Efeitos do gradiente de urbanização sobre assembleias de anfíbios no extremo oeste da Amazônia brasileira

Abstract

Urbanization promotes fragmentation and habitat quality degradation. Urban landscape variations can act as an environmental gradient influencing species composition, generating variations in the beta diversity of amphibian assemblages along this gradient. Were analyzed effects of local and landscape variables over richness, abundance and composition of anuran species, and whether beta diversity is promoted by the substitution or nestedness of species in 22 transects along a urban/forest gradient in the municipality of Tabatinga, in the extreme western of Brazilian Amazon. Were registered 52 species and 5.481 individuals belonging to nine amphibian families. Environments less disturbed by urbanization environments showed the highest richnesses, however, abundance had a pattern different to the expected for the gradient, with the most disturbed environments with the highest abundances of individuals. Beta diversity variation was promoted both by species substitution, with most of species with low abundance and few common species in all environments, as by nestedness, with a gradual loss of species along the gradient, indicating that all registered species at urban and periurban environments were a subset of the registered species at the rural environment. Two environmental variables of landscape (green area and distance from the river) influenced significatively the amphibian community structure along the urban/forest gradient, and for both variables, the species ordinations revealed a significantly nested pattern. Piecewise regression emphasize that, to preserve and conserve a higher species diversity and avoid the amphibian fauna homogenization in urban environments, is necessary to plan the maintenance of green areas as forest cover larger than 68 thousand m2 along urban landscape.