Recent studies predict that tropical ectotherms are at greater risk of extinction due to climate warming than temperate ectotherms. These predictions are based on the temperature dependence of fitness, with fitness quantified as the intrinsic growth rate. Because fitness of real organisms is influenced by density-dependent factors such as resource limitation and natural enemies, the question arises as to whether predictions based on the intrinsic growth rate accurately represent the extinction risk posed by climate warming. I develop dynamical models with temperature-dependent parameters that incorporate the stage structure characteristic of ectotherm life cycles as well as resource limitation and natural enemy effects.
Results/Conclusions
I report three key findings. First, stage structure can reduce the risk of stochastic extinction during low abundances by damping fluctuations that arise due to seasonal variation in temperature. Second, the nature of the temperature dependence of carrying capacity can have a strong effect on population dynamics and long-term persistence. Thus, temperature effects on competition that manifests through carrying capacity can lead to predictions about extinction risk due to climate warming that differ from predictions based on the intrinsic growth rate. Third, the relative temperature sensitivities of prey and natural enemies determine whether predictions of extinction risk based on the intrinsic growth rate hold in the population dynamical analyses. If the natural enemy is more sensitive to climate warming than its prey, predictions based on the intrinsic growth rate are more likely to be accurate than when the natural enemy is less sensitive to warming. These results provide a set of comparative predictions that can apply broadly across ectothermic taxa occupying different habitat types and latitudes. They highlight the importance of incorporating population dynamics and species interactions to analyses of extinction risk due to climate warming.