BATS VERSUS BIRDS - COMPARISONS AMONG PERUVIAN VOLANT VERTEBRATE FAUNAS ALONG AN ELEVATIONAL GRADIENT

Both taxa of volant vertebrates, bats and birds (diurnal and nocturnal), have had approximately equal time to evolve along the eastern slopes of the Peruvian Andes. Bats, however, have been relatively less successful than birds at colonizing and radiating in the higher elevations. Relative species richness (the number of species recorded for each elevational interval expressed as a proportion of the total number of species in each group) decreases more rapidly with increasing elevation in bat faunas than in bird faunas, and fewer bat species are restricted to the highlands relative to birds. The breadths of elevational distributions of bats are greater than those of birds and increase markedly with elevation, unlike the bird distributions. The number of large species, relative to the total number of species, decreases with elevation more rapidly in bat faunas than in diurnal bird faunas. Three dietary groups (i.e. insectivores, frugivores, and nectarivores-insectivores) differ significantly between bats and diurnal birds in their relative representations between the elevational intervals. Differences in respiratory efficiency and energetic requirements, acting independently, or perhaps collectively, with resource differences, have probably made colonization and radiation in the highlands more difficult for bats than for birds.