High temperatures amplify aggressiveness of an invasive lizard toward a native congener

Invasive species cause major disturbances to endemic wildlife and often displace native species. Behavioral aggression can contribute to invasive species success, but little is known about how temperature and aggression interact. We tested for effects of temperature on interspecific aggression between the invasive brown anole lizard (Anolis sagrei) and a native congener, the green anole (A. carolinensis). Anolis sagrei displaces A. carolinensis from perch sites in sympatry, which is hypothesized to result at least in part from higher levels of aggression. We tested hypotheses about the temperature-dependence of interspecific aggression across five ecologically relevant temperature regimes that span cool spring to hot summer conditions. Additionally, we tested whether the presence of A. sagrei disrupts A. carolinensis thermoregulation. The invasive Anolis sagrei was more aggressive than A. carolinensis in all temperature regimes. In addition, the difference in aggression between the species was greatest at high temperatures. In contrast, we found little evidence that A. carolinensis thermoregulation is affected by A. sagrei. Our results indicate that the effects of an invasive lizard on a native competitor may be facilitated by high levels of aggression that could be amplified with rising temperatures. Overall, our results are consistent with aggression facilitating invasive species success, and that the effect can be amplified under climate change.