Survival in spatially variable thermal environments: Consequences of induced thermal defense.

As Earth's climate warms, plants and animals are likely to encounter increased frequency and severity of extreme thermal events, and the ensuing destruction is likely to play an important role in structuring ecological communities. However, accurate prediction of the population-scale consequences of extreme thermal events requires detailed knowledge of the small-scale interaction between individual organisms and their thermal environment. In this study I propose a simple model that allows one to explore how individual-to-individual variation in body temperature and thermal physiology determines what fraction of a population will be killed by an extreme thermal event. The model takes into account the possibility that each individual plant or animal can respond to an event by adjusting its thermal tolerance in proportion to the stress it encounters. When thermal stress is relatively mild, the model shows that a graded physiological response of this sort leads to increased survivorship. However, the model predicts that in more severe events a proportional induced defense can actually reduce survivorship, a counterintuitive possibility that is not predicted by standard theory. The model can easily be tailored to different species and thermal environments to provide an estimate of when, where and how physiology can buffer the effects of climate warming.