Climatic niche evolution is not constant across spatial scales: the case of bats around the globe

Background/Question/Methods

Climatic niches are the climatic conditions that allow species to persist and coexist in space and time. Understanding the speed at which species' climatic niches evolve has been critical to enlightening biogeographical history and predicting the responses of ecological communities to climate change. The evolutionary rates of climatic niches are known to vary greatly across phylogenetic extents, suggesting that taxa vary in their abilities to adapt to environmental changes. Although the evolutionary and ecological responses of species to environmental variation are known to vary across geographical regions, we know little about how evolutionary rates in climatic niches change across spatial scales. Explicitly considering that niche evolution varies from fine to coarse spatial scales may resolve contradictory views about the relative influence of processes underlying species adaptations to past (historical) and future climatic changes. Here, we explore this question and test predictions underlying the scale-dependence of climatic niche evolution. Focusing on worldwide bats, we introduce a framework that quantifies the position and width of species climatic niches across a gradient of hierarchical spatial extents – restricting from global, east-west hemispheres, biogeographical realms, biomes, to ecoregions –, and then estimate and compare the evolutionary rates of their climatic niches across spatial scales.

Results/Conclusions

We found clear evidence that the evolutionary rates of climatic niches vary across spatial scales in bats. The evolutionary rates of climatic niche position decreased consistently with spatial scales. Conversely, although the evolutionary rates of bat climatic niche widths – or how rapidly climatic niche specialization evolved in bats – were generally lower at the broader, global, and at the more local, ecoregional scales, they were higher in both mean and variance at the biogeographical realm scale. The variation in climatic niches depended on the variation in their evolutionary rates, but this relationship differed between the position and the width of niches and varied greatly across spatial scales. By integrating spatial scale-dependence when estimating species climatic niches and their evolutionary rates, we were able to elucidate patterns in the evolution of bat species climatic specialization and preferences that were not apparent when examining global niches independently from spatial scales. Together, our approach and analyses demonstrate the scale-dependency of ecological and evolutionary processes driving climatic niche evolution and provide us with insights into the biological underpinnings of variation in ecological preferences and specialization in bats.