Historical Contingencies in the Ecology and Evolution of Species Diversity

Rachel M. Germain

A thesis submitted in conformity with the requirements for the degree of Doctor of Philosophy

Department of Ecology and Evolutionary Biology University of Toronto

Historical contingencies in the ecology and evolution of species diversity

Rachel M. Germain

Doctor of Philosophy

Department of Ecology and Evolutionary Biology

University of Toronto

2016

Abstract

Ecologists have long-sought to explain the high diversity of species in biological communities, given that classic theory predicts that diversity is limited by available niche space. In recent years, ecologists have looked towards ‘historical contingencies’, the persistent effects of past ecological and evolutionary processes, as possible mechanisms that maintain diverse communities, either by relaxing the constraints of niche availability or by adding temporal dimensions to species’ niches. In this thesis, I use field and greenhouse experiments to explore three ways in which historical contingencies manifest in annual plant communities. First, my work on maternal effects shows that abiotic (ch. 2) and biotic (ch.3) conditions in the maternal generation have diverse effects on offspring phenotypes across an assemblage of species.

Because species differences in environmental responses can facilitate coexistence, these studies suggest that maternal effects could act as a form of niche differentiation, and motivate future research to clarify their influences on coexistence outcomes. Second, I performed, to my knowledge, the first experimental decoupling of dispersal limitation and environmental sorting in

ii a natural landscape by manipulating entire seed pools of annual plants (ch. 4). In doing so, I was able to identify the pervasive and scale-specific influences of dispersal limitation that constrain species distributions in plant communities. Lastly, I used competitive trials to identify macroevolutionary divergence in competitive interactions among species (ch. 5), and found evidence that divergence is contingent on historical competitive interactions in ways that are consistent with character displacement. In sum, my dissertation work has expanded our understanding of (i) the number of potential niche dimensions that might allow species to differentiate, (ii) how this differentiation can arise over evolutionary time, and (iii) the interplay of current and historical conditions in the maintenance of species diversity, and the timescales over which they play out.

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Acknowledgments

I have a long list of friends and colleagues to thank who have helped me complete my PhD and keep my sanity in the process.

First and foremost, I am indebted to my advisor Benjamin Gilbert. It is rare to find an advisor who is the combination of a brilliant mentor, an enthusiast of Ben Stiller movies c. 2000, and willing to shovel (and re-shovel)10 tonnes of soil off of a university driveway when his student makes poor life choices. Choosing a PhD advisor is one of the most important and most difficult decisions that a young scientist can make, and I truly believe that working with Ben was one of the best decisions I have made for myself. He has forever altered the way that I think as a scientist and my perspective of academia, and it has been exciting to watch his lab develop and successes accumulate over the past five years.

I will deeply miss my talented lab family: Natalie Jones, Tess Grainger, Denon Start, and Kelly Carscadden. Natalie is the sister I never had; she has sat ~4ft from me at all times during the last five years, and I am glad to have shared many of life’s big moments with her. Her successes have led her to more xeric pastures living the dream at UC San Diego. Tess has taught