AN ABSTRACT OF THE THESIS OF Charles Patrick Hawkins for the degree of Doctor of Philosophy in Entomology presented on 23 July 1982 Title: Ecological Relationships Among Western Ephemerellidae: Growth, Life Cycles, Food Habits, and Habitat Relationships Abstract approved: Redacted for privacy Norman H. Ahderson The purpose of this study was to describe the life cycles, feeding ecology, and habitat use of western species in themayfly family Ephemerellidae. Data were used to compare the ecological relationships and strategies among species and to examine patterns of adaptive radiation within the family. Data were further used to develop hypotheses describing the general importanceof food, temperature, habitat, and season in affecting the developmentand organization of benthic invertebrate communities in stream ecosystems. Growth rate and length of growth period wereexamined in nine species. Growth rates of most species were related to temperature, but little evidence was found that implicated food as animportant factor affecting individual growth in the field. Growth period and final size were most clearly related to specializationof different species for habitats that differ in duration of stability. Both food specialists and generalists were found among20 species examined for gut contents. Proportion of detritus, diatoms, animal matter, and moss ingested varied among species.Within a species, diet varied with both locality and habitat, but these differences were not sufficient to mask differences indiet among species. Among 14 species, taxa varied in their distribution along a stream continuum (2nd to 7th order) and in their preference for gravel, cobble, boulder, or moss substrates. Most species were habitat specialists and occurred on only one or two substrate types and at only a few stations. When four niche dimensions were considered, overlap between species was found to be least for station, followed by substrate type, season, and food. Complementarity in niche overlaps between niche axes was found for species in the genus Drunella but not among species in the family as a whole. From this study I inferred that stream insects show similar patterns of resource use as do animals in other ecosystems,although evidence for a discrete guild substructure was not strong. I conclude by stressing the need for further research that examines how the multiple and interacting factors in stream ecosystems have shaped both the ecology of single species and the structure of entire communities. Ecological Relationships Among WesternEphemerellidae: Growth, Life Cycles, Food Habits, andHabitat Relationships by Charles Patrick Hawkins A THESIS submitted to Oregon State University in partial fulfillmentof the requirements for the degree of Doctor of Philosophy Completed July 1982 Commencement June 1933 APPROVED: Redacted for privacy Professor Entomology in charge orinajor Redacted for privacy Chairman o, Entomo ogy '- par en Redacted for privacy Dean of Graduate,-School Date thesis is presented 23 July 1982 Typed by Cherri Lynn Spence for Charles Patrick Hawkins ACKNOWLEDGEMENTS I have been fortunate to benefit from the many interactions with students and faculty of the "Stream Team" while a graduate student at Oregon State University. The goals and objectives of this thesis arose, in part, from those interactions, and the final product certainly was strengthened by the many discussions that occurred during all phases of this study. The errors in approach, method, and logic that remain are, of course, my own. I would like to extend special thanks to a few of the many who deserve recognition. Warmest appreciation to Norm Anderson, my major advisor, for sage advice over five years and for the many gentle reminders that natural history is in the domain of the real world and not merely a simple-minded abstraction. Thanks also to my other committee members: to Ken Cummins for many valuable suggestions and for tolerating my seemingly perverse interpretations of data; to Jim Hall for pointing out a tendency or two for "arm - waving" explanations and for his thorough editing; to Pete McEvoy for reminding me that some insects live on land; to Ron Clarke for discussions on the metaphysics and ethics of what scientists do; and to Scott Overton for discussions on inference. I also must briefly thank the following persons as well: Jim Sedell for six years of encouragement and harassment; Stan Gregory for believing in Camelot; Dale McCullouogh for saving me from cowboys and P.I.s; Audrey Millemann for ballerinas and other things; Mike Murphy for many long days; and Peggy Wilzbach for being as stubborn as me. Financial assistance was provided by the National Science Foundation, Environmental Protection Agency, and the Department of Entomology, Oregon State University. TABLE OF CONTENTS Page I. INTRODUCTION 1 Problems, Goals, and Objectives 2 Background 4 Conceptual Framework and Terminology 9 Conceptual Framework . 9 Terminology 10 II. STUDY SITES AND ENVIRONMENTAL CONTRASTS. 15 Description of Sites 15 Methods 18 Results and Interpretation 23 III. GROWTH AND LIFE CYCLES 11 Methods 31 Results 35 Ephemerella infrequens/inermis 35 Drunella coloradensis/fiavilinea 42 Drunella doddsi 45 Drunella IWITTera 48 Drunella pelosa 52 Serratella tibialis 56 Caudatella cascadia 56 rEtaire*Wi3hWx 56 Other Species 60 Effect of Food on Growth Rate 63 Seasonal Differences in Life Cycles F6 Discussion 68 Effects of Temperature and Photoperiod 70 Effect of Food on Growth Rate 76 IV. FOOD HABITS 81 Methods 81 Food Habits 81 Abundances 82 Results 83 Food Habits 83 Abundances 89 Discussion 91 Food Habits 91 Feeding Guilds 101 Abundances 102 TABLE OF CONTENTS (Cont.) Page V. HABITAT RELATIONSHIPS AND DISTRIBUTIONS 105 Methods 105 Results 106 Discussion 113 VI. NICHE RELATIONSHIPS AND PATTERNS OF ADAPTIVE RADIATION 119 Methods 119 Results 120 Discussion 130 Resource Axes and Separation of Species 130 Adaptation and Niches 133 Patterns and Mechanisms 135 Guild Structure 141 VII. ON MAYFLIES, EVOLUTION, AND STREAM ECOSYSTEMS: SOME SPECULATIONS 143 Temperature 144 Habitat Constraints 146 Trophic Structure and Trophic Stability 148 VIII. LITERATURE CITED 160 IX. APPENDICES 181 LIST OF FIGURES Figure Page 1 Map of the main study area. 16 2 Location of the McKenzie River in relation to 19 other studies. 3 Monthly accumulated degree-days at the main study 24 sites. 4 Substrate composition by particle size at the main 27 study sites. 5 Size of E. infrequens at different dates. 36 6 Relationship between growth rates and degree-days 39 for E. infrequens. 7 Size of D. coloradensis at different dates. 43 8 Size of D. doddsi at different dates. 47 9 Size of D. spinifera at different dates. 51 10 Size of D. Delosa at different dates. 54 11 Size of S. tibialis at different dates. 57 12 Size of C. cascadia at different dates. 59 13 Size of C. hystrix at different dates. 61 14 Size of S. velmae and teresa at different dates. 62 15 Idealized growth curves showing differences in life 69 cycles. 16 Relationship between growth rate, size, and 74 temperature. 17 Theoretical relationship between growth, 78 temperature, and food. LIST OF FIGURES (Cont.) Ficure Page 18 Dietary niche breadths of populations in this study 96 compared with other studies. 19 Leaf discs fed upon by large and small larvae of E. 99 infrequens and verruca. 20 Longitudinal distribution of species. 107 21 Length of life cycles in two streams of different 116 habitat stability. 22 Plots of niche overlap on one dimension against 129 overlap on other dimensions. 23 Inger-Colwell analysis for guild structure. 131 LIST OF TABLES Table Page 1 Number of genera and species of Ephemerellidae in 5 North America. 2 Species of Ephemerellidae in Oregon. 6 3 Physical characteristics of the main study sites. 17 4 Physical characteristics of the longitudinal sites. 20 5 Schedule of sampling of environmental variables. 21 6 Annual accumulation of degree-days at the main 25 study sites and other streams. 7 Estimates of the quantity and quality of different 29 food sources found at the six study sites. 8 Regression statistics comparing growth rates of E. 37 infrequens. Growth rates at different sizes and temperatures 41 for E. infreouens. 10 Regression statistics comparing growth rates of D. 44 coloradensis. 11 Growth rates at different sizes for D. 46 coloradensis. 12 Regression statistics comparing growth rates of D. 49 doddsi (large larvae). 13 Regression statistics comparing growth rates of D. 50 doddsi (small larvae). 14 Regression statistics comparing growth rates of D. 53 spinifera. 15 Regression statistics comparing growth rates of D. 55 pelosa. LIST OF TABLES (Cont.) Table Page 16 Regression statistics comparing growth rates of S. 58 tibialis. 17 Comparison of growth rates between MAOG and MACC 64 for six different species. 18 Results of laboratory experiments on effects of 65 food on growth. 19 Percent monthly growth of nine species. 67 20 Comparison of regression models based on days, 72 degree-days, and photoperiod. 21 Percent composition of dietary items in twenty 84 species. 22 Variation in diet with site. 86 23 Variation in diet with habitat. 87 24 Correlations between diet and size. 88 25 Densities and standing crops of four species in 90 shaded and open sites. 26 Mean densities of twelve species in shaded and open 92 reaches. 27 Data of Gilpin and Brusven (1970) on diets of 94 Ephemerellidae. 28 Feeding guilds among western Ephemerellidae. 103 29 Distribution of species among longitudinal 108 stations. 30 Percent habitat use by fourteen species. 110 31 Length and timing of growth period compared with 112 habitat specificity. LIST OF TABLES (Cont.) Table Page 32 Seasonal niche overlap. 122 33 Dietary niche overlap. 123 34 Habitat niche overlap. 124 35 Longitudinal overlap. 125 36 Mean overlap among different sets of species on 126 different niche axes. 37 Overall niche overlap. 128 38 Number of invertebrate genera in different 149 herbivore guilds in upstream, downstream, and lentic environments (Literature data).