ECOLOGICAL RELEASE ANALYZED AMONG INDIVIDUALS, ACROSS TWO GENERATIONS, AND ALONG MULTIPLE NICHE AXES IN ANOLIS CAROLINENSIS

Abstract

A population freed from a constraining interspecific interaction (e.g., competition or predation) may experience niche shifts and expansions. This phenomenon, termed ecological release, is an eco-evolutionary process driven by individual behaviors and interindividual interactions. However, empirical studies of these interactions seldom observe them directly, instead inferring process from pattern. Here, we set up experimental conditions for ecological release of the lizard Anolis carolinensis (green anole) from constraining interactions with its congener, Anolis sagrei (brown anole), by constituting populations of lizards on small islands. We monitored individual and population habitat use along three niche axes (perch height, perch diameter, and lateral movement between perches) on one experimental (one-species) and one control (two-species) island, for three time periods: 1) preremoval, when both islands had both species; 2) postremoval, shortly after A. sagrei were cleared from the experimental island; and 3) delayed postremoval, 7 months later, when long-lived lizards were joined by a second generation born in the intervening months. We found that green anole perch height decreased on the one-species island and increased on the two-species island. These shifts did not occur during postremoval but were evident by delayed postremoval, when both generations on the one-species island were perching nearly 130 cm lower than their counterparts on the two-species island. We also documented correlated changes in perch diameter at both the individual and population level but no changes in the extent of individuals' lateral movement. Lastly, changes in population-level niche width (i.e., perch height and diameter variances) occurred without detectable changes in niche overlap among individuals. Our results demonstrate that that the dynamics of ecological release in nature need not be inferred, because experiments can observe them directly in individuals, across generations, and along multiple niche axes.