Doctor of Philosophy (PhD)
Dispersal is a fundamental process that affects local and regional dynamics, including population persistence, range expansion, and interspecific interactions, particularly as disturbance through habitat fragmentation and climate change. Here, my main objective was to ascertain how fragmentation affects dispersal and the interactions of competitors within the local patch and regional landscape. In my second chapter, I assessed dispersal through a literature review and population persistence model to examine the breadth and frequency of different density-emigration forms that occur in nature, including forms that are not prevalent in the literature. I conclude that these rare forms have important population dynamic consequences and that studies of density dependence should include methods that are better able to test for these forms. In my third chapter, I quantified individual and group movement of Ischnodemus conicus (Van Duzee), and, by using methods proposed in my first chapter, I was able to detect the rare non-linear, u-shaped density-dependent emigration. This form was likely promoted by the edge-avoiding, clustering behavior observed within individual movement experiments. Empirical assays such as this are lacking and can be used in predictive models for population dynamics. In my fourth chapter, I took a novel approach to studying the dispersal-competition-fecundity tradeoff that is predominately studied by changing just one of these traits. I applied concurrent selection pressures of dispersal and competition onto populations to represent the interacting tradeoffs that occur in the evolving range core and range front of an expanding population using Tribolium castaneum (Herbst) and T. confusum (DuVal)) populations. I additionally assessed the traditional single trait selection tradeoffs between competitive and dispersal ability and fecundity by selecting for all traits and assessing responses to each one. Overall, my research evaluates dispersal at multiple scales, from individuals within a patch to communities in a landscape, and examines previous research while suggesting improvement for the future. This work is an important contribution to landscape and dispersal ecology and can be applied to studies of invasion and conservation biology.
Harman, Rachel Roxann, "Habitat Fragmentation and Range Margin Effects on Dispersal and Interactions between Competitors" (2020). LSU Doctoral Dissertations. 5338.