Do Geographic Range Sizes Evolve Faster in Endotherms?

Changes in geographical distributions underlie a variety of fundamental ecological and evolutionary processes, from allopatric speciation to local extinction. However, little is known about general principles governing the evolution of range sizes at macroevolutionary scales. In this study we measure rates of geographical range size and position in a large-scale dataset of nearly 20,000 species including mammals, birds, squamates and anurans to test three predictions regarding the relationship between endothermy and geographical range evolution, namely whether endotherms show (1) larger geographical ranges; (2) faster rates of range size evolution; and (3) faster changes in the geographical position of their ranges. We found evidence in favor of all of these predictions, suggesting that the evolution of endothermy was associated with a fundamental change in the tempo of range evolution in terrestrial vertebrates. These results are consistent with two previously hypothesized relationships between range size and metabolic rate: the thermal plasticity hypothesis, which suggests that high metabolic rate increases thermal tolerance, and the energy constraint hypothesis, which posits that due to the higher, sustained levels of energy requirements, individuals with high metabolic rates would necessitate to forage farther and to space themselves more broadly, which would result in lower population densities, larger home ranges and ultimately larger range sizes. On the other hand, there was substantial variation in rates of range size evolution among the studied taxa that cannot be explained by the evolution of endothermy alone.