Thermal ecology drives alternate responses to rising temperatures in Caribbean anoles

Rapidly rising temperatures threaten populations of ectothermic animals worldwide, with the greatest impacts predicted in the tropics—hotspots for biodiversity. Ectotherms can respond to warming through two primary compensatory responses: behavioral thermoregulation, which buffers exposure to extreme temperatures; and heat tolerance increases via plasticity, adaptation, or both. The relative contribution of these responses is predicted to depend on ecological context, but whether these principles can anticipate organismal responses to contemporary warming remains largely untested. Here, using a decadal resurvey of anole lizards from Hispaniola, Jamaica, and Puerto Rico, we show that simple principles of thermal ecology can reliably anticipate organismal responses to rising temperatures. Species occupying thermally heterogeneous open/edge habitats, such as dry forests, behaviorally thermoregulate and have shown little to no increase in heat tolerance over the past decade. By contrast, species from thermally homogeneous closed-canopy environments are poor thermoregulators and have increased their heat tolerance by 2 °C, on average, over the same period. Seasonal comparisons, acclimation experiments, and laboratory-rearing experiments indicate that contemporary increases in heat tolerance likely reflect contributions from rapid evolutionary change and physiological plasticity. Thermal ecology, not phylogenetic or spatial proximity, is the key factor driving responses to rising temperatures. Our results consistently link organismal responses to habitat complexity and thermoregulatory behavior; we suggest that these factors are key to predicting how ectotherms respond to climate warming.