Geographic and Climatic Correlates of Morphological Variation in Eptesicus fuscus

Abstract

Skull size in continental North American Eptesicus fuscus is inversely related to temperature as predicted by the classical form of Bergmann's rule, but it is positively related to moisture in contradiction to James' (1970) reformulation of the rule. Greater food availability in moister environments is suggested as the explanation of the latter relationship. Wing size is inversely related to temperature, but the relationship is not statistically significant. Wing size is significantly greater in moister environments, suggesting that evaporation from wings is an important selective factor. The geographic coordinates latitude, longitude, and elevation explain significant amounts of morphological variation, but differentiation among the insular subspecies of E. fuscus is not consistent with a gene flow model if a Central American ancestor is assumed. The relationship between body size and island area in the Antillean subspecies of E. fuscus supports Heaney's (1978) selective model of body size in insular mammals. Overall, the results suggest that both climate (natural selection) and geographic factors (barriers to gene flow) are important causes of differentiation in E. fuscus.