Distributions of bats along an elevational gradient in the Andes of south-eastern Peru

At least 193 species of mammals are known to occur within the Manu Biosphere Reserve in south-eastern Peru, contributing to its stature as one of the world's richest protected areas. Bats [Order Chiroptera) comprise more than 42% (82 species) of this diversity. Analyses of bat capture records over a transect extending more than 3 km in elevation show that most bat species at Manu are widely distributed in the Amazon Basin. Few are montane endemics or are localized in south-eastern Peru, although exceptions to this generalization include two species new to science. Highland bat faunas tend to be attenuated versions of those found below, and the elevational zonation of bat communities is weak. Species turnover with elevation is monotonic and more-or-less smooth, with Jaccard's similarity values falling to 0.5 for sites differing by 750m in elevation. Subtle and orderly change in species composition with elevation is also reflected in the nested-subset structure of these communities; over 19 different levels, this pattern of hierarchical structure is both striking and highly significant. Elevational ranges of species generally increase with elevation, in accordance with Stevens' extension of 'Rapoport's rule' of range amplitude. However, support for 'Stevens' rule' may be trivial, given Amazonian richness and Andean impoverishment. Reduced richness and poorly developed endemism in Andean bat communities contrast with patterns shown by sympatric rodent faunas, which are diverse and strongly endemic on the Altiplano and markedly zoned along the Eastern Versant. Contrasts are less sharp with bird communities, which nevertheless exhibit stronger zonation and higher endernicity. Factors responsible for these distinctive distributional patterns are discussed.