Low and high elevation understory bird assemblages at the southernmost portion of the Atlantic Forest

The mechanism of community assembly depends on a basic process: abiotic conditions in combination with biotic interactions define the boundaries within which a given species can inhabit a certain region. Regions with steep elevational gradients occur throughout the range of the Atlantic Forest biome and are characterized by differences in richness, abundance and species composition in several vertebrate groups. We evaluated the composition, richness, diversity and functional diversity of the bird assemblage in two elevational ranges of the Atlantic Forest in its southernmost portion in Brazil. Birds were sampled with mist nets in two environments: Araucaria Forest (900 – 1.020m) and Rain Forest (100 – 200m). Rarefied richness showed no differences in the number of species between the low- and high-elevation. ANOSIM revealed differences in species composition between the groups. There was no difference in functional diversity between altitudes. Differences in composition and diversity in avifauna at different gradient altitudes are a reflection of the vegetation structure and potential difference in the availability of resources found in these environments. Bird species ecological optima seem to be influenced by the altitude and/or complexity of the vegetation, which has immediate consequences for the management and conservation of birds in the Atlantic Forest. The maintenance of the regional species richness depends on the preservation of the species present at the two altitudes, as they harbor distinct compositions and contribute, equitably, to the region’s species pool.