Tolerance breadths, niche breadths, and latitude: implications for climate change in tropical organisms: Supplementary Data

<b>Aim: </b>Tropical species may be more vulnerable to global warming. One potential explanation is the seasonality hypothesis, the idea that a species' exposure to a narrow range of climatic temperatures over the year (low seasonality) limits the evolution of physiological tolerances to a narrower range of temperatures. Low temperature variability in the tropics may explain a higher frequency of climate-related local extinctions, but it is unclear whether this is due to narrow physiological tolerances to temperature extremes. The seasonality hypothesis predicts a strong, positive relationship between species’ climatic niche breadths and their physiological tolerance breadths. It also assumes that both niche breadths and tolerance breadths should be positively related to latitude. Here, we test these ideas using physiological, climatic, and phylogenetic data for 386 species spanning amphibians, squamates, birds, and mammals.<b>Methods: </b>We used phylogenetic comparative methods to test relationships among species' tolerance breadths, niche breadths, and latitude.<b>Results:</b> We found that the relationship between niche breadths (maximum minus minimum annual temperatures) and tolerance breadths (upper minus lower thermal tolerances) differed strongly among clades. In birds and mammals, these relationships were weak and non-significant. Niche breadths were significantly and positively related to tolerance breadths in amphibians and squamates, but niche breadths explained only 6% of the variation in tolerance breadths among squamates compared to 29% in amphibians. Niche breadths were more strongly related to latitude than tolerance breadths. Latitude was significantly related to tolerance breadths in amphibians and squamates, but the relationship was weak among squamates and not significant in birds and mammals.<b>Main Conclusions:</b> These results provide evidence against the seasonality hypothesis and the idea that narrower physiological tolerance breadths in the tropics explain why narrower climatic temperature niche breadths predict climate-driven extinctions. Overall, our results suggest that physiological tolerance breadths may not predict species' vulnerability to warming.