Interactions between introduced and native Anolis lizards in Florida and Grand Cayman Island

I investigated interactions between an invading species of lizard, Anolis sagrei, and native A. carolinensis in Florida and native A. conspersus in Grand Cayman. Anolis sagrei outnumbers both native species in some areas, particularly disturbed habitats, and is suspected of displacing them. Anolis carolinensis and A. conspersus are ecological analogs, and were the only anoles in Florida and Grand Cayman, respectively, until the introduction of A. sagrei. Because anoles are active, aggressive, territorial predators with size-structured populations and generalized feeding habits, I hypothesized that aggressive interference among adults and predation of juveniles by adults were important interspecific interactions. To investigate the importance of these mechanisms, I conducted behavioral experiments in both locations to determine the strength and symmetry of interspecific predation and aggressive interference. Based on the results of the behavioral experiments, I subsequently conducted experiments in the field and in enclosures to test hypotheses of interspecific interaction in relation to habitat structure and disturbance. Behavioral experiments demonstrated that (1) intraguild predation was asymmetrical in favor of A. sagrei in Florida and Grand Cayman, whereas (2) aggressive interference was minimal in Florida, but highly asymmetrical in Grand Cayman in favor of A. conspersus. A field experiment in Grand Cayman demonstrated that A. sagrei is restricted to open, disturbed habitats due to intense interspecific aggression and thus appears to have minimal impact on A. conspersus, despite its demonstrated potential to be an important intraguild predatorIn contrast, enclosure experiments in Florida demonstrated that the survival of A. carolinensis juveniles is significantly reduced in habitats of low structural complexity due to intraguild predation from adult A. sagrei and competition from juvenile A. sagrei. My studies demonstrate that (1) both intraguild predation and interspecific aggression have important influences on anole community structure, (2) the effects of an introduced species on native congeners in one community cannot necessarily be predicted by knowing the effects of that same introduced species on native congeners in a different community, and (3) predicting the effects of one species on another, regardless of taxa, will be enhanced by understanding the nature, strength and symmetry of the mechanisms of interaction.