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An ecological study of some of the chironomidae inhabiting a series of saline lakes in central British… Cannings, Robert Alexander 1973

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AN ECOLOGICAL STUDY OF SOME OF THE CHIRONOMIDAE INHABITING A SERIES OF SALINE LAKES IN CENTRAL BRITISH COLUMBIA WITH SPECIAL REFERENCE TO CHIRONOMUS TENTANS FABRICIUS by Robert Alexander Cannings BSc. Hons., U n i v e r s i t y of B r i t i s h Columbia, 1970 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n the Department of Zoology We accept t h i s t h e s i s as conforming to the r e q u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA May, 1973 In presenting 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 of the requirements f o r an advanced degree at the U n i v e r s i t y of B r i t i s h Columbia, I agree that the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r reference and study. I f u r t h e r agree that permission f o r extensive copying of t h i s t h e s i s f o r s c h o l a r l y purposes may be granted by the Head of my Department or by h i s r e p r e s e n t a t i v e s . I t i s understood that copying or p u b l i c a t i o n of t h i s t h e s i s f o r f i n a n c i a l gain s h a l l not be allowed without my w r i t t e n permission. Department of The U n i v e r s i t y of B r i t i s h Columbia Vancouver 8, Canada Date i i ABSTRACT This t h e s i s i s concerned w i t h a study of the Chironomidae occuring i n a s a l i n e lake s e r i e s i n c e n t r a l B r i t i s h Columbia. I t describes the e c o l o g i c a l d i s t r i b u t i o n of species, t h e i r abundance, phenology and i n t e r a c t i o n , w i t h p a r t i c u l a r a t t e n t i o n being p a i d to Chironomus tentans. Emphasis i s placed on the species of Chironomus that c o e x i s t i n these lakes and a f u r t h e r a n a l y s i s i s made of the chromo-some i n v e r s i o n frequencies i n C. tentans. Of the t h i r t y - f o u r species represented by i d e n t i f i a b l e a d u l t s i n the study, eleven species have not been p r e v i o u s l y r e p o r t e d i n B r i t i s h Columbia, f i v e are new records f o r Canada and seven species are new to science. The chironomid fauna of the lake s e r i e s i s d i v i d e d i n t o dominant a s s o c i a t i o n s whose existence seems to depend on s a l i n i t y and p r o d u c t i v i t y l e v e l s . A Cricotopus albanus -P r o c l a d i u s b e l l u s - Ablabesmyia p e l e e n s i s a s s o c i a t i o n pre-v a i l s i n the lowest s a l i n i t i e s (40 to 80 jumho/cm c o n d u c t i v i t y ) w h i l e i n c o n d u c t i v i t i e s between 400 and 2800 jumho/cm a Glyptotendipes barbipes - E i n f e l d i a pagana a s s o c i a t i o n domin-ates. In the most s a l i n e lakes ( c o n d u c t i v i t y 4100 to 12000 jumho/cm) a Calopsectra g r a c i l e n t a - Cryptotendipes a r i e l a s s o c i a t i o n i s c h a r a c t e r i s t i c . A n a l y s i s of p h y s i c a l and chemical f a c t o r s i n f l u e n c i n g the l i f e c y c l e of C. tentans i n d i c a t e s that c o n d i t i o n s a s s o c i a t e d w i t h h i g h l e v e l s of organic carbon promote l a r g e numbers of l a r v a e and g r e a t e r emergence success. The r e s u l t s suggest that competition between C. tentans and other Chironomus species i s reduced through s p a t i a l s e paration due to d i f f e r e n t preferences f o r s a l i n i t y or r e l a t e d f a c t o r s . Furthermore, temporal s e p a r a t i o n among these and other abundant species such as G. barbipes and E. pagana occurs as a r e s u l t of staggered generation times. The i n v e r s i o n frequency i n chromosome 1 of C. tentans i s n e g a t i v e l y c o r r e l a t e d w i t h organic carbon l e v e l s and p o s i -t i v e l y c o r r e l a t e d w i t h d i s s o l v e d oxygen and the abundance of Glyptotendipes barbipes. Since the i n v e r s i o n frequency i s lowest i n h a b i t a t s where competing species are few and where C. tentans i s most s u c c e s s f u l , i t i s suggested that the i n v e r -s i o n governs a mechanism reducing competition. A major c o n t r i b u t i o n of t h i s work i s the r e v i s i o n of the d i s t r i b u t i o n of many of the chironomid species under c o n s i d e r a -t i o n . In the past, l i t t l e r e search has been done on popula-t i o n s of chironomids i n a s a l i n e l a k e s e r i e s . The present study, i n attempting to f i l l t h i s gap i n entomological research, shows that a s p e c i e s ' l i f e h i s t o r y and p o p u l a t i o n s t r u c t u r e can vary r a d i c a l l y i n c l o s e l y a s s o c i a t e d l a k e s of d i f f e r i n g chemical and b i o l o g i c a l c o n s t i t u t i o n . I V TABLE OF CONTENTS T i t l e Page A b s t r a c t Table of Contents L i s t of Tables L i s t of F i g u r e s L i s t of P l a t e s Acknowledgements Page i i i i v v i v i i i x i x i i I INTRODUCTION 1 I I THE LAKE ENVIRONMENTS 4 A. THE STUDY AREA 4 B. THE PHYSICAL AND CHEMICAL PROPERTIES OF THE LAKES 8 I I I SPECIES DIVERSITY AND THE CHIRONOMID COMPLEX IN THE LAKE SERIES 17 A. MATERIALS AND METHODS 17 1. Temperature Records 17 2. B i o l o g i c a l Sampling Methods 17 a) L a r v a l Sampling 17 b) A d u l t Sampling 19 3. Rearing of Specimens 23 4. P r e p a r a t i o n and I d e n t i f i c a t i o n of Specimens 24 5. A n a l y s i s of the Data 24 6. Storage of the Data f o r Further Study 24 B. RESULTS 1. Water Temperatures i n the Lake S e r i e s 2. Chemical Data 3 The Occurrence of Species i n the Lakes 26 26 30 30 4. Species Considered i n D e t a i l 33 5. The Chironomid Complex and the Lake S e r i e s 85 a) The Cricotopus albanus -P r o c l a d i u s b e l l u s - Ablabesmyia  p e l e e n s i s a s s o c i a t i o n b) The Glyptotendipes barbipes -E i n f e l d i a pagana a s s o c i a t i o n c) The Calo p s e c t r a g r a c i l e n t a -Cryptotendipes a r i e l a s s o c i a t i o n C. DISCUSSION 1. The Chironomidae and the Lake S e r i e s 91 2. Chironomus tentans and the Lake Se r i e s 102 a) P h y s i c a l and Chemical Influences 102 b) B i o t i c I n t e r a c t i o n s 106 IV CHIRONOMUS TENTANS AND SOME BIOTIC FACTORS AFFECTING CHROMOSOME INVERSION 113 A. MATERIALS AND METHODS 113 B. RESULTS 115 C. DISCUSSION 121 r V CONCLUSION 125 85 86 88 L i t e r a t u r e C i t e d Appendix 129 140 LIST OF TABLES v i TABLE I TABLE I I TABLE I I I TABLE IV TABLE V TABLE VI TABLE V I I P h y s i c a l and chemical p r o p e r t i e s of the la k e s . Average water temperature i n the lake s e r i e s . The d i s t r i b u t i o n of chironomids i n the one meter depth zone i n the l a k e s . The d i s t r i b u t i o n of la r v a e u n i d e n t i f i e d to species. Summary of c o r r e l a t i o n c o e f f i c i e n t s d e s c r i b i n g the r e l a t i o n s h i p between environmental f a c t o r s and the amount of emergence of c e r t a i n species. The c o r r e l a t i o n between emergence histogram d i s p e r s i o n and environmental f a c t o r s . Summary of c o r r e l a t i o n c o e f f i c i e n t s d e s c r i b i n g r e l a t i o n s h i p s between environmental f a c t o r s and species abundance. Page 10 27 31 32 76 77 78 TABLE V I I I Summary of c o r r e l a t i o n c o e f f i c i e n t s d e s c r i b i n g the r e l a t i o n s h i p between environmental f a c t o r s and species per cent composition. 79 TABLE IX Summary of c o r r e l a t i o n c o e f f i c i e n t s d e s c r i b i n g the r e l a t i o n s h i p between environmental f a c t o r s and the amount of emergence. 80 TABLE X Summary of the c o r r e l a t i o n c o e f f i c i e n t s d e s c r i b i n g the r e l a t i o n s h i p between environmental f a c t o r s and the number of emergence peaks f o r v a r i o u s species. 81 TABLE XI Summary of c o r r e l a t i o n c o e f f i c i e n t s d e s c r i b i n g the r e l a t i o n s h i p between environmental f a c t o r s and the times of major emergence i n se v e r a l species. 82 V I X TABLE X I I TABLE X I I I TABLE XIV TABLE XV TABLE XVI TABLE XVII Summary of c o r r e l a t i o n c o e f f i c i e n t s d e s c r i b i n g the r e l a t i o n s h i p between l a r v a l abundance, numbers of emerging a d u l t s , number of emergence peaks and emergence time. 83 The developmental r a t e s of C. tentans i n v a r i o u s l a k e s . 84 The percentage composition of species i n the lakes based on the t o t a l a d u l t emergence, May - August, 1970. 90 In v e r s i o n frequencies i n chromosome 1 of C. tentans. 116 Summary of c o r r e l a t i o n c o e f f i c i e n t s d e s c r i b i n g the r e l a t i o n s h i p between the frequency of 1 Rad and some environmental f a c t o r s . 117 Summary of c o r r e l a t i o n c o e f f i c i e n t s d e s c r i b i n g the r e l a t i o n s h i p between the frequency of 1 Rad and the abundance of some chironomids. 118 TABLE X V I I I Summary of c o r r e l a t i o n c o e f f i c i e n t s d e s c r i b i n g the r e l a t i o n s h i p between the frequency of 1 Rad and the per cent composition of some chironomids, 119 TABLE XIX Summary of c o r r e l a t i o n c o e f f i c i e n t s d e s c r i b i n g the r e l a t i o n s h i p between the frequency of 1 Rad and some emergence v a r i a b l e s . 120 v i i i LIST OF FIGURES FIGURE 1 FIGURE 2 FIGURE 3 FIGURE 4 FIGURE 5 FIGURE 6 FIGURE 7 FIGURE 8 FIGURE 9 FIGURE 10 FIGURE 11 The study a r e a ; Springhouse r e g i o n . The study area; water bodies i n the C h i l c o t i n r e g i o n . D e t a i l s of the emergence t r a p . D a i l y temperature range i n some of the lakes where Chironomus tentans i s abundant. Cumulative day degrees measured at the mud surface at a depth of 1 meter i n some of the lakes where Chironomus  tentans i s abundant. The emergence of a d u l t s of P r o c l a d i u s  b e l l u s (Loew) and P r o c l a d i u s freemani Sub l e t t e from the one meter depth zone of s e v e r a l l a k e s . The emergence of a d u l t s of P r o c l a d i u s  dentus Roback from the one meter depth zone of s e v e r a l l a k e s . Page 5 6 22 28 29 35 37 The emergence of a d u l t s of P r o c l a d i u s  clavus Roback and Ablabesmyia p e l e e n s i s (Whalley) from the one meter depth zone of s e v e r a l l a k e s . 40 The emergence of a d u l t s of Cricotopus f l a v i b a s i s M a l l o c h and Cricotopus albanus Curran from the one meter depth zone of s e v e r a l l a k e s . 43 The emergence of a d u l t s of P s e c t r o c l a d i u s barbimanus (Edwards) from the one meter depth zone of s e v e r a l l a k e s . 45 The emergence of a d u l t s of Crypto-tendipes a r i e l ( Sublette) and Calopsectra g r a c i l e n t a (Holmgren) from the one meter depth zone of s e v e r a l l a k e s . 47 i x FIGURE 12 FIGURE 13 FIGURE 14 FIGURE 15 L a r v a l abundance and a d u l t emergence of Perotanypus a l a s k e n s i s (Malloch) i n L. Lye, Boitano L. and L. Jackson. 50 L a r v a l abundance and a d u l t emergence of Derotanypus a l a s k e n s i s (Malloch) i n Rock L., Sorenson L. and East L. 51 L a r v a l abundance and a d u l t emergence of E i n f e l d i a pagana Meigen i n L. Jackson, Rock L. and Westwick L. 55 L a r v a l abundance and a d u l t emergence of E i n f e l d i a pagana Meigen i n Near Opposite Crescent, Barkley L. and East L. 56 FIGURE 16 L a r v a l abundance and a d u l t emergence of Glyptotendipes barbipes (Staeger) i n L. Jackson, Westwick L. and Sorenson L. 58 FIGURE 17 FIGURE 18 FIGURE 19 FIGURE 20 L a r v a l abundance and a d u l t emergence of Glyptotendipes barbipes (Staeger) i n Rock L., Barkley L. and East L. L a r v a l abundance and a d u l t emergence of Chironomus anthracinus Z e t t e r s t e d t i n Boitano L., L. Jackson and Rock L. L a r v a l abundance and a d u l t emergence of Chironomus anthracinus Z e t t e r s t e d t i n Sorenson L., Barkley L. and East L. L a r v a l abundance and a d u l t emergence of Chironomus n.sp. i n Barnes L., Boitano L. and L. Jackson FIGURE 21 L a r v a l abundance and a d u l t emergence of Chironomus n.sp. i n Rock L. and Sorenson L. 59 62 63 66 67 FIGURE 22 L a r v a l abundance and a d u l t emergence of Chironomus n.sp. i n Barkley L. and East L. 68 FIGURE 23 L a r v a l abundance and a d u l t emergence of Chironomus tentans F a b r i c i u s i n L. Jackson, Westwick L. and Sorenson L. 74 FIGURE 24 L a r v a l abundance and a d u l t emergence of Chironomus tentans F a b r i c i u s i n Rock L., Barkley L. and East L. FIGURE 25 Chironomid l a r v a l biomass and index of d i v e r s i t y f o r the l a r v a l complexes at 1.0 m i n the lake s e r i e s FIGURE 26 Graph showing the r e l a t i o n s h i p between . oxygen l e v e l s and organic carbon i n the l a k e s . FIGURE 27 S a l i n i t y t o l e r a n c e s of the i d e n t i f i e d species of the one meter depth zone i n the lake s e r i e s . FIGURE 28 Examples of the spacing of emergence times of Chironomus tentans and three c o e x i s t i n g species. FIGURE 29 Seasonal v a r i a t i o n i n the frequencies of i n v e r s i o n s of chromosome 1. LIST OF PLATES PLATE 1 A B Box 27 Box 27; v e g e t a t i o n Page 11 PLATE 2 A Barkley L. B Barkley L.; Myriophyllum 12 PLATE 3 A Near Phalarope B Near Opposite Crescent 13 PLATE 4 A L. Greer B L. Jackson 14 PLATE 5 A B L. Lye Round-up L. 15 PLATE 6 A B Barnes L. Barnes L.; p r e c i p i t a t e d s a l t s 16 PLATE 7 The emergence t r a p 21 x i i ACKNOWLEDGEMENTS I t i s a pleasure to express my g r a t i t u d e to Professor G.G.E. Scudder who, as my research s u p e r v i s o r , guided me through t h i s work. The time and energy he spent are much appreciated. Dr. T.G. No r t h c o t e 1 s c r i t i c i s m was i n v a l u a b l e during the w r i t i n g of the t h e s i s . I a l s o thank Dr. A.B. Acton f o r reading the manuscript. Dr. M.S. Topping, whose PhD. t h e s i s served as the b a s i s f o r the present study, i s e s p e c i a l l y thanked f o r h i s enthusiasm, support and permission to use much of h i s unpub-l i s h e d data. Glen Jamieson, Tony Dixon and Ken Bowler somehow put up w i t h my innumerable questions about computer programming. Without t h e i r help the data a n a l y s i s would have resembled an i n f i n i t e loop, or worse, would have crashed the system. J u l i a n Reynolds, i n between s n i c k e r s , d i d a l l s o r t s of things to help. I am indebted to Dr. J.E. Sub l e t t e (Eastern New Mexico U n i v e r s i t y ) and Dr. D.R. O l i v e r (Canada A g r i c u l t u r e , Ottawa) f o r t h e i r h e lp w i t h the determinations. Dr. A.M. Hutson ( B r i t i s h Museum: N a t u r a l H i s t o r y ) k i n d l y s u p p l i e d authentic specimens of E i n f e l d i a pagana and P s e c t r o c l a d i u s barbimanus f o r i d e n t i f i c a t i o n purposes. The research was c a r r i e d out w h i l e i n r e c e i p t of a N a t i o n a l Research C o u n c i l of Canada Postgraduate S c h o l a r s h i p and was f u r t h e r aided through an NRC grant to Dr. Scudder. ERRATA 1. Where "Aphanozomenon" a p p e a r s , r e a d " A p h a n i z o m e n o n " . 2 . Page 26 , l i n e 1 8 . " 3 1 ° i n L . J a c k s o n " s h o u l d r e a d " 3 1 ° i n B a r k l e y L . " . 3 . Page 6 1 , l i n e 1 5 . " u n i v o l t i v e " s h o u l d r e a d " u n i v o l t i n e " . 4 . Page 88 , l i n e 1 7 . "12000 umho/cm" . 5 . Page 1 0 2 , l i n e 18 . " n o t r e a l t r e n d " s h o u l d r e a d "no r e a l t r e n d " . 6 . Page 126 , l i n e 2 . " e i g h t e e n s p e c i e s new t o B . C . , t w e l v e s p e c i e s new t o Canada and s e v e n s p e c i e s new t o s c i e n c e " . 1 I INTRODUCTION This t h e s i s i s an e c o l o g i c a l study of some of the Chironomidae i n h a b i t i n g a s a l i n e lake s e r i e s i n the C h i l c o t i n and Cariboo regions of B r i t i s h Columbia. The chironomid complex of a s a l i n e lake s e r i e s has never been thoroughly examined before. Rawson and Moore (1944) and Lauer (1969) have mentioned chironomids i n connection w i t h work on s a l i n e waters, and others have recorded and s t u d i e d v a r i o u s species i n waters of d i f f e r i n g s a l i n i t i e s throughout the world (Remmert, 1955; S u t c l i f f e , 1960; Palmen, 1962; Bayly and W i l l i a m s , 1966), but l i t t l e i n f o r m a t i o n has been gathered on how chironomid populations d i f f e r i n a s e r i e s of lakes of v a r y i n g s a l i n i t y . T his type of study i s p a r t i c u l a r l y i n t e r e s t i n g since i t i s w e l l known th a t chironomids d i s p l a y extensive adaptation to a wide v a r i e t y of environments (Thienemann, 1954; Brundin, 1966) and are o f t e n able to t h r i v e where many other animals cannot. The broad s a l i n i t y t o l e r a n c e of the Chironomidae gives them s p e c i a l prominence i n s a l i n e h a b i t a t s . This f a c t , i n con-j u n c t i o n w i t h t h e i r usual great abundance and wide d i v e r s i t y , makes chironomids u s e f u l organisms w i t h which to study changes i n the s t r u c t u r e of species complexes that occur w i t h v a r i a -t i o n s i n p h y s i c a l , chemical and b i o l o g i c a l c o n d i t i o n s . The data obtained by Topping (1969) on t h i s lake s e r i e s i n c e n t r a l B r i t i s h Columbia showed that i n the d i p t e r a n 2 Chironomus tentans F a b r i c i u s there was a s i g n i f i c a n t c o r r e -l a t i o n between the frequency of l a r v a l chromosome i n v e r s i o n 1 Rad and the t o t a l number of other chironomids present i n the h a b i t a t . Since the s e l e c t i v e value of i n v e r s i o n s i n w i l d pop-u l a t i o n s i s not c l e a r l y understood, and as there have been few c o r r e l a t i o n s of t h i s s o r t , f u r t h e r i n v e s t i g a t i o n of t h i s prob-lem i s considered v a l u a b l e . Although Topping was able to show t h i s c o r r e l a t i o n between i n v e r s i o n frequency and l a r v a l abundance, most emphasis was placed on the chemical composition of the environments and l i t t l e a t t e n t i o n was d i r e c t e d to the b i o t i c f a c t o r s i n v o l v e d . Thus, one of the main aims of t h i s t h e s i s was to a s c e r t a i n the e f f e c t s of some b i o t i c f a c t o r s on the abundance of Chironomus  tentans and the i m p l i c a t i o n s of these f a c t o r s on the r e g u l a t i o n of i n v e r s i o n frequency. In p a r t i c u l a r , i t was considered necessary to know more about the other chironomid species that c o e x i s t w i t h C. tentans i n t h i s l a k e s e r i e s , t h e i r numbers and t h e i r l i f e c y c l e c h a r a c t e r i s t i c s . Only a f t e r determining the v a r i a t i o n s i n the s t r u c t u r e of the chironomid complex throughout the lake s e r i e s i s i t p o s s i b l e to place the populations of C. tentans i n proper pe r s p e c t i v e and to i n v e s t i g a t e the i n f l u e n c e of the va r i o u s species on C. tentans. I n i t i a l l y , a t t e n t i o n i s d i r e c t e d to the lake environments themselves; t h e i r p h y s i c a l and chemical c h a r a c t e r i s t i c s are o u t l i n e d . This i n f o r m a t i o n , i n conjunction w i t h extensive 3 data c o l l e c t e d on l a r v a l numbers and emergence p a t t e r n s , i s used i n an examination of the major species of the one meter depth zone. Questions such as the e f f e c t of lake environments on the d i s t r i b u t i o n and phenology of these species are d i s -cussed as are the p o s s i b l e i n t e r a c t i o n s between the more domin-ant species present. The p h y s i c a l and chemical data are then i n t e g r a t e d w i t h i n f o r m a t i o n on chironomids and thus a d e s c r i p t i o n of a number of species a s s o c i a t i o n s i s advanced. These a s s o c i a t i o n s , vary-ing throughout the lake environments, form the b a s i s f o r the examination of the r e l a t i o n s h i p between C. tentans and the other species. With these data a t hand the p o t e n t i a l e f f e c t of the b i o t i c f a c t o r s on the chromosome i n v e r s i o n frequency i n C. tentans may be more c l o s e l y analyzed. C o r r e l a t i o n c o e f f i c i e n t s are c a l c u l a t e d to determine the types of i n t e r a c t i o n s that may prove important In t h i s respect. A p a r t i c u l a r l y i n t e r e s t i n g problem that a r i s e s from the study 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 i s the apparent coexistence w i t h C. tentans of two other very s i m i l a r Chironomus species, C. anthracinus Z e t t e r s t e d t and C^n.sp. (near a t r i t i b i a M a l l o c h ) . A t t e n t i o n i s focussed on t h i s congeneric i n t e r a c t i o n and com-p e t i t i v e e x c l u s i o n (Hardin, 1960) i s discussed i n t h i s context. 4 I I THE LAKE ENVIRONMENTS A. THE STUDY AREA The study was undertaken i n the Cariboo and C h i l c o t i n areas of c e n t r a l B r i t i s h Columbia. The f i f t e e n water bodies examined are s i t u a t e d i n two d i s t i n c t but adjacent areas: the Springhouse area southwest of W i l l i a m s Lake east of the Fraser R i v e r ; and Becher's P r a i r i e near Riske Creek on the western ( C h i l c o t i n ) side of the Fraser (Fig s . 1, 2). Those named as lakes can be found on maps w h i l e the others have names used f o r the convenience of z o o l o g i s t s . The water bodies i n c l u d e : a) Springhouse a r e a : Sorenson Lake, Westwick Lake and Boitano Lake b) Becher's P r a i r i e ( C h i l c o t i n A r e a ) : Barnes Lake (Box 4 ) , Round-up Lake (Phalarope), Lake Lye (Box 20-21), Lake Jackson (Near Opposite Box 4), Lake Greer (Box 89), Rock Lake, Near Phalarope, Near Opposite Crescent, Box 17, Barkley Lake (Opposite Box 4 ) , East Lake (Racetrack) and Box 27. FIGURE 1 The Study Area: The three lakes i n the Springhouse regi o n . Insets : The F r a s e r Plateau and i t s l o c a t i o n i n the province of B r i t i s h Columbia. 5 FIGURE 2 The Study Area: water bodies i n the C h i l c o t i n r e g i o n 7 The lakes are contained i n the C h i l c o t i n and Cariboo parklands b i o t i c areas (Munro, 1945; Munro and Cowan, 1947) at an e l e v a t i o n of about 1000 meters. The t e r r a i n i s a r o l l i n g savanna-type upland c h a r a c t e r i z e d by Agropyron (bunchgrass) and stands of Populus tremuloides, Pseudotsuga m e n z i e s i i and Pinus c o n t o r t a . The c l i m a t e i s c h a r a c t e r i z e d by r e l a t i v e l y low average annual temperatures (the means f o r January and J u l y at Big o o Creek being -10.6 C and 13.3 C r e s p e c t i v e l y ) , l a r g e f l u c t u a -t i o n s i n seasonal and d a i l y temperatures and low p r e c i p i t a t i o n (12.66 inches at B i g Creek annually) (Scudder and Mann, 1968; Topping, 1971). The lakes are i c e covered from mid October to l a t e A p r i l . 8 B. THE PHYSICAL AND CHEMICAL PROPERTIES OF THE LAKES The water bodies were chosen so as to o b t a i n as wide a range of s a l i n i t y as p o s s i b l e w i t h respect to the occurrence of chironomids. In p a r t i c u l a r , the lake s e r i e s contains the e n t i r e gamut of water chemistry t o l e r a t e d by Chironomus  tentans (Topping, 1971). While s a l i n i t y v a r i e d , the use of t h i s p a r t i c u l a r l a k e s e r i e s kept other environmental para-meters such as p h y s i c a l l o c a t i o n and c l i m a t e as s i m i l a r as p o s s i b l e . In a d d i t i o n , the waters l a c k i n l e t and o u t l e t streams, l a c k f i s h predators and are subject to disturbance by c a t t l e (Scudder, 1969 A). The lakes vary both i n s i z e and c h a r a c t e r ; the l a r g e r , more s a l i n e lakes are g e n e r a l l y dominated by NaHCO^ w h i l e i n the s m a l l e r , f r e s h e r ones MgCO^ p r e v a i l s . This must be con-sid e r e d only a general trend, however, (East Lake i s a r e l a -t i v e l y l a r g e , f r e s h water body w i t h sodium as the dominant c a t i o n w h i l e Near Phalarope i s a much smaller though more s a l i n e l a k e , dominated by the sodium ion) and the chemically prevalent ions are no doubt r e l a t e d to the composition of the un d e r l y i n g rocks r a t h e r than to the s i z e of the water body (Cummings, 1940; Topping, 1969). Some s h o r e l i n e s are r e l a t i v e l y steep and f i r m w h i l e others are very shallow and extremely s o f t . The l a t t e r character seems to be a s s o c i a t e d w i t h c e r t a i n p r o d u c t i v i t y or chemical l e v e l s supporting marginal Scirpus acutus growth (Sorenson Lake, Westwick Lake, Near Phalarope) and heavy 9 concentrations of rooted a q u a t i c s such as Myriophyllum (Rock L., Barkley L . ) , Najas (Sorenson L. , Westwick L.) and Potamogeton (Box 27) (Munro, 1941) ( P l a t e s 1 - 3 ) . From mid-June onwards a l g a l blooms are common i n most l a k e s , e s p e c i a l l y filamentous greens such as Spirogyra and Zygnema i n Sorenson Lake and bluegreens such as Aphanozomenon i n Near Opposite Crescent, L. Jackson, L. Greer and East Lake (P l a t e 4). In the more s a l i n e lakes emergent v e g e t a t i o n i s absent as are heavy a l g a l blooms (P l a t e s 5, 6). These lakes u s u a l l y have r e l a t i v e l y f i r m margins r i n g e d w i t h white s a l t d e p o s i t s ( P l a t e 6). The most s t r i k i n g change i n the fauna between the low and h i g h s a l i n i t y l akes i s the replacement i n the higher s a l i n i t i e s of the v a r i e d amphipod and cladoceran crustacean fauna by great numbers of copepod crustaceans. The general p h y s i c a l and chemical p r o p e r t i e s of the water bodies are shown i n Table I . TABLE 1 The P h y s i c a l and Chemical P r o p e r t i e s of the Lakes. M o d i f i e d from Topping (1969) and Scudder (1969 A). PI CO ga n z po t-1 t-1 w po to G> W o i ro o ro ro 0 o o (u w X ro p> H B n H- c H rr !>r 01 ri ro a 1 7? O t-i rr 3 3 r-* o 3 tl 1 p> Cl ro a ro ro 4^ ro o 01 • f l 3' ro o 3 i 01 3 13 o o ro 7T O c In 3 01 n 01 •a r* t-1 la] on r o ho •o Nl ON 1 Ln CO Ln LO •p- H* Ln Ln CO o 4> ON LO o t LO o o Lo Ui Lo ON •^J CO CO Lo ro O ON CTN o 00 CO LO - J o Ul o CO 4> r o (-* O I-1 h-* 1 r-» t-* r-1 ro to to Ln NO *-J t-* •O LO Lo r-* o •P- ~-j CO ON r-* ON ho to LO 1 4> LO ho ho ro 4> Ul ON j Ul Ul M Lo LO Ln O Ul LO LO Ul ho V S 09 Z pi 09 09 09 09 z p •z » Z m K Z 09 P 1 Z » Z P> Z P n o o o o o EC n o o o EC n n o o 33 O O O O EC O O O O EC n o o o a n o cc n o EC n o W o EC o n o o EC o n o o EC o o o o o o Water Body LO LO Lo LO LO LO Lo Lo Ln O O CO CO ho •P- ui r-1 O ON to •p- ~J o *o •p-•P-CO ON * - -o. o O O O O O O O r-> LO NS Ln O NS t-1 NS -P« t~* 4> LO Ln LO •p-ro LO vD Ln -vj r-1 LO ON h-* •^1 O -0 •P-O LO O O O O O H* VO O O CO NS Co ro NS ON l _ * r-1 NS Ln o vO LO ro -P« o h-' *-J LO -P- ro ro Lo 00 NS O 00 vO 00 LO vO VO LO 4> 00 -P-•P* Ln -p- Ln LO ro ro LO Ln Ln •P* Ln Ln Ln vo LO VO vO ro 00 00 LO LO LO o LO ON •vi <o r-» O MD VO vO VO VO H* O vO VO VO VO VO VO O ^4 r-* NS I-* r-1 H» Ln Ln CO ro ON LO --J CTv 00 00 00 CO 00 00 00 00 03 vO 00 VO VO VO 4> LO ON ON CO VO 4> VO ON o vD ro CO •P* •P* Ln •P- vO t-* ro CO 4> H* r-* Ln ON •vj •P- ro CO vO 4> LO N> 00 LO ro Ln O vO ro o VO ro ro Cn NS ro ro VO o •P-^4 Area (Ha) Mean Depth (m) Max.Depth (m) Main C a t i o n Main Anion Highest Recorded Con-d u c t i v i t y umho/cm Mean Conduc-t i v i t y 0 umho/cm 25 C T.D.S. mg/1 Na meq/1 K meq/1 Ca meq/1 Mg meq/1 co3 meq/1 HCOo meq/1 C l meq/1 S 0 4 meq/1 °2 mg/1 Highest Recorded pH Mean pH Per cent o r g a n i c carbon OT PLATE 1 Box 27, the f r e s h e s t of the l a k e s . Note the extensive mat of emergent Potamogeton natans. A closeup of the v e g e t a t i o n i n Box 27. 11 PLATE 2 A. Barkley Lake, a good example of the shallow, soft-edged type w i t h abundant Myriophyllum. B. Barkley Lake. Myriophyllum sp. 12 PLATE 3 A. Near Phalarope. A lake i n the middle range of s a l i n i t y -c h a r a c t e r i z e d by very s o f t margins and abundant Scirpus acutus. B. Near Opposit Crescent. A shallow, f i r m e r edged lake of medium s a l i n i t y . 13 PLATE 4 Lake Greer, a lake w i t h r a t h e r steep, f i r m margins, growths of Myriophyllum sp. and summer Aphanozomenon blooms. Lake Jackson. Steep, f i r m margins, small stands of Scirpus acutus and very heavy mats of Aphanozomenon. This i s a lake of medium-high s a l i n i t y . 14 PLATE 5 A. Lake Lye. A r i s e i n water l e v e l has k i l l e d the Populus tremuloides stand. B. Round-up Lake. A h i g h s a l i n i t y l ake w i t h a f i r m , g r a v e l l y bottom. No emergent v e g e t a t i o n . Note p r e c i p i t a t e d s a l t s on the shore. 15 PLATE 6 Barnes Lake. The most s a l i n e of the lakes studied. Barnes Lake. The f i r m margin w i t h p r e c i p i t a t e d s a l t s . 16 I l l SPECIES DIVERSITY AND THE CHIRONOMID COMPLEX IN THE LAKE SERIES A. MATERIALS AND METHODS 1. Temperature Records Throughout the summer temperature p r o f i l e s were taken i n the lakes at the mud-water i n t e r f a c e (1 meter) w i t h Ryan D-30 submersible temperature recorders (Ryan Instruments, Inc., S e a t t l e ) . 2. B i o l o g i c a l Sampling Methods a) L a r v a l Sampling At weekly i n t e r v a l s from May 23 to August 29, 1970, d u p l i c a t e l a r v a l samples were taken from each lake (except s i x each i n Westwick Lake and Sorenson Lake) at a depth of one meter. Samples were taken from the 1 meter depth zone since t h i s i s the depth a t which C. tentans i s most abundant. A 15 by 15 cm Ekman dredge was used f o r the sampling. I f the dredge was brought to the surface incompletely c l o s e d the sample was discarded. Samples were then washed and seived through a 0.56 mm mesh screen and the mud and l a r v a e r e t a i n e d were stored i n g l a s s j a r s f o r f u r t h e r s o r t i n g . Since Jonasson (1955) s t a t e s that i t i s the head capsule width of l a r v a l chironomids that determines whether or not they are r e t a i n e d by the mesh, and since Sadler (1935) reported the head capsule diameter of f o u r t h i n s t a r C. tentans ranged 18 from 0.71 to 0.74 mm (my measurements have a mean of 0.76 mm) and that of the t h i r d i n s t a r was l e s s than 0.40 mm (my mean measure i s 0.43), only f o u r t h i n s t a r l a r v a e could be c o l l e c t e d q u a n t i t a t i v e l y . In t h i s study, a l l the species considered i n d e t a i l as l a r v a e have head capsule widths exceeding 0.56 mm i n the f o u r t h i n s t a r . I f populations of a species o c c u r r i n g i n the d i f f e r e n t lakes can be assumed to be composed of the same r e l a t i v e numbers of developmental stages, then i t may a l s o be assumed that the estimates of f o u r t h i n s t a r l a r v a e r e f l e c t the d i f f e r e n c e s i n the abundance of that species i n the l a k e s . For the purpose of e v a l u a t i n g generation time, only an estimate of f o u r t h i n s t a r f l u c t u a t i o n s along w i t h emergence data i s necessary. Q u a n t i t a t i v e a n a l y s i s of bottom fauna i s hindered by the labour i n v o l v e d i n separating the i n s e c t s from the sampled substrate. The us u a l method of e x t r a c t i n g chironomid l a r v a e from mud and dense p l a n t m a t e r i a l i s by the benzene or sugar f l o t a t i o n technique ( S a l t and H o l l i c k , 1944; Anderson, 1951; Mundie, 1957). These methods were considered i m p r a c t i c a b l e f o r one person continuously i n the f i e l d . Mundie (1957) notes that "core sampling would be made much more p r a c t i c a b l e i f the l a r v a e could be q u i c k l y and e f f i c i e n t l y e x t r a c t e d from the mud and counted. P o s s i b l y only treatment of f r e s h cores o f f e r s prospect of t h i s " . Under the circumstances, a n a l y s i s of f r e s h cores presented no problems; p i c k i n g the e a s i l y seen red and green w r i g g l i n g l a r v a e from the c o l l e c t e d samples was no more time consuming and j u s t as e f f i c i e n t as more s o p h i s t i c a t e d 19 treatments of preserved l a r v a e (Pask and Costa, 1971). The sorted l a r v a e i n each sample were preserved i n 70 per cent ethanol. Mundie (1957) s t a t e s that the top 5 cm of mud usually-con t a i n 95 per cent of a l l l a r v a e . I n s p e c t i o n of the dredge samples showed that t h i s s e c t i o n was almost always taken. b) Adult Sampling Pupal and a d u l t midges were q u a n t i t a t i v e l y sampled by emergence t r a p s . Since many of the specimens trapped by t h i s method became wet or damaged, i t was necessary to preserve them i n 70 per cent ethanol. The s o r t i n g of la r g e numbers of a d u l t s and pupae under a d i s s e c t i n g microscope and the pre p a r a t i o n of microscope s l i d e s f o r complete i d e n t i f i c a t i o n of the specimens demand such preserved m a t e r i a l . For these reasons i t was considered most u s e f u l and convenient to preserve trapped m a t e r i a l i n a l c o h o l . This l i n e of reasoning i s f o l l o w e d by Roback (1971) f o r even nett e d a d u l t s , but many workers consider i t important to make i n i t i a l i d e n t i f i c a t i o n s u s i n g pinned specimens (Edwards, 1929) so that wing venation and some s e t a l c o n f i g u r a t i o n s can be more c l e a r l y c h a r a c t e r i z e d . Schlee (1966) and Saether (1969) r a i s e important arguments i n favour of pre-par i n g s l i d e mounted a d u l t specimens. The emergence trap samples were used to i d e n t i f y the chironomids i n h a b i t i n g the one meter depth zone of each l a k e , to c a l c u l a t e the numbers and sequences of i n s e c t s emerging 20 per u n i t area throughout the sampling p e r i o d and to determine the l i f e c y c l e s of the more important species. Two traps were set out i n the one meter depth zone of each la k e w i t h the exception of Sorenson and Westwick Lakes where e i g h t traps were used. The traps were suspended under the water from a wooden cross d r i v e n i n t o the mud. They were emptied every f o u r t h day; care was taken not to d i s t u r b the substrate during the emptying procedure. The t r a p used was a m o d i f i c a t i o n of that designed by Hamilton (1965). E s s e n t i a l l y i t i s a cone of c l e a r acetate p l a s t i c w i t h an e i g h t ounce g l a s s j a r screwed i n t o the apex. Ascending pupae enter the funnel and emerge as a d u l t s i n the a i r space w i t h i n the j a r . The area of the mouth of the trap i s 0.1 square meter (Figure 3; P l a t e 7) (Cannings, 1972). The design i s s i m i l a r to those used by Brundin (1949) and Jonasson (1954) except that metal screening has been replaced by c l e a r p l a s t i c ; t h i s m a t e r i a l makes the trap more transparent and much e a s i e r to c l e a n . For use at one meter these traps seem i d e a l - they are much simpler and cheaper than the deep water models of Mundie (1956), more durable than the simpler cones used by S u b l e t t e and Dendy (1959) and l e s s a f f e c t e d by wind and wave than Corbetfe (1965) f l o a t i n g t r a p s . Mundie (1956, 1957) o u t l i n e s the sources of e r r o r inherent i n the t r a p p i n g method. He s t a t e s that traps may be considered to sample q u a n t i t a t i v e l y i f the i n s e c t s do not avoid them, and PLATE 7 The emergence tra p . The base of o the funnel has an area of 0.1 m . 21 FIGURE 3 D e t a i l s of the emergence tra p . From Cannings (1972). SETTING OF TRAP 2x2 stake ^crossbar supporting 2 traps water level lead weight mouth of trap 12" above bottom 29.5 cm C O N E / TEMPLATE 8oz. jar DETAIL OF COLLECTING JAR small plastic cone bakelite lid hose clamp EXPLODED VIEW OF TRAP extra strips of plastic may be wrapped around cone to prevent cracking supporting cords -air space -water level ends of — \ cords \\~under clamp 23 the catch may be assumed to have come from the bottom d i -r e c t l y below the trap i f water currents do not cause h o r i -z o n t a l movements i n pupal ascents. E f f o r t s were made to make these assumptions v a l i d . Traps were set about a f o o t above the mud i n order to reduce the e f f e c t s of water movements and were cleaned of b a c t e r i a l and a l g a l coatings at each emptying i n order to maintain maximum transparency. No doubt many of the preda-ceous organisms caught i n the traps along w i t h the midges a f f e c t the accuracy of the sample. Species of hydrachnids, zygopterans, n o t o n e c t i d s , c o r i x i d s and d y t i s c i d s were f r e q u e n t l y trapped i n the j a r s . 3. Rearing of Specimens By r e a r i n g a d u l t f l i e s from l a r v a e a l l three stages of the l i f e c y c l e can be i d e n t i f i e d . Complete i d e n t i f i c a t i o n i s i n v a l u a b l e since i t i s f r e q u e n t l y impossible to determine l a r v a e past the generic l e v e l whereas male a d u l t s can u s u a l l y be iden-t i f i e d to species. Fourth i n s t a r l a r v a e were placed i n i n d i v i d u a l screen-covered v i a l s or p e t r i e dishes c o n t a i n i n g d e c h l o r i n a t e d water, shredded Scott t i s s u e paper f o r tube c o n s t r u c t i o n , and small amounts of food i n the form of n e t t l e l e a f powder and powdered m i l k . The containers were kept at room temperature i n a l i g h t regime of 16 hours l i g h t , 8 hours dark. Rearing success im-proved g r e a t l y i f the water was continuously aerated. 24 4. P r e p a r a t i o n and I d e n t i f i c a t i o n of Specimens The l a r v a e were sorted under a d i s s e c t i n g microscope and were d i v i d e d i n t o groups of apparent s p e c i f i c and i n s t a r ranks. The volume displacement of each wet sample was taken as a rough measure of chironomid biomass. A d u l t samples were t r e a t e d i n the same manner; males, females and pupae being considered separately. Permanent mounts of r e p r e s e n t a t i v e specimens were then made on microscope s l i d e s i n order that p o s i t i v e i d e n t i f i c a t i o n of the sorted types could be made. The method f o l l o w e d that of Schlee (1966) and Saether (1969). I d e n t i f i c a t i o n f o l l o w e d Edwards (1929), Townes (1945), Sublette (1960, 1963, 1964, 1967, 1970) and Roback (1971). Further determinations and crosschecking were performed by Dr. D.R. O l i v e r (Ottawa) and Dr. J.E. S u b l e t t e (Eastern New Mexico U n i v e r s i t y ) . The nomenclature f o l l o w s Sublette and S u b l e t t e (1965) and a d d i t i o n s and r e v i s i o n s i n subsequent Sublette papers and Roback (1971). A f t e r the i d e n t i f i c a t i o n s were completed the c o l l e c t i o n s were sorted and counted a second time. E r r o r s due to i n c o r r e c t i d e n t i f i c a t i o n of specimens and miscounting were thus minimized. 5. A n a l y s i s of the Data a) The U.B.C. TRIP (Tr i a n g u l a r Regression Package) program ( B j e r r i n g and Seagreaves, 1972) was used to compute c o r r e l a t i o n c o e f f i c i e n t s between s e l e c t e d v a r i a b l e s . The Kendall rank c o r r e l a t i o n a n a l y s i s ( S i e g e l , 1956) was employed i n the few 25 c o r r e l a t i o n s u s i n g o r d i n a l measurement. These were cor-r e l a t i o n s u s i n g emergence d i s p e r s i o n as a v a r i a b l e . b) For each lake a monthly and t o t a l average species d i v e r s i t y index was c a l c u l a t e d . The f u n c t i o n used i s the entropy formula as a p p l i e d to informat i o n a n a l y s i s (Khinchin, 1957; Margalef, 1968). The use of t h i s f u n c t i o n f o r e s t i m a t i n g species d i v e r s i t y i n ecosystems has been widespread (MacArthur and MacArthur, 1961; L a r k i n et a l , 1970; Johnson and B r i n k h u r s t , 1971). 6. Storage of the Data f o r Further Study The b a s i c data c o l l e c t e d i n t h i s study, i n c l u d i n g computer programs and sp e c i m e n . c o l l e c t i o n s , have been f i l e d f o r f u t u r e use i n the Spencer Entomology Museum, Department of Zoology, U.B.C. 26 B. RESULTS 1. Water Temperatures i n the Lake S e r i e s The temperature at the mud-water i n t e r f a c e (1 meter) i n the lakes i s shown i n Table I I and temperature p r o f i l e s f o r f i v e of the s i x C. tentans lakes under c o n s i d e r a t i o n are found i n F i g u r e 4. Sorenson Lake records are incomplete. A l l the temperature trends are s i m i l a r i n the l a k e s , the major d i f f e r e n c e among them being the v a r i a t i o n i n the d a i l y temper-ature ranges. The d i f f e r e n c e i n d a i l y temperature f l u c t u a t i o n between two lakes such as East Lake and Lake Jackson and two other lakes such as Westwick Lake and Barkley Lake might be a t t r i b u t e d to heavy Aphanozomenon (Cyanophyceae) blooms over the 1 meter depth zone i n the former water bodies throughout a l l but the e a r l y p a r t of the study p e r i o d . Such a l g a l mats may prevent r a p i d d i u r n a l temperature f l u c t u a t i o n s i n the water. Table I I shows that the mean temperature over a l l the lakes during the p e r i o d was 17.8°C. The mean temperature of a l l but three of the lakes was w i t h i n 1°C of t h i s value. The highest temperature reached was 31°C i n L. Jackson on J u l y 13. The range of water temperature on t h i s date was 15°C! (Figure 4). Cumulative day degrees f o r the s i x lakes are graphed i n Figure 5. In the case of Sorenson L. the curve up to May 18 i s that of Westwick L., chosen since the r e s t of the slope i s i d e n t i c a l i n the two lak e s . These p l o t s represent mean temper-at u r e s . From these graphs the number of day degrees that have accumulated between any two dates may be read. Since the TABLE I I Average water temperatures i n the lak e s e r i e s . Temperatures at the mud-water i n t e r f a c e (1970). WATER BODY MAY JUNE JULY AUGUST SUMMER mean mean mean mean mean Barnes L. 12. 6 19. 2 21. 0 18. 3 19. 8 Round-up L. 12. 0 18. 9 20. 0 19. 5 17. 6 L. Lye 13. ,1 19. 4 20. 1 19. 2 18. 0 Boitano L. 13. 3 18. 6 19. ,8 19. 2 17. 7 L. Jackson 12. ,8 1.9. 4 20. ,1 19. 0 17. ,8 L. Greer 12. ,8 18. 6 19. 7 18. 9 17. ,5 Rock L. 13. ,0 18. 3 18. ,5 18. 3 17. ,0 Near Phalarope 10. .5 16. ,4 18. ,2 17. 2 15. ,6 Westwick L. 13. .5 20. ,1 21. ,1 19. 3 18. 5 Sorenson L. 14. ,9 18. ,5 18. .1 17. 8 17. ,3 Near Op. Crescent 12. ,7 19. ,7 20. .5 19. 6 18. ,1 Box 17 13. .2 19. ,1 20. .1 19. 1 17. .9 Barkley L. 14. ,9 19. ,4 21. ,2 18. 3 18. ,4 East L. 12. ,0 17. .9 18. ,9 18. 3 16. ,8 Box 27 15. .3 20. ,2 20. .4 19. 8 18. .9 FIGURE 4 D a i l y temperature range i n some of the l a k e s where Chironomus tentans i s abundant. L. Jackson Rock L FIGURE 5 Cumulative day degrees measured at the mud surface at a depth of 1 meter i n some of the lakes where Chironomus tentans i s abundant. 29 30 generation time of a species i s considered to be a f u n c t i o n of the benthic temperatures (Mundie, 1957), species can be c h a r a c t e r i z e d by the number of day degrees needed to complete t h e i r development. 2. Chemical Data P h y s i c a l and chemical data other than temperature are from Topping (1969) and Scudder (1969 A) (Table I ) . These data represent inform a t i o n gathered from surface waters or at a depth of 1 meter averaged over the summer sampling period. As seasonal v a r i a t i o n i n the physico-chemical p r o p e r t i e s i s l e s s pronounced than are the d i f f e r e n c e s between lakes (Topping, 1969) and as the c o n c e n t r a t i o n data agree f a v o r a b l y w i t h the ten year averages (Scudder, 1969 B; Scudder, pers. comm.), i t was f e l t that the use of these data i n subsequent phases of the work would not adversely a f f e c t the r e s u l t s of the i n v e s t i -g a t i o n . For d e t a i l s on the c o l l e c t i o n and a n a l y s i s of these data, and f o r a more comprehensive d i s c u s s i o n of the p h y s i c a l and chemical p r o p e r t i e s of the l a k e s , see Topping (1969). 3. The Occurrence of Species i n the Lakes Table I I I shows the d i s t r i b u t i o n of species c o l l e c t e d at a depth of 1 meter i n the l a k e s . This should be considered only a p r e l i m i n a r y l i s t of the chironomid fauna of t h i s depth zone. A d u l t s r e p r e s e n t i n g 34 species, 15 genera and 3 sub-f a m i l i e s were trapped and are l i s t e d i n Figure 27 along w i t h TABLE I I I The d i s t r i b u t i o n of chironomids i n the one meter depth zone i n the la k e s . Both a d u l t s and i d e n t i f i e d l a r v a e are inclu d e d . Calopscctra holochlorus Calopsectra gracilenta Polypedilum n.sp. Glyptotendipes barbipes nigricans 1 Endochironoraus Cryptotendipes ariel Cryptochironomus psittacinus Einfeldia pagana Chironomus n.sp. Chironomus n.sp. (near atritibia) Chironomus plumosus Chironomus tentans Chironomus. atrella Chironomus anthracinus Psectrocladius n.sp; Psectrocladius zetterstedti Psectrocladius barbimanus Acricotopus nitidellus Cricotopus trifasciatus Cricotopus .flavibasis Cricotopus albanus Nanocladius n.sp. Ablabesmyia peleensis Procladius n.sp. Procladius sublettei Procladius clavus Procladius dentus Procladius ruris Procladius freemani Procladius nietus Procladius bellus Derotanypus n.sp. Derotanypus alaskensis Tanypus punctipennis o a 9 o • • • • • • • • Barnes L. e o e a o o • • • e a e e Round-up L. • • o • • • o • • • • • • • L. Lye « • • • • • • • • • • • • • • • B o i t a n o L. • • • • • e « a L. Jackson e e o • • e • • • L. Greer • • o • • • • e • a • a Rock L. • • • • • • 0 • Nr.Phalarope e o e • . • • • • • • Westwick L. -• • a • • e • • • • • • a Sorenson L. • a • • a • • e Nr.Op.Crescent • • • e • • • • • • • a Box 17 e a • • e • s • • • • • • e B a r k l e y L. • o a • 6 • • • • • • a E a s t L. e a • • • • • a a Box 27 TABLE IV The d i s t r i b u t i o n of l a r v a e u n i d e n t i f i e d to species. Calopsectra gracilenta ? Tanytarsus sp.B Tanytarsus sp.A Polypedilum sp. Parachironomus sp1. Glyptotendipes sp.B Glyptotendipes sp.A Endochironomus sp. Cryptocladopelma sp. Cryptotendipes ? Cryptochironomus sp. Chironomus sp.E Chironomus sp.D Chironomus sp.C Chironomus sp.B Chironomus sp.A. Chaetolabis sp.B Chaetolabis sp.A Cricotopus ? Ablasbesmyia 1 Procladius sp.B Procladius sp.A Psectrotanypus sp.C Psectrotanypus sp.B Psectrotanypus sp.A Tanypus sp. Clinotanypus sp. 0 0 e © 0 e 0 b » Barnes L. e i © © o e e 0 0 Round-up L. ! o 0 a o o o o o L. Lye e o © a e e 0 o e Boitano L. • a 0 0 0 0 o L. Jackson e O e « e « © 0 L. Greer r " ! 1 e o e 0 e 0 o Rock L. • 9 0 0 o 0 ' 0 0 0 0 Nr. Phalarope 0 0 e 8 e o 0 o Westwick L. 0 • 0 e o a 0 o 0 Sorenson L. o • o • 0 0 o 0 0 o Nr. Op.Crescent o e e 0 0 e Box 17 e o • • e 0 o 0 o o 0 0 0 Barkley L. 0 • 0 « 0 0 0 0 0 0 0 0 0 0 0 East L. e 0 e o 0 0 0 0 0 Box 27 33 t h e i r range of s a l i n i t y t o l e r a n c e . Twelve a d u l t s were a s s o c i a t e d w i t h t h e i r l a r v a l forms. Other t e n t a t i v e species of l a r v a e i d e n t i f i e d to genus are l i s t e d i n Table IV. 4. Species Considered i n D e t a i l In order to define major d i f f e r e n c e s i n the chironomid communities of the lakes i n t h i s s a l i n e s e r i e s , a number of the more d i s t i n c t i v e species are considered i n some d e t a i l . These are P r o c l a d i u s b e l l u s , P r o c l a d i u s freemani, P r o c l a d i u s  dentus, P r o c l a d i u s c l a v u s , Ablabesmyia p e l e e n s i s , Cricotopus  f l a v i b a s i s , Cricotopus albanus, P s e c t r o c l a d i u s barbimanus, Cryptotendipes a r i e l , C alopsectra g r a c i l e n t a , Derotanypus  a l a s k e n s i s , E i n f e l d i a pagana, Glyptotendipes barbipes, Chironomus anthracinus, Chironomus n. sp. and Chironomus tentans. The f i r s t ten species w i l l be discussed p r i m a r i l y w i t h reference to chemical environmental f a c t o r s and w i l l form a b a s i s f o r d i s c u s s i o n of the lake s e r i e s as a gradient of environmental c o n d i t i o n s . The next f i v e species w i l l be con-sid e r e d i n a s i m i l a r manner although b i o t i c f a c t o r s w i l l a l s o be s t r e s s e d . These are the species which p o t e n t i a l l y have the g r e a t e s t i n t e r a c t i o n w i t h C. tentans. C. tentans i s then described w i t h reference to the lake s e r i e s and the i n t e r a c t i o n s w i t h other species that may i n f l u e n c e i t s mode of l i f e . a) P r o c l a d i u s b e l l u s This i s a widespread but not abundant species. The species 34 i s known only from trapped a d u l t s , since the l a r v a e of the l a r g e P r o c l a d i u s genus were found to be l a r g e l y inseparable. The species emerges i n r e l a t i v e l y small numbers ( u s u a l l y l e s s than 10 per square meter) i n a l l lakes i t occurs i n except i n East L. and Box 27 where concerted emergence over a two week pe r i o d amounted to 40 and 180 per square meter r e s p e c t i v e l y (Figure 6). In a l l cases the emergence p e r i o d i s from l a t e May to mid June. P. b e l l u s appears to have only one genera-t i o n , although i n Box 27 two peaks 24 days apart may i n d i c a t e a second generation l a t e i n June. Buckley and S u b l e t t e (1963) and S u b l e t t e (1963) note that P. b e l l u s i s very w i d e l y spread i n North America and tends to be a profundal dweller. S u b l e t t e (1957) found i t reasonably abundant from 3 to 15 meters i n Lake Texoma. Most authors s t a t e that P. b e l l u s emerges from A p r i l or May to September or October w i t h one generation concentrated i n a s p r i n g emergence (S u b l e t t e , 1957). Judd, i n three separate stud i e s (Judd, 1953; 1957; 1961) agrees w i t h t h i s although i n one of h i s emergence s t u d i e s , P. b e l l u s showed two generations, one peak coming on May 30, the second on August 13 (Judd, 1961). P. b e l l u s i s much more abundant i n the f r e s h e r waters of the s e r i e s (Figure 6), being l e s s f r e q u e n t l y found i n waters above a c o n d u c t i v i t y of 800 jumho/cm (Near Opposite Crescent). Small emergences occur i n Westwick, Rock, Jackson and Round-up Lakes. The abundance of P. b e l l u s i s n e g a t i v e l y c o r r e l a t e d w i t h a l l i n d i c a t o r s of c o n c e n t r a t i o n , showing a decided preference f o r low pH values (a c o r r e l a t i o n c o e f f i c i e n t of -.937) (Table V). FIGURE 6 The emergence of a d u l t s of P r o c l a d i u s  b e l l u s (Loew) and P r o c l a d i u s freemani S u b l e t t e from the one meter depth zone of s e v e r a l l a k e s . The or d i n a t e i s a l o g a r i t h m i c s c a l e . C o l l e c t i n g began on May 19, took place every f o u r t h day and terminated on August 29, 1970. PROCLADIUS BELLUS EAST L. BOX 27 M " J ' J ' A ' ' M " 1 J " ' J ' A J  PROCLADIUS FREEMANI ROUND-UP L. L. LYE BOITANO L. M • J ' J ' A ' ' M ' J ' J A ' ' M ' J ' J ' 10 J ROCK L. BARKLEY L. EAST L. M A M A M 36 The only previous record of t h i s species i n B r i t i s h Columbia i s from Cranbrook (Roback, 1971). Further d i s c u s -s i o n of general d i s t r i b u t i o n and ecology of the species may be found i n Wurtz and Roback (1955), Morrissey (1950) and Davis (1960). b) P r o c l a d i u s freemani This m o r p h o l o g i c a l l y v a r i a b l e species can t o l e r a t e most environmental c o n d i t i o n s found i n the lakes (Table V) although i t i s most abundant i n the upper s a l i n i t i e s where i t s emergence d i s p l a y s s t r i k i n g d i f f e r e n c e s among the lakes (Figure 6). In Barnes L. there i s a small emergence of 4 per square meter i n l a t e May; i n Round-up L. a l a r g e r emergence at t h i s time i s f o l l o w e d by another i n e a r l y August. This l a t t e r p a t t e r n i s repeated i n L. Lye.with the a d d i t i o n of a s u b s t a n t i a l l a t e June-early J u l y emergence of 30 per square meter over 20 days. The one emergence peak i n Boitano L. i s as i n Barnes L. ( l a t e May) but i s much l a r g e r , c o n s i s t i n g of 75 per square meter. In Rock Lake, a l a r g e , s i n g l e peak of emergence occurs i n l a t e June-early J u l y . East Lake, the only r e l a t i v e l y f r e s h waterbody supporting l a r g e numbers of emerg-i n g P. freemani has a peak i n l a t e May and one i n l a t e J u l y . Box 17 and Greer L. show s m a l l , s i n g l e peaks i n the June-July p e r i o d ; Near Opposite Crescent and Barkley L. i n e a r l y August. Thus i t i s seen that P. Freemani emerges at three times during the sampling p e r i o d : l a t e May, l a t e June-early J u l y and e a r l y FIGURE 7 The emergence of a d u l t s of P r o c l a d i u s  dentus Roback from the one meter depth zone of s e v e r a l l a k e s . The ordinate i s a l o g a r i t h m i c s c a l e . C o l l e c t i n g began on May 19, took place every f o u r t h day, and terminated on August 29, 1970. 37 BARNES L. ROUND-UP L. L. LYE 100 cc Ul p-ui 5 in ec < o to cc Ul a . Z (3 CC Ul £ Ul 10 J 1 1 1 I 1 1 1 I "~1 1 I I M J J A M J J A M J J A BOITANO L. WESTWICK L. EAST L. 100 q 3 a < u. O cc Ul CO Z 10 M M r J J A M A 38 August. Every combination of these emergence times i s recorded except f o r the sequence of June-July, e a r l y August. Why there i s such d i s p a r i t y between the l i f e c y c l e s i n each lake i s not e a s i l y understood; no doubt i t i s best explained as the r e s u l t of v a r i a t i o n i n the i n s e c t s or the l a k e s . The species has seldom been c o l l e c t e d at the e x t r e m i t i e s of i t s range. The only a v a i l a b l e r e cord from B r i t i s h Columbia i s a s e r i e s of three males from Terrace (Roback, 1971). c) P r o c l a d i u s dentus This d i s t i n c t i v e species has not been p r e v i o u s l y reported i n B r i t i s h Columbia (Roback, 1971). In a l l the lakes i n which i t occurs i n t h i s study, P. dentus has a s i n g l e generation emerging i n l a t e May (Figure 7). I t has a preference f o r the more s a l i n e l a k e s ( c o n d u c t i v i t y above 4000 jumho/cm) such as Boitano L., L. Lye, Round-up L. and Barnes L. The abundance of P. dentus i s h i g h l y c o r r e l a t e d w i t h c o n d u c t i v i t y (p<,.01), t o t a l d i s s o l v e d s o l i d s (p<.05), sodium (p<.05), HCO3 (p<.05) and S 0 4 (p < .01) (Table V). d) P r o c l a d i u s clavus This i s a r e c e n t l y described species (Roback, 1971) and i s recorded p r e v i o u s l y only from the Northwest T e r r i t o r i e s . There i s no doubt that P. clavus i s the most abundant species of the genus i n the l a k e s . Although i t i s r e s t r i c t e d to 39 Boitano L., L. Lye, Round-up L. and Barnes L., P. clavus i s very abundant. In Barnes L. most of the P r o c l a d i u s l a r v a e are probably of t h i s species, making i t the dominant chironomid predator of that l a k e . P. clavus has a l i f e c y c l e c h a r a c t e r i z e d by an extended emergence p e r i o d occupying the e n t i r e month of June and the f i r s t week i n J u l y . The emergence i n t h i s p e r i o d amounts to about 345 per square meter (Figure 8). The emergence i n Round-up L. i s a l i t t l e l e s s concerted and i n L. Lye a second peak appears l a s t i n g from l a t e J u l y to the end of August. The emergence i n Boitano L. occurs i n the June-July p e r i o d , but i s much smaller i n s i z e . The s i g n i f i c a n c e of the second emergence peak i n L. Lye i s not known. The b a s i c p a t t e r n i n the other lakes suggests that a l a r g e emergence of a d u l t s developing from ov e r w i n t e r i n g l a r v a e produce a new generation of l a r v a e that overwinter, but which may emerge e a r l y (L. Lye) depending on the c o n d i t i o n s i n the l a k e s . A l t e r n a t i v e l y , t h i s second emergence may be a r e s u l t of p a r t of the overwintering l a r v a l p o p u l a t i o n extending diapause, or even the occurrence of a l t e r n a t i n g generations. At any r a t e i t i s evident that P. clavus i s an important member of the more s a l i n e environment, and seems e n t i r e l y adapted to the sodium carbonate-bicarbonate l a k e type. Table V shows the h i g h l y s i g n i f i c a n t c o r r e l a t i o n (p < .01) of abundance w i t h c o n d u c t i v i t y , T.D.S., sodium, CO^ and HCO3. FIGURE 8 The emergence of a d u l t s of P r o c l a d i u s  clavus Roback and Ablabesmyia p e l e e n s i s (Whalley) from the one meter depth zone of s e v e r a l l a k e s . The o r d i n a t e i s a l o g a r i t h m i c s c a l e . C o l l e c t i n g began on May 19, took place on every f o u r t h day and terminated on August 29, 1970. 40 PROCLADIUS CLAVUS BARNES L. ROUND-UP L. L LYE 100 q 10: CC UJ H LU s LU CC < => (0 100 g CC LU a a z o I 10 d LU w b a < LL. o cc LU OQ | 100 q z M M BOITANO L. M J J A ABLABESMYIA PELEENSIS M J J A BARKLEY L. EAST L. BOX 27 10 J -i i 1 • — i 1 1 i r 1 -I-* 1 M J J A M J J A M J J A 41 e) Ablabesmyia p e l e e n s i s This i s an uncommon, but d i s t i n c t i v e i n h a b i t a n t of the fr e s h e r l a k e s . I t appears to have two generations i n the very f r e s h waters of Box 27 ( c o n d u c t i v i t y 40 jumho/cm), one i n l a t e May-early June (30 per square meter) and one i n July-August (Figure 8). In the most s a l i n e waters of i t s range (Barkley L., 600-700 umho/cm), Ablabesmyia p e l e e n s i s has only one emergence peak i n J u l y , w h i l e i n East L. the peak i s i n the l a t e May-June pe r i o d . The abundance of A. pe l e e n s i s i s n e g a t i v e l y c o r r e l a t e d w i t h a l l environmental f a c t o r s except d i s s s o l v e d oxygen and e s p e c i a l l y shows a d e f i n i t e r e c i p r o c a l r e l a t i o n s h i p w i t h pH (r= -.938; p < .01) (Table V). Roback (1969) describes the food of the l a r v a e . This species has not p r e v i o u s l y been recorded from B r i t i s h Columbia (Roback, 1971). f ) Cricotopus f l a v i b a s i s This common species of the O r t h o c l a d i i n a e reaches i t s g r e a t e s t abundance i n East L., but i s found i n most lakes up to a c o n d u c t i v i t y of about 7000 umho/cm (Round-up L . ) . I t i s the species determined i n Cannings (1970) as P s e c t r o c l a d i u s  f l a v u s , and i s a denizen of aquatic p l a n t s . The pau c i t y of t h i s species i n benthic samples i n the present study f u r t h e r confirms that t h i s species occurs on aquatic v e g e t a t i o n . The f a c t that the O r t h o c l a d i i n a e (without haemoglobin) are considered to be the group most s e n s i t i v e to oxygen d e f i c i e n c y (Brundin, 1951; Buck, 1953) and t h e i r r e s u l t i n g occurrence near the surface 42 provides a p o s s i b l e reason f o r the absence of t h i s subfamily i n benthic samples and the appearance of l a r v a e i n the emergence t r a p s . Cricotopus f l a v i b a s i s has two generations, one emerging i n l a t e May, the other appearing as a d u l t s i n l a t e June-July. This second generation i s most d i s t i n c t i n East L. and Near Phalarope (Figure 9). In the two lakes r e p r e s e n t i n g the upper ranges of i t s s a l i n i t y t o l e r a n c e (Round-up L. and L. L y e ) , C. f l a v i b a s i s has another emergence peak from mid to l a t e August (Figure 9). This emergence does not appear i n f r e s h e r l a k e s ; whether or not i t i s a r e s u l t of adaptation to high s a l i n i t i e s i n the l a t e summer i s not c l e a r . There i s a great p a u c i t y of records f o r C. f l a v i b a s i s i n the l i t e r a t u r e . The only record a v a i l a b l e i s that of Malloch (1915) who described the species from I l l i n o i s . Thus i t seems C. f l a v i b a s i s i s new to at l e a s t B.C. and perhaps Canada. g) Cricotopus albanus This very small species was c o l l e c t e d only i n the four lakes having c o n d u c t i v i t i e s l e s s than 800 ^imho/cm (Box 17, Barkley L., East L. and Box 27). This d i s t r i b u t i o n , however, seems to be more c l o s e l y a s s o c i a t e d w i t h low pH; the cor-r e l a t i o n i s h i g h l y s i g n i f i c a n t (p<.01), r being -.900 (Table V). C o r r e l a t i o n s w i t h a l l other s o l u t e s and measures of s a l i n i t y are not s i g n i f i c a n t , but are negative i n s i g n . FIGURE 9 The emergence of a d u l t s of Cricotopus  f l a v i b a s i s Malloch and Cricotopus  albanus Curran from the one meter depth zone of s e v e r a l l a k e s . The or d i n a t e i s a l o g a r i t h m i c s c a l e . C o l l e c t i n g began on May 19, took place every f o u r t h day and terminated on August 29, 1970. 43 100 10 LU UJ ROUND-UP L. BOITANO L. NEAR PHALAROPE LU cc < o CO cc LU Q. O z o CC LU 2 LU (/) b ZD a < o cc LU ca 100 10 J 10 1 EAST L. 100 q BOX 17 CRICOTOPUS FLAVIBASIS / CRICOTOPUS ALBANUS BOX 27 T 1 1 BARKLEY L. EAST L. * i i i 1 1— 1 1 r ~i 1 M J J A M J J A M J J A 44 Emergence i s v a r i a b l e . In Box 27 there i s a main emergence i n l a t e May and another peak i n mid June. In East L. a s i n g l e peak i n l a t e June-early J u l y occurs. As the s a l i n i t y increases emergence s h i f t s to l a t e r i n the summer (Figure 9). This i s e x e m p l i f i e d by a small emer-gence i n mid J u l y i n Barkley L. and a s i m i l a r peak i n Box 17 fo l l o w e d by a much l a r g e r capture of a d u l t s i n l a t e August. Only one re c o r d (Curran, 1929) of t h i s species i s reported f o r Canada. h) P s e c t r o c l a d i u s barbimanus This i s the most common of the O r t h o c l a d i i n a e i n the lake s e r i e s . I t v a r i e s i n s i z e and c o l o r a t i o n and i s n o t o r i o u s l y v a r i a b l e i n other morphological f e a t u r e s (Wulker, 1956; Saether, 1967). P. barbimanus corresponds to P s e c t r o c l a d i u s sp. B mentioned i n Cannings (1970). Larvae were found i n benthic samples, but much l a r g e r numbers were captured i n the emergence traps along w i t h pupae and a d u l t s . This species, e s p e c i a l l y i n L. Lye, h a b i t u a l l y b u i l t t h i n mud tubes on the sides of the emergence t r a p s . The l i f e c y c l e appears to c o n s i s t of a s i n g l e generation emerging i n l a t e May, although there are enough exceptions where a mid J u l y emergence appears (East L., Barkley L., Near Phalarope, Boitano L.) to cas t doubt on the idea of a s i n g l e generation (Figure 10). Indeed, the l a t e r emergence i n Boitano L. i s s u f f i c i e n t l y l a r g e to foreshadow the immense FIGURE 10 The emergence of a d u l t s of P s e c t r o c l a d i u s barbimanus (Edwards) from the one meter depth zone of s e v e r a l l a k e s . The or d i n a t e i s a l o g a r i t h m i c s c a l e . C o l l e c t i n g began on May 19, took place every f o u r t h day and terminated on August 29, 1970. i 45 100 q ROUND-UP L. L. LYE BOITANO L. cc ui LU LU CC < O w cc LU a. O z o cc LU s LU CO b Q < U. O CC LU 03 10 , , , ^ . v . r r-*-" n 1 L. JACKSON L. GREER BARKLEY L. 100 a 3 Z 10 J M M M 46 emergences i n l a t e J u l y and August from L. Lye and Round-up L. (Figure 10). This July-August emergence i n L. Lye represents a t o t a l of about 190 a d u l t s emerging per square meter. The histograms i n d i c a t e that i n the more s a l i n e h a b i t a t s P. barbimanus i s more abundant and tends to emerge l a t e r i n the summer. I t appears that i n some l a k e s two generations may occur. That increased s a l i n i t y i s a s s o c i a t e d w i t h a l e s s synchronized emergence i s evident from the s i g n i f i c a n t (p<.01) c o r r e l a t i o n (Table V I ) . P s e c t r o c l a d i u s barbimanus has been reported only once before i n North America. A.L. Hamilton c o l l e c t e d 5 males and pupal exuviae (Houghton, Sask., May 5, 1967) from a s a l i n e p r a i r i e slough of s p e c i f i c c o n d u c t i v i t y 2300 |imhos a t 7.4°C (Saether, 1969). This represents an equivalent reading of about 3400 jumhos at 25°C, or approximately the c o n d u c t i v i t y of L. Jackson or Boitano L. Mundie (1957) r e p o r t s P. barbimanus as an uncommon emerger from the 1 to 3 meter zone.from l a t e A p r i l to l a t e May i n Kempton Park East R e s e r v o i r , London. i ) Cryptotendipes a r i e l This i s a species described by Sublette (1960) from C a l i f o r n i a n m a t e r i a l . As f a r as can be e s t a b l i s h e d , i t has not been reporte d elsewhere. C. a r i e l i s r e s t r i c t e d to the four most s a l i n e lakes i n the s e r i e s ( c o n d u c t i v i t y '> 4000 umho/cm) (Figure 11). In a l l but Barnes L. there are two generations, one emerging i n l a t e May-early June, the other i n FIGURE 11 The emergence of a d u l t s of Cryptotendipes a r i e l ( Sublette) and Calopsectra g r a c i l e n t a (Holmgren) from the one meter depth zone of s e v e r a l l a k e s . The ordinate i s a l o g a r i t h m i c s c a l e . C o l l e c t i n g began on May 19, took place every f o u r t h day and terminated on August 29, 1970. 47 100 : 10 : CC LU 1 UJ 2 Ul cc < o 30 <n cc LU a 10 _ o z -C5 CC LU -LU <n 1 H _ i Q < LL o 400 -rr -LU CD NU 100 z 10: BARNES L BOITANO L. ROUND-UP L. ROUND-UP L 1 r CRYPTOTENDIPES / ARIEL / / CALOPSECTRA / GRACILENTA L. LYE M i M J J A L. LYE BARNES L. BOITANO L — r — 1 1 M J J A 48 August. The numbers i n Boitano L. and L. Lye are sm a l l , but i n Round-up L. a very l a r g e emergence (500 per square meter) appears i n l a t e J u l y through August a f t e r a small (overwinter-ing population) a d u l t emergence i n May. In Barnes L. the August emergence i s completely l a c k i n g and the considerable l a t e May emergence c a r r i e s over w e l l i n t o June. Table VI shows the tendency of the emergence p a t t e r n to spread over a longer p e r i o d as the c o n d u c t i v i t y increases (r= .914 ; p < .01). The p o s s i b i l i t y e x i s t s that the i n c r e a s i n g s a l i n i t y of Barnes L. during the summer evaporation p e r i o d prevents the l a r v a e of the summer generation from developing r a p i d l y enough to emerge before September. j ) Calopsectra g r a c i l e n t a This species of the o l d Tanytarsus ( s e n s . l a t . ) genus i s the most abundant species c o l l e c t e d i n the tra p s . The l a t e May-early June emergence i n Boitano L. alone reached a den s i t y of about 1000 per square meter (Figure 11). In L. Lye there i s a maximum of three generations, the emergences i n c r e a s i n g i n s i z e as the season progresses. In Boitano L. only a s l i g h t emergence occurs i n e a r l y J u l y a f t e r the major May emergence. In Round-up L., C. g r a c i l e n t a repeats the L. Lye p a t t e r n w i t h -out the June-July emergence. In Barnes L. the numbers are very s m a l l , only 12 per square meter emerging i n very l a t e June. C. g r a c i l e n t a i s a circumpolar species, i n North America being reported only from Ellesmere I s l a n d ( O l i v e r , 1963), 49 B a f f i n I s l a n d ( O l i v e r , 1964) and E l l e f Ringes I s l a n d (McAlpine, 1964). The species i s a l s o known from c o n t i n e n t a l and a r c t i c Europe (Lindeberg, 1968). In F i n l a n d i t has been taken from the Gulf of Bothnia i n shallow b r a c k i s h water (3-4 °/oo) but has not been c o l l e c t e d a t Tvarminne (6 °/oo) (Lindeberg, 1968). For comparison, Barnes L. has a s a l i n i t y of 10 u / oo, so that i t appears C. g r a c i l e n t a can i n h a b i t waters more s a l i n e (and probably warmer) than p r e v i o u s l y reported. Lindeberg (1968) a l s o r e p o r t s an I c e l a n d i c population w i t h a J u l y emergence peak. k) Derotanypus a l a s k e n s i s This i s a very widespread b o r e a l species. Roback (1971) gives no B.C. records although h i s map i n d i c a t e s the range probably extends over the northern h a l f of the province. This i s the dominant macropelopian i n the lake s e r i e s and probably represents a l a r g e p a r t of the predaceous chironomid fauna. In the lake s e r i e s D. a l a s k e n s i s has been found i n a l l lakes although emergence was not recorded i n Barnes L. or Box 27. In a l l the lakes except Sorenson L. there i s a l a t e May emergence (Figures 12, 13). A very small emergence i n l a t e J u l y - e a r l y August i n Sorenson L. i s accompanied by a drop i n the f o u r t h i n s t a r l a r v a l numbers from 400 to 200 per square meter. The l a c k of f o u r t h i n s t a r l a r v a e i n l a t e May i n d i c a t e s t h a t a May emergence probably occurred i n Sorenson Lake, but took place before May 19th when the traps were put i n place. FIGURE 12 L a r v a l abundance and a d u l t emergence of Derotanypus a l a s k e n s i s (Malloch) i n L. Lye, Boitano L. and L. Jackson. A. T h i r d ( ) and f o u r t h ( ) i n s t a r numbers per square meter at weekly i n t e r v a l s . B. Ad u l t emergence: numbers per square meter taken every f o u r t h day. C. The percentage of the t o t a l l a r v a l chironomid population represented by D. a l a s k e n s i s l a r v a e . o FIGURE 13 L a r v a l abundance and a d u l t emergence of Derotanypus a l a s k e n s i s (Malloch) i n Rock L., Sorenson L. and East L. A. T h i r d ( ) and f o u r t h ( ) i n s t a r numbers per square meter at weekly i n t e r v a l s . B. Adult emergence: numbers per square meter taken every f o u r t h day. C. The percentage of the t o t a l l a r v a l chironomid p o p u l a t i o n represented by D.alaskensis l a r v a e . 52 The overwintering f o u r t h i n s t a r l a r v a e are no doubt accounted f o r by t h i s u s u a l l y l a r g e emergence i n l a t e May. In the more s a l i n e lakes (Figure 12) there i s an even l a r g e r emergence l a t e r i n the summer. This represents 100 per square meter i n L. Jackson from June 21 to J u l y 27. The second generation emergence i s delayed i n the higher s a l i n i t i e s perhaps owing to c o n c e n t r a t i o n increases as the summer progresses. The s i t u a t i o n i n Boitano L. appears to be intermediate although the l a r v a l abundance curve (Figure 12) suggests a three generation s i t u a t i o n . In summary, D. a l a s k e n s i s appears to have at l e a s t one generation per year i n the f r e s h e r waters, w h i l e i n more s a l i n e l a k e s , d e f i n i t e l y two and i n at l e a s t one case three (Boitano) generations occur. Figures 12 and 13 show D. A l a s k e n s i s i s most abundant i n mid summer, e s p e c i a l l y i n J u l y . In L. Lye i t makes up 60 per cent of the chironomid community i n e a r l y J u l y , i n Sorenson L., 25 per cent. Thus i t s e f f e c t on prey species, at l e a s t l a r g e ones, should be greatest at t h i s time. In general, numbers of D. a l a s k e n s i s are sparse i n the f r e s h e r l a k e s . 1) E i n f e l d i a pagana This i s the most abundant of a l l the species c o l l e c t e d i n the lake s e r i e s . In a l l l a k e s , owing to i t s r e l a t i v e l y l a r g e numbers ( f o u r t h i n s t a r l a r v a e alone sometimes exceeding 40,000 per square meter i n Near Opposite C r e s c e n t ) , E. pagana 53 represents a l a r g e p r o p o r t i o n of the fauna (Figures 14, 15). Numbers are lower i n Westwick L. and Sorenson L. (500 to 1000 per square meter) w h i l e they are higher i n medium-high and medium-low s a l i n i t i e s (averaging about 10,000 to 11,000 per square meter). The l a r v a e probably overwinter i n the t h i r d and f o u r t h i n s t a r s ; the f i r s t emergence of the year beginning i n e a r l y June. In F i g u r e 14 i t i s evident that these.emergences are very d i s c r e e t (though o c c u r r i n g over 3 or 4 weeks). In the f r e s h e r lakes (Figure 15) a second generation emerges. The r e l a t i o n s h i p between c o n d u c t i v i t y and the number of emergence peaks (-.424) (Table X) supports t h i s f a c t . In the very f r e s h East L. the two emergence peaks are found on e a r l i e r dates again i n d i c a t i n g that t h i s species may develop more slowly i n lakes of higher c o n c e n t r a t i o n . S i m i l a r l y , Table V I I I shows that the greater the percentage of E. pagana present, the lower the c o n d u c t i v i t y , T.D.S. and concentrations of sodium, HCO3 and CO^. In these cases the c o e f f i c i e n t s are -.639, -.614, -.658, -.645 and -.589 r e s p e c t i v e l y where -.514 i s s i g n i f i c a n t at p <.05 and -.641 at p <.01. I t i s i n t e r e s t i n g that u n l i k e other E i n f e l d i a pagana l a r v a e ( O l i v e r , 1971 B), the l a r v a e of E. pagana c o l l e c t e d i n t h i s study l a c k v e n t r a l tubules i n a l l i n s t a r s . This phenomenon i s a l s o apparent i n some l a r v a l types of Chironomus, notably C. s a l i n a r i u s where the same morphologi-c a l species may possess or l a c k blood g i l l s (0. Saether, pers. comm.). Since i t i s thought that these s t r u c t u r e s are 54 f u n c t i o n a l i n osmotic r e g u l a t i o n (Wigglesworth, 1933; S u t c l i f f e , 1960), i t i s p o s s i b l e that the l a c k of tubules i s an adaptation a l l o w i n g E. pagana to c o l o n i z e more con-cen t r a t e d waters than i s u s u a l l y the case. Wigglesworth (1933), who notes that dipterous species l i v i n g i n s a l i n e environments (both n a t u r a l l y and i n experimental s i t u a t i o n s ) tend to have reduced tubules, b e l i e v e s that the tubules are the only h i g h l y permeable areas of the body, and thus the r e s i s t a n c e of l a r v a e to hig h osmotic pressures w i l l be favored by the r e d u c t i o n of these s t r u c t u r e s . P h i l l i p s and Meredith (1969), however, have shown that i n the s a l t water mosquito Aedes campestris the anal p a p i l l a e are m o r p h o l o g i c a l l y s i m i l a r to those i n f r e s h water species and are probably able to a c t i v e l y t r a n s p o r t ions i n and out of the body. In most lakes the f o u r t h i n s t a r populations are at t h e i r s m a l l e s t from l a t e June to e a r l y August. Throughout the summer the l a r v a l composition of E. pagana and Glyptotendipes  barbipes shows an almost i n v e r s e r e l a t i o n s h i p (Figures 14, 15, 16 and 17). This may be due to the f a c t that these two species are adapted to the same c o n d i t i o n s . In lakes where they are abundant these two species make up almost 100 per cent of the i n d i v i d u a l s present. I f the percentage composition of one i n c r e a s e s , the percentage composition of the other decreases. That the two species are s i m i l a r l y adapted i s evidenced by the c o r r e l a t i o n c o e f f i c i e n t s between t h e i r abundances (.808) (Table V I I ) and t h e i r per cent composition (.645) (Table V I I I ) , both s i g n i f i c a n t at p<.01. FIGURE 14 L a r v a l abundance and a d u l t emergence of E i n f e l d i a pagana Meigen i n L. Jackson, Rock L. and Westwick L. A. T h i r d ( ) and f o u r t h ( — — ) i n s t a r numbers per square meter at weekly i n t e r v a l s . B. A d u l t emergence: numbers per square meter taken every f o u r t h day. C. The percentage of the t o t a l l a r v a l chironomid population represented by E. pagana l a r v a e . FIGURE 15 L a r v a l abundance and a d u l t emergence of E i n f e l d i a pagana Meigen i n Near Opposite Crescent, Barkley L. and East L. A. T h i r d ( ) and f o u r t h ( — - ) i n s t a r numbers per square meter a t weekly i n t e r v a l s . B. A d u l t emergence: numbers per square meter taken every f o u r t h day. C. The percentage of the t o t a l l a r v a l chironomid p o p u l a t i o n represented by E. pagana l a r v a e . 57 m) Glyptotendipes barbipes Found i n a l l the l a k e s , G. barbipes shows sporadic occurrence i n the higher s a l i n i t i e s and i s most abundant i n the range from 500 to 3000 umho/cm. In these lakes i t reaches a maximum of about 11 , 0 0 0 per square meter. The over w i n t e r i n g l a r v a e emerge i n l a t e May i n a l l l a k e s . In Rock L. and East L. t h i s i n i t i a l emergence extends i n t o e a r l y June. A second generation emerges a t d i f f e r e n t times i n d i f f e r e n t l a k e s , u s u a l l y i n mid or l a t e J u l y . The s i t u a t i o n i n L. Jackson and i n Rock L. (to a l e s s e r degree) i s somewhat d i f f e r e n t . I t i s not too c l e a r whether the second emergence i s a separate generation or simply the emergence of slower developing o v e r w i n t e r i n g f o u r t h i n s t a r l a r v a e (Figures 16 and 17). The small August 29 emergence i n East L. may be the beginning.of a l a r g e r t h i r d generation emergence. That G. barbipes appears to be more abundant and dominant i n the lower s a l i n i t i e s emphasizes the f a c t that the species has more generations i n f r e s h e r waters. A l l c o r r e l a -t i o n c o e f f i c i e n t s (Table V I I I ) measuring the r e l a t i o n s h i p between percentage composition and c o n d u c t i v i t y (-.626), T.D.S. (-.613), sodium (-.628), C 0 3 (-.543) and HCO3 (-.576) are s i g n i f i c a n t at p<.05. The number of emergence peaks i s n e g a t i v e l y c o r r e l a t e d w i t h c o n d u c t i v i t y , T.D.S., sodium, C0o and HCOo (Table X ) . FIGURE 16 L a r v a l abundance and a d u l t emergence of Glyptotendipes barbipes (Staeger) i n L. Jackson, Westwick L. and Sorenson L. A. T h i r d ( ) and f o u r t h ( — - ) i n s t a r numbers per square meter at weekly i n t e r v a l s . B. A d u l t emergence: numbers per square meter taken every f o u r t h day. C. The percentage of the t o t a l l a r v a l chironomid p o p u l a t i o n represented by G. barbipes l a r v a e . FIGURE 17 L a r v a l abundance and a d u l t emergence of Glyptotendipes barbipes (Staeger) i n Rock L., Barkley L. and East L. A. T h i r d ( ) and f o u r t h ( — ) i n s t a r numbers per square meter a t weekly i n t e r v a l s . B. A d u l t emergence: numbers per square meter taken every f o u r t h day. C. The percentage of the t o t a l l a r v a l chironomid community represented by G. barbipes l a r v a e . Larval Composition ( % ) No. emerging per sq.m No. larvae per sq.m VO 60 The time of the main emergence i s l a t e r i n f r e s h e r waters; c o e f f i c i e n t s i n d i c a t i n g t h i s are s i g n i f i c a n t at the 99 per cent l e v e l (Table X I ) . This i s u n l i k e the cases of E. pagana and D. a l a s k e n s i s , but may r e s u l t from adaptations to higher s a l i n i t i e s . For example, i t may r e f l e c t a tendency of G. barbipes populations to complete development e a r l y to avoid the higher s a l i n i t i e s of l a t e summer. In t h i s context i t should a l s o be noted that i n higher s a l i n i t i e s the synchrony of emergence i s greater than i n lower ones (-.559) (Table V I ) . On the whole, G. barbipes i s most abundant i n mid summer ( J u l y ) a f t e r f o u r t h i n s t a r l a r v a e have developed from the i n i t i a l May matings. Throughout the lakes abundance i s very s i g n i f i c a n t l y c o r r e l a t e d to the abundance of D. a l a s k e n s i s (.785) and E. pagana (.808) n) Chironomus anthracinus Although t h i s species has been recorded from A l b e r t a and C a l i f o r n i a (Stone et a l , 1956), there are no records from B r i t i s h Columbia. This i s one of the three Chironomus species commonly found i n the lake s e r i e s . At one meter of depth the l a r v a l d e n s i t y ranges from 100 to 1000 per square meter. The species i s e v i d e n t l y most c h a r a c t e r i s t i c of eutrophic profundals (Lundbeck, 1926; Berg, 1938) and i s o f t e n regarded as an i n d i c a t o r of low oxygen c o n d i t i o n s (Brundin, 1951). Since Topping (1969), c a l l i n g i t Chironomus sp. A, 61 showed C. anthracinus was prevalent a t depths greater than two meters i n the lakes under c o n s i d e r a t i o n , i t i s p o s s i b l e that the main population emergences were missed by the trapping i n the present research, the populations sampled being p e r i p h e r a l ones. In the lakes where no May emergence i s recorded i t i s p o s s i b l e that emergence occurred before the traps were placed i n p o s i t i o n . The low l e v e l s of f o u r t h i n s t a r l a r v a e i n May i n Boitano L. and Sorenson L. may i n d i -cate t h i s . The species i s not obvious i n Rock L. Although i t appears that C. anthracinus u s u a l l y has one generation, emergence patterns are extremely v a r i a b l e ( F i g u r e s 18 and 19). This i s i n accordance w i t h Thienemann (1951) who recorded v a r i a t i o n s i n the time of year C. anthracinus swarmed at a north German la k e . Mundie (1957) found the species u n i v o l t i v e i n S t a i n s South R e s e r v o i r , London, where A p r i l emergences predominated although some September a d u l t s were caught. In Lake Esrom, Denmark, Jonasson (1954) found a month-long emergence p e r i o d w i t h a mode on May 10, 1954. In the lakes s t u d i e d h e r e i n , the amount of C. an thrac inu s emergence i s c o r r e l a t e d w i t h the c o n c e n t r a t i o n of magnesium (p<.01) (Table I X ) . In Rock L., C. anthracinus makes up a major part of the chironomid fauna i n J u l y and August (Figure 18). Levels at one meter i n Westwick L. and Sorenson L. are low (Figure 19). The species i s most abundant i n the h a b i t a t s p r e f e r r e d by E. pagana (Table V I I ) . FIGURE 18 L a r v a l abundance and a d u l t emergence of Chironomus anthracinus Z e t t e r s t e d t i n Boitano L., L. Jackson and Rock L. A. Fourth i n s t a r numbers per square meter at weekly i n t e r v a l s . B. Adult emergence: numbers per square meter taken every f o u r t h day. C. The percentage of the t o t a l l a r v a l chironomid population represented by C. anthracinus l a r v a e . FIGURE 19 L a r v a l abundance and a d u l t emergence of Chironomus anthracinus Z e t t e r s t e d t i n Sorenson L., Barkley L. and East L. A. Fourth i n s t a r numbers per square meter taken a t weekly i n t e r v a l s . B. A d u l t emergence: numbers per square meter taken every f o u r t h day. C. The percentage of the t o t a l l a r v a l chironomid population represented by C. anthracinus l a r v a e . Larval Composition (0/o) No. emerging per sq.m No. larvae per sq.m 64 o) Chironomus n. sp. This i s a h i t h e r t o undescribed species that keys out near C. a t r i t i b i a M a l l o c h i n the keys of Townes (1945). I t w i l l be described by Sublette who i s now r e v i s i n g the North American Chironomus u s i n g g i a n t chromosome charac t e r s . Bassett (1967) c a l l e d t h i s Chironomus species h i s Species V and noted that i t s chromosomes d i s p l a y e d extensive p a i r i n g between centromeres. T h i s , along w i t h other characters such as banding p a t t e r n , separates the new species c y t o l o g i c a l l y from s i m i l a r species l i k e C. anthracinus (Bassett's Species I V ) . The species was recorded by Topping (1969) under Chironomus sp. B as being most abundant below a depth of two meters. I t i s the most common of the Chironomus species i n the l a k e s ; moreover, i t s t o l e r a n c e of high s a l i n i t i e s i s much greater than that of other members of the genus considered h e r e i n . Indeed, t h i s species reaches i t s g r e a t e s t abundance i n Barnes L. (Figure 20) where i t i s by f a r the dominant nonpredaceous chironomid. The species makes up almost 100 per cent of the f o u r t h i n s t a r chironomid fauna i n l a t e summer. Table V I I shows the r e l a t i o n s h i p between the abundance of t h i s species and i o n c o n c e n t r a t i o n . C o r r e l a t i o n s w i t h c o n d u c t i v i t y , T.D.S., sodium, carbonate and bicarbonate concentrations are p o s i t i v e (p<.01). The c o r r e l a t i o n w i t h the c o n c e n t r a t i o n of s u l f a t e i s s i g n i f i c a n t at p<.05. In most la k e s the i n i t i a l emergence occurs i n May. In Sorenson L. the l a c k of f o u r t h i n s t a r l a r v a e i n May suggests 65 an e a r l y emergence. Here there i s an August emergence as w e l l . In Barnes L. a l l the a d u l t s emerging from May to e a r l y J u l y probably are from the same ove r w i n t e r i n g genera-t i o n . A p o r t i o n of the f o u r t h i n s t a r p o p ulation may prolong diapause and not emerge u n t i l June and e a r l y J u l y . The recruitment of the new generation t h i r d i n s t a r l a r v a e i n t o the ranks of the f o u r t h i n s t a r keeps the l e v e l of the l a t t e r r i s i n g even though considerable emergence i s o c c u r r i n g . The m a j o r i t y of new generation l a r v a e are not f o u r t h i n s t a r s i z e before the middle of J u l y , however, so that emergence before t h i s time i s almost c e r t a i n l y due to overwintering a d u l t s . Thus a l l a d u l t s appearing a f t e r mid J u l y are probably of the new generation, and the drop i n f o u r t h i n s t a r l a r v a e numbers at t h i s time (10,000 down to 5,000 per square meter) i s a r e -s u l t of t h i s emergence. I t i s probable that the remaining f o u r t h i n s t a r l a r v a e overwinter alone i n Barnes L. (since i t i s u n l i k e l y that another generation of f o u r t h i n s t a r s can be produced during the short f a l l ) or w i t h second or t h i r d i n s t a r s . I f the smaller i n s t a r s do manage to overwinter, they may be the i n d i v i d u a l s emerging the next year i n June, the overwinter-i n g f o u r t h i n s t a r s emerging i n May. In some of the lakes (Boitano L., L. Jackson, Rock L. and East L.) only one genera-t i o n i s observed (Figures 20,21 and 22). As p r e v i o u s l y mentioned, t h i s new species of Chironomus i s p a r t i c u l a r l y i n t e r e s t i n g because of i t s unique domination of Barnes L., the most s a l i n e lake ( c o n d u c t i v i t y about 12,000 umho/cm) i n the study. The other species of Chironomus were FIGURE 20 L a r v a l abundance and a d u l t emergence of Chironomus n. sp. i n Barnes L., Boitano L. and L. Jackson. A. Fourth i n s t a r numbers per square meter a t weekly i n t e r v a l s . B. Adult emergence: numoers per square meter taken every f o u r t h day. C. The percentage of the t o t a l l a r v a l chironomid population represented by Chironomus n. sp. l a r v a e . Larval Composition (%) No. emerging per sq.m No. larvae per sq.m FIGURE 21 L a r v a l abundance and a d u l t emergence of Chironomus n. sp. i n Rock L. and Sorenson L. A. Fourth i n s t a r numbers per square meter a t weekly i n t e r v a l s . B. A d u l t emergence: numbers per square meter taken every f o u r t h day. C. The percentage of the t o t a l l a r v a l chironomid population represented by Chironomus n. sp. l a r v a e . FIGURE 22 L a r v a l abundance and a d u l t emergence of Chironomus n. sp. i n Barkley L. and East L. A. Fourth i n s t a r numbers per square meter a t weekly i n t e r v a l s . B. Adult emergence: numbers per square meter taken every f o u r t h day. C. The percentage of the t o t a l l a r v a e chironomid p o p u l a t i o n represented by Chironomus n. sp. l a r v a e . 69 not c o l l e c t e d here, although two u n i d e n t i f i e d l a r v a e of d i f f e r e n t species, Chironomus sp. C and Chironomus sp. D occur i n very low numbers (Table I V ) . The great abundance and l a r g e emergence of t h i s Chironomus species i n Barnes L. i s probably due to both i t s s u c c e s s f u l adaptation to the c h e m i c a l l y r i g o r o u s environment and to a considerable r e d u c t i o n i n competition from s i m i l a r species. I t i s notable that the per cent composition and abundance of t h i s species are c o r r e l a t e d w i t h the index of d i v e r s i t y (Tables V I I and V I I I ) . The emergence p a t t e r n d i f f e r s from that i n lakes where C. anthracinus, C. tentans and C. plumosus occur. The tendency f o r the emergence p a t t e r n to spread out i n h a b i t a t s having a h i g h index of d i v e r s i t y i s r e f l e c t e d i n the c o r r e l a t i o n c o e f f i c i e n t -.603 (p<£.05) (Table V I ) . p) Chironomus tentans This species i s common, but not abundant i n the middle range of c o n d u c t i v i t i e s from 500 to 3000 jumho/cm. I t occurs i n Boitano L. ( c o n d u c t i v i t y 4108 umho/cm) i n only very small numbers. In most lakes the d e n s i t y of f o u r t h i n s t a r l a r v a e never exceeds 300 per square meter, making the species only a minor component of the community as f a r as percentage composi-t i o n i s concerned (Figures 23 and 24). C. tentans has i t s g r e a t e s t development at one meter i n Sorenson L. where f o u r t h i n s t a r l a r v a e number 1000 to 1500 per square meter. These r e l a t i v e l y low d e n s i t i e s , however, are s u f f i c i e n t to enable 70 C. tentans to comprise 35 per cent (Westwick L.) and 50 per cent (Sorenson L.) of the chironomid fauna. The amount of emergence i s small i n most l a k e s , u s u a l l y under 10 per square meter and u s u a l l y occurs i n l a t e May. In Westwick L. t h i s May emergence i s spread over 28 days and represents an emergence of about 20 a d u l t s per square meter over 4 days d i r e c t l y a f t e r the traps were s e t ; there-f o r e t h i s may be the end of a l a r g e r emergence beginning e a r l i e r . In the l a t e J u l y emergence t h i s trend i s reversed, Westwick L. having 2 per square meter over 20 days. The number of days between the medians of the emergence peaks i n Westwick L. i s 56, i n Sorenson L. 68 and i n Rock L. 37. At o 25 C i n the l a b o r a t o r y the i n s e c t s have been reared to the a d u l t i n 44 days (16 hours l i g h t , 8 hours dark) (Pat C o l l e n , pers. comm.) and a t the same temperature Sadler (1935) reporte d generations of 35 to 45 days. Chironomus tentans begins development when the water temperature reaches 10°C (Sadler, 1935; Acton, pers. comm.). The number of accumulated degree days between the f i r s t date on which 10°C was recorded and the date of the i n i t i a l emer-gence may thus be c a l c u l a t e d (Table X I I I ) u s i n g F i g u r e 5. o j 10 C was reached during the l a s t days of A p r i l and the f i r s t days of May and the f i r s t recorded emergences began i n the t h i r d and f o u r t h weeks of May (Table X I I I ) . The accumulated day degrees f o r the development of the o v e r w i n t e r i n g f o u r t h i n s t a r l a r v a e amount to 249.75 i n Westwick L., 266.0 i n Sorenson L. and 441.25 i n Rock L. The f a c t that the second 71 emergence peak came most q u i c k l y (37 days and 648.25 day degrees) i n Rock L. i s r a t h e r s u r p r i s i n g . The i n t e r p r e t a t i o n that the J u l y emergences i n L. Jackson, Barkley L. and East L. are due to the progeny of o v e r w i n t e r i n g l a r v a e i s being taken. The low or decreasing numbers of f o u r t h i n s t a r l a r v a e i n l a t e May i n d i c a t e that emergence probably occurred before May 19. I t i s p o s s i b l e that emergence i n these three lakes was postponed because of serious competition or l a c k of favored food. There being l i t t l e or no d i f f e r e n c e i n temperature regimes and day length changes among the l a k e s , these v a r i a b l e s can h a r d l y be the cause of d i f f e r e n c e s i n developmental r a t e . Other f a c t o r s must be producing v a r i a t i o n i n the l i f e c y c l e of C. tentans. The only physico-chemical parameters c o r r e l a t i n g w i t h abundance and per cent composition of C. tentans are oxygen and organic carbon l e v e l s . D i s s o l v e d oxygen c o r r e l a t e d w i t h abundance at -.578 (Table V I I ) and w i t h per cent composition at -.651 (Table V I I I ) . There i s a r e l a t i o n s h i p between organic carbon and abundance (.547) and per cent composition (.648). Although the abundance of C. tentans i s r e l a t e d to environmental f a c t o r s i n f l u e n c i n g other species i n s i m i l a r ways, there i s no c l e a r cut r e l a t i o n s h i p between the abundance or percentage composition of C. tentans and that of p o t e n t i a l competing species. 72 C. tentans abundance i n May, however, i s c o r r e l a t e d w i t h the May abundance of C. anthracinus and Glyptotendipes  barbipes. This may have f u r t h e r i n f l u e n c e on subsequent spacing of emergence periods. There are three groups of predaceous chironomids that may a f f e c t C. tentans - the s e v e r a l P r o c l a d i u s species, Derotanypus a l a s k e n s i s and Cryptochironomus p s i t t a c i n u s . No s i g n i f i c a n t r e l a t i o n s h i p between these predators and C. tentans (regarding abundance or per cent composition) i s suggested by the c o r r e l a t i o n studies (Tables V I I and V I I I ) . As expected, the amount of emergence throughout the summer i s dependent on the abundance of the l a r v a e (.536). This i s f u r t h e r c h a r a c t e r i z e d by the c o r r e l a t i o n of the J u l y emergence w i t h the abundance (.762) and the percentage com-p o s i t i o n (.710) of l a r v a e present i n June. In a d d i t i o n , the amount of May emergence determines the abundance of l a r v a e i n June (.590) and J u l y (.670) as w e l l as the June (.841) and J u l y (.992) percentage composition. These are very basic r e s u l t s r e f l e c t i n g the generation time of C. tentans. The number of emergence peaks i s c o r r e l a t e d w i t h abun-dance (.586) and per cent composition (.703) throughout the summer. In May the c o e f f i c i e n t i s .589 and i n J u l y i t i s .724. The i n i t i a l May emergence and the index of d i v e r s i t y f o r May are c o r r e l a t e d (r.540), the emergence being much l a r g e r i n lakes having lower d i v e r s i t y . 73 The emergences of C. tentans never occur at the same time as those of C. anthracinus and n. sp. In Sorenson L. , f o r example, where at one meter C. tentans i s completely-dominant, a l a t e May C. tentans emergence can be compared to the i n i t i a l emergences of C. anthracinus and n. sp. i n mid June. In Westwick L. the l a r g e C. tentans emergence l a s t i n g from May 19 to June 13 (Figure 23) and the small J u l y peak are the only emergences of the three species i n the l a k e . S i m i l a r instances can be seen i n Figure 28. Table X I I shows that when l a r v a l numbers of C. tentans are h i g h , the emergence times of C. anthracinus tend to occur l a t e r i n the summer (.566). S i m i l a r l y , when the num-bers of C. anthracinus are hig h , C. tentans emerges l a t e r (.597). FIGURE 23 L a r v a l abundance and a d u l t emergence of Chironomus tentans F a b r i c i u s i n L. Jackson, Westwick L. and Sorenson L. A. Fourth i n s t a r numbers per square meter a t weekly i n t e r v a l s . B. A d u l t emergence: numbers per square meter taken every f o u r t h day. C. The percentage of the t o t a l l a r v a l chironomid population represented by C. tentans. l a r v a e . L. JACKSON WESTWICK L. SORENSON L. FIGURE 24 L a r v a l abundance and a d u l t emergence of Chironomus tentans F a b r i c i u s i n Rock L., Barkley L. and East L. A. Fourth i n s t a r numbers per square meter at weekly i n t e r v a l s . B. A d u l t emergence: numbers per square meter taken every f o u r t h day. C. The percentage of the t o t a l l a r v a l chironomid population represented by C. tentans l a r v a e . No. larvae per sq.m Larval Composition ( % ) No. emerging per sq. m _ TABLE V Summary of c o r r e l a t i o n c o e f f i c i e n t s d e s c r i b i n g the r e l a t i o n s h i p between environmental f a c t o r s and the amount of emergence of c e r t a i n species, r = 0.514 i s s i g n i f i c a n t at p=.05; r = 0.641 at p=.01. Conduct-i v i t y T.D.S. Na Mg CO, HCO. SO, „ % organic p carbon Procladius bellus  Procladius freemani  Procladius dentus  Procladius clavus  Cricotopus f l a v i b a s i s  Cricotopus albanus Psectrocladius barbimanus Cryptotendipes a r i e l Calopsectra gracilenta Ablabesmyia peleensis .302 .179 ,652 ,910 .190 ,362 ,272 -.292 .154 .640 .904 -.196 -.351 .230 .465 :447 -.247 .171 .629 .930 -.163 -.302 .275 ,388 .019 .073 .288 .239 .423 .164 .473 -.171 .219 .199 .173 .289 ,318 -.308 -.258 -.432 -.193 .022 .491 .858 -.173 -.224 .104 .293 .024 -.207 -.345 .184 .598 .903 -.136 -.386 .381 .449 ,291 .222 ,642 .472 .252 .375 .092 .199 .167 .473 .345 -.325 .074 .156 .156 .257 .019 .171 .060 .151 .020 .091 -.937 .221 .346 .415 -.101 -.900 .201 .275 -.126 -.094 -.086 -.200 -.139 -.169 -.016 -.079 ,169 .099 ,938 -.210 TABLE VI The c o r r e l a t i o n between emergence histogram d i s p e r s i o n and environmental f a c t o r s . Non parametric s t a t i s t i c s . S i g n i f i c a n c e w i t h p 0.05 i s marked * and p 0.01 **. SPECIES CONDUCTIVITY INDEX OF DIVERSITY Derotanypus a l a s k e n s i s -0. 310 -0. 134 E i n f e l d i a pagana -0. 314 -0. 253 Chironomus tentans -0. 365 -0. 005 Chironomus n.sp. 0. 423 -0. 603 * Chironomus anthracinus -0. 397 0. 075 Glyptotendipes barbipes -0. 559 * 0. 024 Pr o c l a d i u s freemani 0. 213 0. 021 P r o c l a d i u s b e l l u s -0. 390 0. 009 P r o c l a d i u s clavus 0 747 0. 267 P r o c l a d i u s dentus 0 619 0. 121 Calopsectra g r a c i l e n t a 0. 777 +0. 206 P s e c t r o c l a d i u s barbimanus 0 838 ** -0. 441 Ablabesmyia p e l e e n s i s -0 .439 -0. 220 Cricotopus f l a v i b a s i s -0 185 0. 248 Cricotopus albanus - .403 -0. 046 Cryptotendipes a r i e l 0 .914 -0. 025 TABLE V I I Summary of c o r r e l a t i o n c o e f f i c i e n t s d e s c r i b i n g r e l a t i o n s h i p s between environmental f a c t o r s and species abundance. r=0.514 i s s i g n i f i c a n t a t p=.05; 0.641 a t .01. Conduc tivity T.D.S. 2 <n 0 (J cn 0 u X 0 CO Conductivity 1.000 T.D.S. .998 1.000 Na .993 .991 1.000 Mg -.075 -.064 -.190 1.000 C03 .940 .949 .955 -.220 1.000 HC03 .972 .962 .981 -.226 .933 1.000 so 4 .706 .723 .632 .555 .586 .548 1.000 °2 .289 .316 .305 -.133 .261 .220 .309 PH .537 .531 .485 .358 .412 .537 .483 7. Organic Carbon -.186 -.203 -.246 .497 -.274 -.260 .034 Index of -.237 -.279 -.251 .048 -.399 -.202 -.189 0 • cn Tl C 1 u cn c 0 •H rt cttXl a a CO 00 U I* O u eg CU •t-l 0 0 w 0 > CQ •r2 Of (3, cn cn « C •H c « cn rt 4-1 en 61 , c en • led . I D W D 0. cn tile u t J >H .O C»| 1 K3 ,1-1 • O S o l c M l cutu Diversity Biomass Total No. Chironomids Derotanypus  alaskensis Ei n f e l d i a pagana Chironomus  tentans Chironomus n.sp. Chironomus anthracinus Glyptotendipes  barbipes Procladius Call species) Cryptochironomus psittacinus Remainder of s p e c i e s .227 .329 .077 .489 .260 .708 .291 .386 .689 .378 .213 -.202 -.306 -.095 -.471 -.272 .740 -.284 -.371 .671 .336 .182 -.223 -.332 -.102 -.481 -.309 .717 -.258 -.374 .709 .371 .204 -.032 .095 .126 -.022 .417 -.096 -.252 -.098 -.340 -.070 -.041 -.147 -.244 -.175 -.431 -.251 .863 -.215 •,350 .598 .172 .010 -.221 -.286 -.005 -.447 -.264 .681 -.242 -.337 .739 .395 .219 -.127 -.188 -.122 -.347 -.083 .563 •.316 •.288 .304 .112 .250 1.000 .085 -.649 -.362 -.074 -.109 -.159 .036 -.578 .318 .053 .119 .235 -.002 .058 1.000 .087 -.163 .091 .133 .133 -.037 .051 .315 .061 -.037 .310 .208 -.102 1.000 .332 1.000 .005 -.112 .134 -.102 .547 -.407 -.192 -.192 -.219 .291 -.117 -.433 -.486 .062 -.383 .125 -.656 .080 -.331 .045 .442 .574 1.000 .783 1.000 .354 .309 1.000 .871 .823 .362 1.000 -.107 -.073 .287 -.036.1.000 .122 .066 -.161 -.134 -.162 1.000 .506 .316 .035 .541 -.143 -.020 1.000 .787 .785 .356 .808 -.092 -.092 .291 1.000 .031 -.191 .208 -.091 -.365 .305 -.066 -.185 1.000 -.374 -.506 .328 -.463 -.107 -.251 -.262 -.364 .458 1.000 .392 -.418 -.005 -.283 -.269 -.230 -.210 -.216 -.428 .455 1.000 ^ TABLE V I I I Summary of c o r r e l a t i o n c o e f f i c i e n t s d e s c r i b i n g the r e l a t i o n s h i p between environmental f a c t o r s and species per cent composition. r=0.514 i s s i g n i f i c a n t a t p=.05; r=0.641 at p=.01. LO Ln •p- H* o o o O N M 00 •p-O N .p-O N r—• 3 o rt o a w a 3" ro 3" w H- 3 H- 3 B> 1 H a >-< Q> M> 01 o • O m o 3 111 ?r rt 3 3 t-> ro til Ul o a. 3 3 R 3 01 2 c H- g W tn 01 2 .p-•p-o ro 0 3 *o ro LO .p- ro LO ro .p- LO LO V O o ^1 oo o V D 00 I-* 1 •p- ro Lo O N 1 1 1 1 • 1 I - 1 O N O N O N o ro O o ro Ln •P- . •P- vo CO o •P- V O 00 Ln V O O N •p- o i 1 1 1 1 >-• ro t—' LO O o M o J> i> LO LO *o o Ln 00 V O Ln O N LO o 1 1 1 ro ro o ro o O LO O N 00 O V O . 4> LO Co o 1 . I 1 h-1 ro ro ro to O •p- •P- ro 4> O Ln •P- O N vo O 1 i i * J O N «o O ro •p- O U l V O 00 O M oo 00 O 00 CO O N O 00 O LO O •P-•P-00 Conductivity T.D.S. Na Mg CO, HC0-, SO, pH % Organc C. Index of Diversity Biomass Total no. chironomids Derotanypus  alaskensis Ei n f e l d i a  Parana Chironomus Chironomus n. sp. Chironomus  anthracinus Clyptotendipes fr-*E-barbipes Procladius ( a l l species) Cr yptoch ironomus P K i t t a c x n u s Remainder of species 6L TABLE IX Summary of c o r r e l a t i o n c o e f f i c i e n t s d e s c r i b i n g the r e l a t i o n s h i p between environmental f a c t o r s and the amount of emergence. r=0.514 i s s i g n i f i c a n t a t p=.05; r=0.641 a t p=.01. LO M LO >-> o 3 q rt O rj 3* n> 3" P p-H- tn 3 w 3 M X) rr Co t-n O o (U 0 3 ro 3 3 3 3 ft) Q Q CO Q a 2 c C P> CO co N> o O r—1 Ln t-1 »-» \D Ln O Ln IO a* h-* O Lo LO o 1 1 r—1 Co O o J> o to LO 4> LO o 00. ro ro a* o Conductivity T.D.S. Na Mg CO, HCO, SO, pH % Organic Carbon Derotanypus alaskensis Einfeldia  pagana Chironomus tentans Chironomus n. sp. Chironomus anthracinus Clyptotcndlpes  barbipes 08 TABLE X Summary of the c o r r e l a t i o n c o e f f i c i e n t s d e s c r i b i n g the r e l a t i o n s h i p between environmental f a c t o r s and the number of emergence peaks f o r va r i o u s species. r=0.514 i s s i g n i f i c a n t at p=.05; r=0.641 a t p=.01. o 3 rt o o PI r r r r Hi H* p - tn H- ;o 3 H fT <i 0 » O 0» o :i o o w o cx 3 3 i c cn to « 1 * 1 i * 1 O J O J o o cr. Cn cr. t o CO Cn t o ON . . 1 O J r-« O H 1 *-j Ln Oo U i -P-ON cr> O J r o J> 1 a * 1 O J i O t o ro 1 t o Cn Co CO t o h-» l-» CO o i 1 r 1 t ( o> O J H» O J O J o r o Ln vo J> VO O CO IO 1 . 1 I O J O o o O J O CT. yo CO h-* 4> ON o J> ON . 1 i .1 o o O J o t o Cn o t o U i ON t o J> t o CO . . . O I-1 o t o cr> yD o> Cn *-* t o Cn H 1 Cn o 0 0 o o o o o o o o o o o 0 0 Conductivity T.D.S. Na Mg C0 3 HCOq S0 4 PH % Organic Carbon Derotanypus alaskensis Einfeldia  pagana Chironomus tentans Chironomus n. sp. Chironomus anthracinus ciyptot barbipes endlpes 18 TABLE XI Summary of c o r r e l a t i o n c o e f f i c i e n t s d e s c r i b i n g the r e l a t i o n s h i p between environmental f a c t o r s and the times of major emergence i n se v e r a l species. r=0.514 i s s i g n i f i c a n t at p=.05; r=0.641 at p=.01. o 3 Ln r t o O m Ln rD rr H« w H' 3 H* » 3 <~t a H rr H P O o l » 0 3 3 3 3 to o I o g c (A O dia w CO CO o •p-.p-LO o •p- ro t-1 00 -p- CO LO t-< h-» vo ro o ro 1 1 o ro i o i o t o ON CO ON CO Ln Ln cr* 1 1 ro o t-1 H» r-1 i — 1 00 o VO Lo Ln ro LO Ln VO ro . . . M o ro r* (O LO O ON o Ln CO L0 •p- o vo ro . .• I O o • LO O ro vO to Ln VO Ln LO VO VO t~> Ov vo LO H» ro •P- ro H» O O VO CTN o Lo ON O ON O vo O vo O I-1 00 Ln Ln ro O ro ON •P- VO O vO VO t-1 Ln o h-> -P- 4> O •P- - Ln LO o vO Ln Ln o I-" LO ro O 00 Co O ON ro o Conductivity T . D . S . Na Mg C O , HCOo S O , PH % Organic Carbon Derotanypus alaskensis Einfeldia  pagana Chironomus tentans Chironomus n. sp. Chironomus anthracinus Glyptotendipes  barbipe"s Z2 TABLE X I I Summary of c o r r e l a t i o n c o e f f i c i e n t s d e s c r i b i n g the r e l a t i o n s h i p between l a r v a l abundance, numbers of emerg-i n g a d u l t s , number of emergence peaks and emergence time, r=0.514 i s s i g n i f i c a n t a t p=.05; r=0.641 at p=.01. a|co w|oJc M > c u rt n) <u cd > u • Itl O.r-1 CO . 1 c d ol ol id c • no 0. CO a <u •H e QN wlajc o|u D. alaskensis no.emerging E. pagana no.emerging C. tentans no. emerging Cn. sp. no.emerging C.anthracinus no. emerging G.barbipes no.emerging T). alaskensis no.peaks E•pagana ' no.peaks C . tentans no.peaks Cn. sp. no.peaks C•anthracinus no. peaks G.barbipes no. peaTTs D. alaskensis emergence time E. pagana emergence time C.tentans emergence time C.n.sp. emergence time C.anthracinus emergence time G.barbi pes emergence time .294 .088 -.079 -.215 .165 .164 .377 -.087 -.017 -.001 -.089 .172 .526 .064 .082 -.054 .131 .160 .180 .536 -.194 -.191 .235 .668 .232 .722 .007 .401 .158 .537 .320 .591 .384 .425 .284 .653 -.217 -.163 .536 -.227 .064 -.133 -.074 .022 .586 .347 .496 .508 .259 .284 .241 .178 .566 .368 -.152 -.005 -.166 .411 .041 -.074 -.363 -.022 -.125 .183 -.208 -.345 -.424 .196 -.123 .339 -.191 -.332 .355 .785 .154 -.144 .052 .790 .029 .336 .492 .226 .022 .246 .179 .246 .597 .457 .161 .309 .170 .360 -.205 -.146 .105 .488 .123 .678 -.085 .501 -.090 .407 .278 .470 .210 .419 -.025 .578 .660 .203 .095 .001 .021 .036 .409 .116 .254 .135 .096 .058 .165 .401 .558 .177 .032 .328 .198 .314 .816 .465 .214 .381 .364 .000 .898 .088 .060 .318 .185 .179 .615 .070 .024 .355 .228 .073 .250 .182 .281 .115 .108 .188 .203 • .395 .119 .133 .243 .058 .171 .092 .321 .287 .357 .248 .322 .209 .442 .265 .188 .508 .417 .226 .016 .339 .267 .308 .799 .505 .113 .406 .704 .087 .010 .046 .472 .159 .148 .763 .368 .510 .307 .749 .003 .245 .832 .298 .201 .405 .259 .508 .214 .887 .246 .459 .432 .363 .492 .803 .063 .424 .445 .306 .873 .739 .490 .926 OO u> TABLE X I I I The developmental r a t e s of C. tentans i n v a r i o u s l a k e s . LAKE Date on which 10°C was f i r s t reached F i r s t emergence begins Accumulated day degrees between 10°C and 1st emergence Second emergence begins Accumulated day degrees between f i r s t and second emergence Westwick 29 A p r i l 19 May 249.75 27 J u l y 1378.75 Sorenson 29 A p r i l 21 May 266.0 19 J u l y 822.25 Jackson 30 A p r i l - - 3 J u l y 2035.50 Rock 1 May 2 June 441.25 7 J u l y 648.25 Barkley 1 May - - 19 J u l y 1410.0 East 3 May - - 21 J u l y 1296.0 85 5. The Chironomid Complex and the Lake S e r i e s In order to c h a r a c t e r i z e the chironomid complex i n the s a l i n e lake s e r i e s and to c l a r i f y the r e l a t i o n s h i p between C. tentans and other species, i t i s u s e f u l to describe the chironomid a s s o c i a t i o n s and group the lakes according to the dominant species present. R e f e r r i n g to Table XIV i t i s seen that the chironomid a s s o c i a t i o n s can be d i v i d e d i n t o three main groups : a) The Cricotopus albanus - P r o c l a d i u s b e l l u s -Ablabesmyia p e l e e n s i s a s s o c i a t i o n In the lakes s t u d i e d t h i s community i s r e s t r i c t e d to Box 27 where low s a l i n i t y (mean c o n d u c t i v i t y 40 umho/cm and a T.D.S. l e v e l of 15 to 20 ppm) and low pH (6.4) are e s p e c i a l l y evident. The f l o r a i n t h i s magnesium carbonate-bicarbonate lake i s dominated by emergent p l a n t s , notably Potamogeton natans ( P l a t e 1). I t has a v a r i e d fauna w i t h a r e l a t i v e l y high index of d i v e r s i t y (2.14) (Figure 25). Although there i s a high d i v e r s i t y , the den s i t y of lar v a e i s the lowest i n the e n t i r e l a k e s e r i e s . The chironomid fauna i s very d i s t i n c t i v e . Only three emerging species are found: P r o c l a d i u s b e l l u s (64%), Ablabesmyia p e l e e n s i s (14%) and Cricotopus albanus (22%). The Cricotopus albanus l a r v a e mine i n Potamogeton leaves. P. b e l l u s and A. pe l e e n s i s are both f r e e - l i v i n g tanypodine predators. 86 b) The Glyptotendipes barbipes - E i n f e l d i a pagana a s s o c i a t i o n These two species dominate the lakes having mean c o n d u c t i v i t y measures r a n i n g from 488 (East L.) to 2766 (L. Jackson) jumho/cm (Table I ) . The main predator i s Derotanypus a l a s k e n s i s . There i s considerable v a r i e t y i n the species composition of the water bodies i n v o l v e d . For example, i n Near Phalarope, l a r g e d e n s i t i e s of non predatory, mud d w e l l i n g chironomids are l a c k i n g . The dominant species, P s e c t r o c l a d i u s barbimanus, i n h a b i t s aquatic v e g e t a t i o n . Near Phalarope a l s o contains the l a r g e s t c o n c e n t r a t i o n of the predator Tanypus sp. found i n the la k e s . The species i s known only from l a r v a e i n bottom samples (Table I V ) ; whether or not i t i s Tanypus punctipennis (Table I I ) i s not known, sinc e no a d u l t s were trapped here. Nevertheless, Near Phalarope i s i n c l u d e d as a lake i n t h i s s e c t i o n because of i t s s i m i l a r i t i e s to the other lakes i n v o l v e d . The group can be d i v i d e d i n t o three subgroups depending on the abundance of species secondary to G. barbipes and E. pagana i n the f o l l o w i n g manner: ( i ) Cricotopus - Chironomus anthracinus s u b d i v i s i o n contains species prominent i n three lakes (East L., Barkley L., Box 17) having con-d u c t i v i t i e s ranging from 488 to 741 umho/cm and T.D.S. concentrations of 372 to 571 mg/1. The O r t h o c l a d i i n a e , e s p e c i a l l y the genus Cricotopus 87 are important. As w e l l as being t y p i c a l of the profundals of o l i g o t r o p h i c lakes (Brundin, 1951) the O r t h o c l a d i i n a e are o f t e n dominant i n the l i t t o r a l s of eutrophic waters (Sandberg, 1969). j The genus Chironomus, represented e s p e c i a l l y by C. anthracinus, makes an appearance. This sub-d i v i s i o n may be considered a t r a n s i t i o n between the unique freshwater species of Box 27 and the la r g e middle s a l i n i t y a s s o c i a t i o n dominated by G. barbipes and E. pagana. The Chironomus tentans s u b d i v i s i o n i n c l u d e s species c h a r a c t e r i s t i c of c o n d u c t i v i t i e s from 810 to 1500 umho/cm (Near Opposite Crescent to R o c k L . ) . I t reaches i t s most d i s t i n c t i v e form i n Westwick and Sorenson Lakes (1200 to 1500 umho/cm) whose most important f e a t u r e s are high l e v e l s of organic carbon,low oxygen tensions, Najas beds i n deep mud, Scirpus at the margins and la r g e mats of Spirogyra. At 1.0 meter the c h a r a c t e r i s t i c chironomid i s C. tentans. Chironomus n. sp. i s c h a r a c t e r i s t i c of the most s a l i n e lakes dominated by G. barbipes and E. pagana - Lakes Greer and Jackson w i t h an upper l i m i t of 2766 umho/cm c o n d u c t i v i t y and 2.5°/oo s a l i n i t y . Large blue-green a l g a l blooms (Aphanozomenon) are common from June to September. 88 The major predaceous chironomid i s the la r g e Derotanypus a l a s k e n s i s which reaches i t s g r e a t e s t density i n the higher s a l i n i t i e s . The most i n t e r e s t i n g observa-t i o n concerning the G. barbipes - E. pagana a s s o c i a t i o n i s the f a c t that the three species of Chironomus are found i n a l l ten l a k e s , but at 1.0 meter each i s most abundant i n a p a r t i c u l a r group of lake s . Thus C. anthracinus reaches greater proportions i n the f r e s h e r l a k e s , C. tentans i n the medium s a l i n i t i e s and C. n.sp. i n the most s a l i n e lakes dominated by G. barbipes and E. pagana. c) The Calopsectra g r a c i l e n t a - Cryptotendipes a r i e l a s s o c i a t i o n Above a c o n d u c t i v i t y of 4000 jumho/cm and a T.D.S. conc e n t r a t i o n of 3000 mg/1 an e n t i r e l y new species composi-t i o n appears. This group of species i s a s s o c i a t e d w i t h c o n d u c t i v i t i e s up to 1200 umho/cm and mean pH readings from 8.9 to 9.3 (Boitano L., L. Lye, Round-up L. and Barnes L . ) . Calopsectra g r a c i l e n t a i s one of the dominant species of the above three l e s s s a l i n e l a k e s . I t tends to be replaced by Cryptotendipes a r i e l as the s a l i n i t y i n c r e a s e s . Chironomus n.sp. i s the major component of the Barnes L. chironomid fauna (46%) and makes up 16 per cent of the emerging Boitano L. fauna. I t i s not abundant i n Round-up L. or L. Lye. Derotanypus a l a s k e n s i s i s most abundant i n L. Lye, but i s l a r g e l y replaced by Pr o c l a d i u s clavus as the main predaceous chironomid i n the high s a l i n i t i e s of Round-up and Barnes Lakes. The biomass f i g u r e s f o r t h i s a s s o c i a t i o n of species w i t h a hig h tolerance of s a l i n e waters are r e l a t i v e l y low Although there are numerous species and l a r g e numbers of some species present, the l a r v a e of these forms are small The i n d i c e s of d i v e r s i t y f o r Round-up L., L. Lye and e s p e c i a l l y Boitano L. (2.74) are high. Barnes L. has the lowest index of a l l the lakes (0.90); c e r t a i n l y a r e f l e c -t i o n of the lake's high s a l i n i t y . The biomass i s about 16 times that of Round-up L. p r i n c i p a l l y because of the presence of l a r g e numbers of Chironomus n. sp. which reaches a considerable s i z e . TABLE XIV The percentage composition of species i n the lakes based on the t o t a l a d u l t emergence May - August 1970. 90 Barnes L. Chironomus n.sp. 46 Procladius clavus 30 Cryptotendipes a r i e l 17 Procladius dentus 4 Others 3 Boitano L. Calopsectra g r a c i l e n t a 71 Chironomus n.sp. 16 Procladius freemani 4 Derotanypus a l a s k e n s i s 2 Others 7 -Rock L. E i n f e l d i a pagana 37 Glyptotendipes barbipes 31 Derotanypus a l a s k e n s i s 15 Procladius .fr.eemani 7 Others 10 Sorenson L. Glyptotendipes barbipes 36 Chironomus tentans 18 E i n f e l d i a pagana 18 PsectrocTadiiis barbimanus 18 Others 10 f Barkley L. Glyptotendipes barbipes 21 E i n f e l d i a pagana 21 P s e c t r o c l a d i u s barbimanus 12 Cricotopus f l a v i b a s i s 12 Others 34 Round-up L. Cryptotendipes a r i e l 47 Calopsectra g r a c i l e n t a 24 P s e c t r o c l a d i u s barbimanus 6 Procladius clavus 10 Others 13 L. Jackson E i n f e l d i a pagana 35 Glyptotendipes barbipes 29 Derotanypus a l a s k e n s i s 9 Chironomus n.sp. 16 Others 11 Near Phalarope P s e c t r o c l a d i u s barbimanus 65 Cricotopus f l a v i b a s i s 18 Glyptotendipes barbipes 8 Derotanypus a l a s k e n s i s 5 Others 4 Near Opposite Crescent Glyptotendipes barbipes 65 E i n f e l d i a pagana 31 Procladius b e l l u s 1 Per o tanypu s~~ala s kens i s 1 Others 2 East L. Glyptotendipes barbipes 29 E i n f e l d i a pagana 25 Derotanypus a l a s k e n s i s 23 Cricotopus f l a v i b a s i s 11 Others 12 L. Lye P s e c t r o c l a d i u s barbimanus :32 Calopsectra g r a c i l e n t a 28 Derotanypus a l a s k e n s i s 25 Procladius clavus 9 Others 6 L. Greer Glyptotendipes barbipes '22 Derotanypus a l a s k e n s i s 22 E i n f e l d i a pagana 20 Chironomus n.sp. . 16 Others 20 Westwick L. E i n f e l d i a pagana 73 Chironomus tentans 19 Glyptotendipes barbipes 4 P s e c t r o c l a d i u s barbimanus 2 Others 2 Box 17 Glyptotendipes barbipes 29 E i n f e l d i a pagana 23 Chironomus anthracinus 20 Cricotopus albanus 14 Others 14 Box 27 P r o c l a d i u s b e l l u s 64 Cricotopus albanus 22 Ablabesmyia p e l e e n s i s 14 91 C. DISCUSSION 1. The Chironomidae and the Lake S e r i e s I t has long been known that the aquatic d i p t e r a (the Chironomidae i n p a r t i c u l a r ) represent one of the most di v e r s e and adaptable freshwater groups. Suworow (1908) found a species of Chironomus i n Lake Bulack on the K i r g i z Steppe i n s a l i n i t i e s of 285 °/oo, e i g h t times the s a l i n i t y of the sea. Chironomus plumosus i s known to l i v e i n nature a t a pH of 2.3 (Harp and Campbell, 1967). Such v e r s a t i l i t y makes chironomids i d e a l organisms w i t h which to study the e f f e c t s of v a r i a b l e chemical c o n d i t i o n s on an assemblage of r e l a t e d species. Obviously, the chironomids i n the lake s e r i e s are adapted to t h e i r t o t a l environment. But what are the main f a c t o r s determining the general d i s t r i b u t i o n patterns described? In the past, chironomid d i s t r i b u t i o n data has l a r g e l y come from s t u d i e s on the c l a s s i f i c a t i o n of the lake types u s i n g the dominant profundal chironomid fauna present (Brundin, 1949, 1951). An examination of t h i s i n f o r m a t i o n i n the context of the present research may lead to a b e t t e r understanding of the f a c t o r s i n f l u e n c i n g chironomid d i s t r i b u -t i o n i n the l a k e s . The c l a s s i f i c a t i o n of lake t r o p h i c types was f i r s t i ntroduced by Thienemann (1920) and f u r t h e r developed i n works by Lenz (1925), Lundbeck (1926) and Humphries (1936) f o r most of c e n t r a l and northern Europe. Brundin (1958) studi e d t h i s concept on a greater scale and found that the c l a s s i f i c a t i o n , w i t h r e g i o n a l v a r i a n t s i n species, was v a l i d the world over. This c l a s s i f i c a t i o n may be general-i z e d i n the f o l l o w i n g manner. O l i g o t r o p h i c lakes are u s u a l l y dominated by species of the subfamily O r t h o c l a d i i n a e These are small forms l a c k i n g hemoglobin. Lakes becoming more productive (moderately o l i g o t r o p h i c ) are more and more dominated by a Tanytarsus fauna, mesotrophic lakes c o n t a i n p r o p o r t i o n a l l y l a r g e r profundal populations of the Chironomini ( e s p e c i a l l y those without v e n t r a l t u b u l e s ) , w h i l the profundals of eutrophic lakes c o n t a i n mainly l a r g e , hemo gl o b i n - b e a r i n g Chironomus species. These l a r g e l a r v a e have v e n t r a l tubules and are represented by forms such as C. anthracinus and i n the most eutrophic areas, C. plumosus (Brundin, 1958). Deevy (1942), Goulden (1964) and S t a h l (1969) note that i n s t r a t i f i e d lake d e p o s i t s the f o s s i l chironomids o f t e n show a succession from Tanytarsus through to Chironomus, c o r r e l a t e d w i t h the lake's e v o l u t i o n a r y sequence from o l i g o t r o p h y to eutrophy. In one of h i s e a r l i e s t papers on the sub j e c t , Brundin (1949) noted that the a s s o c i a t i o n of chironomids and t r o p h i c lake type i s not d i r e c t , but i s more a f u n c t i o n of the annual minimum oxygen c o n c e n t r a t i o n that can be withstood by the l a r v a e . Since hemoglobin i s known to a i d l a r v a e i n wit h s t a n d i n g low oxygen c o n d i t i o n s (Walshe, 1947 A,B, 1950; Harnish, 1960), the more hemoglobin present and the l a r g e r the s i z e of the l a r v a , the l e s s d i f f i c u l t y there i s i n over-93 coming the m i c r o s t r a t i f i c a t i o n of reducing c o n d i t i o n s on the surface of the sediment (Brundin, 1951). The supply of oxygen to the bottom of the lake i s a f f e c t e d by the volume of the hypolimnion and the du r a t i o n of s t r a t i f i c a t i o n as w e l l as the amount of decomposable organic matter i n the hypolimnion. There i s no r i g i d connec-t i o n between oxygen d e f i c i t and lake p r o d u c t i v i t y since lake morphometry, among other t h i n g s , complicates the s i t u a t i o n . However, as Mundie (1957) e x p l a i n s , " I t so happens that i n very many lakes eutrophy i s a s s o c i a t e d w i t h a high oxygen con c e n t r a t i o n d e f i c i t and o l i g o t r o p h y w i t h a low d e f i c i t , so that a c o r r e l a t i o n between lake type and chironomid type emerges". A s a l i n e l a k e s e r i e s , however, has never before been stud i e d i n t h i s context. The s i m i l a r morphometry and the l a c k of thermocline formation i n the lakes under study (or at l e a s t the l a c k of hypolimnic e f f e c t on the depth zone under c o n s i d e r a t i o n ) r e s u l t i n comparable oxygen concentrations throughtout the lake s e r i e s . As oxygen would seem to have l i t t l e i n f l u e n c e on o v e r a l l d i s t r i b u t i o n p a t t e r n s , an examination of product-i v i t y trends could be i n s t r u c t i v e . I t might be expected that organic carbon would be a s u i t a b l e measure of general p r o d u c t i v i t y , w i t h oxygen l e v e l s decreasing i n areas of abundance much i n the way oxygen d e f i c i t s appear i n h i g h l y eutrophic waters. Although organic 94 carbon and oxygen l e v e l s show an inverse r e l a t i o n s h i p (Figure 26) (the c o r r e l a t i o n i s -.649, p<.01), there i s no i n d i c a t i o n that these parameters f o l l o w the general trend of i n c r e a s i n g p r o d u c t i v i t y w i t h i n c r e a s i n g s a l i n i t y (Rawson and Moore, 1944). A high abundance of chironomids i n Westwick and Sorenson Lakes might be expected, since the organic carbon l e v e l s peak there, but the l a r v a l den-s i t y i s q u i t e low. And i n t h i s case the low numbers are due to low d e n s i t i e s of species that should be able to e a s i l y w i t h s t and the lower oxygen l e v e l s present. No i n d i c a t i o n that t h i s p a u c i t y was due to increased predation was found. The photosynthetic a c t i v i t y i n the lake s e r i e s was not examined. P r e l i m i n a r y l i g h t and dark b o t t l e s t u d i e s have r e c e n t l y been i n s t i g a t e d , however, and seem to i n d i c a t e that the f r e s h and moderately concentrated lakes d i s p l a y three to f i v e times the photosynthetic production of the very s a l i n e water bodies (Reynolds, pers. comm.). The lakes where, the G. barbipes - E. pagana a s s o c i a t i o n p r e v a i l s have s a l i n i t i e s ranging from 0.3 to 2.5 °/oo. These concentrations are not so high as to adversely a f f e c t primary production and con-sequently the lakes have a l a r g e phytoplankton stock and i n most cases a p e r i p h e r a l b e l t of emergent v e g e t a t i o n . Such eutrophic c o n d i t i o n s are i d e a l f o r the l a r g e r Chironomini. Moreover, there i s some evidence that the f r e s h e r lakes are l e s s productive than the moderately s a l i n e ones, according to Reynolds (pers. comm.). In Box 27 chironomids u s u a l l y domi-n a t i n g the substrate of the lakes are conspicuously few, 95 w h i l e the Chironomus species are e n t i r e l y absent. This i s probably due to the l a c k of d i s s o l v e d n u t r i e n t s and a r e s u l -t ant low l e v e l of phytoplankton. D e t r i t u s and algae are the main food items of the l a r g e r tube d w e l l i n g species. L e l l a k (1965) and Jonasson (1954) note that the production of Chironomus species i s dependent on:the amount of phyto-plankton i n the water column. Amounts of d i s s o l v e d s o l i d s i n the water are o f t e n used as measures of p r o d u c t i v i t y . In a l a r g e r number of B r i t i s h Columbia la k e s Northcote and L a r k i n (1956) found that plankton and benthic fauna increased w i t h i n c r e a s i n g T.D.S., although the concentrations they considered were comparable to only the f r e s h e r lakes i n the present study. Rawson and Moore (1944) examined a l a r g e number of lakes on the Saskatchewan p r a i r i e , some of which were s i m i l a r to the lakes i n the C a r i b o o - C h i l c o t i n area. Again, a trend of i n c r e a s i n g abundance of bottom fauna w i t h i n c r e a s i n g T.D.S. was observed up to a c o n c e n t r a t i o n of 2250 ppm. The number of bottom organisms decreased w i t h i n c r e a s i n g s a l i n i t y past t h i s p o i n t . A s a l i n i t y of 2250 ppm approximates that of L. Jackson. Fig u r e 25 shows the chironomid l a r v a l biomass i n the l a k e s e r i e s and r e v e a l s a s i m i l a r decrease i n benthic fauna above a c o n c e n t r a t i o n of 2250 ppm. The low l e v e l s i n Rock L., Near Phalarope, Westwick L. and Sorenson L. are anomalous i n t h i s context. Indeed, a l i n e a r r e g r e s s i o n performed on the p o i n t s i n the graph showed the p r o b a b i l i t y of the slope being FIGURE 25 Chironomid l a r v a l biomass and index of d i v e r s i t y f o r the l a r v a l complexes at 1.0 m i n the lake s e r i e s . INDEX OF DIVERSITY LARVAL BIOMASS (CM3/M2) CO b NO b o o o o o o o o o o Barnes L. Round-up L. L. Lye Boitano L. L. Jackson L. Greer Rock L. N. Phalarope Westwick L. Sorenson L. N. Op.Cres. Box 17 Barkley L. East L. Box 27 « FIGURE 26 Graph showing the r e l a t i o n s h i p between oxygen l e v e l s and organic carbon i n the l a k e s . PER CENT OF ORGANIC CARBON & 0 2 LEVELS (MG / L) rO _ i 4v _ i Ol _ i o i 0 0 I -O Box 27 East L. Barkley L. Box 17 N.Op. Cres. Sorenson L. -Westwick L. -N. Phalarope Rock L. L.Greer L.Jackson Boitano L. L. Lye Round-up L. Barnes L. 98 zero was .29. I t i s p o s s i b l e that chironomid l a r v a l biomass alone i s a poor i n d i c a t o r of r e l a t i v e p r o d u c t i v i t y i n lakes and that the i n c l u s i o n of other benthic and p l a n k t o n i c organisms would a l t e r the r e l a t i v e biomass r e s u l t s . In the lake s e r i e s as a whole, i t would seem that the b a s i c d i s t r i b u t i o n a l p a t t e r n i s l a r g e l y the r e s u l t of i n t e r -play between s a l i n i t y and p r o d u c t i v i t y . The very low d e n s i -t i e s of l a r v a e and the high d i v e r s i t y i n Box 27 are notable, and i n i t s chironomid fauna and chemistry the lake resembles an o l i g o t r o p h i c one. In s a l i n i t i e s above that of Box 27 the species types change markedly and represent e s s e n t i a l l y a eutrophic lake fauna. A c t u a l l y , a l l the lakes considered must be termed eu t r o p h i c , although i f the a r b i t r a r y f i g u r e of W i l l i a m s (1964) i s adopted, only those lakes w i t h a s a l i n i t y of 3 °/oo (Boitano L.) and above can be c l a s s e d as s a l i n e eutrophic l i k e the lakes described by Decksbach (1924), Hutchinson (1932), Rawson and Moore (1944) and Bayly and W i l l i a m s (1966). This demarkation a p p l i e s n i c e l y to t h i s study since the change from a chironomid fauna t y p i c a l of h i g h l y eutrophic waters to a community r a t h e r r e s t r i c t e d to o , high s a l i n i t i e s occurs at t h i s 3 /oo s a l i n i t y p o i n t . The b i o m a s s - d i v e r s i t y r e l a t i o n s h i p s i n t h i s t r a n s i t i o n are a l s o important. Chironomid biomass i n the eutrophic, blue-green algae r i c h L. Greer and L. Jackson i s h i g h , mainly due to l a r g e numbers of G. barbipes, E. pagana and C^n.sp. But because of t h i s domination the numbers of species and the d i v e r s i t y are low. The biomass i n the four lakes r e p r e s e n t i n g s a l i n i t i e s above 3 °/oo i s very low w h i l e the d i v e r s i t i e s i n two of these lakes (Boitano L . j L. Lye) are higher than i n any other l a k e - perhaps due to the presence of species that can t o l e r a t e high s a l i n i t i e s as w e l l as moderate ones. Although i t i s expected that rooted p l a n t s complicate any environment and encourage d i v e r s i t y by i n c r e a s i n g niches and s t a b i l i z i n g i n t e r a c t i o n s (Wohlschlag, 1950), the absence of rooted p l a n t s i n these h i g h s a l i n i t y l akes does not seem to have a great e f f e c t on d i v e r s i t y . The very low d i v e r s i t y i n Barnes L. i s c e r t a i n l y a r e f l e c t i o n of very high i o n i c con-c e n t r a t i o n s r a t h e r than the r e s u l t of any reduced complexity owing to the absence of aquatic p l a n t s . Primary production i n the higher s a l i n i t i e s i s reduced. This s i t u a t i o n , along w i t h the above mentioned p r o d u c t i v i t y - d i v e r s i t y r e l a t i o n s h i p i n L. Greer and L. Jackson, r e i n f o r c e MacArthur 1s (1965) cont e n t i o n that an increase i n p r o d u c t i v i t y i s not always accompanied by an increase i n d i v e r s i t y . Where production i s increased there i s o f t e n a decrease i n resource v a r i e t y and a greater i n e q u a l i t y of e x i s t i n g resources, tending to decrease d i v e r s i t y . The increase i n chironomid biomass i n Barnes L. i s due to the high d e n s i t i e s of Chironomus n.sp. which reaches a cons i d e r a b l e s i z e . The low numbers of t h i s species i n Round-up L. and Lye L. are not c l e a r , but i t would seem to be 100 something other than s o l u t e c o n c e n t r a t i o n . C. n.sp. occurs i n greatest numbers where the d i v e r s i t y i s lowest; t h i s low d i v e r s i t y does not seem to be e n t i r e l y a r e s u l t of i t s owns high numbers. In s i m i l a r s i t u a t i o n s , the absence from f r e s h e r water of a species adapted to hig h s a l i n i t i e s i s not due to hyporegulation d i f f i c u l t i e s , but i s u s u a l l y the r e s u l t of b i o t i c i n t e r a c t i o n s l e a d i n g to e x c l u s i o n by other species (Beadle, 1943; Lauer, 1969; Scudder et a l , 1972). FIGURE 27 S a l i n i t y t o l e r a n c e s of the i d e n t i f i e d species of the one meter depth zone i n the la k e s e r i e s . Tartypus punctlpennls  Derotanypus alaskensis — Derotanypus n.sp. Procladius bellus  Procladius nietus Procladius freemani " Procladius r u r i s — — — Procladius dentus Procladius clavus .  Procladius sublettei , Procladius n.sp. Ablabesmyia peleensis  Nanocladius n.sp. Cricotopus albanus  Cricotopus f l a v i b a s i s — ; _ Cricotopus t r i f a s c i a t u s  Acricotopus n i t i d e l l u s Psectrocladius barbimanus -. — — Psectrocladius zetterstedti -Psectrocladius n.sp. Chironomus anthracinus . Chironomus a t r e l l a — Chironomus tentans . Chironomus plumosus Chironomus n.sp.(near a t r i t i b i a ) Chironomus n.sp. E i n f e l d i a pagana  Cryptochironomus  psittacinus Cryptotendipes a r i e l  Endochironomus nigricans  Glyptotendipe s barbipes 1  Polypedilum n.sp. Calopsectra gracilenta  Calopsectra holochlorus i ' 1 i : 1 1 1 0 3000 ' 6000 9000. 12000 Conductivity (umho/cm at 25°C) 102 2. Chironomus tentans and the Lake Se r i e s Topping (1969, 1971, 1972) has c a r e f u l l y examined the r e l a t i o n s h i p between the d i s t r i b u t i o n of C. tentans l a r v a e and the p h y s i c a l and chemical environment, but l i t t l e has been done to examine how these f a c t o r s , along w i t h b i o t i c i n t e r a c t i o n s , might a f f e c t the i n s e c t ' s l i f e c y c l e . a) P h y s i c a l and Chemical Influences C. tentans i n h a b i t s a s u b s t a n t i a l range of c o n d i t i o n s (Acton and Scudder, 1971). I t has considerable tolerance f o r s a l i n e waters and has been c o l l e c t e d i n the b r a c k i s h waters of the B a l t i c (Palmen and Aho, 1966). In the study area i t s g r e a t e s t abundance and emergence success occurs i n the middle of the s a l i n i t y range, p a r t i c u l a r l y i n Westwick and Sorenson Lakes. There i s much v a r i a t i o n i n developmental time among the C.tentans populations i n h a b i t i n g the s i x l a k e s under c o n s i d e r a t i o n (Table X I I I ) . Comparing the lengths of the s p r i n g generation (second emergence) there i s not r e a l trend, although developmental times i n Sorenson and Rock Lakes are s u b s t a n t i a l l y lower than the r e s t . The r a p i d growth of l a r v a e i n Sorenson L. supports the contention t h a t t h i s i s the most fav o r a b l e h a b i t a t f o r the speci e s , but the s i t u a t i o n i n Rock L. i s more d i f f i c u l t to understand. The b r i e f developmental time (37 days) i s c o n s i s t e n t w i t h r a t e s r e p o r t -ed by Sadler (1935), but i s considerably, shorter than that i n 103 neighboring populations. The postponed emergence of o v e r w i n t e r i n g l a r v a e complicates the s i t u a t i o n f u r t h e r , and i s p o s s i b l y a r e s u l t of a longer w i n t e r diapause or a m a j o r i t y of larvae o v e r w i n t e r i n g i n the t h i r d i n s t a r . Temperature i s u s u a l l y considered a primary f a c t o r i n determining developmental r a t e s ( M i l l e r , 1941; Mundie, 1957; O l i v e r , 1969, 1971). H i l s e n h o f f (1966) found that v a r i a t i o n s i n the development of Chironomus plumosus i n d i f f e r e n t p a r ts of Lake Winnebago could be a t t r i b u t e d to water temperature. Koskinen (1968) a l s o recorded s i m i l a r r e s u l t s f o r y e a r l y v a r i a t i o n i n the emergence times of C. s a l i n a r i u s i n northern Europe. There i s no evidence that d i f f e r e n c e s i n generation times of C. tentans are caused by e i t h e r v a r i a t i o n s i n average temperature (Table I I ) or d i e l temperature range (Figure 4). Considerable work has been done on the e f f e c t of photo-p e r i o d on the development of C. tentans. Englemann and Shappirio (1965) found that diapause at 22°C was maintained by short day periods ( s i x t e e n hours l i g h t ) . C l a r k (1971) recorded t h a t low d a y l i g h t regimes suppressed l a r v a l d e v e l -opment and when such l a r v a e were subsequently placed i n long day length s i t u a t i o n s , emergence success was reduced. Members of the same po p u l a t i o n under i d e n t i c a l tempera-ture and l i g h t regimes may show r a d i c a l l y d i f f e r e n t develop-mental r a t e s . Larvae hatching from the same egg mass o f t e n pupate two or three weeks apart ( C o l l e n , pers. comm.). Up to 90 per cent of f o u r t h i n s t a r s can f a i l to pupate and emerge during the time the r e s t of the pop u l a t i o n does. Numbers of these l a r v a e w i l l emerge along w i t h the a d u l t s of the next generation (Clark, 1971). S i m i l a r asynchrony i n C. tentans populations was e s t a b l i s h e d i n the experimental pond populations studied by H a l l et a l (1970) and Fagan and Enns (1966) observed s i m i l a r e f f e c t s i n populations of Glyptotendipes barbipes i n sewage lagoons. In other i n s e c t s , delayed hatching of eggs has been reported i n the mayfly Ameletus l i n e a t u s (Gibbs, 1971) and t h i s sporadic, asynchro-nous emergence brings a l l the advantages that accrue when the development of segments of the pop u l a t i o n i s staggered. These i n c l u d e the s u r v i v a l of the population through periods of s t r e s s , the l e s s e n i n g of the impact of pre d a t i o n and the re d u c t i o n of crowding and competition. I t must be concluded that since there i s l i t t l e or no d i f f e r e n c e i n the day length changes among the l a k e s , t h i s f a c t o r can ha r d l y be the major cause of d i f f e r e n t i a l s i n the developmental r a t e of the v a r i o u s populations. C. tentans i s most abundant i n h a b i t a t s a s s o c i a t e d w i t h f l o c c u l a n t muds, d e t r i t u s and stands of Scirpus. These c o n d i t i o n s are e s p e c i a l l y w e l l developed i n Sorenson L. and Westwick L. and are a s s o c i a t e d w i t h high l e v e l s of organic carbon (Table I ) . Since C. tentans i s a d e t r i t u s and algae feeder (Sadler, 1935), Topping (1971) used organic carbon as a measure of food abundance i n these same l a k e s . Anderson 105 and Hitchcock (1968) and Palmen and Aho (1966) found that the numbers of Chironomus a t r e l l a and C. tentans r e s p e c t -i v e l y increased i n the presence of organic m a t e r i a l . In stud i e s on the new V o l t a Lake Petr (1971) a l s o noted that areas of h i g h organic content were populated most abundantly by Chironomus species. I t i s p o s s i b l e , then, that the amount of organic carbon i n the mud might be a reasonable measure of food a v a i l a b i l i t y . I f the general c o n d i t i o n s present i n Sorenson L. and Westwick L. are a s s o c i a t e d w i t h high l e v e l s of a v a i l a b l e food, the c o r r e l a t i o n s between l a r v a l abundance and per cent composition of C. tentans and organic carbon may be meaningful. In c o n t r o l l e d experiments, H a l l et a l (1970) found the developmental time of C. tentans l a r v a e was markedly reduced i n treatments w i t h high food l e v e l s and that i n such c o n d i -t i o n s the r a t e of emergence was increased. In the present study organic carbon l e v e l s were found to be c o r r e l a t e d w i t h the number of emerging a d u l t s and the number of emergence peaks. Sorenson Lake, w i t h the l a r g e s t amount of organic carbon, has a Chironomus tentans p o p u l a t i o n that develops much more r a p i d l y than the average. There i s some i n d i c a t i o n , then, that the r e s u l t s reported by H a l l et a l (1970) may be a p p l i e d to t h i s n a t u r a l s i t u a t i o n . The same connection between the p r o d u c t i v i t y of an environment and r e p r o d u c t i v e success i s a l s o reported i n s t u d i e s of the water bug Cenocorixa  b i f i d a h u ngerfordi (Jansson and Scudder, 1973). Females i n 106 h i g h l y productive lakes developed eggs up to a month a f t e r females i n l e s s productive l a k e s ceased reproducing. The increase i n organic carbon i s accompanied by a decrease i n the c o n c e n t r a t i o n of d i s s o l v e d oxygen at the mud surface , r e s u l t i n g i n a negative c o r r e l a t i o n between d i s -solved oxygen and the abundance of C. tentans. Townes (1945), Gerry (1951) and Paine and Gaufin (1956) r e p o r t that C. tentans p r e f e r s low oxygen l e v e l s to high ones and consider the species a good i n d i c a t o r of p o l l u t e d water. b) B i o t i c I n t e r a c t i o n s The l a c k of negative c o r r e l a t i o n s between the abundance of C. tentans and p o t e n t i a l l y competing or predatory species i n d i c a t e s there i s l i t t l e a c t i v e separation of the populations i n the one meter zone, e i t h e r through d i f f e r e n t i a l r e a c t i o n to p h y s i c a l and chemical f a c t o r s or through b e h a v i o r a l a c t i v i t y . F u r t h e r , the l a c k of p o s i t i v e c o r r e l a t i o n s suggests that strong i n t e r a c t i o n between C. tentans and c o e x i s t i n g species i s reduced. Nevertheless, i t i s i n t e r e s t i n g that three species of the genus Chironomus c o e x i s t i n r e l a t i v e l y l a r g e numbers i n the one meter zone. The competitive e x c l u s i o n p r i n c i p l e has been formulated by many w r i t e r s i n c l u d i n g E l t o n (1946), Hutchinson (1957) and Hardin (1960). DeBach (1966) summa-r i z e s the modern v e r s i o n : " D i f f e r e n t species having i d e n t i c a l e c o l o g i c a l niches cannot e x i s t f o r long i n the same h a b i t a t " . 107 In the case of C. tentans, C. anthracinus and n.sp., the e c o l o g i c a l niches appear somewhat d i f f e r e n t . I t has been shown that there i s a general separation of the three species w i t h regard to the lakes i n which each i s dominant, the i m p l i c a t i o n being that the species have d i f f e r e n t preferences towards s a l i n i t y or r e l a t e d f a c t o r s . F u r t h e r , Topping (1971) has observed that C. anthracinus and n.sp. increase i n abundance w i t h depth, showing greater d e n s i t i e s i n areas not i n h a b i t e d by C. tentans. I t i s not c l e a r whether t h i s i n d i c a t e s some i n t e r s p e c i f i c i n t e r -a c t i o n preventing C. tentans from a c t i v e l y l i v i n g below two meters or whether i t simply r e v e a l s d i f f e r e n t t o l e r a n c e s to environmental v a r i a t i o n w i t h depth. At any r a t e , i n the one meter depth zone there i s no i n d i c a t i o n of such strong sepa-r a t i o n . The f a c t that G^_n.sp. i s so abundant i n Barnes L. where C. tentans and C. anthracinus cannot e x i s t may simply be a r e s u l t of the i n s e c t l i v i n g i n i t s most fa v o r a b l e h a b i t a t r a t h e r than a r e s u l t of decreased competition f o r food or space. But the opposite i s suggested by other i n f o r m a t i o n . Although randomness was not t e s t e d , smaller standard devia-t i o n s and the greater smoothness of the abundance curve i n d i c a t e that Cj_ n.sp. i s more randomly d i s t r i b u t e d i n Barnes L. than i n other l a k e s . Paterson and Fernando (1971) found that C. attenuatus and G. barbipes, probably through a b e h a v i o r a l mechanism, tended to become randomly d i s t r i b u t e d i n a uniform environment when present i n h i g h d e n s i t i e s . This was assumed to be a r e s u l t of the l a c k of v a r i a t i o n i n the b i o t i c ( i . e . predation and competition) and a b i o t i c environ-ment. Barnes L. i s a good example of such a h a b i t a t and i t i s not s u r p r i s i n g that s i m i l a r r e s u l t s are found. I t i s a l s o s t r i k i n g that i n Barnes L. where C^n.sp. reaches numbers ten times those i n any other l a k e , the predaceous D. a l a s k e n s i s i s very scarce. In L. Lye i t i s abundant w h i l e C^n.sp. i s completely absent. Whether i t i s the high s a l i n i t y or the reduced competi-t i o n that r e s u l t s i n the asynchronous emergence of C. n.sp. from Barnes L. i s unknown, but the l a t t e r i s a p o s s i b i l i t y . S i m i l a r staggering of developmental times are evident i n the case of C. tentans. The histograms show peaks o c c u r r i n g at d i f f e r e n t times from those of C. anthracinus and n.sp. although the patterns are not i d e n t i c a l i n each l a k e . That C. tentans, C. anthracinus and G. barbipes f o u r t h i n s t a r abundances were c o r r e l a t e d i n May, but not afterwards perhaps i n d i c a t e s that a d i f f e r e n t i a l development r a t e a f t e r the May emergences i s operating to keep the population peaks staggere A spacing of the l i f e c y c l e s of c o e x i s t i n g i n s e c t s w i l l reduc the i n t e n s i t y of competition f o r a v a i l a b l e resources (Ide, 1935; l i l i e s , 1952; Corbet, 1964). Kajak et a l (1968) showed that i n experimental s i t u a t i o n s increased i n t r a - and i n t e r s p e c i f i c competition reduced the i n t e n s i t y of feeding, slowed down growth and increased m o r t a l i t y . FIGURE 28 Examples of the spacing of emer-gence times of Chironomus tentans and three c o e x i s t i n g species. A. Chironomus anthracinus B. Chironomus n.sp. C. Glyptotendipes barbipes 110 Other i n t e r a c t i o n s can be i n f e r r e d from the c o r r e l a -t i o n s t u d i e s . When the l a r v a l numbers of C. tentans are h i g h the emergence times of C. anthracinus are delayed (and v i c e v e r s a ) , perhaps i n d i c a t i n g suppression of the develop-ment of the scarcer species. A dominant species l i k e l y has an advantage i n o b t a i n i n g food. The per cent composition of C. tentans i s c o r r e l a t e d w i t h an i n c r e a s i n g number of emer-gence peaks, suggesting a more r a p i d development i n areas of greater dominance. C. tentans emergence i s a l s o much greater i n h a b i t a t s where the d i v e r s i t y of chironomid l a r v a e i s reduced. The evidence f o r e c o l o g i c a l s eparation of C. tentans and i t s two r e l a t i v e s i s not d e c i s i v e , but there seems to be a mechanism ( i . e . d i f f e r e n c e s i n diapause.length) by which emergence times, and thus maximum development pe r i o d s , are staggered. That C. anthracinus and n.sp. are f u r t h e r separated from C. tentans by depth i n d i c a t e s t h i s asynchrony may be important only i n the p e r i p h e r a l parts of the h a b i t a t where contact i s g r e a t e s t . The problem of the separation of C. anthracinus and n.sp. i s even more d i f f i c u l t . Emer-gence times are more c l o s e l y l i n k e d (Figures 18 - 22); depth preferences are a l s o s i m i l a r . Chemical t o l e r a n c e s are d i f -f e r e n t , but i n areas of coexistence the f a c t o r s that a l l o w the two species to l i v e together are unclear. C o r r e l a t i o n r e s u l t s show that E i n f e l d i a pagana, Glyptotendipes barbipes and D. a l a s k e n s i s i n h a b i t the same type of h a b i t a t . Because i t i s the l a r g e s t and most abundant predaceous chironomid i n the lake system, D. a l a s k e n s i s might be expected to i n f l u e n c e the abundance of C. tentans. Owing to the l a r g e numbers of E. pagana and G. barbipes, these species are probably C. tentans' strongest competition (besides other Chironomus species) f o r food and space. The f o u r t h i n s t a r l a r v a e of D. a l a s k e n s i s reach t h e i r peak abundance during e a r l y July.- This i s the p e r i o d during which the most se r i o u s predation on the l a r g e r chironomids might be expected to occur. At t h i s time the m a j o r i t y of C. tentans l a r v a e are a l s o f o u r t h i n s t a r . Since most l i t e r a -ture on the subject of Tanypodine food s t a t e s that u s u a l l y newly hatched chironomids or l a t e r i n s t a r s of the smaller genera (Tanytarsus, P a g a s t i e l l a ) are eaten (Leathers, 1922; Armitage, 1968; Roback, 1969) perhaps the o v e r a l l predation on C. tentans i s s m a l l . The l i f e c y c l e s of G. barbipes and E. pagana are staggered; t h i s enables both species to dominate the lakes of medium s a l i n i t y . In Westwick and Sorenson Lakes d e n s i t i e s of these two species are unusually low, whereas C. tentans makes up f i f t y per cent of the l a t e summer chironomid fauna i n Sorenson Lake. In the other lakes the l a r g e number of G. b a r b i p e s j E. pagana and to some extent the other Chironomus species creates a more i n t r i c a t e s t r u c t u r e that l i k e l y r e s t r i c t s the success of C. tentans. What i s the explanation f o r the low d e n s i t i e s of G. barbipes and E. pagana i n Sorenson and Westwick Lakes? I f the two species do not t h r i v e i n low oxygen and high organic carbon c o n d i t i o n s , then t h i s would be s u f f i c i e n t to lower t h e i r numbers. But Gerry (1951) and Sturgess and Goulding (1968, 1969) have concluded that Glyptotendipes l o b i f e r u s and G. barbipes are more t o l e r a n t of anaerobiosis than Chironomus species. G. barbipes can s u r v i v e anaerobi-o s i s about ten times longer than C. r i p a r i u s (Sturgess and Goulding, 1968) although low oxygen c o n d i t i o n s reduce i t s growth (Kimerle and Anderson, 1971). No p e r t i n e n t informa-t i o n i s a v a i l a b l e f o r E. pagana, but specimens kept i n b o t t l e d mud and water were able to s u r v i v e at l e a s t f i v e days w h i l e Chironomus c o l l e c t i o n s died a f t e r two days. The reasons f o r the lower numbers of G. barbipes and E. pagana i n Westwick and Sorenson Lakes are not understood; neverthe-l e s s , the absence of high l e v e l s of competition seems to play an important r o l e i n the existence of C. tentans i n these l a k e s . 113 IV CHIRONOMUS TENTANS AND SOME BIOTIC FACTORS AFFECTING CHROMOSOME INVERSION A. MATERIALS AND METHODS 1. Background Topping (1969) has described the i n v e r s i o n frequencies i n the s a l i v a r y chromosomes of some of the same Chironomus  tentans populations that the present study has analyzed. He concluded that the i n v e r s i o n frequencies d i f f e r e d s i g n i f i c a n t -l y i n d i f f e r e n t l a k e s , but d i d not d i f f e r w i t h i n l a k e s . I t i s very important to note that the frequencies of the i n v e r s i o n 1 Rad (the i n v e r s i o n considered i n t h i s study) do not vary s i g n i f i c a n t l y e i t h e r s e a sonally or annually (Acton, pers. comm.; Topping, 1969). The d e t a i l s of these and other chromo-some analyses may be found i n Topping (1969). Topping notes, "The i m p l i c a t i o n of the long term s t a b i l i t y of i n v e r s i o n s i n chromosome 1 i s that the i n v e r s i o n s are adapted to r e l a t i v e l y s t a b l e environmental f a c t o r s " . There-f o r e he attempted to c o r r e l a t e the i n v e r s i o n frequency w i t h p h y s i c a l and chemical parameters. S u r p r i s i n g l y , none of these r a t h e r s t a b l e environmental f a c t o r s c o r r e l a t e d w i t h i n v e r s i o n frequency; the only v a r i a b l e to do so was a b i o l o g i c a l one -the number of other chironomids i n the environment. The long term s t a b i l i t y of i n v e r s i o n 1 Rad enables Topping's data to be used i n f u r t h e r , more d e t a i l e d c o r r e l a -t i o n s t u d i e s . The v a r i a b l e "number of other chironomids" can 114 be d i v i d e d i n t o a number of more r e s t r i c t e d b i o t i c para-meters . 2. The U.B.C. T r i a n g u l a r Regression Package was again used i n the c o r r e l a t i o n a n a l y s i s . U nfortunately the use of a s e r i e s of lakes i n t h i s study s l i g h t l y d i f f e r -ent from the one examined by Topping precludes the d i r e c t comparison of c o r r e l a t i o n s . Topping used twelve lakes f o r h i s a n a l y s i s ; only the eig h t lakes i n the present study having i n v e r s i o n data are used here. 115 B. RESULTS Three environmental f a c t o r s were found to c o r r e l a t e (p<.05) w i t h the i n v e r s i o n frequency of 1 Rad (Table XVI). These are sodium c o n c e n t r a t i o n (.770), d i s s o l v e d oxygen (.740) and the amount of organic carbon i n the h a b i t a t (-.796). A s i g n i f i c a n t c o r r e l a t i o n between the number of Glyptotendipes barbipes l a r v a e and 1 Rad frequencies (.734) was a l s o discovered (Table X V I I ) . There was no s i g n i f i c a n t c o r r e l a t i o n between the 1 Rad frequencies and the t o t a l number of chironomids, biomass or the index of d i v e r s i t y . TABLE XV In v e r s i o n frequencies i n chromosome 1 of C. tentans. Samples c o l l e c t e d i n 1967. From Topping, 1969. Water Body Frequency Frequency Sample of i n v e r s i o n of i n v e r s i o n S i z e Rad Rade L. Jackson L. Greer Near Phalarope Near Opposite Crescent Barkley L. East L. Westwick L. Sorenson L. 79.4 20.6 364 81.4 18.6 220 77.3 22.7 1168 74.3 25.7 214 74.7 25.3 186 78.6 21.4 220 73.6 26.4 1220 74.3 25.7 2066 TABLE XVI Summary of c o r r e l a t i o n c o e f f i c i e n t s d e s c r i b i n g the r e l a t i o n s h i p between the frequency of 1 Rad and some environmental f a c t o r s . With 6 degrees of freedom r = 0.707 i s s i g n i f i c a n t at p=.05 and r = 0.834 at p=.01. Con-duc-1 Rad t i v -it y . TDS Na K Ca Mg co 3 HC03 Cl S°4 °2 PH Car-bon ch i r -on. 1 Rad 1.000 Conductivity .411 1.000 T.D.S. .434 .983 1.000 Na .770 .872 .869 1.000 K .668 .766 .713 .914 1.000 Ca -.135 .747 .717 .405 .312 1.000 Mg -.197 .774 .768 .379 .274 .849 1.000 C0 3 .434 .909 .867 .824 .758 .710 .671 1.000 HCO3 .404 .182 .056 .419 .716 -.092 -.246 .327 1.000 Cl .556 .890 .944 .869 .700 .581 .603 .723 .023 1.000 so 4 .196 .899 .936 .653 .434 .792 .895 .764 -.258 .858 1.000 °2 .740 .419 .540 .620 .387 -.068 .082 .251 -.175 .729 .467 1.000 pH -.245 .652 .673 .328 .196 .607 .867 .507 -.313 .493 .780 .109 1.000 Organic Carbon -.796 -.104 -.140 -.521 -.585 .465 .394 -.152 -.510 -.316 .120 -.631 .351 1.000 Total nos. chironomids .438 -.102 -.030 .275 .272 -.322 -.482 -.004 .281 .125 -.236 .325 -.277 -.637 1.000 Index of d i v e r s i t y -.377 -.129 -.259 .295 -.174 .343 .015 .117 .242 -.451 -.217 -.818 -.195 .569 -.319 Biomass .345 -.096 -.005 .149 -.014 -.097 -.410 -.228 -.131 .222 -.092 .389 -.328 -.187 .595 Org- Total anic nos. Diver-s i t y Bio-Index mass I-1 TABLE XVII Summary of c o r r e l a t i o n c o e f f i c i e n t s d e s c r i b i n g the r e l a t i o n s h i p between the frequency of 1 Rad and the abundance of some chironomids. With 6 degrees of freedom r=0.707 i s s i g n i f i c a n t at p=.05 and r=0.834 at p=.01. 1 Rad Derotany- E i n f e l d i a Chironomus Chironomus Chironomus Glyptoten- Procladius Crypto- Rest of pus pagana tentans n.sp. anthraci- dipes (.all chironomus Species alaskensis nus barbipes species) p s i t t a -cinus 1 Rad 1.000 DegPtanypuji 0-415 1.000 alaskensis. / E i n f e l d i a 0.429 0.272 1.000 pagana Chironomus --344 0.194 -0.648 1.000 tentans Chironomus 0-663 0.385 0.332 -0.318 1.000 n.sp Chironomus 0.064 -0.029 0.639 -0.513 -0.071 1.000 anthracinus Glyptotendipes 0.734 0.291 0.674 -0.561 0.428 0.525 1.000 barbipes Procladius 0.329 0.460 0.690 -0.224 -0.051 0.453 0.278 1.000 ( a l l species) Cryptochironomus "0.512 -0.217 -0.743 0.802 -0.438 -0.243 -0.441 -0.595 1.000 psittacinus Rest of species 0.565 0.646 0.425 -0.057 0.156 -0.173 0.475 0.520 -0.456 1.000 Co TABLE XVIII Summary of c o r r e l a t i o n c o e f f i c i e n t s d e s c r i b i n g the r e l a t i o n s h i p between the frequency of 1 Rad and the per cent composition of some chironomids. With 6 degrees of freedom (samples from 8 la k e s ) r=.707 i s s i g n i f i c a n t at p=.05 and r=.834 at p=.01. 1 Rad Derotany- E i n f e l d i a Chironomus Chironomus Chironomus Glyptoten- P r o c l a d i u s Crypto- Remainder pus pagana tentans n.sp. a n t h r a c i - dipes ( a l l chironomus of a l a s k e n s i s nus barbipes species) p s i t t a - Species cinus 1 Rad 1.000 Derotanypus a l a s k e n s i s .392 1.000 E i n f e l d i a  pagana 0.324 -.714 1.000 Chironomus tentans -.556 .837 .828 1.000 Chironomus n. sp. .564 .041 .262 .100 1.000 Chironomus anthracinus .371 -.672 .109 ,489 -.258 1.000 Glyptotendipes Barbipes .538 .644 .007 -.461 .084 .820 1.000 .Procladius (.ail species) .213 -.004 .024 -.226 .501 .333 .085 1.000 Cryptochironomus p s i t t a c i n u s .570 .790 .648 .863 .016 -.465 -.545 ,273 1.000 Remainder c f species -.141 .606 -.161 ,212 -.133 .583 -.549 .428 .333 1.000 h-1 TABLE XIX Summary of the c o r r e l a t i o n c o e f f i c i e n t s d e s c r i b i n g the r e l a t i o n s h i p between the frequency of 1 Rad and some emergence v a r i a b l e s . With s i x degrees of freedom r=0.707 i s s i g n i f i c a n t a t p=.05 and r=0.834 at p=.01. V a r i a b l e s used are emergence numbers, number of emergence peaks and the time of the main emergence. D. E. £ L aTask- ten- n. sp. ensis gana tans nos. nos. nos. nos. .C*. G. D. P p « anth- EITrb- TTnqV- 7^ — £ L D. E. C r n nos ™ = i . n o * n o - no. no — £ a a s -Cinus jpes p e a k s p e a k s p e a k s p - k s — — « ~ t l m c ti» t l m e ^ P . a l a s k p n s J g .561 1.000 numbers E.pagana .299 .553 1.000 numDers ^ e n ^ n s -.632 -.335 -.164 1.000 A m b e r ' s - 5 ? 5 - ° 9 7 ' S 5 6 - 2 7 1 1.000 . S ^ p i f l u a .324 .057 .543 -.168 .911 1.000 Snipes .097 .391 .832 -.238 .210 .188 1.000 ^ l l g p l l ^ .535 .788 .481 -.594 .215 .315 .400 1.000 ^ f S f r f.peaks ^ ^ ^ - 4 5 0 - 2 5 4 -.370 .474 .445 1.000 S f f p e a k s - 5 1 8 - ° 8 5 - 1 6 5 - 9 1 5 - 0 8 5 .060 .064 -.304 -.316 1.000 tTo-?em ?rg. peaks * 1 7 3 " - 1 6 9 - 2 3 8 - 1 2 2 -°04 -.050 -.070 .316 -.180 1.000 C.anthracinus no.ernerg.peaks -.223 -.032 -.302 -.101 -.048 .324 -.330 .257 -.086 -.026 .436 1. 000 C.barbipes -.002 .356 -.223 .022 -.399 -.186 -.134 .565 .046 .124 -.124 .455 1.000 no.emerg. peaks • •»-/.» J-.^UU D. alaskensis emerg.time .362 .167 .148 -.538 .380 .432 .277 .541 .101 -.288 .576 .540 .319 1.000 i^rfttme ' 3 6 5 ^ '™ - " ° -™ -™ .™ -258 -.863 -.058 .230 .278 .156 1.000 C ^ f | £ f ^ e -.237 .295 .744 .437 .155 .266 .713 .162 . i 0 9 .727 -.200 -.189 .028 -.002 -.748 1.000 - 2 2 3 - 2 9 ? - 3 3 4 - 2 8 ? - 3 ° 6 ' 2 3 4 -230 .472 -.037 .852 .323 -.098 .701 -.242 .256 1.000 C ^ a g n ^ s . .021 .135 -.170 -.257 .036 .339 -.246 .589 -.183 -.139 .018 .827 .711 .556 .437 -.177 .013 1.000 f m ^ i f H - 1 6 5 - 2 « - 0 7 1 - 5 5 3 -.776 -.120 -.515 .376 -.297 .451 -.221 -.294 -.182 .151 -.413 .166 -.540 1.000 to C. DISCUSSION The stimulus f o r attempting a study of the b i o t i c i n t e r a c t i o n s i n f l u e n c i n g C. tentans was Topping's (1969) f i n d i n g that the frequency of i n v e r s i o n s i n chromosome 1 was s i g n i f i c a n t l y c o r r e l a t e d w i t h the number of other chironomids i n the environment. Thus the study up to t h i s p o i n t has been concerned w i t h the examination of environ-mental i n f l u e n c e s that might a f f e c t C. tentans. C o r r e l a t i o n r e s u l t s suggest that C. tentans i s par-t i c u l a r l y s u c c e s s f u l i n Sorenson and Westwick Lakes where oxygen l e v e l s are low and organic carbon l e v e l s are high. Also a s s o c i a t e d w i t h these lakes are the drop i n l a r v a l abundance and the poor emergence of E. pagana and e s p e c i a l -l y G. barbipes. Since oxygen l e v e l s , organic carbon and the abundance of G. barbipes c o r r e l a t e w i t h i n v e r s i o n frequency, the chromosome i n v e r s i o n may i n some way be connected w i t h these f a c t o r s . I n v e r s i o n frequencies are lowest i n Sorenson and Westwick Lakes where C. tentans i s favoured, suggesting the i n v e r s i o n may c o n t r o l a mechanism reducing competition w i t h G. barbipes i n areas where p o t e n t i a l i n t e r a c t i o n i s g r e a t e s t . I t was p r e v i o u s l y noted that the abundances of C. tentans and G. barbipes are c o r r e l a t e d i n May, but not i n FIGURE 29 Seasonal v a r i a t i o n i n the frequencies of i n v e r s i o n s of chromosome 1. Percentages expressed along the ord i n a t e have been converted by a r c s i n transformation. Samples are from Near Phalarope Lake, 1967. From Topping, 1969. 122 90 i 10 A — i j — 1 1 1 1 1 MAY JUNE JULY AUG. SEPT. OCT. NOV. 123 any subsequent months and i t was p o s t u l a t e d that during the emergence of o v e r w i n t e r i n g l a r v a e or e a r l y i n the summer generation a spacing of the peak developmental periods occurred. Figure 29 shows that the f o u r t h i n s t a r l a r v a e c o l l e c t e d i n May had lower i n v e r s i o n frequencies i n chromosome 1 than those c o l l e c t e d throughout the r e s t of the summer. The l a t e May emergences of C. tentans are made up from overwintering f o u r t h i n s t a r l a r v a e . I f these l a r v a e are the ones showing lower i n v e r s i o n frequencies, then subsequent c o l l e c t i o n s of f o u r t h i n s t a r l a r v a e would meet w i t h only o v e r w i n t e r i n g l a r v a e and summer generation l a r v a e d i s p l a y i n g higher i n v e r s i o n frequencies. I f t h i s i s so, then the change i n i n v e r s i o n frequency between May and June i s a s s o c i a t e d w i t h the i n i t i a l emergence of C. tentans. I t i s p o s s i b l e that the p o r t i o n of o v e r w i n t e r i n g l a r v a e destined to emerge i n l a t e May has l e s s tendency to segregate i t s e l f (or somehow reduce i n t e r a c t i o n ) from G. barbipes. This behaviour would not be disadvantageous during diapause. In s p r i n g and summer, when food and space are a t a premium, the i n v e r s i o n frequency i s higher and the mechanism reducing i n t e r a c t i o n would become more important. Thus the mechanism might vary on a temporal as w e l l as a l a k e b a s i s ; whenever the p o t e n t i a l competition from G. barbipes i s h i g h , the frequency of the i n v e r s i o n 1 Rad i s high. Perhaps the i n v e r s i o n i n a l a r v a prolongs diapause. There i s no r e a l evidence to support t h i s theory, but i t f i t s the p o s t u l a t e s o u t l i n e d above. C l a r i f i c a t i o n of the i n t e r a c t i o n s between C. tentans and other species and of the r o l e of the chromosome i n v e r s i o n i s most l i k e l y to come from extensive l a b o r a t o r y experiments conducted on c o n t r o l l e d populations of the species i n v o l v e d . M o n i t o r i n g the e f f e c t s of d i f f e r e n t species and d e n s i t y mixtures, food l e v e l s and l i g h t regimes on l i f e c y c l e s and i n v e r s i o n frequencies should enable more d e f i n i t e conclusions to be drawn than were p o s s i b l e i n t h i s f i e l d study. 125 V CONCLUSION Mundie (1957) i n h i s comprehensive study of the Chironomidae of London r e s e r v o i r s s t a t e s , "The study of chironomids can be seen, h i s t o r i c a l l y , to have followed two main l i n e s which may be termed the l i m n o l o g i c a l and the entomological. One has been concerned w i t h the d i s -t r i b u t i o n of d i f f e r e n t kinds of chironomids i n d i f f e r e n t l a k e s , w i t h the a s s o c i a t i o n of these w i t h lake types, and w i t h numbers and weights of chironomids as aspects of lake p r o d u c t i v i t y . The other has d e a l t w i t h the b i o l o g y of p a r t i c u l a r species, w i t h t h e i r feeding h a b i t s , r e s p i r a t i o n , v o l t i n i s m , e t c . These two l i n e s converge at one p o i n t , the c e n t r a l i s s u e i n ecology, i . e . , the problem of the n a t u r a l c o n t r o l of populations". The present study has d e a l t w i t h both of these major l i n e s . The l i m n o l o g i c a l aspects of the work have placed a somewhat d i f f e r e n t emphasis on chironomid d i s t r i b u t i o n . The d i f f e r e n t chironomid a s s o c i a t i o n s described seem to be determined l a r g e l y by s a l i n i t y and a s s o c i a t e d p r o d u c t i v i t y l e v e l s r a t h e r than by oxygen concentrations as has been claimed f o r other lakes (Brundin, 1951). The second avenue of study, the entomological, plays a prominent r o l e i n the i n v e s t i g a t i o n . A major c o n t r i b u t i o n of the work has been a r e v i s i o n of the d i s t r i b u t i o n of many of the chironomid species under c o n s i d e r a t i o n . The f a c t that 126 t h i s p a r t i c u l a r i n s e c t fauna has been l a r g e l y neglected i n B r i t i s h Columbia i s emphasized by the r e s u l t s : eleven species new to B.C., f i v e species new to Canada and seven species new to science (Appendix). One of the main hindrances to advances i n ecology i s taxonomic ambiguity (Macan, 1963). I f u n d e r l y i n g taxonomy i s confused a l l e c o l o g i c a l d i s c u s s i o n s and conclusions are n e c e s s a r i l y meaningless (Lindeberg, 1967). Great pains were taken to make the best p o s s i b l e i d e n t i f i c a t i o n of the species. The importance of being aware of taxonomic prob-lems i n d e a l i n g w i t h e c o l o g i c a l s t u d i e s cannot be over-emphasized. Topping (1969) has shown that the same populations of C. tentans examined i n t h i s study d i s p l a y d i f f e r e n c e s i n the frequency of chromosome i n v e r s i o n s . The present t h e s i s suggests that these i n v e r s i o n s may r e g u l a t e a mechanism r e -ducing competition between C. tentans and other species, e s p e c i a l l y G. barbipes. Such a r e s u l t i s i n accordance w i t h genetic theory which considers i n v e r s i o n s to be adapted to s p e c i f i c e c o l o g i c a l c o n d i t i o n s (Swanson, 1957; Ford, 1964). Such statements concerning the f u n c t i o n of i n v e r s i o n s i n populations of C. tentans are l a r g e l y s p e c u l a t i v e a t t h i s time. However, since so l i t t l e f i e l d work has been done on s i m i l a r problems, any i n s i g h t at a l l i n t o the question i s of use to e c o l o g i c a l l y o r i e n t e d g e n e t i c s . This work may serve as a b a s i s f o r f u r t h e r l a b o r a t o r y s t u d i e s t e s t i n g the v a l i d i t y of the c o r r e l a t i o n s presented, or st u d i e s examining other aspects of the r e l a t i o n s h i p between the chironomid complex and the chromosome i n v e r s i o n frequencies of C. tentans. Although the main o b j e c t i v e was to attempt to r e l a t e the b i o l o g y of C. tentans to the b i o l o g y of c o e x i s t i n g s p e c i e s , the study has thrown some l i g h t on the way species l i f e c y c l e s and species composition may d i f f e r w i t h i n a s a l i n e l a k e s e r i e s . The t h e s i s that a species' l i f e h i s t o r y and population s t r u c t u r e may vary r a d i c a l l y i n c l o s e l y a s s o c i a t e d lakes of d i f f e r i n g chemical and b i o l o g i c a l con-s t i t u t i o n has never r e a l l y been t e s t e d i n the f i e l d before. The phenology of the species o f t e n v a r i e s considerably from lak e to lake even though the lakes may be c l o s e together and s u p e r f i c i a l l y s i m i l a r . D i f f e r e n c e s i n species composi-t i o n and abundance w i t h i n the same type of h a b i t a t are to be expected; environments are never q u i t e the same even when they appear to be. The research, then, emphasizes a b a s i c concept not always appreciated - what i s considered a species i s capable of much v a r i a t i o n i n i t s response to v a r y i n g environmental c o n d i t i o n s . Although the u l t i m a t e o b j e c t of any study of n a t u r a l communities i s a d e t a i l e d understanding of the o r g a n i z a t i o n and i n t e r a c t i o n s of component popu l a t i o n s , such an under-t a k i n g i s too vast f o r a p r e l i m i n a r y study such as t h i s . Mundie (1957) notes that general short term surveys of the chironomid faunas of lakes are l i k e l y to prove i n s u f f i c i e n t l y i n t e n s i v e to add much new knowledge. In the present case, however, j u s t i f i c a t i o n f o r such a survey (which i s as much concerned w i t h d e f i n i n g problems as s o l v i n g them) r e s t s on the f a c t that a s a l i n e lake s e r i e s has not been p r e v i o u s l y s t u d i e d w i t h chironomids i n mind. The t h e s i s was undertaken to add to the knowledge we have of the s a l i n e lakes i n question, and i s a part of a con t i n u i n g examination of how b i o l o g i c a l systems f u n c t i o n i n such environments. 129 LITERATURE CITED Acton, A.B. and G.G.E. Scudder, 1971. The zoogeography and races of Chironomus (Tendipes) tentans Fab. Limnologica 8:83-92. ' Anderson, J.F. and S.W. Hitchcock. 1968. Biology of Chironomus a t r e l l a i n a t i d a l cove. Ann. ent. Soc. 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APPENDIX Species I d e n t i f i e d i n the Study * New records f o r B r i t i s h Columbia ** New records f o r Canada *** Species new to science FAMILY CHIRONOMIDAE SUBFAMILY TANYPODINAE Trib e Tanypodini Tanypus punctipennis Meigen Tr i b e M a c r o p e l o p i i n i Subtribe Macropelopiina Derotanypus a l a s k e n s i s ( M a l l o c h ) * Derotanypus n.sp.*** Subtribe P r o c l a d i i n a P r o c l a d i u s (Psilotanypus) b e l l u s (Loew) P r o c l a d i u s (Psilotanypus) n i e t u s Roback P r o c l a d i u s freemani S u b l e t t e P r o c l a d i u s r u r i s Roback P r o c l a d i u s dentus Roback * Pr o c l a d i u s clavus Roback * P r o c l a d i u s s u b l e t t e i Roback P r o c l a d i u s n.sp. *** T r i b e P e n t a n e u r i n i Ablabesmyia p e l e e n s i s (Whalley) * SUBFAMILY ORTHOCLADIINAE Tri b e O r t h o c l a d i i n i Nanocladius n.sp. *** Cricotopus albanus Curran * Cricotopus f l a v i b a s i s Malloch ** Cricotopus t r i f a s c i a t u s (Panzer) * Acricotopus n i t i d e l l u s M a l l o c h ** P s e c t r o c l a d i u s barbimanus (Edwards) * P s e c t r o c l a d i u s z e t t e r s t e d t i Brundin ** P s e c t r o c l a d i u s n.sp. *** SUBFAMILY CHIRONOMINAE Tr i b e Chironomini Chironomus anthracinus Z e t t e r s t e d t Chironomus a t r e l l a (Townes) * Chironomus tentans F a b r i c i u s Chironomus plumosus (Linnaeus) Chironomus n.sp. (near a t r i t i b i a ) *** Chironomus n.sp. *** E i n f e l d i a pagana Meigen * Cryptochironomus p s i t t a c i n u s Meigen * Cryptotendipes a r i e l (Sublette) ** 142 Endochironomus n i g r i c a n s Johannsen Glyptotendipes barbipes (Staeger) Polypedilum n.sp. *** T r i b e T a n y t a r s i n i C a lopsectra g r a c i l e n t a (Holmgren) * Calopsectra h o l o c h l o r u s (Edwards) ** 

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