Climatic variability drives greater thermal tolerance breadth and enables larger range size in butterflies

Although climatic variability has been proposed to shape physiological tolerances, and in turn, species distributions, relatively few studies have done so with measured, rather than inferred, tolerances. Here, we use recent syntheses of butterfly distributions and thermal physiological traits to evaluate this hypothesis. Our results support the hypothesis that climatic variation in temperature (annual temperature range and temperature seasonality) shapes thermal tolerance breadth, mostly through low temperature tolerance, rather than high temperature tolerance. In turn, greater tolerance breadth was associated with greater latitudinal range. Together, these results provide support for the Rapoport effect in butterflies and the climatic variability hypothesis as a key mechanism underlying this pattern. Because our study suggests that butterflies are highly sensitive to low temperature variation, contemporary distributional changes in butterflies, especially at leading range edges, are likely to continue in the future amidst rising global temperatures.