The biogeography of thermal risk for terrestrial ectotherms: scaling of thermal tolerance with body size and latitude

1. Many organisms are shrinking in size in response to global warming. However, we still lack a comprehensive understanding of the mechanisms linking body size and temperature of organisms across their geographical ranges. Here we investigate the biophysical mechanisms determining the scaling of body temperature with size across latitudes in terrestrial ectotherms.
2. Using biophysical models, we simulated operative temperatures experienced by lizard-like ectotherms as a function of microclimatic variables, body mass and latitude and use them to generate null predictions for the effect of size on temperature across geographical gradients. We then compared model predictions against empirical data on lizards’ field body temperature (Tb), and thermal tolerance limits (CTmax and CTmin).
3. Our biophysical models predicted that the allometric scaling of operative temperatures with body size varies with latitude, with a positive relationship at low latitudes that vanishes with increasing lati...