Researchers increasingly rely on thermal physiology as the mechanistic basis for guiding extinction predictions in the face of climate change. How such physiological data inform field performance, where environments are variable across space and time and individuals move, remains equivocal and a substantial source of uncertainty. We advance a new approach for estimating field performance of ectotherms based on thermal reaction norms and the properties of the thermal landscape– including mean temperature, spatial variance, and spatial autocorrelation. We develop a theoretical framework and explore its predictions, use this approach to examine the importance of behavior for a global dataset of 38 insect species using fine-grained climate projections, and provide a case-study estimating historic and future performance of the subtropical lizard Agama atra.
Our results show that integrating behavior and highly resolved environmental data into ecological forecasts can reduce or reverse the predicted detrimental responses of ectotherms to warming. Our results predict that warming (2050-2059 projections), particularly in subtropical regions, will substantially increase the importance of behavioral thermoregulation– as evidenced by an increased difference between ectotherm performance estimates with and without allowing for behavior. However, a substantial range of potential outcomes in response to warming exists, depending on the mean costs of thermoregulation and the relationship between the cost of thermoregulation and mean ambient temperature; our results highlight the latter as an underappreciated determinant of performance. For example, there is a strong positive relationship between mean temperature and thermal spatial variation in habitats occupied by Agama atra. This relationship suggests that the cost of thermoregulatory behavior will decrease as mean temperatures increase. Overall, estimates of performance not incorporating behavioral thermoregulation tend to over-predict the severity of the detrimental impacts of warming, but the substantial range of variation in how behavior can modify estimates of performance underscores the importance of examining fine scale environmental characteristics.