Testing Trade-Offs in Dispersal and Competition in a Guild of Semi-Aquatic Backswimmers by Ilia Maria C. Ferzoco A thesis submitted in conformity with the requirements for the degree of Master of Science Graduate Department of Ecology and Evolutionary Biology University of Toronto © Copyright 2019 by Ilia Maria C. Ferzoco Testing Trade-Offs in Dispersal and Competition in a Guild of Semi-Aquatic Backswimmers Ilia Maria C. Ferzoco Master of Science Graduate Department of Ecology and Evolutionary Biology University of Toronto 2019 Abstract Theory has proposed that a trade-off causing negative covariance in competitive and colonization abilities (the competition-colonization trade-off) is an important mechanism enabling coexistence of species across local and regional scales. However, empirical tests of this trade-off are limited, especially in naturalistic conditions with active dispersers; organisms capable of making their own movement decisions. I tested the competition-colonization trade-off in two co-occurring flight-capable semi-aquatic insect backswimmers (Notonecta undulata and Notonecta irrorata). Using field mesocosm experiments and laboratory experiments, I measured components of dispersal and competition to determine if and how the competition-colonization trade-off enables coexistence in this system. This thesis reveals that backswimmer species exhibited clear differences in dispersal behaviour and yet competition proved to be multi-faceted and context-dependent. This work suggests that in active dispersers, there is a great deal of complexity in competition and dispersal. Future studies of the competition-colonization trade-off in naturalistic communities should incorporate these complexities. ii Acknowledgments Thank you to my supervisor, Dr. Shannon McCauley, for her support, encouragement, and guidance throughout my studies. Her passion for science is infectious and she has been a huge inspiration for me to follow this academic path. This MSc thesis could not have been possible without insight and invaluable feedback from Shannon McCauley. Thank you to Profs. Bailey McMeans and Marie-Josee Fortin for serving on my MSc supervisory committee and for invaluable feedback during our committee meetings. Thank you also to Profs. Megan Frederickson, Peter Kotanen, and Bailey McMeans for serving on my MSc Exam committee. To the McCauley lab, I am grateful for all of you – Celina Baines, Rosemary Martin, Rosalind Murray, Dachin Frances, and Sarah French. Not only are they all amazing people to work with and have contributed to many helpful science-related conversations, but also I cherish our friendships. Celina, thank you for showing me the ropes for all things field work and backswimmers and for your moral support and collaboration in research and field work. Thank you also for statistical advice and productive science chats that started during my undergrad and continues still. Thanks also to the members of the McCauley lab for help with specimen collection, field work, and/or company and support at the field station as well as the many McCauley undergraduate lab and field assistants including Carol Megaly, Bansari Patel, Katerina Rozumey, Noha Akram, Momina Asad, and Salma Diab. Thank you to the Koffler Scientific Reserve, Stephan Schneider, Tobi Mankis, and John Stinchcombe, for fantastic research support at the field station. Thank you to Stephan Schneider and Tobi Mankis for help with mesocosm setup and patient field work support. Thank you, Shannon McCauley and Stephan Schneider, for your support and hospitality during my stay at KSR for the 2017 field season and for collection periods during the 2018 field season. Thank you to my 2018 ROP student, Carol Megaly, for her enthusiasm and hard work during the foraging efficiency project. Thank you to the UTM Biology community, to my fellow grad students who provide support, coffee breaks, advice, and exciting discussions. Thank you to my students, who have provided a large amount of motivation and whom have also taught me a lot in the process. Thank you also to my Let’s Talk Science UTM Coordinator partners, Ilapreet Toor, Firyal Ramzan, and Mitchell Bonney, who have made this past year very memorable and whose passion for science outreach and communication is infectious and inspiring. Thank you also to the LTS community at UTM for providing doses of motivation during thesis writing this year. Thank you to my family who have always been a pillar of support and strength during my studies. Thank you to my parents, for always modelling hard work, perseverance, and dedication which has helped me through the completion of this thesis. To my sisters, Alessandra, Francesca, and Fausta, thank you for always being there for me. Thank you to Alexander Axiotis for his companionship, support, patience, and motivation during all stages of this MSc. Thank you for your excitement at all the small steps. Thank you to the Axiotis family for many impromptu weekday dinners, constant warmth and support throughout my studies. iii Table of Contents Acknowledgments ....................................................................................................................iii Table of Contents ..................................................................................................................... iv List of Tables ............................................................................................................................ vi List of Figures ......................................................................................................................... vii List of Appendices .................................................................................................................... ix Chapter 1 Competitive coexistence: the competition-colonization trade-off .......................... 1 1 Thesis Introduction ........................................................................................................... 1 1.1 Competitive coexistence and the niche ................................................................................. 2 1.2 The competition-colonization trade-off ................................................................................ 2 1.3 Study system ......................................................................................................................... 4 1.4 Thesis overview ..................................................................................................................... 5 1.5 References ............................................................................................................................. 7 1.6 Figures .................................................................................................................................. 9 Chapter 2 ................................................................................................................................. 13 2 Breaking down the components of the competition-colonization trade-off .................. 13 2.1 Abstract .............................................................................................................................. 13 2.2 Coexistence across spatial scales ........................................................................................ 14 2.3 Debate on the importance of competition-colonization trade-offs as a coexistence mechanism ....................................................................................................................................... 15 2.4 Bridging the gap between theorized and actual dynamics in natural communities ......... 16 2.5 What do we need to adequately test the competition-colonization trade-off in natural communities? A trait-based and generalized framework .............................................................. 18 2.5.1 Clear and consistent definitions of competition and dispersal matter and integration into a trait-based framework for testing the competition-colonization trade-off ....................................... 19 2.6 Variation in the relative importance of the competition-colonization trade-off in determining patterns of biodiversity in empirical studies.............................................................. 22 2.6.1 Is this really a mechanism of coexistence in natural communities? .................................... 22 2.6.2 Empirical tests of the competition-colonization trade-off .................................................. 23 2.7 Challenges associated with experimental approaches to testing the competition- colonization trade-off ...................................................................................................................... 26 2.7.1 Empirical challenges in natural systems: form of dispersal ................................................ 26 2.7.2 Empirical challenges: Context-dependent outcomes of local competition .......................... 27 2.8 Concluding remarks ........................................................................................................... 28 2.9 Figures ................................................................................................................................ 29 2.10 Tables .................................................................................................................................. 32 2.11 References ........................................................................................................................... 36 2.12 Appendix ............................................................................................................................