The evolution of climatic niche breadth in terrestrial vertebrates

Interspecific variation in climatic niche breadth underlies many ecological phenomena, yet only recently have studies-focused explicitly on the evolution of climatic niche breadth. Here, we integrate data on geographical distributions, bioclimatic variables, and phylogenetic relationships of 18,404 terrestrial vertebrate species to investigate the evolution of climatic niche breadth. We demonstrate that the evolutionary rates of upper and lower climatic niche boundaries are largely uncoupled. For instance, the rate of evolution of low temperature limits was nearly twice that of high-temperature limits, whereas low- and high-precipitation limits remained relatively constant despite a considerable variation in average precipitation. These results suggest that the evolution of climatic niche breadth is fundamentally different between axes. Finally, we found no relationship between climatic niche breadth and speciation rates. The consistency of these patterns across taxa suggests that they represent general principles governing the evolution of climatic niche breadth.