PARTITIONING RESOURCES THROUGH THE SEASONS: A TEST OF THE COMPETITIVE ABILITY – COLD TOLERANCE TRADE-OFF HYPOTHESIS IN SEASONALLY BREEDING BEETLES By Jillian Diane Wettlaufer 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 May 2019 Copyright © Jillian Diane Wettlaufer, 2019 ii Abstract Understanding the factors that maintain and constrain biodiversity and species coexistence is a major goal in ecology. Closely related species that use similar resources often differ in their seasonal patterns of activity, consistent with resource partitioning that is thought to facilitate coexistence. The factors that limit the distributions of these species across seasons, however, are unknown for the majority of species. In my second chapter, we conducted a large- scale survey of a diverse carrion beetle community in southeastern Ontario, Canada from April to October, and found evidence consistent with resource partitioning in Nicrophorus habitat generalists, but limited evidence for seasonal differences in abundance among habitat specialists. In my third chapter, we test one hypothesis that may explain seasonal differences in activity between two burying beetle species (Nicrophorus sayi, N. orbicollis) that co-occur, require carrion for food and reproduction, and differ in their seasonal patterns of activity. Specifically, we tested predictions of the competitive ability – cold tolerance trade-off hypothesis whereby adaptations to cold temperatures compromise competitive ability under warmer conditions, leading to the partitioning of resources along seasonal gradients. Consistent with our hypothesis, we found evidence that the late-season N. orbicollis is less able to function at the cold temperatures that characterize early spring, when the early-season N. sayi is most active. Contrary to our hypothesis, however, we found that the late-season N. orbicollis was not competitively dominant to the early-season N. sayi under warm conditions, but instead the larger beetle always won, regardless of species. Our survey data suggest that N. orbicollis is usually the larger species when competing for the same carrion later in the season, mostly because of its high abundance during this time. The larger size of N. orbicollis thus presents an intense competitive pressure that should limit N. sayi breeding later in the season. Overall, my thesis research provides evidence for seasonal partitioning of resources and the factors that constrain iii the seasonal distributions of two species. My work further suggests that seasonal partitioning of resources may contribute to maintaining local diversity within a diverse community of carrion beetles. iv Co-authorship This thesis conforms to the publication format as outlined in the Department of Biology Guide to Graduate Studies, including consolidated Acknowledgements and Literature Cited sections. Manuscripts resulting from the thesis are outlined below. Chapter 2 Wettlaufer JD, Burke KW, Beresford DV, Martin PR. 2019. Partitioning resources through the seasons: abundance and phenology of carrion beetles (Silphidae) in southeastern Ontario. In preparation for submission to Ecological Entomology. Author contributions: JDW and PRM conceived the study, with study design and planning help from DVB. JDW and KWB collected the data. JDW and PRM completed the statistical analyses. JDW wrote the initial manuscript, with help from PRM. Chapter 3 Wettlaufer JD, Ye A, MacMillan HA, Martin PR. 2019. A test of the cold tolerance – competitive ability trade-off hypothesis in seasonally breeding beetles. In preparation for submission to Proceedings of the Royal Society B. Author contributions: JDW and PRM conceived the study. JDW conducted the cold tolerance assays with guidance and equipment from HAM. AY and PRM conducted the competition experiments. JDW and PRM completed the statistical analyses. JDW wrote the initial manuscript, with help from PRM. v Acknowledgements First and foremost, I would like to thank my supervisor, Paul Martin, for the constant support and guidance, and for pushing me to always remain ambitious. You took a chance when you hired me as a SWEP student with no field experience 3 years ago, and without that opportunity, I would not be here. Thank you to Fran Bonier for the insightful feedback and suggestions, from study design, to analyses, to presentation skills, the support has been immensely helpful throughout my Master’s. Thanks to Heath MacMillan for his expertise and guidance through my cold tolerance assays. Thanks to my committee members, Dr. Bill Nelson and Dr. Mel Robertson, for thoughtful questions and comments during my committee meetings. Thank you to all the members of the Martin/Bonier lab for lab meeting discussions and providing feedback on my presentations. Special thanks to Haley Kenyon, Jaimie Bortolotti, Kevin Burke, Sarena Olsen, Adam Groulx, Matt Macpherson for their friendship, support, and commiseration. Thank you to April Ye for her work on the competition experiments. Thank you to Allison Collard for being an excellent field assistant through long, tough hikes and many rainy days. Thank you to Ali, Lee, and Murray Knowles for graciously inviting me to stay in their home during my time in Ottawa. Thank you to the entire team at the Queen’s University Biological Station. Field seasons were the best time of year and I am forever grateful for the memories and friendships I’ve made at QUBS. Thank you to my family, even though I’ve strayed from the typical family accounting career path and ventured into biology, they’ve shown unwavering love and support, nevertheless. Thank you to Rebz Rahimi and Rachel Goldfarb for the motivation when I needed it the most. Last but certainly not least, thank you Anthony Colangelo, for not only being a wonderful (and free) field assistant when I needed it, but for the endless love and patience as I completed this degree and the truly unwavering optimism. vi Table of Contents Abstract .......................................................................................................................................... ii Co-authorship ............................................................................................................................... iv Acknowledgements ....................................................................................................................... v Table of Contents ......................................................................................................................... vi List of Figures ............................................................................................................................. viii List of Tables ................................................................................................................................ ix List of Abbreviations .................................................................................................................... x Chapter 1: General introduction and literature review ............................................................ 1 Introduction ............................................................................................................................... 1 Scope of thesis ............................................................................................................................ 7 Study System ........................................................................................................................... 8 Thesis Objectives ..................................................................................................................... 9 Chapter 2: Partitioning resources through the seasons: abundance and phenology of carrion beetles (Silphidae) in southeastern Ontario ................................................................ 12 Abstract .................................................................................................................................... 12 Introduction ............................................................................................................................. 13 Methods .................................................................................................................................... 15 Study Site ............................................................................................................................... 15 Study Species ......................................................................................................................... 16 Trapping Methods.................................................................................................................. 18 Species and Sex Identification ............................................................................................... 19 Temperature Data .................................................................................................................. 19 Statistical Analyses ................................................................................................................ 20 Results ...................................................................................................................................... 20 Nicrophorinae – Habitat Generalists ..................................................................................... 23 Nicrophorinae – Habitat Specialists .....................................................................................