Effects of climate and land-use gradients on avian phylogenetic and functional diversity in a tropical dry forest

Climate and habitat influence the distribution and dynamics of biodiversity. Investigating their influence on spatial patterns of phylogenetic (PD) and functional diversity (FD) is essential to understanding the response of ecological assemblages to changes in these factors. Here, we investigate the patterns of PD and FD of birds from the Brazilian dry forest Caatinga, and their relationship to gradients in climate and vegetation heterogeneity. For over 500 species distributed at 123 assemblages, we investigated the effect of these factors on a standardized measure of phylogenetic diversity (sesPD) phylogenetic dispersion (PDis), the functional richness (FRic), functional dispersion (FDis), taxon restrictedness, and functional uniqueness. Climate was the best predictor of all metrics of functional and phylogenetic diversity, whereas forest cover was relevant for FRic only. The independent effects of climate and habitat highlight their different roles in determining ecological and evolutionary diversities of avian assemblages in this semiarid biome. Additionally, most species are geographically restricted, but functionally redundant, suggesting a spatial turnover between different species with similar functional traits. Complementary effects of climate and habitat change act in concert in reducing ecological redundancy in assemblages less disturbed, and functional uniqueness in assemblages at the extreme of the aridity gradient in the Caatinga.