Squamate phylogeny incorporated in PGLS analysesPhylogenetic relationships used to obtain the supertree were compiled from the literature.Supertree_squamates.pdfGlobal map with species geographic locationsLatitudinal and longitudinal co-ordinates of the populations sampled for CTmax, CTmin and Tp were determined from the geographic locations given in each respective study. When locations were not given (26% of the data) or multiple populations were used (<1% of the data), the centre of the species range was determined using species distribution maps and occurrence data from museum specimen records .Species locations.pdfRelationships between parameters of the performance curveAfter accounting for phylogenetic relationships across species, the critical thermal minimum was not related to (a) the critical thermal maximum (CTmax) (PGLS, n = 111, P > 0.05) or to (b) the preferred body temperature (Tp) (PGLS, n = 97, P > 0.05). By contrast, (c) CTmax and Tp were strongly related (PGLS, n = 133, P < 0.05).Regressions_CTmax_CTmin_Tp.pdfSpecies, performance curve parameters and literature sourcesSquamate thermal data compiled from the literature. Tp is the preferred body temperature, CTmax is the critical thermal maximum and CTmin is the critical thermal minimum.Species performance data.pdfCorrelation matrices_climate predictorsCorrelation matrices for all climate predictors used in models predicting Tp, CTmax and CTminCorr_matrices.pdf

Determining organismal responses to climate change is one of biology's greatest challenges. Recent forecasts for future climates emphasize altered temperature variation and precipitation, but most studies of animals have largely focussed on forecasting the outcome of changes in mean temperature. Theory suggests that extreme thermal variation and precipitation will influence species performance, and hence affect their response to changes in climate. Using an information-theoretic approach, we show that in squamate ectotherms (mostly lizards and snakes), two fitness-influencing components of performance, the critical thermal maximum and the thermal optimum, are more closely related to temperature variation and to precipitation, respectively, than either is to mean thermal conditions. By contrast, critical thermal minimum is related to mean annual temperature. Our results suggest that temperature variation and precipitation regimes have had a strong influence on the evolution of ectotherm performance, so that forecasts for animal responses to climate change will have to incorporate these factors, and not only changes in average temperature.