Assembleias de aves em fragmentos florestais em uma grande metrópole tropical: os efeitos da estrutura da paisagem dependem da afinidade de habitat das espécies

Abstract

Urbanization can lead to habitat loss and fragmentation, processes that have been poorly investigated in tropical cities with high biodiversity. In addition, these effects may vary according to the life history characteristics of organism. In this study we analyze how landscape structure affects richness and composition of bird assemblages, considering specific responses of groups of birds with different habitat affinities, that persist in forest fragments in Manaus, the largest city in the Amazon. To characterize the landscape structure we used metrics quantifying area, proximity, core area and shape of the analyzed urban forest fragments. In addition, birds were classified as forest specialists, forest generalists or open area users. Bird assemblages were characterized by species richness and species composition. We also tested whether the species distribution was nested based on the characteristics of fragments. The landscape structure influenced species richness and distribution patterns, but responses were dependent on the habitat affinity of bird species. Larger forest fragments have greater richness of forest specialist and generalist bird species. The degree of isolation and core area of the fragment, on the other hand, were only relevant for forest specialist birds, where more connected fragments and with larger core areas have greater species richness. Birds that use open areas were not influenced by the characteristics of forest fragments. The composition of bird species was different between small (<10 ha), medium (between 10 and 100 ha) and large (> 100 ha) fragments, especially for generalist forest birds. The bird assemblage of forest fragments is composed mainly by forest generalist species (51% of the species) being a subset of the species found in a preserved forest near the city of Manaus (Ducke Reserve) with which we compare the avifauna. In this way, the bird assemblages of the urban forest fragments of Manaus result from a continuous filtering process based on the habitat affinities of bird species. The conservation of forest fragments in Manaus depends on urban planning that prioritizes the preservation of green areas and afforestation, increasing connectivity among fragments which will help maintaining forest specialist and forest generalist bird species and the environmental services these areas offer.