Historical legacies of spatial and temporal climate exposure on thermal physiology shape butterfly vulnerability to recent climate change

Few observations are more indelible in ecology than widespread variation in the spatial and temporal occurrence of species. Although the mechanistic underpinnings of such variation are likely multifarious, temperature is argued to be a key driver. Understanding how temperature shapes species ranges and seasonal activity not only provides insights into historical biogeographic patterns, but also how legacies of historical adaptation to climate impact responses to recent climate change. Butterflies serve as a model taxon for both areas of research. For example, climatic niche attributes are associated with range size, phenology, and shifts in these responses under climate change. Here, we expand on this work to explicitly consider how thermal adaptation in physiological tolerance traits might set the range limits and seasonal activity of butterflies. At a global scale, greater cold tolerance was significantly associated with higher latitude of the cold range edge and cooler climatic niche extremes. Within a temperate butterfly community, greater cold tolerance was also significantly associated with earlier seasonal emergence timing and the cold climatic niche extreme during the adult flight period. By contrast, heat tolerance was not associated with the latitude of the warm range edge. However, greater heat tolerance was weakly associated with warmer climatic niche extremes during the adult flight period. These warm-season butterflies were exposed to more high temperature events. Overall, a greater number of high temperature events during the adult flight season was associated with butterfly population declines over the last two decades. Climate exposure therefore appears to strongly mediate butterfly vulnerability to recent climate change.