Elevation and climatic tolerance: a test using dung beetles

An increase in the altitudinal range of occurrence of species in an assemblage with increasing elevation has been explained as a consequence of individual organisms having to be able to withstand a broader range of climatic conditions at higher elevations; the climatic variability hypothesis. Here we show that for scarab dung beetles (26 species) across an elevational transect (approx. 2500 In) in southern Africa thermal tolerance range does increase with increasing elevation across individuals and across species. The maximal thermal tolerance range exhibited increases slowly with elevation and the minimum range increases more rapidly. The mechanistic basis of the change appears to be one of rapidly changing critical thermal minimum (CTmin) with elevation and only small changes in critical thermal maximum (CTmax). Of course, even if the pattern of tolerance of species assumed by the climatic variability hypothesis is correct, an increase in altitudinal range with increasing elevation need not necessarily follow. However, although sampling has been limited, there does appear to be an elevational increase in altitudinal range for this species assemblage.