UBC Theses and Dissertations

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UBC Theses and Dissertations

Experimental evolution of species ranges and coexistence using competing duckweed species Usui, Takuji


Understanding the evolution of species distributions is a fundamental goal of evolutionary ecology. With global change comes new challenges in predicting the movement of species ranges and the re-assembly of ecological communities. Importantly, these rapid changes in species distributions can provide unique opportunities for ecology to shape evolution, and for evolution to govern population and community dynamics across space and time. However, much remains unknown about how rapid feedbacks between population ecology and genetics (i.e., eco-evolutionary feedbacks) scale up to govern species distributions and community patterns. To make progress, this thesis tests a series of predictions on how evolution can alter species distributions and community assembly, using the evolution of duckweed species in experimental mesocosms. In Chapter 2, I test how evolution during range expansion alters our ability to predict population spread. With selection from an environmental gradient in space, I found that range expansion speed was more variable, and hence less predictable, across replicate populations. This occurred despite slower population spread and higher population densities at the range front – conditions in which models otherwise predict less variable range expansion speeds due to greater selection over genetic drift. In Chapter 3, I test how community context, specifically interspecific competition, alters adaptation during climate-driven range shifts. I found feedbacks between competition and evolution differed across a species experimental range, with competition limiting adaptive evolution at the range core, but promoting adaptation to climate stress at the range edge. I suggest that competition therefore has the potential to promote evolutionary rescue in response to global change. Lastly, in Chapter 4, I test whether and how mechanisms of coexistence evolve over time, from identical lineages to distinct species. I parametrized coexistence of genetically divergent lineages within and across duckweed species to show that coexistence mechanisms evolve in concert with lineage divergence. While evolutionary biology has mainly focused on mechanisms of genetic isolation, I suggest that feedbacks between genetic isolation and ecological differentiation is key for the origins of coexisting species. Overall, my thesis unpacks the diverse, and often surprising, pathways by which eco-evolutionary feedbacks govern population and community trajectories across space and time.

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