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An experimental field study of the effects of interspecific competition of Diaptomus Leptopus (Copepoda:Calanoida)… Olenick, Roberta Jill 1982

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AN EXPERIMENTAL FIELD STUDY OF THE EFFECTS OF INTERSPECIFIC COMPETITION ON DIAPTOMUS LEPTOPUS (COPEPODA:CALANOIDA) IN A MONTANE LAKE by ROBERTA J I L L OLENICK B.Sc. H o n o r s , U n i v e r s i t y of M a n i t o b a , W i n n i p e g , 1978 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n THE FACULTY OF GRADUATE STUDIES (Department o f Z o o l o g y ) We a c c e p t t h i s t h e s i s a s c o n f o r m i n g t o t h e r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA A p r i l 1982 0 R o b e r t a J i l l O l e n i c k , 1982 I n p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f t h e r e q u i r e m e n t s f o r an a d v a n c e d d e g r e e a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e t h a t t h e L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s t u d y . I f u r t h e r a g r e e t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by t h e h e a d o f my d e p a r t m e n t o r by h i s o r h e r r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l n o t be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . Zoology D e p a r t m e n t o f The U n i v e r s i t y o f B r i t i s h C o l u m b i a 2075 Wesbrook P l a c e V a n c o u v e r , Canada V 6 T 1W5 A p r i l , 1982 D a t e DE-6 (2/79) D a v i d I . M a c K e n z i e , f o r a l w a y s c a r i n g i i ABSTRACT D e s p i t e h i g h d e n s i t i e s i n an u p s t r e a m l a k e , t h e h e r b i v o r o u s c a l a n o i d c o p e p o d , Diaptomus l e p t o p u s , i s e x t r e m e l y r a r e i n o l i g o t r o p h i a E u n i c e Lake i n t h e C o a s t a l Range M o u n t a i n s ne a r V a n c o u v e r , B r i t i s h C o l u m b i a . I_n s i t u e x p e r i m e n t s c o n d u c t e d i n 1979 and 1980 t e s t e d t h e h y p o t h e s i s t h a t c o m p e t i t i o n from z o o p l a n k t o n s p e c i e s r e s i d e n t i n E u n i c e Lake p r e v e n t s i m m i g r a n t D. l e p t o p u s from c o l o n i z i n g t h e l a k e . P o l y e t h y l e n e e n c l o s u r e s , e a c h h o l d i n g 29,000 1 of l a k e w a t e r , c o n t a i n e d a l l e x p e r i m e n t a l t r e a t m e n t s . E x p e r i m e n t s i n 1979 e x p o s e d a s t a n d a r d d e n s i t y of D. l e p t o p u s t o a l l E u n i c e Lake z o o p l a n k t o n s p e c i e s a t l a k e d e n s i t i e s ( c o n t r o l ) , t o a l l E u n i c e Lake s p e c i e s a t r e d u c e d d e n s i t i e s (low d e n s i t y ) , and t o a l l E u n i c e Lake s p e c i e s e x c e p t one of D a p h n i a r o s e a ( D a p h n i a - r e m o v a l ) , D i a p t o m u s k e n a i ( k e n a i -r e m o v a l ) , o r Diaptomus t y r e l l i ( t y r e l l i - r e m o v a l ) . Improved p e r f o r m a n c e s of D. l e p t o p u s i n n o n - c o n t r o l t r e a t m e n t s was e v i d e n c e f o r c o m p e t i t i o n i n c o n t r o l s . M e a s u r e s of p e r f o r m a n c e i n c l u d e d d e n s i t y , number of eggs p e r f e m a l e , and a d u l t s i z e . S i m i l a r i t y between D. l e p t o p u s p e r f o r m a n c e s i n c o n t r o l , D a p h n i a - r e m o v a l , and k e n a i - r e m o v a l t r e a t m e n t s p l u s r e l a t i v e l y h i g h c o n c e n t r a t i o n s of D. l e p t o p u s n a u p l i i i n t h e t y r e l l i -r e m o v a l t r e a t m e n t s u g g e s t e d t h a t D. l e p t o p u s d i d not compete w i t h s p e c i e s o t h e r t h a n D. t y r e l l i . However, s i m i l a r i t y between t y r e l l i - r e m o v a l and low d e n s i t y t r e a t m e n t s i n c o n c e n t r a t i o n s of D. l e p t o p u s n a u p l i i c o n f o u n d e d c o m p e t i t i o n between D. l e p t o p u s and D. t y r e l l i w i t h d i f f u s e c o m p e t i t i o n from s e v e r a l E u n i c e Lake s p e c i e s c o m b i n e d . D. l e p t o p u s o v e r l a p p e d i n v e r t i c a l d i s t r i b u t i o n and s e a s o n a l c y c l e more w i t h D. t y r e l l i t h a n w i t h o t h e r s p e c i e s . D i f f e r e n c e s ' among e x p e r i m e n t a l t r e a t m e n t s i n a l g a l s i z e c o m p o s i t i o n s d i d n o t c o n c l u s i v e l y show whether z o o p l a n k t o n p a r t i t i o n e d f o o d r e s o u r c e s . E x p e r i m e n t s i n 1980, d e s i g n e d t o s e p a r a t e D. t y r e l l i c o m p e t i t i o n from d i f f u s e c o m p e t i t i o n , d i d not p r o v i d e any e v i d e n c e of 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 . By i n c r e a s i n g z o o p l a n k t o n m e t a b o l i c e f f i c i e n c i e s , c o o l t e m p e r a t u r e s i n 1980 may have v i r t u a l l y e l i m i n a t e d , c o m p e t i t i o n f o r a l g a l f o o d s . TABLE OF CONTENTS ABSTRACT i i L I S T OF TABLES v i i L I S T OF FIGURES x ACKNOWLEDGEMENTS x i i i INTRODUCTION 1 THE STUDY SYSTEM . 14 MATERIALS AND METHODS 21 EXPERIMENTAL DESIGN, 1979 -25 RESULTS, 1979 '. . 28 1. R e s u l t s C o n f i r m i n g P r o p e r E s t a b l i s h m e n t of E x p e r i m e n t s 28 1.1 E n c l o s u r e D e n s i t i e s of Abundant E u n i c e Lake Z o o p l a n k t o n S p e c i e s 28 1.2 E n c l o s u r e D e n s i t i e s of R a r e E u n i c e Lake Z o o p l a n k t o n S p e c i e s 39 1.3 E f f e c t s of E n c l o s u r e 47 2. R e s u l t s D e s c r i b i n g E f f e c t s of E x p e r i m e n t s 49 2.1 T r e a t m e n t E f f e c t s on T o t a l D e n s i t i e s of Diaptomus  l e p t o p u s 49 2.2 T r e a t m e n t E f f e c t s on D e n s i t i e s of Diaptomus  l e p t o p u s Eggs, N a u p l i i , C o p e p o d i t e s , and A d u l t s .. 57 2.3 T r e a t m e n t E f f e c t s on A d u l t S i z e of Diaptomus  l e p t o p u s 62 2.4 S e a s o n a l C y c l e s , V e r t i c a l D i s t r i b u t i o n and P h y t o p l a n k t o n Biomass 64 3. Summary of 1979 R e s u l t s 86 EXPERIMENTAL DESIGN, 1980 88 RESULTS, 1980 91 1. R e s u l t s C o n f i r m i n g P r o p e r E s t a b l i s h m e n t of E x p e r i m e n t s 91 1.1 E n c l o s u r e D e n s i t i e s of Abundant E u n i c e Lake Z o o p l a n k t o n S p e c i e s 91 1.2 E n c l o s u r e D e n s i t i e s of Rare E u n i c e Lake Z o o p l a n k t o n S p e c i e s 103 1.3 E f f e c t s of E n c l o s u r e 109 2. R e s u l t s D e s c r i b i n g E f f e c t s of E x p e r i m e n t s 110 2.1 T r e a t m e n t E f f e c t s on T o t a l D e n s i t i e s of D i a p t o m u s  l e p t o p u s 110 2.2 T r e a t m e n t E f f e c t s on D e n s i t i e s of Diaptomus  l e p t o p u s Eggs, N a u p l i i , C o p e p o d i t e s , and A d u l t s ..116 2.3 T r e a t m e n t E f f e c t s on A d u l t S i z e of Diaptomus  l e p t o p u s 116 2.4 S e a s o n a l C y c l e s , V e r t i c a l D i s t r i b u t i o n and P h y t o p l a n k t o n B i omass 121 3. Summary of 1980 R e s u l t s 130 DISCUSSION 132 S e p a r a t i o n of Diaptomus t y r e l l i C o m p e t i t i o n from D i f f u s e C o m p e t i t i o n 132 V u l n e r a b i l i t y of Diaptomus l e p t o p u s N a u p l i i t o • C o m p e t i t i o n 136 R e l e v a n c e of E x p e r i m e n t a l R e s u l t s t o t h e S i z e - E f f i c i e n c y v i H y p o t h e s i s . 137 R e l a t i o n s h i p Between T e m p e r a t u r e and I n t e n s i t y of C o m p e t i t i o n .139 L i m i t a t i o n s of P h y t o p l a n k t o n S t a n d i n g S t o c k D a t a 145 SUMMARY AND CONCLUSIONS .' 150 LITERATURE CITED 153 L I S T OF TABLES T a b l e I . P h y s i c a l , c h e m i c a l , and b i o l o g i c a l c h a r a c t e r i s t i c s of G w e n d o l i n e and E u n i c e L a k e s 17 T a b l e I I . Summary of 1979 e x p e r i m e n t a l t r e a t m e n t s 26 T a b l e I I I . T - t e s t s t a t i s t i c s c o m p a r i n g mean d e n s i t i e s of major E u n i c e Lake s p e c i e s i n E u n i c e Lake and i n c o n t r o l e n c l o s u r e s a t s t a r t of 1979 e x p e r i m e n t s 29 T a b l e IV. S t a t i s t i c a l t e s t s c o m p a r i n g mean d e n s i t i e s of Diaptomus t y r e l l i a c r o s s t r e a t m e n t s on i n i t i a l s a m p l i n g d a t e of 1979 e x p e r i m e n t s 30 T a b l e V. S t a t i s t i c a l t e s t s c o m p a r i n g mean d e n s i t i e s o f ,Diaptomus k e n a i a c r o s s t r e a t m e n t s on i n i t i a l s a m p l i n g d a t e of 1979 e x p e r i m e n t s 31 T a b l e V I . S t a t i s t i c a l t e s t s c o m p a r i n g mean d e n s i t i e s of D a p h n i a r o s e a a c r o s s t r e a t m e n t s on i n i t i a l s a m p l i n g d a t e of 1979 e x p e r i m e n t s 32 T a b l e V I I . S t a t i s t i c a l t e s t s c o m p a r i n g a c r o s s t r e a t m e n t s f o r mean maximum d e n s i t i e s o f Bosmina l o n g i r o s t r i s a t t a i n e d d u r i n g 1979 e x p e r i m e n t s 42 T a b l e V I I I . S t a t i s t i c a l t e s t s c o m p a r i n g a c r o s s t r e a t m e n t s f o r mean maximum d e n s i t i e s of c y c l o p o i d c o p e p o d i t e s p l u s a d u l t s a t t a i n e d d u r i n g 1979 e x p e r i m e n t s 46 T a b l e IX. Summary of s t a t i s t i c a l t e s t s c o m p a r i n g mean d e n s i t i e s of n a u p l i i , c o p e p o d i t e s , a d u l t s , and mean t o t a l d e n s i t i e s of Diaptomus l e p t o p u s a c r o s s t r e a t m e n t s v i i i f o r e a c h s a m p l i n g d a t e o f 1979 e x p e r i m e n t s 50 T a b l e X. S t a t i s t i c a l t e s t s c o m p a r i n g a c r o s s t r e a t m e n t s f o r mean maximum d e n s i t i e s of Diaptomus l e p t o p u s a t t a i n e d d u r i n g 1979 e x p e r i m e n t s 55 T a b l e X I . S t a t i s t i c a l t e s t s c o m p a r i n g a c r o s s t r e a t m e n t s f o r mean p e r s i s t e n c e t i m e s of Diaptomus l e p t o p u s i n 1979 e x p e r i m e n t s 56 T a b l e X I I . S t a t i s t i c a l t e s t s c o m p a r i n g a c r o s s t r e a t m e n t s f o r mean number of Di a p t o m u s l e p t o p u s eggs p r o d u c e d p e r f e m a l e d u r i n g 1979 e x p e r i m e n t s 60 T a b l e X I I I . L e n g t h s of a d u l t d i a p t o m i d c o p e p o d s and of D a p h n i a r o s e a i n 1979 e x p e r i m e n t s 63 T a b l e XIV. Summary of 1980 e x p e r i m e n t a l t r e a t m e n t s 89 T a b l e XV. T - t e s t s t a t i s t i c s c o m p a r i n g mean d e n s i t i e s of major E u n i c e Lake s p e c i e s i n E u n i c e Lake and i n c o n t r o l e n c l o s u r e s a t s t a r t o f 1980 e x p e r i m e n t s 92 T a b l e X V I. S t a t i s t i c a l t e s t s c o m p a r i n g mean d e n s i t i e s of Dia p t o m u s t y r e l l i a c r o s s t r e a t m e n t s on i n i t i a l s a m p l i n g d a t e o f 1980 e x p e r i m e n t s 93 T a b l e X V I I . S t a t i s t i c a l t e s t s c o m p a r i n g mean d e n s i t i e s of Dia p t o m u s k e n a i a c r o s s t r e a t m e n t s on i n i t i a l s a m p l i n g d a t e o f 1980 e x p e r i m e n t s 98 T a b l e X X V I I I . S t a t i s t i c a l t e s t s c o m p a r i n g mean d e n s i t i e s o f D a p h n i a r o s e a a c r o s s t r e a t m e n t s on i n i t i a l s a m p l i n g d a t e of 1980 e x p e r i m e n t s 99 T a b l e XIX. S t a t i t i c a l t e s t s c o m p a r i n g mean d e n s i t i e s of H o l o p e d i u m q i b b e r u m a c r o s s t r e a t m e n t s on i n i t i a l s a m p l i n g d a t e of 1980 e x p e r i m e n t s 100 T a b l e XX. S t a t i s t i c a l t e s t s c o m p a r i n g a c r o s s t r e a t m e n t s f o r mean maximum d e n s i t i e s o f c y c l o p o i d c o p e p o d s a t t a i n e d d u r i n g 1980 e x p e r i m e n t s 108 T a b l e X X I . Summary of s t a t i s t i c a l t e s t s c o m p a r i n g mean d e n s i t i e s of n a u p l i i , c o p e p o d i t e s , a d u l t s , and mean t o t a l d e n s i t i e s of Diaptomus l e p t o p u s a c r o s s t r e a t m e n t s f o r e a c h s a m p l i n g d a t e of 1980 e x p e r i m e n t s .111 T a b l e X X I I . A n a l y s i s of v a r i a n c e c o m p a r i n g a c r o s s t r e a t m e n t s f o r mean number of Diaptomus l e p t o p u s eggs p r o d u c e d p e r f e m a l e d u r i n g 1980 e x p e r i m e n t s 119 T a b l e X X I I I . L e n g t h s o f a d u l t d i a p t o m i d c o p e p o d s and o f D a p h n i a r o s e a i n 1980 e x p e r i m e n t s 120 T a b l e XXIV. Maximum l e n g t h s arid maximum summer d e n s i t i e s o f c a l a n o i d c o p e p o d s and Daphn i a r o s e a i n R a t h e r i n e , G w e n d o l i n e , and E u n i c e L a k e s 134 X L I S T OF FIGURES F i g u r e 1 •. Map showing l o c a t i o n of s t u d y s i t e 15 F i g u r e 2. D e n s i t i e s of D i aptomus t y r e l l i i n E u n i c e Lake and i n 1979 e x p e r i m e n t s 33 F i g u r e 3. D e n s i t i e s of D i a p t o m u s k e n a i i n E u n i c e Lake and i n 1979 e x p e r i m e n t s 35 F i g u r e 4. D e n s i t i e s of D a p h n i a r o s e a and H o l o p e d i u m gibberurn i n E u n i c e Lake and i n 1979 e x p e r i m e n t s 37 F i g u r e 5. D e n s i t i e s of Bosmina l o n g i r o s t r i s i n E u n i c e Lake and i n 1979 e x p e r i m e n t s 40 F i g u r e 6. D e n s i t i e s of c y c l o p o i d c o p e p o d s i n E u n i c e Lake and i n 1979 e x p e r i m e n t s 43 F i g u r e 7. T o t a l d e n s i t i e s of D i a p t o m u s l e p t o p u s i n 'Eunice Lake and i n 1979 e x p e r i m e n t s 53 F i g u r e 8. D e n s i t i e s of n a u p l i i and of c o p e p o d i t e s p l u s a d u l t s of D i aptomus l e p t o p u s i n E u n i c e Lake and i n 1979 e x p e r i m e n t s 58 F i g u r e 9. L i f e c y c l e of D i aptomus l e p t o p u s i n G w e n d o l i n e Lake 66 F i g u r e 10. L i f e c y c l e of D i a p t o m u s t y r e l l i i n E u n i c e Lake . 68 F i g u r e 11. L i f e c y c l e of D i aptomus k e n a i i n E u n i c e Lake ... 70 F i g u r e 12. V e r t i c a l d i s t r i b u t i o n s of z o o p l a n k t o n s p e c i e s i n 1979 e x p e r i m e n t s d u r i n g J u l y 73 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 s of z o o p l a n k t o n s p e c i e s i n 1979 e x p e r i m e n t s d u r i n g September 75 F i g u r e 14. J u l y v e r t i c a l d i s t r i b u t i o n s of D iaptomus l e p t o p u s n a u p l i i i n t h e p r e s e n c e and i n t h e a b s e n c e of D i a p t o m u s t y r e l l i 77 F i g u r e 15. T e m p e r a t u r e p r o f i l e f o r E u n i c e Lake d u r i n g 1979 e x p e r i m e n t s 79 F i g u r e 16. P h y t o p l a n k t o n s t a n d i n g s t o c k s i n E u n i c e Lake and i n 1979 e x p e r i m e n t s 83 F i g u r e 17. D e n s i t i e s of D i a p t o m u s t y r e l l i i n E u n i c e Lake and i n 1980 e x p e r i m e n t s 94 F i g u r e 18. D e n s i t i e s of D iaptomus k e n a i i n E u n i c e L a k e and i n 1980 e x p e r i m e n t s 96 F i g u r e 19. D e n s i t i e s of D a p h n i a r o s e a and H o l o p e d i u m g i b b e r u m i n E u n i c e Lake and i n 1980 e x p e r i m e n t s 101 F i g u r e 20. D e n s i t i e s of Bosmina l o n g i r o s t r i s i n E u n i c e Lake and i n 1980 e x p e r i m e n t s 104 F i g u r e 21. D e n s i t i e s of c y c l o p o i d c o p e p o d s i n E u n i c e Lake and i n 1980 e x p e r i m e n t s 106 F i g u r e 22. T o t a l d e n s i t i e s of Diaptomus l e p t o p u s i n E u n i c e L a k e and i n 1980 e x p e r i m e n t s 114 F i g u r e 23. D e n s i t i e s of n a u p l i i and of c o p e p o d i t e s p l u s a d u l t s o f Diaptomus l e p t o p u s i n E u n i c e Lake and i n 1980 e x p e r i m e n t s ..117 F i g u r e 24. V e r t i c a l d i s t r i b u t i o n s of z o o p l a n k t o n s p e c i e s i n 1980 e x p e r i m e n t s d u r i n g J u l y 122 F i g u r e 25. T e m p e r a t u r e p r o f i l e f o r E u n i c e Lake d u r i n g 1980 e x p e r i m e n t s 125 F i g u r e 26. P h y t o p l a n k t o n s t a n d i n g s t o c k s i n E u n i c e Lake and i n 1980 e x p e r i m e n t s ...127 F i g u r e 27. D i a p t o m i d r e s p i r a t i o n r a t e s as a f u n c t i o n of t e m p e r a t u r e 140 ACKNOWLEDGEMENTS I thank my s u p e r v i s o r , D r . W.E. N e i l l , f o r a d v i c e , a s s i s t a n c e , and encouragement t h r o u g h o u t my t e n u r e as h i s s t u d e n t . In p a r t i c u l a r , I b e n e f i t t e d f r o m t h e h e a l t h y s c e p t i c i s m and e d i t o r i a l s k i l l w i t h w h i c h he a p p r o a c h e d e a r l i e r d r a f t s of t h e m a n u s c r i p t . I a l s o thank t h e members of my a d v i s o r y c o m m i t t e e , D r s . C . J . K r e b s and J.D. M c P h a i l , f o r t h o u g h t f u l i n p u t d u r i n g t h e p l a n n i n g and w r i t i n g s t a g e s of t h e t h e s i s . I a c k n o w l e d g e J . W a l t e r s and t h e s t a f f o f t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a R e s e a r c h F o r e s t f o r p e r m i s s i o n t o c o n d u c t my r e s e a r c h t h e r e and f o r g e n e r a l h e l p f u l n e s s . G. B o r c h e r t , S. B r i s s o n , A. Copsey, I . F o r s t e r , A. L e i t a e , D. Marmorek, W. N e i l l , A. P e a c o c k , J . Pennan t , A. Reddenbach, and C. Wyatt worked l o n g h o u r s i n t h e r a i n s e t t i n g up or s a m p l i n g e x p e r i m e n t a l e n c l o s u r e s . I am g r a t e f u l t o M.A. Chapman, J . G r e e n , W. N e i l l , A. P e a c o c k , and G. S a n d e r c o c k f o r h e l p i n g w i t h z o o p l a n k t o n i d e n t i f i c a t i o n , t o G. Jung and E. K r a u s e f o r c o u n t i n g p h y t o p l a n k t o n s a m p l e s , and t o E. K r a u s e , D. Marmorek, W. N e i l l , and A. Peaco c k f o r s h a r i n g c r i t i c a l i n s i g h t s g l e a n e d f r o m t h e i r e x t e n s i v e e x p e r i e n c e w i t h z o o p l a n k t o n s y s t e m s . I a p o l o g i z e t o t h e h u n d r e d s of t h o u s a n d s of. z o o p l a n k t e r s whose l i v e s I u n w i l l i n g l y , but I hope humanely, s a c r i f i c e d t o s c i e n c e . I a c k n o w l e d g e P. DeJong, D. W i l l i a m s , and e s p e c i a l l y N. G i l b e r t f o r u s e f u l s t a t i s t i c a l c o n s u l t a t i o n s . A. Cop s e y , S. H a r r i s o n , D. Marmorek, T. T e n i s c i , C. W a l t e r s , and D. Z i t t e n p r o v i d e d computer programs and p a t i e n t l y a n s w e r e d e n d l e s s x i v q u e s t i o n s a b o u t them. I p a r t i c u l a r l y thank D. Marmorek f o r t h e computer p l o t program t h a t s a v e d me eons of d r a f t i n g by p r o d u c i n g most of t h e f i g u r e s i n t h e t h e s i s . F a c u l t y and s t u d e n t s o f t h e I n s t i t u t e of A n i m a l R e s o u r c e E c o l o g y g e n e r a t e d t h e i n t e l l e c t u a l l y s t i m u l a t i n g and s o c i a l l y s u s t a i n i n g e n v i r o n m e n t t h a t made g r a d u a t e s t u d i e s a m u l t i -f a c e t e d and r e w a r d i n g e d u c a t i o n . The u n f a i l i n g s u p p o r t and g e n u i n e c o n c e r n of L. Gass and C. K r e b s e a s e d t h e t r y i n g and d i s c o u r a g i n g t i m e s . As a l w a y s , and i n a l l ways, I am g r a t e f u l t o my two f r i e n d s and m e n t o r s , D.I. M a c K e n z i e and A. P e a c o c k . To my s i s t e r , Debby O l e n i c k H i r s c h , who made me r e a l i z e t h a t c o n t r a d i c t o r y , c o n f u s i n g , and i n c o n c l u s i v e r e s u l t s a r e e x c i t i n g r e s u l t s , I owe my own e n t h u s i a s m f o r t h i s p r o j e c t . .To h e r , and t o my p a r e n t s , I am i n d e b t e d f o r u n d e r s t a n d i n g , r e a s s u r a n c e , and l o v e . D u r i n g t h e s t u d y , p e r s o n a l s u p p o r t came from a N a t u r a l S c i e n c e s and E n g i n e e r i n g R e s e a r c h C o u n c i l S c h o l a r s h i p , a U n i v e r s i t y o f B r i t i s h C o l u m b i a G r a d u a t e F e l l o w s h i p , and a T e a c h i n g A s s i s t a n t s h i p . R e s e a r c h s u p p o r t was p r o v i d e d by an O p e r a t i n g G r a n t from t h e N a t u r a l S c i e n c e s and E n g i n e e r i n g R e s e a r c h C o u n c i l of Canada t o W.E. N e i l l . 1 INTRODUCTION Many e c o l o g i s t s a c c e p t t h a t t h e p r o c e s s o f i n t e r s p e c i f i c c o m p e t i t i o n d e t e r m i n e s p a t t e r n s of s p e c i e s d i s t r i b u t i o n and abundance, s p e c i e s d i v e r s i t y , and community o r g a n i z a t i o n ( Crombie 1947; M i l l e r 1967; L e v i n s 1968; M a c A r t h u r 1972; Cody 1974; P i a n k a 1976; Diamond 1978). T h r e e t y p e s o f s t u d i e s l a b o r a t o r y e x p e r i m e n t s , f i e l d o b s e r v a t i o n s , and c o n t r o l l e d f i e l d e x p e r i m e n t s - have c o n t r i b u t e d t o t h e s e c o n v i c t i o n s . The e a r l i e s t c o m p e t i t i o n s t u d i e s were l a b o r a t o r y e x p e r i m e n t s i n w h i c h s p e c i e s were c u l t u r e d t o g e t h e r i n s i m p l e , a r t i f i c i a l e n v i r o n m e n t s . Gause's (1934) famous e x p e r i m e n t s d e m o n s t r a t e d t h a t , a l t h o u g h Paramec ium caudatum c o u l d be s u c c e s s f u l l y c u l t u r e d a l o n e , when grown w i t h P. a u r e l i a i t was i n v a r i a b l y o u t c o m p e t e d f o r l i m i t e d b a c t e r i a l f o o d . Which of T r i b o l i u m c o nfusum and T. c a s t a n e u m d i s p l a c e d t h e o t h e r depended on t e m p e r a t u r e and h u m i d i t y c o n d i t i o n s ( P a r k 1954). From t h e s e and s i m i l a r e x p e r i m e n t s d e v e l o p e d t h e C o m p e t i t i v e E x c l u s i o n P r i n c i p l e , w h i c h s t a t e s t h a t " c o m p l e t e c o m p e t i t o r s c a n n o t c o e x i s t " ( H a r d i n 1960). The a p p l i c a b i l i t y of t h i s t e n e t t o n a t u r a l p o p u l a t i o n s i s u n c l e a r b e c a u s e t h e l a b o r a t o r y s y s t e m s g e n e r a t i n g i t may o v e r e s t i m a t e t h e i m p o r t a n c e o f c o m p e t i t i o n . S i n g l e - r e s o u r c e l a b o r a t o r y e n v i r o n m e n t s f o r c e s p e c i e s t o compete, but i n n a t u r a l e n v i r o n m e n t s m u l t i p l e f a c t o r s c a n a l l e v i a t e c o m p e t i t i o n . P r e d a t i o n and e n v i r o n m e n t a l v a r i a t i o n c a n h o l d . p o p u l a t i o n s of p o t e n t i a l c o m p e t i t o r s below c a r r y i n g c a p a c i t y ( P a i n e 1966; Wiens 1977), and r e s o u r c e h e t e r o g e n e i t y can f a c i l i t a t e r e s o u r c e p a r t i t i o n i n g ( S c h o e n e r 1974). More 2 e l a b o r a t e l a b o r a t o r y e x p e r i m e n t s have e x e m p l i f i e d t h e i m p o r t a n c e of m e d i a t i n g f a c t o r s . P a r a s i t e s a l t e r e d c o m p e t i t i v e outcomes between T r i b o l i u m s p e c i e s ( P a r k 1948). Crombie (1945) d e m o n s t r a t e d p r o l o n g e d c o e x i s t e n c e of two g r a i n b e e t l e s p r o v i d e d w i t h two f o o d r e s o u r c e s . Paramecium a u r e l i a and P. b u r s a r i a c o e x i s t e d i n complex c u l t u r e media where t h e y c o u l d v e r t i c a l l y s e g r e g a t e (Gause 1936). R e s u l t s from even t h e s e s o p h i s t i c a t e d l a b o r a t o r y e n v i r o n m e n t s a r e e x t e n s i b l e t o f i e l d s i t u a t i o n s o n l y w i t h c a u t i o n b e c a u s e t o t a l r e p l i c a t i o n of complex n a t u r a l e n v i r o n m e n t s i n an a r t i f i c i a l c o n t e x t i s not p o s s i b l e . D e s p i t e t h e s e l i m i t a t i o n s , t h e f i r s t e c o l o g i s t s t o s t u d y c o m p e t i t i o n i n t h e f i e l d t o o k t h e i r l e a d from l a b o r a t o r y r e s u l t s . They a t t e m p t e d t o v a l i d a t e t h e C o m p e t i t i v e E x c l u s i o n P r i n c i p l e w i t h d e t a i l e d o b s e r v a t i o n s on r e s o u r c e use p a t t e r n s o f p o t e n t i a l l y c o m p e t i n g s p e c i e s ( u s u a l l y s y m p a t r i c c o n g e n e r s ) . They l o o k e d among t h e s e p a t t e r n s f o r s p e c i e s d i f f e r e n c e s i n t e r p r e t a b l e a s c o m p e t i t i o n - r e d u c i n g c o e x i s t e n c e mechanisms. I f t h e y d e t e c t e d no d i f f e r e n c e s , t h e y assumed t h a t c o e x i s t e n c e mechanisms r e m a i n e d among as y e t unmeasured n i c h e d i m e n s i o n s ( H a r d i n 1960; P e t e r s 1976). B e c a u s e i n f i n i t e l y d i m e n s i o n e d n i c h e s a r e n e v e r e n t i r e l y q u a n t i f i a b l e ( H u t c h i n s o n 1957), t h e C o m p e t i t i v e E x c l u s i o n P r i n c i p l e i s u n t e s t a b l e . A c l a s s i c example o f a s e a r c h f o r d i f f e r e n c e s among c o e x i s t i n g c o n g e n e r i c s i s M a c A r t h u r ' s (1958) s t u d y of f o r a g i n g b e h a v i o u r of f i v e i n s e c t i v o r o u s . D e n d r o i c a w a r b l e r s . M a c A r t h u r c o n c l u d e d t h a t d i s p a r i t i e s i n p o s i t i o n o f f e e d i n g , i n methods o f p r e y c a p t u r e , and i n d i r e c t i o n and s p e e d o f movement were 3 s u f f i c i e n t t o a l l o w c o e x i s t e n c e . C o u n t l e s s s i m i l a r s t u d i e s on v a r i o u s o r g a n i s m s e x i s t ( e . g., Rand 1964; Cody 1968; Brown and L i e b e r m a n 1973; r e v i e w e d i n S c h o e n e r 1974). Many of them have summarized o b s e r v a t i o n s on r e s o u r c e use w i t h i n d i c e s of n i c h e o v e r l a p ( M a c A r t h u r and L e v i n s 1967; L e v i n s 1968; W i l l i a m s o n 1971; Brown 1975; P i a n k a 1975). A l l of t h e s e f i e l d s t u d i e s s h a r e a s e r i o u s f l a w . They have i n f e r r e d t h e p r o c e s s o f c o m p e t i t i o n f r o m an o b s e r v e d p a t t e r n o f r e s o u r c e u s e . In f a c t , s e v e r a l p r o c e s s e s c o u l d have p r o d u c e d t h e same p a t t e r n (Dayton 1973). F o r example, r a t h e r t h a n c o m p e t i t i o n , s p e c i e s d i f f e r e n c e s i n p r e d a t o r a v o i d a n c e s t r a t e g i e s ( R o s e n z w e i g 1973), i n p h y l o g e n e t i c a l l y - d e t e r m i n e d p r e f e r e n c e s , o r i n p h y s i o l o g i c a l t o l e r a n c e s (Dumas 1956) can c a u s e d i f f e r e n c e s i n h a b i t a t u s e . The r e l a t i o n s h i p between n i c h e o v e r l a p and c o m p e t i t i o n i s ambiguous; h i g h o v e r l a p i n use o f p a r t i c u l a r r e s o u r c e s i n d i c a t e s i n t e n s e c o m p e t i t i o n when t h o s e r e s o u r c e s a r e l i m i t e d , and no c o m p e t i t i o n when t h e y a r e n o t ( C o l w e l l and Futuyma 1971; Z a r e t and Rand 1971; P i a n k a 1974). Knowledge of r e s o u r c e abundance and a v a i l a b i l i t y , t h e n , i s c r i t i c a l t o i n t e r p r e t i n g w h i c h p r o c e s s e s u n d e r l i e r e s o u r c e use p a t t e r n s . O b t a i n i n g s u c h - i n f o r m a t i o n i s n o t o r i o u s l y d i f f i c u l t ( e . g., J a e g e r 1972; F r a s e r 1976) b e c a u s e i t r e q u i r e s b e i n g a b l e t o p e r c e i v e r e s o u r c e s a s a n i m a l s t h e m s e l v e s do. In a d d i t i o n t o d i f f e r e n c e s i n r e s o u r c e use p a t t e r n s among s y m p a t r i c s p e c i e s , e c o l o g i s t s have i n f e r r e d c o m p e t i t i o n f r o m e v i d e n c e o f n i c h e s h i f t s and c h a r a c t e r d i s p l a c e m e n t (Brown and W i l s o n 1956) among s i m i l a r s p e c i e s o c c u r r i n g b o t h s y m p a t r i c a l l y 4 and a l l o p a t r i c a l l y . G r e a t e r s i m i l a r i t y i n a l l o p a t r y t h a n i n s y mpatry of r e s o u r c e u s e , o r o f m o r p h o l o g i c a l c h a r a c t e r s c o r r e l a t e d w i t h r e s o u r c e u s e , p r e s u m a b l y r e f l e c t s c o m p e t i t i o n i n t h e zone of sympatry • ( G r a n t 1972a; Diamond 1978). L i s t e r (1976) n o t e d n i c h e e x p a n s i o n i n h a b i t a t use by A n o l i s where c o n g e n e r i c c o m p e t i t o r s were few. Beak s i z e s (and t h e r e f o r e p r o b a b l y d i e t s ) of G e o s p i z a f u l i q i n o s a and G. f o r t i s a r e more d i s s i m i l a r on t h o s e i s l a n d s of G a l a p a g o s where t h e y o c c u r s y m p a t r i c a l l y (Lack 1947; A b b o t t e t a l . 1977). T h e s e t y p e s of o b s e r v a t i o n s form n a t u r a l " e x p e r i m e n t s " i n t h a t z o n e s o f sympatry and a l l o p a t r y c o r r e s p o n d t o w i t h - and w i t h o u t - c o m p e t i t o r " t r e a t m e n t s " , but t h e y a r e u n c o n t r o l l e d e x p e r i m e n t s i n t h a t c o m p e t i t o r abundance i s not t h e s o l e d i f f e r e n c e between z o n e s . C o n s e q u e n t l y , n i c h e s h i f t s c a n r e s u l t from d i f f e r e n c e s between a r e a s of s y m p a t r y and a l l o p a t r y i n p r e d a t o r abundance, p r e y t y p e , a b i o t i c f a c t o r s , or any number o f a t t r i b u t e s u n r e l a t e d t o c o m p e t i t i o n i n t e n s i t y . G r a n t (1972a) d e m o n s t r a t e d t h a t c l i n a l v a r i a t i o n i n m o r p h o l o g i c a l f e a t u r e s e x p l a i n e d many c l a s s i c a l e xamples of c h a r a c t e r d i s p l a c e m e n t . S t r o n g e t a l . (1979) a r g u e d t h a t random p r o c e s s e s a l o n e were s u f f i c i e n t t o a c c o u n t f o r d i f f e r e n c e s i n m o r p h o l o g y among b i r d s p e c i e s s y m p a t r i c on i s l a n d s ( b u t see G r a n t and A b b o t t 1980). The s t r o n g e s t e v i d e n c e f o r c o m p e t i t i o n has come n o t from l a b o r a t o r y e x p e r i m e n t s or f i e l d o b s e r v a t i o n s , but from c o n t r o l l e d f i e l d e x p e r i m e n t s . T h e s e i n v o l v e m o n i t o r i n g p e r f o r m a n c e s of s p e c i e s e x p o s e d t o a r t i f i c i a l l y m a n i p u l a t e d c o m p e t i t o r d e n s i t i e s under o t h e r w i s e n a t u r a l c o n d i t i o n s . 5 M e a s u r e s o f p e r f o r m a n c e i n c l u d e i n d i c e s of f i t n e s s s u c h as s u r v i v a l , f e c u n d i t y , d e n s i t y , a bundance, and g r o w t h r a t e . B e t t e r p e r f o r m a n c e o f one s p e c i e s i n t h e a b s e n c e t h a n i n t h e p r e s e n c e of a s e c o n d d e m o n s t r a t e s c o m p e t i t i o n between t h e two ( G r a n t 1972b). C o n n e l l ' s (1961) e a r l y f i e l d e x p e r i m e n t on b a r n a c l e s showed t h a t C h t h a m a l u s s t e l l a t u s e x i s t e d i n t h e lo w e r i n t e r t i d a l o n l y when B a l a n u s b a l a n o i d e s , w h i c h r e d u c e d s u r v i v a l and r e p r o d u c t i o n of C h t h a m a l u s , was removed. J a e g e r (1971) e x p e r i m e n t a l l y d e m o n s t r a t e d t h a t t h e s a l a m a n d e r P l e t h o d o n  c i n e r e u s c o m p e t i t i v e l y e x c l u d e d P. r i c h m o n d i from o p t i m a l m o i s t h a b i t a t s . R e c i p r o c a l i n c r e a s e s i n d e n s i t i e s of g r a n i v o r o u s a n t s and r o d e n t s i n t h e a b s e n c e o f e a c h o t h e r v e r i f i e d c o m p e t i t i v e i n t e r a c t i o n s between t a x o n o m i c a l l y d i s s i m i l a r o r g a n i s m s ( D a v i d s o n e t a l . 1980). F i e l d e x p e r i m e n t s combine a d v a n t a g e s of f i e l d o b s e r v a t i o n s and l a b o r a t o r y e x p e r i m e n t s . As i n d e s c r i p t i v e s t u d i e s , t h e y r e t a i n c o m p l e x i t y of n a t u r a l s y s t e m s . As i n l a b o r a t o r y s t u d i e s , t h e c o m p e t i t i v e p r o c e s s i s i n d e x e d d i r e c t l y a s p e r f o r m a n c e , r a t h e r t h a n i n f e r r e d f r o m a p a t t e r n . T h i s p e r m i t s a f f i r m a t i o n o f c o m p e t i t i o n w i t h o u t o f t e n u n o b t a i n a b l e knowledge of r e s o u r c e abundance and a v a i l a b i l i t y . The major l i m i t a t i o n i n f i e l d e x p e r i m e n t s i s t h a t p o p u l a t i o n s o f l a r g e o r m o b i l e s p e c i e s , s u c h as l a r g e mammals or b i r d s , a r e n o t r e a d i l y m a n i p u l a b l e ( C o n n e l l 1975). Many s t u d i e s have e f f e c t e d p e r t u r b a t i o n s by c o n f i n i n g p o p u l a t i o n s ( e . g., J a e g e r 1971; W i l b u r 1972; D e B e n e d i c t i s 1974). T h e s e s t u d i e s must c o n s i d e r c o n f o u n d i n g of c o m p e t i t i v e outcomes w i t h r e d u c e d d i s p e r s a l ( B o o n s t r a and R r e b s 1977), 6 p r e d a t o r e x c l u s i o n , l i m i t e d n u t r i e n t f l o w (Lehman 1980a and b ) , and o t h e r p o s s i b l e e n c l o s u r e e f f e c t s ( C o n n e l l 1975). O b s e r v a t i o n a l and e x p e r i m e n t a l f i e l d s t u d i e s can be c o m p l e m e n t a r y . O b s e r v a t i o n s a r e u s e f u l i n r e c o g n i z i n g p o t e n t i a l l y c o m p e t i t i v e s i t u a t i o n s . Once e x p e r i m e n t a t i o n has c o n f i r m e d t h a t c o m p e t i t i o n i s i n v o l v e d , o b s e r v a t i o n s on p a t t e r n s of r e s o u r c e use can a s s i s t i n i d e n t i f y i n g l i m i t e d , c o m p e t e d - f o r r e s o u r c e s . (However, r e s p o n s e s of c o m p e t i t o r s t o e x p e r i m e n t a l a l t e r a t i o n s of r e s o u r c e l e v e l s more r e l i a b l y d e t e c t c r u c i a l r e s o u r c e s [Vance 1972; Brown and D a v i d s o n 1977; but see Thomson 1 9 8 0 ] ) . Werner and H a l l (1976,1977) and Werner (1977) s u c c e s s f u l l y amalgamated o b s e r v a t i o n and e x p e r i m e n t i n t h e i r work on c e n t r a r c h i d f i s h e s . On t h e o t h e r hand, d i s a g r e e m e n t between o b s e r v a t i o n a l and e x p e r i m e n t a l r e s u l t s f o r two s p e c i e s of Dipodomys e m p h a s i z e d t h e need t o t e s t o b s e r v a t i o n s e x p e r i m e n t a l l y . H i g h o v e r l a p i n h a b i t a t use i n d i c a t e d i n t e n s e i n t e r s p e c i f i c c o m p e t i t i o n between t h e r o d e n t s ; y e t , r e m o v a l e x p e r i m e n t s i m p l i c a t e d o n l y i n t r a s p e c i f i c c o m p e t i t i o n ( S c h r o d e r and R o s e n z w e i g 1975). S i n c e c o m p e t i t i o n may o c c u r o n l y p e r i o d i c a l l y i f e n v i r o n m e n t a l c o n d i t i o n s a r e v a r i a b l e (Wiens 1977), b o t h o b s e r v a t i o n a l and e x p e r i m e n t a l s t u d i e s must be l o n g -t e r m r e l a t i v e t o g e n e r a t i o n t i m e s o f c o m p e t i t o r s ( J o h a n n e s and L a r k i n 1-961; S c h r o d e r and R o s e n z w e i g 1975; Wiens 1977). F i e l d e x p e r i m e n t s a r e more p r o f i t a b l e t o t h e s t u d y of c o m p e t i t i o n than e i t h e r l a b o r a t o r y e x p e r i m e n t s o r p u r e l y d e s c r i p t i v e f i e l d s t u d i e s b e c a u s e t h e y p r o v i d e e x p l i c i t e v i d e n c e f o r t h e p r o c e s s i n n a t u r a l e n v i r o n m e n t s . I n c r e a s i n g l y , f i e l d 7 e x p e r i m e n t s have been e x a m i n i n g c o m p e t i t i o n among a l l t y p e s of o r g a n i s m s , from mammals ( G r a n t 1972b; K r e b s 1977; P r i c e 1978), b i r d s ( D a v i s 1973), r e p t i l e s (Dunham 1980), a m p h i b i a n s ( W i l b u r 1972; J a e g e r 1974; H a i r s t o n 1980), and f i s h (Werner 1977; H i x o n 1979, 1980; L a r s o n " l 9 8 0 ) , t o i n v e r t e b r a t e s ( P a i n e 1971, 1974; Underwood 1.978). F u l l e v a l u a t i o n o f t h e i m p o r t a n c e o f c o m p e t i t i o n t o e c o l o g i c a l s y s t e m s r e q u i r e s more f i e l d e x p e r i m e n t s i n a w i d e r v a r i e t y of communties ( C o n n e l l 1975; P i a n k a 1976; MacLean and Magnuson 1977; Wiens 1977). Among t h o s e c o m m u n i t i e s r e q u i r i n g f u r t h e r c o m p e t i t i o n s t u d i e s a r e l a c u s t r i n e h e r b i v o r o u s z o o p l a n k t o n c o m m u n i t i e s ( L y n c h 1977a). C u r r e n t i d e a s on z o o p l a n k t o n community o r g a n i z a t i o n stem from t h e s i z e - e f f i c i e n c y h y p o t h e s i s ( B r o o k s and Dodson 1965; K e r f o o t and DeMott 1980). T h i s h y p o t h e s i s s t a t e s t h a t , b e c a u s e t h e y f e e d l e s s e f f i c i e n t l y on s m a l l p a r t i c l e s and consume a n a r r o w e r s i z e r ange of p a r t i c l e s , s m a l l h e r b i v o r o u s z o o p l a n k t o n s p e c i e s a r e c o m p e t i t i v e l y i n f e r i o r t o l a r g e s p e c i e s . C o n s e q u e n t l y , o n l y under i n t e n s e s i z e - s e l e c t i v e p r e d a t i o n on l a r g e s p e c i e s can s m a l l ones d o m i n a t e t h e community ( B r o o k s and Dodson 1965; H a l l e t a l . 1976) A v a r i a t i o n o f t h e s i z e - e f f i c i e n c y h y p o t h e s i s , t h e c o m p l e m e n t a r y f e e d i n g n i c h e h y p o t h e s i s (Dodson 1970), c l a i m s t h a t v i s u a l v e r t e b r a t e p r e d a t o r s enhance t h e s m a l l z o o p l a n k t o n p r e y of i n v e r t e b r a t e p l a n k t i v o r e s by s e l e c t i n g c o m p e t i t i v e l y s u p e r i o r p r e y . T h e s e and s i m i l a r v i e w s of z o o p l a n k t o n community o r g a n i z a t i o n s t r e s s t h e r o l e o f p r e d a t i o n w h i l e i m p l i c i t l y a s s u m i n g t h e i m p o r t a n c e of d i f f e r e n t i a l c o m p e t i t i v e a b i l i t i e s of l a r g e and s m a l l 8 h e r b i v o r e s . Numerous s t u d i e s , some of them c o n t r a d i c t o r y and many of them e x p e r i m e n t a l , have examined c o n t r i b u t i o n s , e s p e c i a l l y o f v e r t e b r a t e p r e d a t i o n , t o o r g a n i z a t i o n of z o o p l a n k t o n c o m m u n i t i e s ( H a l l e t a l . 1970; L y n c h 1979; O ' B r i e n 1979; Z a r e t 1980). E x p e r i m e n t a l a d d i t i o n s o f f i s h t o f i s h l e s s l a k e s o f t e n ( B r o o k s and Dodson 1965; A n d e r s o n 1972), but n o t a l w a y s ( N o r t h c o t e e t a l . 1978), have c a u s e d s h i f t s i n z o o p l a n k t o n s p e c i e s c o m p o s i t i o n s from l a r g e r t o s m a l l e r o r g a n i s m s . F i e l d e x p e r i m e n t s have s u p p o r t e d t h e c o m p l e m e n t a r y f e e d i n g n i c h e h y p o t h e s i s f o r s a l a m a n d e r s and C h a o b o r u s l a r v a e (Dodson 1970; G i g u e r e 1979). S e v e r a l s t u d i e s have e m p h a s i z e d t h e impact of i n v e r t e b r a t e p r e d a t i o n on community s t r u c t u r e and p o p u l a t i o n d y n a m i c s of h e r b i v o r o u s p r e y (McQueen 1969; A l l a n 1973; Dodson 1974; L e w i s 1979; L y n c h 1979; r e v i e w e d i n Z a r e t 1980), t h o u g h f i e l d e x p e r i m e n t s i n o l i g o t r o p h i c l a k e s have shown r e s i s t a n c e o f z o o p l a n k t o n p o p u l a t i o n s t o v a r i a t i o n s i n d e n s i t i e s of C h a o b o r u s l a r v a e and p r e d a c e o u s c y c l o p o i d c o p e p o d s ( N e i l l and P e a c o c k 1980; N e i l l 1981a; Pe a c o c k 1981). W h i l e p r e d a t i o n i n z o o p l a n k t o n c o m m u n i t i e s has been amply i n v e s t i g a t e d , c o m p e t i t i o n has not ( H a l l e t a l . 1976; L y n c h 1979). Most z o o p l a n k t o n c o m p e t i t i o n s t u d i e s have been o b s e r v a t i o n a l , d e s c r i b i n g d i f f e r e n c e s among c o - o c c u r r i n g s p e c i e s i n s e a s o n a l c y c l e , s p a t i a l d i s t r i b u t i o n or d i e t a s c o e x i s t e n c e mechanisms ( e . g., Tappa 1965; H e i p 1973; Lane and McNaught 1970, 1973; Lane 1975; P o u l e t 1978; R a n t a 1979; S e i t z 1980). L i k e most d e s c r i p t i v e s t u d i e s , t h e s e have assumed r a t h e r t h a n 9 d e m o n s t r a t e d c o m p e t i t i o n . Many l a b o r a t o r y e x p e r i m e n t s have e x h i b i t e d c o m p e t i t i v e e x c l u s i o n among c l a d o c e r a n s ( e . g., F r a n k 1952, 1957; P a r k e r 1960, 1961; d e B e r n a r d i 1979; G o u l d e n and H o r n i g 1980), but b e c a u s e f i e l d t e s t s have shown c o e x i s t e n c e i n n a t u r e of s p e c i e s i n c o m p a t i b l e i n t h e l a b o r a t o r y ( A l l a n 1973; d e B e r n a r d i 1979; K e r f o o t and DeMott 1980), l a b o r a t o r y d a t a a r e s u s p e c t . The l a b o r a t o r y m i c r o c o s m work of N e i l l (1975a and b) d e m o n s t r a t e d t h a t , c o n t r a r y t o t h e s i z e - e f f i c i e n c y h y p o t h e s i s , s m a l l C e r i o d a p h n i a o u t c o m p e t e d l a r g e r c l a d o c e r a n s . In an u n u s u a l example of a l l e l o p a t h y among c o p e p o d s , Fol-t and Goldman (1981) f o u n d t h a t E p i s c h u r a n e v a d e n s i s i n l a b o r a t o r y s y s t e m s r e l e a s e d a c h e m i c a l c a u s i n g Diaptomus t y r e l 1 i t o r e d u c e i t s f i l t e r i n g c a p a c i t y by 60%. Few f i e l d e x p e r i m e n t s on z o o p l a n k t o n c o m p e t i t i o n e x i s t . None has been v e r y c o n c l u s i v e , and a l l have been on c l a d o c e r a n s . Dodson (1974) c o n c l u d e d t h a t D i a p t o m u s shoshone p r e d a t i o n on s m a l l D a p h n i a minnehaha e x p l a i n e d t h e l a t t e r ' s a b s e n c e f r o m ponds c o n t a i n i n g l a r g e D a p h n i a m i d d e n d o r f f i a n a . W o r k i n g on t h e same s y s t e m i n a p r e v i o u s y e a r , S p r u l e s (1972) c o n c l u d e d t h a t t h e l a r g e r s p e c i e s c o m p e t i t i v e l y e x c l u d e d t h e s m a l l e r one. In e x p e r i m e n t a l l y e n c l o s e d c o m m u n i t i e s , s m a l l C e r i odaphn i a r e t i c u l a t a e i t h e r c o e x i s t e d w i t h l a r g e Daphn i a p u l e x or o u t c o m p e t e d i t ( L y n c h 1978). S i m i l a r l y , c o m p e t i t i o n between D. p u l e x and s m a l l Bosmina l o n g i r o s t r i s p r o d u c e d no c o n s i s t e n t outcome ( K e r f o o t and DeMott 1980). Amending the l a c k of c o n c l u s i v e f i e l d e x p e r i m e n t s on z o o p l a n k t o n c o m p e t i t i o n c o u l d w e l l b e g i n w i t h t h e c a l a n o i d 1 0 c o p e p o d genus D i a p t o m u s . A l t h o u g h some l a k e s u r v e y s t u d i e s have s t r e s s e d t h a t Diaptomus s p e c i e s do not commonly c o e x i s t ( G r a i n g e r 1952; Pennak 1957; P a t a l a s 1971), examples o f c o -o c c u r r e n c e s abound i n t h e l i t e r a t u r e ( C o l e 1961). Reed (1964) r e c o r d e d f o u r d i a p t o m i d c o p e p o d s i n one n o r t h S a s k a t c h e w a n l a k e . D a v i s (1954, 1961) n o t e d f i v e d i a p t o m i d s i n L a k e E r i e . C o l e (1961) c i t e d 34 d i f f e r e n t c o m b i n a t i o n s of 2 or more c o e x i s t i n g D iaptomus s p e c i e s . F i f t y - o n e o f 100 s o u t h O n t a r i o l a k e s s a m p l e d c o n t a i n e d more than one d i a p t o m i d ( R i g l e r and L a n g f o r d 1967). To d a t e , t h e many f i e l d s t u d i e s i n v e s t i g a t i n g 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 among Diaptomus s p e c i e s have been p u r e l y o b s e r v a t i o n a l . T o g e t h e r t h e y have p r o v i d e d a n o t i o n of d i a p t o m i d c o m p e t i t i o n t h a t needs e x p e r i m e n t a l v a l i d a t i o n . D e s c r i p t i v e s t u d i e s on c o m p e t i t i o n i n D i a p t o m u s t y p i c a l l y have i n t e r p r e t e d d i f f e r e n c e s among c o - o c c u r r i n g s p e c i e s as c o e x i s t e n c e mechanisms. T h r e e main mechanisms have d o m i n a t e d t h e d i a p t o m i d l i t e r a t u r e . (1) D i e t a r y d i f f e r e n c e s f a v o u r d i a p t o m i d c o e x i s t e n c e ( H u t c h i n s o n 1951; C o l e 1961; S a n d e r c o c k 1967). C o e x i s t i n g D. g r a c i 1 i s and D. l a t i c e p s e a t s m a l l g r e e n a l g a l c e l l s and t h e d i a t o m M e l o s i r a , r e s p e c t i v e l y ( F r y e r 1954). S m a l l D. m i n u t u s and l a r g e r D. o r e g o n e n s i s c o e x i s t i n G u l l L a k e by p a r t i t i o n i n g f o o d c e l l s by s i z e ( M e l l i n g e r 1974). H u t c h i n s o n (1951) s u g g e s t e d d i a p t o m i d s i z e d i s p a r i t y a s a c o e x i s t e n c e mechanism e q u i v a l e n t t o d i e t a r y d i f f e r e n c e . D. p r i b i l o f e n s i s and D. a r c t i c u s d i f f e r i n l e n g t h by a 11 f a c t o r of two, and c o e x i s t i n A l a s k a n l a k e s ( T a s h and A r m i t a g e 1967). S i m i l a r l y - s i z e d D. t y r e l l i and D. l i n t o n i do n o t c o - o c c u r i n h i g h a l t i t u d e Wyoming l a k e s ( W i l l i a m s 1976). (2) V e r t i c a l s e g r e g a t i o n p r o m o t e s d i a p t o m i d c o e x i s t e n c e ( C o l e 1961; S a n d e r c o c k 1967). D. m i n u t u s c o e x i s t s w i t h D. s i c i l i s i n l a k e s i n n o r t h w e s t e r n O n t a r i o ( P a t a l a s 1971) and w i t h D. o r e g o n e n s i s i n l a k e s i n s o u t h e r n O n t a r i o ( R i g l e r and L a n g f o r d 1967) b e c a u s e i t r e s i d e s h i g h e r i n t h e water c o l u m n . (3) S e a s o n a l s e p a r a t i o n f a c i l i t a t e s d i a p t o m i d c o e x i s t e n c e ( C o l e 1961; D a v i s 1961). Up t o f o u r d i a p t o m i d s can i n h a b i t one s h a l l o w S a s k a t c h e w a n pond b e c a u s e s p r i n g and summer b r e e d i n g s p e c i e s o c c u r a s y n c h r o n o u s l y (Sawchyn 1966; Hammer and Sawchyn 1968; Sawchyn and Hammer 1968). D. s a n g u i n e u s and D. b i r q e i s i m i l a r l y s e g r e g a t e i n M a r y l a n d ponds (Smrchek 1973). W h i l e s t u d y i n g t h r e e d i a p t o m i d s i n C l a r k e L a k e, O n t a r i o , S a n d e r c o c k (1965, 1967) f o u n d t h a t two of t h e s e c o e x i s t e n c e mechanisms o p e r a t e d f o r e a c h s p e c i e s p a i r . D. m i n u t u s and D. s a n g u i n e u s d i f f e r e d i n s i z e and v e r t i c a l d i s t r i b u t i o n ; D. o r e q o n e n s i s and D. s a n g u i n e u s , i n v e r t i c a l d i s t r i b u t i o n and s e a s o n a l c y c l e ; and D. m i n u t u s and D. o r e g o n e n s i s , i n s i z e , and s e a s o n a l c y c l e . She s u g g e s t e d t h a t i n g e n e r a l two mechanisms i n c o m b i n a t i o n a r e needed f o r d i a p t o m i d c o e x i s t e n c e . Most Diaptomus 1 2 s t u d i e s have i n v o k e d a t l e a s t two of t h e s e t h r e e f a c t o r s ( e . g., C o l e 1961; T a s h and A r m i t a g e 1967; Hammer and Sawchyn 1968; S p r u l e s 1972; Ma l y and Maly 1974; M a l y 1976; P e d e r s o n and L i t t 1976). C o e x i s t e n c e mechanisms o t h e r t h a n t h e s e t h r e e common ones have o c c a s i o n a l l y been i n v o k e d . The s h o r t d u r a t i o n o v e r w h i c h c o m p e t i t i o n o p e r a t e s a l l o w s many s i m i l a r d i a p t o m i d s p e c i e s t o c o e x i s t i n t e m p o r a r y ponds ( C o l e 1966; A n d e r s o n and F a b r i s 1970) and i n a r c t i c e n v i r o n m e n t s w i t h s h o r t g r o w i n g s e a s o n s ( T a s h and A r m i t a g e 1967). F u g i t i v e s p e c i e s c an t e m p o r a r i l y evade s u p e r i o r c o m p e t i t o r s by i n v a d i n g e n v i r o n m e n t s n o t y e t c o l o n i z e d by them ( E l t o n 1929; H u t c h i n s o n 1951). C o l e (1961) s u g g e s t e d t h a t d i s s i m i l a r i t i e s among Diaptomus s p e c i e s i n d i f f e r e n t s u b g e n e r a a r e s u f f i c i e n t t o p e r m i t c o e x i s t e n c e , but T u r v e y (1968) showed s t a t i s t i c a l l y t h a t s u b g e n e r i c c o - o c c u r r e n c e s happen as f r e q u e n t l y a s p r e d i c t e d by c h a n c e . In o c c a s i o n a l c a s e s of d i a p t o m i d c o - o c c u r r e n c e , no c o e x i s t e n c e mechanism i s a p p a r e n t ( D a v i s 1961; Hoffman 1979). V e r i f i c a t i o n of d i f f e r e n c e s among Diaptomus i n d i e t , v e r t i c a l d i s t r i b u t i o n , and s e a s o n a l c y c l e a s c o e x i s t e n c e mechanisms needs e x p e r i m e n t a l d e m o n s t r a t i o n of d i a p t o m i d c o m p e t i t i o n , p a r t i c u l a r l y i n non-headwater l a k e s . C o n t i n u o u s i n f l u x i n t o t h e s e l a k e s from u p s t r e a m w a t e r s c an o b s c u r e d i a p t o m i d i n t e r a c t i o n s by m a i n t a i n i n g p o p u l a t i o n s o f i m m i g r a n t s u n a b l e t o compete w i t h r e s i d e n t s p e c i e s ( T o n o l l i 1953; C o w e l l 1967; T u r v e y 1968). Y e t no d i a p t o m i d r e s e a r c h e r s have examined e x p e r i m e n t a l l y whether non-headwater c o - o c c u r r e n c e s r e l y on 13 s p e c i e s d i f f e r e n c e s as c o e x i s t e n c e mechanisms or on s u c c e s s i v e i m m i g r a t i o n s . Few even have i n d i c a t e d t h e h y d r o l o g i c s t a t u s of t h e i r s t u d y l a k e s ( T u r v e y 1968). T h i s t h e s i s e x p e r i m e n t a l l y e v a l u a t e s e f f e c t s of c o m p e t i t i o n from z o o p l a n k t o n r e s i d e n t i n a non-headwater l a k e on p e r f o r m a n c e of a d i a p t o m i d c o p e p o d t h a t r e g u l a r l y i m m i g r a t e s from an u p s t r e a m headwater l a k e . H o p e f u l l y , i n s i g h t s g a i n e d w i l l b e g i n t o remedy t h e s h o r t a g e of c o n c l u s i v e e x p e r i m e n t a l i n f o r m a t i o n on c o m p e t i t i o n i n z o o p l a n k t o n c o m m u n i t i e s . 1 4 THE STUDY SYSTEM The s t u d y s i t e i s a c o a s t a l montane l a k e i n t h e U n i v e r s i t y of B r i t i s h C o l u m b i a R e s e a r c h F o r e s t , near Haney, B r i t i s h C o l u m b i a ( F i g . 1 ) . L o n g - t e r m m o n i t o r i n g s t u d i e s ( E f f o r d 1967; N o r t h c o t e and C l a r o t t o 1975) and e x p e r i m e n t a l m a n i p u l a t i o n s ( N o r t h c o t e e t a l . 1978; N e i l l 1978, 1981a; N e i l l and Peac o c k 1980; P e a c o c k 1981) p r o v i d e b a c k g r o u n d i n f o r m a t i o n on R e s e a r c h F o r e s t l a k e s . In g e n e r a l , t h e y a r e s m a l l , o l i g o t r o p h i c , t h e r m a l l y s t r a t i f i e d i n summer, w e l l o x y g e n a t e d , and deep ( N e i l l 1978). P l a n k t i v o r o u s f i s h n a t u r a l l y o c c u r i n some of them ( N o r t h c o t e and C l a r o t t o 1975), and r e c e n t l y have been i n t r o d u c e d i n t o o t h e r s ( N o r t h c o t e e t a l . 1978). The l a k e s c o n t a i n s i m i l a r c r u s t a c e a n z o o p l a n k t o n s p e c i e s i n d i f f e r e n t r e l a t i v e a b u ndances ( N o r t h c o t e and C l a r o t t o 1975). D e t r i t u s , b a c t e r i a , and a l g a e p r o v i d e f o o d f o r f i l t e r - f e e d i n g s p e c i e s . C o n c e n t r a t i o n s of g r a z a b l e (<30 urn i n d i a m e t e r ) p a r t i c u l a t e o r g a n i c m a t t e r a r e low, u s u a l l y v a r y i n g between 0.3 and 0.9 mg/1 a s h - f r e e d r y w e i g h t ( N e i l l 1978), b ut i n c r e a s i n g t o n e a r l y 1.6 mg/1 a f t e r heavy r a i n s ( P e a c o c k 1981; N e i l l and W a l t e r s u n p u b l . d a t a ) . T a b l e I summarizes a b i o t i c and b i o t i c c h a r a c t e r i s t i c s of two c o n n e c t e d R e s e a r c h F o r e s t l a k e s . A s m a l l s t r e a m j o i n s G w e n d o l i n e , a headwater l a k e , t o E u n i c e L a k e . E x c e p t f o r D i a p t o m u s t y r e l l 1 , w h i c h o c c u r s o n l y i n E u n i c e L a k e , s p e c i e s c o m p o s i t i o n s i n t h e two l a k e s a r e s i m i l a r . E x c e p t f o r Diaptomus  l e p t o p u s , w h i c h i s abundant i n G w e n d o l i n e L a k e , d e n s i t i e s of s p e c i e s common t o b o t h l a k e s a r e h i g h e r i n E u n i c e L a k e . D. l e p t o p u s o c c u r s a t b a r e l y d e t e c t a b l e l e v e l s i n E u n i c e d e s p i t e 15 F i g u r e 1. Map showing l o c a t i o n of s t u d y s i t e . From N e i l l (1978) 16 1 7 T a b l e I . P h y s i c a l , c h e m i c a l , and b i o l o g i c a l c h a r a c t e r i s t i c s of G w e n d o l i n e and E u n i c e L a k e s . C r u s t a c e a n d e n s i t i e s a r e maximum summer d e n s i t i e s i n l i m n e t i c r e g i o n , a v e r a g e d o v e r water column sampled n e a r midday. A d a p t e d from N o r t h c o t e . and C l a r o t t o (1975) C h a r a c t e r i s i t i c G w e n d o l i n e E u n i c e E l e v a t i o n (m) 522 480 D r a i n a g e a r e a (ha) 81 191 S u r f a c e a r e a (ha) 13.0 18.2 Maximum d e p t h (m) 27 42 Mean d e p t h (m) 13.4 15.8 T o t a l d i s s o l v e d s o l i d s (mg/1) 18 16 pH 6.6 6.4 C o l o u r ( Pt u n i t s ) 15 15 T r a n s p a r e n c y ( S e c c h i d i s c , m) 5-7.2 6-10 E p i l i m n i o n d e p t h , l a t e summer (m) 5 4-6 H y p o l i m n i o n 0 2 , minimum (mg/1) 4.0 0.6 C r u s t a c e a n d e n s i t y ( # / l 0 0 1) Daphn i a r o s e a 95 233 H o l o p e d i u m g i b b e r u m 45 124 Diaphanosoma b r a c h y u r u m 194 253 Polyphemus p e d i c u l u s 4.5 13 C e r i o d a p h n i a p u l c h e i l a r a r e r a r e Bosmina l o n g i r o s t r i s 116 230 Dia p t o m u s k e n a i 10 70 D i a p t o m u s l e p t o p u s 13 0.5 D i a p t o m u s t y r e l l i -- 800 C y c l o p o i d c o p e p o d s 14 27 Y e a r s z o o p l a n k t o n s a m p l e d 1967, 1969 1967, 1969 1971, 1972 18 a r e a d y means o f i m m i g r a t i o n v i a t h e s t r e a m from G w e n d o l i n e . T h i s s t u d y e x p e r i m e n t a l l y t e s t s t h e h y p o t h e s i s t h a t c o m p e t i t i o n f r o m one or more r e s i d e n t z o o p l a n k t o n s p e c i e s p r e v e n t s i m m i g r a n t D. l e p t o p u s from c o l o n i z i n g i n E u n i c e L a k e . The o c c u r r e n c e of D. t y r e l l i o n l y i n E u n i c e Lake and t h e h i g h e r c r u s t a c e a n d e n s i t i e s t h e r e t h a n i n G w e n d o l i n e Lake b o t h s u p p o r t a c o m p e t i t i v e e x p l a n a t i o n o f D. l e p t o p u s r a r i t y i n E u n i c e . Two o t h e r p o s s i b l e e x p l a n a t i o n s - a b i o t i c f a c t o r s and p r e d a t i o n -can be d i s r e g a r d e d a p r i o r i . C o n s i d e r i n g t h e i r c o n n e c t i o n , t h e s t r i k i n g p h y s i c a l and c h e m i c a l s i m i l a r i t i e s between G w e n d o l i n e and E u n i c e L a k e s a r e not s u r p r i s i n g ( T a b l e I ) . T h a t some a b i o t i c c h a r a c t e r i s t i c u n i q u e t o E u n i c e i s u n f a v o u r a b l e t o D. l e p t o p u s i s t h u s u n l i k e l y . . T h a t some E u n i c e Lake p r e d a t o r e l i m i n a t e s D. l e p t o p u s i s e q u a l l y i m p r o b a b l e . H i s t o r i c a l l y , b o t h E u n i c e and G w e n d o l i n e L a k e s c o n t a i n e d l a r v a e of C h a o b o r u s a m e r i c a n u s and C. t r i v i t t a t u s as major p r e d a t o r s ( F e d o r e n k o and S w i f t 1972? N o r t h c o t e and C l a r o t t o 1975). C u t t h r o a t t r o u t (Salmo c l a r k i ) i n t r o d u c e d i n t o E u n i c e i n 1974-76 e l i m i n a t e d C h a o b o r u s , and a r e now t h e m s e l v e s t h e major p r e d a t o r ( N o r t h c o t e e t a l . 1978). T h r o u g h o u t t h e s e d i s p a r a t e p r e d a t i o n r e g i m e s , D. l e p t o p u s has r e m a i n e d r a r e i n E u n i c e L a k e . D iaptomus l e p t o p u s i s a h e r b i v o r o u s , f i l t e r - f e e d i n g c a l a n o i d ( S c h i n d l e r and C o m i t a 1966; A n d e r s o n 1970). T h i s w i d e s p r e a d s p e c i e s o c c u r s a c r o s s N o r t h A m e r i c a from V i r g i n i a and Oregon i n t h e s o u t h t o A l a s k a i n t h e n o r t h ( W i l s o n 1959). I t s u r v i v e s i n a l p i n e and s u b a l p i n e l a k e s ( W i l s o n 1959; A n d e r s o n 1971), but i s more common i n montane l a k e s ( P a t a l a s 1964; 1 9 A n d e r s o n 1974) and p r a i r i e ponds (Reed and O l i v e 1958; A n d e r s o n 1971). A l t h o u g h i t o c c u r s i n o l i g o t r o p h i c e n v i r o n m e n t s (Winner 1970; P a t a l a s 1971; S c h i n d l e r and Noven 1971), many r e c o r d s a r e from e u t r o p h i c w a t e r s (Hazelwood and P a r k e r 1961; H e a l e y 1967; S m i t h 1968; A n d e r s o n and F a b r i s 1970) and from t e m p o r a r y (Hammer and Sawchyn 1968; O ' B r i e n e t a l . 1973) or semi-permanent ponds ( W h i t t a k e r and F a i r b a n k s 1958). In montane E u n i c e L a k e , D. l e p t o p u s c o - o c c u r s a t low d e n s i t y w i t h two o t h e r h e r b i v o r o u s ( A n d e r s o n • 1970) d i a p t o m i d s . B o t h D. t y r e l l i ( C a r l 1940; W i l s o n 1959; A n d e r s o n 1971, 1972) and D. k e n a i ( W i l s o n 1959; P e d e r s o n and L i t t 1976) a r e more c h a r a c t e r i s t i c o f o l i g o t r o p h i c , h i g h a l t i t u d e l a k e s t h a n D. l e p t o p u s . D. t y r e l l i i s s m a l l e r ( l e n g t h = 1.1 - 1.9 mm), and D. k e n a i l a r g e r ( l e n g t h = 1.8 - 3.0 mm) t h a n ' D. l e p t o p u s ( l e n g t h = 1.25 - 2.5 mm) ( W i l s o n 1959). C o l e (1961) c i t e d c o -o c c u r r e n c e s of D. l e p t o p u s w i t h D. w i l s o n a e and D. m i n u t u s . From a s u r v e y of 52 C o l o r a d o l a k e s , P a t a l a s (1964) c o n c l u d e d t h a t D. l e p t o p u s t e n d s not t o c o - o c c u r w i t h c o n g e n e r s . Of s e v e n d i a p t o m i d s i n S a s k a t c h e w a n ponds, o n l y D. l e p t o p u s o c c u r s a l o n e f o r p e r i o d s of more t h a n 3 weeks (Hammer and Sawchyn 1968). I n f o r m a t i o n e x i s t s f o r D. l e p t o p u s on r e s p o n s e s t o a b i o t i c f a c t o r s ( Hazelwood and P a r k e r 1961, 1963; Winner 1970; O ' B r i e n e t a l . 1973), on f e e d i n g ( S c h i n d l e r and C o m i t a 1966; Levy and C o m i t a 1971) and r e s p i r a t i o n r a t e s ( C o m i t a 1968), and on r e p r o d u c t i v e p h y s i o l o g y (Watras 1980; W a t ras and Haney 1980), g e n e r a l e c o l o g y , and l i f e h i s t o r y (Sawchyn and Hammer 1968; Winner 1970; O ' B r i e n e t a l . 1973). As i s t y p i c a l of d i a p t o m i d s , 20 D. l e p t o p u s d e v e l o p s from s e x u a l l y r e p r o d u c e d eggs t h r o u g h s i x n a u p l i a r and s i x c o p e p o d i t e s t a g e s . The f i n a l c o p e p o d i t e i s t h e a d u l t ( O ' B r i e n e t a l . 1973). D. l e p t o p u s p r o d u c e s from one ( O ' B r i e n e t a l . 1973) t o t h r e e g e n e r a t i o n s (Sawchyn and Hammer 1968) p e r y e a r . G e n e r a t i o n t i m e v a r i e s from 4.6 weeks a t 20-25°C i n a t e m p o r a r y pond ( O ' B r i e n e t a l . 1973) t o 7.2 weeks a t 8-16°C i n a bog l a k e (Winner 1970). Winner (1970) f o u n d t h a t a d u l t s of f a l l g e n e r a t i o n s i n a bog l a k e p r o d u c e d o v e r w i n t e r i n g r e s t i n g e g g s . D. l e p t o p u s i n a t e m p o r a r y pond p r o d u c e d o n l y s u b i t a n e o u s eggs, b ut not a l l o f t h e s e h a t c h e d i m m e d i a t e l y ( O ' B r i e n e t a l . 1973). 21 MATERIALS AND METHODS E x p e r i m e n t s d e s i g n e d t o e v a l u a t e e f f e c t s o f i n t e r s p e c i f i c c o m p e t i t i o n on Diaptomus l e p t o p u s i n E u n i c e Lake i n v o l v e d c o n f i n i n g t h i s s p e c i e s w i t h v a r i o u s c o m b i n a t i o n s of E u n i c e Lake s p e c i e s . S p e c i f i c e x p e r i m e n t a l d e s i g n s and t h e h y p o t h e s e s t h e y t e s t a r e d e s c r i b e d w i t h t h e i r r e s u l t s . T h i s s e c t i o n d e t a i l s t h e g e n e r a l methods of e s t a b l i s h i n g and m o n i t o r i n g a l l m a n i p u l a t i o n s . E x p e r i m e n t s were c o n d u c t e d i n E u n i c e L a k e from J une t o O c t o b e r , 1979 and from May t o September, 1980. L a r g e e n c l o s u r e s s i m i l a r t o t h o s e of N e i l l (1978) c o n t a i n e d t h e e x p e r i m e n t a l t r e a t m e n t s . Tubes of 6 m i l (1979) o r u l t r a v i o l e t - r e s i s t a n t 4 m i l (1980) t r a n s p a r e n t p o l y e t h y l e n e formed t h e e n c l o s u r e s . Wood and s t y r o f o a m f r a m e s s u s p e n d e d them f r o m t h e s u r f a c e of t h e l a k e , and t i e d o f f low e r ends p r e v e n t e d c o n t a c t w i t h t h e s e d i m e n t s . E n c l o s u r e s measured 1.5 m wide by 12-13 m deep. A p p r o x i m a t e l y 29,000 1 o f l a k e w a t e r , f i l t e r e d t h r o u g h a 54 urn n e t t o remove z o o p l a n k t o n but not g r a z a b l e s e s t o n , f i l l e d e a c h one. Ten v e r t i c a l h a u l s , t a k e n from E u n i c e L a k e a t random p o i n t s w i t h a 54 urn p l a n k t o n n e t , d e t e r m i n e d n a t u r a l l a k e d e n s i t i e s of e a c h z o o p l a n k t o n s p e c i e s . E x p e r i m e n t a l d e n s i t i e s were d e r i v e d from t h e s e d e t e r m i n a t i o n s ( s e e d e s c r i p t i o n s o f e x p e r i m e n t a l d e s i g n s ) . A n i m a l s r e q u i r e d f o r t h e m a n i p u l a t i o n s were o b t a i n e d by t o w n e t , and t h e n s o r t e d by s i e v e and p i p e t t e i n t o t h e a p p r o p r i a t e c o m b i n a t i o n s . To r e d u c e m o r t a l i t y d u r i n g s o r t i n g , z o o p l a n k t o n were kept o u t of t h e l a k e f o r l e s s t h a n 24 h r and were m a i n t a i n e d a t c o o l t e m p e r a t u r e s . S o r t e d z o o p l a n k t o n were 22 r e l e a s e d i n t o t h e e n c l o s u r e s o v e r a p e r i o d of a p p r o x i m a t e l y 21 d a y s i n 1979, and 5 d a ys i n 1980. A l l a n i m a l s , e x c e p t D. l e p t o p u s from G w e n d o l i n e , came from E u n i c e L a k e . Z o o p l a n k t o n were sampled from e a c h e n c l o s u r e a t a p p r o x i m a t e l y 5-day i n t e r v a l s w i t h a 2.5-cm d i a m e t e r hose a t t a c h e d t o an e l e c t r i c b i l g e pump c a p a b l e of pumping 25 1/min. Samples of 150 1 were f i l t e r e d t h r o u g h a 54 urn n e t t o c o n c e n t r a t e t h e a n i m a l s . E q u a l volumes were f i l t e r e d a t 1-m i n t e r v a l s f r o m t h e s u r f a c e t o 11 m (1979) o r 12 m ( 1 9 8 0 ) . A s i m i l a r p r o c e d u r e a l o n g a m i d - l a k e t r a n s e c t sampled E u n i c e L a k e . P e a c o c k (1981) showed t h a t t h i s method p r o v i d e s random and non-s e l e c t i v e s amples of t h e d i f f e r e n t c r u s t a c e a n s . C o l l e c t e d z o o p l a n k t o n were p r e s e r v e d i n d i l u t e f o r m a l i n . T w i c e i n 1979 ( J u l y 5-6 and September 18-19), 50 1 samples were c o l l e c t e d f r o m e a c h of 0-2, 2-4, 4-7, and >7 m d e p t h s t r a t a . T h e s e d e p t h - s t r a t i f i e d s a m p l e s were c o l l e c t e d i n b o t h d a y l i g h t and d a r k n e s s t o d e t e r m i n e v e r t i c a l and d i e l d i s t r i b u t i o n s o f z o o p l a n k t o n i n e a c h e n c l o s u r e . On J u l y 10, 1980, v e r t i c a l l y s t r a t i f i e d s amples were t a k e n from one r e p l i c a t e p e r t r e a t m e n t i n d a y l i g h t o n l y . Z o o p l a n k t o n samples were examined f o r s p e c i e s i d e n t i t y , i n s t a r d i s t r i b u t i o n , and r e p r o d u c t i v e c o n d i t i o n (number of o v i g e r o u s f e m a l e s , number of eggs p e r f e m a l e , and number o f u n a t t a c h e d e g g s ) of c a l a n o i d c o p e p o d s , f o r i n s t a r d i s t r i b u t i o n of c y c l o p o i d c o p e p o d s , and f o r s p e c i e s i d e n t i t y o f c l a d o c e r a n s . A l l a n i m a l s i n a l l samples were c o u n t e d a c c o r d i n g t o t h e s e c a t e g o r i e s under a d i s s e c t i n g m i c r o s c o p e a t 25x m a g n i f i c a t i o n 23 f o r n a u p l i i and a t 1 0X m a g n i f i c a t i o n f o r o t h e r o r g a n i s m s . Immature c a l a n o i d s were i d e n t i f i e d t o s p e c i e s u s i n g t a x o n o m i c d e s c r i p t i o n s d e v e l o p e d s p e c i f i c a l l y f o r t h e R e s e a r c h F o r e s t l a k e s (A. Chapman and J . G r e e n p e r s . comm. and u n p u b l . d a t a ) . O t h e r z o o p l a n k t o n were i d e n t i f i e d u s i n g keys i n Edmondson (1959) and Pennak ( 1 9 7 8 ) . Under 25x m a g n i f i c a t i o n , l e n g t h s of t h e f i r s t 10 i n d i v i d u a l s of c a l a n o i d and major c l a d o c e r a n s p e c i e s e n c o u n t e r e d i n a sample were measured f o r samples c o l l e c t e d a p p r o x i m a t e l y 10-14 d a y s a p a r t . Copepod measurements e x t e n d e d from a n t e r i o r t i p of c e p h a l o t h o r a x t o p o s t e r i o r end o f urosome, e x c l u d i n g s e t a e . C l a d o c e r a n s were measured from a n t e r i o r t o p o s t e r i o r t i p o f c a r a p a c e , e x c l u d i n g c a u d a l s p i n e s , h e l m e t s , and o t h e r a c c e s s o r y s t r u c t u r e s . O n l y a d u l t c a l a n o i d s were s i z e d . C l a d o c e r a n s were measured r e g a r d l e s s of m a t u r i t y . A n a l y s e s on z o o p l a n k t o n d a t a i n c l u d e d A n a l y s i s of V a r i a n c e (ANOVA), A n a l y s i s of C o v a r i a n c e (ANCOVA), and t - t e s t c o m p a r i s o n s ( S n e d e c o r and C o c h r a n 1967; S o k a l and R o h l f 1969; N e t e r and Wasserman 1974) computed by MIDAS s t a t i s t i c a l p a c k a g e s (Fox and G u i r e 1976). To s t a b i l i z e t h e v a r i a n c e , s p e c i e s c o u n t s were l o g -t r a n s f o r m e d ( l o g { x + l } ) p r i o r t o a n a l y s i s ( E l l i o t 1977). P h y t o p l a n k t o n were sampled from e n c l o s u r e s and from E u n i c e Lake e v e r y 10-14 d a y s . From a m i x t u r e c o n t a i n i n g 1 1 o f water pumped from e a c h of f o u r d e p t h s (1.5, 4.5, 7.5, and 10.5 m), a 250-ml sample was p r e s e r v e d i n L u g o l ' s s o l u t i o n . A 100-ml subsample was a l l o w e d t o s e t t l e f o r a t l e a s t 24 h. Then 75 ml of t h e s u p e r n a t a n t was d e c a n t e d and t h e r e m a i n i n g 25 ml a l l o w e d t o 24 s e t t l e f o r a f u r t h e r 24 h. U s i n g an i n v e r t e d m i c r o s c o p e a t 400x m a g n i f i c a t i o n , c e l l s were c o u n t e d u n t i l a t l e a s t 200 c e l l s >2 urn i n d i a m e t e r or two m i c r o s c o p e f i e l d s were i n s p e c t e d . C o u n t s were c o n v e r t e d t o b i o m a s s a s s u m i n g a c e l l s p e c i f i c g r a v i t y of 1 g/ml and c e l l v o l u m e s of 4, 42, 286, 497, 1571, and 3252 urn 3 f o r s i n g l e c e l l s <2, 2-6, 6-10, 10-14, 14-20, and >20 urn i n d i a m e t e r , r e s p e c t i v e l y , and volumes o f 300 urn 3 f o r c o l o n i e s and f i l a m e n t s . Water t e m p e r a t u r e s were r e c o r d e d f o r e a c h s a m p l i n g d a t e a t 1-m d e p t h i n t e r v a l s by pumping water from t h e a p p r o p r i a t e d e p t h o v e r a thermometer a c c u r a t e t o ± 0 . 5 ° C . The s u b r o u t i n e CNTOUR from t h e U n i v e r s i t y of B r i t i s h C o l u m b i a Computing C e n t r e ( M a i r 1980) i n t e r p o l a t e d t e m p e r a t u r e i s o c l i n e s o v e r d e p t h and t i m e . 25 EXPERIMENTAL DESIGN, 197 9 1979 e x p e r i m e n t s a t t e m p t e d t o d e t e r m i n e w h i c h , i f any, a bundant E u n i c e Lake z o o p l a n k t o n s p e c i e s c o m p e t i t i v e l y p r e v e n t s D i a ptomus l e p t o p u s from c o l o n i z i n g t h e l a k e . S i m i l a r t o most c o m p e t i t i o n e x p e r i m e n t s , t h e s e compared s e v e r a l i n d i c e s of p e r f o r m a n c e of D. l e p t o p u s i n t h e p r e s e n c e and i n t h e a b s e n c e of p o t e n t i a l c o m p e t i t o r s . Improved p e r f o r m a n c e i n t h e a b s e n c e of a s p e c i e s i m p l i c a t e d t h a t s p e c i e s as a c o m p e t i t o r . I n d i c e s of p e r f o r m a n c e i n c l u d e d d e n s i t y , r e p r o d u c t i o n and a d u l t s i z e . T a b l e II o u t l i n e s t h e e x p e r i m e n t s and t h e h y p o t h e s e s t h e y t e s t . P o l y e t h y l e n e t u b e s d e s c r i b e d i n M a t e r i a l s and Methods e n c l o s e d two r e p l i c a t e s of e a c h t r e a t m e n t . A l l e n c l o s u r e s c o n t a i n e d a s t a n d a r d d e n s i t y o f 0.14 .D. l e p t o p u s p e r l i t r e ( a d u l t s and c o p e p o d i t e s c o m b i n e d ) . T h i s d e n s i t y , a l t h o u g h c o n s i d e r a b l y h i g h e r t h a n t h a t i n E u n i c e Lake d u r i n g i n i t i a t i o n of e x p e r i m e n t s , was t h e minimum deemed d e t e c t a b l e i n z o o p l a n k t o n s a m p l e s . In a d d i t i o n t o D. l e p t o p u s , e x p e r i m e n t a l c o n t r o l s c o n t a i n e d t h e e n t i r e E u n i c e L a k e c r u s t a c e a n a s s e m b l a g e a t n a t u r a l l a k e d e n s i t i e s . T h r e e t r e a t m e n t s , by a l m o s t e n t i r e l y e x c l u d i n g one o f D a p h n i a r o s e a , D i a p t o m u s k e n a i , or Diaptomus  t y r e l l i , t e s t e d c o m p e t i t i v e e f f e c t s of t h e s e s p e c i e s on D. l e p t o p u s . L i k e D. l e p t o p u s , a l l t h r e e a r e h e r b i v o r o u s f i l t e r -f e e d e r s . I t s a b s e n c e from G w e n d o l i n e L a k e , where D. l e p t o p u s t h r i v e s , makes D. t y r e l l i a l i k e l y c a n d i d a t e f o r c o m p e t i t o r . D. k e n a i and D. r o s e a c o e x i s t w i t h D. l e p t o p u s i n G w e n d o l i n e , b u t may compete w i t h i t i n E u n i c e where t h e y r e a c h h i g h e r d e n s i t i e s ( T a b l e I ) . B e c a use z o o p l a n k t o n b i o m a s s i s lower i n Table II. Summary of 1979 experimental treatments at 1979 natural lake densities. Treatment Species composition Control N + D i aptomus 1eptopus Low density 10% N + D. 1 eptopus Daphnia-removal N - Daphnia rosea + D. 1eptopus kenai-removal N - Diaptomus kenai + D. 1eptopus tyrel1i-removal N - Diaptomus t y r e l 1 i + D. 1eptopus = Eunice Lake zooplankton assemblage Hypothesis tested Compare performance of D. 1eptopus here with that in a l l other treatment to test a l l hypotheses. Diffuse competiti zooplankton speci D. 1eptopus from Eunice Lake. on from several es prevents co1 on i z i ng Competition with Daphnia rosea prevents D. 1eptopus from colonizing Eunice Lake. Competition with D i aptomus kenai prevents D. 1eptopus from colonizing Eunice Lake. Competition with Diaptomus tyrel1i prevents D. 1eptopus from colonizing Eunice Lake. 27 G w e n d o l i n e t h a n i n E u n i c e L a k e , a low d e n s i t y t r e a t m e n t t e s t e d f o r e f f e c t s o f d i f f u s e c o m p e t i t i o n on D. l e p t o p u s i n E u n i c e . Lowered b i o m a s s e s of D. r o s e a , D. k e n a i , and D. t y r e l l i i n r e m o v a l t r e a t m e n t s p o t e n t i a l l y c o n f o u n d e d d i f f u s e c o m p e t i t i v e e f f e c t s w i t h e f f e c t s of c o m p e t i t i o n from s p e c i f i c s p e c i e s . T h e r e f o r e , t h e biomass o f s p e c i e s e x c l u d e d from r e m o v a l t r e a t m e n t s was r e p l a c e d w i t h a r o u g h l y e q u i v a l e n t b i o m a s s of r e m a i n i n g E u n i c e Lake s p e c i e s i n t h e i r l a k e r e l a t i v e p r o p o r t i o n s . In a d d i t i o n t o t r e a t m e n t s o u t l i n e d i n T a b l e . I I , two r e p l i c a t e e n c l o s u r e s c o n t a i n e d t h e e n t i r e E u n i c e L a k e a s s e m b l a g e w i t h o u t D. l e p t o p u s . D i r e c t c o m p a r i s o n between t h e s e and E u n i c e Lake would d e t e c t e n c l o s u r e e f f e c t s on z o o p l a n k t o n p o p u l a t i o n d y n a m i c s . 28 RESULTS, 197 9 j _ . R e s u l t s C o n f i r m i n g P r o p e r E s t a b l i s h m e n t of E x p e r i m e n t s J_.J_ E n c l o s u r e D e n s i t i e s o f Abundant E u n i c e Lake Z o o p l a n k t o n  Spec i e s S i m i l a r i t i e s between t h e c o n t r o l t r e a t m e n t and E u n i c e Lake i n s t a r t i n g d e n s i t i e s of Di a p t o m u s t y r e l l i , D i a ptomus k e n a i , Daphn i a r o s e a , and H o l o p e d i u m gibberurn ( T a b l e I I I ) i n d i c a t e p r o p e r s t o c k i n g o f c o n t r o l e n c l o s u r e s w i t h z o o p l a n k t o n . The e x p e r i m e n t a l d e s i g n d e s i g n a t e s d e n s i t i e s i n r e m a i n i n g t r e a t m e n t s as p e r t u r b a t i o n s of c o n t r o l d e n s i t i e s . S t a t i s t i c a l a n a l y s e s p r e s e n t e d i n T a b l e s IV, V, and VI show t h a t i n i t i a l e n c l o s u r e c o n c e n t r a t i o n s of common E u n i c e Lake s p e c i e s f u l f i l l e d d e s i g n r e q u i r e m e n t s . R e l a t i v e t o c o n t r o l s , t y r e 1 1 i - , k e n a i - , and Daphn i a - r e m o v a l t r e a t m e n t s c o n t a i n e d fewer of t h e e x c l u d e d s p e c i e s . Low d e n s i t y e n c l o s u r e s c o n t a i n e d fewer o f a l l s p e c i e s . H. g i b b e r u m l e v e l s d i d not d i f f e r among t r e a t m e n t s (ANOVA: F = 1.80; p = 0.266). F i g s . 2, 3, and 4 r e v e a l t h a t , o v e r a l l , t h e s e t r e a t m e n t d i f f e r e n c e s p e r s i s t e d t h r o u g h o u t t h e e x p e r i m e n t . B e c a u se t h e y were us e d t o r e p l a c e removed b i o m a s s , u n e x c l u d e d s p e c i e s were s l i g h t l y more common i n r e m o v a l t h a n i n c o n t r o l t r e a t m e n t s . 29 T a b l e I I I . T - t e s t s t a t i s t i c s c o m p a r i n g mean d e n s i t i e s (numbers of a n i m a l s p e r 150 1 s a m p l e s ) o f major E u n i c e Lake s p e c i e s i n E u n i c e Lake and i n c o n t r o l e n c l o s u r e s a t s t a r t of 1979 e x p e r i m e n t s . T e s t s a n a l y z e d l o g - t r a n s f o r m e d c o u n t s from t h e f i r s t two s a m p l i n g d a t e s , but means and s t a n d a r d d e v i a t i o n s shown a r e of u n t r a n s f o r m e d d a t a . N = n a u p l i i ; C = c o p e p o d i t e s ; A = a d u l t s ; J = j u v e n i l e s . Spec i e s L o c a t i o n Lake C o n t r o l s df D i a p tomus t y r e l l i (N+C+A) X: 541.5 s: 211.4 n: 2 482, 1 55, 4 0.39 4 0.719 Diaptomus k e n a i (N+C+A) X: 68.5 s: 0.7 n: 2 1 1 1 44 4 3 5 -0.97 4 0.387 D a p h n i a r o s e a (J+A) X: s: n: 21 1 1 52 2 5 0 1 09.8 20.0 4 1 . 40 4 0.233 H o l o p e d i u m q i b b e r u m (J+A) X: 131.0 s: 127.3 n: 2 84 69 4 0.46 4 0.671 30 T a b l e IV. S t a t i s t i c a l t e s t s c o m p a r i n g mean d e n s i t i e s o f D i a p t o m u s t y r e l l i (numbers of n a u p l i i , c o p e p o d i t e s , and a d u l t s combined p e r 150 1 sample) a c r o s s t r e a t m e n t s on i n i t i a l s a m p l i n g d a t e (June 20) of 1979 e x p e r i m e n t s . S i n c e ANOVA c o m p a r i n g a l l t r e a t m e n t s i s s i g n i f i c a n t , p a i r w i s e m u l t i p l e c o m p a r i s o n s o f c o n t r o l s w i t h e a c h p e r t u r b a t i o n a r e shown. T e s t s a n a l y z e d l o g - t r a n s f o r m e d c o u n t s , but means and s t a n d a r d d e v i a t i o n s shown a r e o f u n t r a n s f o r m e d d a t a . One-way A n a l y s i s of V a r i a n c e : S o u r c e d f Sum of S q u a r e s Mean Square F p Between 4 16.40 4.10 16.59 0.004 W i t h i n 5 1.24 0.25 T o t a l 9 17.64 P a i r w i s e M u l t i p l e C o m p a r i s o n s : T r e a t m e n t Mean (#/150 1) S t d . Dev, C o n t r o l : :Low d e n s i t y : D a p h n i a - r e m o v a l : k e n a i - r e m o v a l : t y r e l l i - r e m o v a l 603.0 114.6 56.0 485.5 593.0 29.0 7. 1 208.6 444 . 1 15.6 22.45 0.26 0.12 38.03 0.005 0.629 0.744 0.002 31 T a b l e V. S t a t i s t i c a l t e s t s c o m p a r i n g mean d e n s i t i e s o f Diaptomus k e n a i (numbers o f n a u p l i i , c o p e p o d i t e s , and a d u l t s combined p e r 150 1 sample) a c r o s s t r e a t m e n t s on i n i t i a l s a m p l i n g d a t e (June 20) of 1979 e x p e r i m e n t s . S i n c e ANOVA c o m p a r i n g a l l t r e a t m e n t s i s s i g n i f i c a n t , p a i r w i s e m u l t i p l e c o m p a r i s o n s of c o n t r o l s w i t h e a c h p e r t u r b a t i o n a r e shown. T e s t s a n a l y z e d l o g - t r a n s f o r m e d c o u n t s , but means and s t a n d a r d d e v i a t i o n s shown a r e of u n t r a n s f o r m e d d a t a . One-way A n a l y s i s of V a r i a n c e : S o u r c e d f Sum of S q u a r e s Mean Square F p Between 4 18.81 4.70 8.54 0.019 W i t h i n 5 2.75 0.55 T o t a l 9 21.56 P a i r w i s e M u l t i p l e C o m p a r i s o n s : T r e a t m e n t C o n t r o l : :Low d e n s i t y : D a p h n i a - r e m o v a l :k_ena_i-removal : t y r e l l i - r e m o v a l Mean (#/150 1) 1 33.5 21.5 489.5 11.5 80.5 S t d . Dev. 9.2 23.3 234. 1 6.4 51 .6 8.58 2.77 10.85 0.68 0.033 0. 157 0.022 0.447 32 T a b l e V I . S t a t i s t i c a l t e s t s c o m p a r i n g mean d e n s i t i e s of D a p h n i a  r o s e a (numbers p e r 150 1 sample) a c r o s s t r e a t m e n t s on i n i t i a l s a m p l i n g d a t e (June 20) of 1979 e x p e r i m e n t s . S i n c e ANOVA c o m p a r i n g a l l t r e a t m e n t s i s s i g n i f i c a n t , p a i r w i s e m u l t i p l e c o m p a r i s o n s of c o n t r o l s w i t h e a c h p e r t u r b a t i o n a r e shown. T e s t s a n a l y z e d l o g - t r a n s f o r m e d c o u n t s , but means and s t a n d a r d d e v i a t i o n s shown a r e of u n t r a n s f o r m e d d a t a . One-way A n a l y s i s of V a r i a n c e : S o u r c e d f Sum of S q u a r e s Mean Square F p Between 4 7.91 .1.98 9.48 0.015 W i t h i n 5 1.04 0.21 T o t a l 9 8.95 P a i r w i s e M u l t i p l e C o m p a r i s o n s : T r e a t m e n t Mean (#/l50 1) S t d . Dev. F p C o n t r o l : 109.0: 26.9: .-Low d e n s i t y :33.0 :26.9 8.69 0.032 : D a p h n i a - r e m o v a l :10.5 :3.5 24.65 0.004 :kena_i-removal :86.5 :21 .9 0.25 .0.636 : t y r e l l i - r e m o v a l :101.0 :15.6 0.02 0.890 33 F i g u r e 2. D e n s i t i e s o f Diaptomus t y r e l l i ( n a u p l i i , c o p e p o d i t e s , and a d u l t s combined) i n E u n i c e L a k e and i n 1979 e x p e r i m e n t s . P l o t s f o r r e p l i c a t e e n c l o s u r e s a r e s i d e by s i d e . A = E u n i c e Lake; B = C o n t r o l ; C = Low d e n s i t y ; D = Daphn i a - r e m o v a l ; E = k e n a i - r e m o v a l ; F = t y r e l l i - r e m o v a l . NUMBER OF ANIMALS PER 150 LITRES 35 F i g u r e 3. D e n s i t i e s o f Diaptomus k e n a i ( n a u p l i i , c o p e p o d i t e s , and a d u l t s combined) i n E u n i c e Lake and i n 1979 e x p e r i m e n t s . P l o t s f o r r e p l i c a t e e n c l o s u r e s a r e s i d e by s i d e . A = E u n i c e L a k e ; B = C o n t r o l ; C = Low d e n s i t y ; D = D a p h n i a - r e m o v a l ; E = k e n a i - r e m o v a l ; F = t y r e l l i - r e m o v a l . NUMBER OF ANIMALS PER 150 LITRES 37 F i g u r e 4. D e n s i t i e s of D a p h n i a r o s e a and H o l o p e d i u m g i b b e r u m i n E u n i c e Lake and i n 1979 e x p e r i m e n t s . P l o t s f o r r e p l i c a t e e n c l o s u r e s a r e s i d e by s i d e . A = E u n i c e Lake; B = C o n t r o l ; C = Low d e n s i t y ; D = D a p h n i a - r e m o v a l ; E = k e n a i - r e m o v a l ; F = t y r e l l i - r e m o v a l . NUMBER OF ANIMALS PER 150 LITRES B o o o o o o ° o o o o o B cs o o o B 39 J_.2_ E n c l o s u r e D e n s i t i e s of Rare E u n i c e Lake Z o o p l a n k t o n Spec i e s E n c l o s u r e d e n s i t i e s were n o t r e g u l a t e d f o r s p e c i e s r a r e ( < 0 . 5 / l ) i n E u n i c e L a k e a t t h e s t a r t of t h e e x p e r i m e n t s . N e v e r t h e l e s s , maximum d e n s i t i e s o f C h y d o r u s spp. d i d not d i f f e r a c r o s s t r e a t m e n t s (ANOVA: F = 0.39; p = 0.810). C e r i o d a p h n i a  p u l c h e l l a , S c a p h o l e b e r i s s p . , Diaphanosoma b r a c h y u r u m , Polyphemus p e d i c u l u s , and e s p e c i a l l y l a r v a l c h i r o n o m i d s and C h a o b o r u s r e m a i n e d r a r e i n a l l e n c l o s u r e s t h r o u g h o u t t h e e x p e r i m e n t s . R e l a t i v e l y h i g h l e v e l s (1/1) i n D a p h n i a - r e m o v a l s o f C e r i o d a p h n i a , S c a p h o l e b e r i s , and Diaphanosoma combined s u g g e s t c l a d o c e r a n . c o m p e t i t i o n . These t h r e e s p e c i e s and Bosmina  l o n g i r o s t r i s r e a c h e d h i g h e r d e n s i t i e s i n kena_i-removals t h a n i n c o n t r o l s . Bosmina was most abundant i n low d e n s i t y and D a p h n i a -r e m o v a l t r e a t m e n t s ( F i g . 5; T a b l e V I I ) . In low d e n s i t y s i t u a t i o n s , i t p r o b a b l y r e s p o n d e d t o e x c e s s f o o d made a v a i l a b l e t h r o u g h r e d u c e d g r a z i n g . H i g h l e v e l s i n D a p h n i a - r e m o v a l s i m p l y c o m p e t i t i o n w i t h D. r o s e a . In G o u l d e n and H o r n i g ' s (1980) l a b o r a t o r y e x p e r i m e n t s , Daphn i a q a l e a t a mendotae o u t c o m p e t e d s m a l l B. l o n g i r o s t r i s b e c a u s e t h e l a r g e r s p e c i e s was more a b l e t o a c c u m u l a t e l i p i d r e s e r v e s . However, i n K e r f o o t and D e M o t t ' s (1980) f i e l d e x p e r i m e n t s , Daphn i a and Bosmina a v o i d e d c o m p e t i t i o n by u s i n g d i f f e r e n t f o o d r e s o u r c e s . D e n s i t i e s of c y c l o p o i d c o p e p o d s , w h i c h i n c l u d e d m o s t l y D i a c y c l o p s t h o m a s i and some T r o p o c y c l o p s p r a s i n u s , were i n c o n s i s t e n t between r e p l i c a t e s and among t r e a t m e n t s ( F i g . 6 ) . Low d e n s i t y and D a p h n i a - r e m o v a l t r e a t m e n t s e a c h h a d . one r e p l i c a t e w i t h h i g h and one w i t h low c y c l o p o i d l e v e l s . In 40 F i g u r e 5. D e n s i t i e s of Bosmina l o n q i r o s t r i s i n E u n i c e L a k e and i n 1979 e x p e r i m e n t s . P l o t s f o r r e p l i c a t e e n c l o s u r e s a r e s i d e by s i d e . A = E u n i c e Lake; B = C o n t r o l ; C = Low d e n s i t y ; D = D a p h n i a - r e m o v a l ; E = k e n a i - r e m o v a l ; F = t y r e l l i - r e m o v a l . NUMBER OF ANIMALS PER 150 LITRES 42 T a b l e V I I . S t a t i s t i c a l t e s t s c o m p a r i n g a c r o s s t r e a t m e n t s f o r mean maximum d e n s i t i e s of Bosmina l o n g i r o s t r i s a t t a i n e d d u r i n g 1979 e x p e r i m e n t s . V a l u e s a n a l y z e d a r e l o g -t r a n s f o r m e d maximum numbers o f a n i m a l s c o l l e c t e d from e n c l o s u r e s i n a 150 1 sample r e g a r d l e s s o f s a m p l i n g d a t e . S i n c e ANOVA c o m p a r i n g a l l t r e a t m e n t s i s s i g n i f i c a n t , p a i r w i s e m u l t i p l e c o m p a r i s o n s of c o n t r o l s w i t h e a c h p e r t u r b a t i o n a r e shown. Means and s t a n d a r d d e v i a t i o n s shown a r e of u n t r a n s f o r m e d d a t a . One-way A n a l y s i s of V a r i a n c e : S o u r c e d f Sum of S q u a r e s Mean S q u a r e F p Between' 4 2.55 0.64 ' 9.55 0.015 W i t h i n 5 0.33 ' 0.07 T o t a l 9 2.88 P a i r w i s e M u l t i p l e C o m p a r i s o n s : T r e a t m e n t Mean (#/l50 1) S t d . Dev. F p C o n t r o l : 357.5: 55.9: :Low d e n s i t y :1396.0 :463.9 26.84 0.004 : D a p h n i a - r e m o v a l :1084.5 :125.2 18.50 0.008 : k e n a i - r e m o v a l :1009.5 :303.4 15.58 0.011 r t y r e l l i - r e m o v a l :513.5 :150.6 1.79 0.239 g u r e 6. D e n s i t i e s of c y c l o p o i d c o p e p o d s ( n a u p l i i , c o p e p o d i t e s , and a d u l t s of D i a c y c l o p s t h o m a s i and T r o p o c y c l o p s p r a s i n u s combined) i n E u n i c e L a k e and i n 1979 e x p e r i m e n t s . P l o t s f o r r e p l i c a t e e n c l o s u r e s a r e s i d e by s i d e . A = E u n i c e L a k e ; B = C o n t r o l ; C = Low d e n s i t y ; D = D a p h n i a - r e m o v a l ; E = k e n a i - r e m o v a l ; F = t y r e l l i - r e m o v a l . NUMBER OF ANIMALS PER 150 LITRES 4 5 g e n e r a l , l e v e l s were s i m i l a r i n c o n t r o l and t y r e l l i - r e m o v a l e n c l o s u r e s ( F i g . 6 ) . Keria_i-removals c o n t a i n e d r e l a t i v e l y many c y c l o p o i d s . ANOVAs c o m p a r i n g maximum d e n s i t i e s of n a u p l i i (ANOVA: F = 0.40; p = 0.803) and of c o p e p o d i t e s p l u s a d u l t s ( T a b l e V I I I ) show a s i g n i f i c a n t d i f f e r e n c e among t r e a t m e n t s o n l y f o r more mature c y c l o p o i d s . D i s s i m i l a r i t i e s among e n c l o s u r e s i n D. t h o m a s i d e n s i t i e s p o t e n t i a l l y m o d i f i e d t r e a t m e n t e f f e c t s on D i a p t o m u s l e p t o p u s t h r o u g h c o m p e t i t i o n from h e r b i v o r o u s n a u p l i i and e a r l y c o p e p o d i t e s a n d / o r t h r o u g h p r e d a t i o n from l a t e r s t a g e s ( P e a c o c k 1981). E n c l o s u r e e x p e r i m e n t s i n G w e n d o l i n e L a k e d e m o n s t r a t e d r e l a t i v e immunity of t h e h e r b i v o r o u s z o o p l a n k t o n community t o v a r i a t i o n s i n numbers of p r e d a c e o u s D. t h o m a s i ( N e i l l and Pe a c o c k 1980; N e i l l 1981a; P e a c o c k 1981). H i g h p r e y s u r v i v a l c o i n c i d e d w i t h , and c o u n t e r b a l a n c e d e f f e c t s o f , i n c r e a s e s i n c y c l o p o i d c o n c e n t r a t i o n s b e c a u s e h e r b i v o r o u s s t a g e s o f D. t h o m a s i e x p e r i e n c e d t h e same a l g a l f o o d c o n s t r a i n t s a s t h e p r e y of l a t e r p r e d a c e o u s s t a g e s . T h a t r e s u l t , and t h e low p r o p o r t i o n of p r e d a c e o u s s t a g e s among c y c l o p o i d s e n c l o s e d i n t h i s s t u d y , r e f u t e p r e d a t i o n e f f e c t s . ANCOVAs u s i n g t o t a l c y c l o p o i d d e n s i t y . a s t h e c o v a r i a t e i n d i c a t e t h a t f o r no s a m p l i n g d a t e d i d u n c o n t r o l l e d c y c l o p o i d s i n f l u e n c e t r e a t m e n t e f f e c t s on d e n s i t i e s o f Diaptomus l e p t o p u s n a u p l i i , c o p e p o d i t e s , a d u l t s , o r on d e n s i t i e s of a l l t h r e e c o m b i n e d . In o n l y 2 o f t h e 72 a n a l y s e s (18 s a m p l i n g d a t e s x 4 v a r i a t e s ) i s t h e c o v a r i a t e s i g n i f i c a n t a t p = 0.05. T h i s f r e q u e n c y l i e s w e l l w i t h i n t h e 5% s t a t i s t i c a l l y e x p e c t e d w i t h an i n s i g n i f i c a n t c o v a r i a t e . S i m i l a r i t i e s between 46 T a b l e V I I I . S t a t i s t i c a l t e s t s c o m p a r i n g a c r o s s t r e a t m e n t s f o r mean maximum d e n s i t i e s o f c y c l o p o i d c o p e p o d i t e s p l u s a d u l t s a t t a i n e d d u r i n g 1979 e x p e r i m e n t s . V a l u e s a n a l y z e d a r e l o g - t r a n s f o r m e d maximum numbers of a n i m a l s c o l l e c t e d from e n c l o s u r e s i n a 150 1 sample r e g a r d l e s s of s a m p l i n g d a t e . S i n c e ANOVA c o m p a r i n g a l l t r e a t m e n t s i s s i g n i f i c a n t , p a i r w i s e m u l t i p l e c o m p a r i s o n s o f c o n t r o l s w i t h e a c h p e r t u r b a t i o n a r e shown. Means and s t a n d a r d d e v i a t i o n s shown a r e of u n t r a n s f o r m e d d a t a . One-way A n a l y s i s of V a r i a n c e : S o u r c e d f Sum of S q u a r e s Mean Sq u a r e F p Between 4 ' 11.54 2.89 11.20 0.010 W i t h i n 5 1.29 0.26 T o t a l 9 12.83 P a i r w i s e M u l t i p l e C o m p a r i s o n s : T r e a t m e n t Mean (#/150 1) S t d . Dev C o n t r o l : 5.0 :Low d e n s i t y :Daphn i a - r e m o v a l : k e n a i - r e m o v a l : t y r e l l i - r e m o v a l 4.2: 95.0 :56.6 30.87 0.003 6.5 :2.1 0.47 0.525 48.5 :16.3 19.23 0.007 22.0 :7.1 8.31 0.035 47 D. l e p t o p u s r e s p o n s e s t o b o t h r e p l i c a t e s of low d e n s i t y and of D a p h n i a - r e m o v a l t r e a t m e n t s u n d e r s c o r e ANCOVA r e s u l t s . In a bog l a k e , Winner (1970) f o u n d no c o r r e l a t i o n " between c y c l o p o i d and D. l e p t o p u s d e n s i t i e s . In summary, u n c o n t r o l l e d e n c l o s u r e d i f f e r e n c e s i n d e n s i t i e s of z o o p l a n k t o n uncommon i n E u n i c e Lake do n o t c o n f o u n d i n t e n d e d d i f f e r e n c e s i n d e n s i t i e s of common s p e c i e s . E x c e p t f o r c y c l o p o i d s , most i n c i d e n t a l s p e c i e s r e m a i n e d r a r e i n e n c l o s u r e s . E v i d e n c e i n d i c a t e s no c y c l o p o i d m o d i f i c a t i o n of t r e a t m e n t e f f e c t s on D. l e p t o p u s . J_.3_ E f f e c t s of E n c l o s u r e E a r l y c o l l a p s e o f e n c l o s u r e s c o r r a l l i n g E u n i c e L a k e s p e c i e s w i t h o u t D. l e p t o p u s p r e v e n t e d p r o p e r a s s e s s m e n t of c o n t a i n m e n t e f f e c t s on z o o p l a n k t o n p o p u l a t i o n s . In e n c l o s u r e s i n o t h e r R e s e a r c h F o r e s t l a k e s , c o n f i n e d p o p u l a t i o n s t r a c k e d l a k e p o p u l a t i o n s f o r up t o 3 months ( N e i l l 1978, 1981a; P e a c o c k 1981). D i s s i m i l a r i t i e s i n c r e a s e d w i t h d u r a t i o n o f e n c l o s u r e . E n c l o s u r e s m i m i c k e d l a k e s i n oxygen, t e m p e r a t u r e and g r a z a b l e s e s t o n l e v e l s . In t h i s s t u d y , d i f f e r e n c e s o c c u r r e d between u n c o l l a p s e d e n c l o s u r e s and E u n i c e Lake i n d e n s i t i e s of s e v e r a l z o o p l a n k t o n s p e c i e s . The p r e s e n c e of p l a n k t i v o r o u s t r o u t i n t h e l a k e , and not i n e n c l o s u r e s , may. have c a u s e d some of t h e s e d i f f e r e n c e s . D e n s i t i e s of C e r i o d a p h n i a , S c a p h o l e b e r i s , and Diaphanosoma were h i g h e r i n e n c l o s u r e s t h a n i n t h e l a k e . H o l o p e d i u m ( F i g . 4) and 48 Polyphemus r a p i d l y d e c r e a s e d t o e x t i n c t i o n o n l y i n e n c l o s u r e s . D a p h n i a r o s e a ( F i g . 4) and c y c l o p o i d c o p e p o d s ( F i g . 6) a c h i e v e d h i g h e r l e v e l s i n t h e l a k e and i n e n c l o s u r e s , r e s p e c t i v e l y . L a t e i n t h e s t u d y , when e p i p h y t i c a l g a l f o o d was b e g i n n i n g t o d e v e l o p on t h e p o l y e t h y l e n e , e n c l o s u r e d e n s i t i e s of C h y d o r u s and c h i r o n o m i d l a r v a e e x c e e d e d l a k e l e v e l s . O t h e r e n c l o s u r e s t u d i e s v e r i f y t h e s e e f f e c t s on H o l o p e d i u m ( N e i l l p e r s . comm.), on D a p h n i a and D i a c y c l o p s (Smyley 1976), and on C h y d o r u s and c h i r o n o m i d l a r v a e ( P e a cock 1981). T h e s e m i n o r d i f f e r e n c e s between t h e l a k e and e n c l o s u r e s do not i n v a l i d a t e t h e e x p e r i m e n t a l d e s i g n b e c a u s e c o m p a r i s o n s between c o n t r o l and n o n - c o n t r o l e n c l o s u r e s , r a t h e r t h a n between e n c l o s u r e s and t h e l a k e , . measured e f f e c t s of t r e a t m e n t s on D. l e p t o p u s . 49 2. R e s u l t s D e s c r i b i n g E f f e c t s of E x p e r i m e n t s 2.J_ T r e a t m e n t E f f e c t s on T o t a l D e n s i t i e s of D i a p t o m u s l e p t o p u s I n i t i a l s i m i l a r i t i e s among t r e a t m e n t s i n combined d e n s i t i e s of n a u p l i i , c o p e p o d i t e s , and a d u l t s ( T a b l e IX) p r o v i d e e v i d e n c e f o r p r o p e r s t o c k i n g of e a c h e n c l o s u r e w i t h 4000 D. l e p t o p u s . In c o n t r o l s , D. l e p t o p u s i n c r e a s e d s l i g h t l y from s t o c k i n g d e n s i t i e s b e f o r e r a p i d l y d e c r e a s i n g t o n e a r e x t i n c t i o n by e a r l y A u g u s t . P a r a l l e l p a t t e r n s o c c u r r e d i n Daphn i a - and k e n a i - r e m o v a l s . D. l e p t o p u s r e a c h e d h i g h e r l e v e l s i n low d e n s i t y and t y r e l l i -r e m o v a l t r e a t m e n t s than i n c o n t r o l s . I t p e r s i s t e d u n t i l l a t e A u g u s t i n low d e n s i t y e n c l o s u r e s , and u n t i l l a t e September i n t y r e l l i - r e m o v a l s . T h e s e t r e n d s a r e a p p a r e n t from F i g . 7. S t a t i s t i c a l a n a l y s e s c o m p a r i n g t o t a l D. l e p t o p u s a c r o s s t r e a t m e n t s f o r e a c h s a m p l i n g d a t e s u b s t a n t i a t e them ( T a b l e I X ) . S i g n i f i c a n t d i f f e r e n c e s were not c o n s i s t e n t l y e v i d e n t u n t i l a f t e r m i d - J u l y . Then, D. l e p t o p u s d e n s i t i e s r e l a t i v e t o t h o s e i n c o n t r o l s were s i m i l a r i n D a p h n i a -and i n k_ena_i-removals, and h i g h e r i n t y r e l l i - r e m o v a l and low d e n s i t y e n c l o s u r e s . Maximum D. l e p t o p u s d e n s i t i e s e x h i b i t e d s i m i l a r d i s p a r i t i e s ( T a b l e X ) . T a b l e XI compares p e r s i s t e n c e t i m e s f o r D. l e p t o p u s i n t h e d i f f e r e n t t r e a t m e n t s . " P e r s i s t e n c e t i m e " i s t h e number of d a y s e l a p s e d from t h e f i r s t s a m p l i n g d a t e u n t i l D. l e p t o p u s r e m a i n e d a t d e n s i t i e s o f ^10 a n i m a l s p e r 150 1 s ample. R e l a t i v e t o c o n t r o l s , p e r s i s t e n c e t i m e s were g r e a t e r i n t y r e l l i - r e m o v a l and, t o a l e s s e r e x t e n t , i n low d e n s i t y t r e a t m e n t s . 50 T a b l e IX. Summary o f s t a t i s t i c a l t e s t s c o m p a r i n g mean d e n s i t i e s of n a u p l i i , c o p e p o d i t e s , a d u l t s , and mean t o t a l d e n s i t i e s of Diaptomus l e p t o p u s a c r o s s t r e a t m e n t s f o r e a c h s a m p l i n g d a t e of 1979 e x p e r i m e n t s . V a l u e s a n a l y z e d a r e l o g - t r a n s f o r m e d numbers o f a n i m a l s p e r 150 1 sample. F o r e a c h d a t e , t h e f i r s t e n t r y f o r e a c h d e v e l o p m e n t s t a g e i n d i c a t e s whether ANOVA c o m p a r i n g d e n s i t i e s of t h a t s t a g e a c r o s s t r e a t m e n t s i s s i g n i f i c a n t a t p = 0.05. E n t r i e s f o l l o w i n g s i g n i f i c a n t ANOVAs i n d i c a t e whether p a i r w i s e m u l t i p l e c o m p a r i s o n s between c o n t r o l s and e a c h p e r t u r b a t i o n and between low d e n s i t y and t y r e l l i - r e m o v a l t r e a t m e n t s a r e s i g n i f i c a n t , a nd g i v e p r o b a b i l i t y l e v e l s i f p < 0.05. NS = i n s i g n i f i c a n t a t p = 0.05. [ l ] = C o n t r o l ; [2] = Low d e n s i t y ; [3] = D a p h n i a - r e m o v a l ; [4] = kena i - r e m o v a l ; [5] = t y r e l l i - r e m o v a l . (+) = h i g h e r mean d e n s i t i e s o f - a n i m a l s i n p e r t u r b a t i o n t h a n i n c o n t r o l t r e a t m e n t s or i n t y r e l l i - r e m o v a l t h a n i n low d e n s i t y ; (-) = h i g h e r mean d e n s i t i e s i n c o n t r o l t h a n i n p e r t u r b a t i o n t r e a t m e n t s or i n low d e n s i t y t h a n i n t y r e l l i - r e m o v a l . Table IX Naupli i Copepod i tes Adults Total dune 20 NS NS NS NS June 26 NS NS NS NS duly 1 p<0. 05 NS NS NS [ 2 ] - [ 1 ] p=0. 01 1 ( + ) [3]-[1] NS [ 4 ] - [ 1 ] NS [5]-[1] P=o. 034 ( + ) [5]-[2] NS du 1 y 5 p<0. 05 NS p<0.05 ( + ) p<0. 05 ( + ) [2]-[1] p=0. 014 ( + ) p=0.022 p = 0. 005 [3]-[1] NS p=0.012 ( + ) p=0. 034 ( + ) [ 4 ] - [ 1 ] NS p=0.026 ( + ) p=0. 018 ( + ) [ 5 ] - [ 1 ] . p = 0. 025 ( + ) p=0.007 ( + ) p=0. .004 ( + ) [5]-[2] NS NS NS duly 11 p<0. .05 NS NS NS [2]-[1] p<0. 001 ( + ) [3]-[1] p=0. .025 ( + ) t 4 ] - [ 1 ] p=0. ,008 ( + ) [5]-[1] p<0. .001 ( + ) [5]-[2] p=p. .019 (-) duly 16 NS NS NS NS duly 21 p<0 .05 NS NS NS [2]-[1] p = 0 .010 •( + ) [ 3 ] - [ 1 ] NS [4]-[1] NS [5]-[1] NS [5]-[2] NS duly 26 p<0 .05 NS • NS p<0 .05 ( + ) [2]-[1] p=0 .007 ( + ) p=0 .014 [3]-[1] NS NS [4]-[1] NS NS ( + ) [5]-[1] p = 0 .037 < + ) p=0 .032 [5]-[2] NS NS August 2 p<0 .05 NS NS p<0 .05 ( + .) [2]-[1] p<0 .001 ( + ) p=0 .004 t3]-[1] NS NS [4]-[ 1] NS NS ( + ) [5]-[1] p=0 .007 ( + ) p=0 .034 [5]-[2] p=0 .008 (-) NS Table IX. continued Nauplii Copepodites Adults Total August 7 p<0. 05 NS NS NS [2]-[1] p=0. 002 ( + ) [3]-[1] NS [4]-[1] NS [5]-[1] p=0. .020 ( + ) [5]-[2] p=0. 045 (-) August 12 p<0. 05 NS ' NS p<0. 05 ( + ) [2]-[1] p=0. 030 ( + ) p=0. 005 [3]-[1] NS p=0. 029 ( + ) [4]-[1] NS p=0. .020 ( + ) [5]-[1] p=0. 032 ( + ) p=0. 004 ( + ) [5]-[2] NS NS August 19 NS NS p<0. .05 p<0. .05 [2]-[1] NS NS [3]-[ 1] NS NS [4]-[1] NS NS [5]-[1] p=0. .015 ( + ) p = 0 .021 ( + ) [5]-[2] NS NS August 24 NS NS NS NS August 31 NS NS NS NS September 10 p<0. .05 p<0 .05 NS p<0 .05 ( + ) [2]-[1] NS p=0. .007 ( + ) p=0 .047 [3]"[ 1 ] NS NS NS ( + ) [4]-[1] p=0 .010 ( + ) NS p=0 .017 [5]-[1] NS p<0 .001 ( + ) p=0 .013 ( + ) [5]-[2] NS p=0 .003 ( + ) NS September 19 NS NS p<0. .05 p<0 .05 [2]-[ 1] NS NS [3]-[1] NS NS [4]-[ 1 ] NS NS ( + ) [5]-[1] p = 0 .020 ( + ) p=0 .015 [5]-[2] NS NS September 29 NS NS p<0 .05 p<0 .05 [2]-[1] p=0 .003 ( + ) NS [3]-[1] NS NS [4]-[1] p=0 .01 1 ( + ) NS ( + ) [5]-[1] p=0 .001 ( + ) p=0 .022 [5]-[2] NS NS October 12 NS NS NS NS 53 F i g u r e 7. D e n s i t i e s of Diaptomus l e p t o p u s ( n a u p l i i , c o p e p o d i t e s , and a d u l t s combined) i n E u n i c e Lake and i n 1979 e x p e r i m e n t s . . P l o t s f o r r e p l i c a t e e n c l o s u r e s a r e s i d e by s i d e . A = E u n i c e L a k e ; B = C o n t r o l ; C = Low d e n s i t y ; D = Daphn i a - r e m o v a l ; E = ke_na_i - r e m o v a l ; F = t y r e l l i - r e m o v a l . NUMBER OF ANIMALS PER 150 LITRES 55 T a b l e X. S t a t i s t i c a l t e s t s c o m p a r i n g a c r o s s t r e a t m e n t s f o r mean maximum d e n s i t i e s of Diaptomus l e p t o p u s ( n a u p l i i , c o p e p o d i t e s , and a d u l t s combined) a t t a i n e d d u r i n g 1979 e x p e r i m e n t s . V a l u e s a n a l y z e d a r e l o g - t r a n s f o r m e d numbers of a n i m a l s c o l l e c t e d from e n c l o s u r e s i n a 150 1 sample r e g a r d l e s s of s a m p l i n g d a t e . S i n c e ANOVA c o m p a r i n g a l l t r e a t m e n t s i s s i g n i f i c a n t , p a i r w i s e m u l t i p l e c o m p a r i s o n s of c o n t r o l s w i t h e a c h p e r t u r b a t i o n a r e shown. Means and s t a n d a r d d e v i a t i o n s shown a r e o f u n t r a n s f o r m e d d a t a . One-way A n a l y s i s of V a r i a n c e : S o u r c e d f Sum of S q u a r e s Mean S q u a r e F p Between 4 . 1.75 0.44 7.83 0.022 W i t h i n 5 0.28 0.06 T o t a l 9 2.03 P a i r w i s e M u l t i p l e C o m p a r i s o n s : T r e a t m e n t Mean (#/150 1) S t d . Dev. F p C o n t r o l : 52.0: 8.5: :Low d e n s i t y :121.0 :31.1 12.15 0.018 :Da_pjinia-removal :43.0 :14.1 0.76 0.423 r k e n a i - r e m o v a l :44.0 :1.4 0.44 0.535 : t y r e l l i - r e m o v a l :96.0 :26.9 6.26 0.054 56 T a b l e X I . S t a t i s t i c a l t e s t s c o m p a r i n g a c r o s s t r e a t m e n t s f o r mean p e r s i s t e n c e t i m e s of Diaptomus l e p t o p u s i n 1979 e x p e r i m e n t s . S i n c e ANOVA c o m p a r i n g a l l t r e a t m e n t s i s a l m o s t s i g n i f i c a n t , p a i r w i s e m u l t i p l e c o m p a r i s o n s of c o n t r o l s w i t h e a c h p e r t u r b a t i o n a r e shown. One-way A n a l y s i s of V a r i a n c e : S o u r c e df Sum of S q u a r e s Mean Sq u a r e F p Between 4 3651.0 912.75 3.66 0.094 W i t h i n 5 1247.0 249.40 T o t a l 9 4898.0 P a i r w i s e M u l t i p l e C o m p a r i s o n s T r e a t m e n t Mean ( d a y s ) S t d . Dev. C o n t r o l : :Low d e n s i t y : D a p h n i a - r e m o v a l : k e n a i - r e m o v a l : t y r e l l i - r e m o v a l 46.5 74.5 49.0 66.0 99.0 3.5: : 12.0 :0.0 :24.0 :22.6 3 0 1 1 1 1 4 03 52 05 0. 136 0.880 0.272 0.021 57 2.2 T r e a t m e n t E f f e c t s on D e n s i t i e s of Diaptomus l e p t o p u s Eggs, N a u p l i i , C o p e p o d i t e s , and A d u l t s T a b l e IX summarizes s t a t i s t i c a l a n a l y s e s c o m p a r i n g n a u p l i a r , c o p e p o d i t e , and a d u l t d e n s i t i e s a c r o s s t r e a t m e n t s f o r e a c h s a m p l i n g d a t e . I n s i g n i f i c a n t d i f f e r e n c e s i n e a r l y s amples f o r a l l d e v e l o p m e n t a l s t a g e s i m p l y i n i t i a l l y c o m p a r a b l e age d i s t r i b u t i o n s f o r a l l e n c l o s e d D. l e p t o p u s p o p u l a t i o n s . T h r o u g h o u t t h e e x p e r i m e n t s , c o p e p o d i t e s and a d u l t s c o n t i n u e d t o e x p e r i e n c e no c o n s i s t e n t t r e a t m e n t e f f e c t s . Most c o p e p o d i t e s i n c o n t r o l , Daphn i a - r e m o v a l and k_enai_- r e m o v a l e n c l o s u r e s were among t h o s e o r i g i n a l l y s t o c k e d from G w e n d o l i n e L a k e . O n l y i n t y r e l l i -r e m o v a l and low d e n s i t y t r e a t m e n t s d i d D. l e p t o p u s p e r s i s t l o n g enough f o r n a u p l i i p r o d u c e d w i t h i n t h e e n c l o s u r e s t o m a t u r e . T r e a t m e n t d i f f e r e n c e s i n n a u p l i a r d e n s i t i e s ( F i g . 8) p a r a l l e l t h o s e n o t e d i n F i g . 7 f o r t o t a l D. l e p t o p u s . From e a r l y J u l y t o m i d - A u g u s t , n a u p l i i were more numerous i n t y r e l l i - r e m o v a l and low d e n s i t y t h a n i n o t h e r t r e a t m e n t s . A f t e r l a t e A u g u s t , no s i g n i f i c a n t d i f f e r e n c e s i n t h e i r d e n s i t i e s o c c u r r e d b e c a u s e most had a l r e a d y m a t u r e d i n t o l a t e r s t a g e s . T a b l e X I I compares t h e t o t a l number of D. l e p t o p u s eggs e n c o u n t e r e d i n e a c h t r e a t m e n t t h r o u g h o u t t h e e x p e r i m e n t d i v i d e d by t h e t o t a l number of f e m a l e s . Egg t o t a l s i n c l u d e eggs c a r r i e d by f e m a l e s and u n a t t a c h e d e g g s . L o o s e D. t y r e l l i and D. l e p t o p u s eggs were n o t r e l i a b l y d i s t i n g u i s h a b l e . B e c a u se most a t t a c h e d D. t y r e l l i and D. l e p t o p u s c l u t c h e s c o n t a i n e d <5 and >5 e g g s , r e s p e c t i v e l y , u n a t t a c h e d egg bunches were s i m i l a r l y a s s i g n e d t o s p e c i e s . R e l a t i v e t o c o n t r o l s , r e p r o d u c t i o n i n c r e a s e d o n l y i n 58 F i g u r e 8. D e n s i t i e s of n a u p l i i and of c o p e p o d i t e s p l u s a d u l t s o f D i a p t o m u s l e p t o p u s i n E u n i c e Lake and i n 1979 e x p e r i m e n t s . P l o t s f o r r e p l i c a t e e n c l o s u r e s a r e s i d e by s i d e . A = E u n i c e L a k e ; B = C o n t r o l ; C = Low d e n s i t y ; D = D a p h n i a - r e m o v a l ; E = k e n a i - r e m o v a l ; F = t y r e l l i - r e m o v a l . NUMBER OF ANIMALS PER 150 LITRES 60 T a b l e X I I . S t a t i s t i c a l t e s t s c o m p a r i n g a c r o s s t r e a t m e n t s f o r mean number of D i a p t o m u s l e p t o p u s eggs p r o d u c e d p e r f e m a l e d u r i n g 1979 e x p e r i m e n t s . V a l u e s a n a l y z e d a r e l o g - t r a n s f o r m e d t o t a l numbers of l o o s e and a t t a c h e d eggs d i v i d e d by t o t a l numbers of a d u l t f e m a l e s c o l l e c t e d from e n c l o s u r e s i n 150 1 samples from a l l s a m p l i n g d a t e s c o m b i n e d . S i n c e ANOVA c o m p a r i n g a l l t r e a t m e n t s i s s i g n i f i c a n t , p a i r w i s e m u l t i p l e c o m p a r i s o n s of c o n t r o l s w i t h e a c h p e r t u r b a t i o n a r e shown. Means and s t a n d a r d d e v i a t i o n s shown a r e of u n t r a n s f o r m e d d a t a . One-way A n a l y s i s of V a r i a n c e : S o u r c e df- Sum of S q u a r e s Mean Square- F p Between 4 5.44 1.36 5.76 0.041 W i t h i n 5 1.18' 0.24 T o t a l 9 6.62 P a i r w i s e M u l t i p l e C o m p a r i s o n s : T r e a t m e n t Mean (#/female) S t d . Dev C o n t r o l : 0.00 :Low d e n s i t y :Daphn i a - r e m o v a l : k e n a i - r e m o v a l : t y r e l l i - r e m o v a l 0.00: 8.35 :2.76 20.73 0.006 1.65 :1.91 2.88 0.151 1.10 :1.13 1.86 0.231 0.75 :0.64 1.17 0.329 61 low d e n s i t y e n c l o s u r e s , where r e d u c e d g r a z i n g p r e s s u r e s p r e s u m a b l y had e n h a n c e d f o o d a v a i l a b l e t o r e p r o d u c t i v e f e m a l e s . T o g e t h e r t h e s e r e s u l t s have s e v e r a l i m p l i c a t i o n s . (1 ) Lack of t r e a t m e n t e f f e c t s o f D a p h n i a - o r kena_i-removals i m p l i e s no c o m p e t i t i o n between t h e s e s p e c i e s and D. l e p t o p u s . (2) S i m i l a r l e v e l s of D. l e p t o p u s c o p e p o d i t e s and a d u l t s i n a l l e n c l o s u r e s , d e s p i t e h i g h d e n s i t i e s o f n a u p l i i i n t y r e l l i - r e m o v a l and low d e n s i t y p e r t u r b a t i o n s , s u g g e s t p o o r s u r v i v a l of n a u p l i u s t o a d u l t i n t h e s e two t r e a t m e n t s . (3) H i g h n a u p l i a r d e n s i t i e s r e l a t i v e t o c o n t r o l s i n t y r e l l i - r e m o v a l s , d e s p i t e r e l a t i v e l y unenhanced r e p r o d u c t i o n , i n d i c a t e h i g h s u r v i v a l of egg t o n a u p l i u s i n t h e a b s e n c e of c o m p e t i t i o n f r o m D. t y r e l l i . The e x p e r i m e n t s were n o t d e s i g n e d t o d e t e r m i n e w h i c h d e v e l o p m e n t a l s t a g e s of D. t y r e l l i compete. C o r r e l a t i o n s between d e n s i t i e s of D. l e p t o p u s n a u p l i i and D. t y r e l l i of d i f f e r e n t s t a g e s p r o v i d e no unambiguous c l u e s . (4) R e d u c t i o n of e i t h e r c o m p e t i t i o n from D. t y r e l l i a n d / o r d i f f u s e c o m p e t i t i o n c o u l d e x p l a i n h i g h n a u p l i a r c o n c e n t r a t i o n s i n low d e n s i t y e n c l o s u r e s . Lowered d e n s i t i e s of a l l s p e c i e s , i n c l u d i n g D. t y r e l l i , c o n f o u n d e d e f f e c t s of D. t y r e l l i c o m p e t i t i o n on egg t o n a u p l i u s s u r v i v a l w i t h 62 e f f e c t s of d i f f u s e c o m p e t i t i o n on egg p r o d u c t i o n . A b s e n c e s of i n t e r a c t i o n s between D. l e p t o p u s and e i t h e r D. k e n a i or D. r o s e a i m p l y t h a t D. t y r e l l i c o m p e t i t i o n , r a t h e r t h a n d i f f u s e c o m p e t i t i o n , a f f e c t e d D. l e p t o p u s . S i m i l a r i t i e s between t y r e l l i - r e m o v a l and low d e n s i t y t r e a t m e n t s i n c o p e p o d i t e , a d u l t , and t o t a l D. l e p t o p u s d e n s i t i e s a l s o i m p l y t h i s b e c a u s e b o t h t r e a t m e n t s c o n t a i n e d s i m i l a r D. t y r e l l i c o n c e n t r a t i o n s ( F i g . 2; p a i r w i s e c o m p a r i s o n s between low d e n s i t y and t y r e l l i - r e m o v a l t r e a t m e n t s i n T a b l e I X ) . In c o n t r a s t , t h e h i g h e r p r o p o r t i o n of D. l e p t o p u s n a u p l i i i n low d e n s i t y t h a n i n t y r e l l i - r e m o v a l e n c l o s u r e s ( F i g . 8) a r g u e s f o r t h e i m p o r t a n c e of d i f f u s e c o m p e t i t i o n . However, due t o i n t e r - r e p l i c a t e v a r i a t i o n , p a i r w i s e c o m p a r i s o n s between t h e s e two t r e a t m e n t s y i e l d d i f f e r e n c e s i n n a u p l i a r d e n s i t i e s a t p < 0.05 on o n l y two s a m p l i n g d a t e s ( T a b l e I X ) . B e c a u s e t h e s e c o m p a r i s o n s were s u g g e s t e d a p o s t e r i o r i by t h e d a t a , whether t h e s e d i f f e r e n c e s a r e s i g n i f i c a n t i s u n c e r t a i n ( S n e d e c o r and C o c h r a n 1967). 2.3 T r e a t m e n t Ef f e c t s on A d u l t S i z e of D i aptomus l e p t o p u s T r e a t m e n t d i f f e r e n c e s i n l e n g t h s o f a d u l t D. l e p t o p u s were e v i d e n t on o n l y two of t h e s e v e n s a m p l i n g d a t e s f o r w h i c h z o o p l a n k t o n were measured (ANOVAs: p < 0.05). T h e s e d i f f e r e n c e s may not have been t r e a t m e n t e f f e c t s ; u n c o n t r o l l e d s h r i n k a g e due t o f o r m a l i n .and u n r e c o r d e d sex d i f f e r e n c e s i n s i z e (males a r e s m a l l e r [ W i l s o n 1959]) a l s o i n f l u e n c e d measurements. T a b l e X I I I 63 T a b l e X I I I . L e n g t h s (mm) o f a d u l t d i a p t o m i d c o p e p o d s and o f D a p h n i a r o s e a i n 1979 e x p e r i m e n t s . Means a r e b a s e d on a l l a n i m a l s measured, r e g a r d l e s s of t r e a t m e n t or s a m p l i n g d a t e . S p e c i e s N Mean S t d . Dev. Diaptomus k e n a i 4 1 9 2 . 46 0. 1 3 Diaptomus l e p t o p u s 332 1 .70 0. 09 Diaptomus t y r e l l i 525 1 .29 0. 06 D a p h n i a r o s e a 627 2 .07 0. 33 64 d i s p l a y s mean l e n g t h of D. l e p t o p u s and, f o r c o m p a r i s o n , l e n g t h s of D. t y r e l l i , D. k e n a i , and D a p h n i a r o s e a a v e r a g e d o v e r a l l t r e a t m e n t s and d a t e s . Low s t a n d a r d d e v i a t i o n s f o r a l l s p e c i e s s u g g e s t t h a t s e a s o n a l c h a n g e s i n s i z e were s m a l l . I n c l u s i o n of b o t h j u v e n i l e and a d u l t s i z e s i n f l a t e d t h e s t a n d a r d d e v i a t i o n f o r D. r o s e a . 2.4 S e a s o n a l C y c l e s , V e r t i c a l D i s t r i b u t i o n and P h y t o p l a n k t o n  Biomass T e m p o r a l a s y n c h r o n y , s p a t i a l s e p a r a t i o n , and d i e t a r y d i f f e r e n c e s can moderate i n t e n s i t y of c o m p e t i t i o n among d i a p t o m i d s . C o m p a r i s o n s of s e a s o n a l c y c l e s and v e r t i c a l d i s t r i b u t i o n s between D. l e p t o p u s and E u n i c e Lake z o o p l a n k t o n and c o m p a r i s o n of p h y t o p l a n k t o n b i o m a s s among t r e a t m e n t s seek e v i d e n c e of t h e s e c o e x i s t e n c e mechanisms. S e a s o n a l C y c l e s H i g h v a r i a t i o n among s m a l l s a m p l e s and l i m i t e d d u r a t i o n of e x p e r i m e n t s p r e v e n t e d r e s o l u t i o n of a n n u a l c y c l e s f o r e n c l o s e d d i a p t o m i d s . P r e s u m a b l y t h e i r l i f e c y c l e s were s i m i l a r t o t h o s e Chapman and G r e e n ( u n p u b l . d a t a ) d e f i n e d f o r c a l a n o i d c o p e p o d s from R e s e a r c h F o r e s t l a k e s . F i g s . 10 and 11 s c h e m a t i c a l l y p r e s e n t s e a s o n a l c y c l e s of D. t y r e l l i and D. k e n a i i n E u n i c e L a k e . B e c a u s e D. l e p t o p u s i s b a r e l y d e t e c t a b l e i n E u n i c e L a k e , 65 F i g . 9 shows i t s l i f e h i s t o r y i n G w e n d o l i n e L a k e , i n s t e a d . T i m i n g of s e a s o n a l c h a n g e s i n d e n s i t i e s of d i f f e r e n t d e v e l o p m e n t s t a g e s i s s i m i l a r from y e a r t o y e a r , but a c t u a l d e n s i t i e s a t t a i n e d a r e v a r i a b l e . In G w e n d o l i n e L a k e , o v e r w i n t e r i n g D. l e p t o p u s a d u l t s d i e a f t e r r e p r o d u c i n g i n e a r l y s p r i n g . T h e i r o f f s p r i n g r e a c h a d u l t h o o d by J u l y or l a t e August and t h e n p r o p a g a t e a f a l l g e n e r a t i o n ( F i g . 9 ) . In E u n i c e L a k e , even i n low d e n s i t y and t y r e l l i - r e m o v a l t r e a t m e n t s , no f a l l g e n e r a t i o n o c c u r r e d i n 1979 ( F i g . 8 ) . D. t y r e l l i o v e r w i n t e r s i n E u n i c e Lake as r e s t i n g e g g s . N a u p l i i h a t c h i n g i n s p r i n g mature i n t o a d u l t s by June o r J u l y . T h e s e p r o d u c e a s e c o n d g e n e r a t i o n w h i c h i n t u r n p r o d u c e s o v e r w i n t e r i n g eggs ( F i g . 10). O v e r w i n t e r i n g D. k e n a i n a u p l i i a c h i e v e m a t u r i t y . b y A p r i l or May. S p r i n g a d u l t s b r e e d a f a l l g e n e r a t i o n . F a l l a d u l t s p r o d u c e e i t h e r s u b i t a n e o u s o r r e s t i n g eggs ( F i g . 11). G r e a t e r t e m p o r a l s y n c h r o n y of D. l e p t o p u s w i t h D. t y r e l l i t h a n w i t h D. k e n a i i s c o n s i s t e n t w i t h i m p r o v e d D. l e p t o p u s p e r f o r m a n c e i n t y r e l l i - r e m o v a l and not i n kena i - r e m o v a l t r e a t m e n t s . D u r i n g J u l y and A u g u s t , when marked t r e a t m e n t e f f e c t s on D. l e p t o p u s n a u p l i i o c c u r r e d , a l l s t a g e s of D. t y r e l l i were r e p r e s e n t e d i n t h e e n c l o s u r e s . B e c a u s e i t d e v e l o p s e a r l i e r t h a n D. l e p t o p u s , no n a u p l i i and few e a r l y c o p e p o d i t e s of D. k e n a i o c c u r r e d s i m u l t a n e o u s l y w i t h t h e s e s t a g e s of D. l e p t o p u s . T e m p o r a l o v e r l a p between D. l e p t o p u s and D a p h n i a r o s e a i s d i f f i c u l t t o a s s e s s b e c a u s e d e v e l o p m e n t a l s t a g e s of c l a d o c e r a n s 66 F i g u r e 9. L i f e c y c l e of Diaptomus l e p t o p u s i n G w e n d o l i n e L a k e . Shaded a r e a s s c h e m a t i c a l l y r e p r e s e n t s e a s o n a l c h a n g e s i n abundances o f d i f f e r e n t d e v e l o p m e n t s t a g e s . S m a l l a r r o w s t r a c e c o h o r t s . L a r g e a r r o w s i n d i c a t e r e p r o d u c t i o n . A f t e r Chapman ( u n p u b l . ) DIAPTOMUS LEPTOPUS E G G S s u b i t o n e o u s s u b i t a n e o u s NAUPLII \ COPEPODITES \ \ ADULTS 68 F i g u r e 10. L i f e c y c l e of D i aptomus t y r e l l i i n E u n i c e L a k e . Shaded a r e a s s c h e m a t i c a l l y r e p r e s e n t s e a s o n a l c h a n g es i n a b u n d a n c e s of d i f f e r e n t d e v e l o p m e n t s t a g e s . S m a l l a r r o w s t r a c e c o h o r t s . L a r g e a r r o w s i n d i c a t e r e p r o d u c t i o n . A f t e r Chapman ( u n p u b l . ) DIAPTOMUS TYRELLI EGGS 70 F i g u r e 11. L i f e c y c l e of Diaptomus k e n a i i n E u n i c e L a k e . Shaded a r e a s s c h e m a t i c a l l y r e p r e s e n t s e a s o n a l c h a n g e s i n a b u n d a n c e s of d i f f e r e n t d e v e l o p m e n t s t a g e s . S m a l l a r r o w s t r a c e c o h o r t s . L a r g e a r r o w s i n d i c a t e r e p r o d u c t i o n . A f t e r Chapman ( u n p u b l . ) DIAPTOMUS KENAI EGGS 72 and c o p e p o d s do not c o r r e s p o n d . D. r o s e a , a f a c u l t a t i v e p a r t h e n o g e n , b r e e d s a s e x u a l l y t h r o u g h o u t s p r i n g and summer. As t e m p e r a t u r e and f o o d c o n d i t i o n s d e c l i n e i n t h e f a l l , s e x u a l e p h i p p i a l eggs a p p e a r . In t h e e n c l o s u r e s , r e p r o d u c t i o n was p r i m a r i l y a s e x u a l . B o t h a d u l t and j u v e n i l e D. r o s e a were c o n s i s t e n t l y p r e s e n t . V e r t i c a l D i s t r i b u t i o n s F i g s . 12 and 13 d i s p l a y J u l y and September d i s t r i b u t i o n s of D. t y r e l l i , D. k e n a i , D. l e p t o p u s , and D a p h n i a r o s e a w i t h i n t h e w a ter c o l u m n . D a t a from a l l e n c l o s u r e s were combined b e c a u s e no d i s t i n c t or c o n s i s t e n t t r e a t m e n t d i f f e r e n c e s were e v i d e n t . No D. k e n a i n a u p l i i o c c u r r e d i n e i t h e r J u l y or September. R e s t r i c t i o n of D. l e p t o p u s and D. t y r e l l i n a u p l i i p r i m a r i l y t o t h e u p p e r 2 m ( F i g s . 12 and 13) was e s p e c i a l l y marked f o r D. l e p t o p u s i n t h e a b s e n c e of D. t y r e l l i ( F i g . 14). These s t a g e s e x p e r i e n c e d warm (>20°C) s u r f a c e t e m p e r a t u r e s ( F i g . 15). In most e n c l o s u r e s , c o p e p o d i t e s and a d u l t s o f D. l e p t o p u s and D. t y r e l l i c o n c e n t r a t e d above 4 and 7 m, r e s p e c t i v e l y ( F i g s . 12 and 13). D. k e n a i e x i s t e d below t h e t h e r m o c l i n e o c c u r r i n g a t 4-5 m ( F i g . 1.5). D. r o s e a d i s p e r s e d more d e e p l y i n summer t h a n i n f a l l . No s p e c i e s e x h i b i t e d p r o m i n e n t d i e l v e r t i c a l m i g r a t i o n s , but D. t y r e l l i moved s l i g h t l y up, and D. k e n a i and D. l e p t o p u s moved s l i g h t l y down d i u r n a l l y d u r i n g September. 73 F i g u r e 12. N o c t u r n a l ( s o l i d b a r s ) and d i u r n a l (open b a r s ) v e r t i c a l d i s t r i b u t i o n s o f D i a p t o m u s l e p t o p u s , D i a p t o m u s  t y r e l l i , D i a p t o m u s k e n a i , and D a p h n i a r o s e a i n 1979 e x p e r i m e n t s d u r i n g J u l y . O b s e r v a t i o n s from a l l e n c l o s u r e s a r e combined. LN = D. l e p t o p u s n a u p l i i ; LC = D. l e p t o p u s c o p e p o d i t e s ; LA = D. l e p t o p u s a d u l t s ; TN = D. t y r e l l i n a u p l i i ; TC = D. t y r e l l i c o p e p o d i t e s ; TA = D. t y r e l l i a d u l t s ; KC = D. k e n a i c o p e p o d i t e s ; RA = D. k e n a i a d u l t s ; DA = D. r o s e a . N, = s i z e o f n o c t u r n a l s a m p l e s ; N 2 = s i z e of d i u r n a l s a m p l e s . 0-2 2 -4 4 - 7 >7 LN N, = 274 ] N, = 304 N2>332 i — 1 1 i — — 1 1 i ' r 1 0 50 100 0 50 100 0 50 100 •/•OCCURRENCE g u r e 13. N o c t u r n a l ( s o l i d b a r s ) and d i u r n a l (open b a r s ) v e r t i c a l d i s t r i b u t i o n s o f Diaptomus t y r e l l i , D i a p t o m u s  k e n a i , D i a p t o m u s l e p t o p u s , and D a p h n i a r o s e a i n 1979 e x p e r i m e n t s d u r i n g September. O b s e r v a t i o n s from a l l e n c l o s u r e s a r e c o m b i n e d . LN = D. l e p t o p u s n a u p l i i ; LC = D. l e p t o p u s c o p e p o d i t e s ; LA = D. l e p t o p u s a d u l t s ; TN = D. t y r e l l i n a u p l i i ; TC = D. t y r e l l i c o p e p o d i t e s ; T A = 2- t y r e l l i a d u l t s ; KC = D. k e n a i c o p e p o d i t e s ; KA = D. k e n a i a d u l t s ; DA = D. r o s e a . N, = s i z e o f n o c t u r n a l s a m p l e s ; N 2 = s i z e of d i u r n a l s a m p l e s . 0-2 2-4 4-7 L N N2=6 3 I LC N2*S8 3 L A N,=29 N2*88 0-2 2-4 X I-0. 4-7 UJ Q 7 TN N, =19 N2=3I TC N,=340 N2=3T9 TA N| s|409 N_=648 0-2 2-4 4-7 .r-0 DA N, =670 N2=604 50 100 KC N,=69 N2=46 — I — 50 loo % O C C U R R E N C E 1 u KA • N,=I36 N2=88 I— 0 50 "Joo cn 77 F i g u r e 14. J u l y v e r t i c a l d i s t r i b u t i o n s of D i aptomus l e p t o p u s n a u p l i i i n t h e p r e s e n c e ( s o l i d b a r s ) and i n t h e a b s e n c e (open b a r s ) o f Diaptomus t y r e l l i . D a t a from c o n t r o l , Daphn i a - r e m o v a l , and k_ena_i-removal t r e a t m e n t s a r e combined t o g i v e n a u p l i a r d i s t r i b u t i o n s i n t h e p r e s e n c e of D. t y r e l l i • D a t a f r o m t y r e l l i - r e m o v a l and low d e n s i t y t r e a t m e n t s a r e combined t o g i v e n a u p l i a r d i s t r i b u t i o n s i n t h e a b s e n c e o f D. t y r e l l i . B o t h n o c t u r n a l and d i u r n a l d a t a a r e i n c l u d e d . 2-4 X I-CL UJ O 4-7 >7 With D.tvrellh N = I80 Without D. tvrellh N=6I0 50 1 100 % OCCURRENCE g u r e 15. T e m p e r a t u r e p r o f i l e f o r E u n i c e Lake d u r i n g 1979 e x p e r i m e n t s . O CM *T CD CO CM ^" CD 00 (N) Hld30 81 L a c k of s p a t i a l s e g r e g a t i o n between s u r f a c e - d w e l l i n g D. l e p t o p u s and D. t y r e l l i a c c o r d s w i t h e x p e r i m e n t a l e v i d e n c e of D. t y r e l l i c o m p e t i t i o n . N on-competing D. k e n a i and D. r o s e a i n h a b i t e d d e e p e r s t r a t a . P h y t o p l a n k t o n Biomass S t u d i e s on f i l t e r - f e e d i n g h e r b i v o r o u s c r u s t a c e a n s s u g g e s t a p o s i t i v e c o r r e l a t i o n between s i z e of a n i m a l and s i z e o f p a r t i c l e f i l t e r e d ( B u r n s 1968; H a l l e t a l . 1976; P o u l e t 1979). In t h e a b s e n c e of a p a r t i c u l a r z o o p l a n k t o n s p e c i e s , p h y t o p l a n k t o n of s i z e s e a t e n by t h a t s p e c i e s s h o u l d i n c r e a s e i n biomass ( P o r t e r 1972; L y n c h and S h a p i r o 1981). From a v e r a g e l e n g t h s of E u n i c e Lake z o o p l a n k t o n ' s p e c i e s ( T a b l e X I I I ) , t h e f o l l o w i n g t r e a t m e n t d i f f e r e n c e s i n p h y t o p l a n k t o n s t a n d i n g s t o c k s a r e p r e d i c t e d : r e l a t i v e t o c o n t r o l s , s m a l l p a r t i c l e s s h o u l d i n c r e a s e i n t y r e l l i - r e m o v a l s ; l a r g e p a r t i c l e s , i n k e n a i - and D a p h n i a -r e m o v a l s ; and a l l p a r t i c l e s , i n low d e n s i t y e n c l o s u r e s . P r e d i c t i o n s c o u l d be d e r i v e d from s i z e s of a d u l t c a l a n o i d s , w i t h o u t c o n s i d e r a t i o n of p o p u l a t i o n age d i s t r i b u t i o n s , b e c a u s e i n t h e e n c l o s u r e s o n l y l a t e c o p e p o d i t e s and a d u l t s of D. k e n a i o c c u r r e d , and t h e s e were l a r g e r t h a n a l l D. t y r e l l i . I f , as N e i l l (1975a and b) f o u n d i n h i s m i c r o c o s m s , E u n i c e Lake z o o p l a n k t o n s p e c i e s p a r t i t i o n f o o d by s i z e and not by taxonomy, t h e n d a t a s u p p o r t i n g t h e s e p r e d i c t i o n s would p r o v i d e i n d i r e c t e v i d e n c e of d i e t d i f f e r e n c e s among z o o p l a n k t o n . R e s u l t s do not s u p p o r t a p o s i t i v e c o r r e l a t i o n between 82 z o o p l a n k t o n s i z e and f o o d s i z e ( F i g . 16). T h r o u g h o u t t h e e x p e r i m e n t s , b i o m a s s of s m a l l p h y t o p l a n k t o n (<20 urn i n d i a m e t e r ) was a p p r o x i m a t e l y e q u a l i n a l l t r e a t m e n t s . R e l a t i v e t o c o n t r o l s , l a r g e c e l l s (>20 urn) i n c r e a s e d s u b s t a n t i a l l y i n t y r e l l i - r e m o v a l and low d e n s i t y t r e a t m e n t s , i n c r e a s e d s l i g h t l y i n D a p h n i a -r e m o v a l s , and d e c r e a s e d i n k e n a i - r e m o v a l s . P r e s u m a b l y , t r e a t m e n t d i f f e r e n c e s i n z o o p l a n k t o n g r a z i n g c a u s e d t h e s e c h a n g e s b e c a u s e t h e y o c c u r r e d w i t h i n t h e f i r s t 4 t o 6 weeks of t h e e x p e r i m e n t . L a t e r i n c r e a s e s of l a r g e p a r t i c l e s and c o l o n i e s o c c u r r e d i n a l l e n c l o s u r e s a f t e r o t h e r f a c t o r s ( e . g., s e a s o n a l s u c c e s s i o n s of p h y t o p l a n k t o n and z o o p l a n k t o n s p e c i e s , r e c y c l i n g o f n u t r i e n t s , s i n k i n g and s h a d i n g of a l g a e ) had had s u f f i c i e n t t i m e t o i n f l u e n c e p h y t o p l a n k t o n s i z e d i s t r i b u t i o n s . C e l l s <2 urn were m o s t l y c o c c o i d b a c t e r i a . Among t h o s e 2-20 urn were c h l o r o p h y t e s ( O o s y s t i s ) , c h r y s o p h y t e s ( M a l l o m o n a s , Ochromonas, D i n o b r y o n ) , d i a t o m s , and C r y p t o m o n a s . C e l l s >20 urn and c o l o n i e s i n c l u d e d c h l o r o p h y t e s ( A n k i s t r o d e s m u s , S c e n e d e s m u s) , c h r y s o p h y t e s ( D i n o b r y o n , C h r y s o c a p s a ) , and c o l o n i a l c y a n o p h y t e s ( C h r o o c o c c u s , D a c t y l o c o c c o p s i s, Mer i s m o p e d i a ) . g u r e 16. P h y t o p l a n k t o n s t a n d i n g s t o c k s i n E u n i c e Lake and i n 1979 e x p e r i m e n t s . P l o t s f o r r e p l i c a t e e n c l o s u r e s a r e s i d e by s i d e . F o r e a c h e n c l o s u r e , upper p l o t shows t o t a l b i o m a s s ; lower p l o t shows p e r c e n t s i z e c o m p o s i t i o n of t o t a l b i o m a s s . A = E u n i c e L a k e ; B = C o n t r o l ; C = Low d e n s i t y ; D = D a p h n i a - r e m o v a l ; E = k_ena_i-removal; F = t y r e l l i - r e m o v a l . 84 5 A £ 1 . 6 TOTAL BICWRSS O PERCENT 6IDMBSS l r <2 MICRONS 100 JULT | RUG. I SEPT. | OCT. J I JULT | RUG. | SEPT. | OCT. 1979 PERCENT BIOMASS s . s TOTAL BIOMASS 1MG/L) a b) ' ' ' ' ' I I I A I I I I <B I I PERCENT BIOMASS PERCENT BIOMASS TOTAL BJOMHSS 1MG/LJ o o o CD oi TOTAL BIOMASS (MG/L) \ 0 0 86 3. Summary of 1979 R e s u l t s At t h e s t a r t of t h e e x p e r i m e n t s , e n c l o s u r e s c o n t a i n e d z o o p l a n k t o n i n d e n s i t i e s a p p r o p r i a t e t o t h e t r e a t m e n t s . E f f e c t s of c o n f i n e m e n t on z o o p l a n k t o n p o p u l a t i o n s d i d not i n v a l i d a t e e x p e r i m e n t s b e c a u s e e n c l o s u r e s c o n t a i n i n g t h e E u n i c e Lake z o o p l a n k t o n a s s e m b l a g e p l u s D i a p t o m u s l e p t o p u s s e r v e d as c o n t r o l s . S i m i l a r i t i e s between p e r f o r m a n c e s of D. l e p t o p u s i n c o n t r o l , D a p h n i a - r e m o v a l , and t y r e l l i - r e m o v a l t r e a t m e n t s i n d i c a t e d no c o m p e t i t i o n from Daphn i a r o s e a o r Diaptomus  k e n a i . D. l e p t o p u s p e r s i s t e d l o n g e r i n t y r e l l i - r e m o v a l and low d e n s i t y e n c l o s u r e s t h a n i n c o n t r o l s . Numbers o f eggs p e r D. l e p t o p u s f e m a l e were h i g h e s t i n low d e n s i t y e n c l o s u r e s . I n c r e a s e d D. l e p t o p u s n a u p l i a r d e n s i t i e s i n t y r e l l i -r e m o v a l s r e l a t i v e t o c o n t r o l s i n d i c a t e d c o m p e t i t i o n from D i a p t o m u s t y r e l l i . I n c r e a s e d D. l e p t o p u s n a u p l i a r d e n s i t i e s i n low d e n s i t y 87 e n c l o s u r e s r e l a t i v e t o c o n t r o l s c o n f o u n d e d d i f f u s e w i t h D. t y r e l l i c o m p e t i t i o n . 8. D e n s i t i e s of D. l e p t o p u s c o p e p o d i t e s and a d u l t s were s i m i l a r i n a l l t r e a t m e n t s . 9. A d u l t s i z e of D. l e p t o p u s was s i m i l a r i n a l l t r e a t m e n t s . 10. V e r t i c a l and s e a s o n a l d i s t r i b u t i o n s of D. l e p t o p u s and D. t y r e l l i o v e r l a p p e d . D. k e n a i and D. r o s e a o c c u r r e d d e e p e r t h a n D. l e p t o p u s , and D. k e n a i r e p r o d u c e d e a r l i e r . 11. T r e a t m e n t d i f f e r e n c e s i n s t a n d i n g s t o c k s of s m a l l and l a r g e p h y t o p l a n k t o n p r o v i d e d no e v i d e n c e f o r d i f f e r e n c e s i n d i a p t o m i d d i e t s . 88 EXPERIMENTAL DESIGN, 1980 E x p e r i m e n t s i n 1980 a t t e m p t e d t o v e r i f y e f f e c t s of 1979 t y r e l l i - r e m o v a l e n c l o s u r e s , and t o s e p a r a t e them from e f f e c t s of low d e n s i t y e n c l o s u r e s . In 1980, e i g h t e n c l o s u r e s c o n t a i n e d f o u r t w i c e - r e p l i c a t e d t r e a t m e n t s . E a c h e n c l o s u r e c o n t a i n e d a s t a n d a r d d e n s i t y of 0.64 D i a p t o m u s l e p t o p u s p e r l i t r e ( n a u p l i i , c o p e p o d i t e s , and a d u l t s c o m b i n e d ) . T h i s d e n s i t y e x c e e d e d t h a t from 1979 b e c a u s e i n i t i a l d e n s i t i e s of D. l e p t o p u s i n E u n i c e Lake were h i g h e r i n 1980 and b e c a u s e numbers o f D. l e p t o p u s i n samples had been low i n 1979. T a b l e XIV d e s c r i b e s 1980 t r e a t m e n t s and t h e h y p o t h e s e s t h e y t e s t . E x c e p t t h a t t h e i r z o o p l a n k t o n d e n s i t i e s r e f l e c t e d l a k e d e n s i t i e s from a d i f f e r e n t y e a r , 1980 c o n t r o l and t y r e l l i -r e m o v a l t r e a t m e n t s d u p l i c a t e d t h o s e from 1979. Two t r e a t m e n t s e n c l o s e d r e d u c e d b i o m a s s e s of E u n i c e Lake z o o p l a n k t o n . Low d e n s i t y c o n t a i n e d a l l s p e c i e s i n l a k e r e l a t i v e p r o p o r t i o n s , w h i l e t y r e l l i / l o w d e n s i t y c o n t a i n e d m o s t l y D i a p t o m u s t y r e l l i . T h e se t r e a t m e n t s r e d u c e d b i o m a s s by 70%, r a t h e r t h a n by 90% as i n 1979, b e c a u s e D. t y r e l l i formed a g r e a t e r m a j o r i t y of E u n i c e Lake z o o p l a n k t o n i n 1980. The l e s s e r r e d u c t i o n e n h a n c e d t r e a t m e n t d i f f e r e n c e s i n D. t y r e l l i c o n c e n t r a t i o n s . D. t y r e l l i was l e s s d e n s e i n t y r e l l i / l o w d e n s i t y e n c l o s u r e s t h a n i n t h e l a k e and i n c o n t r o l s , and more dense t h a n i n low d e n s i t y e n c l o s u r e s . T o g e t h e r , low d e n s i t y and t y r e l l i / l o w d e n s i t y t r e a t m e n t s aimed t o d i s t i n g u i s h d i f f u s e and D. t y r e l l i c o m p e t i t i o n c o n f o u n d e d i n 1979. H i g h d e n s i t i e s o f D. l e p t o p u s n a u p l i i r e l a t i v e t o c o n t r o l s - i n b o t h t r e a t m e n t s would p r o v i d e T a b l e XIV. Summary of 1980 experimental treatments. N = Eunice Lake z o o p l a n k t o n assemblage at 1980 n a t u r a l l ake d e n s i t i e s ; B = N c o n v e r t e d to biomass. Treatment S p e c i e s c o m p o s i t i o n H y p o t h e s i s t e s t e d Contro1 N + D i aptomus 1eptopus Compare performance of D. 1eptopus here w i t h t h a t i n a l l o t h e r t r e a t m e n t s to t e s t a l l hypotheses. t y r e l 1 i - r e m o v a l N - Diaptomus t y r e l 1 i + D. 1eptopus C o m p e t i t i o n w i t h Diaptomus t y r e l 1 i p r e v e n t s D. 1eptopus from c o l o n i z i n g Eunice Lake. Low d e n s i t y 30% N + D. 1eptopus D i f f u s e c o m p e t i t i o n from s e v e r a l z o o p l a n k t o n s p e c i e s p r e v e n t s D. 1eptopus from c o l o n i z i n g E u n i c e Lake. t y r e l 1 i / 30% B as D. t y r e l 1 i C o m p e t i t i o n with D. t y r e l 1 i low d e n s i t y + D. 1eptopus e x p l a i n s e f f e c t s of 1979 low d e n s i t y e n c l o s u r e s on D. 1eptopus. CO 90 e v i d e n c e f o r d i f f u s e c o m p e t i t i o n . H i g h n a u p l i a r d e n s i t i e s i n o n l y low d e n s i t y e n c l o s u r e s would p r o v i d e e v i d e n c e f o r D. t y r e l l i c o m p e t i t i o n by i m p l y i n g t h a t r e l a t i v e l y abundant D. t y r e l l i s u p p r e s s e d D. l e p t o p u s i n t y r e l l i / l o w d e n s i t y e n c l o s u r e s . H i g h egg p r o d u c t i o n i n b o t h t r e a t m e n t s would r e f l e c t r e d u c e d g r a z i n g p r e s s u r e s i n b o t h . 91 RESULTS, 1980 J_. R e s u l t s C o n f i r m i n g P r o p e r E s t a b l i s h m e n t of E x p e r i m e n t s J_.J_ E n c l o s u r e D e n s i t i e s of Abundant E u n i c e Lake Z o o p l a n k t o n  Spec i e s I n i t i a l s i m i l a r i t i e s between E u n i c e Lake and c o n t r o l e n c l o s u r e s i n t o t a l d e n s i t i e s of D i aptomus t y r e l l i , D. k e n a i , Daphn i a r o s e a , and H o l o p e d i u m g i b b e r u m d e m o n s t r a t e p r o p e r s t o c k i n g of c o n t r o l s w i t h t h e s e s p e c i e s ( T a b l e X V ) . R e m a i n i n g t r e a t m e n t s c o n t a i n e d v a r i a t i o n s on c o n t r o l d e n s i t i e s . D. t y r e l l i o c c u r r e d i n i n c r e a s i n g l y g r e a t e r c o n c e n t r a t i o n s i n t y r e l l i -remo.val, low d e n s i t y , t y r e l l i / l o w d e n s i t y , and c o n t r o l t r e a t m e n t s ( T a b l e XVI; F i g . 17). R e l a t i v e t o c o n t r o l s , D. k e n a i d e n s i t i e s were low i n low d e n s i t y and, e s p e c i a l l y , i n t y r e l l i / l o w d e n s i t y e n c l o s u r e s ( F i g . 1 8 ) . They were h i g h e r i n t y r e l l i - r e m o v a l s ( T a b l e X V I I ) . C o n t r o l and t y r e l l i - r e m o v a l l e v e l s o f c l a d o c e r a n s were s i m i l a r ( T a b l e s X V I I I and XIX; F i g . 1 9 ) . B o t h low d e n s i t y t r e a t m e n t s c o n t a i n e d e q u a l l y r e d u c e d D. r o s e a c o n c e n t r a t i o n s ( F i g . 19). T hese r e s u l t s i n d i c a t e t h a t , w i t h two e x c e p t i o n s , e n c l o s u r e d e n s i t i e s of common E u n i c e Lake z o o p l a n k t o n s p e c i e s c o n f o r m e d t o t h e e x p e r i m e n t a l d e s i g n . T o . f u l l y c o n f o r m , D. r o s e a s h o u l d have been l e s s dense i n t y r e l l i / l o w d e n s i t y t h a n i n low d e n s i t y e n c l o s u r e s ; and D. k e n a i , as d ense i n t y r e l l i - r e m o v a I s as i n c o n t r o l s . 92 T a b l e XV. T - t e s t s t a t i s t i c s c o m p a r i n g mean d e n s i t i e s (numbers of a n i m a l s p e r 150 1 s a m p l e s ) o f major E u n i c e l a k e s p e c i e s i n E u n i c e Lake and i n c o n t r o l e n c l o s u r e s a t s t a r t o f 1980 e x p e r i m e n t s . T e s t s a n a l y z e d l o g - t r a n s f o r m e d c o u n t s from t h e f i r s t two s a m p l i n g d a t e s , but means and s t a n d a r d d e v i a t i o n s shown a r e of u n t r a n s f o r m e d d a t a . N = n a u p l i i ; C = c o p e p o d i t e s ; A = a d u l t s ; J = j u v e n i l e s . Spec i e s L o c a t i o n Lake C o n t r o l s df D i a p t o m u s t y r e l l i (N+C+A) X: 464.5 s: 328.8 n: 2 763 .8 304.3 4 -1 .24 4 0.283 Dia p t o m u s k e n a i (N+C+A) X: s: n: 84.0 19.8 2 17.0 11.7 4 3.73 4 0.020 Daphn i a r o s e a (J+A) X: s: n: 192.0 72. 1 2 65.0 7.0 4 5.70 4 0.005 H o l o p e d i u m g i b b e r u m (J+A) ~~ X: 77.0 s: 59.4 n: 2 32.3 12.0 1 .62 4 0.182 93 T a b l e X V I. S t a t i s t i c a l t e s t s c o m p a r i n g mean d e n s i t i e s of Diaptomus t y r e l l i (numbers of n a u p l i i , c o p e p o d i t e s , and a d u l t s combined p e r 150 1 sample) a c r o s s t r e a t m e n t s on i n i t i a l s a m p l i n g d a t e (May 13) of 1980 e x p e r i m e n t s . S i n c e ANOVA c o m p a r i n g a l l t r e a t m e n t s i s s i g n i f i c a n t , p a i r w i s e m u l t i p l e c o m p a r i s o n s of c o n t r o l s w i t h e a c h p e r t u r b a t i o n a r e shown. T e s t s a n a l y z e d l o g - t r a n s f o r m e d c o u n t s , b u t means and s t a n d a r d d e v i a t i o n s shown a r e of u n t r a n s f o r m e d d a t a . One-way A n a l y s i s of V a r i a n c e : S o u r c e df Sum of S q u a r e s Mean Sq u a r e F p Between 3 9.19 3.06 71.04 0.001 W i t h i n 4 0.17 0.04 T o t a l 7 9.36 P a i r w i s e M u l t i p l e C o m p a r i s o n s : T r e a t m e n t Mean (#/l50 1) S t d . Dev. C o n t r o l : 1023.0 : t y r e l l i - r e m o v a l :Low d e n s i t y : t y r e l l i / l o w d e n s i t y 68.5 131.0 512.0 18.4 16, 36, 97, 169.65 99.27 11.38 <0.001 0.001 0.028 94 F i g u r e 17. D e n s i t i e s of Diaptomus t y r e l l i ( n a u p l i i , c o p e p o d i t e s , and a d u l t s combined) i n E u n i c e Lake and i n 1980 e x p e r i m e n t s . P l o t s f o r r e p l i c a t e e n c l o s u r e s a r e s i d e by s i d e . A = E u n i c e L a k e ; B = C o n t r o l ; C = t y r e l l i - r e m o v a l ; D = Low d e n s i t y ; E = t y r e l l i / l o w d e n s i t y . NUMBER OF ANIMALS PER 150 LITRES 96 F i g u r e 18. D e n s i t i e s o f Diaptomus k e n a i ( n a u p l i i , c o p e p o d i t e s , and a d u l t s c o m b i n e d ! i n E u n i c e Lake and i n 1980 e x p e r i m e n t s . P l o t s f o r r e p l i c a t e e n c l o s u r e s a r e s i d e by s i d e . A = E u n i c e L a k e ; B = C o n t r o l ; C = t y r e l l i -r e m o v a l ; D = Low d e n s i t y ; E = t y r e l l i / l o w d e n s i t y . NUMBER OF ANIMALS PER 150 LITRES 98 T a b l e X V I I . S t a t i s t i c a l t e s t s c o m p a r i n g mean d e n s i t i e s o f Diaptomus k e n a i (numbers of n a u p l i i , c o p e p o d i t e s , and a d u l t s combined p e r 150 1 sample) a c r o s s t r e a t m e n t s on i n i t i a l s a m p l i n g d a t e (May 13) of 1980 e x p e r i m e n t s . S i n c e ANOVA c o m p a r i n g a l l t r e a t m e n t s i s s i g n i f i c a n t , p a i r w i s e m u l t i p l e c o m p a r i s o n s of c o n t r o l s w i t h e a c h p e r t u r b a t i o n a r e shown. T e s t s a n a l y z e d l o g - t r a n s f o r m e d c o u n t s , but means and s t a n d a r d d e v i a t i o n s shown a r e of u n t r a n s f o r m e d d a t a . One-way A n a l y s i s o f V a r i a n c e : S o u r c e d f Sum of S q u a r e s Mean Sq u a r e F p-Between 3 5.94 1.98 5.82 0.061 W i t h i n 4 1.36 0.34 T o t a l 7 7.30 P a i r w i s e M u l t i p l e C o m p a r i s o n s : T r e a t m e n t Mean (#/l50 1) S t d . Dev, C o n t r o l : 13.0 : t y r e l l i - r e m o v a l :Low d e n s i t y : t y r e l l i / l o w d e n s i t y 71.5 24.5 5.5 2.8 24.7 23.3 0.7 7.76 0.34 1 .70 0.050 0.593 0.263 99 T a b l e X V I I I . S t a t i s t i c a l t e s t s c o m p a r i n g mean d e n s i t i e s of Daphn i a r o s e a (number p e r 150 1 sample) a c r o s s t r e a t m e n t s on i n i t i a l s a m p l i n g d a t e (May 13) of 1980 e x p e r i m e n t s . S i n c e ANOVA c o m p a r i n g a l l t r e a t m e n t s i s s i g n i f i c a n t , p a i r w i s e m u l t i p l e c o m p a r i s o n s of c o n t r o l s w i t h each p e r t u r b a t i o n a r e shown. T e s t s a n a l y z e d l o g - t r a n s f o r m e d c o u n t s , but means and s t a n d a r d d e v i a t i o n s shown a r e of u n t r a n s f o r m e d d a t a . One-way A n a l y s i s of V a r i a n c e : S o u r c e d f Sum of S q u a r e s Mean Square F p Between 3 2.77 0.92 5.65 0.064 W i t h i n 4 0.65 0.16 T o t a l 7 3.43 P a i r w i s e M u l t i p l e C o m p a r i s o n s : T r e a t m e n t Mean ( # / l50 1) S t d . Dev. F p C o n t r o l : 68.5: 9.2: : t y r e l l i - r e m o v a l :75.0 :46.7 0.001 0.980 :Low d e n s i t y :16.0 :4.2 12.33 0.025 : t y r e l l i / l o w d e n s i t y : 57 .0 : 21. 2 0. 27 0 . 629 100 T a b l e XIX. S t a t i s t i c a l t e s t s c o m p a r i n g mean d e n s i t i e s o f H o l o p e d i u m g i b b e r u m (numbers p e r 150 1 sample) a c r o s s t r e a t m e n t s on i n i t i a l s a m p l i n g d a t e (May 13) of 1980 e x p e r i m e n t s . S i n c e ANOVA c o m p a r i n g t r e a t m e n t s i s s i g n i f i c a n t , p a i r w i s e m u l t i p l e c o m p a r i s o n s o f c o n t r o l s w i t h e a c h p e r t u r b a t i o n a r e shown. T e s t s a n a l y z e d l o g -t r a n s f o r m e d c o u n t s , but means and s t a n d a r d d e v i a t i o n s shown a r e of u n t r a n s f o r m e d d a t a . One-way A n a l y s i s of V a r i a n c e : S o u r c e df Sum of S q u a r e s Mean Sq u a r e F p Between 3 3.83 1.28 12.14 0.018 W i t h i n 4 0 . 42 0.. 1 1 T o t a l 7 4.25 P a i r w i s e M u l t i p l e C o m p a r i s o n s : T r e a t m e n t Mean (#/l50 1) S t d . Dev, C o n t r o l : 40.5 : t y r e l l i - r e m o v a l :Low d e n s i t y : t y r e l l i / l o w d e n s i t y 47. 5 14.5 8.5 12.0 9 4 5 0.29 9.65 21 .07 0.619 0.036 0.010 101 F i g u r e 19. D e n s i t i e s of Daphn i a r o s e a and H o l o p e d i u m gibberurn i n E u n i c e Lake and i n 1980 e x p e r i m e n t s . P l o t s f o r r e p l i c a t e e n c l o s u r e s a r e s i d e by s i d e . A = E u n i c e L a k e ; B = C o n t r o l ; C = t y r e l l i - r e m o v a l ; D = Low d e n s i t y ; E = t y r e l l i / l o w d e n s i t y . NUMBER OF ANIMALS PER 150 LITRES o ro 103 E x c e s s i v e D. k e n a i l e v e l s o c c u r r e d i n t y r e l l i - r e m o v a l s b e c a u s e D. k e n a i was u s e d t o compensate f o r t h e l a r g e D. t y r e l l i b iomass removed. O n l y D. t y r e l l i d e n s i t i e s were c r u c i a l t o t h e e x p e r i m e n t , and t h e s e s a t i s f i e d r e q u i r e m e n t s . ]_.2 E n c l o s u r e D e n s i t i e s of R a re Eun i c e Lake Z o o p l a n k t o n Spec i e s As i n 1979, e n c l o s u r e d e n s i t i e s of i n c i d e n t a l E u n i c e Lake z o o p l a n k t o n were u n c o n t r o l l e d . E x c e p t f o r C h y d o r u s spp., Bosmina  l o n g i r o s t r i s , and c y c l o p o i d c o p e p o d s , a l l s p e c i e s m a i n t a i n e d low d e n s i t i e s ( < 0 . 3 / l ) i n a l l e n c l o s u r e s . C h y d o r u s a t t a i n e d h i g h e r d e n s i t i e s o n l y d u r i n g t h e l a s t two weeks o f t h e e x p e r i m e n t s . P r e s u m a b l y i n r e s p o n s e t o d e c r e a s e d g r a z i n g p r e s s u r e s , Bosmina i n c r e a s e d r e l a t i v e t o c o n t r o l s i n b o t h low d e n s i t y t r e a t m e n t s ( F i g . 2 0 ) . T h e s e i n c r e a s e s c o u l d not have c o n f o u n d e d t r e a t m e n t e f f e c t s b e c a u s e t h e y p r i m a r i l y o c c u r r e d o n l y a f t e r Diaptomus  l e p t o p u s became e x t i n c t i n a l l e n c l o s u r e s . C y c l o p o i d c o p e p o d s , m o s t l y n a u p l i a r D i a c y c l o p s t h o m a s i , were l e s s c o n s i s t e n t among t r e a t m e n t s and more c o n s i s t e n t between r e p l i c a t e s t h a n i n 1979. R e p l i c a t e s o f o n l y t h e t y r e l l i / l o w d e n s i t y t r e a t m e n t c o n t a i n e d n o t a b l y d i f f e r e n t c y c l o p o i d d e n s i t i e s ( F i g . 2 1 ) . T y r e l l i - r e m o v a l and low d e n s i t y t r e a t m e n t s c o n t a i n e d fewer c y c l o p o i d s t h a n c o n t r o l s ( T a b l e X X ) . As i n 1979, ANCOVAs c o m p a r i n g d e n s i t i e s of D. l e p t o p u s a c r o s s t r e a t m e n t s f o r e a c h s a m p l i n g d a t e y i e l d an i n s i g n i f i c a n t c y c l o p o i d c o v a r i a t e f o r most d a t e s . 1 04 F i g u r e 20. D e n s i t i e s of Bosmina l o n g i r o s t r i s i n E u n i c e Lake and i n 1980 e x p e r i m e n t s . P l o t s f o r r e p l i c a t e e n c l o s u r e s a r e s i d e by s i d e . A = E u n i c e L a k e ; B = C o n t r o l ; C = t y r e l l i - r e m o v a l ; D = Low d e n s i t y ; E = t y r e l l i / l o w d e n s i t y . NUMBER OF ANIMALS PER 150 LITRES o 106 F i g u r e 21. D e n s i t i e s of c y c l o p o i d c o p e p o d s ( n a u p l i i , c o p e p o d i t e s , and a d u l t s of D i a c y c l o p s t h o m a s i and T r o p o c y c l o p s p r a s i n u s combined) i n E u n i c e Lake and i n 1980 e x p e r i m e n t s . P l o t s f o r r e p l i c a t e e n c l o s u r e s a r e s i d e by s i d e . A = E u n i c e L a k e ; B = C o n t r o l ; C = t y r e l l i - r e m o ' v a l ; D = Low d e n s i t y ; E = t y r e l l i / l o w d e n s i t y . 108 T a b l e XX. S t a t i s t i c a l t e s t s c o m p a r i n g a c r o s s t r e a t m e n t s f o r mean maximum d e n s i t i e s of c y c l o p o i d c o p e p o d s ( n a u p l i i , c o p e p o d i t e s , and a d u l t s combined) a t t a i n e d d u r i n g 1980 e x p e r i m e n t s . V a l u e s a n a l y z e d a r e l o g - t r a n s f o r m e d maximum numbers of a n i m a l s c o l l e c t e d from e n c l o s u r e s i n a 150 1 sample r e g a r d l e s s of s a m p l i n g d a t e . S i n c e ANOVA c o m p a r i n g a l l t r e a t m e n t s i s s i g n f i c a n t , p a i r w i s e m u l t i p l e c o m p a r i s o n s of c o n t r o l s w i t h e a c h p e r t u r b a t i o n a r e shown. Means and s t a n d a r d d e v i a t i o n s shown a r e o f u n t r a n s f o r m e d d a t a . One-way A n a l y s i s of V a r i a n c e : S o u r c e . df Sum of S q u a r e s Mean Square F p Between 3 5.10 1.70 13.65 0.014 W i t h i n 4 0.50 0.12 T o t a l 7 5.60 P a i r w i s e M u l t i p l e C o m p a r i s o n s : T r e a t m e n t Mean (#/i50 1) S t d . Dev. C o n t r o l : 688.5 : t y r e l l i - r e m o v a l :Low d e n s i t y : t y r e l l i / l o w d e n s i t y 184.0 81.0 405.0 20. 5 36.8 19.8 240.4 14.10 36.88 3.14 0.020 0.004 0.151 109 J_.3 E f f e c t s of E n c l o s u r e D i f f e r e n c e s between e n c l o s u r e and E u n i c e Lake d e n s i t i e s of z o o p l a n k t o n i n 1980 p a r a l l e l e d 1979 d i f f e r e n c e s . A g a i n , H o l o p e d i u m g i b b e r u m and Polyphemus p e d i c u l u s became e x t i n c t i n e n c l o s u r e s . A g a i n , D a p h n i a r o s e a a t t a i n e d h i g h e r l e v e l s i n t h e l a k e ; C h y d o r u s and l a r v a l c h i r o n o m i d s , h i g h e r l e v e l s i n e n c l o s u r e s . In c o n t r a s t t o 1979, E u n i c e Lake d e n s i t i e s of c y c l o p o i d s a p p r o a c h e d c o n t r o l c o n c e n t r a t i o n s i n 1980. 1 1 0 2. R e s u l t s D e s c r i b i n g E f f e c t s o f E x p e r i m e n t s 2 . J_ T r e a t m e n t E f f e c t s on T o t a l D e n s i t i e s of D i a p t o m u s l e p t o p u s I n s i g n i f i c a n t t r e a t m e n t d i f f e r e n c e s i n combined d e n s i t i e s of n a u p l i i , c o p e p o d i t e s , and a d u l t s f r o m e a r l y s a m p l i n g d a t e s i n d i c a t e p r o p e r s t o c k i n g of e a c h e n c l o s u r e w i t h 19500 D. l e p t o p u s ( T a b l e X X I ) . In c o n t r o l s , a peak d e n s i t y of t h r e e t o f i v e D. l e p t o p u s per l i t r e i n mid-June p r e c e d e d a c r a s h t o n e a r e x t i n c t i o n i n e a r l y t o m i d - J u l y ( F i g . 2 2 ) . E q u i v a l e n t d e n s i t y c h a n g e s o c c u r r e d i n a l l o t h e r t r e a t m e n t s . A l l ANOVAs c o m p a r i n g t r e a t m e n t s f o r t o t a l D. l e p t o p u s on e a c h s a m p l i n g d a t e ( T a b l e XXI) or f o r maximum D. l e p t o p u s from a l l s a m p l i n g d a t e s (ANOVA: F = 0.72; p = 0.591) were i n s i g n i f i c a n t . D. l e p t o p u s a p p r o a c h e d e x t i n c t i o n s y n c h r o n o u s l y (mean p e r s i s t e n c e t i m e ± 1S.D. = 58 ± 9 d a y s ) i n a l l t r e a t m e n t s (ANOVA:.F = 0.26; p = 0.852). Peak D. l e p t o p u s d e n s i t i e s i n 1980 were a t l e a s t 5x g r e a t e r t h a n d e n s i t i e s i n 1979 low d e n s i t y and t y r e l l i - r e m o v a l t r e a t m e n t s . D. l e p t o p u s p e r s i s t e d t w i c e as l o n g i n a l l 1980 e n c l o s u r e s as i n 1979 c o n t r o l s . 111 T a b l e X X I . Summary o f s t a t i s t i c a l t e s t s c o m p a r i n g mean d e n s i t i e s of n a u p l i i , c o p e p o d i t e s , a d u l t s , and mean t o t a l d e n s i t i e s of Diaptomus l e p t o p u s a c r o s s t r e a t m e n t s f o r e a c h s a m p l i n g d a t e of 1980 e x p e r i m e n t s . V a l u e s a n a l y z e d a r e l o g - t r a n s f o r m e d numbers of a n i m a l s p e r 150 1 sample. F o r e a c h d a t e , t h e f i r s t e n t r y f o r e a c h d e v e l o p m e n t s t a g e i n d i c a t e s whether ANOVA c o m p a r i n g d e n s i t i e s of t h a t s t a g e a c r o s s t r e a t m e n t s i s s i g n i f i c a n t a t p = 0.05. E n t r i e s f o l l o w i n g s i g n i f i c a n t ANOVAs i n d i c a t e whether p a i r w i s e m u l t i p l e c o m p a r i s o n s of c o n t r o l s w i t h e a c h p e r t u r b a t i o n a r e s i g n i f i c a n t , and g i v e p r o b a b i l i t y l e v e l s i f p < 0.05. NS =' i n s i g n i f i c a n t a t p = 0.05. [1] = C o n t r o l ; [2] = t y r e l l i - r e m o v a l ; [3] = Low d e n s i t y ; [4] = t y r e l l i / l o w d e n s i t y . (+) = h i g h e r mean d e n s i t i e s of a n i m a l s i n p e r t u r b a t i o n t h a n i n c o n t r o l t r e a t m e n t s ; (-) = h i g h e r mean d e n s i t i e s i n c o n t r o l t h a n i n p e r t u r b a t i o n t r e a t m e n t s . T a b l e XXI N a u p l i i May 13 NS May 18 NS May 22 NS May 26 NS May 29 NS June 2 [ 2 ] - [ 1 ] [ 3 ] - [ 1 ] [ 4 ] - [ 1 ] NS June 6 NS June 9 [ 2 ] - [ 1 ] [ 3 ] - [ 1 ] t 4 ] - [ 1 ] NS June 12 NS June 16 NS June 19 NS June 23 [ 2 ] - [ 1 ] [ 3 ] - [ 1 ] [ 4 ] - [ 1 ] NS June 27 [ 2 ] - [ 1 ] [ 3 ] - [ 1 ] [ 4 ] - [ 1 ] NS C o p e p o d i t e s A d u l t s T o t a l NS NS NS -NS NS NS NS p<0.05 p=0.026 p=0. p = 0. NS 018 018 < + ) ( + ) ( + ) p<0.05 p=0.015 (+) p=0.027 (+) p=0.024 (+) NS NS NS p<0.05 p=0.013 (+) p=0.014 (+) p=0.026 (+) NS NS NS NS NS NS NS NS NS NS NS NS p<0.05 p=0.015 (• NS NS NS NS NS NS NS NS NS NS NS NS NS p<0.05 p=0.005 NS NS T a b l e XXI. c o n t i n u e d N a u p l i i C o pepodites A d u l t s T o t a l J u l y 3 [ 2 ] - [ 1 ] [ 3 ] - [ 1 ] C4]-[ 1 ] NS p<0. p=0. p=0. NS .05 .020 .006 ( + ) ( + ) NS NS J u l y 10 [ 2 ] - [ 1 ] [ 3 ] - [ 1 ] [ 4 ] - [ 1 ] NS p<0. p=0. p<0. NS .05 001 .001 ( + ) ( + ) NS NS J u l y 17 [ 2 ] - [ 1 ] [ 3 ] - [ 1 ] [ 4 ] - [ 1 ] NS NS p<0. p=0. p=0. p=0. .05 .008 .04 .016 ( ( ( -) -) -) NS J u l y 24 NS NS NS NS J u l y 3 1 NS NS NS NS August 7 NS NS NS NS August 21 [ 2 ] - [ 1 ] [ 3 ] - [ 1 ] [ 4 ] - [ 1 ] p<0.05 p=0.011 (+) NS NS NS NS NS September 4 NS NS NS NS 1 14 F i g u r e 22. D e n s i t i e s of Diaptomus l e p t o p u s ( n a u p l i i , c o p e p o d i t e s , and a d u l t s combined) i n E u n i c e Lake and i n 1980 e x p e r i m e n t s . P l o t s f o r r e p l i c a t e e n c l o s u r e s a r e s i d e by s i d e . A = E u n i c e L a k e ; B = C o n t r o l ; C = t y r e l l i - r e m o v a l ; D = Low d e n s i t y ; E = t y r e l l i / l o w d e n s i t y . 115 13 18222629 2 6 912 16192327 3 MOT I JUNE | 10 17 24 31 JULT | 13 18222629 2 6 912 161923 27 3 MAT | JUNE | 10 17 24 31 JULT I 1980 1 16 2.2 T r e a t m e n t E f f e c t s on D e n s i t i e s of Diaptomus l e p t o p u s Eggs, N a u p l i i , C o p e p o d i t e s , and A d u l t s T a b l e XXI summarizes ANOVAs c o m p a r i n g n a u p l i a r , c o p e p o d i t e , and a d u l t d e n s i t i e s a c r o s s t r e a t m e n t s f o r e a c h s a m p l i n g d a t e . On e a r l y d a t e s , a l l t r e a t m e n t s c o n t a i n e d c o m p a r a b l e d e n s i t i e s of D. l e p t o p u s i n e a c h d e v e l o p m e n t a l s t a g e . On l a t e r d a t e s , no n o t a b l e t r e a t m e n t d i f f e r e n c e s o c c u r r e d f o r n a u p l i i or a d u l t s . On f i v e d a t e s , c o p e p o d i t e s were more dense i n p e r t u r b a t i o n s t h a n i n c o n t r o l s . T hese d i f f e r e n c e s p r o v i d e l i t t l e e v i d e n c e f o r t r e a t m e n t e f f e c t s b e c a u s e sample s i z e s f o r c o p e p o d i t e s were s m a l l ( F i g . 23) and b e c a u s e , u n l i k e n a u p l i i and a d u l t s , D. l e p t o p u s c o p e p o d i t e s were d i f f i c u l t t o d i s t i n g u i s h f r o m c o r r e s p o n d i n g s t a g e s o f D. t y r e l l i . R e l a t i v e t o c o n t r o l s , numbers of eggs per f e m a l e i n c r e a s e d i n s i g n i f i c a n t l y i n t h e two low d e n s i t y t r e a t m e n t s ( T a b l e X X I I ) . In c o n t r a s t t o 1979, 1980 t r e a t m e n t s had no marked e f f e c t s on D. l e p t o p u s of any s t a g e . They n e i t h e r s u p p o r t t h e D. t y r e l l i c o m p e t i t i o n e f f e c t s from 1979 nor d i s t i n g u i s h them from d i f f u s e c o m p e t i t i o n e f f e c t s . 2.3 T r e a t m e n t Ef f e c t s on A d u l t S i z e of Diaptomus l e p t o p u s As i n 1979, l e n g t h s of a d u l t D. l e p t o p u s d i d not d i f f e r among t r e a t m e n t s (ANOVA: p < 0.05). A d u l t c a l a n o i d s and D a p h n i a r o s e a were s m a l l e r i n 1980 t h a n i n 1979 ( T a b l e X X I I I ) . 1 1 7 F i g u r e 23. D e n s i t i e s of n a u p l i i and of c o p e p o d i t e s p l u s a d u l t s o f D i a p t o m u s l e p t o p u s i n E u n i c e Lake and i n 1980 e x p e r i m e n t s . P l o t s f o r r e p l i c a t e e n c l o s u r e s a r e s i d e by s i d e . A = E u n i c e L a k e ; B = C o n t r o l ; C = t y r e l l i -r e m o v a l ; D = Low d e n s i t y ; E = t y r e l l i / l o w d e n s i t y . NUMBER OF ANIMALS PER 150 LITRES 1 19 T a b l e X X I I . A n a l y s i s of v a r i a n c e c o m p a r i n g a c r o s s t r e a t m e n t s f o r mean numbers of D i a p t o m u s l e p t o p u s eggs p r o d u c e d p e r f e m a l e d u r i n g 1980 e x p e r i m e n t s . V a l u e s a n a l y z e d a r e l o g - t r a n s f o r m e d t o t a l numbers of l o o s e and a t t a c h e d eggs d i v i d e d by t o t a l numbers of a d u l t f e m a l e s c o l l e c t e d from e n c l o s u r e s i n 150 1 s a m p l e s from a l l s a m p l i n g d a t e s c o m b i n e d . Means and s t a n d a r d d e v i a t i o n s shown a r e of u n t r a n s f o r m e d d a t a . One-way A n a l y s i s of V a r i a n c e : S o u r c e df Sum of S q u a r e s Mean Squ a r e F p Between 3 0.32 0.11 0.81 0.511 W i t h i n 4 0.46 0.12 T o t a l 7 0.78 D e s c r i p t i v e S t a t i s t i c s : T r e a t m e n t Mean (#/ f e m a l e ) S t d . Dev, C o n t r o l 1.25 0.49 t y r e l l i - r e m o v a l 1.65 0.64 Low d e n s i t y 3.00 1.98 t y r e l l i / l o w d e n s i t y 2.20 0.85 120 T a b l e X X I I I . L e n g t h s (mm) of a d u l t d i a p t o m i d c o p e p o d s and of D a p h n i a r o s e a i n 1980 e x p e r i m e n t s . Means a r e b a s e d on a l l a n i m a l s measured, r e g a r d l e s s of t r e a t m e n t o r s a m p l i n g d a t e . S p e c i e s N Mean S t d . Dev. Diaptomus k e n a i 466 2 . 1'4 0 . 1 6 D i a p t o m u s ' l e p t o p u s 353 1 .53 0 .07 Diaptomus t y r e l l i 592 1 . 1 0 0 .07 D a p h n i a r o s e a 718 1 .04 0 .30 121 2.4 S e a s o n a l C y c l e s , V e r t i c a l D i s t r i b u t i o n and P h y t o p l a n k t o n  Biomass S e a s o n a l C y c l e s A few o v e r w i n t e r i n g n a u p l i i and e a r l y c o p e p o d i t e s o f D. k e n a i p e r s i s t e d p a s t t h e b e g i n n i n g of 1980 e x p e r i m e n t s . A l a t e r s t a r t t o e x p e r i m e n t s and h i g h e r w a t e r t e m p e r a t u r e s e x c l u d e d t h e s e immature s t a g e s f r o m 1979 e x p e r i m e n t s . In b o t h y e a r s , a l l d e v e l o p m e n t s t a g e s of D. t y r e l l i and D. l e p t o p u s o c c u r r e d , b ut a g r e a t e r p r o p o r t i o n of D. l e p t o p u s were n a u p l i i i n 1980. As i n 1979, b o t h j u v e n i l e and a d u l t D a p h n i a r o s e a were p r e s e n t t h r o u g h o u t 1980 e x p e r i m e n t s . V e r t i c a l D i s t r i b u t i o n s D. l e p t o p u s was a l m o s t e x t i n c t when v e r t i c a l l y s t r a t i f i e d s a m p l i n g o c c u r r e d i n J u l y , 1980. The few r e m a i n i n g i n d i v i d u a l s c o n c e n t r a t e d , as i n 1979, i n t h e upper 2 o r 4 m of t h e water column. V e r t i c a l d i s t r i b u t i o n s o f D. t y r e l l i , D. k e n a i , and D a p h n i a r o s e a d i d n o t d i f f e r w i t h d e v e l o p m e n t a l s t a g e o r e x p e r i m e n t a l t r e a t m e n t . D. t y r e l l i o c c u r r e d i n t h e upper 2 m; D. k e n a i , a t a l l d e p t h s ; and D. r o s e a , i n t h e upper 4 m ( F i g . 2 4 ) . R e l a t i v e t o J u l y 1979, a l l t h r e e s p e c i e s were 1 22 F i g u r e 24. D i u r n a l v e r t i c a l d i s t r i b u t i o n s o f D i aptomus t y r e l l i , D i a p t o m u s k e n a i , and D a p h n i a r o s e a i n 1980 e x p e r i m e n t s d u r i n g J u l y . O b s e r v a t i o n s from a l l t r e a t m e n t s a r e combined. N - 2 2 8 0 D D. kenoi N - 2 1 9 Dgphnia N = I I 3 9 - i — 5 0 0 100 % OCCURRENCE 1 24 d i s p l a c e d upward. T h e s e h i g h e r v e r t i c a l d i s t r i b u t i o n s i n 1980 c o r r e s p o n d e d t o c o o l e r t e m p e r a t u r e s t h e n t h a n i n 1979 ( F i g . 2 5 ) . They c a u s e d i n c r e a s e d s p a t i a l o v e r l a p between D. k e n a i and o t h e r d i a p t o m i d s . P h y t o p l a n k t o n Biomass In 1980, few c l e a r d i f f e r e n c e s o c c u r r e d among t r e a t m e n t s i n s t a n d i n g s t o c k s of l a r g e and s m a l l p h y t o p l a n k t o n ( F i g . 2 6 ) . However,' a f t e r t h e f i r s t 3-4 weeks of t h e e x p e r i m e n t , l a r g e c e l l s c o n t r i b u t e d more b i o m a s s i n c o n t r o l s t h a n i n t y r e l l i -r e m o v a l s , where d e n s i t i e s of l a r g e D. k e n a i were h i g h . Biomass of l a r g e p h y t o p l a n k t o n - p e a k e d d u r i n g J u n e - J u l y i n . 1980 e x p e r i m e n t s , and d u r i n g S e p t e m b e r - O c t o b e r i n 1979 e x p e r i m e n t s . S i m i l a r p h y t o p l a n k t o n g e n e r a o c c u r r e d i n b o t h y e a r s . 1 25 F i g u r e 25. T e m p e r a t u r e p r o f i l e f o r E u n i c e Lake d u r i n g 1980 e x p e r i m e n t s . TEMPERATURE PROFILE (OCJ - 1980 i g u r e 26. P h y t o p l a n k t o n s t a n d i n g s t o c k s i n E u n i c e L a k e and i n 1980 e x p e r i m e n t s . P l o t s f o r r e p l i c a t e e n c l o s u r e s a r e s i d e by s i d e . F o r e a c h e n c l o s u r e , u p p e r p l o t shows t o t a l b i o m a s s ; lower p l o t shows p e r c e n t s i z e c o m p o s i t i o n o f t o t a l b i o m a s s . A = E u n i c e L a k e ; B = C o n t r o l ; C = t y r e l l i - r e m o v a l ; D = Low d e n s i t y ; E = t y r e l l i / l o w d e n s i t y . 29 9 19 3 10 24 • 21 18 29 9 19 3 24 21 HAT | JUNE | JULT | AUG. MAT | JUNE | JULT | AUG. 1980 1 30 3_. Summary o f 1980 R e s u l t s 1. A t t h e s t a r t of t h e e x p e r i m e n t , e n c l o s u r e s c o n t a i n e d D i a p t o m u s t y r e l l i i n d e n s i t i e s a p p r o p r i a t e t o t h e t r e a t m e n t s . 2. D e v i a t i o n s from e x p e r i m e n t a l d e s i g n i n d e n s i t i e s of Daphn i a r o s e a and Diaptomus kena i r e f l e c t e d r e p l a c e m e n t of removed D. t y r e l l i b i o m a s s . 3. P e r f o r m a n c e s of Diaptomus l e p t o p u s n a u p l i i , c o p e p o d i t e s , and a d u l t s d i d not d i f f e r among t r e a t m e n t s . T o t a l D. l e p t o p u s d e n s i t i e s p e a k e d and d e c l i n e d s i m u l t a n e o u s l y i n a l l e n c l o s u r e s . T h e s e r e s u l t s n e i t h e r v e r i f i e d e f f e c t s of 1979 t y r e l l i - r e m o v a l e n c l o s u r e s nor s e p a r a t e d them from e f f e c t s o f low d e n s i t y e n c l o s u r e s from t h a t y e a r . 4. D. l e p t o p u s r e a c h e d h i g h e r maximum d e n s i t i e s and p e r s i s t e d l o n g e r i n e n c l o s u r e s i n 1980 t h a n i n 1979. 5. A g r e a t e r p r o p o r t i o n of e n c l o s e d D. l e p t o p u s were n a u p l i i i n 1980 t h a n i n 1979. D. k e n a i n a u p l i i and e a r l y c o p e p o d i t e s o c c u r r e d i n e n c l o s u r e s i n 1980 o n l y . 6. R e l a t i v e t o 1979, water t e m p e r a t u r e s were c o o l e r i n 1980. C o r r e s p o n d i n g l y , z o o p l a n k t o n s p e c i e s o c c u r r e d h i g h e r i n 131 t h e water column and were l e s s v e r t i c a l l y s e g r e g a t e d . 7. The o n l y t r e a t m e n t e f f e c t on p h y t o p l a n k t o n s t a n d i n g s t o c k s i n 1980 was an i n c r e a s e f o r l a r g e c e l l s i n t y r e l l i - r e m o v a l e n c l o s u r e s . Peak b i o m a s s o c c u r r e d e a r l i e r i n 1980 t h a n i n 1979. 1 32 DISCUSSION E x a m i n i n g why r a r e s p e c i e s a r e r a r e can p r o v i d e v a l u a b l e i n f o r m a t i o n a b o u t o r g a n i z a t i o n of e c o l o g i c a l c o m m u n i t i e s ( R o b i n s o n and V a l e n t i n e 1979). In p a r t i c u l a r , t h o s e s p e c i e s h a v i n g c o n t i n u a l m i g r a t o r y a c c e s s t o t h e c o m m u n i t i e s where t h e y a r e r a r e d e s e r v e i n v e s t i g a t i o n . D i a p t o m u s l e p t o p u s i n E u n i c e Lake i s one of t h e s e s p e c i e s . A l t h o u g h i t i s abundant i n an u p s t r e a m l a k e , i t d o e s not c o l o n i z e E u n i c e L a k e . T h i s e x p e r i m e n t a l s t u d y has t e s t e d t h e h y p o t h e s i s t h a t c o m p e t i t i o n from r e s i d e n t z o o p l a n k t o n s p e c i e s p r e v e n t s d e n s i t i e s o f i m m i g r a n t D. l e p t o p u s from i n c r e a s i n g i n E u n i c e L a k e . S e p a r a t i o n of Diaptomus t y r e l l i C o m p e t i t i o n from P i f f u s e C o m p e t i t i o n H i g h c o n c e n t r a t i o n s r e l a t i v e t o c o n t r o l s o f D. l e p t o p u s n a u p l i i i n 1979 i n b o t h t y r e l l i - r e m o v a l and low d e n s i t y t r e a t m e n t s ( F i g . 8) c o n f o u n d e d c o m p e t i t i o n from D. t y r e l l i w i t h d i f f u s e c o m p e t i t i o n from s e v e r a l E u n i c e Lake s p e c i e s combined. E x p e r i m e n t s i n 1980 a l s o f a i l e d t o d i s t i n g u i s h t h e s e . However, t h e e v i d e n c e o u t l i n e d below s u p p o r t s D. t y r e l l i c o m p e t i t i o n . (1) In 1979, D. l e p t o p u s d e n s i t i e s were s i m i l a r i n t y r e l l i -r e m o v a l and low d e n s i t y e n c l o s u r e s ( T a b l e I X ) , d e s p i t e r e m o v a l of s p e c i e s b e s i d e s D. t y r e l l i f r o m t h e l a t t e r e n c l o s u r e s . 1 33 (2) R e l a t i v e t o c o n t r o l s , D. l e p t o p u s d e n s i t i e s i n c r e a s e d i n t y r e l l i - r e m o v a l s , b u t n o t i n D a p h n i a - and k_ena_i-removals ( T a b l e I X ) . (3) D. l e p t o p u s c o e x i s t s w i t h Daphn i a r o s e a and Diaptomus  k e n a i i n G w e n d o l i n e L a k e , where D. t y r e l l i i s l a c k i n g ( T a b l e X X I V ) . (4) Among UBC R e s e a r c h F o r e s t l a k e s , D. l e p t o p u s c o - o c c u r s a t d e t e c t a b l e l e v e l s w i t h D. t y r e l l i o n l y i n K a t h e r i n e L a k e , where maximum D. t y r e l l i d e n s i t i e s a r e a mere 1.3% of maximum d e n s i t i e s i n E u n i c e L a k e ( f r o m d a t a i n T a b l e X X I V ) . G r e a t e r s i m i l a r i t y i n s i z e between D. l e p t o p u s and D. t y r e l l i i n E u n i c e t h a n i n K a t h e r i n e L a k e ( T a b l e XXIV) i n c r e a s e s p o t e n t i a l i n E u n i c e f o r c o m p e t i t i o n f o r s i m i l a r l y - s i z e d f o o d s ( H u t c h i n s o n 1967; B u r n s 1968; P o u l e t 1977). (5) H u t c h i n s o n (1967) s u g g e s t e d t h a t d i e t a r y d i f f e r e n c e s between d i a p t o m i d s d i f f e r i n g i n l e n g t h by a t l e a s t 35% a r e s u f f i c i e n t t o e n s u r e c o e x i s t e n c e . In E u n i c e L a k e , D. k e n a i i s 84% and 150% l a r g e r t h a n D. l e p t o p u s and D. t y r e l l i , r e s p e c t i v e l y ( T a b l e X X I V ) . D. l e p t o p u s and D. t y r e l l i d i f f e r by a m a r g i n a l 36%. Hammer and Sawchyn (1968) s u b m i t t e d t h a t c o e x i s t i n g d i a p t o m i d s must d i f f e r i n l e n g t h by more t h a n 0.5 mm. D. l e p t o p u s and D. t y r e l l i from E u n i c e L a k e ' d i f f e r by o n l y 0.41 mm ( T a b l e X X I V ) . Table XXIV. Maximum lengths and copepods and Daphni a rosea i n Eunice (EU) Lakes, 1963-1974. maximum summer densities of calanoid Katherine (KA), Gwendoline (GW), and From Northcote and Clarotto (1975) Maximum length (mm) Maximum density (#/100 1) KA GW EU KA GW EU Diaptomus kenai 2 . 97 2 . 70 2 .87 8.9 10 70 Diaptomus leptopus 1 . .92 1 . .68 1 . 56 2 . 5 13 0.5 Diaptomus t y r e l l i 0. .99 -- 1 . 15 10 -- 800 Daphnia rosea 2 . 25 2 .61 2 .50 12 95 233 CO 135 (6) S a n d e r c o c k (1967) p r o p o s e d t h a t , t o c o e x i s t , d i a p t o m i d s must s e g r e g a t e by a t l e a s t two o f d i e t , s e a s o n a l o c c u r r e n c e , and v e r t i c a l d i s t r i b u t i o n . In 1979 i n E u n i c e L a k e , e x t e n s i v e s e a s o n a l s y n c h r o n y ( F i g s . 9 and 10) and v e r t i c a l o v e r l a p ( F i g . 12) h i n d e r e d c o e x i s t e n c e between D. l e p t o p u s and D. t y r e l l i . D. k e n a i b r e d e a r l i e r ( F i g . 11) and d i s t r i b u t e d d e e p e r ( F i g . 12) t h a n e i t h e r of t h e s e two s p e c i e s , and c o e x i s t e d w i t h b o t h . D. l e p t o p u s and D a p h n i a  r o s e a s e g r e g a t e d v e r t i c a l l y ( F i g . 1 2 ) . They p r o b a b l y a l s o p a r t i t i o n e d f o o d r e s o u r c e s b e c a u s e c a l a n o i d s g e n e r a l l y consume c o a r s e r p a r t i c l e s t h a n c l a d o c e r a n s ( H u t c h i n s o n 1967). A l m o s t a l l e v i d e n c e from 1979 i n d i c t s . D. t y r e l l i c o m p e t i t i o n f o r p r e v e n t i n g D. l e p t o p u s from i n c r e a s i n g i n E u n i c e L a k e . O n l y i n c r e a s e d D. l e p t o p u s eggs p e r f e m a l e i n f o o d - r i c h low d e n s i t y t r e a t m e n t s ( T a b l e XI) i m p l i c a t e s d i f f u s e c o m p e t i t i o n . However, d i f f u s e c o m p e t i t i o n c a n n o t e x p l a i n D. l e p t o p u s r a r i t y i n E u n i c e Lake b e c a u s e e n h a n c e d r e p r o d u c t i o n f a i l e d t o g e n e r a t e h i g h e r D. l e p t o p u s l e v e l s i n low d e n s i t y e n c l o s u r e s t h a n i n t y r e l l i - r e m o v a l s ( T a b l e I X ) . L y n c h (1978) f o u n d a s i m i l a r s i t u a t i o n among c l a d o c e r a n s . In t h e p r e s e n c e o f C e r i o d a p h n i a and Bosmina, e n h a n c e d D a p h n i a p u l e x r e p r o d u c t i o n c a u s e d no p o p u l a t i o n i n c r e a s e s b e c a u s e o f r e d u c e d j u v e n i l e s u r v i v a l . By g r a z i n g t h e s m a l l f o o d s of j u v e n i l e D a p h n i a , C e r i o d a p h n i a and Bosmina enhanced l a r g e p h y t o p l a n k t o n f o r r e p r o d u c t i v e a d u l t Daphn i a . L y n c h ' s r e s u l t s u g g e s t s an e x p l a n a t i o n f o r why D. l e p t o p u s c o n c e n t r a t i o n s were s i m i l a r ' i n 136 t y r e l l i - r e m o v a l and low d e n s i t y t r e a t m e n t s when r e p r o d u c t i v e p o t e n t i a l s were n o t : A l t e r a t i o n i n r e l a t i v e a b u ndances of f o o d r e s o u r c e s due t o g r a z i n g by D. t y r e l l i may a f f e c t D. l e p t o p u s more a d v e r s e l y t h a n d e p r e s s i o n of a b s o l u t e r e s o u r c e a b undances due t o g r a z i n g by a l l E u n i c e Lake z o o p l a n k t o n s p e c i e s combined. V u l n e r a b i l i t y of D i aptomus l e p t o p u s N a u p l i i t o C o m p e t i t i o n In 1979 e x p e r i m e n t s , c o m p e t i t i o n from D. t y r e l l i a d v e r s e l y a f f e c t e d p r i m a r i l y n a u p l i a r s t a g e s of D. l e p t o p u s ( T a b l e I X ) . S t a g e - r e l a t e d e n e r g e t i c d i f f e r e n c e s may e x p l a i n t h i s , r e s u l t . I f , a s G r e e n (1975) f o u n d f o r C a l a m o e c i a l u c a s i , b a l a n c e between a s s i m i l a t e d f o o d i n t a k e and r e s p i r a t o r y o u t p u t i s p o s i t i v e f o r a l l but n a u p l i a r D. l e p t o p u s , t h e n n a u p l i i s h o u l d be p a r t i c u l a r l y v u l n e r a b l e t o f o o d s h o r t a g e s . B o t h l a t e n a u p l i i , w h i c h f i l t e r - f e e d ( M a r s h a l l and O r r 1956; P a f f e n h o f e r 1971), and e a r l y n a u p l i i , w hich c a r r y s t o r e d f o o d i n amounts d e p e n d e n t on n u t r i t i v e c o n d i t i o n s of r e p r o d u c i n g f e m a l e s ( C o o l e y e t a l . 1978; Cooney and G e h r s 1980), would be a f f e c t e d . The s t r o n g e r p o s i t i v e c o r r e l a t i o n between m e t a b o l i c r a t e and body w e i g h t f o r n a u p l i i t h a n f o r c o p e p o d i t e s and a d u l t s (Epp and L e w i s 1979, 1980) f u r t h e r s u p p o r t s n a u p l i a r s u s c e p t i b i l i t y . M e t a b o l i s m i n c r e a s e s a b r u p t l y d u r i n g t h e r a d i c a l m o r p h o l o g i c a l and b e h a v i o u r a l t r a n s i t i o n from N6 t o CI ( G e h r s and R o b e r t s o n 1975; Epp and L e w i s 1979, 1980). H i g h m o r t a l i t y r e l a t e d t o t h e s e i n c r e a s e s may e x p l a i n low d e n s i t i e s of c o p e p o d i t e and a d u l t D. l e p t o p u s i n t y r e l l i - r e m o v a l and low d e n s i t y e n c l o s u r e s d e s p i t e h i g h n a u p l i a r 1 37 c o n c e n t r a t i o n s . 1979 e x p e r i m e n t s were u n a b l e t o d e t e r m i n e w h i c h s t a g e ( s ) of D. t y r e l l i o u t c o m p e t e d D. l e p t o p u s n a u p l i i . U n e q u i v o c a l d e t e r m i n a t i o n would r e q u i r e e x p o s u r e of D. l e p t o p u s t o e a c h D. t y r e l l i s t a g e s e p a r a t e l y . P a r a l l e l s between n a u p l i i of b o t h s p e c i e s i n s i z e , m o r p h o l o g y , and b e h a v i o u r (Epp and L e w i s 1979) and i n v e r t i c a l d i s t r i b u t i o n ( F i g . 12) i m p l i c a t e immature D. t y r e l l i as c o m p e t i t o r s . A l t e r n a t i v e l y , c o p e p o d i t e s and a d u l t s of s m a l l D. t y r e l l i may have s t a r v e d n a u p l i i o f l a r g e r D. l e p t o p u s by u s i n g - s m a l l f o o d p a r t i c l e s more e f f i c i e n t l y . S m a l l c l a d o c e r a n s ( A l o n e l l a , C e r i o d a p h n i a ) may impose s u c h c o m p e t i t i v e b o t t l e n e c k s on immature s t a g e s of l a r g e r h e r b i v o r o u s c r u s t a c e a n s ( D i a p t o m u s , Daphn i a ) ( N e i l l 1975a; L y n c h 1978). R e l e v a n c e of E x p e r i m e n t a l R e s u l t s t o t h e S i z e - E f f i c i e n c y H y p o t h e s i s The r e s u l t from 1979 t h a t s m a l l D. t y r e l l i o u t c o m p e t e d l a r g e r D. l e p t o p u s r e v e r s e s p r e d i c t i o n s of t h e s i z e - e f f i c i e n c y h y p o t h e s i s ( B r o o k s and Dodson 1965). In s e v e r a l o t h e r z o o p l a n k t o n c o m m u n i t i e s , s m a l l h e r b i v o r e s a r e s u p e r i o r c o m p e t i t o r s (Dodson 1974; Bogdan and McNaught 1975; N e i l l 1975a and b; K e r f o o t 1977; L y n c h 1977b, 1978, 1979, 1980). L y n c h (1977b) r e c o g n i z e d t h r e e r e l e v a n t c r i t i c i s m s of t h e h y p o t h e s i s . (1) The s i z e - e f f i c i e n c y h y p o t h e s i s f a l s e l y assumes c o m p e t i t i v e i n t e r a c t i o n s among a d u l t s o n l y . As a l r e a d y 138 d i s c u s s e d , a d u l t s of s m a l l z o o p l a n k t o n s p e c i e s c a n c r e a t e c o m p e t i t i v e b o t t l e n e c k s f o r j u v e n i l e s of l a r g e s p e c i e s ( N e i l l 1975a). I f j u v e n i l e m o r t a l i t y i s s u f f i c i e n t , l a r g e a d u l t s can c o e x i s t w i t h s m a l l s p e c i e s even when f o o d i s s c a r c e . H i g h s u r v i v a l of D. l e p t o p u s n a u p l i i i n t y r e l l i -r e m o v a l s and l a c k of t r e a t m e n t e f f e c t s on a d u l t s ( T a b l e X I I ) s u g g e s t t h a t i n 1979 D. t y r e l l i c r e a t e d a c o m p e t i t i v e b o t t l e n e c k f o r D. l e p t o p u s . L a r g e c o p e p o d s t h a t r e p r o d u c e b e f o r e s m a l l ones a v o i d b o t t l e n e c k s by c o - o c c u r r i n g as l a t e c o p e p o d i t e s and a d u l t s w i t h younger s t a g e s of t h e s m a l l e r s p e c i e s ( W i l l i a m s 1976). In E u n i c e L a k e , e a r l y - b r e e d i n g D. k e n a i ( F i g . 12) c o e x i s t s w i t h b o t h D. l e p t o p u s and D. t y r e l l i (2) The s i z e - e f f i c i e n c y h y p o t h e s i s f a l s e l y assumes s i m i l a r r e l a t i o n s h i p s between p h y s i o l o g i c a l r a t e s and body s i z e f o r a l l s p e c i e s . S p e c i e s d i f f e r e n c e s o c c u r a t l e a s t f o r r e s p i r a t i o n r a t e ( G a u l d and Raymont 1953; C o m i t a 1968; G r e e n 1975; Epp and L e w i s 1979). A s s i m i l a t i o n r a t e p r o b a b l y depends more on f o o d s o u r c e t h a n on z o o p l a n k t o n s i z e ( S c h i n d l e r 1971). T h e s e and o t h e r r a t e s a r e p o o r l y s t u d i e d as f u n c t i o n s of body s i z e ( H a l l e t a l . 1976). In a community of m a r i n e c o p e p o d s , P o u l e t (1978) f o u n d t h a t n e t e n e r g y i n t a k e p e r u n i t body w e i g h t was g r e a t e r f o r s m a l l t h a n f o r l a r g e s p e c i e s . P e r h a p s a g r e a t e r e n e r g e t i c e f f i c i e n c y o f s m a l l D. t y r e l l i e x p l a i n s i t s c o m p e t i t i v e s u p e r i o r i t y o v e r D. l e p t o p u s . 1 39 (3) The s i z e - e f f i c i e n c y h y p o t h e s i s f a l s e l y assumes e q u a l a d a p t a t i o n of a l l s p e c i e s t o p r e v a i l i n g e n v i r o n m e n t a l c o n d i t i o n s . S m a l l D a p h n i a p u l e x f o r a g e more e f f i c i e n t l y t h a n l a r g e i n d i v i d u a l s a t h i g h c o n c e n t r a t i o n s of s m a l l f o o d s and a t h i g h t e m p e r a t u r e s ( L y n c h 1977b). I t s more o l i g o t r o p h i c d i s t r i b u t i o n ( W i l s o n 1959) s u g g e s t s t h a t D. t y r e l l i i s b e t t e r a d a p t e d t h a n D. l e p t o p u s t o t h e low f o o d l e v e l s i n E u n i c e L a k e . R e l a t i o n s h i p Between T e m p e r a t u r e and I n t e n s i t y of C o m p e t i t i o n • In 1979 e x p e r i m e n t s , D. t y r e l l i o u t c o m p e t e d D. l e p t o p u s n a u p l i i , y e t 1980 .experiments p r o d u c e d no . e v i d e n c e of c o m p e t i t i o n between t h e s e s p e c i e s ( T a b l e X X I ) . T e m p e r a t u r e d i f f e r e n c e s between t h e two y e a r s may r e c o n c i l e t h e s e c o n t r a r y r e s u l t s ( F i g s . 15 and 2 5 ) . C o m p e t i t i o n f o r l i m i t e d f o o d c o u l d have been s e v e r e i n warm 1979 and u n d e t e c t a b l e i n c o o l 1980 b e c a u s e c o p e p o d m e t a b o l i c demands, and t h e r e f o r e f o o d r e q u i r e m e n t s , i n c r e a s e w i t h t e m p e r a t u r e ( F i g . 2 7 ) . T e m p e r a t u r e -d e p e n d e n t i n c r e a s e s i n f o o d i n t a k e p o t e n t i a l l y o f f s e t i n c r e a s e s i n m e t a b o l i s m , but a t t h e low f o o d c o n c e n t r a t i o n s i n UBC R e s e a r c h F o r e s t l a k e s , z o o p l a n k t o n f e e d i n g r a t e s a r e p r o b a b l y i n d e p e n d e n t of t e m p e r a t u r e (Buckingham 1978). O c c u r r e n c e of c o m p e t i t i o n between D. l e p t o p u s and D. t y r e l l i p r i m a r i l y a t warm t e m p e r a t u r e s f i t s w i t h Wiens' (1977) p r o p o s a l t h a t - v a r i a t i o n i n e n v i r o n m e n t a l c o n d i t i o n s r e g u l a t e s i n t e n s i t y of c o m p e t i t i o n by d e t e r m i n i n g whether 1 40 F i g u r e 27. D i a p t o m i d r e s p i r a t i o n r a t e s as a f u n c t i o n of t e m p e r a t u r e . B e c a use r a t e s f o r D iaptomus t y r e l l i u n a v a i l a b l e , t h o s e f o r a s i m i l a r spec i e s r D i a p t o m u s  o r e g o n e n s i s ) a r e shown. From C o m i t a (19681 OXYGEN UPTAKE (ul'Vhr) 0 0 O O Q Q O O o p b b b b — — — ro ho ro 0 0 1 o> <o ro on 03 — ->i -i 1 1 1 1 1 1 1 1 r • i i i i i 1 LH 1 42 r e s o u r c e s a r e e f f e c t i v e l y l i m i t e d . S u p p o r t i n g e v i d e n c e e x i s t s f o r r a i n f a l l and t e m p e r a t u r e v a r i a t i o n s . Amount of r a i n f a l l c o r r e l a t e s w i t h f o o d abundance i n t r o p i c a l f i s h ( Z a r e t and Rand 1971) and d e s e r t r o d e n t c o m m u n i t i e s ( S c h r o d e r and R o s e n z w e i g 1975), and w i t h f o o d a v a i l a b i l i t y i n t e r r e s t r i a l s a l a m a n d e r c o m m u n i t i e s ( J a e g e r 1972). E x p e r i m e n t a l r e m o v a l o f one i n s e c t i v o r o u s l i z a r d s p e c i e s e f f e c t e d i m p r o v e d p e r f o r m a n c e i n a n o t h e r d u r i n g a r t h r o p o d - p o o r d r y y e a r s , and n o t d u r i n g f o o d -r i c h wet y e a r s (Dunham 1980). O n l y a t c o o l t e m p e r a t u r e s f a v o u r i n g i t s f e e d i n g e f f i c i e n c y c an D a p h n i a p u l e x o utcompete C e r i o d a p h n i a r e t i c u l a t a ( L y n c h 1978). P e r c i d s , c e n t r a r c h i d s , and s a l m o n i d s c o e x i s t o n l y i n w i n t e r , when m e t a b o l i c c o s t s c o r r e l a t e d w i t h f o o d demands a r e low (MacLean and Magnuson 1977). C o r r e s p o n d i n g l y , v e r t i c a l o v e r l a p between D. t y r e l l i and D. k e n a i i n E u n i c e Lake i n c r e a s e d i n c o o l 1980 ( F i g . 2 4 ) . In t h e s e t y p i c a l s y s t e m s , c o m p e t i t i o n i s d e t e c t a b l e o n l y when s t r e s s f u l e n v i r o n m e n t a l c o n d i t i o n s i n c r e a s e demands f o r r e s o u r c e s a n d / o r d e c r e a s e r e s o u r c e c o n c e n t r a t i o n s (Wiens 1977). I f , as e x p e r i m e n t a l e v i d e n c e s u g g e s t s , h i g h t e m p e r a t u r e s i n t e n s i f y c o m p e t i t i o n between D. l e p t o p u s and D. t y r e l l i , t h e n D. l e p t o p u s d e n s i t i e s i n E u n i c e Lake s h o u l d be r e l a t i v e l y h i g h o n l y d u r i n g c o o l p e r i o d s . Warm t e m p e r a t u r e s s h o u l d o c c u r f r e q u e n t l y enough f o r D. t y r e l l i t o c h e c k D. l e p t o p u s a d v a n c e s . The p r e s e n c e of d e t e c t a b l e D. l e p t o p u s l e v e l s i n E u n i c e Lake d u r i n g o n l y two p e r i o d s - a f t e r t e m p e r a t u r e s d e c r e a s e d i n f a l l 1979 ( F i g . 7A) and b e f o r e t h e y i n c r e a s e d i n s p r i n g 1980 ( F i g . 22A) - u p h o l d s t h e s e p r e d i c t i o n s . U n f o r t u n a t e l y , b e s i d e s 1 43 low t e m p e r a t u r e s ( F i g s . 15 and 2 5 ) , r e l a t i v e l y h i g h p h y t o p l a n k t o n b i o m a s s ( F i g s . 16A and 26A) and p o t e n t i a l l y h i g h D. l e p t o p u s e m i g r a t i o n f r o m G w e n d o l i n e due t o heavy r a i n f a l l a l s o o c c u r r e d d u r i n g t h e s e two p e r i o d s . F o r D. l e p t o p u s i n an a c i d i c bog l a k e , l a r v a l s u r v i v a l was h i g h e s t a t low t e m p e r a t u r e s (Winner 1970). One i m p o r t a n t r e s u l t a p p a r e n t l y c o n t r a d i c t s t h e h y p o t h e s i s t h a t c o m p e t i t i o n between D. l e p t o p u s and D. t y r e l l i i s t e m p e r a t u r e - d e p e n d e n t . L a t e i n 1980 e x p e r i m e n t s , a s t e m p e r a t u r e s i n c r e a s e d t o 1979 l e v e l s , D. l e p t o p u s d e c r e a s e d t o e x t i n c t i o n s i m u l t a n e o u s l y i n a l l t r e a t m e n t s ( F i g . 2 2 ) , r e g a r d l e s s of D. t y r e l l i c o n c e n t r a t i o n . S t r o n g e r c o m p e t i t i o n from c o n s p e c i f i c s t h a n from D. t y r e l l i may have been r e s p o n s i b l e . B e f o r e t e m p e r a t u r e s i n c r e a s e d , D. l e p t o p u s i n a l l 1980 e n c l o s u r e s had r e a c h e d e x t r e m e l y h i g h d e n s i t i e s . T h e s e e x c e e d e d by 5x d e n s i t i e s i n 1979 t y r e l l i - r e m o v a l s ( F i g s . 7 and 2 2 ) . In a d d i t i o n t o g r e a t e r i n i t i a l s t o c k i n g d e n s i t i e s , f a v o u r a b l e f o o d and t e m p e r a t u r e c o n d i t i o n s e a r l y i n 1980 c o n t r i b u t e d t o h i g h D. l e p t o p u s c o n c e n t r a t i o n s . P r o b a b l y r e f l e c t i n g e x p e r i m e n t a l f e r t i l i z a t i o n o f G w e n d o l i n e Lake from May t o September 1979 (Hay 1981), t h e p h y t o p l a n k t o n b i o m a s s i n e n c l o s u r e s d u r i n g s p r i n g r e p r o d u c t i o n was l a r g e r i n 1980 t h a n i n 1979 ( F i g s . 16 and 2 6 ) . C o o l s p r i n g c o n d i t i o n s a l l o w e d r e p r o d u c i n g f e m a l e s t o make f u l l use o f t h e added f o o d by r e d u c i n g t h e i r m e t a b o l i c demands (Sawchyn and Hammer 1968; O ' B r i e n e t a l . 1972; Kamps 1978). S l o w e d d e v e l o p m e n t r a t e s a t low t e m p e r a t u r e s (McLaren 1963; R i g l e r and C o o l e y 1974; Kamps 1978) c a u s e d a c c u m u l a t i o n s of D. l e p t o p u s n a u p l i i i n a l l 1980 e n c l o s u r e s ( F i g . 2 3 ) . C o n s e q u e n t 1 44 c o n c u r r e n c e of t e m p e r a t u r e i n c r e a s e s w i t h h i g h c o n c e n t r a t i o n s of D. l e p t o p u s a t t h e e n e r g e t i c a l l y c r i t i c a l N6 t o CI t r a n s i t i o n (Epp and L e w i s 1980) p r o b a b l y e x a g g e r a t e d e f f e c t s of i n t r a s p e c i f i c c o m p e t i t i o n on e n c l o s e d D. l e p t o p u s . In E u n i c e L a k e , where D. l e p t o p u s d e n s i t i e s a r e a l w a y s much l e s s t h a n i n 1980 e n c l o s u r e s , i n t e r a c t i o n s w i t h c o n s p e c i f i c s a r e p r o b a b l y n e g l i g i b l e compared t o c o m p e t i t i o n w i t h D. t y r e l l i . P r o p e r a s s e s s m e n t of t h e r e l a t i o n s h i p between t e m p e r a t u r e and i n t e n s i t y of c o m p e t i t i o n between D. t y r e l l i and D. l e p t o p u s would r e q u i r e a l a b o r a t o r y e x p e r i m e n t s i m i l a r t o N e i l l ' s ( u n p u b l . ) on two h e r b i v o r o u s c l a d o c e r a n s . D e s p i t e h i g h a b u n d a n c e s i n n e a r b y e u t r o p h i c l a k e s , D a p h n i a p u l e x does n o t c o -o c c u r w i t h D. r o s e a i n o l i g o t r o p h i c R e s e a r c h F o r e s t l a k e s ( N e i l l 1978).. N e i l l c o n f i n e d b o t h s p e c i e s t o g e t h e r i n a f a c t o r i a l e x p e r i m e n t w i t h t h r e e f o o d c o n c e n t r a t i o n s (0.4, 0.7, and 1.0 mg/1 d r y w e i g h t ) and t h r e e t e m p e r a t u r e l e v e l s (12, 15, and 21°C) ( s e e N e i l l 1981b). R e g a r d l e s s of t e m p e r a t u r e , D. p u l e x e x c l u d e d D. r o s e a a t i n t e r m e d i a t e and h i g h f o o d c o n c e n t r a t i o n s . A t low f o o d c o n c e n t r a t i o n s , b o t h s p e c i e s c o e x i s t e d a t t h e two l o w e r t e m p e r a t u r e s . C o m p e t i t i v e s u p e r i o r i t y o f D. r o s e a a t t h e h i g h e s t t e m p e r a t u r e r e f l e c t e d i t s a d a p t a t i o n t o o l i g o t r o p h y . F o r a c o r r e s p o n d i n g e x p e r i m e n t on d i a p t o m i d s , t h e h y p o t h e s i z e d c o r r e l a t i o n between t e m p e r a t u r e and c o m p e t i t i o n p r e d i c t s p a r a l l e l s of D. l e p t o p u s w i t h D. p u l e x , and of D. t y r e l l i w i t h D. r o s e a . The more o l i g o t r o p h i c d i s t r i b u t i o n o f D. t y r e l l i ( W i l s o n 1959) t h a n of D. l e p t o p u s (Reed and O l i v e 1958) s t r e n g t h e n s t h e s e p r e d i c t i o n s . C o n s i s t e n t w i t h them a r e 1 45 e x t i n c t i o n of D. l e p t o p u s ( F i g . 22A) and s u r v i v a l of D. t y r e l l i ( F i g . 17A) i n E u n i c e Lake d u r i n g c o n c u r r e n t t e m p e r a t u r e i n c r e a s e s ( F i g . 25) and p h y t o p l a n k t o n d e c r e a s e s ( F i g . 2 6A). L i m i t a t i o n s of P h y t o p l a n k t o n S t a n d i n g S t o c k D a t a Most o f t h e f o r e g o i n g d i s c u s s i o n i m p l i c i t l y assumes t h a t D. l e p t o p u s and D. t y r e l l i i n E u n i c e Lake a r e f o o d l i m i t e d . Low z o o p l a n k t o n d e n s i t i e s make sp a c e l i m i t a t i o n and i n t e r f e r e n c e c o m p e t i t i o n i m p l a u s i b l e ; low p h y t o p l a n k t o n l e v e l s make e x p l o i t a t i o n c o m p e t i t i o n f o r f o o d p r o b a b l e . S u p p o r t i n g e v i d e n c e i n c l u d e s b i o m a s s and d e n s i t y i n c r e a s e s of z o o p l a n k t o n i n E u n i c e (Marmorek 1982) and G w e n d o l i n e L a k e s ( N e i l l and Peacock 1980; Peacoc k 1981; Hay 1981) i n r e s p o n s e t o e x p e r i m e n t a l f e r t i l i z a t i o n s . B ecause egg p r o d u c t i o n i s a p a r t i c u l a r l y s e n s i t i v e i n d i c a t o r of f o o d abundance ( M a r s h a l l and O r r 1958; Edmondson e t a l . 1962; Weglenska 1971; Dagg 1977; Cooney e t a l . 1978), e l e v a t e d D. l e p t o p u s and D. t y r e l l i r e p r o d u c t i o n i n 1979 low d e n s i t y e n c l o s u r e s ( T a b l e X I I ) i m p l i e s f o o d l i m i t a t i o n i n o t h e r t r e a t m e n t s from t h a t y e a r . I n c r e a s e d D. l e p t o p u s p e r fe m a l e egg numbers i n a l l e n c l o s u r e s i n c o o l 1980 ( T a b l e X X I I ) i m p l i e s a c o n n e c t i o n between r e d u c e d f o o d l i m i t a t i o n and t h e a b s e n c e of e x p e r i m e n t a l e v i d e n c e f o r c o m p e t i t i o n . However, t h i s l i n k i s o b s c u r e d by t h e i n v e r s e c o r r e l a t i o n between t e m p e r a t u r e and d i a p t o m i d c l u t c h s i z e (Sawchyn and Hammer 1968; Kamps 1978). The a s s u m p t i o n o f f o o d l i m i t a t i o n i s c e n t r a l t o t h e h y p o t h e s i s t h a t t e m p e r a t u r e g o v e r n s c o m p e t i t i o n between 1 46 D. l e p t o p u s and D. t y r e l l i . T h i s h y p o t h e s i s assumes t h a t t e m p e r a t u r e i s p o s i t i v e l y c o r r e l a t e d w i t h z o o p l a n k t o n demands f o r f o o d r e s o u r c e s , but u n c o r r e l a t e d w i t h r e s o u r c e c o n c e n t r a t i o n s . S i m i l a r i t i e s between warm 1979 and c o o l 1980 i n p h y t o p l a n k t o n s t a n d i n g s t o c k s ( F i g s . 16 and 26) do n o t n e c e s s a r i l y c o n f i r m i n d e p e n d e n c e o f t e m p e r a t u r e and r e s o u r c e l e v e l s b e c a u s e s t a n d i n g s t o c k s do not i n c o r p o r a t e p h y t o p l a n k t o n t u r n o v e r r a t e s (Cooper 1973). As t e m p e r a t u r e s i n c r e a s e , t u r n o v e r r a t e s may i n c r e a s e , h o l d , or d e c r e a s e , d e p e n d i n g on whether i n c r e a s e s i n p h y t o p l a n k t o n p r o d u c t i o n r a t e s ( W e t z e l 1975) a r e g r e a t e r t h a n , e q u a l t o , o r l e s s t h a n i n c r e a s e s i n n u t r i e n t d e p l e t i o n r a t e s . Unchanged or i n c r e a s e d t u r n o v e r r a t e s s u p p o r t t e m p e r a t u r e m e d i a t i o n of c o m p e t i t i o n by i m p l y i n g more i n t e n s e c o m p e t i t i o n i n 1979 d e s p i t e e q u a l l y or more f a v o u r a b l e f o o d c o n d i t i o n s t h a n i n 1980. As an a l t e r n a t i v e t o h i g h e r z o o p l a n k t o n f o o d r e q u i r e m e n t s , d e c r e a s e d t u r n o v e r r a t e s p r o v i d e lower f o o d l e v e l s as an e x p l a n a t i o n f o r 1979 c o m p e t i t i o n . Which of t h e s e p o s s i b i l i t i e s a p p l i e d d u r i n g t h e e x p e r i m e n t s i s unknown b e c a u s e t u r n o v e r r a t e s were not m e a s u r e d . I f z o o p l a n k t o n g r a z i n g d e c r e a s e s b i o m a s s o f e d i b l e a l g a e ( P o r t e r 1972), t h e n d i f f e r e n c e s among 1979 t r e a t m e n t s i n p h y t o p l a n k t o n s i z e c o m p o s i t i o n s u p p o r t an i n v e r s e f e e d i n g r e l a t i o n s h i p between z o o p l a n k t o n body s i z e and f o o d p a r t i c l e s i z e . R e l a t i v e t o c o n t r o l s , s t a n d i n g s t o c k s o f l a r g e p a r t i c l e s i n c r e a s e d i n t y r e l l i - r e m o v a l and low d e n s i t y e n c l o s u r e s , and d e c r e a s e d i n k e n a i - r e m o v a l s w i t h i n t h e f i r s t 6 weeks of t h e e x p e r i m e n t ( F i g . 16). S t a n d i n g s t o c k s of s m a l l c e l l s d i d not 147 d i f f e r a c r o s s t r e a t m e n t s . These r e s u l t s v i o l a t e p r e d i c t i o n s d e r i v e d from z o o p l a n k t o n f e e d i n g s t u d i e s showing a p o s i t i v e c o r r e l a t i o n between a n i m a l and f o o d s i z e s ( B u r n s 1968). However, s t a n d i n g s t o c k s may i m p r o p e r l y e s t i m a t e r e l a t i v e i m p o r t a n c e of l a r g e and s m a l l c e l l s b e c a u s e t u r n o v e r r a t e s a r e h i g h e r f o r s m a l l c e l l s ( K a l f f 1972; G u t e l m a c h e r 1975; R e d f i e l d 1980). F u r t h e r l i m i t i n g t h e u s e f u l n e s s of s t a n d i n g s t o c k d a t a i s t h e d e p endence o f t u r n o v e r r a t e s on n u t r i e n t r e g e n e r a t i o n r a t e s ( T i t m a n 1976; Lehman 1980a and b ) , w h i c h a r e t h e m s e l v e s f u n c t i o n s o f z o o p l a n k t o n e x c r e t i o n r a t e s ( P o r t e r 1977; Lehman 1980a), body s i z e s (Lehman 1980b), and n u t r i t i o n a l s t a t e s ( S c h i n d l e r 1971). A t l e a s t two e x p l a n a t i o n s a r e c a p a b l e of a l i g n i n g p h y t o p l a n k t o n r e s u l t s o b s e r v e d i n 1979 w i t h t h o s e p r e d i c t e d from z o o p l a n k t o n f e e d i n g s t u d i e s . (1) I f g r a z i n g by z o o p l a n k t o n i n c r e a s e s , r a t h e r than d e c r e a s e s , biomass o f g r a z e d a l g a e , t h e n d e c r e a s e s r e l a t i v e t o c o n t r o l s of l a r g e p h y t o p l a n k t o n i n k e n a i - r e m o v a l s and l a c k o f i n c r e a s e s of s m a l l p h y t o p l a n k t o n i n t y r e l l i -r e m o v a l s may a f f i r m a p o s i t i v e c o r r e l a t i o n between z o o p l a n k t o n s i z e and f o o d s i z e . M o d e r a t e g r a z i n g i n c o n t r o l s may have e n h a n c e d p r o d u c t i v i t y a n d / o r b i o m a s s of g r a z e d p h y t o p l a n k t o n by c a u s i n g c o m p e n s a t o r y i n c r e a s e s i n t h e i r t u r n o v e r r a t e s (Cooper 1973) a n d / o r i n c r e a s e s i n n u t r i e n t r e g e n e r a t i o n r a t e s ( G l i w i c z 1975). 1 48 (2) Low g r a z i n g p r e s s u r e s on s m a l l e d i b l e a l g a e may e x p l a i n why o n l y l e s s e d i b l e l a r g e c e l l s i n c r e a s e d i n low d e n s i t y and t y r e l l i - r e m o v a l e n c l o s u r e s . S m a l l p h y t o p l a n k t o n c e l l s w i t h h i g h s u r f a c e t o volume r a t i o s may be c o m p e t i t i v e l y s u p e r i o r t o l a r g e c e l l s under o l i g o t r o p h i c c o n d i t i o n s ( P a r s o n s and T a k a h a s h i 1973; G l i w i c z 1975; M c C a u l e y and B r i a n d 1979). However, a f t e r g r a z i n g p r e s s u r e s a r e r e d u c e d , s m a l l a l g a l s p e c i e s may i n i t i a l l y i n c r e a s e t o c o n c e n t r a t i o n s a t w h i c h t h e y d e p l e t e n u t r i e n t s not l i m i t i n g t o l a r g e s p e c i e s . Then, b o t h th e b i o m a s s of s m a l l a l g a e and t h e i r c o m p e t i t i v e a d v a n t a g e o v e r l a r g e a l g a e f o r use of common r e s o u r c e s s h o u l d d e c r e a s e , and b i o m a s s of l a r g e p h y t o p l a n k t o n s h o u l d i n c r e a s e . T h i s i n t e r p r e t a t i o n does not seem t o h o l d f o r n o n - o l i g o t r o p h i c s y s t e m s ; i n s m a l l e n c l o s u r e e x p e r i m e n t s , G l i w i c z (1975) f o u n d a d i r e c t r e l a t i o n s h i p between biomass o f i n e d i b l e n e t p l a n k t o n and i n t e n s i t y of g r a z i n g by Daphn i a p u l e x on n a n n o p l a n k t o n . I n t e r a c t i o n s between l a r g e and s m a l l c e l l s a r e c o m p l i c a t e d by enhancement e f f e c t s of v i a b l e gut p a s s a g e on c e r t a i n l a r g e i n e d i b l e a l g a e ( P o r t e r 1973, 1975, 1976, 1977). A l t h o u g h t h e s e two mechanisms a r e p o s s i b l e c a u s e s of o b s e r v e d t r e a t m e n t d i f f e r e n c e s i n a l g a l s i z e c o m p o s i t i o n s , whether t h e y were t h e a c t u a l c a u s e s c a n n o t be d e t e r m i n e d w i t h o u t d a t a on p h y t o p l a n k t o n t u r n o v e r r a t e s . U n f o r t u n a t e l y , methods of e s t i m a t i n g t u r n o v e r r a t e s s e p a r a t e l y f o r c e l l s of d i f f e r e n t s i z e s a r e complex and u n r e l i a b l e ( s e e V o l l e n w e i d e r 1969; 1 49 r e v i e w e d i n K n o e c h e l and K a l f f 1976). In a d d i t i o n t o unknown t u r n o v e r r a t e s , i n a d e q u a t e knowledge of c o p e p o d d i e t s impedes i n t e r p r e t a t i o n of a l g a l s i z e c o m p o s i t i o n s . B a c t e r i a and d e t r i t u s , r a t h e r t h a n a l g a e , may be p r i n c i p a l f o o d s f o r some z o o p l a n k t o n s p e c i e s (Pennak 1946; Nauwerck i n S a u n d e r s 1969; G l i w i c z 1969; Moore 1977, 1978, 1979; N e i l l 1981b). A b i l i t y of l a r g e z o o p l a n k t o n t o f i l t e r s m a l l p a r t i c l e s ( B r o o k s and Dodson 1965) and a b i l i t y of s m a l l z o o p l a n k t o n t o r a p t o r i a l l y c a p t u r e l a r g e p a r t i c l e s ( M u l l i n 1963; McQueen 1970; P o r t e r 1977) c l o u d p o s i t i v e c o r r e l a t i o n s between z o o p l a n k t o n s i z e and f o o d s i z e . B o t h n a u p l i i and a d u l t s of C a l a n u s f i n m a r c h i c u s e a t p a r t i c l e s of s i m i l a r s i z e ( M a r s h a l l and O r r 1956). L i m i t e d i n f o r m a t i o n on d i a p t o m i d d i e t s i s a v a i l a b l e . D. m i n u t u s • f i l t e r s p a r t i c l e s <20 urn i n d i a m e t e r (Bogdan and McNaught 1975); D. o r e g o n e n s i s , p a r t i c l e s £30 urn (Richman e t a l . 1980); and D. c o l o r a d e n s i s and D. Shoshone, p a r t i c l e s <120-150 urn (Maly and Maly 1974). C o n t r a d i c t o r y s t u d i e s have r e p o r t e d a l g a e £60 urn (Hazelwood and P a r k e r 1961) and d e t r i t u s <22 urn (Winner 1970) as d i e t s o f D. l e p t o p u s . Even t h e s e few d a t a a r e q u e s t i o n a b l e b e c a u s e methods u s e d t o s t u d y z o o p l a n k t o n f e e d i n g have been u n r e l i a b l e ( H a r b i s o n and M c A l i s t e r 1980; Roman and R u b l e e 1980). 1 50 SUMMARY AND CONCLUSIONS T h i s s t u d y e x p e r i m e n t a l l y t e s t e d t h e h y p o t h e s i s t h a t i n t e r s p e c i f i c c o m p e t i t i o n from r e s i d e n t z o o p l a n k t o n s p e c i e s p r e v e n t s i m m i g r a n t D i a p t o m u s l e p t o p u s from c o l o n i z i n g o l i g o t r o p h i c , montane E u n i c e L a k e . E x p e r i m e n t s were c o n d u c t e d i n t h e l a k e i n l a r g e p o l y e t h y l e n e e n c l o s u r e s d u r i n g s p r i n g , summer, and f a l l of 1979 and 1980. C o n t r o l t r e a t m e n t s i n b o t h y e a r s c o n f i n e d D. l e p t o p u s w i t h a l l E u n i c e Lake s p e c i e s a t l a k e d e n s i t i e s . O t h e r t r e a t m e n t s i n 1979 c o n f i n e d D. l e p t o p u s w i t h a l l s p e c i e s a t low d e n s i t i e s or w i t h a l l s p e c i e s e x c e p t one of D a p h n i a r o s e a , Diaptomus k e n a i , o r Di a p t o m u s t y r e l l i . T r e a t m e n t s i n 1980 e x p o s e d D. l e p t o p u s t o v a r i o u s c o n c e n t r a t i o n s of D. t y r e l l i . C o m p a r i s o n s between D. l e p t o p u s r e s p o n s e s t o c o n t r o l and n o n - c o n t r o l t r e a t m e n t s y i e l d e d t h e f o l l o w i n g c o n c l u s i o n s : 1. i n 1979 e x p e r i m e n t s , e q u a l and p o s i t i v e r e s p o n s e s of D. l e p t o p u s t o t y r e l l i - r e m o v a l and low d e n s i t y t r e a t m e n t s p r e v e n t e d s e p a r a t i o n of c o m p e t i t i o n between D. l e p t o p u s and D. t y r e l l i from d i f f u s e c o m p e t i t i o n . O t h e r r e s u l t s s u p p o r t e d D. t y r e l l i c o m p e t i t i o n . E x p e r i m e n t a l e v i d e n c e i n c l u d e d n e u t r a l r e s p o n s e s of D. l e p t o p u s t o D a p h n i a - and k e n a i - r e m o v a l s . N o n - e x p e r i m e n t a l e v i d e n c e i n c l u d e d marked s p a t i a l and t e m p o r a l o v e r l a p between D. l e p t o p u s .and D. t y r e l l i i n E u n i c e Lake and d i s j u n c t o c c u r r e n c e s of t h e s e two s p e c i e s i n l a k e s o t h e r t h a n E u n i c e . 2. Low b i o m a s s of p h y t o p l a n k t o n i n most e n c l o s u r e s and h i g h 151 numbers o f eggs p e r D. l e p t o p u s f e m a l e i n low d e n s i t y e n c l o s u r e s s u g g e s t e d t h a t c o m p e t i t i o n between D. l e p t o p u s and D. t y r e l l i i n 1979 was f o r f o o d . T r e a t m e n t d i f f e r e n c e s i n a l g a l s i z e c o m p o s i t i o n d i d not i n d i c a t e whether c o m p e t i t o r s p a r t i t i o n e d l i m i t e d r e s o u r c e s . O n l y D. l e p t o p u s n a u p l i i were v u l n e r a b l e t o c o m p e t i t i o n from D. t y r e l l i p o s s i b l y b e c a u s e n a u p l i i a r e e n e r g e t i c a l l y l e s s e f f i c i e n t t h a n l a t e r s t a g e s . 1979 e x p e r i m e n t s c o u l d not d i s t i n g u i s h w h i c h s t a g e s o f D. t y r e l l i competed. In c o n t r a s t t o 1979, D. l e p t o p u s r e s p o n d e d s i m i l a r l y i n 1980 t o a l l t r e a t m e n t s , r e g a r d l e s s of D. t y r e l l i c o n c e n t r a t i o n s . Low t e m p e r a t u r e s d u r i n g most o f 1980 p r o b a b l y c u r t a i l e d c o m p e t i t i o n between D. l e p t o p u s and D. t y r e l l i by r e d u c i n g t h e i r f o o d r e q u i r e m e n t s . D. l e p t o p u s n a u p l i i r e a c h e d e x t r e m e l y h i g h c o n c e n t r a t i o n s i n a l l e n c l o s u r e s b e c a u s e c o o l c o n d i t i o n s p r o m o t e d r e p r o d u c t i o n and r e t a r d e d d e v e l o p m e n t . P r e s u m a b l y , c o m p e t i t i o n from c o n s p e c i f i e s , r a t h e r t h a n from D. t y r e l l i , c a u s e d e x t i n c t i o n s of D. l e p t o p u s i n a l l e n c l o s u r e s as t e m p e r a t u r e s i n c r e a s e d l a t e i n 1980 e x p e r i m e n t s . In E u n i c e Lake, where D. l e p t o p u s d e n s i t i e s a r e a l w a y s v e r y low, i n t r a s p e c i f i c c o m p e t i t i o n u n d o u b t e d l y i s i n s i g n i f i c a n t . C o m p e t i t i o n w i t h D. t y r e l l i p r o b a b l y i s t e m p e r a t u r e - d e p e n d e n t . At low t e m p e r a t u r e s d u r i n g f a l l 1979 1 52 and s p r i n g 1980, d e n s i t i e s of D. l e p t o p u s i n E u n i c e Lake were r e l a t i v e l y h i g h . U n d e t e c t a b l e d e n s i t i e s o c c u r r e d when h i g h e r t e m p e r a t u r e s i n c r e a s e d p o t e n t i a l f o r c o m p e t i t i o n w i t h D. t y r e l l i . H i g h t e m p e r a t u r e s p r e s u m a b l y - o c c u r f r e q u e n t l y enough f o r D. t y r e l l i t o p r e v e n t D. l e p t o p u s from c o l o n i z i n g E u n i c e L a k e . 1 53 LITERATURE CITED A b b o t t , I . , L.K. A b b o t t , and P.R. G r a n t . 1977. C o m p a r a t i v e e c o l o g y o f G a l a p a g o s Ground F i n c h e s ( G e o s p i z a G o u l d ) : e v a l u a t i o n of t h e i m p o r t a n c e of f l o r i s t i c d i v e r s i t y and i n t e r s p e c i f i c c o m p e t i t i o n . E c o l . Monogr. 47:151-184. A l l a n , J.D. 1973. C o m p e t i t i o n and t h e r e l a t i v e a b u n d a n c e s of two c l a d o c e r a n s . E c o l o g y 54:484-498. A n d e r s o n , R.S. 1970. P r e d a t o r - p r e y r e l a t i o n s h i p s and p r e d a t i o n r a t e s f o r c r u s t a c e a n z o o p l a n k t e r s from some l a k e s i n w e s t e r n Canada. Can. J . Z o o l . 48:1229-1240. A n d e r s o n , R.S. 1971. C r u s t a c e a n p l a n k t e r s o f 146 a l p i n e and s u b a l p i n e l a k e s and ponds i n w e s t e r n Canada. J . F i s h . Res. Bd. Canada 28:311-321 . A n d e r s o n , R.S. 1972. Z o o p l a n k t o n c o m p o s i t i o n and change i n an a l p i n e l a k e . V e r h . I n t e r n a t . V e r e i n . L i m n o l . 18:264-268. A n d e r s o n , R.S. 1974. C r u s t a c e a n p l a n k t o n c o m m u n i t i e s of 340 l a k e s and ponds i n and n e a r t h e N a t i o n a l P a r k s of t h e C a n a d i a n Rocky M o u n t a i n s . J . F i s h . Res. Bd. Canada 31:855-869. A n d e r s o n , R.S., and G.L. F a b r i s . 1970. A new s p e c i e s of d i a p t o m i d c opepod f r o m S a s k a t c h e w a n w i t h n o t e s on t h e c r u s t a c e a n community of t h e pond. Can. J . Z o o l . 48:49-54. Bogdan, K.G., and D.C. McNaught. 1975. S e l e c t i v e f e e d i n g by D i a p t o m u s and D a p h n i a . V e r h . I n t e r n a t . V e r e i n . L i m n o l . 19: 2935-2942. B o o n s t r a , R., and C . J . K r e b s . 1977. A f e n c i n g e x p e r i m e n t on a h i g h - d e n s i t y p o p u l a t i o n of M i c r o t u s t o w n s e n d i i . Can. J . Z o o l . 55:1166-1175. B r o o k s , J . L . , and S . I . Dodson. 1965. P r e d a t i o n , body s i z e , and c o m p o s i t i o n of p l a n k t o n . S c i e n c e 150:28-35. o 1 54 Brown, J.H. 1975. G e o g r a p h i c a l e c o l o g y of d e s e r t r o d e n t s . I n : M.L. Cody and J.M. Diamond, e d s . 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C o n t r a s t s among c a l a n o i d c o p e p o d s from permanent and t e m p o r a r y ponds i n A r i z o n a . Am. M i d i . N a t . 76:351-368. 1 55 C o l w e l l , R.K., and D.J. Futuyma. 1971. On t h e measurement of n i c h e b r e a d t h and o v e r l a p . E c o l o g y 52;567-576. C o m i t a , G.W. 1968. Oxygen c o n s u m p t i o n i n D i a p t o m u s . L i m n o l . O c e a n o g r . 13:51-57. C o n n e l l , J.H. 1961. 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 p e t i t i o n and o t h e r f a c t o r s on t h e d i s t r i b u t i o n of t h e b a r n a c l e C h t h a m a l u s s t e l l a t u s . E c o l o g y 42:710-723. C o n n e l l , J.H. 1975. Some mechanisms p r o d u c i n g s t r u c t u r e i n n a t u r a l c o m m u n i t i e s : a model and e v i d e n c e from f i e l d e x p e r i m e n t s . I_n: M.L. Cody and J.M. Diamond, e d s . E c o l o g y and E v o l u t i o n of C o m m u n i t i e s . 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