SPECIES TURNOVER AND RICHNESS OF AQUATIC COMMUNITIES IN NORTH TEMPERATE LAKES by SHELLEY ELIZABETH ARNOTT A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy (Zoology) at the UNIVERSITY OF WISCONSIN-MADISON 1998 TABLE OF CONTENTS Abstract ii Acknowledgments iv Preface 1 Chapter 1: 9 Crustacean zooplankton species richness: single- and multiple-year estimates. Chapter 2: 45 Inter-annual variability and species turnover of crustacean zooplankton in Shield lakes. Chapter 3: 86 Long-term species turnover and richness estimates: a comparison among aquatic organisms. Chapter 4: 146 Lakes as islands: biodiversity, invasion, and extinction. Summary of Thesis 173 II ABSTRACT SPECIES TURNOVER AND RICHNESS OF AQUATIC COMMUNITIES IN NORTH TEMPERATE LAKES SHELLEY ELIZABETH ARNOTT Under the supervision of Professor John J. Magnuson At the University of Wisconsin- Madison I estimated annual species turnover rates for three groups of aquatic organisms in relatively undisturbed north temperate lakes. Apparent turnover rates (i.e. measured turnover rates) were high, averaging 18% for phytoplankton, 16% for zooplankton, and 20% for fishes. Based on life history characteristics and dispersal abilities, I expected phytoplankton to have higher turnover rates than zooplankton, which would have higher turnover rates than fishes. Results were contrary to my expectations; apparent turnover was high and similar for each of the taxonomic groups. Comparison of apparent turnover rates, however, was problematic because sampling error could account for much of the apparent turnover. Because the turnover that could be attributed to sampling error was so high, it should be taken into consideration when assessing species turnover. I have developed a new and unique method for quantifying potential sampling error in which I calculate the species turnover that could be attributed to failing to detect species that were present but at low abundance. Sampling error was influenced by sampling intensity. When sampling effort was increased, the proportion of turnover attributable to sampling error decreased. iii The result of high apparent turnover is that biodiversity assessments are dependent on the extent of the sampling programme. I assessed crustacean zooplankton richness in eight lakes at different temporal and spatial scales, using three methods of estimation: cumulative, asymptotic, and Chao's index. Percent species detected increased with the number of spatial, intra-annual, or inter-annual samples taken. Single samples detected only 50% of the annual species pool and 33% of the total estimated species pool. This suggests that previous estimates of zooplankton richness, based on single samples in individual lakes, were seriously underestimated. Single-year richness estimates provided poor predictions of multiple-year richness. The relationship between richness and environmental variables was dependent on the method of estimation and the number of samples used. I conclude that richness should be treated as an 'index' rather than an absolute and sampling efforts should be standardized. Approved: iv ACKNOWLEDGEMENTS I am indebted to many people who have contributed to this research over the past five years. Some have contributed directly through field and technical assistance whereas others have contributed by sharing their ideas and enthusiasm about science. Equally important are those who shared their friendship, provided support, and patience throughout this endeavor. By no means is this thesis exclusively my own effort. It is a product of many people, including co-authors, advisors, mentors, colleagues, friends, and family. I have had the tremendous good fortune to have several advisors; John Magnuson, Tom Frost, and Norman Yan. John was my official advisor and mentor. His enthusiasm, positive approach, and excitement for the complexities and unanswered questions in science were a continuous source of inspiration. He guided me through my graduate studies with pep talks, discussions about how to be a scientist with diverse interests, and advise about teaching, dealing with difficult situations, and developing practical skills associated with being a scientist. Through this, and by John's example, I learned the importance of projecting self-confidence while still being able to laugh at yourself, the necessity of directness, the value of taking the time to observe wonders around you, and the importance of having a good heart. Tom Frost has been an active mentor through both my master's and dissertation work. He always seemed to have a knack for asking me the tough questions that I hadn't considered and was able to keep me grounded when my ideas became too airy-fairy. His encouragement and support were greatly appreciated. Sometimes seemingly insignificant events lead to important changes in the direction of your work. I met Norm Yan because I had the 'nerve' to phone him and ask for all his v data. From that moment, Norm became a very active and important collaborator. I have learned much from Norm during the course of my dissertation. He has given me advice on writing, illustrated the importance of integrity, directness, and friendship in science. Norm has been an important mentor during the course of this research and continues to be a role model and inspiration. I have also had the good fortune to interact/collaborate with several outstanding scientists. Dave Findlay, Alex Saiki, and Mike Patterson, from the Freshwater Institute in Winnipeg have provided data, discussed analyses, reviewed papers, and helped shape and refine this thesis. Tony Ives, Stephen Carpenter, Diana Padilla, Stanley Dodson, and Eric Triplett were valued members of my committee, contributing ideas and insights to some difficult problems. Advice and wisdom from Jim Kitchell was always appreciated. Now comes the difficult part. How do I begin to acknowledge the tremendously important role that the people at the Center for Limnology have played? I'm afraid that I can't possibly express my gratitude in a manner that would do everyone justice. Paul Hanson has provided endless computer assistance, transformed my monte carlo programme into Visual C++, and was a valued friend. Glen Lee not only built equipment, but most importantly provided stories, jokes, and car advice. The office staff, Linda, Alice, Sue, Mindy, and Joe were indispensable. With regard to students and post-docs, it's impossible to pin down individual thank yous. They have been my Wisconsin family, colleagues who critiqued my ideas, helped me put together talks, reviewed papers, shared their ideas, gave advice, provided friendship, and kept me in line when I got too out of control. In particular, I can't imagine how things would have been without Beth Sanderson, Janet Fischer, Kathy Webster, Jen Klug, Tara Reed, vi David Lewis, Chris Harvey, and Tim Johnson. There is so much more I could say and so many more I could thank..... I am indebted to all those who have made the Center for Limnology such a wonderful place to learn and grow. During the final year of my dissertation, I took a 9-month 'sabbatical' to teach at Michigan Technological University in Houghton Michigan. I am indebted to John Adler, the chair of the Department of Biological Sciences, for providing me this opportunity. My year at Michigan Tech was stressful, challenging, overwhelming, and overall completely wonderful! It was an incredible learning experience. I discovered how to juggle teaching, research, and other faculty responsibilities through strategies such as time management, long hours, and locking my office door (thanks Sue Bagley). Janice Glime and Tom Snyder provided lots of advice and guidance on teaching. The staff was wonderful in helping me get settled and making my job and research run smoothly (thanks Debbie, Pat, Donna, Jeff, and Tom). Stephen Bowen was not only a running partner, he was also an important mentor. Thanks Stephen for advice, insights into the inner-workings of a university, friendship, and those incredible 20-mile runs along Lake Superior. Finally, there were friends who provided me with wonderful memories of my time at MTU: Scot, Doug, Jeff, Paul and most of all, Pete. Last, but certainly not least, there were several people who indirectly contributed to this thesis by directly contributing to my overall well-being. Jennifer Morgan faithfully met with me three times a week to lift weights, talk about life, and laugh ourselves silly. She was and continues to be a constant source of inspiration. Eva Schindler has been a soul-mate for many years. She has been a source of strength and love, helping me keep my sanity by means of many phone calls, canoe trips, and wonderful vacations. Finally, I want to thank vii my family. They have all been incredibly supportive throughout my entire graduate career. I can't begin to explain their importance in this whole process. It has something to do with unconditional support, extreme generosity, never-ending love and concern, and the fact that no matter what the challenge was they believed I could handle it. PREFACE Over the past few decades, there has been increasing concern about biodiversity (Wilson 1986, Schulze and Mooney 1993, Richlefs and Schulter 1993, Heywood 1995, Humphries et at. 1995). Biodiversity is generally defined as the 'variability among living organisms from all sources and the ecological systems of which they are a part' and can encompass scales ranging from genes to species to populations to ecosystems (Heywood 1995). Most frequently, biodiversity is equated with species richness, i.e. the number of species in a particular habitat or area. It is at this level, that I have focussed my studies. Human activities have had a large impact on ecosystems worldwide, with the frequent result of loss of species. This has resulted in a number of actions, including laws and policies such as the Endangered Species Act (Endangered Species Act 1988). In addition, there have been an increased number of regional and international biodiversity initiatives (e.g., Global Biodiversity Strategy. Guidelines for Action to Save, Study, and Use Earth's Biotic Wealth Sustainably and Equitably.