May 8th, 16h ET
Anne McLeod
Natural communities are undergoing accelerated changes due to human pressures such as habitat fragmentation, over-harvesting, and species invasions.  Here, I use bioinformatics and mathematical models to examine the environmental and ecological drivers of food-web structure and dynamics. First, I use a spatially expansive food-web to examine drivers of spatial turnover in food-web interactions across an environmental gradient. I demonstrate that predicting local realizations of community structure is very difficult, but critical since environmental perturbations occur at the local scale. Then, I integrate empirical data and mathematical models to explore the consequences of different structural metrics, including omnivory, on food-web stability and persistence. I demonstrate that the importance of omnivory depends on both the type of omnivory and the food-web within which it appears. Finally, I derive a novel multi-trophic metacommunity model which demonstrate how movement is a product of both a species’ ability to move and the landscape across which it moves. Treating patch connectivity as a species’ specific property can change our conclusions about multi-patch stability. Overall, my thesis integrates data and theory to test the impacts of environmental gradients and change on food webs and provide testable predictions to guide future research in spatial food web ecology.

May 15th, 16h ET
Sarah Amundrud
Species distributions and the composition of ecological communities result from the interplay of three constraints: physical barriers to dispersal, species-specific environmental requirements, and species interactions. While the relative importance of these factors is known to depend on spatial scale, the effects of climate change on the interplay of abiotic and biotic constraints are still poorly understood. I combined manipulative experiments, observational surveys along environmental gradients, and species distribution models to explore the relative importance of abiotic and biotic constraints on aquatic invertebrate communities inside bromeliad plants across a range of spatial scales: the geographic scale (Central and South America), the landscape scale (elevational gradients in Costa Rica), and the local scale (the bromeliad system). While species interactions were the main drivers of community change at the local scale, biotic effects were not important in driving species distributions at the large geographic scale. Notably, the relative importance of abiotic and biotic processes at the landscape scale depended on environmental context, an important insight given that environmental conditions are already shifting as a result of climate change. This hierarchical set of studies demonstrates the scale-dependence of the interplay of abiotic and biotic processes in affecting species distributions and community assemblages, as well as the potential role of environmental context at the intermediate scale of the landscape.

May 22nd, 16h ET
Ruth Rivkin
Urban habitats are more fragmented and degraded than nonurban habitats, which can impact both the ecology and evolution of species interactions. Species interaction may be particularly sensitive to urbanization because the species involved may be responding to urbanization separately, and together through effects on the strength of and direction of the interaction. We studied the effects of urbanization on a mutualistic interaction and an antagonistic interaction. We measured reproductive success of Brassica rapa plants across 30 experimental sites in Toronto, ON, and tracked within-site pollen dispersal and pollinator community variation among these sites. We found that urbanization influences plants reproductive success, but whether the effects on fitness were positive or negative depended on season and pollinator dispersal. We also studied the interaction between Darwin’s finches and Tirbulus cistoides in towns on three Galapagos Islands. We tested the effects of urbanization on seed predation rates, selection on mericarp size and defense traits, and ground finch community composition across 40 sites per island. Predation rates were elevated in urban sites, which corresponded to stronger selection on mericarp morphology and altered ground finch communities due to urbanization. Together, our results demonstrate the sensitivity of the ecology and evolution of species interactions to urbanization.

May 29th, 16h ET
Ken Thompson
In my talk, I’ll describe the progress I made during my Ph.D. to ‘push the peanut forward’ in arriving at generalities about the mechanisms of natural and sexual selection that act on hybrids in nature. Because the phenotype of otherwise viable and fertile hybrids determines their fate, we must document patterns and test theoretical predictions to better understand the mechanisms of so-called ‘extrinsic’ post-zygotic isolation and its importance for speciation. I’ll discuss the results of a systematic literature review where I find that hybrid traits are typically more dominant than intermediate, resulting in hybrids that are often quite ‘mismatched’ for divergent parental traits. Using recombinant hybrid sunflowers grown in a common field environment, I experimentally demonstrate negative fitness consequences of trait mismatches in the field. I’ll then talk about some preliminary results from ongoing work illustrating the extent to which mismatched traits are expressed in first-generation vs. segregating (backcross and F2) hybrids. Finally, I’ll conclude with a brief summary of an ongoing field experiment in threespine stickleback testing whether parallel phenotypic evolution is an engine of speciation in nature.