Supplementary material from "Thermal tolerance patterns across latitude and elevation"

Linking variation in species' traits to large-scale environmental gradients can lend insight into the evolutionary processes that have shaped functional diversity, and future responses to environmental change. Here, we ask how heat and cold tolerance vary as a function of latitude, elevation and climate extremes, using an extensive global dataset of ectotherm and endotherm thermal tolerance limits, while accounting for methodological variation in acclimation temperature, ramping rate and duration of exposure among studies. We show that previously reported relationships between thermal limits and latitude in ecotherms are robust to variation in methods. Heat tolerance of terrestrial ectotherms declined slightly towards higher latitudes but did not vary with elevation, whereas heat tolerance of freshwater and marine ectotherms declined more steeply towards higher latitudes. By contrast, cold tolerance limits declined steeply with latitude in marine, intertidal, freshwater and terrestrial ectotherms, and towards higher elevations on land. In all realms, both upper and lower thermal tolerance limits increased with extreme daily temperature, suggesting that different experienced climate extremes across realms explain the patterns, as predicted under the Climate Extremes Hypothesis. Statistically accounting for methodological variation in acclimation temperature, ramping rate and exposure duration improved model fits, and increased slopes with extreme ambient temperature. Our results suggest that fundamentally different patterns of thermal limits found among the earth's realms may be largely explained by differences in episodic thermal extremes among realms, updating global macrophysiological ‘rules’.This article is part of the theme issue ‘Physiological diversity and global patterns of biodiversity in a time of global climate change: testing and generating key hypotheses involving temperature and oxygen’.