Understanding how life-history traits and environmental gradients structure diversity by Natalie Tamara Jones A thesis submitted in conformity with the requirements for the degree of Doctor of Philosophy Department of Ecology and Evolutionary Biology University of Toronto © Copyright by Natalie Jones 2016 Understanding how life-history traits and environmental gradients structure diversity Natalie T. Jones Doctor of Philosophy Department of Ecology and Evolutionary Biology University of Toronto 2016 Abstract Determining how diversity is distributed through space and time is a fundamental goal of ecology. My research tested how species’ life-history traits structure diversity at landscape and broader scales and over time. I first asked how traits related to seed dispersal shape plant diversity in a naturally fragmented landscape by testing the relationship between diversity and patch characteristics (size and isolation) for species with different dispersal modes. Dispersal mode altered outcomes predicted from theory ‒ while fragment isolation had a negative effect on wind-dispersed species, it did not influence the diversity of animal-dispersed species. I then examined how zooplankton traits (body size and dormancy) correlate with species distributions at a large scale using lakes across an 1800 km north-south gradient in western Canada. Despite predictions that body size should decrease with latitude and low temperatures, I found only weak evidence for any effect of latitude on inter- and intra- specific body size. Zooplankton dormancy dynamics are virtually impossible to test through sampling, yet dormancy underpins seasonal fluctuations in abundance and long term persistence, and it is expected to vary with climate. I therefore used an experimental approach to test how temperature and photoperiod affect hatching rates of dormant eggs from lakes across the latitudinal gradient. My results suggest that mismatches between temperature and photoperiod, as predicted to result from climate change, could drive latitude-dependent shifts in zooplankton emergence. Finally, I examined the temporal stability of diversity across the same latitudinal gradient by examining species ii colonization and extinction over 50 years. I found that low-latitude communities are increasingly diverse and comprised of small-bodied species despite more rapid temperature change at higher latitudes. Overall, my research has implications for how global changes, such as fragmentation and climate change, alter diversity by changing the viability of specific life-history strategies. iii Acknowledgments The completion of this thesis was accomplished with the assistance of many people. First and foremost, I thank my supervisor, Benjamin Gilbert. Ben has been a wonderful mentor, editor, constructive critic, sounding board all for which I am truly grateful. Ben was patient and generous with his time and challenged me to mature as a researcher. His sage advice and thoughtful perspective greatly improved this thesis. I continue to learn from Ben every day and consider myself incredibly fortunate to have had the opportunity to be his first doctoral student. I have no doubt that Ben will continue to find creative ways to tackle the big questions in ecology. In the Gilbert lab I found a group of lifelong friends. I can’t imagine a more fun and supportive group of people to work with; together we laughed and commiserated, sharing the highs and lows of graduate school. Each member has a unique approach to science and life that has influenced my perspective. I am particularly indebted to Rachel Germain, who I have worked with for my entire tenure at UofT. Rachel continues to impress me every day with her ecological knowledge, problem solving skills and perspective on academia and life outside it. Tess Grainger is an excellent researcher and was an incredible addition to the lab. Tess taught me the importance of preparation, realistic expectations and being direct. Rachel and Tess are truly mentors to me. Kelly Carscadden became a wonderful friend and has taught me much about hard work and perseverance. Finally, Denon Start brought a youthful exuberance to the lab; his positive energy and cleverness is a pleasure to be around. All members have helped me to become a better scientist. The EEB department at large both past and present has had an incredible impact on me. I have seen countless inspirational talks and had many discussions with the people working in EEB. I learnt a great deal from discussions with the Jackson and Krkosek labs. As committee members, Don Jackson and Megan Frederickson offered guidance that was very helpful over the years. I have made many wonderful friends. In particular, Alex De Serrano, Nicholas Mirotchnick, Frances Hauser and Jane Ogilvie have enriched my time at UofT. This work could not have been completed without the tireless help of dedicated undergraduate students at the University of Toronto and beyond. Alexandra Barany, Ewelina Chojecka, Nathan iv Lo, Patrick Beh, Jillian Moran and Veronica Jones were invaluable and approached the tedium of ecological lab and field work with a sense of humor and tenacity that was much appreciated. Many staff members in EEB and CSB provided technical support for my research. Donna Wheeler, Jim Dix, Trung Luu, Bruce Hall and Andrew Petrie lent equipment, constructed experimental gear and fixed growth chambers for my projects. Kitty Lam and Helen Rodd were very helpful over the years. Helen in particular always put students first and does everything she can to help us succeed. Andrew MacDougall and Lyn Baldwin were early mentors to me. They both helped me cultivate a love of plant ecology and natural history. There is no doubt that without their thoughtful supervision I would not have been inspired to pursue a PhD. I could not have completed this work without the unwavering support of my family, especially my partner Scott Forster, who has been my best friend and cheerleader throughout the entire process. My siblings are a constant source of inspiration for me. Gwyneth has attended talks I have given and was my roommate for the first two years of my PhD. Her opinion was important to me during the early years of my dissertation. Veronica never ceases to amaze me with her cleverness and kind spirit. My brother Brendan has been in Toronto for the last year of my PhD and being in the same city as him for the first time in 20 years was an amazing bonus. Beyond EEB I have been lucky to become friends with an amazing cast of characters; we have had many wonderful adventures over the years. Christina Doris, Elysse Schlein, Asher Miller and Linda Naccarato are amazing friends and I can’t wait to see what lies ahead for all of them. This research was generously supported by Ontario Graduate Scholarships and fellowships from the University of Toronto and the Department of Ecology and Evolutionary Biology. v Table of Contents Acknowledgments.......................................................................................................................... iv List of Tables ...................................................................................................................................x List of Figures ................................................................................................................................ xi List of Appendices ....................................................................................................................... xiii CHAPTER 1 ....................................................................................................................................1 GENERAL INTRODUCTION ........................................................................................................1 Spatially structured landscapes ...................................................................................................2 Traits that affect dispersal rates ..................................................................................................2 The effect of temperature on traits that influence dispersal ........................................................3 Dormancy, climate & dispersal through time .............................................................................4 Latitude & community stability ..................................................................................................5 Thesis overview ..........................................................................................................................6 Literature cited ............................................................................................................................7 CHAPTER 2 ..................................................................................................................................12 DISPERSAL MODE MEDIATES THE EFFECT OF PATCH SIZE AND PATCH CONNECTIVITY ON METACOMMUNITY DIVERSITY… ...............................................12 Abstract .....................................................................................................................................12 Introduction ...............................................................................................................................13 Materials & methods .................................................................................................................16 Study site & species sampling ...........................................................................................16 Data analyses .....................................................................................................................19