Costs and benefits of thermoregulation revisited: both the heterogeneity and spatial structure of temperature drive energetic costs.

In recent years, ecologists have stepped up to address the challenges imposed by rapidly changing climates. Some researchers have developed niche-based methods to predict how species will shift their ranges. Such methods have evolved rapidly, resulting in models that incorporate physiological and behavioral mechanisms. Despite their sophistication, these models fail to account for environmental heterogeneity at the scale of an organism. We used an individual-based model to quantify the effects of operative environmental temperatures, as well as their heterogeneity and spatial structure, on the thermoregulation, movement, and energetics of ectotherms. Our simulations showed that the heterogeneity and spatial structure of a thermal landscape are as important as its mean temperature. In fact, temperature and heterogeneity interact to determine organismal performance. Consequently, the popular index of environmental quality (d(e)), which ignores variance and spatial structure, is inherently flawed as a descriptor of the thermal quality of an environment. Future efforts to model species' distributions should link thermoregulation and activity to environmental heterogeneity at fine scales.