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Factors influencing the vertical distributions of two intertidal porcelain crab populations Zittin, David 1979

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FACTORS INFLUENCING THE VERTICAL DISTRIBUTIONS OF <J3 TWO INTEST.IDAL PORCELAIN CRAB POPULATIONS BY DAVID ZITTIN B.A.,. C a l i f o r n i a State U n i v e r s i t y , Humboldt, 1971 H.A. , C a l i f o r n i a State U n i v e r s i t y , Humboldt, 1973 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOB THE DEGREE OF DOCTOR OF PHILOSOPHY i n THE FACULTY OF GRADUATE STUDIES (Department of Zoology) Je accept the t h e s i s as conforming to the r e q u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA October, 1979 <§) David Z i t t i a , 1979 In presenting th i s thes i s in pa r t i a l fu l f i lment of the requirements for an advanced degree at the Univers i ty of B r i t i s h Columbia, I agree that the L ibrary shal l make it f ree ly ava i l ab le for reference and study. I fur ther agree that permission for extensive copying of th i s thesis for scho lar ly purposes may be granted by the Head of my Department or by his representat ives. It is understood that copying or pub l i ca t ion of th is thes is for f inanc ia l gain sha l l not be allowed without my writ ten permission. Department of The Univers i ty of B r i t i s h Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 Date • 6 ABSTRACT Overlapping p o p u l a t i o n s of p o r c e l a i n crabs were observed on s e v e r a l beaches i n Barkley Sound, B r i t i s h Columbia. The lower l i m i t of the higher p o p u l a t i o n ( P e t r p l i s t h e s c i n c t i p e s ) and the upper l i m i t of the lower p o p u l a t i o n ( P e t r o l i s t h e s eriomerus) were observed t o be temporally and s p a t i a l l y s t a b l e f o r t h r e e years. What prevented the higher zoned p o p u l a t i o n from i n h a b i t i n g i n t e r t i d a l l e v e l s below the lower l i m i t of i t s p o p u l a t i o n and what f a c t o r s s e t the upper l i m i t of the lower p o p u l a t i o n ? When P. eriomerus were t r a n s p l a n t e d above the upper l i m i t of t h e i r d i s t r i b u t i o n , they had higher m o r a t a l i t y r a t e s than c o n t r o l s which were l o c a t e d w i t h i n t h e i r p o p u l a t i o n band. T h i s s p e c i e s cannot l i v e as l i t t l e as 0.3 m above i t s normal p o p u l a t i o n range. The cause of these m o r t a l i t i e s were not determined. In c o n t r a s t , P. c i n c t i p e s demonstrated low m o r t a l i t y r a t e s at a l l i n t e r t i d a l l e v e l s i n c l u d i n g those which were w e l l below the lower l i m i t of i t s p o p u l a t i o n band. Thus, p h y s i c a l f a c t o r s do not determine the lower d i s t r i b u t i o n a l l i m i t of the higher p o p u l a t i o n . Observations made on i n t r a s p e c i f i c s p a c i n g p a t t e r n s i n a l a b o r a t o r y arena showed t h a t both s p e c i e s tended to maintain even s p a c i n g p a t t e r n s by v a r i o u s types of a g o n i s t i c behavior which were s i m i l a r f o r both s p e c i e s . The lower i n t e r t i d a l s p e c i e s , however, demonstrated a g r e a t e r mean d i s t a n c e t o i i i n e a r e s t n e i g h b o r t h a n d i d the h i g h e r s p e c i e s . I h y p o t h e s i z e d t h a t t h e l o w e r s p e c i e s was a s u p e r i o r c o m p e t i t o r f o r space. I f I f a i l e d t o r e j e c t t h i s h y p o t h e s i s , i t would suggest t h a t P- c i n c t i p e s i s u n a b le t o i n h a b i t t h e low i n t e r t i d a l zone because of e x c l u s i o n by a g o n i s t i c i n t e r a c t i o n s w i t h R- e r i p m e r u s . R e s u l t s of the arena e x p e r i m e n t s d i d not s u p p o r t t h i s h y p o t h e s i s and i n f a c t suggested t h e c o n t r a r y ; R' c i n c t i p e s c o n s i s t e n t l y a c q u i r e d and m a i n t a i n e d a d i s p r o p o r t i o n a t e amount of space over a f a v o r a b l e h a b i t a t i n t h e a r e n a . I n t r a - and i n t e r s p e c i f i c e f f e c t s on v e r t i c a l d i s t r i b u t i o n were t e s t e d f o r i n an experiment which employed l o n g , narrow e n c l o s u r e s ( r u n s ) . By comparing the d i s t r i b u t i o n s of t h e two s p e c i e s i n t h e i r s i n g l e s p e c i e s c o n t r o l e n c l o s u r e s , I found t h a t P. e r i o m e r u s demonstrated a s t r o n g p r e f e r e n c e f o r l o w e r p o r t i o n s o f t h e r u n s . In c o n t r a s t , P. c i n c t i p e s demonstrated no p r e f e r e n c e f o r v e r t i c a l range i n t h e e n c l o s u r e s . When mixed, t h e e x p e r i m e n t a l P. c i n c t i p e s p o p u l a t i o n s h i f t e d s l i g h t l y upwards. However, t h e r e was no c l e a r i n d i c a t i o n t h a t z o n a t i o n was o c c u r r i n g w i t h i n t h e e n c l o s u r e s . R e s u l t s of t h e run e x p e r i m e n t s a l s o showed t h a t P. c i n c t i p e s reduced d e n s i t i e s of t h e e x p e r i m e n t a l P. e r i o m e r u s p o p u l a t i o n near t h e upper l i m i t of i t s v e r t i c a l range. T h i s i s u n u s u a l i n t h a t i t d i f f e r s from t h e p r e v a i l i n g i d e a t h a t upper d i s t r i b u t i o n a l l i m i t s a r e caused by p h y s i c a l f a c t o r s ( C o n n e l l 1972) and not by b i o t i c f a c t o r s . Other z o n a t i o n s t u d i e s have suggested t h a t the proximate cause of upper l i m i t s of an i n t e r t i d a l p o p u l a t i o n are l e t h a l s t r e s s e s from the p h y s i c a l environment (Connell 1961a, 1961b, 1972, Paine 1974). These s t u d i e s were conducted on s e s s i l e or very slow moving i n v e r t e b r a t e s p e c i e s . In c o n t r a s t , my r e s u l t s show that the proximate cause of the v e r t i c a l d i s t r i b u t i o n l i m i t a t i o n f o r the lower p o p u l a t i o n i s a b e h a v i o r a l response of the lower s p e c i e s t o an i n c r e a s i n g l y harsh p h y s i c a l environment with i n c r e a s i n g i n t e r t i d a l h e i g h t . However, the d e n s i t y of t h i s p o p u l a t i o n near i t s upper l i m i t i s probably a l s o lowered by c o m p e t i t i o n with the h i g h e r s p e c i e s . The nature of the f a c t o r ( s ) which determine the lower l i m i t of the P. c i n c t i p e s p o p u l a t i o n remain unresolved. However, i t i s u n l i k e l y t h a t p h y s i c a l s t r e s s e s prevent t h i s s p e c i e s from l i v i n g below the lower l i m i t of i t s p o p u l a t i o n band. I was unable to o b t a i n evidence t h a t c o m p e t i t i o n f o r space with the lower s p e c i e s determined the lower l i m i t of the £« c i n c t i p e s p o p u l a t i o n . TABLE OF CONTENTS LIST OF TABLES . ... v i i i LIST OF FIGURES « i x ACKNOWLEDGEMENTS x i GENERAL INTRODUCTION ... . . . . . . . . i 1 I . FIELD OBSERVATIONS , 7 Methods 7 The F i e l d S i t e s 7 Survey Methods 7 V e r t i c a l D i s t r i b u t i o n s 10 Transect Surveys ................................ 10 Herrin g - r o e and Mil k - b a s k e t Traps 11 P a t i o Blocks 13 I n t e r t i d a l Predators 14 The Organisms and t h e i r D i s t r i b u t i o n s 14 Zoogeography 14 V e r t i c a l D i s t r i b u t i o n s i n Barkley Sound ........... 15 Transect Surveys ................................ 16 Herrin g - r o e and Milk-basket Traps .............. 18 V e r t i c a l D i s t r i b u t i o n of Megalopa and J u v e n i l e s 19 I n t e r t i d a l Predators ........................... 24 D i s c u s s i o n 25 I I . TRANSPLANT EXPERIMENTS , 27 I n t r o d u c t i o n 27 Methods 27 Tra n s p l a n t Cages and Experimental Animals 27 The 1976 Experiments 28 v i The 1977 Experiments ........ 29 Developmental Stages 29 R e s u l t s 30 S u r v i v a l of T r a n s p l a n t e d P. eriomerus .............. 30 Embryonic Development of Tra n s p l a n t e d P. eriomerus 33 S u r v i v a l of T r a n s p l a n t e d P. c i n c t i p e s ............. . 34 Embryonic Development of Tra n s p l a n t e d P. c i n c t i p e s 35 D i s c u s s i o n . 37 I I I . ARENA EXPERIMENTS 39 I n t r o d u c t i o n 39 Methods .... ... 40 The Arena and Seawater System 40 Experimental Animals and Holding Procedure 43 Data C o l l e c t i o n and S t a t i s t i c a l Analyses ............ 44 S i n g l e Species Experiments 46 Mixed Species Experiments 46 B e h a v i o r a l Observations 47 R e s u l t s 48 S i n g l e Species Experiments 48 Some B e h a v i o r a l Observations 48 I n t e r s p e c i f i c D i f f e r e n c e s ...................... 51 Mixed Species Experiments 59 D i s c u s s i o n 68 IV. RUN EXPERIMENTS ............ 70 I n t r o d u c t i o n 70 M a t e r i a l s and. Methods 71 1976 Experiments ................................... 72 v i i Run C o n s t r u c t i o n 72 I n t e r t i d a l P o s i t i o n of the En c l o s u r e s 72 Experimental Animals 73 i Experimental Procedure 73 Counting .. 74 1977 Experiments ................................... 74 Run C o n s t r u c t i o n 74 I n t e r t i d a l P o s i t i o n of the En c l o s u r e s 74 Experimental Procedure 75 Counting 75 S t a t i s t i c a l Analyses ................................ 75 T i d a l Experiments 76 R e s u l t s ...... ... -. - 80 E f f e c t s of Mixing on g. c i n c t i p e s .................... 80 Pre f e r e n c e f o r V e r t i c a l L o c a t i o n by P . . c i n c t i p e s ... 85 E f f e c t s of Mixing on P. eriomerus ................... 86 Pre f e r e n c e f o r V e r t i c a l L o c a t i o n by P. eriomerus .. 91 T i d a l Experiments........ 91 D i s c u s s i o n 95 GENERAL DISCUSSION 97 Densi t y and V e r t i c a l D i s t r i b u t i o n of the P. eriomerus P o p u l a t i o n 97 The Lower L i m i t of the P. c i n c t i p e s P o p u l a t i o n ....... 103 REFERENCES CITED 105 v i i i LIST OF TABLES Table I. R e s u l t s of the t r a n s e c t surveys 17 Table I I . Number of crabs which entered the h e r r i n g - r o e t r a p s . . 18 Table I I I . Developmental stages of embryos c a r r i e d by t r a n s p l a n t e d P. eriomerus. 33 Table IV. Developmental stages of embryos c a r r i e d by t r a n s p l a n t e d P. c i n c t i p e s . . 36 Table V. Nearest neighbor s t a t i s t i c s f o r P. c i n c t i p e s . . . . 49 Table VI. Nearest neighbor s t a t i s t i c s f o r P. eriomerus... 50 Table V I I . Forced and pas s i v e e x i t s from under the block d u r i n g the f i r s t hour of i n t r a s p e c i f i c arena exper-iments.... 66 Table V I I I . Observed k values and t h e i r r a t i o s . . . 67 Table IX. Mean percentages of each s p e c i e s i n t h e i r r e s p e c t i v e t e s t and c o n t r o l runs....................... 85 Table X. Some t i d a l s t a t i s t i c s 94 i x LIST OF FIGURES Fi g u r e 1. Map of southeastern Barkley Sound., 8 F i g u r e 2. S i z e c l a s s d i s t r i b u t i o n s of the 1975 t r a p e n t r i e s . . . . . . . . . . . . . . . 20 F i g u r e 3. Number of crabs l e s s than 2.0 mm found under the p a t i o b l o c k s . . . . . . . . . . . . . . . . . . . . . . 22 F i g u r e 4. S u r v i v a l r a t e s o f . t r a n s p l a n t e d P e t r o l i s t h e s . . . 31 F i g u r e 5. The arena... 41 F i g u r e 6. Distance t o nearest neighbor............. 52 F i g u r e 7. D i s t a n c e s moved by crabs d u r i n g i n t r a s p e c i f i c encounters. 54 F i g u r e 8. E f f e c t s of i n i t i a l d e n s i t y on k...., .....57 Fi g u r e 9. F i g h t r a t e s 60 F i g u r e 10. Mixed s p e c i e s arena experiments............... 62 F i g u r e 11. Large vs. s m a l l crabs i n mixed s p e c i e s encounters. 64 F i g u r e 12. Diagram of one of the t i d a l tanks... 78 F i g u r e 13. V e r t i c a l d i s t r i b u t i o n of P. c i n c t i p e s i n the runs i n 1976 81 F i g u r e 14. V e r t i c a l d i s t r i b u t i o n of P. c i n c t i p e s i n the runs i n 1977... 83 F i g u r e 15. V e r t i c a l d i s t r i b u t i o n of P. eriomerus i n the runs i n 1976.. ............... 87 F i g u r e 16. V e r t i c a l d i s t r i b u t i o n o f P. eriomerus i n the runs i n 1977 89 X F i g u r e 17 - .Crabs i n the upper h a l f of the t i d a l tank.,-.. 92 F i g u r e 18. Summary of the d i s t r i b u t i o n s of c r a b s i n the t r a p s and runs.... 98 ACKNOWLEDGEMENTS I wish t o thank my a d v i s o r , Dr* P.A. Dehnel f o r h i s ad v i c e , support and encouragement duri n g the course of t h i s study. My committee members, Drs. T.H. Carefoot, R.E. Foreman, W.S. Hoar, C.J. Krebs and G.G.E. Scudder o f f e r e d many v a l u a b l e comments. Many people from the town of Bamfie l d , B r i t i s h Columbia, gave a s s i s t a n c e and companionship. John Boom, Wendy C r a i k , Dominique Gascon, C l i f f Haylock, Myriam Haylock and Tom Herman gave help and advic e above and beyond the c a l l of duty. I a l s o wish t o thank Dr. John Mclnerny who provided housing and shop f a c i l i t i e s at the Bamfield Marine S t a t i o n . Geoff Lindsey and Rob Saunders of Canadian Benthic L t d . generously made a v a i l a b l e f l o o r space i n t h e i r delux l a b o r a t o r y complex. Canadian Packers L t d . provided t h e i r s t a t e l y mansion i n Bamfield so t h a t many of us had a place to l i v e during the summer of 1975. T i d a l s t r i p c h a r t r e c o r d i n g s from the Bamfield t i d e gauge s t a t i o n were obtained from the I n s t i t u t e of Ocean S c i e n c e s , Sydney, B r i t i s h Columbia. The U n i v e r s i t y of B r i t i s h Columbia Computer Center s t a f f were most h e l p f u l during the course of the data a n a l y s i s . T h e i r c o n s i d e r a t e s e r v i c e and p r o f e s s i o n a l a d v i c e should stand as a s h i n i n g example f o r any campus o r g a n i z a t i o n which provides s e r v i c e s to students and r e s e a r c h e r s . The s t a f f of the B i o l o g y Data Center were a l s o extremely h e l p f u l . I w i l l always be g r a t e f u l t o B i l l Webb f o r g i v i n g me help with v a r i o u s computer programming problems. Most i m p o r t a n t l y my warmest thanks t o my wife F l o y . Without her help i n the f i e l d and her encouragement, t h i s study would not have been p o s s i b l e . I am a l s o deeply g r a t e f u l f o r the time she spent drawing the f i g u r e s f o r t h i s t h e s i s . T h i s r e s e a r c h was supported by a grant t o Dr. Dehnel from the N a t i o n a l Research C o u n c i l of Canada. 1 GENERAL INTRODUCTION One of the more abrupt e c o l o g i c a l t r a n s i t i o n s on e a r t h i s the i n t e r f a c e between a q u a t i c and t e r r e s t r i a l environments. Within t h e rocky i n t e r t i d a l environment, b e n t h i c p o p u l a t i o n s o f t e n demonstrate c l e a r l y demarcated v e r t i c a l ranges. The term zonation or banding has been used t o d e s c r i b e these conspicuous d i s t r i b u t i o n s of i n v e r t e b r a t e and p l a n t p o p u l a t i o n s . A c o n s i d e r a b l e l i t e r a t u r e d e s c r i b i n g z o n a t i o n p a t t e r n s has accumulated ( f o r reviews see Doty 1957, Southward 1958, Lewis 1964, R i c k e t t s and C a l v i n 1968, Hedgpeth 1976) . Many attempts have been made to determine the causes of zonation p a t t e r n s . Some r e s e a r c h e r s have attempted t o use v a r i o u s t i d a l phenomena, such as c r i t i c a l t i d e l e v e l s , to e x p l a i n zonation but, have l a r g e l y been u n s u c c e s s f u l ( f o r reviews see Doty 1957, C o n n e l l 1972, Hedgpeth 1976, Ca r e f o o t 1977) . Because steep g r a d i e n t s i n p h y s i c a l f a c t o r s occur over the i n t e r t i d a l zone, s e v e r a l i n v e s t i g a t o r s have attempted t o show t h a t t o l e r a n c e s to p h y s i c a l s t r e s s e s demonstrated by i n d i v i d u a l organisms l i m i t v e r t i c a l d i s t r i b u t i o n s of i n t e r t i d a l p o p u l a t i o n s . R e l a t i o n s h i p s between l a b o r a t o r y determined t o l e r a n c e s and zonati o n f r e q u e n t l y demonstrate t h a t h i g h e r i n t e r t i d a l s p e c i e s have g r e a t e r t o l e r a n c e s to p h y s i c a l s t r e s s e s r e l a t i v e t o s p e c i e s which i n h a b i t lower p o s i t i o n s on the shore (Foster 1969,1971a,1971b, Wolcott 1973). Although these s t u d i e s p r o v i d e c o n t r a s t s i n r e l a t i v e a d a p t a t i o n , they cannot 2 i n themselves e x p l a i n what causes i n t e r t i d a l z o nation. One reason f o r t h i s i s t h a t when l a b o r a t o r y determined t o l e r a n c e s are compared with p h y s i c a l s t r e s s e s encountered i n nature, these t o l e r a n c e s o f t e n exceed extreme f i e l d c o n d i t i o n s (Wolcott 1973). A l s o , lower l i m i t s do not always r e p r e s e n t p h y s i o l o g i c a l l y imposed l i m i t a t i o n s . Some i n t e r t i d a l organisms demonstrate i n c r e a s e d m o r t a l i t i e s or slower growth when s u b j e c t e d t o abnormally high p e r i o d s of submergence (Connell 1972). However, many s p e c i e s , when t r a n s p l a n t e d , are abl e t o l i v e , grow and reproduce at i n t e r t i d a l l e v e l s below observed lower l i m i t s o f the p o p u l a t i o n (Barnes and Powell 1953, C o n n e l l 1961b,1972, Paine 1974). Apparently mechanisms other than a b i o t i c f a c t o r s are i n v o l v e d (denHartog 1968). . C o n s t r a i n t s from both the p h y s i c a l and b i o t i c environments seem t o determine s p e c i e s ' d i s t r i b u t i o n s . Hutchinson's (1958) n i c h e concept has provoked s e v e r a l i n v e s t i g a t i o n s and s t i m u l a t e d much thought concerning the qu e s t i o n : why do s p e c i e s occur where they do? An important i d e a presented i n h i s model i s t h a t of the fundamental ( p r e i n t e r a c t i v e ) and r e a l i z e d (post-i n t e r a c t i v e ) n i c h e s . B r i e f l y , the fundamental niche l i e s w i t h i n the ranges of a l l environmental g r a d i e n t s i n which a s p e c i e s can l i v e and reproduce and before i n t e r a c t i o n s with competitors has oc c u r r e d . The r e a l i z e d n i c h e i s a s m a l l e r p o r t i o n of the fundamental niche t o which the s p e c i e s i s c o n s t r a i n e d by competitive i n t e r a c t i o n s (concepts reviewed by Vandermeer 1972, C o n n e l l 1975, Hutchinson 1978).. In a d d i t i o n 3 to c o m p e t i t i o n , p r e d a t i o n can be another important b i o t i c i n t e r a c t i o n which c o n s t r a i n s s p e c i e s t o a p o r t i o n of t h e i r fundamental n i c h e s (Paine 1974, C o n n e l l 1975) . Some of the most c o n v i n c i n g evidence f o r the u s e f u l n e s s of Hutchinson's niche concept as a model e x p l a i n i n g p a t t e r n s i n nature comes from e c o l o g i c a l i n v e s t i g a t i o n s conducted i n the rocky i n t e r t i d a l zone. C o n n e l l (1961a,b, 1970) and Paine (1974) have shown t h a t i n t e r t i d a l s p e c i e s l i v e w i t h i n v e r t i c a l ranges which are c o n s i d e r a b l y s m a l l e r than those they are p h y s i o l o g i c a l l y capable of i n h a b i t i n g . These s t u d i e s and others (reviewed by C o n n e l l ' 1972) have suggested t h a t upper l i m i t s occur at the extremes of a s p e c i e s ' p h y s i o l o g i c a l t o l e r a n c e to an i n c r e a s i n g l y t e r r e s t r i a l environment. Species of barnacles and limpets demonstrated m o r t a l i t i e s at the upper p o r t i o n of t h e i r ranges at times when neap t i d e s c o i n c i d e d with warm weather, s u b j e c t i n g these animals to u n u s u a l l y long p e r i o d s of thermal and d e s i c c a t i o n s t r e s s e s (Lewis 1954, Hodgkin 1960, C o n n e l l 1961a, Frank 1965, Sutherland 1970, F o s t e r 1971a, Wolcott 1973). Lower l i m i t s seem to be determined by b i o t i c i n t e r a c t i o n s e i t h e r w i t h i n or between t r o p h i c l e v e l s (competition and p r e d a t i o n , r e s p e c t i v e l y ) . A f t e r a thorough study of p o p u l a t i o n s of the barnacle Balanus b a l a n p i d e s , Connell (1970) concluded that "...the b r e e d i n g p o p u l a t i o n does not l i v e i n the optimum p h y s i o l o g i c a l environment. I n t e r a c t i o n with other s p e c i e s . . . i n e f f e c t push the a d u l t p o p u l a t i o n against one margin of i t s h a b i t a t , f o r c i n g 4 i t to l i v e i n l e s s f a v o r a b l e p h y s i o l o g i c a l c o n d i t i o n s . 1 1 U n l i k e b a r n a c l e s and mussels, mot i l e s p e c i e s are ab l e to ad j u s t t h e i r v e r t i c a l p o s i t i o n s i n response t o p h y s i o l o g i c a l s t r e s s e s . Upper l i m i t s of some gastropod p o p u l a t i o n s are u l t i m a t e l y s e t by p h y s i c a l f a c t o r s . In some cases, the v e r t i c a l p o s i t i o n s of these l i m i t s f l u c t u a t e s e a s o n a l l y . Some limpet s p e c i e s have been shown to move from high l e v e l s on the shore i n response to s t r e s s e s which occurred during hot, dry summer months, r e t u r n i n g t o these l e v e l s i n the winter when c o o l e r weather and i n c r e a s e d wave a c t i v i t y made these r e g i o n s i n h a b i t a b l e (Lewis 1954, Frank 1965, Breen 1972, Branch 1975, 1976). Branch (1975) suggested t h a t the adapt i v e importance of seasonal m i g r a t i o n i s t h a t i t probably allows these p o p u l a t i o n s to p e r i o d i c a l l y a l t e r t h e i r f o r a g i n g ranges, a l l e v i a t i n g i n t r a s p e c i f i c competition on a temporal b a s i s . P e r i w i n k l e s ( L i t t o r i n a spj>.) apparently maintain v e r t i c a l ranges which present them with e i t h e r f a v o r a b l e food s o u r c e s , f a v o r a b l e p h y s i c a l c o n d i t i o n s or both (Gowanloch and Hayes 1926, Bock and Johnson 1967). These s t u d i e s i n d i c a t e t h a t motile s p e c i e s a c t i v e l y maintain v e r t i c a l p o s i t i o n s on the shore which are f a v o r a b l e f o r t h e i r s u r v i v a l . U n l i k e b a r n a c l e s and mussels, p e r i w i n k l e s a d j u s t t h e i r upper l i m i t s as c o n d i t i o n s warrant. F a c t o r s which i n f l u e n c e the lower l i m i t s of motil e s p e c i e s are not w e l l known. P e r i w i n k l e s and some l i m p e t s migrate to 5 higher p o s i t i o n s when a r t i f i c i a l l y p l a c e d at l e v e l s below which they normally occur (Gowanloch and Hayes 1926, North 1954, C a s t e n h o l t z 1961, Bock and Johnson 1967, C o n n e l l 1972).. P o p u l a t i o n s of two s p e c i e s of p o r c e l a i n c r a b s , P e t r o l i s t h e s c i n c t i p e s (Randall) and P. eriomerus Stimpson were observed to have d i f f e r e n t v e r t i c a l ranges i n the i n t e r t i d a l zone on the west coast of Vancouver I s l a n d , B r i t i s h Columbia. The higher of these two s p e c i e s , P. c i n c t i p e s , demonstrated a lower l i m i t s l i g h t l y below the upper l i m i t of the P. eriomerus p o p u l a t i o n . Both s p e c i e s are h i g h l y motile and, l i k e o t h e r p o r c e l a i n c r a b s , a c q u i r e food by f i l t e r f e e d i n g ( N i c o l 1932, Wicksten 1973, Caine 1975) i n a manner s i m i l a r t o b a r n a c l e s ( i . e . , by a setose f i l t e r i n g b a s k e t ) . The purpose of t h i s i n v e s t i g a t i o n was to determine what r o l e s i n t e r s p e c i f i c a g o n i s t i c i n t e r a c t i o n s and h a b i t a t preference had on s e t t i n g the lower l i m i t of the P. c i n c t i p e s - p o p u l a t i o n and the upper l i m i t of the P. eriomerus p o p u l a t i o n . This t h e s i s i s composed of f o u r p a r t s . The f i r s t p a r t reviews the z o o g e o g r a p h i c a l l i t e r a t u r e f o r these two s p e c i e s and d e s c r i b e s t h e i r v e r t i c a l d i s t r i b u t i o n s i n Barkley Sound. The second s e c t i o n p r e s e n t s r e s u l t s of t r a n s p l a n t experiments conducted i n the i n t e r t i d a l zone. I conducted these experiments to determine whether P. eriomerus- can l i v e h i g h e r than i t s observed upper l i m i t and whether P* c i n c t i j o e s can s u r v i v e lower than i t s observed lower l i m i t . The t h i r d s e c t i o n i s concerned with l a b o r a t o r y arena experiments which I 6 conducted t o determine whether b e h a v i o r a l d i f f e r e n c e s e x i s t e d between t h e s e two s p e c i e s . S p e c i f i c a l l y , I wished t o know whether t h e r e were any i n t e r s p e c i f i c d i f f e r e n c e s i n s p a t i a l r e q u i r e m e n t s and whether i n t e r s p e c i f i c a g o n i s t i c i n t e r a c t i o n s , i f p r e s e n t , would l e a d t o the e x c l u s i o n o f one s p e c i e s from a p r e f e r r e d h a b i t a t . The f o u r t h s e c t i o n p r e s e n t s r e s u l t s from f i e l d e n c l o s u r e e x p e r i m e n t s which I conducted t o d e t e r m i n e whether t h e upper l i m i t of P. e r i o m e r u s or t h e . l o w e r l i m i t of P« c i n c t i p e s were i n f l u e n c e d by i t s r e s p e c t i v e c o n g e n i t o r and what r o l e , i f any, p r e f e r e n c e f o r v e r t i c a l l o c a t i o n by e i t h e r s p e c i e s had on t h e s e l i m i t s . 7 I . FIELD OBSERVATIONS Methods The F i e l d S i t e s A l l f i e l d experiments were conducted at the Diana I s l a n d s i t e ( F i g . 1 ) . This s i t e was a g e n t l y s l o p i n g beach which had a boulder f i e l d extending down t o about datum ( 0 . 0 m). The Diana I s l a n d s i t e was chosen because i t had dense p o p u l a t i o n s of both s p e c i e s , i t was p r o t e c t e d from heavy wave a c t i v i t y and was a c c e s s i b l e throughout most of the year. O b s e r v a t i o n s of n a t u r a l p o p u l a t i o n s were made at f i v e s i t e s : Diana I s l a n d i n Dodger Channel, Grappler I n l e t , Haines I s l a n d , Ross I s l e t s and T a y l o r I s l e t ( F i g . 1 ) . The f i r s t f o u r s i t e s had i n t e r t i d a l p o p u l a t i o n s of both s p e c i e s . Only s u b t i d a l o b s e r v a t i o n s were made at the T a y l o r I s l e t s i t e . The Haines I s l a n d and Ross I s l e t s s i t e s had i n t e r t i d a l boulder beaches which were continuous to a depth of about 5 m below datum. Haines I s l a n d and T a y l o r I s l e t r e c e i v e d c o n s i d e r a b l e pounding from waves during storms, while the other s i t e s were w e l l p r o t e c t e d . Survey Methods V e r t i c a l h e i g h t s were determined with a surveyor's l e v e l and a rod t o the nearest 0 . 0 1 f t and w i l l be expressed to the nearest 0 . 1 m. Datum i s that adopted by the Canadian 3 Figure 1. Map of southeastern Barkley Sound. A, the Diana I s l a n d s i t e ; B, the Grappler I n l e t s i t e ; C, the f l o a t s h e d ; D, boulder beach near Cape Beale. 9 10 Hydrographic S e r v i c e : the plane of the lowest normal tides,. V e r t i c a l p o s i t i o n s were measured r e l a t i v e t o a bench mark cemented i n t o bedrock. The bench mark was c a l i b r a t e d a g a i n s t a s t a f f gauge at Bamfield, B r i t i s h Columbia ( F i g . 1). V e r t i c a l D i s t r i b u t i o n s V e r t i c a l d i s t r i b u t i o n s of n a t u r a l p o p u l a t i o n s of P e t r o l i s t h e s were determined by t h r e e methods. These methods were: t r a n s e c t surveys, two types of t r a p s ( h e r r i n g - r o e and milk-basket traps) and cement p a t i o b l o c k s . Transect Surveys F i v e to e i g h t v e r t i c a l t r a n s e c t s were e s t a b l i s h e d at the Diana I s l a n d s i t e during low t i d e s (dates i n Table I) . T r a n s e c t s were at l e a s t two meters apart and were s e l e c t e d so t h a t boulders were contiguous over the length of the t r a n s e c t l i n e , i . e . , sand b a r r i e r s d i d not l i m i t d i s t r i b u t i o n s . Boulders along the t r a n s e c t were turne d over i n search of the lowest P. c i n c t i p e s and the highest P. eriomerus. The v e r t i c a l p o s i t i o n s of these i n d i v i d u a l s below bench mark were measured. On 12 September 1977 the p o s i t i o n s of these l i m i t s were marked during a high t i d e of a neap t i d e s e r i e s with the a i d of SCUBA. This was done using the same methods as the t r a n s e c t surveys which are d e s c r i b e d above except t h a t cement markers, which were pai n t e d white, were p l a c e d at the upper 11 l i m i t of P. eriomerus and markers which were p a i n t e d red were placed a t the lower l i m i t of P. c i n c t i p e s . The v e r t i c a l p o s i t i o n s of these markers were determined d u r i n g the lower low water of the next s p r i n g t i d e s e r i e s . H e r r i n g - r o e and Milk-basket Trap_s-In order to determine the v e r t i c a l p o s i t i o n s of j u v e n i l e s (<5.0 mm maximum carapace width), p e r f o r a t e d h e r r i n g - r o e baskets (Columbia P l a s t i c s L t d . , Vancouver, B.C.) were used. These baskets were set out at f o u r l e v e l s i n May 1975 with an i n i t i a l i n t e n t of t r a p p i n g megalopa (the post l a r v a l s t a g e ) . In a d d i t i o n t o e n t r i e s by smal l c r a b s , I found crabs i n the baskets with carapace widths of up to 14 mm. I l a t e r determined i n the l a b o r a t o r y that e n t r i e s could e a s i l y be made by crabs of <13 mm. Crabs l a r g e r than t h i s s i z e c o u l d not ent e r these t r a p s . Size c l a s s f r e q u e n c i e s were compared to determine whether d i f f e r e n c e s i n the abundance of s m a l l e r c r a b s , r e l a t i v e to a l l other s i z e c l a s s e s , occurred over the f o u r t r a p l e v e l s . Crabs equal to or g r e a t e r than 3.0 mm max-imum carapace width were measured with a m i l l i m e t e r r u l e . Those l e s s than 3.0 mm were measured with an o c u l a r micrometer mounted i n a d i s s e c t i n g microscope t o the nearest 0.04 mm. The s i d e s of the baskets f l a r e d outward towards t h e i r open ends. The i n s i d e bottom dimensions were 41 x 28 cm, the open end dimensions were 44 x 31 cm and the depth was 9.5 cm. 12 Baskets were f i l l e d with rocks c o l l e c t e d from high i n the i n t e r t i d a l zone at the Diana I s l a n d s i t e . Baskets were enclosed by l a s h i n g p l a s t i c screen t o t h e i r open ends. They were p l a c e d among boulders at the Diana I s l a n d s i t e i n May 1975 at f o u r d i f f e r e n t v e r t i c a l l e v e l s . V e r t i c a l h e ights were measured from the bottom of each basket. These h e i g h t s were s e l e c t e d on the b a s i s of adjacent a d u l t d i s t r i b u t i o n s : +0.3 m (no P. c i n c t i p e s observed a t t h i s l e v e l ) , 0. 6 m above datum (both s p e c i e s p r e s e n t ) , 0.9 m above datum (the upper l i m i t of P. eriomerus) and 1.2 m above datum (P. c i n c t i p e s present o n l y ) . Three r e p l i c a t e s , approximately one meter apart, were placed a t each of the f o u r l e v e l s . Baskets were r e t r i e v e d i n October 1975 by q u i c k l y p l a c i n g each one i n t o a separate p l a s t i c garbage bag. In the l a b o r a t o r y , c r a b s were removed from the bags and preserved f o r l a t e r counting and i d e n t i f i c a t i o n . On 4 May 1977 t r a p s were again placed at the Diana I s l a n d s i t e , u s ing p l a s t i c milk-baskets i n s t e a d of h e r r i n g - r o e baskets. These baskets had openings which allowed e n t r y of a l l s i z e c l a s s e s . The milk-basket t r a p s had equal l e n g t h -width dimensions of 33 cm and were 24 cm high. The s i d e s and the bottom of the baskets were'perforated with s e v e r a l diamond-shaped h o l e s . Holes on the bottom had dimensions of 24 mm along both axes, those on the s i d e s had a x i a l dimensions of 54 x 31 mm. I have not observed crabs a t the Diana I s l a n d s i t e with carapace widths g r e a t e r than 20 mm, making i t 13 u n l i k e l y that hole s i z e l i m i t e d e n t r i e s by crabs of any s i z e c l a s s . Rocks were c o l l e c t e d i n the same manner as f o r the 1975 t r a p s . Crabs were removed by q u i c k l y p l a c i n g a milk-basket t r a p i n t o a l a r g e p l a s t i c dishpan to catch escapes. Rocks were removed s i n g l y from the basket and examined f o r the presence of P e t r o l i s t h e s , which were placed i n t o a j a r with some seawater. Species and carapace widths were recorded l a t e r i n the l a b o r a t o r y . The r o c k s were r e p l a c e d and the basket r e t u r n e d to i t s o r i g i n a l p o s i t i o n . The milk-basket t r a p s were set at the Diana I s l a n d s i t e e a r l y i n J u l y 1977 at the same v e r t i c a l p o s i t i o n s and with the same number of r e p l i c a t e s (three per l e v e l ) as the 1975 basket t r a p s . Baskets were t o be examined on every low t i d e i n which a l l l e v e l s were exposed between 29 June 1977 and 13 October 1977 i n c l u s i v e . This attempt a t s e r i a l sampling was not s u c c e s s f u l . F o l l o w i n g the second o b s e r v a t i o n there were s e v e r a l basket l o s s e s from unknown causes. I have used the data c o l l e c t e d from the f i r s t t r a p o b s e r v a t i o n (29 J u l y 1977) which are complete except f o r the l o s s of one basket. P a t i o Blocks The t h i r d method employed cement p a t i o b l o c k s and was used to determine v e r t i c a l d i s t r i b u t i o n s of j u v e n i l e s with carapace widths of <2.0 mm. The dimension of a block was 30.5 x 30.5 x 5.1 cm. Blocks were p l a c e d at f o u r d i f f e r e n t v e r t i c a l l e v e l s at the Diana I s l a n d and Grappler I n l e t s i t e s i n 14 August 1974. These l e v e l s are the same as those at which the h e r r i n g - r o e and milk-basket t r a p s were s e t . There were t h r e e r e p l i c a t e s about one meter apart a t each l e v e l . Blocks were examined f o r smal l j u v e n i l e s on t h e i r u ndersurfaces d u r i n g each s p r i n g t i d e s e r i e s (approximately monthly) from 16 August 1974 t o 5 October 1975. Carapace widths were measured with an o c u l a r micrometer mounted on a d i s s e c t i n g microscope.. I n t e r t i d a l Predators I attempted to determine whether p o r c e l a i n crab p r e d a t o r s were present i n the i n t e r t i d a l zone. A suspected predator s p e c i e s was brought to the l a b o r a t o r y and placed i n t o an aquarium. A f t e r t h r e e t o f i v e days two or three a d u l t p o r c e l a i n crabs (>10 mm maximum carapace width) were dropped i n t o the aquarium. In one case encounters were staged by p l a c i n g crabs under the a n t e r i o r g i r d l e of the predacious c h i t o n P l a c i p h o r e l l a y e l l a t a . The Organisms and t h e i r D i s t r i b u t i o n s -Zoogeography Based on g e o g r a p h i c a l d i s t r i b u t i o n (Haig 1960, Gore and Abele 1976) i t i s reasonable t o assume that p o r c e l a i n crabs underwent the major p a r t of t h e i r e v o l u t i o n a r y divergence i n t r o p i c a l seas. P e t r o l i s t h e s c i n c t i p e s and P. eriomerus a r e , 15 however, abundant i n c o o l e r marine waters of the n o r t h e a s t e r n P a c i f i c Ocean. Both s p e c i e s have s i m i l a r l a t i t u d i n a l d i s t r i b u t i o n s , namely, southern C a l i f o r n i a to about southern Alaska (Haig 1960, Hart 196 8), but demonstrate d i f f e r e n t v e r t i c a l d i s t r i b u t i o n s i n the i n t e r t i d a l zone. Both s p e c i e s are f i l t e r - f e e d i n g anomuran crabs which l i v e - under b o u l d e r s . In a d d i t i o n t o o c c u r r i n g under b o u l d e r s , P. c i n c t i p e s i s a l s o abundant among the b y s s a l t h r e a d s of M y t i l u s c a l i f o r n i a n u s (Hewatt 1935, R i c k e t t s and C a l v i n 1968). V e r t i c a l D i s t r i b u t i o n s i n Barkley-Sound -P e t r o l i s t h e s c i n c t i p e s i s almost e x c l u s i v e l y an i n t e r t i d a l s p e c i e s (Haig 1960). At the Ross I s l e t s and the e a s t e r n shore of Haines I s l a n d ( F i g . . 1) , P. c i n c t i p e s - h a s i t s lower l i m i t i n the low i n t e r t i d a l zone. During s e v e r a l d i v e s at the f i v e s i t e s over a 4 yr p e r i o d , I was unable to f i n d any P. c i n c t i p e s below datum t i d e l e v e l . The upper l i m i t of the P. eriomerus p o p u l a t i o n was i n the low i n t e r t i d a l zone. In c o n t r a s t t o P. c i n c t i p e s , P. eriomerus, was commonly found under boulders down t o the maximum depth of the boulder f i e l d s (about 5 m below datum) at a l l s i t e s except the Diana I s l a n d s i t e . The a c t u a l lower l i m i t of P. eriomerus-may be even lower. I have o c c a s i o n a l l y found t h i s s p e c i e s i n the gut contents of a d u l t Sebastes nebulosus which were caught at depths g r e a t e r than 10 m below datum. Sebastes nebulosus i s a demersal f i s h , which as an a d u l t , r a r e l y occurs i n i n t e r t i d a l r e g i o n s 16 (personal communication from N.J. Wilimovsky).. In C a l i f o r n i a , £• eriomerus has been observed at -86 m (Haig 1960). Transect Surveys The t r a n s e c t survey data (Table I) show t h a t the v e r t i c a l p o s i t i o n s of the upper l i m i t of P. eriomerus and the lower l i m i t of P. c i n c t i p e s a t the Diana I s l a n d s i t e demonstrated l i t t l e change. A l s o , the s m a l l standard e r r o r s of the means (Table I) suggest t h a t these l i m i t s v a r i e d l i t t l e h o r i z o n t a l l y ( i . e . p a r a l l e l t o water's edge). The h i g h e s t l e v e l a t which P. eriomerus was observed i n any of the t r a n s e c t surveys was 0.9 m above datum, and the lowest P. c i n c t i p e s was found at 0,6 m above datum. On 29 August 1977 I searched f o r the upper l i m i t of the c i n c t i p e s p o p u l a t i o n at the Diana I s l a n d s i t e . The h i g h e s t P. c i n c t i p e s was found at 2.4 m above datum which a l s o r e p r e s e n t s the upper l i m i t of boulders a t t h i s s i t e . T h e r e f o r e , i t i s l i k e l y t h a t the upper l i m i t of the £- c i n c t i p e s p o p u l a t i o n was caused by h a b i t a t d i s c o n t i n u i t y . The 12 September 1977 t r a n s e c t s (Table I) estimated these l i m i t s d u r i n g the high water of a neap t i d e s e r i e s and suggest t h a t n e i t h e r the lower l i m i t of P. c i n c t i p e s nor the upper l i m i t of P. eriomerus change l i t t l e , i f at a l l , during high t i d e . A l s o , during three other d i v e s made at high t i d e d u r i n g summer 1977, I noted p o s i t i o n s of these l i m i t s r e l a t i v e to the 17 Table I . R e s u l t s of the t r a n s e c t . s u r v e y s . Means and standard e r r o r s are i n meters above datum. Lower L i m i t Upper L i m i t of of P. c i n c t i p e s P. eriomerus n mean 16 Oct 1974 7 0. 7 10 J u l y 1975 10 0. 6 4 Nov 8 0. 7 3 Dec 6 0. 6 1 1 June 1976 6 0. 6 25 Aug 8 0. 6 25 Sept 7 0. 6 16 June 1977 6 0. 6 29 Aug 5 0. 6 12 Sept 7 0. 7 se mean se 0.04 0.8 0.04 0.07 0.7 0.06 0.06 0.8 0.04 0.04 0.8 0.07 0.05 0.8 0.03 0.04 0.8 0.03 0.06 0.03 0.8 0.03 0.03 0. 8 0.04 0.05 0. 7 0.03 cement p a t i o b l o c k s and p l a s t i c markers which were wired t o rocks at +0.3, +0.6 and +0.9 m. I d i d not observe d i f f e r e n c e s i n the l o c a t i o n of the lower l i m i t of the P. c i n c t i p e s p o p u l a t i o n from +0.6 m or the upper l i m i t of P. eriomerus- from +0.9 m. T h i s supports my e a r l i e r o b s e r v a t i o n t h a t these l i m i t s a r e the same during p e r i o d s of t i d a l submergence and exposure. 18 Her r i n g - r o e and Milk-basket Traps Data presented i n Tables I I and I I I f u r t h e r support the t r a n s e c t survey data (Table I) i n t h a t there were no Table I I . Number of crab e n t r i e s i n t o the h e r r i n g -roe basket t r a p s i n 1975 and i n t o the milk-basket t r a p s i n 1977. P. c i n c t i p e s P. eriomerus r e p l i c a t e : 1 2 3 1 2 3 1975 1.2 m 393 4 16 n. a. 0 0 n. a. 0.9 366 2 52 267 0 0 0 0.6 89 250 249 79 48 166 0.3 24 • 0 0 172 226 290 1977 1.2 m 26 12 23 0 ' 0 0 0.9 34 4 15 7 25 11 0.6 2 2 n. a. 7 18 n. a. 0.3 0 0 0 35 14 19 P- eriomerus e n t r i e s at the 1.2 m l e v e l s i n e i t h e r year and none a t the +0.9 m l e v e l i n 1975 (Table I I ) . However, there were 43 P. eriomerus e n t r i e s a t the +0.9 m l e v e l i n 1977. Conversely, t h e r e were no P. c i n c t i p e s e n t r i e s at +0.3 ra i n 1977, and only 24 i n d i v i d u a l s had entered one of the t r a p s at t h i s l e v e l i n 1975 (Table II) . This suggests t h a t the lower 19 l i m i t of P. c i n c t i p e s was about +0.6 m above datum (or at l e a s t t h a t there i s a sharp break i n the abundance o f t h i s s p e c i e s somewhere between +0.6 m and +0.3 m above datum) , and t h a t the upper l i m i t of P. eriomerus was around +0.9 m above datum. V e r t i c a l D i s t r i b u t i o n of Megalopa-and J u v e n i l e s Megalopa and j u v e n i l e s demonstrated v e r t i c a l d i s t r i b u t i o n s s i m i l a r t o . those of c o n s p e c i f i c a d u l t s . The r e l a t i v e p r o p o r t i o n s of crabs <5.0 mm of e i t h e r s p e c i e s were s i m i l a r at each l e v e l (at which c o n s p e c i f i c s o c c u r r e d ) , which suggests t h a t the v e r t i c a l ranges i n h a b i t e d by a d u l t s are a l s o f a v o r a b l e to the s u r v i v a l of small j u v e n i l e s ( F i g . 2). R e s u l t s of the 1977 t r a p s e t s were s i m i l a r to those of 1975. The p r o p o r t i o n of P. c i n c t i p e s j u v e n i l e s (<5.0 mm) at each l e v e l i n 1977 were 0.47 a t +1.2 m (n=61), and 0.43 a t +0.9 m (n=53) . There were fou r P. c i n c t i p e s e n t r i e s at +0.6 m and none at +0.3 m (Table I I ) . The p r o p o r t i o n of P. eriomerus j u v e n i l e s were 0.54 at +0.9 m (n=43) , 0,36 at +0.6 m (n=25) and 0.76 a t +0.3 m (n=68). R e l a t i v e l y high p r o p o r t i o n s of P. eriomerus j u v e n i l e s were observed at +0.3 m, but c l e a r l y j u v e n i l e s c o n s t i t u t e a l a r g e p r o p o r t i o n of the p o p u l a t i o n s of both s p e c i e s d u r i n g the l a t e summer and e a r l y autumn. T h i s i s a l s o supported by the p a t i o b l o c k data ( F i g . 3). Crabs <2.0 mm were found only at l e v e l s a t which p o p u l a t i o n s of c o n s p e c i f i c s o c c u r r e d . 20 F i g u r e 2. S i z e c l a s s d i s t r i b u t i o n s of the 1975 t r a p e n t r i e s . There were no P. eriomerus e n t r i e s at the 0.9 and 1.2 m l e v e l s . The number of e n t r i e s i n t o each basket are shown i n Table 2. P. cinctipes P. eriomerus Carapace Width (mm) ure 3. Number of crabs l e s s than 2.0 mm found under t h p a t i o b l o c k s . The curves are. drawn through the mean o three r e p l i c a t e s at each l e v e l . V e r t i c a l l i n e s are ranges. C i r c l e s are f o r P. c i n c t i p e s ; t r i a n g l e s , P. eriomerus; c l o s e d symbols are f o r the Diana I s l a n d s i t e and open symbols f o r the Grapp l e r I n l e t s i t e . 23 20 I I 8 4r 1.2 m /t co _ct> C > ~) «+— o L . (D 0 I 1 CrJ " - O - J -8 0 ' L — A - l 1 0 A S O N.D J 1974 l - A - L - O j i - Q - d - A - 1  0.9 m 0.6 m 0.3 m i-M-^-do-m-d—^—LA L O - * 1 - 0 1 _J#. 1 F M A M J J A S O N 1975 24 I n t e r t i d a l Predators I was unable to f i n d a predator which was abundant or e f f e c t i v e enough to e x p l a i n the w e l l d e f i n e d lower l i m i t of the £* c i n c t i p e s p o p u l a t i o n band (Table I ) . Large perch (probably Rhacqchilus vacca) o f t e n foraged over the Diana I s l a n d s i t e at high t i d e . However, the l a r g e body s i z e of t h i s s p e c i e s prevented i t from e n t e r i n g boulder i n t e r s t i c e s i n h a b i t e d by P e t r o l i s t h e s . O l i g o c o t t u s maculosus, a s m a l l t i d e - p o o l s c u l p i n was abundant over the Diana I s l a n d s i t e at high t i d e , but from l a b o r a t o r y encounters I d i d not observe l a r g e i n d i v i d u a l s of t h i s s p e c i e s ( t o t a l l e n g t h 6.0-6.9 cm) to eat a d u l t s of e i t h e r P e t r o l i s t h e s s p e c i e s , although they r e a d i l y consumed s m a l l amphipods and b i t s of mussel. On boulder beaches near T r i n i d a d , C a l i f o r n i a , I have observed remnants of P. c i n c t i p e s at the den entrances of s m a l l i n t e r t i d a l octopods. I found no evidence t h a t octopods occurred at the Diana I s l a n d s i t e d u r i n g t h i s study. I observed that the c a r n i v o r o u s c h i t o n , P. v e l a t a , w i l l k i l l and e at both P e t r o l i s t h e s s p e c i e s . However, d e n s i t i e s of t h i s c h i t o n at the Diana I s l a n d s i t e were very low ( i n d i v i d u a l s were r a r e l y c l o s e r than 2 m ) . T h e r e f o r e , i t seems u n l i k e l y t h a t P. v e l l a t a prevents £- c i n c t i p e s from i n h a b i t i n g areas below +0.6 m.. High s u r v i v a l r a t e s of P. c i n c t i p e s which were t r a n s p l a n t e d to the low i n t e r t i d a l zone . (see Chapter II) , suggest t h a t vermiform p r e d a t o r s , i p a r a s i t e s and microbes do not r e s t r i c t P. c i n c t i p e s t o the high i n t e r t i d a l zone. 25 D i s c u s s i o n I t i s c l e a r from o b s e r v a t i o n s made by Haig (1960) and from my data, t h a t both P e t r o l i s t h e s - s p e c i e s have d i f f e r e n t v e r t i c a l ranges i n the i n t e r t i d a l zone. My data a l s o show t h a t the p o s i t i o n s of the lower l i m i t of P. c i n c t i p e s and the upper l i m i t of P. eriomerus are temporally s t a b l e (Table I) . J u v e n i l e s appear to i n h a b i t v e r t i c a l ranges which are i d e n t i c a l t o t h a t of c o n s p e c i f i c a d u l t s ( F i g s . 2 and 3), The n e a r l y t o t a l absence of P. c i n s t i p e s i n the lower i n t e r t i d a l zone and i t s complete absence from the shallow s u b t i d a l zone, suggests t h a t i t s observed lower l i m i t (+0.6 m) r e p r e s e n t s an abrupt d i s c o n t i n u i t y of d i s t r i b u t i o n r a t h e r than abundance. Mussels are a b l e t o i n h a b i t wide v e r t i c a l ranges from the high i n t e r t i d a l t o s e v e r a l meters below datum (Paine 1974, Suchanek 1978), but i n f a c t most occur w i t h i n a r e l a t i v e l y narrow i n t e r t i d a l band. In c o n t r a s t to the lower l i m i t of R* c i n c t i p e s , the lower l i m i t of the mussel band r e p r e s e n t s an abrupt d i s c o n t i n u i t y i n abundance r a t h e r than d i s t r i b u t i o n . The reason f o r these sharp breaks were c o m p e t i t i o n and/or p r e d a t i o n (Paine 1974, Suchanek 1978). Although these b i o t i c i n t e r a c t i o n s were severe, mussels were able t o grow and reproduce s u b t i d a l l y , p r o v i d i n g t h a t refuge from predators was a v a i l a b l e . The t o t a l absence of P. c i n c t i p e s s u b t i d a l l y suggests t h a t 26 e i t h e r extremely e f f e c t i v e b i o t i c i n t e r a c t i o n s occur, p h y s i c a l c o n d i t i o n s below +0.6 m are i n t o l e r a b l e t o t h i s s p e c i e s or h a b i t a t s e l e c t i o n has evolved and i s used t o a v o i d lower i n t e r -t i d a l and s u b t i d a l areas f o r e i t h e r or both of the f i r s t two reasons, I w i l l show l a t e r t h a t t h i s s p e c i e s can not only s u r v i v e , but i s able t o reproduce below +0.6 m, r e f u t i n g the idea t h a t an i n t o l e r a n c e t o p h y s i c a l f a c t o r s i s the cause of t h i s d i s t r i b u t i o n a l break. The.upper l i m i t of P. eriomerus r e p r e s e n t s a sharp break i n the v e r t i c a l d i s t r i b u t i o n of t h i s s p e c i e s . Data presented i n t h i s chapter show t h a t n e i t h e r a d u l t s nor j u v e n i l e s of t h i s s p e c i e s were observed higher than +0.9 m. T h i s sharp break i n d i s t r i b u t i o n probably r e p r e s e n t s an i n a b i l i t y o f t h i s s p e c i e s to s u r v i v e at l e v e l s above 0. 9 m above datum. I w i l l present data below t o support t h i s h y p o t h e s i s . 27 II,. TRANSPLANT EXPERIMENTS Intro-duct ion I n d i v i d u a l s of P. eriomerus- were t r a n s p l a n t e d a s h o r t d i s t a n c e above the upper l i m i t of the P. eriomerus p o p u l a t i o n to determine whether t h i s s p e c i e s can l i v e a t abnormally high p o s i t i o n s on the beach. At the same time, c o u l d P. c i n c t i j o e s s u r v i v e and reproduce a t i n t e r t i d a l l e v e l s below the lower l i m i t of i t s p o p u l a t i o n band? I f the answer to t h i s q u e s t i o n was yes, then b i o t i c f a c t o r s would be the most l i k e l y cause of the r a r i t y of t h i s s p e c i e s i n the low i n t e r t i d a l : . and i t s t o t a l absence s u b t i d a l l y . M e t hod-s -Tr a n s p l a n t Cages and Experimental-Animals Crabs were t r a n s p l a n t e d i n cages which were made of s t a i n l e s s s t e e l wire. These cages measured 30.5 x 30.5 x 10.2 cm and had mesh openings of 0.6 x 0.6 cm.. Seventy-six percent of the s u r f a c e was open. Cage l i d s were made of the same m a t e r i a l . Cages were f i l l e d with rocks c o l l e c t e d i n the same manner as f o r the h e r r i n g - r o e and milk-basket t r a p s . Experimental animals of both P e t r o l i s t h e s - s p e c i e s were c o l l e c t e d from w i t h i n the middle and lowest p o r t i o n s of t h e i r r e s p e c t i v e v e r t i c a l d i s t r i b u t i o n s i n the i n t e r t i d a l zone. 28 Nine males and nine females were p l a c e d i n each cage. These crabs had maximum carapace widths of 11.5 to 14.9 mm (measured by v e r n i e r c a l i p e r t o the nearest 0.1 mm). Crabs were c o l l e c t e d at the t r a n s p l a n t s i t e w i t h i n 30 min of being p l a c e d i n t o the cages and were randomly a s s i g n e d to a cage by b l i n d l y grabbing i n d i v i d u a l s from a dishpan. T r a n s p l a n t cages were p l a c e d among boulders a t the Diana I s l a n d s i t e . The J.976 Experiments L i d s were secured by l a s h i n g them with woven f i s h i n g l i n e to the cages' s i d e s . Cage c l o s u r e was again checked on the day f o l l o w i n g data c o l l e c t i o n . I placed two cages about one meter a p a r t at each of f o u r l e v e l s : 0.3, 0.9, 1.3 and 1.6 m above datum. One of the cages c o n t a i n e d P. eriomerus, the other P. c i n c t i p e s . Cages a t the highest (1.6 m) and at the lowest (0.3 m) l e v e l s were e s t a b l i s h e d on 15 A p r i l 1976. The two i n t e r m e d i a t e l e v e l s were e s t a b l i s h e d on 12 May 1976. Those at 0.3 and 1.6 m were examined at lower low water on 12 May 1976. A l l cages were examined at lower low water of a l l s p r i n g t i d e s which f o l l o w e d u n t i l 26 September 1976 i n c l u s i v e . A f i n a l o b s e r v a t i o n was made on 15 A p r i l 1977. During o b s e r v a t i o n s , counts of s u r v i v o r s and developmental stages of the embryos were made. Crabs were immediately returned t o t h e i r cage and the l i d secured. 29 The 1977 Experiments The f o l l o w i n g m o d i f i c a t i o n s were made i n 1977. S t a i n l e s s s t e e l stove b o l t s secured the l i d s of the cages i n s t e a d of l a s h i n g . No l i d s were found to have come open during the 1977 experiments (see r e s u l t s below). The t r a n s p l a n t l e v e l s were changed t o 0.3, 0.6, 0.9 and 1.2 m above datum. Two cages of R' eriomerus were placed at 0.6 and two at 0.9 m above datum. There were th r e e cages a t each of the 0.3 and 1.2 m l e v e l s . Two c o n t a i n e d P. eriomerus and one c o n t a i n e d P. c i n c t i p e s . Number o f s u r v i v o r s was the o n l y i n f o r m a t i o n c o l l e c t e d . These experiments were s t a r t e d on 6 A p r i l 1977 and cages were examined at lower low water of each s p r i n g t i d e s e r i e s u n t i l 29 August 1977 i n c l u s i v e -Deyelopmental Stages Developmental stages were measured on a f i v e c ategory nominal s c a l e . The f i r s t c ategory i n c l u d e d eggs which were homogeneous throughout, that i s , t h e r e were no c l e a r s i g n s of l a r v a l f e a t u r e s . Category two embryos had d i s t i n c t l a r v a l f e a t u r e s with u n d i f f e r e n t i a t e d ommatidia and t h e i r volumes were about t h r e e - q u a r t e r s yolk. Embryos i n the t h i r d category were about h a l f y o l k and the ommatidia were d i s t i n c t as was an obvious heart beat. Embryos scored i n category f o u r were about one-quarter yolk and moved about w i t h i n the eggs i f prodded. A l s o , category f o u r eggs hatched i n the l a b o r a t o r y 30 w i t h i n about one weeJc. F i n a l l y , the f i f t h c ategory c o n s i s t e d of nongravid females-R e s u l t s S u r v i v a l of T r a n s p l a n t e d P. eriomerus Res u l t s presented i n F i g . 4 show t h a t P. eriomerus t r a n s p l a n t e d t o 1.3 and 1.6 m xn 1976 and to 1.2 m i n 1977 had s u r v i v a l r a t e s which were c o n s i d e r a b l y lower than those at and below 0.9 m above datum i n e i t h e r year. In 1976 I p l a c e d r e p l i c a t e s a t 1.6 and 1.3 m above datum i n May and August, r e s p e c t i v e l y . R e s u l t s from these r e p l i c a t e s again show r e l a t i v e l y low s u r v i v a l r a t e s of P. eriomerus ( F i g . 4). The sharp d e f l e c t i o n of the 0.3 m P. eriomerus s u r v i v o r curve ( F i g . .4) between 28 J u l y and 24 August 1976 was accounted f o r by four crabs which escaped because of a l i d which had become u n t i e d between 28 J u l y and 29 J u l y 1976. The 1977 P. eriomerus s u r v i v a l r a t e s a t 0.9 m appear t o be lower than at 0.6 m ( F i g - 4 ) , but the 0.9 m r a t e s are c l e a r l y g r e a t e r than those demonstrated by the two P. eriomerus r e p l i c a t e s at 1.2 m-These data suggest t h a t P. eriomerus- cannot t o l e r a t e the p h y s i c a l c o n d i t i o n s which e x i s t as l i t t l e as 0.3 m above the observed upper l i m i t of the p o p u l a t i o n at the Diana I s l a n d s i t e . 31 Fi g u r e 4. S u r v i v a l r a t e s of t r a n s p l a n t e d Petrolisthes» Dashed l i n e s with c l o s e d c i r c l e s r e f e r to P. c i n c t i p e s , s o l i d l i n e s with open c i r c l e s t o P. eriomerus. Two d i f f e r e n t l e v e l s are i n d i c a t e d i n the second graph from the top: the 1976 data (1.3 m) i s represented by c l o s e d and open t r i a n g l e s (P. c i n c t i p e s and P. eriomerus r e s p e c t i v e l y ) , the 1977 data (1.2 m) i s represented with c l o s e d and open squares (P. c i n c t i p e s and P. eriomerus r e s p e c t i v e l y ) . V e r t i c a l arrows on the r i g h t i n d i c a t e approximate i n t e r -t i d a l ranges of both s p e c i e s . Dashed arrow, P. c i n c t i p e s ; s o l i d arrow P. eriomerus. 32 <l» > cz 2 0 10 5 1 2 0 10 5 1 2 0 10 5 1 1*6 m Above D a t u m -1 L 1 1 1 I I -1 1 I l i i ' • 1.2 m (•,.) 1.3 •m ( A , A ) — J 1- I L_ J I 1_ -  1 I 1 I 1_ 0.9 m 0.9 m - J 1 1 1 1 L_ 1 I I I I I i I I I I 2 0 101-5 0.6 m 11—i—_i_ i_ i_ 2 0 r ^ 10 —i—,_i 1 i i i ' ' 0.5 m 0.3 m -j—i—i—1_ i i i ' ' J—i—i i i i i A M J J A S O N D J F M A M J J A 1976 1977 33 Embryonic Development of Transplanted P. eriomerus Data presented i n Table I I I show t h a t P. eriomerus females d e p o s i t e d and hatched eggs at the 0-3 and 0.9 m t r a n s p l a n t l e v e l s . When the 0.3 m t r a n s p l a n t cages were e s t a b l i s h e d Table I I I . Developmental stages of the eggs h e l d DY R- eriomerus females at the 0.3 and 0.9 m t r a n s -p l a n t l e v e l s . The a b b r e v i a t i o n ng stands f o r not g r a v i d . n n category: ng 2 3 4 ng 1 2 3 4 15 A p r i l 1976 9 1 8 0 0 0 12 May 9 0 4 4 1 0 9 0 2 3 3 1 29 May 8 0 2 0 2 4 8 0 2 0 0 6 30 June 5 2 3 0 0 0 7 1 5 0 1 0 29 J u l y 5 1 2 0 1 1 6 0 3 1 2 0 26 Aug 5 2 1 1 0 1 6 2 2 1 0 1 26 Sept 5 4 0 0 0 1 6 3 1 1 1 0 5 A p r i l 1977 5 0 5 0 0 0 6 0 5 0 0 1 (15 A p r i l 1976), most of the females (8/9) at t h i s l e v e l bore category one eggs. On 12 May (Table III) more than h a l f of these females (0.3 m) bore embryos which matured beyond the f i r s t developmental category, and on 30 June the m a j o r i t y (6/7) were e i t h e r nongravid or bore category one eggs. T h i s 34 suggests that a hatch occurred p r i o r t o 30 June. On 29 J u l y (Table I I I ) a second mode of r e p r o d u c t i v e a c t i v i t y was beginning at t h i s l e v e l (0.3 m) and. by 26 August f o u r of the remaining s i x females were e i t h e r nongravid or bore category one eggs. The 26 September data (Table III) suggest a t h i r d s e s s i o n of r e p r o d u c t i v e a c t i v i t y , but t h i s was not i n v e s t i g a t e d f u r t h e r . P e t r o l i s t h e s eriomerus t r a n s p l a n t e d to 0.9 m above datum a l s o demonstrated at l e a s t two separate r e p r o d u c t i v e s e s s i o n s which occ u r r e d between 12 May and 26 September 1976 (Table I I I ) . These r e s u l t s are s i m i l a r t o those of Knudsen (1964) who observed two broods i n one r e p r o d u c t i v e season f o r t h i s s p e c i e s i n Puget Sound, Washington. I observed t h a t category f o u r embryos from both l e v e l s appeared normal and had strong heart beats, f u r t h e r s u p p o r t i n g the c o n c l u s i o n t h a t hatching was s u c c e s s f u l . Females became ovigerous the f o l l o w i n g year (5 A p r i l 1977, Table I I I ) again s u g g e s t i n g t h a t t h i s s p e c i e s i s a b l e t o reproduce w i t h i n i t s e n t i r e i n t e r t i d a l range. S u r v i v a l of Transplanted P. c i n t i p e s P e t r o l i s t h e s c i n c t i p e s demonstrated high s u r v i v a l r a t e s at a l l l e v e l s t o which t h i s s p e c i e s was t r a n s p l a n t e d ( F i g . 4 ) , suggesting t h a t i t i s p h y s i o l o g i c a l l y a b l e to s u r v i v e below i t s lower l i m i t . Furthermore, r e s u l t s of a p i l o t study i n which 30 P. c i n c t i p e s were t r a n s p l a n t e d to 2.8 m below datum i n Bamfield I n l e t ( F i g . 1), suggest t h a t t h i s s p e c i e s i s a b l e to 35 s u r v i v e a t depths which are c o n s i d e r a b l y below the lower l i m i t of p o p u l a t i o n s of t h i s s p e c i e s . A f t e r 194 days, these t r a n s p l a n t e d P. c i n c t i p e s were a l i v e and otherwise appeared h e a l t h y . A l s o , remnants of exuvia present i n the cage suggest that at l e a s t some of the i n d i v i d u a l s grew. Embryonic Development of Transplanted-P. c i n t i p e s Reproductive c o n d i t i o n s of t r a n s p l a n t e d P. c i n c t i p e s females at the highest and lowest l e v e l s (0.3 and 1.6 m. Table IV) suggest that t h i s s p e c i e s i s a b l e t o reproduce at i n t e r t i d a l l e v e l s below which i t normally o c c u r s . At the onset o f these experiments n e a r l y a l l of the females at both l e v e l s bore category one eggs (15 A p r i l 1976, Table I V ) . On 28 May 1976 (Table IV) about h a l f of the females a t both l e v e l s were c a r r y i n g embryos which had matured beyond category one. On 27 June there were two females a t 1.6 m and one female a t 0.3 m which were not g r a v i d , suggesting that h a t c h i n g had occurred between 28 May and 27 June. T h e i r o v a r i e s were f i l l e d with eggs ( e a s i l y observable through the v e n t r a l s u r f a c e s of the membranous abdomen and p o s t e r i o r t h o r a x ) , sug g e s t i n g t h a t t r a n s p l a n t a t i o n had no e f f e c t on oogenesis. A l s o , on 27 June I examined category f o u r embryos of females at the 0.3 and 1.6 m l e v e l s . These embryos appeared normal and had s t r o n g heart beats. On 28 J u l y more than h a l f of the females were nongravid at e i t h e r l e v e l (Table I V ) , again sug g e s t i n g t h a t eggs observed on 27 June had hatched p r i o r to 36 Table IV. Developmental stages of the eggs held by P. c i n c t i p e s females at the h i g h e s t and lowest t r a n s -p l a n t l e v e l s . The a b b r e v i a t i o n ng stands f o r not g r a v i d . 1.6 m 0. 3 m n n category: nq 1 2- 3 4 net 2 3 4 15 A p r i l 1976 9 1 8 0 0 0 9 0 9 0 0 0 12 May 9 2 7 0 0 0 9 0 9 0 0 0 28 May 9 0 5 3 1 0 9 0 4 4 1 0 27 June 8 2 2 0 2 2 9 1 0 1 4 3 28 J u l y 7 5 1 0 1 0 9 6 3 0 0 0 24 Aug 7 6 0 0 1 0 9 5 4 0 0 0 26 Sept 7 7 0 0 0 0 9 7 0 0 1 1 5 A p r i l 1977 7 0 7 0 0 0 8 1 7 0 0 0 t h i s time. At the 1.6 m l e v e l on 24 August- one of seven remaining females bore category three eggs which presumedly had hatched s i n c e a l l females at t h i s l e v e l were nongravid on 26 September. In c o n t r a s t , f o u r out of nine females a t the 0.3 m l e v e l on 24 August bore category one eqqs. Data c o l l e c t e d on 26 September (0.3"m) suqqest t h a t two of these f o u r females had s u c c e s s f u l hatches. I t i s not known what became o f embryos which the other two females c a r r i e d on the previous o b s e r v a t i o n date. Data presented i n Table IV show t h a t at l e a s t one s e s s i o n of r e p r o d u c t i v e a c t i v i t y o c c u r r e d , beginning on 15 A p r i l 1976 and reached completion around 37 24 August at both l e v e l s . D i s c u s s i o n I have provided evidence ( F i g . 4) which s t r o n g l y suggests t h a t P. eriomerus cannot s u r v i v e as l i t t l e as 0.3 m above the upper l i m i t of the p o p u l a t i o n band. F a c t o r s which s e t the upper l i m i t of t h i s p o p u l a t i o n remain unresolved, but may be r e l a t e d t o the e f f e c t s of reduced f e e d i n g time and/or s t r e s s e s from the a b i o t i c environment. Based on d i s t r i b u t i o n a l r e c o r d s (Haig 1960) and the high m o r t a l i t i e s of P. eriomerus above i t s upper l i m i t , t h i s s p e c i e s seems to be adapted to l i f e i n the low i n t e r t i d a l and s u b t i d a l r e g i o n s . Competitors and predators are known to set the lower l i m i t s of some i n t e r t i d a l p o p u l a t i o n s (e.g. C o n n e l l 1961a, 1961b, 1970, Paine 1974). These i n v e s t i g a t o r s found t h a t s e t t l e m e n t occurred below the lower l i m i t s of c o n s p e c i f i c p o p u l a t i o n s . However, i n no case were b i o t i c f a c t o r s found to be so severe as to cause the immediate and t o t a l e l i m i n a t i o n of low s e t t l e r s w i t h i n s h o r t time p e r i o d s s i n c e t h e r e were u s u a l l y some o p p o r t u n i t i e s f o r s u r v i v a l and growth- Furthermore, i f the r e f u g e was adequate to allow these i n d i v i d u a l s t o grow to a s u f f i c i e n t s i z e , r e p r o d u c t i o n would occur (Paine 1974, 1976, Suchanek 1978). P e t r o l i s t h e s c i n c t i p e s of any s i z e c l a s s were not found below the observed lower l i m i t of the p o p u l a t i o n band. Because t h i s s p e c i e s was not found below +0.6 m and 38 because the t r a n s p l a n t experiments showed t h a t a d u l t s s u r v i v e d and reproduced below the lower l i m i t of the p o p u l a t i o n ( F i g . 4 and Table I V ) , I conclude t h a t h a b i t a t s e l e c t i o n has evolved and i s used by t h i s s p e c i e s t o avoid i n t e r t i d a l r e g i o n s below +0.6 m. C l e a r l y then, P. c i n c t i p e s i s p h y s i o l o g i c a l l y a b l e t o i n h a b i t a much wider v e r t i c a l range than i t a c t u a l l y does i n nature. 39 I I I . ARENA EXPERIMENTS I n t r o d u c t i o n I n t e r s p e c i f i c encounters between s m a l l t e r r e s t r i a l v e r t e b r a t e s can l e a d to the e x c l u s i o n of i n f e r i o r c o mpetitors from p r e f e r r e d h a b i t a t s i n both f i e l d and l a b o r a t o r y s t u d i e s (e.g. Jaeger 1971, H e l l e r 1971, review by Grant 1972). S i m i l a r b i o t i c i n t e r a c t i o n s occur among freshwater i n v e r t e b r a t e s . Bovbjerg (1970) s t u d i e d two s p e c i e s of c r a y f i s h and observed t h a t one of the two s p e c i e s was r e s t r i c t e d t o ponds even though i t was a l s o adapted to l i v i n g i n streams. He suggested t h a t the pond s p e c i e s was excluded from i n h a b i t i n g streams because of a g o n i s t i c i n t e r a c t i o n s with the dominant stream s p e c i e s . On the other hand, the stream s p e c i e s was unable to s u r v i v e i n the r e l a t i v e l y r i g o r o u s pond environment because of i t s i n a b i l t y t o burrow and escape l e t h a l c o n d i t i o n s when the pond d r i e d . To my knowledge there i s no evidence t h a t e x c l u s i o n by i n t e r s p e c i f i c a g o n i s t i c behavior among motil e i n t e r t i d a l s p e c i e s s e t s e i t h e r upper or lower l i m i t s o f p o p u l a t i o n s . Molenock (1976) s t u d i e d i n t r a s p e c i f i c encounters of both P e t r o l i s t h e s s p e c i e s and found t h a t s e v e r a l d i s p l a y s and types of a g g r e s s i v e contact were used t o maintain spacing d i s t a n c e s between i n d i v i d u a l s . She d i d not, however, study i n t e r s p e c i f i c i n t e r a c t i o n s . The p o t e n t i a l f o r s p e c i e s no e x c l u s i o n by n o n d e s t r u c t i v e a g o n i s t i c behavior among p o r c e l a i n crabs has not been s t u d i e d -Random s p a t i a l p a t t e r n s suggest t h a t the presence of an i n d i v i d u a l does not i n f l u e n c e the p o s i t i o n of a neighbor ( E l l i o t 1971). S i n g l e s p e c i e s arena experiments allowed me t o determine whether each s p e c i e s demonstrated nonrandom s p a t i a l p a t t e r n s . Mixed s p e c i e s arena experiments were designed to t e s t f o r the e x c l u s i o n of P. c i n c t i p e s by P. eriomerus from p r e f e r r e d h a b i t a t s . Instead of t e s t i n g v a r i o u s combinations of s p e c i e s d e n s i t i e s , I chose t o examine the c o m p e t i t i v e outcome under c o n d i t i o n s where the lower zoned s p e c i e s c o u l d p o t e n t i a l l y s a t u r a t e the h a b i t a t . I f e x c l u s i o n of P . . c i n c t i p e s by P. eriomerus could not be shown under these extreme c o n d i t i o n s , i t i s u n l i k e l y t h a t i t would occur at lower d e n s i t y combinations of the two s p e c i e s . Methods • The Arena and Seawater System The arena was a 91.4 x 20-3 x 15.2 cm p l e x i g l a s s tank with a 30.5 x 30.5 x 5.1 cm p a t i o block placed near one c o r n e r of the tank ( F i g . 5). Small diameter rubber p i l l a r s placed at each of f o u r c o r n e r s , e l e v a t e d the block about 2 cm from the bottom of the arena. A c e n t r a l d r a i n with a standpipe kept the seawater depth at about 5 cm. The arena was l o c a t e d i n a 41 Figure 5. The arena. Seawater Line Plexiglass Tank 43 f l o a t s h e d at the mouth of Bamfield I n l e t ( F i g . 1). U n f i l t e r e d seawater was pumped from about 2 m below sea l e v e l by a L i t t l e Giant b r i n e - a c i d pump (model 3-MD) and flowed i n t o the arena at about 8 1/min. Within 10 m of the f l o a t s h e d was an i n t e r t i d a l boulder beach over which both s p e c i e s o c c u r r e d . I have assumed t h a t seawater q u a l i t y was s i m i l a r to t h a t a v a i l a b l e t o n a t u r a l p o p u l a t i o n s . The undersurface of the b l o c k was probably the most f a v o r a b l e s u b s t r a t e i n the arena, s i n c e crabs on the p l e x i g l a s s bottom c o u l d not r e a d i l y move f o r l a c k pf t r a c t i o n and were o f t e n t o s s e d about by c u r r e n t s . These c r a b s would u s u a l l y p i l e i n t o the c o r n e r s of the tank; those on the bottom d i d not have enough room to extend t h e i r t h i r d m a x i l l i p e d s and f e e d . Some crabs p o s i t i o n e d themselves on v e r t i c a l s i d e s of the bloc k , but never on the emerged upper s u r f a c e . Experimental Animals and Holding - Procedure Experimental animals were c o l l e c t e d from Dodger Channel near the Diana I s l a n d s i t e and i n the channel north of Cape Beale ( F i g . 1). These crabs were h e l d i n h e r r i n g - r o e baskets or p l a s t i c dishpans with screen covers through which a continuous flow of u n f i l t e r e d seawater was maintained. Crabs appeared healthy and vigorous throughout the h o l d i n g p e r i o d of up to two months before s u b j e c t i n g them t o the arena. 44 Data C o l l e c t i o n and S t a t i s t i c a l Analyses -Arena experiments began by p l a c i n g crabs under the block and l e a v i n g them undisturbed f o r a t l e a s t 60 h. Counts of crabs on the undersurface of the block were made every 0.5 h f o r the f i r s t 2.0 h, every 4.0 h up to 12.0 h and at 12.0 h i n t e r v a l s beyond the t w e l f t h hour. To compare e q u i l i b r i u m values i . e . the s t a b l e number of crabs under the block a f t e r i n i t i a l f l u c t u a t i o n s , the value k was c a l c u l a t e d . T h i s value (k) was the grand mean of the number of crabs under the block at the l a s t t h r e e o b s e r v a t i o n times f o r a l l r e p l i c a t e s . I f r e p l i c a t e s were not made then k was the mean o f the l a s t t h r e e o b s e r v a t i o n s . P o s i t i o n s of crabs c l i n g i n g t o the undersurface of the block were mapped at 72 h by t a p i n g a sheet of c l e a r p l a s t i c t a r p to the bottom of the arena tank and p l a c i n g a dot on the sheet at a p o i n t corresponding to the c e n t e r of each crab's carapace with an I n d i a ink marking pen. P r i o r t o mapping, an o u t l i n e o f the block was drawn on the p l a s t i c sheet and a l i g n e d with the perimeter of the b l o c k . T h i s o u t l i n e was a r e f e r e n c e f o r l a t e r a n a l y s i s . Spacing p a t t e r n s (from the p l a s t i c maps) were analyzed by the method of C l a r k and Evans (1954). T h e i r method employs the c a l c u l a t i o n of a t h e o r e t i c a l n e a r e s t neighbour d i s t a n c e f o r a random d i s t r i b u t i o n of p o i n t s having the same d e n s i t y as t h a t of the sample. T h i s t h e o r e t i c a l nearest neighbor mean i s 45 compared with the sample mean as the r a t i o Observed Mean/Theoretical Mean = R. When R = 1, the sample p o i n t s are spaced randomly. As R approaches z e r o , sample p o i n t s approach a clumped d i s t r i b u t i o n . When R approaches 2.1419 (= p e r f e c t l y uniform, C l a r k and Evans 1954) sample p o i n t s approach a uniform d i s t r i b u t i o n . A t h e o r e t i c a l standard e r r o r f o r a random d i s t r i b u t i o n of p o i n t s with the same d e n s i t y as the sample can be c a l c u l a t e d . T h i s allows one to determine whether R i s s i g n i f i c a n t l y d i f f e r e n t from u n i t y . An aspect of spacing p a t t e r n s that C l a r k and Evans (1954) did not d i s c u s s i s the degree of v a r i a n c e one should expect as R departs from u n i t y . When the d i s t r i b u t i o n of p o i n t s i s p e r f e c t l y uniform, v a r i a n c e w i l l equal zero, when the p o i n t s are d i s t r i b u t e d i n a p e r f e c t l y clumped manner ( i . e . one on the other) there w i l l a l s o be zero v a r i a n c e . T h e r e f o r e , i f nonrandom spacing o c c u r r e d , one would expect t h a t sample v a r i a n c e s would be s m a l l e r on the average than t h e o r e t i c a l v a r i a n c e s . I have presented both v a r i a n c e s i n order to make t h i s comparison. To reduce edge e f f e c t s , p o i n t s w i t h i n 3 cm of the b l o c k ' s perimeter were not used as c e n t e r s of measurement when measuring nearest neighbor d i s t a n c e s . These p e r i p h e r a l p o i n t s were, however, used as nearest neighbors. 46 S i n g l e S p e c i e s Experiments These experiments were conducted to determine what e f f e c t s i z e , sex and i n i t i a l d e n s i t y had on the spacing p a t t e r n s and e q u i l i b r i u m d e n s i t i e s of both s p e c i e s . They a l s o served as c o n t r o l s f o r mixed s p e c i e s experiments. Crabs were s i z e d by t h e i r maximum carapace widths which were measured by v e r n i e r c a l i p e r t o the n e a r e s t 0.1 mm. S i z e c l a s s e s w i l l be expressed as t h e i r c l a s s marks. Each s i z e c l a s s was a r b i t r a r i l y assigned l i m i t s of ±0.8 mm. Three s i z e c l a s s e s were t e s t e d : 9.0, 12.0 and 15.0 mm. F o r t y - e i g h t males of e i t h e r s p e c i e s were used f o r each s i z e c l a s s . A l s o , 32 c r a b s o f each sex (64 t o t a l ) were t e s t e d to determine whether the s p a t i a l p a t t e r n s of mixed sex groups were s i m i l a r t o those of males alone. Mixed Species Experiments These experiments were designed t o determine whether one s p e c i e s excluded the other from under the arena block. E i t h e r 50, 60 or 64 crabs of each s p e c i e s were placed under the block ( t o t a l s : 100, 120 and 128 c r a b s , r e s p e c t i v e l y ) . A p p r o p r i a t e s i n g l e s p e c i e s experiments (50, 60 or 64 c r a b s , r e s p e c t i v e l y ) served as c o n t r o l s . Mixed s p e c i e s experiments were run on males of the 12.0 mm s i z e c l a s s , on males and females (32 males and 32 females of each species) of the 12.0 mm s i z e c l a s s , on l a r g e P. eriomerus (14.0-15.4 mm) vs. s m a l l P. c i n c t i p e s (11.3-12.8 mm) , sma l l P. eriomerus - (11.3-12.8 mm) vs. l a r g e 47 R' c i n c t i p e s (14-0-15.4 mm) and on males which ranged from 14.0 to 17.0 mm. These 14.0-17.0 mm males were su b j e c t e d to s l i g h t l y d i f f e r e n t experimental c o n d i t i o n s . Instead of 64 crabs of each s p e c i e s , s i x t y were used, and i n s t e a d of one b l o c k , two were placed s i d e by s i d e with t h e i r long a x i s p e r p e n d i c u l a r to the seawater i n f l o w ( F i g . 5). B e h a v i o r a l Observations B e h a v i o r a l o b s e r v a t i o n s were made during 30 min i n t e r v a l s which began 0, 1, 4, 24 and 48 h a f t e r the s t a r t of a l l arena experiments. In s i n g l e s p e c i e s experiments, records were kept on the number of a g g r e s s i v e encounters d u r i n g the 30 min i n t e r v a l as w e l l as the types of behavior used by crabs d u r i n g encounters. I a l s o recorded d i s t a n c e moved by winning and l o s i n g crabs d u r i n g a g g r e s s i v e encounters. For the mixed s p e c i e s experiments I noted whether encounters were i n t r a s p e c i f i c or i n t e r s p e c i f i c ; i f i n t e r s p e c i f i c , which s p e c i e s won. I have used the terminology of Molenock (1976) when d e s c r i b i n g the v a r i o u s types of behavior observed during these experiments. 48 R e s u l t s S i n g l e S p e c i e s Experiments Tables V and VI show that r e g a r d l e s s of s i z e (over the range t e s t e d ) , or sex (P. eriomerus females alone were not t e s t e d . Table V I ) , both s p e c i e s tended t o have nonrandom d i s t r i b u t i o n s . A l l cases which were d i f f e r e n t (p<0.05) from randomness (eight out of twelve f o r both species) were i n the d i r e c t i o n of even spacing. A d d i t i o n a l evidence t h a t s p a c i n g i s nonrandom comes from sample v a r i a n c e s which were c o n s i s t e n t l y lower than t h e o r e t i c a l v a r i a n c e s (Tables V and V I ) . Some B e h a v i o r a l Observations The mechanism causing t h i s nonrandom spacing i s a c t i v e maintenance of nearest neighbor d i s t a n c e by i n d i v i d u a l s . I observed t h a t f o u r types o f behavior were o f t e n used by both s p e c i e s t o maintain these d i s t a n c e s (see Molenock 1976 f o r o t h e r s ) . Two i n v o l v e d c o n t a c t and two i n v o l v e d d i s p l a y : 1. Chelae shove (contact):one crab d e l i v e r s r a p i d , powerful jabs with i t s c h e l i p e d , pushing the r e t r e a t i n g crab from i t s space. 2. C h e l i p e d probe ( d i s p l a y ) : c h e l i p e d s are f u l l y extended towards the i n t r u d i n g crab at f u l l gape. T h e : r e c e i v i n g crab e i t h e r backs o f f or takes the c h a l l e n g e and makes a g g r e s s i v e c o n t a c t . 3. C h e l i p e d grasp ( c o n t a c t ) : one or both c h e l i p e d s 49 Table V. Nearest neighbor s t a t i s t i c s f o r R- c i n c t i p e s . A s t e r i s k s mean t h a t p<0.05. obs. obs,. t h e o r . s i z e i n i t i a l mean S2 S2 sex c l a s s d e n s i t y n (mm) (mm2) (mm2) R m 9.0 48 26 28. 2 36.7 157.7 1. 17 ns m 9.0 48 27 25. 1 30.5 151. 9 1.07 ns m 12.0 48 30 31.2 92.4 136. 7 1. 40 * m 12.0 48 20 31. 1 80.6 205.0 1. 29 ns m 12.0 64 36 27.8 42.3 113. 9 1.36 * m 12.0 64 26 34.0 64.3 157.7 1.42 * m 12.0 84 40 27.0 28.6 10 2. 5 1. 44 * m 12.0 84 28 28.3 51. 1 146. 5 1-23 * m 15.0 48 20 32.8 34.9 205.0 1. 20 ns m 15. 0 48 22 35.7 44.5 185.6 1,41 * f 12. 0 48 29 31.6 41.9 141. 4 1. 39 # m + f 12.0 32+32 29 28. 5 6 0.4 14 1. 4 1. 25 * of the r e c e i v i n g crab are clenched by the c h e l a or chelae r e s p e c t i v e l y of the other crab. The c h e l i p e d ( s ) i s u s u a l l y h e l d f o r s e v e r a l seconds. Once r e l e a s e d , the crab which was held e i t h e r r e t r e a t s or f i g h t s with the crab which was h o l d i n g i t . 4. C h e l i p e d rock ( d i s p l a y ) : Molenock (1976) d e s c r i b e s t h i s as c h e l i p e d movement only. My o b s e r v a t i o n s d i f f e r from hers. Instead o f v i b r a t i n g the c h e l i p e d s , the e n t i r e body of the crab o s c i l l a t e d around an a x i s p e r p e n d i c u l a r t o the s u r f a c e on which i t was s t a n d i n g . T h i s a x i s i n t e r s e c t e d a p o i n t at about the middle of the carapace. The c h e l i p e d s are r e t r a c t e d 50 Table VI. Nearest neighbor s t a t i s t i c s f o r P. eriomerus. A s t e r i s k s mean t h a t p<0.05. obs. obs. t h e o r . s i z e i n i t i a l mean s2 s 2 sex c l a s s d e n s i t y n (mm) (mm2) (mm2) R m 9.0 48 16 38.7 82.5 256. 3 1. 26 ns m 9.0 48 15 39. 1 42.8 273. 4 1. 24 ns m 12.0 48 10 55. 1 85.4 410.0 1. 42 * m 12. 0 48 13 45.3 212.0 315.0 1. 33 * m 12.0 64 13 45.8 132.7 315.0 1. 34 * m 12.0 64 11 4 4. 3 236.9 372. 8 1. 20 ns m 12.0 84 16 43.3 94.0 256. 3 1.41 * m 12.0 84 12 45.6 50.3 341.7 1. 29 ns m 15. 0 48 13 53.5 184.9 315. 4 1.57 * m 15.0 48 15 43.9 132.5 27 3. 4 1.39 * f n.a. — — f+ m 12.0 32 + 32 12 48. 6 232.3 341.7 1. 37 * t i g h t l y a g a i n s t the body while o s c i l l a t i n g . O s c i l l a t i o n s are short and r a p i d and give the crab and appearance of q u i v e r i n g . Sometimes these o s c i l l a t i o n s ceased momentarily while advancement was made on the r e c e i v e r . The " r e c e i v i n g crab e i t h e r r e t r e a t e d or fought. Although both s p e c i e s r e a d i l y autotomize c h e l i p e d s when c o l l e c t e d from the f i e l d , I d i d not observe t h i s during i n t r a - or i n t e r s p e c i f i c s p a c i n g encounters. Both s i g h t and touch are important i n determining the presence of an i n t r u d e r . Contact i s made by the long f l e x i b l e antennae. Each antenna scans an arc s l i g h t l y g r e a t e r than 180 51 degrees and i s long enough t o c o n t a c t i n t r u d e r s approaching from the r e a r . When a r e a r approach was f e l t , the crab u s u a l l y turned and faced the i n t r u d e r . Antennal a c t i v i t y (antennal l a s h and antennal tap, Molenock 1976) i n c r e a s e d markedly dur i n g encounters, i n d i c a t i n g the importance of t h i s sensory device i n d e t e c t i n g the presence o f nearby crabs. Neither s p e c i e s was t e r r i t o r i a l i n the sense t h a t an i n d i v i d u a l a c g u i r e d and defended a f i x e d area ( v i o l a t i n g the f i r s t c o n d i t i o n of t e r r i t o r i a l i t y given by Brown and Orians 1970). From o b s e r v a t i o n s which were made at 12 h i n t e r v a l s I noted t h a t n a t u r a l l y marked crabs (barnacles and/or worm tubes on the exoskeleton were the most common ty p e s of n a t u r a l markings) were never i n the same p l a c e . T h i s agrees with Molenock (1976) who observed i n c e s s a n t e x p l o r a t o r y behavior by P e t r o l i s t h e s . I n t e r s p e c i f i c D i f f e r e n c e s Tables V and VI show t h a t i n d i v i d u a l P. eriomerus main-t a i n e d a gr e a t e r mean d i s t a n c e to nearest neighbor than d i d R- c i n c t i p e s . The only o v e r l a p of the 95% c o n f i d e n c e i n t e r v a l s ( F i g . 6) i s between 15.0 mm P. c i n c t i p e s and 9.0 mm P. eriomerus. D i s t a n c e s t r a v e r s e d by winners and l o s e r s d u r i n g i n t r a s p e c i f i c f i g h t s between 12 mm males ( F i g . 7) suggest a p o s s i b l e mechanism f o r the d i f f e r e n c e s i n spacing p a t t e r n s ure 6. Distance to nearest neighbor. R e s u l t s are from two s i n g l e s p e c i e s r e p l i c a t e s per s i z e c l a s s . Data from male at i n i t i a l d e n s i t i e s of 48 crabs. H o r i z o n t a l l i n e s : means; v e r t i c a l l i n e s : 95% c o n f i d e n c e i n t e r v a l s . 53 (UJUJ) SDUE^SIQ JoqgSiaN i s s j e a N 54 Fi g u r e 7. D i s t a n c e s moved by crabs dur i n g i n t r a s p e c i f i c encounters. Data c o l l e c t e d from s i n g l e s p e c i e s arena experiments from the 12.0 mm s i z e c l a s s . ADVANCES RETREATS 80 n=4l n = 32 P. cinctipes 4 0 1 u c O J ZD cr <U P. eriomerus 801 40 i n = 28 x n = 20 x 0 20 40 60* 0 20 40 60• Distance Moved (mm) 56 observed between these two species.. On the average, 2* c i n c t i p e s winners advanced d i s t a n c e s which were l e s s than those of P. eriomerus winners ( F i g . 7, K r u s k a l - W a l l i s t e s t , p<0.01) du r i n g i n t r a s p e c i f i c encounters.. F i g u r e 7 a l s o shows that the average d i s t a n c e r e t r e a t e d by P. eriomerus l o s e r s was g r e a t e r than t h a t f o r P. c i n c t i p e s - l o s e r s ( K r u s k a l - W a l l i s t e s t , p<0.001) . Losers of both s p e c i e s t r a v e r s e d d i s t a n c e s about th r e e times g r e a t e r than p u r s u i t d i s t a n c e s t r a v e l l e d by c o n s p e c i f i c winners ( F i g . 7) . The e f f e c t of t h i s behavior i s t h a t winners do not move as f a r from t h e i r p o i n t of o r i g i n as l o s e r s a f t e r the i n t e r a c t i o n was completed. T h i s would seem a necessary p r e r e g u i s i t e f o r the maintenance of non-random spacing p a t t e r n s f o r any motile s p e c i e s i n which a g o n i s t i c behavior causes even spacing p a t t e r n s . These data suggest t h a t the r e l a t i v e l y g r e a t e r nearest neighbor d i s t a n c e s maintained by P. eriomerus ( F i g - 6) are due to two f a c t o r s : r e l a t i v e l y g r e a t e r d i s t a n c e s t r a v e r s e d by winners during enforcement of i n d i v i d u a l s p a c i n g d i s t a n c e s and r e l a t i v e l y g r e a t e r r e t r e a t s made by P. eriomerus which l o s e spacing d i s p u t e s . F i g u r e 8 shows t h a t s t a r t i n g d e n s i t y has r e l a t i v e l y l i t t l e e f f e c t on the e q u i l i b r i u m values (k) f o r P. eriomerus compared to P. c i n c t i p e s at the same s t a r t i n g d e n s i t i e s , suggesting t h a t s a t u r a t i o n values of P. eriomerus-under the block were probably approached when the s t a r t i n g d e n s i t y was'greater than 48 c r a b s . The most p l a u s i b l e reason f o r these d i f f e r e n c e s i s the g r e a t e r 57 F i g u r e 8. E f f e c t s of i n i t i a l d e n s i t y on k. I n i t i a l d e n s i t were 48, 64 and 84 c r a b s . P o i n t s : means of two r e p l i c a t e s ; v e r t i c a l l i n e s : ranges. 59 spacing d i s t a n c e maintained by P. eriomerus ( F i g . 6). T h i s was not the case f o r P. c i n c t i p e s s i n c e e q u i l i b r i u m values i n c r e a s e d with i n c r e a s i n g s t a r t i n g d e n s i t y . The much higher k values demonstrated by P. c i n c t i p e s seem to be r e l a t e d t o t h e i r r e l a t i v e l y s m a l l e r nearest neighbor d i s t a n c e . A s p e c i e s which maintains a g r e a t e r s p a c i n g d i s t a n c e by a g o n i s t i c behavior would be expected to have a higher f i g h t r a t e i n crowded c o n d i t i o n s . T h i s appears to be the case based on the r e s u l t s shown i n F i g . 9: P. eriomerus had a much higher i n i t i a l f i g h t r a t e with c o n s p e c i f i c s than d i d P. c i n c t i p e s . The higher f i g h t r a t e of P. eriomerus dropped s h a r p l y d u r i n g the f i r s t f o u r hours; a t and beyond f o u r hours, r a t e s were s i m i l a r f o r both s p e c i e s . In a d d i t i o n , the higher i n i t i a l f i g h t r a t e of P. eriomerus l e d to a g r e a t e r number of e x c l u s i o n s of c o n s p e c i f i c s from under the b l o c k during the f i r s t hour than was the case f o r P. c i n c t i p e s (Table V I I ) . Mixed Species Experiments R e s u l t s of the i n t e r s p e c i f i c arena experiments show ( F i g s . 10 and 11) that i n the presence of P. c i n c t i p e s , P- eriomerus had d i s p r o p o r t i o n a t e l y lower k v a l u e s compared to those p r e d i c t e d by the s i n g l e s p e c i e s c o n t r o l s . These r e s u l t s are summarized i n Table VIII where the r a t i o k c i n c t i p e s / k eriomerus i n c r e a s e d when the two s p e c i e s were mixed compared t o the same r a t i o of s i n g l e s p e c i e s k. v a l u e s . 60 F i g u r e 9. F i g h t r a t e s . Data from s i n g l e s p e c i e s arena exper-iments. P o i n t s : means of two r e p l i c a t e s ; v e r t i c a l l i n e s : r a n ges. c E o T O CO L 2 0 0 r 150 100 5.0± Ou Single Species Arena Experiments o P. cinctipes A P. eriomerus 4 24 Time at Start of Observation Interval (h) 4 8 CD 52 Figure 10. Mixed s p e c i e s arena experiments. R e s u l t s are from 12.0 mm males only and a f i f t y - f i f t y mixture of 12.0 mm males and females. Data from two r e p l i c a t e s f o r the s i n g l e s p e c i e s c o n t r o l s and t h r e e r e p l i c a t e s (unless otherwise i n d i c a t e d ) f o r the mixed s p e c i e s t e s t . P o i n t s : means of two r e p l i c a t e s (unless otherwise i n d i c a t e d ) ; v e r t i c a l l i n e s : ranges. 63 males and females ' males single species control mixed species test A A O- -O 60 30 ko46.2 k * 4 5 3 B cipciipes' 0 1 1 ' - J — ^ - L -E eriomerus k=27.7 k=23.5 k » 8 w 5 2 4 12 24 4 8 Time (h) 72 96 120 64 Figure 1 1 . Large vs. s m a l l crabs i n mixed s p e c i e s encounters. P o i n t s : means of two r e p l i c a t e s (unless otherwise i n d i c a t e d ) ; v e r t i c a l l i n e s : ranges. 0 1 — i — i — i i i-2 4 24 4 8 72 T ime (h) B. L a r g e P. c i n c t i pe s A l one ••••••Mixed w i t h Sma l l P. e r i o m e r u s J 1 J . '—/r—I 1 - J I : . ' D. Smal l P. c inc t ipes A l o n e M i x ed w i t h L a r g e P. e r i o m e r u s j • ' i—/f i i \ i_ i ' 1 2 4 24 48 72 Time (h) 66 Table V I I . Forced and p a s s i v e e x i t s from under the block d u r i n g the f i r s t hour of i n t r a s p e c i f i c arena experiments. These data are from males and females of the 14-17 mm s i z e c l a s s . I n i t i a l d e n s i t i e s under the block were 60 c r a b s . R e p l i c a t e i n parentheses. time i n t e r v a l f o r c e d e x i t s p a s s i v e e x i t s (min) c i n c t i p e s eriomerus c i n c t i p e s eriomerus 0-15 0(0) 7(10) 3(2) 0(1) 15-30 0 (0) 3(1) 2 (4) 1 (0) 30-45 1 (0) 4(3) 2(1) 0 (0) 45-60 1 (0) 9 (7) 2(0) 0 (0) t o t a l s 2(1) 23(21) 9(7) 1(1) R e s u l t s of f i f t y - f i f t y sex mixture experiment ( F i g . 10 and Table VIII) sugggest t h a t sex does not a f f e c t t h i s outcome: the k r a t i o (Table VIII) almost doubled. Furthermore, b i a s i n g the experiment i n f a v o r of P. eriomerus by mixing l a r g e i n d i v i d u a l s of t h i s s p e c i e s with s m a l l e r P. c i n c t i p e s ( F i g . 11), and by a l l o w i n g P. eriomerus 60 h to reach e q u i l i b r i u m before adding c i n c t i p e s (Table V I I I ) , d i d not a l t e r the outcome s i n c e t h e r e was a d i s p r o p o r t i o n a t e r e d u c t i o n i n the number of P. eriomerus. The mechanism by which P. c i n c t i p e s a c q u i r e s and maintains space under the block i n r e l a t i v e l y higher p r o p o r t i o n s i s due 67 Table V I I I . Observed k values and t h e i r . r a t i o s . With the exception of the data f or ( 14. 0-17. 0 mm males, these r a t i o s have been taken from Figs..10 and 11. Experiments i n which 14.0-17.0 ram males were used, shared a common c o n t r o l . The a b b r e v i a t i o n s sm and l g stand f o r s m a l l (11.3-12.8 mm) and l a r g e crabs (14.0-15.4 mm), r e s p e c t i v e l y . P. c i n c t i p e s eriomerus k c i n c t i p e s ^ k eriomerus 12 mm males c o n t r o l 52.5 mixed 46.2 23.5 8.5 2.23 4. 44 12 mm males & females c o n t r o l 52.0 mixed 45.3 27. 7 15.0 1. 88 3.02 14-17 mm males c o n t r o l 53.5 mixed 40.3 (both s p e c i e s added at t=0 h) mixed 34.7 ( c i n c t i p e s added a t t=60 h) 31.0 11.0 13.7 1.73 3.70 2.5 3 l g eriomerus; sm c i n c t i p e s c o n t r o l 43.2 21.8 mixed 37.1 14.0 1.98 2.65 sm eriomerus; l g c i n c t i p e s c o n t r o l 35.7 28.5 mixed 32.8 11.1 1.25 2.78 to the s u p e r i o r a b i l i t y of i n d i v i d u a l s o f t h i s s p e c i e s to defend a spacing r a d i u s . Of 104 i n t e r s p e c i f i c f i g h t s observed during 30 min i n t e r v a l s beginning at 24, 48 and 72 h, e i g h t y of 68 these (77%) were won by P. c i n c t i p e s . T h i s i s s i g n i f i c a n t l y g r e a t e r than 50% (chi-square test;p<0. 05) . D i s c u s s i o n Both P e t r o l i s t h e s s p e c i e s tend t o maintain nonrandom spacing p a t t e r n s (Table V and VI). In c o n t r a s t , P. eriomerus maintains a g r e a t e r d i s t a n c e t o nearest neighbor than does R- c i n c t i p e s ( F i g . 6). The most l i k e l y reason f o r these d i f f e r e n c e s i s t h a t P. eriomerus-winners and l o s e r s t r a v e r s e g r e a t e r d i s t a n c e s i n i n t r a s p e c i f i c encounters than P. c i n c t i p e s winners and l o s e r s ( F i g . 7 ) . Since the maintenance of i n d i v i d u a l space r e q u i r e s time and energy (Tinbergen 1957), i t i s l i k e l y t h a t the defense of an i n d i v i d u a l r a d i u s and subsequent even spacing are b e n e f i c i a l t o both P e t r o l i s t h e s s p e c i e s . The adaptive advantages which might accrue from t h i s behavior were not s t u d i e d here. C e r t a i n l y , p o r c e l a i n crabs r e q u i r e a minimum feed i n g r a d i u s i n t o which t h e i r long s e t o s e t h i r d m a x i l l i p e d s are extended ( N i c o l 1932, Wicksten 1972). T h i s became apparent when p i l i n g o c c u r r e d i n the cor n e r s of the arena and i n d i v i d u a l s on the bottom of these p i l e s were unable to feed. I t i s a l s o p o s s i b l e t h a t the maintenance of an i n d i v i d u a l spacing r a d i u s ensures the adequate passage of oxygen and food laden sea water c u r r e n t s through the boulder i n t e r s t i c e s . This c o u l d be e s p e c i a l l y important i n areas where high d e n s i t i e s of P e t r o l i s t h e s occur. 69 Both s p e c i e s demonstrate s i m i l a r , r i t u a l i z e d s pacing behavior. T h i s type of behavior could be used by P. eriomerus as an i n t e r s p e c i f i c i n t e r f e r e n c e mechanism ( M i l l e r 1967) which might e x p l a i n the absence of P. cinctip.es from the lower i n t e r -t i d a l zone. I f t h i s were the case i t would be expected t h a t P. eriomerus would be a dominant c o n t e s t a n t f o r space i n i n t e r s p e c f i c arena experiments. However, the mixed s p e c i e s arena experiments (Table VIII) show the o p p o s i t e ; without e x c e p t i o n P. c i n c t i p e s demonstrated a s u p e r i o r a b i l i t y at p r o c u r i n g and maintaining a d i s p r o p o r t i o n a t e amount of underblock space i n the arena (Table V I I I ) . In c o n c l u s i o n , i t seems very u n l i k e l y t h a t the s h a r p l y d e l i n e a t e d lower l i m i t of the higher i n t e r t i d a l s p e c i e s , P. c i n c t i p e s (Table I ) , i s caused by e x c l u s i o n from a g g r e s s i v e encounters with i t s lower zoned c o n g e n i t o r , P. eriomerus. 70 IV. RUN EXPERIMENTS I n t r o d u c t i o n L a b o r a t o r y experiments i n d i c a t e that the outcome of c o m p e t i t i o n between c l o s e l y r e l a t e d s p e c i e s i s i n f l u e n c e d by the p h y s i c a l environment (e.g. temperature, moisture) i n which the c o n t e s t takes place (Park 1962). The i n t e r t i d a l zone i s an environment i n which steep g r a d i e n t s i n p h y s i c a l f a c t o r s oc-cur over r e l a t i v e l y s h o r t d i s t a n c e s ( R i c k e t t s and C a l v i n 1968). One purpose of the run experiments was t o determine the e f f e c t s of c o m p e t i t i v e i n t e r a c t i o n s on the v e r t i c a l d i s t r i b u t i o n s of both P e t r o l i s t h e s s p e c i e s i n an experimental s e t t i n g which o f f e r e d a more n a t u r a l environment than t h a t of the arena. The second purpose of the run experiments was to determine whether the observed v e r t i c a l d i s t r i b u t i o n s of both P e t r o l i s t h e s p o p u l a t i o n s were caused by h a b i t a t s e l e c t i o n . For example, when a p h y s i c a l f a c t o r (s) i s provided over a continuous range, m o t i l e s p e c i e s may segregate a c c o r d i n g to t h e i r p r e f e r e n c e s f o r d i f f e r e n t l o c a t i o n s along the g r a d i e n t ( s ) (King and Dawson 1973). Nyblade (1975) observed t h a t s i x s p e c i e s of i n t e r t i d a l hermit crabs i n h a b i t e d t h r e e d i f f e r e n t v e r t i c a l ranges, two i n the high i n t e r t i d a l , one i n the m i d - i n t e r t i d a l and t h r e e i n the low i n t e r t i d a l zone. A f t e r removing the middle dominant s p e c i e s , n e i t h e r the higher nor the lower p o p u l a t i o n s expanded t h e i r v e r t i c a l ranges. He a l s o observed t h a t l a r v a l r e c r u i t m e n t o c c u r r e d over the v e r t i c a l 71 ranges of the c o n s p e c i f i c a d u l t zones. Nyblade i n t e r p r e t e d t h i s r e c r u i t m e n t p a t t e r n as g e n e t i c a l l y f i x e d h a b i t a t s e l e c t i o n . He s p e c u l a t e d t h a t c o m p e t i t i o n i n the past has l e d these s p e c i e s toward g r e a t e r niche s p e c i a l i z a t i o n and t h a t resource' p a r t i t i o n i n g ( h a b i t a t s e l e c t i o n i n t h i s case) has l e d to c o e x i s t e n c e of these i n t e r t i d a l s p e c i e s . A s p e c i e s removal experiment l i k e the one Nyblade d i d , would be i m p r a c t i c a l f o r the two s p e c i e s I s t u d i e d . The reason f o r t h i s i s t h a t P e t r o l i s t h e s occur under rocks and are extremely a g i l e ( E i c k e t t s and C a l v i n 1968, Molenock 1975) . The t h r e e dimensional aspect of the b o u l d e r s a t the Diana I s l a n d s i t e would have made the removal and sampling of both s p e c i e s d e s t r u c t i v e and d i f f i c u l t . Instead I chose to examine the v e r t i c a l d i s t r i b u t i o n s of experimental p o p u l a t i o n s i n long e n c l o s u r e s (runs) . M a t e r i a l s and Methods -Run experiments were conducted dur i n g the summers of 1976 and 1977. Because of d i f f e r e n c e s i n the design of exper-i m e n t a l apparatus between the two years, I w i l l d e s c r i b e them s e p a r a t e l y . 72 19 76 Experiments Run C o n s t r u c t i o n These runs had o v e r a l l dimensions of 1.50 x 0.29 x 0.11 m and were c o n s t r u c t e d by f a s t e n i n g together s e c t i o n s cut from the bottoms of p l a s t i c h e r r i n g row baskets ( d e s c r i b e d i n Chapter I) with s t a i n l e s s s t e e l b o l t s . Walls of the runs had p e r f o r a t i o n s which measured 7.0 x 8.0 mm and were about 30% opening. A s i n g l e l a y e r of rocks was p l a c e d i n t o each run. Rocks were c o l l e c t e d from the i n t e r t i d a l zone near the Diana I s l a n d s i t e from a v e r t i c a l range which was the same as t h a t occupied by the runs. I S i S i i i d a l P o s i t i o n of the Enclosures-Three runs were p o s i t i o n e d p a r a l l e l t o each other at a d i s t a n c e of approximately one meter apart and p e r p e n d i c u l a r t o the shore. The lowest ends were at 0.4 m above datum, th e highest ends were at 0.7 m above datum. One of the t h r e e runs was a mixed s p e c i e s t e s t , the other two were s i n g l e s p e c i e s c o n t r o l s . 73 Experimental Animals Crabs were c o l l e c t e d , without regard t o sex, from w i t h i n a v e r t i c a l range approximately the same as t h a t occupied by the runs. Crabs s m a l l e r than 10 mm maximum carapace width were not used i n order to reduce the chance of escape through the p e r f o r a t i o n s i n the run w a l l s . Experimental Procedure The s i n g l e s p e c i e s runs c o n t a i n e d egual numbers of e i t h e r s p e c i e s . The mixed s p e c i e s run contained e g u a l numbers of both s p e c i e s , such t h a t t h e i r sum was equal t o the number i n e i t h e r o f the s i n g l e s p e c i e s runs. The number of experimental animals v a r i e d from 60 t o 72 crabs per run. R e p l i c a t e s were s t a r t e d d u r i n g the lower low water of s p r i n g t i d e s by p l a c i n g crabs i n t o p l a s t i c dishpans and randomly a s s i g n i n g each t o a run by b l i n d l y grabbing i n d i v i d a l s from a dishpan. Crabs were p l a c e d i n t o a run at i t s c e n t e r . The covers were secured and the runs l e f t u n d i s t u r b e d , u s u a l l y u n t i l the next s p r i n g t i d e ( d u ration between r e p l i c a t e s shown on F i g s . 13 and 15). E i g h t r e p l i c a t e s were obtained d u r i n g the summer of 1976. Crabs remaining i n the runs at the completion of a r e p l i c a t e were reused ( a f t e r random reassiqnment) i n the next r e p l i c a t e . Losses which oc c u r r e d from unkown reasons were made up by c o l l e c t i n q a d d i t i o n a l crabs in from the f i e l d . No b i a s i n the p r o p o r t i o n s of e i t h e r s p e c i e s l o s t during e i t h e r year was apparent ( s i g n t e s t , p>0.2). Counting Counting was accomplished by removing rocks from each t i o n , one s e c t i o n a t a time, s t a r t i n g from the lowest end run and working towards the h i g h e s t . Crabs obtained from s e c t i o n were i d e n t i f i e d to s p e c i e s and counted. 1977 Experiments Run C o n s t r u c t i o n Run dimensions were 3-66 x 0.135 x 0.105 m. A wood frame, most of which was c o n s t r u c t e d of 19 x 13 mm sto c k , supported a f l o o r made from s e c t i o n s of p l a s t i c h e r r i n g roe basket bottoms. The s i d e s and the cover were 10 mm nylon f i s h net s t a p l e d t o the frame. I n t e r t i d a l P o s i t i o n of the E n c l o s u r e s These runs were placed at the Diana I s l a n d s i t e and span-ned an i n t e r t i d a l range from +0.1 to +0.9 m. 75 Experimental Procedure There were 72 crabs i n each run i n each r e p l i c a t e . Nine r e p l i c a t e s were ob t a i n e d . Euns i n s i x of the nine r e p l i c a t e s ( F i g s . 14,A-E,G and 16,A-E, G) contained a s i n g l e row of contiguous r o c k s over the e n t i r e l e n g t h of the run. There were 4-5 rocks per s e c t i o n . The other t h r e e r e p l i c a t e s ( F i g s . 14,F,H,I and 16,F rH,I) had two rocks per counting sec-t i o n . I determined that a rock p a i r had approximately 300 cm 2 of s u r f a c e area which was u t i l i z a b l e by the crabs- Counts of crabs under these rock p a i r s showed t h a t d e n s i t i e s were s i m i l a r to those which occurred on the bottom of the arena block (arena:0.02-0.04 cr a b s per cm 2, 12.0 mm maximum carapace width; rock p a i r s : 0.00-0.04 crabs per cm 2). The time between r e p l i c a t e s v a r i e d from 2 t o 56 days ( F i g s . 14 and 16). Counting Counting procedure was s i m i l a r to the 1976 experiments except t h a t t h e r e were nine equal l e n g t h s e c t i o n s . S t a t i s t i c a l Analyses S i n g l e s p e c i e s d i s t r i b u t i o n s are expressed as the percentage 76 number of crabs i n the i t h s e c t i o n X 100. Number of s p e c i e s A i n the run Mixed s p e c i e s d i s t r i b u t i o n s are expressed as the percentage number of species_A i n - t h e i t h s e c t i o n X 100. Number of s p e c i e s A i n the run To dete c t d i f f e r e n c e s between s i n g l e and mixed s p e c i e s runs, p r o p o r t i o n s i n each s e c t i o n were subjected t o the a r c s i n e t r a n s f o r m a t i o n and then analyzed by the p a i r e d comparison t e s t (randomized b l o c k s with two t r e a t m e n t s ) . Mixed and s i n g l e s p e c i e s runs were the treatment e f f e c t s f o r a s p e c i e s and blocks were a count s e c t i o n taken 'over the t o t a l number of r e p l i c a t e s (eight:1976, nine:1977). Depth-abundance r e l a t i o n s h i p s f o r each s p e c i e s were t e s t e d f o r by the Spearman rank c o r r e l a t i o n c o e f f i c i e n t method ( S i e g e l 1956), which w i l l be designated as r . T i d a l Experiments During the course of the run experiments i t became apparent t h a t P. eriomerus- had a st r o n g preference f o r lower p o r t i o n s of the runs (discussed below). A n a l y s i s of t i d a l s t r i p c h a r t r e c o r d i n g s from the Bamfield t i d e gauge s t a t i o n 77 (Table X) suggested a sharp i n c r e a s e between +0.6 and +0.9 m i n one of the t i d a l parameters s t u d i e d (exposure frequency; see r e s u l t s ) . I hypothesized that t h i s sharp i n c r e a s e might be used by P. eriomerus to determine when t o make compensatory movements towards lower i n t e r t i d a l l e v e l s , p o s s i b l y e x p l a i n i n g what maintains p o p u l a t i o n s of t h i s s p e c i e s i n the lowest p o r t i o n s of the i n t e r t i d a l zone (Table I ) . To t e s t the e f f e c t of fre q u e n t s h o r t d u r a t i o n exposure on the v e r t i c a l d i s t r i b u t i o n of P. eriomerus, crabs were s u b j e c t e d to l a b o r a t o r y t i d a l tank experiments. Two t i d a l tanks ( F i g . 12) were placed behind a screen of heavy black p l a s t i c t a r p . Observations were made through two holes c u t i n t o the t a r p i n f r o n t of each tank. O n f i l t e r e d seawater pumped from 2 m below sea l e v e l flowed c o n t i n u a l l y through the two s e c t i o n s of each tank at a r a t e of about 3.0 1/m/section. Crabs were randomly assigned t o the tanks. There were f i f t e e n males and f i f t e e n females of one species i n each o f the two tank compartments. Maximum carapace widths ranged from 12 t o 14 mm. A c o i n f l i p at the s t a r t of each r e p l i c a t e decided which one of the two tanks was to serve as t e s t and c o n t r o l . Crabs were l e f t undisturbed i n the tanks a t l e a s t 24 h before s t a r t i n g the experiments. Experimental procedure c o n s i s t e d of f i r s t c ounting the crabs i n the upper h a l f of each compartment. A l i n e drawn with wax grease p e n c i l on the outer s u r f a c e of the tanks d i v i d e d them i n t o h a l v e s . A few minutes l a t e r the t e s t tank 78 F i g u r e 1 2 . Diagram o f one o f t h e t i d a l t a n k s . Dimensions are i n c e n t i m e t e r s . 79 Drain Hose 80 was d r a i n e d . D r a i n i n g s t a r t e d a t 0900 h on each day. P r i o r o b s e r v a t i o n s showed t h a t d r a i n i n g too f a s t caused some crabs t o s c u r r y . By d r a i n i n g the tank over a 5 min p e r i o d , I c o u l d d e t e c t no responses of crabs to the r e c e d i n g water l i n e . Water l e v e l was kept a t the h a l f way mark f o r 1 h a f t e r d r a i n i n g , at which time the tank was r e f i l l e d over a 5 min p e r i o d . Three r e p l i c a t e s were conducted, each with a d u r a t i o n of f o u r days. R e s u l t s E f f e c t s of Mixing on P. cintip.es R e s u l t s of the 1976 run experiments show t h a t fewer P. c i n c t i p e s occurred i n the lowest s e c t i o n (four) of the mixed s p e c i e s run (mean d i f f e r e n c e = 14%, p<0.05; F i g . 13 and Table I X ) . A s i m i l a r t r e n d occurred i n 1977. When a l l nine r e p l i c a t e s are con s i d e r e d ( F i g . 14 and Table I X ) , there are no s i g n i f i c a n t d i f f e r e n c e s (p>0.05) between mixed s p e c i e s and s i n g l e s p e c i e s percentages f o r any of the nine s e c t i o n s . However, when s e c t i o n s are pooled i n such a way as t o d i v i d e the run l e n g t h i n t o t h i r d s , there i s an o v e r a l l i n c r e a s e of 9% (p<0.05) of P. c i n c t i p e s i n the h i g h e s t t h i r d of the t e s t run (Table IX) . Reducing the number of rocks t o two per s e c t i o n caused no apparent d i f f e r e n c e s i n d i s t r i b u t i o n s between r e p l i c a t e s . ure 13. V e r t i c a l d i s t r i b u t i o n of P. c i n c t i p e s i n the runs i n 1976 the h i g h e s t end of the run i s represented by s e c t i o n one and the lowest by s e c t i o n f o u r . Dotted l i n e s r e present d i s t r i b u t i o n s i n the mixed s p e c i e s runs, s o l i d l i n e s r e p r e s e n t s i n g l e s p e c i e s d i s t r i b u t i o n s . Duration of each r e p l i c a t e (days) i s shown on the i n d i v i d u a l graphs. 83 F i g u r e 14. V e r t i c a l d i s t r i b u t i o n of P. c i n c t i p e s i n the runs i n 1977 the highest end of the run i s represented by s e c t i o n one and the lowest by s e c t i o n n i n e . Dotted l i n e s r e present d i s t r i b u t i o n s i n the mixed s p e c i e s runs, s o l i d l i n e s r e p r e s e n t s i n g l e s p e c i e s d i s t r i b u t i o n s . Duration of each r e p l i c a t e (days) i s shown on the i n d i v i d u a l graphs. Frequency (%) 85 Table IX. Pooled mean percentages (unblocked data) of crabs i n each s e c t i o n of s i n g l e and mixed s p e c i e s runs. There were e i g h t r e p l i c a t e s i n 1976 and nine r e p l i c a t e s i n 1977 sectxon P. c i n c t i p e s alone mixed P. eriomerus alone mixed +0.7 m 1976 +0.4 1 2 3 4 22 24 16 37 15 31 30 23 9 18 33 41 4 15 31 50 + 0.9 1977 + 0. 1 1 2 3 4 5 6 7 8 9 19 7 8 12 12 10 6 8 17 20 11 12 14 7 5 6 10 15 2 5 6 9 10 14 10 16 27 0 2 8 9 10 13 11 15 33 T h i s i s apparent when comparing F i g . 14,F,H,I which had two rocks per s e c t i o n a g a i n s t the r e s u l t s of a l l other r e p l i c a t e s (4-5 r o c k s per s e c t i o n , F i g . 14,A-E,G). Pref e r e n c e f o r V e r t i c a l L o c a t i o n by_ P. c i n c t i p e s P e t r o l i s t h e s c i n c t i p e s demonstrated l i t t l e or no pre f e r e n c e f o r i n t e r t i d a l depth. From a t o t a l of 34 Spearman rank c o r r e l a t i o n c o e f f i c i e n t s (8+9 s i n g l e and 8+9 mixed s p e c i e s r u n s ) , t h r e e were s i g n i f i c a n t . One of the three c o e f f i c i e n t s 86 was c a l c u l a t e d f o r a s i n g l e s p e c i e s run i n 1976 ( F i g . 13, mid-d l e of the top row; r = +1.00). The other two were c a l c u l a t e d from the 1977 data, one was a s i n g l e s p e c i e s run ( F i g . 14,E; r = +0.630) and the other i n a mixed s p e c i e s run ( F i g . 14,H; r = -0.661). The c o e f f i c i e n t r was not s i g n i f i c a n t l y d i f f e r e n t from zero i n a l l other r e p l i c a t e s . C l e a r l y , r e s u l t s of these experiments ( F i g . 13, 14 and Table IX) provide no evidence to support the h y p o t h e s i s that t h i s s p e c i e s has a p r e f e r e n c e f o r higher i n t e r t i d a l p o s i t i o n s . The abundance-depth curves ( F i g s . 13 and 14) show t h a t P. c i n c t i p e s had a uniform d i s t r i b u t i o n over the l e n g t h s of the runs. E f f e c t s of Mixing on P. eriomerus The p a i r e d comparisons t e s t showed t h a t i n 1976 and i n 1977 t h e r e were s l i g h t decreases i n the number of P,. eriomerus i n the highest p o r t i o n s o f the mixed s p e c i e s r e p l i c a t e s ( F i g s . 15 and 16). In 1976 t h e r e were, on the average, 5% fewer P. eriomerus i n s e c t i o n one (p<0.05), and 2% and 3% fewer i n s e c t i o n s one and two i n 1977 (p<0.05. Table I X ) . A l l other comparisons were not s i g n i f i c a n t . Reducing the number of rocks t o two per s e c t i o n caused no apparent d i f f e r e n c e between mixed and s i n g l e s p e c i e s d i s t r i b u -t i o n s ( F i g . 16 F,H,I) compared to a l l other r e p l i c a t e s (4-5 r o c k s per s e c t i o n , F i g . 16A-E,G). 87 F i g u r e 15- V e r t i c a l d i s t r i b u t i o n of P. eriomerus i n the runs i n 1976 the highest end of the run i s represented by s e c t i o n one and the lowest by s e c t i o n f o u r . Dotted l i n e s r e present d i s t r i b u t i o n s i n the mixed s p e c i e s runs, s o l i d l i n e s r e p r e s e n t s i n g l e s p e c i e s d i s t r i b u t i o n s . Duration of each r e p l i c a t e (days) i s shown on the i n d i v i d u a l graphs. 89 F i g u r e 16. V e r t i c a l d i s t r i b u t i o n of P. eriomerus- i n the runs i n 1977. The h i g h e s t end of the run i s represented by s e c t i o n one and the lowest by s e c t i o n nine. Dotted l i n e s r e present d i s t r i b u t i o n s i n the mixed s p e c i e s runs, s o l i d l i n e s r e p r e s e n t s i n g l e s p e c i e s d i s t r i b u t i o n s . Duration of each r e p l i c a t e (days) i s shown on the i n d i v i d u a l graphs. 90 o o o o o o o o o ao 'q- co "T • . • oo T ( ° / 0 ) / f o u a n b ' s j j 91 Preference f o r V e r t i c a l l o c a t i o n by P. eriomerus In c o n t r a s t to P. c i n c t i p e s P . eriomerus-demonstrated a strong p r e f e r e n c e f o r lower p o r t i o n s of mixed and s i n g l e s p e c i e s runs. T h i s i s apparent from the nJ"-shaped abundance curves i n F i g s . 15 and 16 as w e l l as by twenty-three s i g -n i f i c a n t Spearman c o r r e l a t i o n c o e f f i c i e n t s ( a l l p o s i t i v e ; 1976:three s i n g l e and f i v e mixed s p e c i e s runs, p<0.05; 1977:seven s i n g l e and e i g h t mixed s p e c i e s runs, p<0.05). T i d a l Experiments R e s u l t s of the t i d a l experiment ( F i g . 17) suggest t h a t 1 h exposure per day caused P. eriomerus to move i n t o the lower h a l f o f the t i d a l tank. C o n t r o l and t e s t curves showed s i m i l a r i n c r e a s e s d u r i n g the f i r s t day. A f t e r the f i r s t day, the P. eriomerus t e s t curves s t e a d i l y dropped ( F i g . 17). By the f o u r t h day t h e r e was no o v e r l a p of the ranges f o r the t h r e e r e p l i c a t e s . These r e s u l t s ( F i g . 17) suggest that P. eriomerus u t i l i z e s exposure frequency as an environmental c l u e to determine when compensatory movement i s r e q u i r e d to decrease i t s i n t e r t i d a l h e i g h t . Table X i s a summary of t i d a l exposure ranges and f r e g u e n c i e s which occurred between 1 June 1977 and 30 September 1977. Other t i d a l parameters were examined f o r the +1.2, +0.9, +0.6 and +0.3 m l e v e l s (e.g. t o t a l p r o p o r t i o n of time ure 1 7 . Crabs i n the upper h a l f of the were a t o t a l of t h i r t y c r a b s i n each bars are ranges of three r e p l i c a t e s , means. t i d a l tank. There treatment. V e r t i c a l p o i n t s are the 2 0 R cinctipes cu X <D Q. CL o 1 5 t 10 o ' control / — -T ime (d) 94 Table X. Some t i d a l s t a t i s t i c s , these were obtained from s t r i p c h a r t r e c o r d i n g s made at the Bamfield t i d e gauge s t a t i o n between 1 June 1977 and 30 September 1977 (122 d ) . The number of exposures per day ranged from zero t o two. m above exposure t o t a l number datum range (h) of exposures 1.2 5.8 - 0.5 131 0.9 4.9 - 0.5 106 0.6 4.0 - 0.5 42 0.3 3.2 - 1.2 14 exposed and maximum number of d a i l y exposures) . Of a l l the parameters examined, exposure freguency between +0.6 and +0.9 m showed the sharpest i n c r e a s e . Over a 122 d p e r i o d t h e r e were 42 exposures at +0.6 m and 106 exposures at +0.9 m (Table X). Thi s sharp i n c r e a s e i n exposure freguency between these two l e v e l s and the r e d u c t i o n of P. eriomerus i n the upper h a l f of the t e s t t i d a l tank ( F i g . 17) suggest t h a t exposure freguency i s an environmental c l u e used by t h i s s p e c i e s to make compensatory movements towards lower i n t e r t i d a l l e v e l s . In c o n t r a s t to P. eriomerus, P. c i n c t i p e s demonstrated no response t o d a i l y exposure ( F i g . 17). 95 D i s c u s s i o n The run experiments show t h a t P. c i n c t i p e s tended to i n h a b i t higher p o r t i o n s of the e n c l o s u r e s when mixed with P. eriomerus (Figs..13 and 14). However, the magnitude of t h i s displacement was s m a l l : 1455 fewer (p<0.05) P. c i n c t i p e s i n the lowest s e c t i o n of the 1976 e n c l o s u r e s and 9% more (p<0.05) £• c i n c t i p e s i n the upper o n e - t h i r d of the 1977 e n c l o s u r e s . These data a l s o show t h a t P. c i n c t i p e s - demonstrated an approximately e g u a l chance of o c c u r r i n g i n any one s e c t i o n of the mixed s p e c i e s e n c l o s u r e s , i n c l u d i n g the lowest, where P. eriomerus always demonstrated i t s highest d e n s i t i e s . I t i s u n l i k e l y t h a t i n t e r a c t i o n s with P. eriomerus determine the lower l i m i t of the P. c i n c t i p e s p o p u l a t i o n . In a d d i t i o n , the uniform d i s t r i b u t i o n of P. c i n c t i p e s i n s i n g l e and mixed s p e c i e s e n c l o s u r e s suggests t h a t t h i s s p e c i e s has no p r e f e r e n c e f o r higher areas i n the i n t e r t i d a l zone. When mixed with P. c i n c t i p e s , P. eriomerus s h i f t e d t o lower p o r t i o n s of the mixed s p e c i e s e n c l o s u r e s compared to i t s d i s t r i b u t i o n s i n s i n g l e s p e c i e s c o n t r o l runs. The magnitude of t h i s s h i f t was s m a l l , but s t a t i s t i c a l l y s i g n i f i c a n t (p<0.05) and was l e s s than or egual to 5% fewer P. eriomerus i n the highest s e c t i o n s of the 1976 and 1977 runs.. In c o n t r a s t t o P. c i n c t i p e s , P. eriomerus demonstrated a preference f o r lower i n t e r t i d a l r e g i o n s (Figs 15 and 16). I t i s l i k e l y t h a t P. eriomerus uses t i d a l exposure frequency t o determine when t o 96 move downward (Fig,. 17 and Table X). In c o n c l u s i o n , the presence of P. eriomerus-had a s m a l l , but s t a t i s t i c a l l y s i g n i f i c a n t e f f e c t on the v e r t i c a l d i s t r i b u t i o n of the higher s p e c i e s , P. c i n c t i p e s . Although fewer P. c i n c t i p e s occurred i n the lower p o r t i o n of the mixed s p e c i e s run, there are no tren d s i n data which suggest t h a t £• eriomerus s e t s the lower l i m i t of P. c i n c t i p e s . A l s o , s p a t i a l d i s t r i b u t i o n s demonstrated by P. c i n c t i p e s i n s i n g l e and mixed s p e c i e s runs suggest no p r e f e r e n c e by t h i s s p e c i e s f o r higher i n t e r t i d a l l e v e l s . In comparison, P, c i n c t i p e s - h a d a small, but s t a t i s t i c a l l y s i g n i f i c a n t (p<0.05) e f f e c t on the v e r t i c a l d i s t r i b u t i o n of P. eriomerus; mixing with P. c i n c t i p e s reduced the p r o p o r t i o n of P. eriomerus i n the highest p a r t s of the mixed s p e c i e s runs r e l a t i v e t o the s i n g l e s p e c i e s P- eriomerus c o n t r o l d i s t r i b u t i o n . In c o n t r a s t t o P. c i n c t i p e s , P. eriomerus demonstrated a strong preference f o r the lowest p o r t i o n s of the i n t e r t i d a l zone. 97 GENERAL DISCUSSION Density and V e r t i c a l D i s t r i b u t i o n of the-P. eriomerus PQ£JJ l a t i on The run experiments (summarized i n F i g . 18) show that behavior determines the position of the upper l i m i t of the P. eriomerus population in the i n t e r t i d a l zone. Petrolisthes eriomerus has a strong preference for the low i n t e r t i d a l zone. Furthermore, the v e r t i c a l d i s t r i b u t i o n of the experimental pop-ulation i n the runs i n 1977 i s si m i l a r to that of the natural population estimated from trap data (Fig. 18). The adaptive importance of avoiding the higher i n t e r t i d a l zone i s that i t maintains P. eriomerus below i n t e r t i d a l l e v e l s which were found to be s t r e s s f u l or l e t h a l to t h i s species (Fig. 4) . The upper l i m i t of the P. eriomerus population varied l i t t l e during the course of th i s study. The mean position of t h i s l i m i t was approximately +0.8 m (Table I ) , with ind i v i d u a l s ranging up to +0.9 m. Results of the transplant experiments c l e a r l y show that t h i s species i s unable to survive at i n t e r t i d a l heights as l i t t l e as 0.3 m above the +0.9 m tide l e v e l (Fig. 4). I t seems unlikely that the upper portion of the P. eriomerus population would be subjected to catastrophic mor t a l i t i e s when warm weather, calm seas and spring tides coincide as has been suggested for barnacle populations (Connell 1961a, Foster 1971a). Unlike barnacles, however, 98 F i g u r e 18. Summary of the d i s t r i b u t i o n s of crabs i n the t r a p s and runs. P o i n t s r e p r e s e n t the mean frequency of crabs at each l e v e l f o r a l l r e p l i c a t e s . Dotted l i n e s r e p r e s e n t the mean frequency of P. c i n c t i p e s which entered a t each of the f o u r t r a p l e v e l s i n 1975 and 1977. Dashed l i n e s r e present the mean frequency of P. eriomerus which entered at each of the f o u r t r a p l e v e l s i n 1975 and 1977. S o l i d l i n e s r e p r e s e n t the mean freguency of P. eriomerus i n the the combined s i n g l e and mixed s p e c i e s runs i n 1976 and 1977. The run d i s t r i b u t i o n s of P. c i n c t i p e s - a r e not shown here, but the 1975 and 1977 curves would be aproximately h o r i z o n t a l and have Y - i n t e r c e p t s a t about 25% and 10% r e s p e c t i v e l y (see Table IX). Position of Run Sect ions Depth (Meters above Datum) CD 100 p o r c e l a i n crabs a r e h i g h l y m o t i l e and possess r e l a t i v e l y advanced sensory systems. More i m p o r t a n t l y , P e t r o l i s t h e s demonstrated i n c e s s a n t e x p l o r a t o r y behavior (Molenock 1972, personal o b s e r v a t i o n from arena experiments). The a d a p t i v e importance of e x p l o r a t o r y behavior, however, i s unknown. The f a c t t h a t i n d i v i d u a l s of both s p e c i e s r e a d i l y invade newly a v a i l a b l e s u b s t r a t a ( F i g . .2 and Table II) , suggests t h a t e x p l o r a t o r y behavior occurs i n nature. I f we assume t h a t e x p l o r a t i o n d u r i n g p e r i o d s of submergence places i n d i v i d u a l s of P. eriomerus at l e v e l s which are l e t h a l when exposed ( e s p e c i a l l y during s p r i n g t i d e s ) , i t would seem reasonable to p o s t u l a t e s e l e c t i o n f o r an a b i l i t y to assess i n t e r t i d a l h e i g h t . V e r t i c a l p o s i t i o n i s determined by the i n d i v i d u a l d e t e c t i n g a n o n s t r e s s f u l environmental c l u e . One such c l u e , t i d a l exposure frequency, showed a marked i n c r e a s e i n frequency below the upper l i m i t of the P. eriomerus p o p u l a t i o n (Table X). Results of t i d a l tank experiments suggest t h a t P. eriomerus respond t o f r e q u e n t , short d u r a t i o n exposures by moving down i n t o areas which were not exposed (Fig,. .17). I d i d not examine other t i d a l parameters and i t i s p o s s i b l e t h a t exposure frequency i s not the only one i n v o l v e d . I b e l i e v e t h a t the upper l i m i t of the P. eriomerus p o p u l a t i o n i s the r e s u l t of a dynamic e q u i l i b r i u m between the a b i l i t y of i n d i v i d u a l s to determine when they have wandered to p o t e n t i a l l y s t r e s s f u l or l e t h a l l e v e l s , and t o compensate by movinq t o lower i n t e r t i d a l l e v e l s . The run experiments ( F i g s . 15, 16 and 18) showed the e f f e c t of compensation a f t e r the e q u i l i b r i u m was perturbed. 101 Some limpet s p e c i e s demonstrate responses to p h y s i c a l f a c t o r s which are s i m i l a r t o those demonstrated by P. eriomerus. For example, numerous p o p u l a t i o n s of l i m p e t s have been shown to expand t h e i r ranges when c o o l , moist winter weather p e r m i t t e d , r e t r e a t i n g t o lower l e v e l s during hot dry summer months (Lewis 1954, Frank 1965, Breen 1972, Branch 1975, 1976). However, pa r t of the summer po p u l a t i o n s h i f t of li m p e t s t o lower i n t e r t i d a l areas was caused by death from d e s i c c a t i o n . U n l i k e limpet p o p u l a t i o n s , my o b s e r v a t i o n s s t r o n g l y suggest t h a t the upper l i m i t of the P. eriomerus p o p u l a t i o n i s tem p o r a l l y s t a b l e (Table I ) . I conclude t h a t t h i s s t a b i l i t y i s due, i n l a r g e p a r t , to the f a c t t h a t both s p e c i e s are f i l t e r f e e d e r s , which means t h a t f o r a g i n g e x c u r s i o n s are probably unnecessary as compared t o a scavenging brachyuran crab (e.g. Cancer productus) or some lim p e t p o p u l a t i o n s which move i n t o more f a v o r a b l e g r a z i n g areas when seasonal c o n d i t i o n s permit (Frank 1965, Branch 1975, 1976). Small j u v e n i l e s of P. eriomerus were found only below +0.6 m, suggesting t h a t they s e t t l e from the plankton i n the lowest p o r t i o n s of the i n t e r t i d a l zone ( F i g , 3). However, i t i s d i f f i c u l t t o use s i t e - s p e c i f i c s ettlement as an s u f f i c i e n t e x p l a n a t i o n of the upper l i m i t of the P. eriomerus p o p u l a t i o n . The reason f o r t h i s i s t h a t megalopa may e i t h e r be s p e c i f i c f o r the i n t e r t i d a l range i n t o which they s e t t l e , or they may s e t t l e w i t h i n higher i n t e r t i d a l ranges and move t o lower l e v e l s w i t h i n 102 a short time p e r i o d , or they are k i l l e d by harsh p h y s i c a l f a c t o r s i n h i g h e r areas. In any event the l a t t e r two p o s s i b i l i t i e s would have had to occur w i t h i n the 2 wk i n t e r v a l s between o b s e r v a t i o n s i n 1975 ( F i g . 3). A l s o , s i t e - s p e c i f i c s e ttlement f a i l s to e x p l a i n what keeps the h i g h l y mobile a d u l t P..eriomerus below 0.9 m above datum. R e s u l t s of the arena experiments (Table VIII) showed t h a t £* c i n c t i p e s i s a dominant competitor f o r space, s u g g e s t i n g t h a t lower d e n s i t i e s of P. eriomerus i n the h i g h e r p o r t i o n of the mixed s p e c i e s e n c l o s u r e s were caused by i n t e r f e r e n c e from P, c i n c t i p e s (Table IX and F i g s . 15 and 16). However, as pointed out i n the d i s c u s s i o n of Chapter IV, the magnitude of t h i s s h i f t was s m a l l (Table I X ) , suggesting t h a t c o m p e t i t i o n with P. c i n c t i p e s has a minor r o l e i n i n f l u e n c i n g the abundance of the P. eriomerus p o p u l a t i o n over i t s v e r t i c a l d i s t r i b u t i o n compared to t h i s s p e c i e s p r e f e r e n c e f o r low i n t e r t i d a l r e g i o n s . The p r e v a l i n g i d e a t h a t upper l i m i t s of marine i n t e r t i d a l p o p u l a t i o n s are caused d i r e c t l y by p h y s i c a l f a c t o r s (Connell 1972) has l a r g e l y been derived from s t u d i e s conducted on s e s s i l e i n v e r t e b r a t e s p e c i e s . P h y s i c a l f a c t o r s and, to a l e s s e r e x t e n t , b i o t i c i n t e r a c t i o n s with P. c i n c t i p e s , are probably the u l t i m a t e f a c t o r s which determine the upper l i m i t of the P. eriomerus p o p u l a t i o n . But, the proximate cause of the upper l i m i t of the P. eriomerus p o p u l a t i o n i s a b e h a v i o r a l response t o an i n c r e a s i n g l y harsh environment with i n c r e a s i n g i n t e r t i d a l h e i g h t . By t h i s process of h a b i t a t s e l e c t i o n , 103 P. eriomerus avoids d i r e c t l i m i t a t i o n by p h y s i c a l f a c t o r s at i t s upper i n t e r t i d a l l i m i t . The Lower L i m i t of the P. c i n c t i p e s P o p u l a t i o n The t r a n s p l a n t data c l e a r l y show t h a t P. c i n c t i p e s i s able to s u r v i v e and reproduce below the lower l i m i t of the Diana I s l a n d s i t e d i s t r i b u t i o n ( F i g . 4 and Table I V ) . These data agree with those of other s t u d i e s which have shown t h a t p h y s i c a l f a c t o r s do not prevent i n t e r t i d a l s p e c i e s from l i v i n g below the lower d i s t r i b u t i o n a l l i m i t (Barnes and Powell 1953, C o n n e l l 1961b, 1972, Paine 1974, Suchanek 1978). Since the e a r l y 1960s (Connell 1961a,b), a g r e a t d e a l of evidence has accumulated which suggests t h a t lower l i m i t s are caused by b i o t i c s t r e s s e s , t y p i c a l l y c o mpetition or p r e d a t i o n . P e t r o l i s t h e s eriomerus d i s p l a c e d some P. c i n c t i p e s from the low i n t e r t i d a l zone (Figs 13, 14 and Table I X ) . However, the magnitude of t h i s s h i f t was very s m a l l and i t , t h e r e f o r e , seems u n l i k e l y t h a t P. eriomerus i s a b l e to c o m p e t i t i v e l y exclude P. c i n c t i p e s from l e v e l s below +0.6 m (Table I ) . Recently s e t t l e d P. c i n c t i p e s - were found only w i t h i n the range of the c o n s p e c i f i c a d u l t p o p u l a t i o n . I t i s d i f f i c u l t , however, to use s i t e - s p e c i f i c settlement as a s u f f i c i e n t e x p l a n a n t i o n o f the lower l i m i t of the P. c i n c t i p e s p o p u l a t i o n (Table I).. The reason f o r t h i s i s t h a t t h a t s i t e - s p e c i f i c s e ttlement f a i l s t o e x p l a i n what l i m i t s the h i g h l y mobile a d u l t 104 R- c i n c t i p e s t o l e v e l s above 0.6 m above datum even though they are able t o l i v e w e l l below t h i s h e i g h t (Fig.. .4). In c o n c l u s i o n , p h y s i c a l f a c t o r s do not seem to prevent R- c i n c t i p e s from i n h a b i t i n g the lowest areas of the i n t e r t i d a l zone. Some co m p e t i t i o n with P-. eriomerus may d i s p l a c e a few P. c i n c t i p e s from the low i n t e r t i d a l zone, but, the magnitude of t h i s displacement was s m a l l and there were no i n d i c a t i o n s t h a t i t caused z o n a t i o n . I t i s u n l i k e l y that P. c i n c t i p e s has a b e h a v i o r a l preference f o r h i g h e r i n t e r t i d a l r e g i o n s , even though the p o p u l a t i o n d e n s i t y was g r e a t e s t above the upper l i m i t of the P. eriomerus p o p u l a t i o n ( F i g . 18). I f b i o t i c f a c t o r s were r e s p o n s i b l e f o r s e t t i n g lower l i m i t o f the R- c i n c t i p e s p o p u l a t i o n , they were not apparent d u r i n g the course o f t h i s study. 105 REFERENCES CITED Barnes, H and H.T Powell. 1953. The growth of Balanus-b a l a n o i d e s (L.) and B. cr e n a t u s Brug. under v a r y i n g c o n d i t i o n s of submergence. J . Mar. b i o l . ass. O.K. 32: 107-128. B i r c h , L.C. 1957. The meanings of competition. . Amer. . Nat. 9.1:5-18. Bock, C E . and R.E. Johnson. 1967. The r o l e of behavior i n determining the i n t e r t i d a l z o n a t i o n of L i t t o r i n a p l a n a x i s P h i l i p p i , 1847 and L i t t o r i n a s c u t u l a t a Gould, 1849. V e l i g e r . JO: 4 2-54. Bovbjerg R.V. 1970. E c o l o g i c a l i s o l a t i o n and c o m p e t i t i v e e x c l u s i o n i n two c r a y f i s h (Orconectes y i r i l i s and Orconectes immunis). Ecology. 51:225-236. Branch, G.M. 1975. Mechanisms reducing i n t r a s p e c i f i c c o m p etition i n P a t e l l a spjp.: m i g r a t i o n , d i f f e r e n t i a t i o n and t e r r i t o r i a l behaviour- J . Anim. E c o l . 44:575-600. . 1976. I n t e r s p e c i f i c c o m p e t i t i o n experienced by South A f r i c a n P a t e l l a s p e c i e s . J . Anim. E c o l . 45:507-529. Breen, P.A. 1972. Seasonal m i g r a t i o n and p o p u l a t i o n r e g u l a t i o n i n the limpet Acmaea ( C o l i s e l l a ) d i g i t a l i s . . V e l i g e r . 15: 133-141. Brown, J.L. and G.H. Orians. 1970. Spacing p a t t e r n s i n mobile animals. Ann. Rev. E c o l . Syst. .1 :239^262. Caine, E.A. 1975. Feeding and ma s t i c a t o r y s t r u c t u r e s of s e l e c t e d anomura Crustacea. J . Expt. Mar. B i o l . E c o l . 18:277-302-C a r e f o o t , T.H- 1977- P a c i f i c seashores: a guide t o i n t e r t i d a l e cology. J . J . Douglas L t d . , Vancouver. 208 p. 106 C a s t e n h o l t z , R.W- 1961. The e f f e c t of g r a z i n g on marine l i t t o r a l diatom p o p u l a t i o n s . Ecology. 42:738-749. C o n n e l l , J.H. 1961a. E f f e c t s of c o m p e t i t i o n , p r e d a t i o n by Th a i s l a p i l l u s and other f a c t o r s on n a t u r a l p o p u l a t i o n s of the barnacle Balanus balanoides. E c o l . Monogr. 31:61-104. . 1961b. The i n f l u e n c e of i n t e r s p e c i f i c c o m petition and other f a c t o r s on the d i s t r i b u t i o n of the b a r n a c l e Chthamalus s t e l l a t u s . Ecology. 42:710-723. . 1970. A predator-prey system i n the marine i n t e r -t i d a l r e g i o n . I . Balanus q l a n d u l a and s e v e r a l predatory s p e c i e s of T h a i s . E c o l . Monogr. 40:49-78. . 1972. Community i n t e r a c t i o n on marine rocky i n t e r t i d a l shores. Ann. Rev. E c o l . Syst. 3:169-192. . 1975. Some mechanisms producing s t r u c t u r e i n n a t u r a l communities. In:M.L. Cody and J.M. Diamond (ed.), Ecology and e v o l u t i o n of communities- Belknap Press. Harvard Univ. 545 p. Darwin, C. 1859- The o r i g i n of s p e c i e s by means of n a t u r a l s e l e c t i o n . Reprinted by Atheneum. 502 p. DenHartog, C. 1968. The l i t t o r a l environment of rocky shores as a border between the sea and the l a n d and beneath the sea and f r e s h water. Blumea. .16:374-393. Doty, M.S. 1957. Rocky i n t e r t i d a l s u r f a c e s . I n : J.H. Hedgpeth (ed.), Geol. Soc. America. Mem. 67 v o l . 1. p.535-585. E l l i o t , J.M. 1971. Some methods f o r the s t a t i s t i c a l a n a l y s i s of samples of b e n t h i c i n v e r t e b r a t e s . Freshwater B i o l . Assoc. No. 25. 148p. F o s t e r , B.A. 1969. Tolerances of high temperatures by some i n t e r t i d a l b a r n a c l e s . Mar. B i o l . 4:326-332-1 0 7 . 1971a. On the determinants of the upper l i m i t of i n t e r t i d a l d i s t r i b u t i o n of b a r n a c l e s (Crustacea: C i r r e p e d i a ) . J . Anim. E c o l . 40:33-48. . 1971b. D e s i c c a t i o n as a f a c t o r i n the i n t e r t i d a l z onation of b a r n a c l e s . Mar. B i o l . 8:12-29. Frank, P.W. 1965. The biodemography of an i n t e r t i d a l s n a i l p o p u l a t i o n . Ecology- 46:831-844. Gore, R. H. And L.G. Abele. 1976. Shallow water p o r c e l a i n crabs from the P a c i f i c Coast of Panama and adjacent Caribbean waters (Crustacea: Anomura: P o r c e l l a i n i d a e ) . Smithsonian C o n t r i b . Z o o l . No. 27 3. Gowanloch, J.N. and F.R. Hayes. 1926. C o n t r i b u t i o n s to the study of marine gastropods. I . The p h y s i c a l f a c t o r s , behaviour and i n t e r t i d a l l i f e of L i t t o r i n a . C o n t r i b . Canad. B i o l . F i s h . 3: 133-166-Grant, P.R. 1972. I n t e r s p e c i f i c c o m p e t i t i o n among rodents. Ann. Rev. E c o l . S yst. 3:79-106. Haig, J . 1960. The P o r c e l l a i n i d a e (Crustacea Anomura) Of The Eastern P a c i f i c . A l l a n Hancock Pac. Exped. 24:1-440. Hart, J.F.L. 1968. C r a b - l i k e anomura and brachyura (Crustacea:Decapoda) from so u t h e a s t e r n A l a s k a and P r i n c e W i l l i a m Sound. Nat. Mus. Can- Nat. H i s t . No. 38. Hedgepeth, J. W. 1976. The l i v i n g edge. Geoscience and Man. 14: 17-51. H e l l e r , H.C. 1971. A l t i t u d i n a l z o n a t i o n of chipmunks (Eutamias): i n t e r s p e c i f i c a g g r e s i o n . Ecology. 52:312-329. Hewatt, W.G. 1935. E c o l o g i c a l s u c c e s s i o n i n the M y t i l u s c a l i f o r n i a n u s h a b i t a t as observed i n Monterey Bay. Ecology. .16:244-251. 108 Hodgkin, E.P. 1960. Patterns of l i f e on rocky shores. J . Roy. Soc. West. A u s t r a l . 43:35-45. Hutchinson, G.E. 1958. Concluding remarks. Cold Spring Harbor Symp. Quant. B i o l . 22:415-427. . 1978. An i n t r o d u c t i o n t o p o p u l a t i o n ecology. Yale Dniv. P r e s s . 260 p. Jaeger, R.G. 1971. Competitive e x c l u s i o n as a f a c t o r i n f l u e n c i n g the d i s t r i b u t i o n s of two s p e c i e s of t e r r e s t r i a l salamanders. Ecology. 52:623-637. King, C.E. and P.S. Dawson. 1973. H a b i t a t s e l e c t i o n by f l o u r b e e t l e s i n complex environments. P h y s i o l . Z o o l . 46:297-309. Knudsen, J.W. 1964. Observations on brachyura and anomura of Puget Sound. Pac. S c i . 1.8:3-3 3. Lewis, J.R. 1954. Observations on a h i g h - l e v e l p o p u l a t i o n of l i m p e t s . J . Anim. E c o l . 23:85-100. . 1964. The ecology of rocky shores. E n g l i s h Univ. P r e s s , London. 323 p. M i l l e r , R.S. 1967. P a t t e r n s and process i n c o m p e t i t i o n . Adv. E c o l . Res. 4:1-74. Molenock, J . 1976. A g o n i s t i c i n t e r a c t i o n s of the crab Pet ro l i s t he s (Crustacea, Anomura). Z. T i e r p s y c h o l . 41.: 277-294. N i c o l , E.A.T. 1932. The fee d i n g h a b i t s of the G a l a t h e i d e a . J . Mar. b i o l . ass. U.K. 1.8:87-106. North, W.J. 1954. Si z e d i s t r i b u t i o n , e r o s i v e a c t i v i t i e s , and gros s metabolic e f f i c i e n c y of the marine i n t e r t i d a l s n a i l s L i t t o r i n a p l a n a x i s and L. S c u t u l a t a . B i o l . B u l l . 106:185-197. 109 Nyblade, C F . 1975. Coexistance i n sympatric hermit c r a b s . Ph.D. t h e s i s . Univ. Washington, S e a t t l e . 312 p. Paine, R.T. 1974. I n t e r t i d a l community s t r u c t u r e . Experimental s t u d i e s on the r e l a t i o n s h i p between a dominant competitor and i t s p r i n c i p a l predator. O e c o l o g i a . .15:93-120. Park, T. 1962. B e e t l e s , competition, and p o p u l a t i o n s . S c i . 138:1396-1375. R i c k e t t s , E.F. And J . C a l v i n . 1968. Between P a c i f i c t i d e s . F o u r t h e d i t i o n , r e v i s e d by J . W. Hedgpeth. S t a n f o r d Univ. P r e s s , Palo A l t o . 614 p. S i e g e l , S. 1956. Nonparametric s t a t i s t i c s f o r the behavior s c i e n c e s . McGraw-Hill, new York. 312 p. Sokal, R.R. And F.J. Rohlf. 1969. Biometry: the p r i n c i p l e s and p r a c t i c e of s t a t i s t i c s i n b i o l o g i c a l r e s e a r c h . W. H. Freeman Co., San F r a n c i s c o . 776 p. Southward, A.J. 1958. The zonation of p l a n t s and animals on rocky sea shores. B i o l . Rev. 33: 137-177. Suchanek, T.H. 1978. The ecology of M y t i l u s e d u l i s L. i n exposed rocky i n t e r t i d a l communities. J . Expr. Mar. B i o l . E c o l . 11 : 105- 12C. Sutherland, J.P. 1972. E n e r g e t i c s of high and low p o p u l a t i o n s of the l i m p e t , Acmaea scabra (Gould). Ecology. 53: 430-437, Tinbergen, N. 1957. The f u n c t i o n s of t e r r i t o r y . B i r d Study. 4:14-27. Vandermeer, J.H. 1972. Niche theory. Ann. Rev. E c o l . S y s t . 3:107-132. Wicksten, M.K. 1973. Feeding i n the p o r c e l a i n crab, P e t r o l i s t h e s c i n c t i p e s (Randall) (Anomura:Porcellainidae). B u l l - South. C a l i f . Acad. S c i . 72:161-163. 110 Wolcott, T.G. 1973. P h y s i o l o g i c a l ecology and i n t e r t i d a l z o n a t i o n i n l i m p e t s (Acmaea): a c r i t i c a l look at " l i m i t i n g f a c t o r s " . B i o l . B u l l . 145:389-422. 

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