v a l s ( e x c e p t where two p s e u d o s c o r p i o n s were drowned i n c o n d e n s a t i o n on t h e c o n t a i n e r w a l l s ) . I n g e n e r a l , the change with time had v e r y s t r o n g l i n e a r (p < 0.0001) and g u a d r a t i c (p=0.0008) components w i t h no s i g n i f i c a n t h i g h e r degree t r e n d s (p=0.1121; Table 6d). I had p r e v i o u s l y h y p o t h e s i z e d t h a t t e m p e r a t u r e s h o u l d change t h i s r e l a t i o n s h i p because o f e x p e c t e d changes i n a c t i v i t y , metabolism and n u t r i t i o n a l needs of t h e p r e d a t o r , but t h i s does not seem t o have happened (Time X Temperature i n t e r a c t i o n , T a b l e 5 ) . Prey s i z e , however, d i d cause a s i g n i f i c a n t (p=0.0007) l i n e a r change i n c a p t u r e s over t i m e , as was e x p e c t e d . The change from t h e f i r s t 12-hour p e r i o d t o t h e l a s t was g r e a t e r f o r s m a l l p r e y , s u g g e s t i n g t h a t t h e p s e u d o s c o r p i o n s " a d j u s t " t o e a t i n g s m a l l e r prey. . I I . . S i z e - s e l e c t i o n by t h e P r e d a t o r s . The r e s u l t s of t h e two r u n s of t h e s i z e - s e l e c t i o n experiment were very s i m i l a r , so the data were p o o l e d . D u r i n g t h e p e r i o d a l l o w e d , t h e p s e u d o s c o r p i o n s a t e 26 of t h e 221 prey a v a i l a b l e ( F i g u r e 1 2 ) . As i n o t h e r e x p e r i m e n t s not r e p o r t e d h e r e , none of the p r e y eggs were e a t e n , even when hundreds were o f f e r e d . The d a t a s u g g e s t a s t r o n g p r e f e r e n c e f o r prey i n d i v i d u a l s around 1 mm i n l e n g t h . I showed i n the f u n c t i o n a l response e x p e r i m e n t s t h a t A. minimus d i d not r e f u s e the s m a l l e r prey when no c h o i c e was 58 • y .1 .2 .3 .4 .5 .6 .7 .8 .9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 l e n g t h c l a s s ( m m ) F i g u r e 12. S i z e frequency d i s t r i b u t i o n o f prey p o p u l a t i o n a v a i l a b l e to A. minimus and the prey eaten. 59 a v a i l a b l e . The e q u a t i o n s of Manly (1973, 1974) f o r Type Two S e l e c t i o n E x p e r i m e n t s (without prey replacement) were used t o e s t i m a t e s e l e c t i v i t y s t a t i s t i c s . The p r o b a b i l i t y , J5c , t h a t a p r e y i n d i v i d u a l from the i t h s i z e c l a s s would have been s e l e c t e d had t h e r e been an e q u a l number of i n d i v i d u a l s i n each c l a s s i s shown i n T a b l e 8. . S i n c e A. minimus uses i t s l a r g e p a l p a l c l a w s t o " p i n c h " t h e prey on t h e abdomen or p r o t h o r a x , and g u i c k l y t r a n s f e r them t o t h e c h e l i c e r a e , i t i s u n l i k e l y t h a t t h e p r e f e r r e d prey s i z e i s d e t e r m i n e d by the maximum s i z e t h a t can be grasped by the f o r e l e g as i n the mantid H i e r p d u l a c r a s s a ( H o l l i n g , 196 4; see a l s o H o l l i n g e t a l . , 1976). I s u s p e c t t h a t t h e s i z e of prey i s l i m i t e d by the a b i l i t y of the s m a l l e r c h e l i c e r a e t o h o l d and macerate i t so t h a t body f l u i d s can be drawn o f f . . But i t i s a l s o p o s s i b l e , g i v e n t h e morphology of t h e p a l p a l hand and the manner i n which I have observed i t b e i n g used t o " f e e l " p r e y , t h a t i t i s used t o e s t i m a t e prey s i z e at t h e moment when the d e c i s i o n t o attempt c a p t u r e i s made. I b e l i e v e t h a t a h u n t i n g p s e u d o s c o r p i o n f i r s t d e t e c t s prey movement and t h e n , as i t r e a c h e s f o r t h e prey, r o u g h l y measures prey s i z e w i t h t h e l o n g t a c t i l e s e t a e on t h e dorsum of the p a l p a l hand (see F i g u r e 13). A d e c i s i o n t o a t t a c k t h u s c o u l d be based on prey s i z e , p r e d a t o r hunger, and perhaps o t h e r i n f o r m a t i o n , such as t e x t u r e or s m e l l . (I have noted t h a t A. minimus r e f u s e s t o eat O n y c h i u r u s spp. (Collembola) of s i m i l a r s i z e , shape, a c t i v i t y , and c o l o r t o F . , C a n d i d a . . Weygoldt (1969) suggested t h a t t h e r e may be an o l f a c t o r y r e c e p t o r on t h e t i p o f t h e p a l p a l f i n g e r s and a t a s t e r e c e p t o r near t h e p r e o r a l c a v i t y which a l l o w p s e u d o s c o r p i o n s t o r e c o g n i z e t h e u n p a l a t a b l e Table S. sel e c t i v i t y s t a t i s t i c s foe length classes o£ prey. 2 . / Class pooled lenqth classes L e. £i 1 0.2 ,0.3 21 0 21 0.00 0 0 2 0.4 ,0.5 42 0 42 0.0000 3 0.6 ,0.7 60 1 59 0.0176 4 0.8 ,0.9 35 6 29 0. 1963 \ 5 1.0 ,1.1 43 16 27 0.4858 6 1.2, 1.3, 1.4,1.5 20 5 15 0.3003 2./ HAH LY 1 s (1973) & i s calculated as - log (Ci / KI /J^logU:, / AJ where kc = the nuaber of prey of class i i n i t i a l l y available e; = the number of prey of class i eaten r ( = the number of prey remaining K = total nuaber of size classes = 6 F i g u r e 1 3 . T a c t i l e setae on the " p i n c e r ( p a l p a l or c h e l a l hand) of A. minimus. ( M a g n i f i c a t i o n : 2 1 0 X) 62 O n y c h i u r i d s . ) The s i z e of prey t h a t i s p r e f e r r e d may change over a p r e d a t o r ' s l i f e t i m e . C a s u a l o b s e r v a t i o n s of A..minimus nymphs suggest t o me t h a t these s m a l l e r s i z e d p r e d a t o r s ( l e n g t h < 1.5 mm) u s u a l l y p r e f e r s m a l l e r , though not n e c e s s a r i l y p r o p o r t i o n a t e l y s m a l l e r , F. Candida. Goddard (1976) noted t h a t t h e f e e d i n g r e s p o n s e of the p s e u d o s c o r p i o n Neobisium muscorum i s i n i t i a t e d by movement of the p r e y . . S i m i l a r l y , the o b s e r v a t i o n s o f E r n s t i n g e t a l . . (1977) show t h a t movement of c o l l e m b o l a n prey i s n e c e s s a r y ' f o r t h e i r d e t e c t i o n , p u r s u i t and a t t a c k by t h e c a r a b i d b e e t l e N o t i o p h i l u s b i g u t t a t u s F.. D u r i n g p e r i o d s o f r e l a t i v e i n a c t i v i t y , such as e c d y s i s , the prey are not d e t e c t e d by the b e e t l e . The r e l a t i v e p r e d a t i o n r i s k of prey s p e c i e s depends on the r a t i o of a c t i v e and i n a c t i v e i n d i v i d u a l s o f a p a r t i c u l a r s p e c i e s (and o t h e r s p e c i e s p r e s e n t ) as w e l l as on r e l a t i v e d e n s i t i e s ( E r n s t i n g e t a l . , 1977).. Iwao and W e l l i n g t o n (1970) found t h a t a c t i v i t y l e v e l s of the t e n t c a t e r p i l l a r , Malacosoma c a l i f o r n i c u m p l u y i a l e ( D y a r ) , i n f l u e n c e d p r e d a t i o n by t h e p e n t a t o m i d bug, P o d i u s m a c u l i y e n t r i s Say. The conseguences of movement by the more a c t i v e l a r v a e changed w i t h p r e y ' s i n s t a r . The p r e d a t o r was a t t r a c t e d by t h e movements of s m a l l a c t i v e l a r v a e but was unable t o a t t a c k t h e a c t i v e i n d i v i d u a l s s u c e s s f u l l y i n l a t e r i n s t a r s because t h e i r d e f e n s i v e movements were t o o v i g o r o u s . I do not b e l i e v e t h a t s i z e - s e l e c t i v e p r e d a t i o n by A..minimus i s a d i r e c t f u n c t i o n of prey a c t i v i t y . I have not seen any g r e a t d i f f e r e n c e s i n a c t i v i t y among o l d and young i n d i v i d u a l s , a l t h o u g h o l d e r F. C a n d i d a had a tendency t o d i s p e r s e f a r t h e r t h a n t h e 6 3 younger i n s - t a r s i n s e p a r a t e d i s p e r s a l e x p e r i m e n t s (see Appendix F ) . . Sudden b u r s t s of prey a c t i v i t y among i t s prey i n some c i r c u m s t a n c e s s t i m u l a t e A. minimus t o b e g i n s e a r c h i n g b e h a v i o r , but t h e r e a r e many e n c o u n t e r s i n which the p r e d a t o r makes no attempt t o c a p t u r e moving prey. Sometimes, i n f a c t , movements by the prey l e a d t o f l i g h t by the p s e u d o s c o r p i o n s . ( P s e u d o s c o r p i o n s have t h e i r own p r e d a t o r s , p a r t i c u l a r l y c e n t i p e d e s ; and Jones (1975) a l s o documents s p i d e r p r e d a t i o n on pseudoscorpions.) The e x p e r i m e n t s on f u n c t i o n a l r e s p o n s e demonstrate t h a t A. minimus w i l l f e e d on s m a l l F. Candida i f no a d u l t prey i s a v a i l a b l e , but the s a t u r a t i o n number of prey e a t e n and the a t t a c k r a t e a r e c o n s i s t e n t l y h i g h e r f o r s m a l l prey. When A. minimus can choose among v a r i o u s s i z e s of prey, however, i t d i s p l a y s a w e l l -d e f i n e d p r e f e r e n c e f o r m i d - s i z e t o l a r g e F. C a n d i d a . Because t h e s e s i z e c l a s s e s (see Cha p t e r Two f o r the a g e - l e n g t h r e -l a t i o n s h i p ) r e p r e s e n t d i f f e r e n t age c l a s s e s w i t h d i f f e r e n t r e p r o d u c t i v e r a t e s , I t e l i e v e t h a t t h e p r e d a t o r ' s p r e f e r e n c e f o r l a r g e r p r e y has s i g n i f i c a n t e f f e c t s on t h e s t r u c t u r e and a t t r i b u t e s of a n a t u r a l p o p u l a t i o n . A d d i t i o n a l o b s e r v a t i o n s suggest t h a t A. minimus has t h e same t y p e of s i z e p r e f e r e n c e when f e e d i n g on L e p i d o c y r t u s sp. _and Isotoma spp., o t h e r s p r i n g t a i l s i n my s t u d y s i t e . Because of t h e i r p e c u l i a r p o s t - e m b r y o n i c growth and dev e l o p m e n t a l p a t t e r n , a l l s p r i n g t a i l p o p u l a t i o n s may be p a r t i c u l a r l y v u l n e r a b l e t o the r a m i f y i n g e f f e c t s of s i z e -s e l e c t i v e p r e d a t i o n . I i n v e s t i g a t e t h e s e e f f e c t s i n t h e nex t c h a p t e r . CHAPTER POUR PREDATION OF APOCHTHONIUS MINIMUS (PSEUDOSCORPIONIDA: CHTHONIIDAE) ON FOLSOMIA CANDIDA (COLLEMBOLA: ISOTOMIDAE) I I . EFFECTS OF PREDATION ON PREY POPULATIONS 65 INTRODUCTION When age or s i z e c l a s s e s a re easy t o d i s t i n g u i s h w i t h i n a p o p u l a t i o n , i n v e s t i g a t o r s can stu d y t h e s t r u c t u r a l as w e l l as the n u m e r i c a l consequences of s e l e c t i v e p r e d a t i o n f o r p o p u l a t i o n s or f o r whole communities. F o r example, P a i n e (1976) d e s c r i b e d a s i t u a t i o n i n which l a r g e r mussels escaped p r e d a t i o n by s t a r f i s h . G a l b r a i t h (1967) found t h a t s i z e - s e l e c t i v e p r e d a t i o n by t r o u t and perch e l i m i n a t e d one l a r g e s p e c i e s of Daphnia and s h i f t e d s i z e d i s t r i b u t i o n s o f o t h e r s t o the s m a l l e r c l a s s e s . Brooks (1968) and Brooks and Dodson (1965) r e p o r t e d a p r e d a t o r p r e f e r e n c e f o r l a r g e r s p e c i e s of C l a d o c e r a , w i t h l a r g e r i n d i v i d u a l s b e i n g s e l e c t e d w i t h i n each s p e c i e s . Brooks (1968) found t h a t prey s u r v i v a l t ime was i n v e r s e l y p r o p o r t i o n a l t o prey l e n g t h , so t h a t p r e d a t i o n p r e s s u r e s h i f t e d the s p e c i e s c o m p o s i t i o n of the prey towards s p e c i e s w i t h s m a l l e r body s i z e . Dodson (1974) demonstrated t h a t z o o p l a n k t o n a s s o c i a t i o n s a re s u b j e c t t o s i z e -s e l e c t i o n a t b o t h ends o f the s i z e spectrum, and d i s c u s s e d t h e community conseguences. A d d i c o t t (1974) showed how t h e p r o t o z o a n communities of p i t c h e r p l a n t s a r e a l t e r e d i n r e l a t i o n t o t h e d i s t r i b u t i o n and d e n s i t y of p r e d a t o r y mosquito l a r v a e . A l t h o u g h most of t h e s e s t u d i e s have been concerned w i t h p r e d a t i o n - r e l a t e d changes i n c o m m u n i t i e s , the e f f e c t s o f s e l e c t i v e p r e d a t i o n on p o p u l a t i o n s may be as d r a m a t i c . I t h i n k t h a t one reason r e s e a r c h on the e f f e c t s of s i z e - s e l e c t i v e p r e d a t i o n has so o f t e n c o n cerned communities r a t h e r t h a t s i n g l e - s p e c i e s p o p u l a t i o n s may be t h a t prey t y p e s and s i z e s ( i . e . s p e c i e s or genera) are e a s i e r t o d i s t i n g u i s h i n communities. 6 6 A s s e s s i n g t h e s e s t r u c t u r a l consequences of p r e d a t i o n may be more d i f f i c u l t when age or s i z e c l a s s e s a r e s u p e r f i c i a l l y i n d i s t i n g u i s h a b l e , or a p p a r e n t l y u n r e l a t e d . Among the i n s e c t s and t h e i r near r e l a t i v e s such assessments have i n most c a s e s been r e s t r i c t e d t o the p r e d a t o r (e.g. B e d d i n g t o n and F r e e , 1 9 7 6 ; LeCato, 1 9 7 8 ; E v e l e i g h , 1 9 7 9 ) . . In c o n s t r a s t t o most i n s e c t s , however, t h e C o l l e m b o l a , because of t h e i r p e c u l i a r form of growth p r o v i d e e x c e p t i o n a l o p p o r t u n i t i e s f o r a s s e s s i n g t h e s t r u c t u r a l as w e l l as t h e n u m e r i c a l p o p u l a t i o n consequences o f s e l e c t i v e p r e d a t i o n . . I have used t h e p r e f e r e n c e of the p s e u d o s c o r p i o n , A p o c h t o n i u s minimus, f o r c e r t a i n s i z e s of F o l s o m i a Candida ( C o l l e m b o l a ) t o a s s e s s t h e p o p u l a t i o n conseguences of s e l e c t i v e p r e d a t i o n . My more immediate g o a l was t o determine i f t h i s s o r t of p r e d a t i o n c o u l d be s i g n i f i c a n t l y a f f e c t i n g the s i z e and g u a l i t y o f s p r i n g t a i l p o p u l a t i o n s . METHODS O b j e c t i v e s : t o q u a n t i f y t h e e f f e c t s of p r e d a t i o n on growth and age ( s i z e ) s t r u c t u r e of F . . c a n d i d a p o p u l a t i o n s and t o t e s t the h y p o t h e s i s t h a t t h e presence of p r e d a t o r s r e s u l t s i n reduced prey numbers. A s i m p l e e xperiment wi t h a c o m p l e t e l y randomized d e s i g n was performed i n which th e o n l y t r e a t m e n t was t h e presence or absence of a d u l t A. minimus. L i t t e r from t h e f o r e s t f l o o r of the s t u d y s i t e a t t h e UBC Research F o r e s t was d r i e d a t 6 0 0 c f o r 4 8 hours t o k i l l and d e s i c a t e a l l m i c r o a r t h r o p o d s . A p p r o x i m a t e l y 8 to 10 grams o f t h i s l i t t e r were added t o each of 16 p l a s t i c p i p e 67 c o n t a i n e r s (I.D. 5 cm; l e n g t h 10 cm), m oistened, and i n c u b a t e d at 16° C f o r one day. Ten a d u l t s from F. Candida l a b o r a t o r y s t o c k ( r a n g i n g from 1.0 - 1.2 mm i n l e n g t h ) were added t o each of t h e c o n t a i n e r s . . (F. Candida i s p a r t h e n o g e n e t i c and I suspect t h a t no males e x i s t e d i n my l a b o r a t o r y p o p u l a t i o n s . ) The 16 c o n t a i n e r s were randomly d i v i d e d i n t o two groups: 8 had no p r e d a t o r s and 8 r e c e i v e d 3 a d u l t A. minimus per c o n t a i n e r . The p s e u d o s c o r p i o n s had been c o l l e c t e d t h e day b e f o r e a t t h e s t u d y s i t e and s t o r e d i n i n c u b a t o r s t h a t mimicked th e f i e l d e n v ironment. The c o n t a i n e r s were c o v e r e d at b oth ends w i t h 54-micron p l a s t i c mesh h e l d by snap-on r i n g s and s e a l e d w i t h t a p e . P r e l i m i n a r y f i e l d t r i a l s and o b s e r v a t i o n s under a d i s s e c t i n g m icroscope showed t h a t not even newly hatched F. C a n d i d a c o u l d escape t h r o u g h the mesh. The c o n t a i n e r s were g u i c k l y t r a n s p o r t e d i n a humid, i n s u l a t e d c o o l e r t o t h e s t u d y s i t e , l a i d on t h e i r s i d e s , and c o v e r e d w i t h l e a f l i t t e r u n t i l o n l y t h e uppermost c e n t i m e t e r of t h e i r s u r f a c e was exposed. T h e i r p o s i t i o n s were randomly a s s i g n e d i n a 2m X 2m area shaded by 4 c o r n e r t r e e s . . Every two weeks t h e c o n t a i n e r s were checked f o r damage and danger of d r y i n g . Temperatures a t t h e l i t t e r s u r f a c e were monitored w i t h a 7-day thermograph i n a shaded s c r e e n on the f o r e s t f l o o r . A f t e r 46 days {enough time f o r about 3 g e n e r a t i o n s of the prey) the c o n t a i n e r s were r e t r i e v e d and r e t u r n e d t o the l a b o r a t o r y i n t h e i n s u l a t e d c o o l e r . There t h e y were e x t r a c t e d w i t h a p r e v i o u s l y c a l i b r a t e d Macfadyen (1961) h i g h - g r a d i e n t e x t r a c t o r which had a measured e x t r a c t i o n e f f i c i e n c y of ~ 96% f o r F. Candida ( d i s c u s s e d below). The s p r i n g t a i l s and 68 p s e u d o s c o r p i o n s were e x t r a c t e d over a 6-day p e r i o d i n t o c o l d p i c r i c a c i d , c o u n t e d , and measured. I grouped the s p r i n g t a i l s i n t o n i n e t e e n 0.1-mm s i z e c l a s s e s (measured from the mouth t o the p o s t e r i o r t i p of the a n a l segment) over t h e range, 0.2 - 2.0 mm. The c y l i n d e r s were weighed b e f o r e e x t r a c t i o n and a g a i n a f t e r d r y i n g at 70° C i n o r d e r t o e s t i m a t e m o i s t u r e c o n t e n t o f t h e l i t t e r . RESULTS AND DISCUSSION U n c o n t r o l l e d E n v i r o n m e n t a l V a r i a b l e s A i r t e m p e r a t u r e s and r a i n f a l l data r e c o r d e d 1 km from my s t u d y a r e a by t h e UBC Research F o r e s t S t a f f a r e shown i n Appendix D. The t e m p e r a t u r e s o f t h e l i t t e r s u r f a c e ranged from 8.5 t o 23.5° C d u r i n g t h e e x p e r i m e n t . Means and s t a n d a r d e r r o r s of t h e s u r f a c e t e m p e r a t u r e a t t h r e e hour i n t e r v a l s f o r t h e f i r s t , middle and l a s t week were 14. 1 + 0.48, 16. 1 + 0.46 and 14.5 + 0.27° c. The range o f s u r f a c e t e m p e r a t u r e was not extreme (between 10 and 20° C ) , s i n c e t h e s t u d y s i t e was w e l l shaded. The t e m p e r a t u r e at a depth o f 5 cm was n o t c o n t i n u o u s l y m o n i t o r e d , b u t was c o n s i s t e n t l y 0.5 - 1.0" C c o o l e r than t h e s u r f a c e temperature whenever checked. R a i n f a l l d u r i n g t h e experiment was l i g h t , amounting t o a t o t a l o f 15.6 cm. Mean m o i s t u r e (water l o s s as a p e r c e n t of dry weight) o f the l i t t e r and s o i l i n t h e c o n t a i n e r s was 179.6 + 14.35. P e r c e n t m o i s t u r e a t c o l l e c t i o n time d i d not d i f f e r between t h e 8 treatment (183.0 + 19.5) and the 8 c o n t r o l c o n t a i n e r s (176.2 + 22.4). M o i s t u r e c o n t e n t of t h e s o i l and T a b l e 9. D e s c r i p t i o n o f t h e f i n a l p o p u l a t i o n s and c o n t e n t s o f t h e c o n t a i n e r s a t the end of t h e e x p e r i a e n t . F. Candida C o n t a i n e r P e r c e n t T o t a l i a a a t u r e s a d u l t s Bean l e n g t h a e d i a n r e m a i n i n g "H»ber M o i s t u r e .no,. K . 7 5 an) (>.75aa) . ( v a r i a n c e ! l e n g t h i j r e d a t a t i . C o n t r o l p o p u l a t i o n s : 1 66.67 136 48 88 2 162.50 202 94 108 3 196.00 86 23 63 4 2 16.67 9 1 12 79 5 198.33 132 67 65 6 164. 81 438 170 268 7 206.25 6 0 6 8 252.94 243 133 110 P o p u l a t i o n s w i t h p r e d a t o r s : 9 283. 54 371 179 192 10 109. 14 0 0 0 1 1 215.63 215 10 1 114 12 203.77 440 193 247 13 198.55 0 0 0 IV 125.61 0 0 0 15 177.05 0 0 0 16 115. 63 20 6 143 63 . 845 (.070) .816 (.123) .987 (.096) .986 (.042) .817 (.120) .843 (.06 1) 1.23 (.016) . 743 (. 100) . 872 .779 . 998 . 985 .710 . 881 1.22 . 683 .780 (.058) .758 ( E x t i n c t ) .821 (.081) .77* .827 (.078) .803 ( E x t i n c t ) ( E x t i n c t ) ( E x t i n c t ) .664 (.065) .596 3 1 2 3 0 0 1 3 70 l i t t e r p l a y s an i m p o r t a n t r o l e i n t h e s u r v i v a l and s t r u c t u r e o f C o l l e m b o l a p o p u l a t i o n s and communities (Ve r h o e f , 1977; E r n s t i n g , 1977). I n t h i s e x p e r i m e n t , however, th e d i f f e r e n c e s i n m o i s t u r e were n e i t h e r l a r g e nor c o r r e l a t e d w i t h p o p u l a t i o n s i z e , c o m p o s i t i o n , or mean body l e n g t h a t c o l l e c t i o n t ime (p > 0.3). M o i s t u r e , p o p u l a t i o n s i z e , and mean and median l e n g t h s are shown i n T a b l e 9. . I n t e r p r e t a t i o n of Length-Frequency D i s t r i b u t i o n s S e v e r a l o f t h e l e n g t h - f r e q u e n c y d i s t r i b u t i o n s of the p o p u l a t i o n s t h a t s u r v i v e d the p r e d a t i o n t r e a t m e n t ( F i g u r e 14) and o f the c o n t r o l p o p u l a t i o n s ( F i g u r e 15) tended t o be b i m o d a l . N o r m a l l y , s i z e - f r e g u e n c y d i s t r i b u t i o n s of C o l l e m b o l a p o p u l a t i o n s c o u l d be e x p e c t e d t o be n e a r l y c o n t i n u o u s , because t h e i n s e c t s can l a y eggs through most o f t h e i r l i v e s (from the 6th t o the 40th i n s t a r a c c o r d i n g t o S n i d e r , 1971). The b i m o d a l form of t h e d i s t r i b u t i o n s shown he r e i s a r e s u l t of t h e f a c t t h a t the s t a r t i n g p o p u l a t i o n s were composed e n t i r e l y of a d u l t s . Most o f t h e d i s t r i b u t i o n s shown here t h e r e f o r e must i n c l u d e a t l e a s t t h r e e g e n e r a t i o n s : t h e o r i g i n a l a d u l t s , t h e i r o f f s p r i n g , and t h e l a s t wave of j u v e n i l e s t o h a t c h b e f o r e the f i e l d c o n t a i n e r s were r e t u r n e d t o t h e l a b o r a t o r y . There was g r e a t v a r i a b i l i t y i n the t o t a l number o f i n d i v i d u a l s per c o n t a i n e r , as might be expected when the e x p e r i m e n t a l u n i t s are c o n f i n e d , growing p o p u l a t i o n s . T h i s h i g h v a r i a n c e may be due toz (1) t h e s e n s i t i v i t y of p o p u l a t i o n s t o changes i n t h e i r own s t r u c t u r e or q u a l i t y (as w i t h T r i b o l i u m , M e r t z , 1969); (2) t h e t r e a t m e n t s , [ a s w i t h the v a r i a b i l i t i e s i n 71 40, .0 0) 3 U 0) n r — —i , , , , .1 J .« .4 .6 M .7 » .• 1.0 i.l 1J l » 1.4 l » t. ( 1.7 l.« i t 2.0 .1 J a 4 .» • ,T .1 t 1.0 1.1 1.1 1.3 14 IS 1.C 1.7 1.1 l.t 1.0 l e n g t h c l a s s ( m m ) F i g u r e 14. The l e n g t h - f r e q u e n c y d i s t r i b u t i o n s o f the f o u r p o p u l a t i o n s t h a t s u r v i v e d the p r e d a t i o n treatment. I J 3 C 9) <*- 10; J l V « V I 1 * 1.T V I V I 1.0 J • * • * •* • * - • J * 1 * VI V I 1.3 1.4 1.5 V I 1.? 1.8 1.9 2.0 length class (mm) F i g u r e 15- The l e n g t h - f r e q u e n c y d i s t r i b u t i o n s of the e i g h t c o n t r o l p o p u l a t i o n s . 73 s i z e and y i e l d examined by Watt (1955), Usher e t a l . (197 1) , S l o b o d k i n and Richman (1956) and Hoppenheit (1975) ]; or (3) u n c o n t r o l l e d e n v i r o n m e n t a l i n f l u e n c e s or u n d e t e c t e d d i f f e r e n c e s i n e x p l o i t a t i o n r a t e s . I n a l l but c o n t a i n e r #7, f i n a l p o p u l a t i o n s i z e ranged between 86 - 440 i n d i v i d u a l s . . There was s c a r c e l y any r e p r o d u c t i o n i n c o n t a i n e r #7. I t i s p o s s i b l e t h a t u n d e t e c t e d adverse e n v i r o n m e n t a l i n f l u e n c e s or f u n g a l growth a f f e c t e d the f e c u n d i t y and s u r v i v a l o f the s p r i n g t a i l s i n t h i s c o n t a i n e r . The f o l l o w i n g a n a l y s e s a c c o r d i n g l y t a k e t h i s p o s s i b i l i t y i n t o a c c o u n t , by i n c l u d i n g and then e x c l u d i n g #7. I t a k e t h i s approach t o be c o n s e r v a t i v e . I n c l u s i o n of #7 i n t h e a n a l y s e s would s t r e n g t h e n the observed d i f f e r e n c e s and f a v o r my i n t e r p r e t a t i o n . The presence o f the p s e u d o s c o r p i o n s markedly a f f e c t e d t h e p r o b a b i l i t y of s u r v i v a l of the prey p o p u l a t i o n s . Four (out of e i g h t ) of t h e s e p o p u l a t i o n s became e x t i n c t (Table 9 ) . . In t h e s e c a s e s , t h e p s e u d o s c o r p i o n s p r o b a b l y managed t o f i n d most or a l l of the o r i g i n a l s p r i n g t a i l s b e f o r e t h e y c o u l d r e p r o d u c e . In c o n t r a s t , none of the e i g h t c o n t r o l s became e x t i n c t . But t h e o t h e r f o u r e x p e r i m e n t a l p o p u l a t i o n s t h a t s u r v i v e d a l o n g w i t h t h e i r p r e d a t o r s produced an unexpected r e s u l t : t h e s e f o u r were among the l a r g e s t of the s u r v i v i n g c o l l e m b o l a n p o p u l a t i o n s ( F i g u r e s 14 and 15).. Although the t o t a l numbers ( i g n o r i n g s i z e c l a s s e s ) do not d i f f e r s i g n i f i c a n t l y between t h e t r e a t m e n t and c o n t r o l groups (0.1 < p < 0.2) , t h e numbers of s u r v i v i n g immmatures do. The f i n d i n g s of M a r s h a l l and Kevan (1962), S n i d e r (1971), 74 S n i d e r and B u t c h e r (1973) and m y s e l f suggest t h a t F. Candida b e g i n s o v i p o s i t i o n i n the 6th i n s t a r , when i n d i v i d u a l s u s u a l l y vary from 0.7 - 0.8 mm i n l e n g t h and a r e about 16 - 21 days o l d , a l t h o u g h [ M a r s h a l l and Kevan ( 1962), S n i d e r and B u t c h e r (1973), and Hutson (1978) have shown t h a t age a t f i r s t o v i p o s i t i o n may vary w i t h t e m p e r a t u r e , pH and g e n e t i c s ] . Table 9 shows t o t a l s f o r l e n g t h c l a s s e s 0.2 t o 0.7 mm (immatures) and 0.8 t o 2.0 mm ( a d u l t s ) . . The p o p u l a t i o n s s u r v i v i n g p r e d a t i o n have more immatures than t h e c o n t r o l s (p=0.048; or p=0.03 i f #7 i s i n c l u d e d ) . S i n c e the m a j o r i t y of t h e "immatures" i n each c o n t a i n e r must be members of t h e most r e c e n t g e n e r a t i o n , t h i s d i f f e r e n c e , though not l a r g e , i s worth n o t i n g . R e l a t i v e f r e q u e n c i e s of t h e s i z e c l a s s e s are shown i n T a b l e 10. I p r e v i o u s l y r e c o r d e d l e n g t h s of F. C a n d i d a (from the same l a b p o p u l a t i o n s as those used i n t h i s experiment) over 75 days at t h r e e f l u c t u a t i n g t e m p e r a t u r e s with means of 8, 16 and 24° C (Chapter Two).. F i g u r e 5 shows the a g e - l e n g t h r e l a t i o n s h i p . A l t h o u g h f e c u n d i t y and l o n g e v i t y may be o v e r e s t i m a t e d i n such l a b o r a t o r y s t u d i e s , subseguent c o n f i r m a t o r y i n v e s t i g a t i o n s w i t h a n o t h e r p o p u l a t i o n suggest t h a t t h e a g e - l e n g t h r e l a t i o n s h i p f o r t h i s s p e c i e s i s , i n f a c t , r e l a t i v e l y i n f l e x i b l e , so t h a t t h e r e l a t i o n s h i p shown i n F i g u r e 5 s h o u l d a d e q u a t e l y r e p r e s e n t growth r a t e s o f i n d i v i d u a l s under n a t u r a l c o n d i t i o n s . . I n any c a s e , t h e r e can be no doubt t h a t s i z e i s a f u n c t i o n of age and t h a t s i z e c l a s s e s r e p r e s e n t age c l a s s e s , though not e x a c t l y . Some a r t h r o p o d p o p u l a t i o n s have been shown t o a d j u s t mean l e n g t h and weight i n r e l a t i o n t o p o p u l a t i o n d e n s i t y ( r e v i e w e d by P e t e r s and Barbosa, 1977). . Hoppenheit (1976) has shown t h a t mean T a b l e 10. R e l a t i v e f r e q u e n c i e s (S of s i z e s o f t t SSSiiSa i n the t o t a l ) of the d i f f e r e n t 16 p o p u l a t i o n s . C o n t a i n e r No. :0.2 0. 3 0.4 0.5 — 1 0.0 0.7 4.4 14.0 2 0.0 5.0 9.4. 16.8 3 0.0 0. 0 0.0 5.8 4 0.0 0. 0 0.0 1. 1 5 0.0 3.0 10.6 15.2 6 0.0 0.0 2.7 12.6 7 "0.0 0.0 0.0 0.0 8 0.0 3.7 17.3 18. 1 9 0.0 1.9 5. 1 8.4 10 { E x t i net ) 1 1 0.0 1. 4 4.2 12.6 12 0.5 3.0 3.2 10.7 13 ( E x t i n c t ) 14 ( E x t i n c t ) 15 ( E x t i n c t ) 16 0.0 5.8 15.0 16.0 SIZE CLASS ( 0.6 0.7 0.8 0. 9 1.0 10.3 5.9 11.0 14. 0 19. 1 8.4 6.9 8.9 8.4 10. 9 17.4 3.5 9.3 7.0 14.0 3.3 8.8 9.9 20. 9 16.5 12.9 9. 1 9. 1 6.8 5. 3 9.4 14.2 13.7 12.3 13.0 0.0 0.0 0.0 0.0 16. 7 6.2 9.5 10. 7 7.8 7.0 17.0 15.9 15.9 12. 4 11.3 18.6 10.2 7.9 10. 7 13.0 13.9 12.7 8.6 12. 3 14. 3 15.5 17.0 12.1 8.3 2.9 1. 1 1. 2 1. 3 1.4 1.5 ---10.3 5. 1 2. 2 1.5 0.7 7.9 6. 4 4.0 3. 0 1.0 11.6 9. 3 8. 1 5.8 7.0 18.7 16. 5 .1. 3 0. 0 0.0 5. 3 6. 1 6.8 6. 1 3.0 9. 8 7. 3 3. 7 1. 1 0.0 0.0 33. 3 33. 3 16.7 0.0 9.9 2. 5 3. 7 1.2 0.8 6. 7 1.9 2. 2 0. 3 (1. 3 7. 0 6.5 5.6 0.9 0.0 6. a 7.7 3. 6 1.4 0.9 2. 9 1. 5 1.5 0. 0 0.0 1.6 1.7 i . a 1. 1 7. n — — — 0. 7 0.0 0. 0 0. 0 0. 0 1.0 0.5 0. 5 0. 5 0.5 0. 0 0. 0 1.2 0. 0 0. 0 0. 0 0.0 n. n 1. 1 0. 0 0. 8 0. 0 0. 0 0. 0 O.n 0. 2 0.0 0. 0 0. 0 0.0 0. 0 0.0 0. 0 0. 0 n. o 0.8 0.8 0. 0 n. f) 0. n 0. 3 0.3 0. 3 0. 0 o. n 0.5 0.5 0.5 0. 0 o. n 0. 2 0.0 0. 0 0. 2 n. o 0..5 0.5 0.5 o. n 0.0 7 6 weight and l e n g t h of a d u l t copepods may be i n v e r s e l y r e l a t e d t o mean p o p u l a t i o n d e n s i t y , but Green (1964b) found no d i f f e r e n c e between t h e r a t e of development of i s o l a t e d F. C a n d i d a i n d i v i d u a l s and t h o s e i n mass c u l t u r e s . I t h e r e f o r e assume t h a t the s p r i n g t a i l s i n a l l 16 c o n f i n e d p o p u l a t i o n s grew at t h e same r a t e , and t h a t t h e f r e g u e n c y d i s t r i b u t i o n s of t h e i r l e n g t h s do not i n c l u d e any d e n s i t y - i n d u c e d changes i n l e n g t h . In f a c t , t h e method I used s h o u l d have prevented such changes, s i n c e I s t a r t e d each of t h e e x p e r i m e n t a l p o p u l a t i o n s w i t h 10 a d u l t s , and t h e f i n a l d e n s i t i e s of the s u r v i v i n g p o p u l a t i o n s d i d not vary a p p r e c i a b l y at t h e end of the e x p e r i m e n t . One might a l s o argue t h a t t h e s m a l l number of i n d i v i d u a l s i n t h e younger c l a s s e s (0.2 - 0.4 mm i n l e n g t h ) merely i m p l i e s t h a t a l l o f t h e s e p o p u l a t i o n s were e i t h e r d e c l i n i n g or l o s i n g a p r e v i o u s l y dominant age c l a s s as t h e young matured (Dapson, 1971; Tanner, 1978). A l t e r n a t i v e l y , t h i s s m a l l number might be e x p l a i n e d by Takeda's (1973, 1979) d i s c o v e r y t h a t the e f f i c i e n c y of the Macfadyen h i g h g r a d i e n t e x t r a c t o r i s low f o r very s m a l l s p r i n g t a i l s . (Although he c o u l d e s t i m a t e l a r g e r s i z e c l a s s e s of F o l s o m i a o c t o c u l a t a r e a s o n a b l y w e l l w i t h t h i s eguipment, Takeda found t h a t h i s e s t i m a t e s of c l a s s e s < 0.5 mm had t o be c o r r e c t e d by m u l t i p l y i n g by 6.) S i m i l a r f i n d i n g s have been r e p o r t e d by P e t e r s e n (1978) f o r a v a r i e t y of s p r i n g t a i l s p e c i e s . Thus i t might be argued t h a t t h e young F. Candida i n my e xperiment might a l s o have been u n d e r e s t i m a t e d d u r i n g e x t r a c t i o n . I f t h i s were s o , however, a l l of t h e p o p u l a t i o n s s h o u l d have been s i m i l a r l y a f f e c t e d and t h e e f f e c t s of p r e d a t i o n would not have been o b s c u r e d by a c o n f o u n d i n g e f f i c i e n c y e f f e c t . The d i f f e r e n c e s i n 77 the numbers of immatures shown i n T a b l e s 9 and 10 and F i g u r e s 14 and 15 t h e r e f o r e must r e f l e c t a r e a l d i f f e r e n c e between t h e tr e a t m e n t and the c o n t r o l groups, so th e y have not been a d j u s t e d . P r e l i m i n a r y e x p e r i m e n t s by Usher e t a l . (1971) showed t h a t F. Candida p o p u l a t i o n s i n 15.7 cm 2 c u l t u r e v i a l s grew r a p i d l y a t f i r s t and then s t a b i l i z e d a f t e r 10-15 weeks, a t 700 - 1300 i n d i v i d u a l s , p r o b a b l y because o f c o m p e t i t i o n f o r space and f o o d . T h i s f i n d i n g r o u g h l y agrees w i t h my o b s e r v a t i o n s o f F. Candida c u l t u r e s i n 18 cm 2 p o t s . . I s u s p e c t t h a t t h e c o n f i n e d p o p u l a t i o n s i n the l a r g e r , l i t t e r - f i l l e d c o n t a i n e r s used i n my experiment were a t o r near s i m i l a r l i m i t s . There a r e e m p i r i c a l and t h e o r e t i c a l grounds { d i s c u s s e d by Watt, 1968 and Emlen, 1977) which s u g g e s t t h a t p o p u l a t i o n s which a r e near e n v i r o n m e n t a l l y imposed l i m i t s may i n c r e a s e t h e i r p r o d u c t i v i t y i f they are e x p l o i t e d . The magnitude of any such i n c r e a s e i n p r o d u c t i v i t y would depend on t h e r a t e o f e x p l o i t a t i o n and t h e age d i s t r i b u t i o n o f the s u r v i v o r s . I n e f f e c t , t h e degree t o which the a d d i t i o n a l e x p l o i t a t i o n might reduce c o m p e t i t i o n , t o g e t h e r w i t h the number and t y p e o f i n d i v i d u a l s s u r v i v i n g d e n s i t y - i n d e p e n d e n t m o r t a l i t y , would s e t the new p r o d u c t i o n r a t e . In such s i t u a t i o n s , the t y p e o f i n d i v i d u a l which s u r v i v e s t o re p r o d u c e i s as i m p o r t a n t as t h e number. Mertz (1969) has drawn a t t e n t i o n t o t h e correspondence between methods which use b e h a v i o r a l and p h y s i o l o g i c a l t y p e s t o determine p o p u l a t i o n g u a l i t y ( W e l l i n g t o n , 1964) and methods which a n a l y z e and c a t e g o r i z e i n s e c t p o p u l a t i o n s a c c o r d i n g t o age-groups. Both t y p e s o f s t u d y are concerned w i t h p o p u l a t i o n g u a l i t y and w i t h the c o n t r i b u t i o n s of d i f f e r e n t t y p e s of i n d i v i d u a l s t o t h e 7 8 performance of the t o t a l p o p u l a t i o n . M e rtz has shown t h a t b e h a v i o r a l d i f f e r e n c e s among T r i b o l i u m castaneum a d u l t s of d i f f e r e n t ages may be as i m p o r t a n t as p h y s i o l o g i c a l and r e p r o d u c t i v e d i f f e r e n c e s between i n s t a r s . F or example, t h e r e are s t r i k i n g d i f f e r e n c e s i n the r a t e s a t which d i f f e r e n t a d u l t s e a t eggs; b e e t l e s 45 - 135 days o l d are most e f f e c t i v e i n p r e v e n t i n g o u t b r e a k s . Thus i f a p r e d a t o r f e d p r e f e r e n t i a l l y on b e e t l e s i n t h i s age group t h e end r e s u l t might be a h i g h e r ^ r a t h e r t h a n a l o w e r , p o p u l a t i o n d e n s i t y . C e r t a i n l y , p r o d u c t i v i t y would t e m p o r a r i l y i n c r e a s e . My data suggest t h a t t h e l a r g e r s p r i n g t a i l s i n t h e c o n t a i n e r s were e x e r t i n g comparable p r e s s u r e s , d i r e c t or i n d i r e c t , on t h e immature members of the c o n f i n e d p o p u l a t i o n s , a l l of which were near t h e i r e n v i r o n m e n t a l l i m i t . Thus when the p s e u d o s c o r p i o n s at e the l a r g e r i n d i v i d u a l s , more immatures were a b l e t o s u r v i v e , and t h e mean age (as e v i d e n c e d by the mean l e n g t h ) of t h e e x p e r i m e n t a l p o p u l a t i o n s d e c r e a s e d i n r e l a t i o n t o t h e mean age of t h e c o n t r o l s . The a c t u a l dynamics o f e x p l o i t e d p o p u l a t i o n s d i f f e r s g r e a t l y from c a l c u l a t e d v a l u e s t h a t a r e o b t a i n e d by i g n o r i n g age- and s i z e - s t r u c t u r e . Watt (1955) measured the p r o d u c t i v i t y and s t a n d i n g c r o p of p o p u l a t i o n s of the f l o u r b e e t l e T r i b o l i u m confusum a t d i f f e r e n t r a t e s of e x p l o i t a t i o n of d i f f e r e n t s t a d i a , and found t h a t t h e regimen p r o d u c i n g the optimum y i e l d was one i n which o n l y a s m a l l number of a d u l t s were l e f t b e h i n d . Because of such a g e - r e l a t e d f a c t o r s , the maximum s u s t a i n e d y i e l d d i f f e r e d g r e a t l y from t h a t p r e d i c t e d by a l o g i s t i c e q u a t i o n . In f a c t , the age c o m p o s i t i o n t h a t would u l t i m a t e l y produce the maximum number of a d u l t s was one from which a d u l t s were i n i t i a l l y absent. 79 N i c h o l s o n (1955) observed a s i m i l a r response a f t e r removing 99% of the a d u l t b l o w f l i e s from h i s e x p e r i m e n t a l p o p u l a t i o n . And S l o b o d k i n and Eichman ,(1956) a l s o found t h a t age s t r u c t u r e i n f l u e n c e d t h e r e s p o n s e of e x p l o i t e d p o p u l a t i o n s o f Daphnia p u l i c a r i a . In s h o r t , b e f o r e t h e e f f e c t s of f u r t h e r e x p l o i t a t i o n o f p o p u l a t i o n s can be gauged, one must know t h e e f f e c t s of age s t r u c t u r e on p r o d u c t i v i t y , and the p r o b a b l e age d i s t r i b u t i o n a f t e r h a r v e s t (Watt, 1955).. A. .minimus preys upon F. Candida i n the 0.7 - 1.3 mm range when t h e s e i n d i v i d u a l s are a v a i l a b l e (Chapter T h r e e ) . The e f f e c t s o f t h i s s i z e - s e l e c t i v e p r e d a t i o n on the p r o d u c t i v i t y of t h e s u r v i v o r s t h u s w i l l depend on the b e h a v i o r and r e p r o d u c t i v e v a l u e o f t h i s e x p l o i t e d age c l a s s as w e l l as on any d e n s i t y - r e l a t e d changes i n f e c u n d i t y . Green (1964a) found t h a t l a b o r a t o r y p o p u l a t i o n s of F o l s o m i a C a n d i d a a t t a i n e d t h e i r maximum f e c u n d i t y when a v a i l a b l e space per i n d i v i d u a l neared 1.2 cm 2.. Reduced f e c u n d i t y a t h i g h e r d e n s i t i e s was due t o : (1) t h e complete i n h i b i t i o n o f o v i p o s i t i o n by some i n d i v i d u a l s ; (2) a g e n e r a l r e d u c t i o n i n t h e number of eggs l a i d by o t h e r s , and (3) a r e d u c t i o n i n t h e d u r a t i o n of o v i p o s i t i o n . . Green s u g g e s t e d t h a t " j o s t l i n g " and g e n e r a l i n t e r f e r e n c e w i t h o v i p o s i t i o n among crowded a d u l t s were c o n t r i b u t i n g f a c t o r s . A l t h o u g h t h e number o f F. C a n d i d a w i t h o v a r i e s r e d u c e d - i n s i z e was t h e same i n dense and l e s s dense p o p u l a t i o n s , a g r e a t e r p r o p o r t i o n of i n d i v i d u a l s were c a p a b l e of o v i p o s i t i n g i n t h e s p a r s e r p o p u l a t i o n s ( j u d g i n g by t h e appearance of the g e n i t a l a p e r t u r e ) . . C a n n i b a l i s m was e q u a l l y h i g h i n dense and l e s s dense p o p u l a t i o n s i n Green's e x p e r i m e n t s . Average l o s s e s t o c a n n i b a l i s m u s u a l l y approached 2 eggs per a n i m a l per day ( u s u a l l y 80 11 - 18% o f t h e t o t a l number o f e g g s ) . Green was a l s o a b l e t o show t h a t crowding d u r i n g e a r l y l i f e , c o n d i t i o n i n g of the s u b s t r a t e , c o m p e t i t i o n f o r f o o d , and c o m p e t i t i o n f o r o v i p o s i t i o n s i t e s d i d not s i g n i f i c a n t l y a f f e c t f e c u n d i t y . H i s data on f e c u n d i t y v e r s u s d e n s i t y show an " A l l e e " p a t t e r n ( F u j i t a , 1954) i n which f e c u n d i t y i s maximal a t some low t o i n t e r m e d i a t e d e n s i t y . [ I t i s n o t c l e a r t o me why a p a r t h e n o g e n e t i c i n s e c t s h o u l d e x h i b i t t h i s type of p a t t e r n i n s t e a d o f a s i m p l e monotonic d e c r e a s i n g f u n c t i o n of d e n s i t y ( " D r o s o p h i l a type") o r an e f f e c t a t h i g h d e n s i t y o n l y ( " i n t e r m e d i a t e t y p e " ; Watt, 1960). A g g r e g a t i o n has been shown to be i m p o r t a n t i n t h e e c d y s i s and subsequent r e p r o d u c t i o n o f s e x u a l l y r e p r o d u c i n g s p e c i e s of C o l l e m b o l a (Verhoef and N a g e l k e r k e , 1979). Perhaps a g g r e g a t i o n c o u l d s t i m u l a t e o v i p o s i t i o n i n p a r t h e n o g e n e t i c s p e c i e s as w e l l . ] The p o s s i b i l i t y of an A l l e e e f f e c t on f e c u n d i t y o f f e r s an a l t e r n a t i v e e x p l a n a t i o n o f the e x t i n c t i o n s , as w e l l as t h e r e l a t i v e l y l a r g e p o p u l a t i o n s , t h a t o c c u r r e d i n my e x p e r i m e n t a l c o n t a i n e r s . I f p r e d a t i o n by A. minimus on the o r i g i n a l £• - C a n d i d a a d u l t s i n the s e c o n t a i n e r s h e l d the prey numbers below 0.5 i n d i v i d u a l s per cm 2 ( c f . Green's data) d u r i n g t h e i n i t i a l s t a g e s of p o p u l a t i o n growth, f e c u n d i t y would drop below t h e r e c o v e r y l e v e l , and such p o p u l a t i o n s would become e x t i n c t . On t h e o t h e r hand, s l i g h t l y h i g h e r d e n s i t i e s ( e g u i v a l e n t t o 0.5 - 2 i n d i v i d u a l s per cm 2) would a l l o w much h i g h e r f e c u n d i t y i n t h e s u r v i v i n g t r e a t e d p o p u l a t i o n s than t h e g r e a t e r crowding i n the unchecked c o n t r o l p o p u l a t i o n s would p e r m i t . I f such an e f f e c t d i d o c c u r i n the e x p e r i m e n t a l p o p u l a t i o n s , the mean l e n g t h o f 81 t h e i r i n d i v i d u a l s would be reduced by t h e second o r t h i r d g e n e r a t i o n because of the l a r g e r number o f j u v e n i l e s t h o s e p o p u l a t i o n s would t h e n c o n t a i n . (In f a c t , as l o n g as t h e r e were fewer a d u l t s i n the e x p e r i m e n t a l c o n t a i n e r s t h a n i n the c o n t r o l s d u r i n g t h e f i r s t two g e n e r a t i o n s , t h i s r e s u l t c o u l d s t i l l be o b t a i n e d , even i f t h e numbers of a d u l t s were n e a r l y e g u a l by t h e end of the t h r e e g e n e r a t i o n s . ) S i n c e t h i s s c e n a r i o c o u l d have l e d t o our r e s u l t s , i t s u n d e r l y i n g h y p o t h e s i s s h o u l d not be r e j e c t e d u n t i l i t can be t e s t e d f u r t h e r . The mean l e n g t h o f t h e s p r i n g t a i l s i n the f o u r p o p u l a t i o n s t h a t s u r v i v e d p r e d a t i o n was o n l y 0.784 mm (n=1232, SD=0. 300), whereas the i n d i v i d u a l s i n t h e e i g h t c o n t r o l p o p u l a t i o n s had a mean l e n g t h of 0.839 mm (n=1334, SD=.279; see a l s o T a b l e 1 ) . The d i f f e r e n c e i s h i g h l y s i g n i f i c a n t (p < 0.001) whether o r not c o n t a i n e r #7 i s i n c l u d e d ( i f e x c l u d e d , t h e mean l e n g t h o f t h e c o n t r o l s i s reduced t o 0.837 because #7 c o n s i s t e d of a d u l t s o n l y ) . Usher e t a l . . (1971) performed a s e r i e s of remo v a l e x p e r i m e n t s t o t e s t t h e hypotheses t h a t p r o d u c t i v i t y of F. Candida p o p u l a t i o n s would i n c r e a s e w i t h i n c r e a s i n g e x p l o i t a t i o n , t h a t s e l e c t i v e e x p l o i t a t i o n would r e s u l t i n h i g h e r p r o d u c t i v i t y t h a n n o n - s e l e c t i v e e x p l o i t a t i o n , and t h a t t h e a v a i l a b i l i t y of f o o d would change t h e r e l a t i o n s h i p of p r o d u c t i v i t y t o e x p l o i t a t i o n . They found t h a t , i n g e n e r a l , e x p l o i t a t i o n i n c r e a s e d p r o d u c t i o n because r e p r o d u c t i o n i n c r e a s e d , a l t h o u g h d i f f e r e n c e s among s t a n d i n g c r o p s a t d i f f e r e n t r a t e s o f e x p l o i t a t i o n were not s i g n i f i c a n t . I n c r e a s i n g the p r o p o r t i o n of a d u l t s removed from one- t o t w o - t h i r d s e v e r y two weeks i n c r e a s e d b o th t h e n u m e r i c a l and biomass p r o d u c t i o n by 150%.. ( I f t h e same 82 i n c r e a s e i n e x p l o i t a t i o n r a t e was a p p l i e d n o n - s e l e c t i v e l y t o t h e t o t a l p o p u l a t i o n , n u m e r i c a l p r o d u c t i o n i n c r e a s e d by 50% and biomass p r o d u c t i o n i n c r e a s e d o n l y 10.5%.) R e l a t i v e l y h i g h r a t e s of e x p l o i t a t i o n a l s o r e s u l t e d i n s h o r t e r mean body l e n g t h , because t h e c o m p e t i t i v e b a r r i e r s t o r e p r o d u c t i o n were r e l a x e d when more o f t h e o l d e r i n d i v i d u a l s were removed. As noted e a r l i e r , t h i s l a t t e r response might e x p l a i n the r e l a t i v e l y h i g h numbers o f a n i m a l s and the reduced mean l e n g t h s r e c o r d e d i n my e x p e r i m e n t a l p o p u l a t i o n s . . S e l e c t i v e e x p l o i t a t i o n of the a d u l t s by t h e p s e u d o s c o r p i o n s would be f o l l o w e d by i n c r e a s e d f e c u n d i t y (or egg and j u v e n i l e s u r v i v a l ) among the r e m a i n i n g s p r i n g t a i l s . A l t h o u g h such p o p u l a t i o n s might not change much n u m e r i c a l l y , a t t h e end of 46 days t h e y would have t h e l a r g e number of j u v e n i l e s and the s h o r t mean l e n g t h s t h a t were d e s c r i b e d above.. 83 SUMMARY In C h a p t e r One, I d i s c u s s e d t h e d i s t r i b u t i o n and abundance of m i c r o a r t h r o p o d s , m a i n l y C o l l e m b o l a , i n a s i t e i n t h e UBC Research F o r e s t . I s e t out t o measure th e e f f e c t s of p r e d a t i o n on s p r i n g t a i l p o p u l a t i o n s . I n o r d e r t o do t h i s I needed a t e c h n i g u e f o r d e t e r m i n i n g t h e age o f i n d i v i d u a l s p r i n g t a i l s . T h i s was a c c o m p l i s h e d i n Chapter Two where i t was shown ( f o r two s p e c i e s of s p r i n g t a i l s ) t h a t l e n g t h i n c r e a s e s as a power f u n c t i o n of age. I n C h a p t e r Three, I i n v e s t i g a t e d t h e f u n c t i o n a l r e s p o n s e o f t h e predaceous p s e u d o s c o r p i o n , Apochthonius minimus, t o d e n s i t y of t h e s p r i n g t a i l , F o l s o m i a Candida, as w e l l as t h e e f f e c t s of t e m p e r a t u r e and prey s i z e on h a n d l i n g time and a t t a c k r a t e . Temperature s l i g h t l y a l t e r e d t h e o v e r a l l r i s e i n r e s p o n s e . Both the r i s e and shape of the r e s p o n s e d i f f e r e d f o r t h e two prey s i z e s used. The changes i n number of prey e a t e n over a 48-hour p e r i o d were a l s o examined, and t h e a t t a c k and f e e d i n g b e h a v i o r of ik- minimus were d e s c r i b e d and d i s c u s s e d i n r e l a t i o n to the p r e d a t i o n e x p e r i m e n t s . The p s e u d o s c o r p i o n p r e f e r r e d young a d u l t F..Candida, 0.8 - 1.2 mm i n l e n g t h , when o f f e r e d prey i n the range, 0.2 - 1.5 mm.. The experiment d e s c r i b e d i n Chapter Four u t i l i z e d the p r e f e r e n c e t h e p s e u d o s c o r p i o n , A. minimus, d i s p l a y s f o r c e r t a i n s i z e s o f t h e s p r i n g t a i l , F. Candida, i n o r d e r t o a s s e s s t h e p o p u l a t i o n conseguences o f t h i s s e l e c t i v e p r e d a t i o n . Although 84 p r e d a t i o n drove h a l f of t h e t r e a t e d c o l l e m b o l a n p o p u l a t i o n s t o e x t i n c t i o n , • t h e p o p u l a t i o n s which s u r v i v e d were n o t reduced i n s i z e and were i n f a c t l a r g e r t h a n most o f the c o n t r o l p o p u l a t i o n s due t o s i g n i f i c a n t l y l a r g e r numbers of immatures.. During t h e f i r s t two to t h r e e weeks of t h e e x p e r i m e n t , the p r e d a t o r s a p p a r e n t l y f e d mainly on the o r i g i n a l a d u l t s and the l a r g e r i n d i v i d u a l s of t h e second g e n e r a t i o n , t h u s i n c r e a s i n g a v a i l a b l e space and i m p r o v i n g t h e prey's chances f o r s u c c e s s f u l r e p r o d u c t i o n . The r e s u l t i n g demographic s h i f t a c c o u n t s f o r t h e s i g n i f i c a n t d e c r e a s e i n mean l e n g t h t h a t o c c u r r e d i n the e x p e r i m e n t a l p o p u l a t i o n s w i t h o u t any accompanying s i g n i f i c a n t change i n t h e i r t o t a l numbers.. Some e f f e c t s of d e n s i t y , f o o d , and a g e - s t r u c t u r e on the t o t a l f e c u n d i t y of F. C a n d i d a , a c t i n g i n c o n c e r t w i t h t h e e f f e c t s of s i z e - s e l e c t i v e p r e d a t i o n , may l e a d t o a v a r i e t y of p o p u l a t i o n conseguences. I n some c i r c u m s t a n c e s , p r e d a t i o n may cause i n c r e a s e d p r o d u c t i o n w i t h d e c r e a s e d mean s i z e , and no d r a s t i c change i n s t a n d i n g c r o p . In d i f f e r e n t c i r c u m s t a n c e s , a l o c a l p o p u l a t i o n may become e x t i n c t . These r e s u l t s s h o u l d f u r t h e r our u n d e r s t a n d i n g of t h e s p o r a d i c r e c o r d o f e s t a b l i s h m e n t and growth d i s p l a y e d by s p r i n g t a i l p o p u l a t i o n s i n the s m a l l , moist l i t t e r patches where t h e y t e n d t o ag g r e g a t e . 85 LITERATURE CITED A d d i c o t t , J . F. 1974. 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B i o s t a t i s t i c a l a n a l y s i s . . P r e n t i c e - H a l l , I n c . , Englewood C l i f f s , N. J . . 102 APPENDIX A C a l i b r a t i o n of t h e E x t r a c t o r The Macfadyen h i g h - g r a d i e n t e x t r a c t o r ( F i g u r e 4) used i n the c o l l e c t i o n of m i c r o a r t h r o p o d s i n t h i s s t u d y i s n e a r l y i d e n t i c a l to e x t r a c t o r s t h a t have been used i n a l a r g e number of s i m i l a r s t u d i e s s i n c e the mid 1960's. The e x t r a c t o r was d e s c r i b e d by Macfadyen (196 1 ) . . H u m i d i t y and t e m p e r a t u r e c h a r a c t e r i s t i c s of s i m i l a r e x t r a c t o r s were d e t a i l e d by Macfadyen (1962) and B l o c k (1966). In a d d i t i o n . B l o c k (1 966) monitored t h e emergence p a t t e r n s of m i t e s and C o l l e m b o l a . He e s t i m a t e d t h e e x t r a c t i o n e f f i c i e n c y f o r s o i l m i tes as a group a t 76%. . E x t r a c t i o n e f f i c i e n c i e s f o r a number of C o l l e m b o l a s p e c i e s were e s t i m a t e d by P e t e r s e n (1978) and by Takeda (1979). To c a l i b r a t e t h e e x t r a c t o r t h a t I used, I r a n one e x t r a c t i o n as a f a c t o r i a l experiment with a randomized complete b l o c k d e s i g n . . The f a c t o r s were s p e c i e s o f C o l l e m b o l a ( H y p o g a s t r u r a §£Si|t.a ( N i c o l e t ) 1841; O n y c h i u r u s f i m e t a r i u s (?) (Linne) , 1958; and F o l s o m i a C a n d i d a W i l l e m , 1902) and t y p e of e x t r a c t i o n f l u i d ( s a t u r a t e d p i c r i c a c i d o r 10% methylene b l u e s o l u t i o n ) . B l o c k s were t h e r i g h t , l e f t and c e n t e r rows i n the e x t r a c t o r . S i x i n d i v i d u a l s of each of t h e s p r i n g t a i l s p e c i e s ( a l l from l a b p o p u l a t i o n s ) were used i n each t r e a t m e n t . They were added t o moistened c o r e s ( t h a t had p r e v i o u s l y been d r i e d a t 70 C) and a l l o w e d two h o u r s t o a d j u s t . A f t e r a 6-day e x t r a c t i o n p e r i o d (with t e m p e r a t u r e i n c r e a s i n g 5 t o 10 C per day) t h e e x t r a c t e d 103 i n s e c t s were co u n t e d . A n a l y s i s of t h e percentage r e t r i e v e d showed t h a t p o s i t i o n i n t h e e x t r a c t o r , e x t r a c t i o n f l u i d t y p e and s p e c i e s - f l u i d i n t e r a c t i o n d i d not have s i g n i f i c a n t e f f e c t s . . S p e c i e s was t h e o n l y h i g h l y s i g n i f i c a n t (p<.0001) f a c t o r and a c o n s i s t e n t l y lower e f f i c i e n c y f o r t h e c o l o r e d , s i g h t e d H..armata than f o r t h e two unpigmented, b l i n d s p e c i e s (p<.00 1) was i n d i c a t e d . E s t i m a t e s of r e t r i e v a l e f f i c i e n c y , w i t h s t a n d a r d o e r r o r s , were as f o l l o w s : H. armata 84.3% ± 2.7% F. C a n d i d a 96.3% + 1.5% 0. f i m e t a r i u s 95.4% + 1.4% As d i s c u s s e d i n C h apter F o u r , t h e s e e s t i m a t e s are h i g h e r t h a n t h o s e of Takeda (1979). The d i f f e r e n c e i s p r o b a b l y due t o the methods of h a n d l i n g and p r e p a r i n g t h e c o r e s , t o the t y p e s of c o m p a r i s o n s made and t o t h e age of the i n s e c t s i n v o l v e d . . I i n c l u d e d o n l y a d u l t s i n my t e s t , whereas Takeda (1973, 1979) found t h a t e x t r a c t i o n e f f i c i e n c y of a d u l t s i s o f t e n much h i g h e r t han t h a t of younger s p r i n g t a i l s . Other f a c t o r s i n measuring e f f i c i e n c y are c o u n t i n g a c c u r a c y ( e s t i m a t e d e m p i r i c a l l y t o be about 95%) and l o s s e s due t o c o m p r e s s i o n d u r i n g c o r i n g . In l o o s e l y - p a c k e d f o r e s t s o i l and l i t t e r , however, compression i s not as g r e a t a problem as, f o r example, i n some p r a i r i e s o i l s . I s u s p e c t t h a t c o r i n g l o s s e s ranged from 5 - 20%, but I have no way of making an e x a c t e s t i m a t e . APPENDIX B Abundance and d i s t r i b u t i o n o f s o i l m icroarthropods a t the UBC Research F o r e s t s i t e , 1979. P a r t I. P o p u l a t i o n d e n s i t i e s . 20. 000 IS. 000 01 +1 £ 1 0 . O O 0 + 111 a cc UJ r 9000 15 May 5 June 26 j u n e 17 J u l y Total Collembola Figure Bl 8 A u g u s t 8 S e p t e m b e r JOOO Figure B2 O ON 4 0 0 Ul cn +1 r tc Ul a cc Ul ca E 300 100 " 1 . 7 t ' 1 . 7 •113. 3 15 May 5 June 2 6 June 17 J u l y 8 A u g u s t 8 September Apochthonius minimus, adults Figure B3 o Hi in + 1 Ct UJ a. cc UJ 300 200 • 100 J> ±1:11 *5b. 2 15 May 5 Ju n e 26 J u n e 17 J u l y 8 A u g u s t 8 September Apochthonius minimus, nymphs Figure Bk o oo 2h June 17 J u l y 8 A u g u s t 8 September Isotomurus palustris. Isotoma trispinata, I. oliyacea (?), I. v i r i d i s (Family Isotomidae) Figure B5 O 15 May 5 June 26 June 17 J u l y 8 A u g u s t 8 S e p t e m b e r Family Hypogastruridae. Includes Hypogastrura pseudarmata, H. vulgaris, H. virgo, Xenylla grisea and X- sp. Figure B 6 1 * 3 3 750 • c a + i r UJ a. ct LU ca E 250 + 1 5 M a y 5 June 26 June 17 J u l y 8 A u g u s t 8 September Onychiurus flavescens. 0. armatus, Lophognathella choreutes (rare) (Family Onychiuridae, Subfamily Onychiurinae Figure B7 8000 Tullbergia sp. (Family Onychiuridae, Subfamily Tullberg iinae) Figure B8 300 Entomobrya quadralineata. E. multifasciata, E. comparata, E. intermedia and E. n i v a l i s TFamily Entomobryidae) Figure B9 1500 LU 01 +1 cc Ul EL CC 111 •2 1000 + soo • 156 ± 3 5 5 • 9 7 3 11 30 | : « 3 - 3 + 168 M 7 9 15 May 5 June 26 J u n e 17 J u l y B A u g u s t 8 September Lepidocyrtus cinereus, L. lignorum and L. sp. CFamily Entomobryidae) Figure BIO 130 LU 11 +1 cc LU a De ul cc £ 5 2 100 90 + 15 May SB.?. 3 • 41 7 •65. 3 • 4 1 . 7 June 26 June 17 J u l y 8 A u g u s t 8. September Tomocerus celsus, T. sp. (Family Entomobryidae, Subfamily Tomocerinae) Figure B l l 0\ NUMBER PER M 2 t+ SE) 9TT , 5 5 JOO • Ul 01 + 1 01 E CC LU CL CC LU 2 1 0 0 • 15 May 5 June 26 J u n e 17 J u l y 8 A u g u s t 8 S Family Sminthuridae Figure B13 ep tember •U06 3 0 0 0 UJ Ul tl 0 J CC U l a ct ui 03 E 3 z 2 0 0 0 1 0 0 O 15 May 5 June 2& June 17 J u l y 8 A u g u s t 8 September Unidentified mesostigmatid mites Figure Blk Co 130 APPENDIX B Abundance and d i s t r i b u t i o n of s o i l m i croarthropods a t the UBC Research F o r e s t s i t e , 1979. P a r t I I . S p a t i a l d i s t r i b u t i o n . Table B l . D i s t r i b u t i o n o f Folsomia sp. Date Depth s / X ^ a=SSx/ x 15 May 0 . 2 . 5 cm 2 . 5 - 5 . 0 cm 5 . 0 - 7 . 5 cm/ 8.34 30.96 13-34 91.73 340.50 146.61 5 June 0 -2 .5 cm 2 . 5 - 5 . 0 cm 5 . 0 - 7 . 5 cm 3.0 2.31 33-0 25.43 26 June 0 -2 .5 cm 2 . 5 - 5 . 0 cm 5 . 0 - 7 . 5 cm - -17 J u l y 0 -2 .5 cm 2 . 5 - 5 . 0 cm 5.O-7.5 cm 3-0 ' 33-0 8 August 0 -2 .5 cm 2 . 5 - 5 . 0 cm 5 . 0 - 7 . 5 cm 1 .0 11 .0 8 Sept. 0 -2 .5 cm 2 . 5 - 5 . 0 cm 5 . 0 - 7 . 5 cm 4 .02 4 .88 5 .0^ 4-44.22 53-65 55 .^5 D i s t r i b u t i o n contagious contagious contagious contagious contagious contagious random contagious contagious contagious 122 Table B2. D i s t r i b u t i o n of Apochthonius minimus a d u l t s Date 15 May 5 June 26 June 17 J u l y 8 August 8 Sept. Depth 0 . 2 . 5 cm 2 . 5 - 5 . 0 cm 5 . 0 - 7 . 5 cm 0 - 2 . 5 cm 2 . 5 - 5 . 0 cm 5 . 0 - 7 . 5 cm 0 - 2 . 5 cm 2 . 5 - 5 . 0 cm 5.O-7.5 cm 0 -2 .5 cm 2 . 5 - 5 . 0 cm 5 . 0 - 7 . 5 cm 0 -2 .5 cm 2 . 5 - 5 . 0 cm 5.O-7.5 cm 0 - 2 . 5 cm 2 . 5 - 5 . 0 cm 5 . 0 - 7 . 5 cm s*/ x K~=SSx/ x D i s t r i b u t i o n 1.00 1 .00 1.00 1 .00 1.00 1 .00 2.00 1.55 11 .00 11 .00 11 .00 11 .00 11 .00 11.00 22.00 17.00 random random random random random • random contagious random Table B3- D i s t r i b u t i o n o f Apochthonius minimus nymphs Date Depth sV x ^ 2=SSx/ x D i s t r i b u t i o n 15 May 5 June 26 June 17 J u l y 8 August 8 Sept. 0 . 2 . 5 cm 2 .5 -5 -0 cm 5 . 0 - 7 . 5 cm 0 -2 .5 cm 2 . 5 - 5 . 0 cm 5 . 0 - 7 . 5 cm 0 -2 .5 cm 2 .5 -5 -0 cm 5 . 0 - 7 - 5 cm 0 - 2 . 5 cm 2 . 5 - 5 . 0 cm 5 . 0 - 7 . 5 cm 0 -2 .5 cm 2 . 5 - 5 . 0 cm 5 . 0 - 7 . 5 cm 0 -2 .5 cm 2 . 5 - 5 . 0 cm 5 . 0 - 7 - 5 cm 13.00 1.00 0.91 6.00 1.27 0.91 1.64 143.01 11.00 10 .00 66.00 14.00 10.00 18.00 contagious random random contagious random random random 124 Table B4. D i s t r i b u t i o n of Isotomids other than Folsomia spp. Date Depth 2. , _ S / X 9f2=SSx/ x D i s t r i b u t i o n 15 May 0 . 2 . 5 cm 15.21 167.31 contagious 2 . 5 - 5 . 0 cm 3.60 39.63 contagious 5.O-7.5 cm' 3.52 38.77 contagious 5 June 0 -2 .5 cm 9.24 101.67 contagious 2 . 5 - 5 . 0 cm 22.34 245.76 contagious 5 . 0 - 7 . 5 cm 10.96 120.5^ contagious 26 June 0-2 .5 cm 19.12 210.35 contagious 2 . 5 - 5 . 0 cm 7.93 87.24 contagious 5 . 0 - 7 . 5 cm 5.00 55.00 contagious 17 J u l y 0-2 .5 cm 31.96 351.53 contagious 2 . 5 - 5 . 0 cm 62.41 686.50 contagious 5 . 0 - 7 . 5 cm ^ • 7 3 52.00 contagious 8 August 0 -2 .5 cm 9.44 103.88 contagious 2 . 5 - 5 . 0 cm 3.64 40 .05 contagious 5 . 0 - 7 . 5 cm 5-89 64 .75 contagious 8 Sept. 0 -2 .5 cm 12.31 135-37 contagious 2 . 5 - 5 . 0 cm 8.21 90.35 contagious 5 . 0 - 7 . 5 cm 10 .24 112.60 contagious 125 Table B5. D i s t r i b u t i o n o f Hypogasturids Date Depth s / X ^ 2=SSx/ x D i s t r i b u t i o n 15 May 0 . 2 . 5 cm 8.69 95.58 contagious 2 . 5 - 5 . 0 cm 9 .9^ 109.30 contagious 5 - 0 - 7 . 5 cm 5.42 59.60 contagious 5 June 0-2 .5 cm 3-9^ 43.34 contagious 2 .5 -5 .0 cm 12.91 142 .00 contagious 5 . 0 - 7 . 5 cm 12.67 139.33 contagious 26 June 0-2 .5 cm 3.64 40 .00 contagious 2 . 5 - 5 . 0 cm 1.73 19.00 contagious 5 . 0 - 7 . 5 cm 1.55 17.00 random 17 J u l y 0-2 .5 cm 1 .00 11.00 random 2 . 5 - 5 . 0 cm 7.22 79.^6 contagious 5.O-7.5 cm 3.62 39.80 contagious 8 August 0 -2 .5 cm 0.91 10.00 random 2 . 5 - 5 . 0 cm 1.73 19.00 random 5 . 0 - 7 . 5 cm 2.36 26.00 contagious 8 Sept. 0 -2 .5 cm 3.77 41 .50 contagious 2 . 5 - 5 . 0 cm 6.25 68.74 contagious 5 . 0 - 7 . 5 cm 3.26 35-80 contagious Table B 6 . D i s t r i b u t i o n o f On y c h i u r i d s (other than T u l l b e r g i a sp. Date Depth s / X nC* s s x / 15 May 0 . 2 . 5 cm 2 .5 -5 .0 cm 5 . 0 - 7 . 5 cm 4.00 2.00 11.16 44.00 22.00 122.80 5 June 0-2 .5 cm 2 . 5 - 5 . 0 cm 5.O-7.5 cm 3.00 33.00 26 June 0-2 .5 cm 2 . 5 - 5 . 0 cm 5 . 0 - 7 . 5 cm - -17 J u l y 0 -2 .5 cm 2 . 5 - 5 . 0 cm 5 . 0 - 7 . 5 cm - -8 August 0-2 .5 cm 2 . 5 - 5 . 0 cm 5 . 0 - 7 . 5 cm - -8 Sept. 0 -2 .5 cm 2 . 5 - 5 . 0 cm 5 . 0 - 7 . 5 cm — — D i s t r i b u t i o n contagious contagious contagious contagious 127 Table B 7. D i s t r i b u t i o n of T u l l b e r g i a sp. Date Depth s / X ^*=SSx/ x D i s t r i b u t i o n 15 May 0 . 2 . 5 cm 5-98 62 .72 contagious 2 .5 -5 .0 cm 11.09 122.00 contagious 5 . 0 - 7 - 5 cm 8.23 90.55 contagious 5 June 0 -2 .5 cm 3.03 33.37 contagious 2 . 5 - 5 . 0 cm 4 .94 5^-36 contagious 5.O-7.5 cm 4 .02 44.18 contagious 26 June 0-2 .5 cm 5.14 56.55 contagious 2 . 5 - 5 . 0 cm 13.18 145.00 contagious 5 . 0 - 7 . 5 cm 8.63 94.94 contagious 17 J u l y 0-2 .5 cm 7.91 87 .03 contagious 2 . 5 - 5 . 0 cm 8.91 97-98 contagious 5.O-7.5 cm 10 .21 112.28 contagious 8 August 0 -2 .5 cm - - -2 . 5 - 5 . 0 cm 11 .87 130.54 contagious 5 . 0 - 7 . 5 cm 17.01 187.17 contagious 8 Sept. 0-2 .5 cm 32.93 362.24 contagious 2 . 5 - 5 . 0 cm 14.70 161 .69 contagious 5 . 0 - 7 . 5 cm 14 .69 161 .63 contagious 128 Table B8. D i s t r i b u t i o n o f Entomobryids Date Depth s"/ x SSx/ x D i s t r i b u t i o n 15 May 0 . 2 . 5 cm 2 . 5 - 5 . 0 cm -5 . 0 - 7 . 5 cm/ -5 June 0 -2 .5 cm 2 . 5 - 5 . 0 cm 5 . 0 - 7 . 5 cm 26 June 0-2 .5 cm 1.00 11.00 random 2 .5-5.0 cm - - -5.0-7 .5 cm - - -17 J u l y 0-2 .5 cm 0.91 10.00 random 2 .5-5.0 cm 1.00 11 .00 random 5.O-7.5 cm 1 .00 11.00 random 8 August 0-2 .5 cm 0 .64 7.00 random 2 .5-5.0 cm 1 .27 14.00 random 5.0-7 .5 cm - - -8 Sept. 0-2 .5 cm 1 .00 11.00 random 2 .5-5.0 cm 1 .00 11.00 random 5.0-7 .5 cm 2.00 22.00 contagious 129 Table B9. D i s t r i b u t i o n o f L e p i d o c y r t u s spp. Date Depth s / X -#a=SSx/ x D i s t r i b u t i o n 15 May 0 . 2 . 5 cm 2.01 22.14 contagious 2 . 5 - 5 . 0 cm 1.55 17.00 random 5 . 0 - 7 . 5 cm 1 .00 11 .00 random 5 June 0-2 .5 cm . 4 .06 44.60 contagious 2 . 5 - 5 . 0 cm 0.91 10.00 random 5 . 0 - 7 . 5 cm 0.91 10.00 random 26 June 0-2 .5 cm 2.60 28 .57 contagious 2 . 5 - 5 . 0 cm 1.39 15.26 random 5 . 0 - 7 . 5 cm 2.00 22.00 contagious 17 J u l y 0 -2 .5 cm 1 .70 18.727 random 2 . 5 - 5 . 0 cm 2.82 31.00 contagious 5 . 0 - 7 . 5 cm 3.00 33-00 contagious 8 August 0 - 2 . 5 cm 1 .08 11.86 random 2 . 5 - 5 . 0 cm 2.00 22.00 contagious 5.O-7.5 cm - - -8 Sept. 0-2 .5 cm 2.36 26 .00 contagious 2 . 5 - 5 . 0 cm 3.20 35.80 contagious 5 . 0 - 7 . 5 cm 3.09 34.00 contagious 130 Table BIO. D i s t r i b u t i o n o f Tomocerus spp. Date 15 May 5 June 26 June Depth 0 . 2 . 5 cm 2 . 5 - 5 . 0 cm 5 . 0 - 7 . 5 cm 0-2 .5 cm 1.00 2 . 5 - 5 . 0 cm 5 . 0 - 7 . 5 cm 0-2 .5 cm 1.00 2 . 5 - 5 . 0 cm 2.00 5 . 0 - 7 . 5 cm 17 J u l y 0 0 -2 .5 cm 2 .5 -5 .0 cm 5 . 0 - 7 . 5 cm s / x "X - SSx/ x D i s t r i b u t i o n 8 August 0-2 .5 cm 1.00 2 . 5 - 5 . 0 cm 5 . 0 - 7 . 5 cm 8 Sept. 0-2 .5 cm 0.82 2 . 5 - 5 . 0 cm 5 . 0 - 7 . 5 cm 11.00 11.00 22.00 2.91 31.96 11.00 9.00 random random contagious contagious random random 131 Table B l l . D i s t r i b u t i o n o f Neanura Date 15 May Depth 0 . 2 . 5 cm 2 . 5 - 5 . 0 cm 5 . 0 - 7 . 5 cm sV x ^ 2=SSx/ x D i s t r i b u t i o n 5 June 0 -2 .5 cm 26 J une 17 J u l y 8 Augus t 8 Sept. 2 . 5 - 5 . 0 cm 0.91 io.oo 5 . 0 - 7 . 5 cm 1.00 11.00 0 -2 .5 cm - -2 .5 -5 .0 cm - -5 . 0 - 7 . 5 cm - -0-2 .5 cm 1 .00 11.00 2 . 5 - 5 . 0 cm • - -5.O-7.5 cm - -0 - 2 . 5 cm 1 .00 11 .00 2 . 5 - 5 . 0 cm 8.04 88.41 5.O-7.5 cm 1.55 17.00 0 -2 .5 cm - -2 . 5 - 5 . 0 cm 9.05 99.50 5 . 0 - 7 . 5 cm 4.00 44.00 random random random random contagious random contagious contagious 132 Table B12. D i s t r i b u t i o n of Sminthurids Date 15 May 5 June 26 June 17 J u l y 8 Augus t 8 Sept. Depth 0 . 2 . 5 cm 2 . 5 - 5 . 0 cm 5 . 0 - 7 . 5 cm 0 - 2 . 5 cm 2 . 5 - 5 . 0 cm 5 . 0 - 7 . 5 cm 0 - 2 . 5 cm 2 . 5 - 5 . 0 cm 5 . 0 - 7 . 5 cm 0 -2 .5 cm 2 . 5 - 5 . 0 cm 5 . 0 - 7 - 5 cm 0 -2 .5 cm 2 . 5 - 5 . 0 cm 5 . 0 - 7 . 5 cm 0 -2 .5 cm 2 . 5 - 5 . 0 cm 5 . 0 - 7 - 5 cm s / x 3-57 4.18 2.82 .82 0.91 4 .15 2 >C = SSx/ x D i s t r i b u t i o n 39-29 46 .00 31.00 9.00 10.00 45.66 contagious contagious contagious random random contagious Table B13- D i s t r i b u t i o n of Mesostigmata Date Depth S / X ^ 2=SSx/ x D i s t r i b u t i o n 1 5 May 0.2.5 cm 4 . 4 3 48.77 contagious 2.5-5.0 cm 7 . 2 1 79-33 contagious 5.0-7.5 cm - - -5 June 0-2.5 cm 3 . 3 0 36 . 2 9 contagious 2.5-5.0 cm 3 . 3 1 36.40 contagious 5 . O - 7 . 5 cm 7 . 0 0 77-00 contagious 2 6 June 0-2.5 cm 3 . 7 4 41.12 contagious 2.5-5.0 cm 7 . 5 2 82 . 71 contagious 5.0-7.5 cm 3 . 5 8 39.3^ contagious 17 J u l y 0-2.5 cm 5 . 2 9 58.24 contagious 2.5-5.0 cm 2 . 7 9 3 0 . 7 ^ contagious 5.0-7.5 cm 9 . 1 6 100 . 7 1 contagious 8 August 0-2.5 cm 2.00 22.00 contagious 2.5-5.0 cm 6-33 69.64 contagious 5.0-7.5 cm 4 . 2 7 47.00 contagious 8 Sept. 0-2.5 cm 3.83 4 2 .13 contagious 2.5-5.0 cm 2.01 22.14 contagious 5.0-7.5 cm 1.00 11.00 random Table Bl4. D i s t r i b u t i o n of C h i l o p o d a Date 15 May 5 June 26 June 17 J u l y 8 August 8 Sept. Depth 0 . 2 . 5 cm 2 . 5 - 5 . 0 cm 5 . 0 - 7 . 5 cm' 0-2 .5 cm 2 . 5 - 5 . 0 cm 5.O-7.5 cm 0 -2 .5 cm 2 . 5 - 5 . 0 cm 5 . 0 - 7 . 5 cm 0-2 .5 cm 2 . 5 - 5 . 0 cm 5 . 0 - 7 - 5 cm 0-2 .5 cm 2 . 5 - 5 . 0 cm 5 . 0 - 7 . 5 cm 0-2 .5 cm 2 . 5 - 5 . 0 cm 5 . 0 - 7 . 5 cm sV x ^*=SSx/ x 0.82 1.00 0.91 1.00 1.00 1.00 1 .00 9.00 11.00 10.00 11 .00 11.00 11.00 11.00 D i s t r i b u t i o n random random random random random random random 1 3 5 APPENDIX C S o i l moisture a t the study s i t e d u r i n g 1 9 7 9 . 136 Table C I . S o i l moisture a t three depths from May to September 1979- Water l o s s i s from 2.5 cm x 5 ' 0 cm d i a co r e s . Moisture i s c a l c u l a t e d as 1 0 Q /water l o s s weightN . \dry s o i l weight / 5 June 26 June V a r i a b l e L e v e l Mean SE n Water l o s s 0 - 2.5 cm 8.88g 0.93g 12 2.5 - 5-0 cm 13-89g 0.91g 12 5.0 - 7.5 cm 15.57g 0.84g 12 M o i s t u r e (as 0 - 2.5 cm 78.67% 9.78$ 12 $ o f dry weight) 2.5 - 5.0 cm 70.73% 9.65$ 12 5.0 - 7.5 cm 72.89/2 14.84$ 12 Water l o s s 0 - 2.5 cm 12.56g 1.60g 12 2.5 - 5 .0 cm 15-21g 2.25g 12 5.0 - 7-5 cm 13-66g 1.15s 12 M o i s t u r e (as 0 - 2.5 cm 85.92$ 9.26$ 12 $ of dry weight) 2.5 - 5 .0 cm 52.78$ 9.22$ 12 5.0 - 7.5 cm 35.90f* 3.00$ 12 Water l o s s 0 - 2.5 cm 7-33g 1.03g 12 2.5 - 5-0 cm 10.76g 0.96g 12 5.0 - 7-5 cm 11.20g 1.29g 12 M o i s t u r e (as 0 - 2.5 cm 73.75$ 11.91$ 12 $ o f d r y weight) 2.5 - 5 .0 cm 46.61$ 6.43$ 12 5.0 - 7.5 cm 40.23$ 6.87$ 12 137 Table C l continued 17 J u l y V a r i a b l e L e v e l Mean SE n Water l o s s 0 - 2.5 cm 5-63g 0.8lg 12 2.5 - 5.0 cm 8.19g 1.12g 12 5-0 - 7.5 cm 9-3^g 0.87g 12 M o i s t u r e (as % 0 - 2.5 cm 50.27% 6.44% 12 o f dry weight) 2.5 - 5.0 cm 33-33% 5.42% 12 5.0 - 7-5 cm 38.81% 7.46% 12 8 August Water l o s s 0 - 2.5 cm 1.66g 0.21g 12 2.5 - 5.0 cm 4.52g o.33g 12 5.0 - 7.5 cm 5.27g o.50g 12 M o i s t u r e (as % 0 - 2.5 cm 13-78% 1.32% 12 of d r y weight) 2.5 - 5.0 cm 18.37% 1.84% 12 5.0 - 7.5 cm 20.54% 2.41% 12 8 September Water l o s s 0 - 2.5 cm 13-56g 1.12g 12 2.5 - 5.0 cm 11.19g l-59g 12 5.0 - 7.5 cm 8.69g 1.34g 12 M o i s t u r e (as % 0 - 2.5 cm 153.22% 17.63% 12 o f dry weight) 2.5 - 5.0 cm 49.81% 11.01% 12 5.0 - 7.5 cm 37.30% 6.60% 12 138 Table C2. Mean weights of s o i l samples. A l l samples were 2 . 5 cm x 5-0 cm d i a c o r e s . Dry s o i l weight ( a l l dates) L e v e l Mean SE n 0 - 2.5 cm 13.68g 1.02g 72 2.5 - 5-0 cm 26.90g 1.33g 72 5.0 - 7.5 cm 30.91g l . 5 0 g 72 APPENDIX D R a i n f a l l and d a i l y mean temperatures at the study s i t e d u r i n g 1979. -»» • E E ~ 30h or a . 181-it l • I 35 30 28 20 18 10 8 i s M a y 2 6 J u n e 17 J u l y 6 A u g u s t S S o o t Figure Dl. Rainfall at the study site during the sampling period, May to September, 1979-O 141 F i g u r e D2. D a i l y mean temperature [approximated by ( d a i l y maximum + d a i l y minimum)/2] a t the study s i t e . The b l a c k l i n e i s a polynomial used to r e p r e s e n t the degree-day accumulation t r e n d over the p e r i o d . 1 4 2 APPENDIX E O r t h o g o n a l C o n t r a s t C o e f f i c i e n t s When t r e a t m e n t s are e g u a l l y spaced, s t a n d a r d o r t h o g o n a l c o n t r a s t s c o e f f i c i e n t s l i s t e d i n most b i o m e t r i c s t e x t b o o k s can be used.. However, because of the need f o r r e a l i s t i c p r e d a t o r - p r e y r a t i o s and f o r enough measurements t o a c h i e v e a c c e p t a b l e p r e c i s i o n and b e t t e r a l l o c a t i o n of e f f o r t i n t h e ranges where parameters are c h a n g i n g r a p i d l y , e q u a l l y - s p a c e d d e n s i t y t r e a t m e n t s a r e not o f t e n employed i n most f u n c t i o n a l r e s ponse experiment s. C o e f f i c i e n t s f o r the d e n s i t y t r e a t m e n t s used i n my f u n c t i o n a l response experiment (Chapter Three) are shown below i n T a b l e E1._ Standard c o e f f i c i e n t s were used f o r the e g u a l l y - s p a c e d p e r i o d s . 143 o Source of v a n a t i on MEAN'S i i X2 *3 M. *1 X6 11 i i *2 >U.o COEFFICIENTS': P r e y d e n s i t y - i s - 1 3 - 3 7 CL. 1 Q a a d v a t i c 1059 155 - 9 S i - i 2 2 1 99S C u b i c -505 51 1 531 -6B2 145 The r e s t 64 -135 120 -54 5 D a n s i t u y S i x * L i n e a r - - I B -13 -3 7 27 IB 13 3 -7 -27 Quadratic 1059 1 55 -961-1221 988- 1059 -155 981 1221 -986 Cub i c -505 51 i 531 -682 145 505 -531 682 -145 The r e s t 64 --135 120 -54 5 -64 135 -120 54 -5 T a b l e E l . O r t h o g o n a l c o n t r a s t c o e f f i c i e n t s . 144 APPENDIX F. D i s p e r s a l of F. Candida In C h a p t e r F o u r , I d i s c u s s e d f a c t o r s which may i n f l u e n c e s i z e - s e l e c t i v e p r e d a t i o n by t h e p s e u d o s c o r p i o n A. minimus on F. . C a n d i d a .. I noted t h a t t h e g e n e r a l a c t i v i t y l e v e l of F. C a n d i d a i n d i v i d u a l s d i d not appear t o vary s i g n i f i c a n t l y between age c l a s s e s . The p o s s i b i l i t y e x i s t e d , however, t h a t t h e tendency t o move about v a r i e d w i t h age ( s i z e ) even though g e n e r a l a c t i v i t y d i d n o t . . I d e s i g n e d the f o l l o w i n g e x p e r i m e n t s t o t e s t t h e hypotheses t h a t d i s t a n c e t r a v e l l e d by F. Candida i n d i v i d u a l s i s not a f u n c t i o n of age or the presence of f e e d . METHODS P o p u l a t i o n s of F. C a n d i d a were r a i s e d i n 18 cm 2 c u l t u r e p o t s f o r s e v e r a l months and a l l o w e d to a t t a i n some semblance of a s t a b l e age d i s t r i b u t i o n . Random samples from s e v e r a l p o p u l a t i o n s were combined t o produce the t h r e e p o p u l a t i o n s used i n the f o l l o w i n g e x p e r i m e n t s . The p o p u l a t i o n s were kept t o g e t h e r f o r one week b e f o r e s t a r t i n g t h e e x p e r i m e n t s . I n each e x p e r i m e n t , a p o p u l a t i o n was t r a n s f e r r e d to area 1 of a d i s p e r s a l t r a y s i m i l a r t o t h e one shown i n F i g u r e F1. G l a s s p l a t e s (4 X 7.5 cm) d i v i d e d the t r a y i n t o 5 a r e a s . The a n g l e s of the g l a s s w a l l s h e l p e d t o l i m i t t r a v e l t o one-way movement. The s u b s t r a t e o f the t r a y s was t h e same moistened c h a r c o a l - p l a s t e r m i x t u r e d e s c r i b e d i n Chapter Two. At t h e s t a r t of each r u n , the p o p u l a t i o n was a l l o w e d t o begin d i s p e r s i n g from area 1. A f t e r a s p e c i f i e d p e r i o d , t h e F i g u r e F l . The d i s p e r s a l t r a y used i n the experiments d e s c r i b e d i n Appendix F. (top view) 146 s p r i n g t a i l s were k i l l e d w i t h 95% e t h a n o l and t h e i r l e n g t h s were measured t o t h e n e a r e s t 0.1 mm. RESULTS Experiment 1: Two-hour p e r i o d ; no f o o d . I t can be c l e a r l y seen i n F i g u r e F2 t h a t t h e l a r g e r ( o l d e r ) i n d i v i d u a l s had a tendency t o t r a v e l f a r t h e r (p < .0001). A l l i n d i v i d u a l s i n a r e a 5 are > 0.8 mm i n l e n g t h w h i l e most of t h o s e r e m a i n i n g i n a r e a 1 are < 1.0 mm. Experiment 2: Two-hour p e r i o d ; w i t h f o o d . . The presence o f about 20 g r a i n s of ye a s t i n a r e a 1 seems t o have changed t h e tendency o f t h e o l d e r a n i m a l s t o move (p < .001). The d i s t r i b u t i o n s o f a n i m a l s i n a r e a s 2 t o 5 ( F i g u r e F3) are s i m i l a r , a l t h o u g h o v e r a l l d i f f e r e n c e s are s t r o n g (p < .000 1) due t o the l a r g e number o f very s m a l l i n s e c t s l e f t behind i n a r e a 1. Experiment 3: Twenty-four hour p e r i o d ; no f o o d . A g a i n , the e f f e c t o f l e n g t h on d i s t a n c e t r a v e l e d ( F i g u r e F4) i s h i g h l y s i g n i f i c a n t (p < .0001). I t seems t h a t the extended 147 p e r i o d d i d not change the b a s i c p a t t e r n apparent i n F i g u r e F2.. The e f f e c t i s a c c e n t u a t e d by t h e l a r g e r number of a n i m a l s i n t h e 0.9 t o 1.5 mm c l a s s e s . .1 .2 .3 .4 .5 .6 .7 .8 .8 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9. 2.0 l e n g t h c l a s s (mm) S t a r t i n g p o p u l a t i o n F i g u r e F2. D i s p e r s a l over two h o u r s ; no f o o d i n a r e a 1. .1 .2 .3 .4 .5 .8 .7 .8 .9 1.0 1.1 1.2 1.3 1.4 1.5 1.9 1.7 1.8 1 9 2.0 l e n g t h c l a s s (mm) D i s t r i b u t i o n a t end o f 2 hours .1 .2 .3 .4 .5 .9 .7 .8 .9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 l e n g t h c l a s s (mm) S t a r t i n g p o p u l a t i o n F i g u r e F3. D i s p e r s a l over two hours; w i t h food i n area 1. n - i r~i _•= .2 ' .3 ' .4' .6 .9' r' .a' .9 1.0 1.1 1.2 1» 14 VS 1-8 1.7 1.8 1.9 2.0 l e n g t h c l a s s (mm) D i s t r i b u t i o n at end of 2 hours. 10 mm .1 .2 .3 .4 .5 .6 .7 .8 .9 1.0 1.1 1.2 1.3 1.4 1.5 1.8 1.7 1.8 1.9 2.0 S t a r t i n g p o p u l a t i o n F i g u r e F4. D i s p e r s a l over twenty-four hours j no food. 1 r - n H " T h .1 .2 .3 .4 .5 .6 .7 .8 .9 1.0 1.1 12 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 length c l a s s (mm) D i s t r i b u t i o n a t end of 24 hours. 

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