Date of Award
Doctor of Philosophy (PhD)
Brett A. Melbourne
We are facing a global biodiversity crisis as extinction risks increase for species around the globe as a result of anthropogenic activities. Some of the most prominent causes of this trend include habitat fragmentation and invasive species. While these threats to biodiversity differ in their ultimate causes, they share a unifying theme: they both threaten biodiversity via mechanisms involving the spatial structure of populations. In the case of habitat fragmentation, a once continuous population is broken into smaller subpopulations, thus potentially increasing extinction risk. For an invading population, on the other hand, spatial structure is created from the expansion front to the core, potentially increasing invasion success. In my dissertation, I consider extinction risk in spatially subdivided populations and expansion speeds of spatially structured invaders. In Chapter 2, I detail the derivation and validation of a hierarchical model to assess extinction risk for poorly known species with little available data. The model accomplishes this by leveraging the spatial population structure characteristic of habitat fragmentation. In Chapters 3 and 4, I consider the context of invasive species and test the role of spatial structure during range expansions in driving the evolution of key traits at the expansion edge. In Chapter 3, I present data from a tightly controlled microcosm experiment to show that this trait evolution not only increases expansion speed on average, but also dramatically increases variability in expansion speeds. In Chapter 4 I present genomic data from these experimental populations to explore and quantify the evolutionary mechanisms underlying the increased speed and variance. Finally, Chapter 5 considers the intersection of habitat fragmentation and invasive species by considering the role of evolution due to spatial population structure in range expansions through fragmented habitat. I combine empirical data with a theoretical model to demonstrate that habitat heterogeneity reduces overall variance in spread rates, primarily due to the role of dispersal evolution at the expansion edge. Throughout my dissertation, I use a combination of empirical and theoretical approaches which allows me to provide greater mechanistic understanding of the importance of population spatial structure to ecological dynamics.
Weiss-Lehman, Christopher, "Spatial Structure in Extinction and Range Expansion: Models and Experiments" (2017). Ecology & Evolutionary Biology Graduate Theses & Dissertations. 97.