Nick Herrmann Thesis Defense (David Haig Lab)


Friday, July 16, 2021, 1:00pm

Title: Competition, character displacement, and ecological release in Anolis lizards

Abstract: The addition or subtraction of species in a community can alter the ecology and evolution of resident species. As human-mediated introductions and extinctions have become commonplace, understanding the consequences of changing species interactions is more important than ever. In this dissertation, colleagues and I investigate two closely related processes that connect competition between species to evolutionary change: ecological character displacement and ecological release.

In Chapter 1, we measure competitive interactions in the field between the arboreal lizards Anolis carolinensis (the native green anole) and Anolis sagrei (the introduced brown anole) in Florida. Previous work on islands in Florida showed that green anoles perch higher and adaptively evolve larger adhesive toepads in the presence of brown anoles. In Chapter 2, we revisit these same islands to test hypotheses about how this process of competition-driven habitat and morphological divergence, termed ecological character displacement, varies across space and time.  In Chapter 3, we explore historical and recent trends in the study of ecological release, a phenomenon often described as the opposite of ecological character displacement. In Chapter 4, we experimentally induce ecological release of green anoles from brown anoles, monitoring individual and population habitat use along three niche axes (perch height, perch diameter, and lateral movement between perches) for two generations. Overall, this dissertation demonstrates ways in which eco-evolutionary processes can be studied directly in the field.

Committee: David Haig (Advisor), Robin Hopkins (Chair), Jonathan Losos (Washington U.) and Naomi Pierce