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AN EXPERIMENTAL FIELD STUDY OF THE EFFECTS OF INTERSPECIFIC COMPETITION ON DIAPTOMUS LEPTOPUS (COPEPODA:CALANOIDA) IN A MONTANE LAKE by ROBERTA JILL OLENICK B.Sc. Honors, University of Manitoba, Winnipeg, 1978 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES (Department of Zoology) We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA April 1982 0 Roberta Jill Olenick, 1982 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Zoology Department of The University of British Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 April, 1982 Date DE-6 (2/79) David I. MacKenzie, for always caring i i ABSTRACT Despite high densities in an upstream lake, the herbivorous calanoid copepod, Diaptomus leptopus, is extremely rare in oligotrophia Eunice Lake in the Coastal Range Mountains near Vancouver, British Columbia. I_n situ experiments conducted in 1979 and 1980 tested the hypothesis that competition from zooplankton species resident in Eunice Lake prevents immigrant D. leptopus from colonizing the lake. Polyethylene enclosures, each holding 29,000 1 of lake water, contained all experimental treatments. Experiments in 1979 exposed a standard density of D. leptopus to all Eunice Lake zooplankton species at lake densities (control), to all Eunice Lake species at reduced densities (low density), and to all Eunice Lake species except one of Daphnia rosea (Daphnia-removal), Diaptomus kenai (kenai- removal), or Diaptomus tyrelli (tyrelli-removal). Improved performances of D. leptopus in non-control treatments was evidence for competition in controls. Measures of performance included density, number of eggs per female, and adult size. Similarity between D. leptopus performances in control, Daphnia-removal, and kenai-removal treatments plus relatively high concentrations of D. leptopus nauplii in the tyrelli- removal treatment suggested that D. leptopus did not compete with species other than D. tyrelli. However, similarity between tyrelli-removal and low density treatments in concentrations of D. leptopus nauplii confounded competition between D. leptopus and D. tyrelli with diffuse competition from several Eunice Lake species combined. D. leptopus overlapped in vertical distribution and seasonal cycle more with D. tyrelli than with other species. Differences' among experimental treatments in algal size compositions did not conclusively show whether zooplankton partitioned food resources. Experiments in 1980, designed to separate D. tyrelli competition from diffuse competition, did not provide any evidence of interspecific interactions. By increasing zooplankton metabolic efficiencies, cool temperatures in 1980 may have virtually eliminated, competition for algal foods. TABLE OF CONTENTS ABSTRACT ii LIST OF TABLES vii LIST OF FIGURES x ACKNOWLEDGEMENTS xiii INTRODUCTION 1 THE STUDY SYSTEM . 14 MATERIALS AND METHODS 21 EXPERIMENTAL DESIGN, 1979 -25 RESULTS, 1979 '. 28 1. Results Confirming Proper Establishment of Experiments 28 1.1 Enclosure Densities of Abundant Eunice Lake Zooplankton Species 28 1.2 Enclosure Densities of Rare Eunice Lake Zooplankton Species 39 1.3 Effects of Enclosure 47 2. Results Describing Effects of Experiments 49 2.1 Treatment Effects on Total Densities of Diaptomus leptopus 49 2.2 Treatment Effects on Densities of Diaptomus leptopus Eggs, Nauplii, Copepodites, and Adults .. 57 2.3 Treatment Effects on Adult Size of Diaptomus leptopus 62 2.4 Seasonal Cycles, Vertical Distribution and Phytoplankton Biomass 64 3. Summary of 1979 Results 86 EXPERIMENTAL DESIGN, 1980 88 RESULTS, 1980 91 1. Results Confirming Proper Establishment of Experiments 91 1.1 Enclosure Densities of Abundant Eunice Lake Zooplankton Species 91 1.2 Enclosure Densities of Rare Eunice Lake Zooplankton Species 103 1.3 Effects of Enclosure 109 2. Results Describing Effects of Experiments 110 2.1 Treatment Effects on Total Densities of Diaptomus leptopus 110 2.2 Treatment Effects on Densities of Diaptomus leptopus Eggs, Nauplii, Copepodites, and Adults ..116 2.3 Treatment Effects on Adult Size of Diaptomus leptopus 116 2.4 Seasonal Cycles, Vertical Distribution and Phytoplankton Biomass 121 3. Summary of 1980 Results 130 DISCUSSION 132 Separation of Diaptomus tyrelli Competition from Diffuse Competition 132 Vulnerability of Diaptomus leptopus Nauplii to • Competition 136 Relevance of Experimental Results to the Size-Efficiency vi Hypothesis . 137 Relationship Between Temperature and Intensity of Competition .139 Limitations of Phytoplankton Standing Stock Data 145 SUMMARY AND CONCLUSIONS .' 150 LITERATURE CITED 153 LIST OF TABLES Table I. Physical, chemical, and biological characteristics of Gwendoline and Eunice Lakes 17 Table II. Summary of 1979 experimental treatments 26 Table III. T-test statistics comparing mean densities of major Eunice Lake species in Eunice Lake and in control enclosures at start of 1979 experiments 29 Table IV. Statistical tests comparing mean densities of Diaptomus tyrelli across treatments on initial sampling date of 1979 experiments 30 Table V. Statistical tests comparing mean densities of ,Diaptomus kenai across treatments on initial sampling date of 1979 experiments 31 Table VI. Statistical tests comparing mean densities of Daphnia rosea across treatments on initial sampling date of 1979 experiments 32 Table VII. Statistical tests comparing across treatments for mean maximum densities of Bosmina longirostris attained during 1979 experiments 42 Table VIII. Statistical tests comparing across treatments for mean maximum densities of cyclopoid copepodites plus adults attained during 1979 experiments 46 Table IX. Summary of statistical tests comparing mean densities of nauplii, copepodites, adults, and mean total densities of Diaptomus leptopus across treatments vi i i for each sampling date of 1979 experiments 50 Table X. Statistical tests comparing across treatments for mean maximum densities of Diaptomus leptopus attained during 1979 experiments 55 Table XI. Statistical tests comparing across treatments for mean persistence times of Diaptomus leptopus in 1979 experiments 56 Table XII. Statistical tests comparing across treatments for mean number of Diaptomus leptopus eggs produced per female during 1979 experiments 60 Table XIII. Lengths of adult diaptomid copepods and of Daphnia rosea in 1979 experiments 63 Table XIV. Summary of 1980 experimental treatments 89 Table XV. T-test statistics comparing mean densities of major Eunice Lake species in Eunice Lake and in control enclosures at start of 1980 experiments 92 Table XVI. Statistical tests comparing mean densities of Diaptomus tyrelli across treatments on initial sampling date of 1980 experiments 93 Table XVII. Statistical tests comparing mean densities of Diaptomus kenai across treatments on initial sampling date of 1980 experiments 98 Table XXVIII. Statistical tests comparing mean densities of Daphnia rosea across treatments on initial sampling date of 1980 experiments 99 Table XIX. Statitical tests comparing mean densities of Holopedium qibberum across treatments on initial sampling date of 1980 experiments 100 Table XX. Statistical tests comparing across treatments for mean maximum densities of cyclopoid copepods attained during 1980 experiments 108 Table XXI. Summary of statistical tests comparing mean densities of nauplii, copepodites, adults, and mean total densities of Diaptomus leptopus across treatments for each sampling date of 1980 experiments .111 Table XXII. Analysis of variance comparing across treatments for mean number of Diaptomus leptopus eggs produced per female during 1980 experiments 119 Table XXIII. Lengths of adult diaptomid copepods and of Daphnia rosea in 1980 experiments 120 Table XXIV. Maximum lengths arid maximum summer densities of calanoid copepods and Daphn ia rosea in Ratherine, Gwendoline, and Eunice Lakes 134 X LIST OF FIGURES Figure 1 •. Map showing location of study site 15 Figure 2. Densities of Diaptomus tyrelli in Eunice Lake and in 1979 experiments 33 Figure 3. Densities of Diaptomus kenai in Eunice Lake and in 1979 experiments 35 Figure 4. Densities of Daphnia rosea and Holopedium gibberurn in Eunice Lake and in 1979 experiments 37 Figure 5. Densities of Bosmina longirostris in Eunice Lake and in 1979 experiments 40 Figure 6. Densities of cyclopoid copepods in Eunice Lake and in 1979 experiments 43 Figure 7. Total densities of Diaptomus leptopus in 'Eunice Lake and in 1979 experiments 53 Figure 8. Densities of nauplii and of copepodites plus adults of Diaptomus leptopus in Eunice Lake and in 1979 experiments 58 Figure 9. Life cycle of Diaptomus leptopus in Gwendoline Lake 66 Figure 10. Life cycle of Diaptomus tyrelli in Eunice Lake . 68 Figure 11. Life cycle of Diaptomus kenai in Eunice Lake ... 70 Figure 12. Vertical distributions of zooplankton species in 1979 experiments during July 73 Figure 13. Vertical distributions of zooplankton species in 1979 experiments during September 75 Figure 14. July vertical distributions of Diaptomus leptopus nauplii