INVASIVE SPECIES IMPACTS ON ECOSYSTEM STRUCTURE AND FUNCTION By Andrea L. Jaeger A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Fisheries and Wildlife 2006 ABSTRACT INVASIVE SPECIES IMPACTS ON ECOSYSTEM STRUCTURE AND FUNCTION By Andrea L. Jaeger Exotic species invasion is a worldwide threat to the integrity of aquatic ecosystems. To understand ecosystem level response to the introduction of exotic species, I compared food web characteristics of two eutrophic Great Lakes ecosystems - the Bay of Quinte, Lake Ontario, Canada, and Oneida Lake, New York, USA - before and after zebra mussel (Dreissena polymorpha) invasion using ecological network analysis (ENA) and a social network analysis method, cohesion analysis (CA). ENA quantifies ecosystem function through an analysis of food web transfers, while CA assesses ecosystem structure by organizing food web members into subgroups of strongly interacting predators and prey. In Oneida Lake and the Bay of Quinte, zebra mussel invasion increased food web organization and the potential for system development. Additionally, zebra mussel invasion stimulated benthic production in both systems. Effects on food web structure were strongest in the Bay of Quinte where zebra mussel invasion removed subgroup structure entirely. In Oneida Lake, over 33% of taxa changed subgroup association after invasion, with benthically associated subgroups gaining the most members. This analysis suggested that the effects of zebra mussel introduction are similar in ecosystems of comparable trophic status and that future invasions of eutrophic systems could have similar impacts on ecosystem structure and function. Dedicated to the memory of Beryl Timmer iii ACKNOWLEDGEMENTS This research was supported by the Great Lakes Fishery Commission, the NOAA Great Lakes Environmental Research Laboratory, and Michigan State University. I am indebted to the numerous people at these organizations that made this work possible. My major professor, Dr. Doran M. Mason, has been a valuable mentor throughout this research. Despite the distance between his office and mine, he has motivated, guided, and inspired me. My committee members have also contributed greatly to this work. Dr. Kenneth A. Frank offered much assistance with cohesion analysis methods and interpretation; Dr. William W. Taylor was a source of boundless energy and enthusiasm; and Dr. Scott D. Peacor always provided insightful feedback. The graduate work of Dr. Ann E. Krause formed the foundation for much of this research. I highly value her insight in the merging of ecological and social network analysis methods, and the effort she devoted to these analyses. I would also like to thank Dr. Stefano Allesina for his willingness to discuss network analysis, and Drs. Michael L. Jones and James R. Bence for making me a part of their lab. This research was linked with another food web modeling effort to understand the effects of zebra mussel invasion on Oneida Lake and the Bay of Quinte. The Bay of Quinte – Oneida Lake Comparative Modelling Project Workgroup, a group composed of many respected scientists including Dr. E. Scott Millard, P.I. (DFO-GLLFAS), Dr. Edward L. Mills, P.I. (Cornell University), and Dr. Marten Koops (DFO-GLLFAS), provided extensive data and guidance. Additionally, Dr. Mills and the staff at the Cornell iv University Biological Field Station graciously hosted me during June 2004 for Oneida Lake data collection. I would also like to acknowledge the many others who surround and influence my daily life. My (über) labmates were an abundant source of intellectual discussion and entertainment. My close friends and colleagues at the Illinois Natural History Survey Lake Michigan Biological Station, my previous employer, have continued to encourage me throughout this research. The instruction of Drs. Stephen B. Hager (Augustana College), C. Kevin Geedey (Augustana College), and Jason Powell (Zion-Benton Township High School) still inspires me even today; these teachers brought learning outside the classroom and into my life. I thank my parents, Douglas and Barbara Jaeger, and brother, Jeffrey Jaeger, for encouraging me to explore all that holds my curiosity. Finally, I thank Scott M. Miehls, my fiancé, for unwavering support and companionship. v TABLE OF CONTENTS LIST OF TABLES...........................................................................................................viii LIST OF FIGURES .........................................................................................................x CHAPTER 1 A Prologue and Context to Understanding Invasive Species Impacts on Ecosystems....1 References ...........................................................................................................6 CHAPTER 2 Invasive Species Impacts on Ecosystem Structure and Function: A comparison of Oneida Lake, USA, Before and After Zebra Mussel Invasion ........................................8 Abstract ...............................................................................................................8 Introduction .........................................................................................................9 Methods ...............................................................................................................13 Study Site...................................................................................................13 Network Construction................................................................................14 Ecological Network Analysis.....................................................................17 Cohesion Analysis......................................................................................19 Results .................................................................................................................22 Ecological Network Analysis – Entire Network........................................22 Cohesion Analysis......................................................................................24 Ecological Network Analysis – Grouped Network....................................25 Discussion ...........................................................................................................29 Cohesion Analysis – Structure...................................................................30 Ecological Network Analysis – Function ..................................................32 Acknowledgements .............................................................................................38 References ...........................................................................................................59 CHAPTER 3 Invasive Species Impacts on Ecosystem Structure and Function: A Comparison of the Bay of Quinte, Canada, and Oneida Lake, USA, Before and After Zebra Mussel Invasion............................................................................................................................65 Abstract ...............................................................................................................65 Introduction .........................................................................................................66 Methods ...............................................................................................................70 Study Site...................................................................................................70 Network Construction................................................................................71 Ecological Network Analysis.....................................................................71 Cohesion Analysis......................................................................................73 Results .................................................................................................................75 Ecological Network Analysis – Entire Network........................................75 Cohesion Analysis......................................................................................76 vi Ecological Network Analysis – Grouped Network....................................77 Discussion ...........................................................................................................78 Cohesion Analysis – Structure...................................................................79 Ecological Network Analysis – Function ..................................................80 Acknowledgements .............................................................................................84 References ...........................................................................................................96 APPENDICES .................................................................................................................101 vii LIST OF TABLES Table 2.1 List of food web taxa. Cisco were present in the pre-zebra mussel time stanza but not the post-zebra mussel time stanza; lake sturgeon, zebra mussels, and Camptocercus harpae were present in the post- zebra mussel time stanza, but not the pre-zebra mussel time stanza .........40 Table 2.2 Association between common subgroup membership and the occurrence of ties between predators and prey (adapted from Frank 1995). The odds ratio method maximizes the ratio AD : BC ...................41 Table 2.3 Ecosystem indices for the full Oneida Lake food web network before and after zebra mussel invasion. The percent difference