Predation on the Crustacean Zooplankton Community of a Small
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THE EFFECTS OF THERMAL HABITAT AND MACROINVERTEBRATE PREDATION ON THE CRUSTACEAN ZOOPLANKTON COMMUNITY OF A SMALL BOREAL SHIELD LAKE by SHANNON ANNE MACPHEE A thesis submitted to the Department of Biology in conformity with the requirements for the degree of Master of Science Queen’s University Kingston, Ontario, Canada March 2009 Copyright © Shannon A. MacPhee, 2009 i ISBN:978-0-494-48187-5 ABSTRACT Climate change will affect all freshwater ecosystems via both direct physiological and indirect, biologically-mediated effects. Small lakes (< 10 ha) numerically dominate the Boreal Shield and represent an important habitat for aquatic biota. Small, shallow lakes are particularly responsive to climate-induced changes in thermal structure. Furthermore, biological interactions may be particularly important in small lakes where space, habitat heterogeneity, and thermal refugia are limited. Therefore, it is critical to understand and predict the consequences of climate change for community dynamics in small Boreal Shield lakes. Using 10 years of monitoring data and a field experiment I tested for differences in crustacean zooplankton community structure between warm and cool lake habitats. I classified years from a small, shallow Boreal Shield lake as ‘warm’ or ‘cool’ based on several characteristics of lake thermal structure. Since macroinvertebrates are often the main predators in small, shallow lakes, I further tested for potential interactions between lake thermal structure and spatially-dependent macroinvertebrate predation using in situ mesocosms. Body sizes of two ubiquitous crustacean zooplankton taxa, Leptodiaptomus minutus and Bosmina spp., were reduced in warm years, but no differences in abundance or diversity were detected at the annual scale. In contrast, in 15d enclosure experiments, crustacean zooplankton abundance and calanoid copepodid body size were reduced by the vertically-migrating predator Chaoborus punctipennis, but only in warm isothermal conditions. Zooplankton lowered their daytime depth distribution to avoid the surface- orienting notonectid predator, Buenoa macrotibialis, regardless of thermal habitat. No ii predation effect was detected in a hot (25ºC) isothermal habitat where both Chaoborus and notonectids were likely heat-stressed. Differences in abundance effects between the enclosure and monitoring data are likely due to the scales at which the analyses were conducted. Over short timescales predator-prey dynamics depended on lake thermal structure. However, over annual timescales zooplankton response was averaged across periods of seasonal change in thermal structure and biological processes, which may dampen the short-term effects associated with strong predation in isothermal conditions. Therefore, the importance of macroinvertebrate predators in regulating crustacean zooplankton community structure may increase if small lakes become progressively more isothermal with future climate change. iii CO-AUTHORSHIP This thesis conforms to the manuscript format as outlined by the School of Graduate Studies and Research. The Acknowledgements and References sections apply to the entire thesis. The manuscripts that are a direct result of this thesis and its coauthors are: MacPhee, S.A., Keller, W., and Arnott, S.E. In preparation. Differences in crustacean zooplankton community structure between warm and cool years in a small Boreal Shield lake. MacPhee, S.A., Arnott, S.E., and Keller, W. In preparation. The effects of lake thermal habitat and spatially-dependent macroinvertebrate predation on crustacean zooplankton community structure. iv ACKNOWLEDGEMENTS Thanks to my two supervisors, Shelley Arnott and Bill Keller. I consider you both as role models who manage to balance being successful scientists with your active personal lives. Thank you both for supporting me by sharing your homes during the field season and during the final stages of writing. You are both optimistic individuals who inspire me to stay in the field of aquatic ecology and I hope to interact with you in the future. To the Arnott lab – Thank you to Angela Strecker and Alison Derry for being leaders during the early stages of my thesis. Liz Hatton, you are a true friend. Anneli Jokela, I appreciate all of your helpful comments, constructive criticism, advice, and support - you are a natural leader and a great friend. Leah James, it was wonderful to share discussions with you, both academic and personal. Thanks also to Justin Shead, Mike Pedruski, Colleen Inglis, Derek Gray, Johanna Pokorny, Theresa Patenaude, Shirley French, Amy Tropea and Adam Jeziorski for being supportive colleagues and friends. Thanks to Leah James, Hannah Kent, and Colin MacLeod for help with the experimental set-up. Corrine Daly – I could not have done this without you. You are a truly amazing, motivated individual and incredible friend. Thanks for your support, hard work and friendship. Your honours project (2008) provided much insight into the interpretation of my experimental results. Thanks to the MacPhee’s, especially to John for help with data management, to Mike for help with programming, to Kathy for help editing and to Matt for letting me convert your room into an office. v Leon Boegman kindly provided example MatLab® code. Thanks to Tom and Karen Johnston for use of your personal canoe on Clearwater Lake. Thanks to Chantal Sarazin-Delay, Kim Fram, Dan Dechaine and Donna Strang from the Bughouse for lending equipment and for help collecting notonectids, and to Lynn Witty for patient taxonomic training – Say “No”-to- nectids! To the Waterhouse – Amanda Valois, you were a wonderful peer and were exactly far enough ahead of me to provide ‘fresh’ advice. I consider you a friend and colleague. Nat Webster, thanks for your emotional support, especially during the field season and writing process, and for your friendship and zest for life. Andrea Ford, thank you for your help with data sharing, data management suggestions, and bug collection. Jocelynne Heneberry, you are a true mentor, colleague and friend, and I can’t thank you enough for the positive experiences we’ve shared at the Coop Unit. You are diligent with sample collection and management and have deep knowledge of your long-term monitoring dataset. Thanks to the entire Cooperative Freshwater Ecology Unit, including those aforementioned plus Karen Oman for your friendship. Thanks to the Dorset Environmental Science Center for my first working exposure to limnology. I am grateful for all previous opportunities made available to me along the way, including the U of G Coop program, the DESC, CWS, and the ELA. Committee members John Smol and Paul Grogan provided helpful comments to improve the thesis. Funding was provided by an Ontario Ministry of the Environment ‘Best in Science’ grant to Shelley Arnott and Bill Keller and a Queen’s Graduate Award to Shannon MacPhee. vi TABLE OF CONTENTS ABSTRACT....................................................................................................................... ii CO-AUTHORSHIP ..........................................................................................................iv ACKNOWLEDGEMENTS ..............................................................................................v TABLE OF CONTENTS ............................................................................................... vii LIST OF ABBREVIATIONS ..........................................................................................ix LIST OF TABLES .............................................................................................................x LIST OF FIGURES ..........................................................................................................xi CHAPTER 1: GENERAL INTRODUCTION AND LITERATURE REVIEW .............................1 1.1 Global Climate Change .............................................................................................1 1.2. Implications of Climate Change in the Boreal Shield Ecozone................................1 1.3. Climate Effects on Lake Thermal Structure..............................................................2 1. 4. Freshwater Crustacean Zooplankton ......................................................................5 1.5 Implications of Climate Warming for Freshwater Zooplankton Communities .........7 1.6 Macroinvertebrate Predators ....................................................................................9 1.7 Thesis Objectives .....................................................................................................13 CHAPTER 2 THE INFLUENCE OF LAKE THERMAL STRUCTURE ON MEAN ANNUAL CRUSTACEAN ZOOPLANKTON COMMUNITY STRUCTURE................................................17 Abstract.........................................................................................................................18 Introduction..................................................................................................................19 Methods.........................................................................................................................22 Study site ....................................................................................................................22 Field collections.........................................................................................................23 Chemical analyses .....................................................................................................24 Zooplankton Enumeration