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. Here, 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 evaluate interactions in the field between the arboreal lizards Anolis carolinensis (the native green anole) and Anolis sagrei (the introduced brown anole) in Florida. We show that brown anoles are more aggressive and less flighty than green anoles, suggesting a competitive asymmetry. 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. We show that while ecological release was originally defined as niche expansion following a reduction in interspecific competition, current definitions are broad and highly varied. Viewing this development as a potential impediment to clear communication and hypothesis testing, we suggest a consensus definition for ecological release, highlight the various ways the process can unfold, and make suggestions for future studies of ecological release and its evolutionary implications. 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. Our results suggest that that the eco-evolutionary dynamics of ecological release in nature need not be solely inferred, because experiments can observe them directly at level of individuals, across generations, and along multiple niche axes.