Allen's Rule in hares (Lepus spp.)

    Allen's Rule predicts chunkier bodies with short extremities in cold climates versus leaner bodies with longer extremities in hot climates. Closely-related species of the genus Lepus [Leporidae: Lagomorpha] show progressively longer extremities (legs & ears) and leaner bodies, from the northern arctic hare (L. arcticus) through the temperate L. americanus to desert form in the Mojave L. californicus and Sonoran desert jackrabbit (L. alleni). This is adaptive because a lower surface-to-body ratio in colder climates conserves heat, whereas a higher ratio provides a means of exhausting heat to the environment in hotter climates.