Como gradientes ambientais influenciam a diversidade de aves em cidades tropicais? Assembleia de aves em uma metrópole amazônica

Abstract

The biotic and abiotic attributes that characterize urban environmental gradients affect species diversity and abundance, but these effects are best documented in cities located in temperate regions. We investigated how bird assemblages are distributed along environmental gradients in Manaus, a large tropical city. Birds were counted at 84 sampling points. Local (e.g. number of trees) and landscape (e.g. forest cover) variables that characterize the urban gradients of Manaus were also quantified at the same points. We analyzed the distribution of 184 bird species distributed in 3,745 individuals. The local diversity (alpha diversity) of birds was higher in sites with greater forest cover (> 50%) compared to sites with lower cover (< 25%) or intermediate cover (25-50%). In contrast, the dominance of individuals is higher in sites with lower forest coverage compared to intermediate and higher coverage areas. Sites with lower and higher forest cover harbor bird assemblages with significantly different bird species composition (beta diversity). Twelve families and 37 species of birds were significantly associated with a specific forest cover class. Twelve biotic and abiotic variables were quantified locally (at points) and at the landscape level (within a 500 m radius of points) and only four had a significant influence on bird assemblages. Forest cover positively affected bird richness and diversity, but not species abundance and composition. Noise level negatively affected bird species richness, while the relative abundance of trees had a positive effect on the same parameter. Locations with higher edge density and high number of trees have a greater abundance of birds. Species composition was affected only by edge density. Responses of bird assemblages to urbanization can be complexes, as they depend both on the variables that characterize the environmental gradients and how the alpha and beta diversity parameters are measured. Our study indicates that afforestation of places with low noise levels and expansion of forested areas including officially protected areas are the best strategies to increase alpha and beta diversity of birds in Manaus.