Determinants of bird beta diversity patterns in a landscape with a relict habitat in northern Argentina

Understanding the determinants of beta diversity patterns is important in ecology and conservation. However, few vertebrate studies have been conducted in landscapes with relict vegetation formed by historical natural processes. For birds, only similarities between relicts and surrounding habitats or other relicts were assessed. Here, we evaluated the determinants of bird beta diversity patterns in a landscape with relict vegetation in the Guasayán mountain range, Dry Chaco ecoregion, northern Argentina. In this landscape, a relict of humid forest develops on the humid slope, whereas dry forests typical of the Dry Chaco develop on the dry slopes and piedmont. These habitats, which harbor three bird communities, differ in their representativeness of the region. We evaluated if the environmental differences among habitats determine bird beta diversity at the local scale (species replacement hypothesis). We found a significant correlation between habitat characteristics and bird communities, a lower bird beta diversity between the most similar habitats, a dominance of species turnover over nestedness, and a species turnover dominated by birds closely associated with the Dry Chaco and humid forests. These findings support the species replacement hypothesis. As other forest relicts, this relict evidences that, in the long-term, an isolated habitat fragment can undergo the loss of species closely associated with that habitat, while maintaining a distinctive bird community in the region. Thus, at the local scale, relicts are important for conservation management, and at the biogeographic scale, they indicate the risk of the extinction of species closely associated with particular habitats.