Climate drove taxonomic, functional, and phylogenetic bird diversity in an elevational gradient in eastern Brazil

Understanding how biodiversity patterns are related to elevation is crucial for predicting the effects of environmental change on species distributions. Eastern Brazil harbors ancient, ecologically important mountain systems that remain understudied along elevational gradients. Here, we analyzed taxonomic, phylogenetic, and functional diversity of bird assemblages along an elevational gradient in the Chapada Diamantina to assess how environmental variation influences avian assemblage structure. Our results revealed a consistent non-linear decline in species richness, phylogenetic diversity (PD) and functional richness (FRic) with increasing elevation, whereas richness-independent metrics, including Mean Nearest Taxon Distance (MNTD) and functional divergence (FDiv), showed no clear relationship with elevation. Climatic variables, particularly annual mean temperature, were positively associated with richness, PD, and FRic, while terrain ruggedness showed a weaker negative association with richness, PD, and functional richness. These findings indicate that elevational patterns of bird diversity in the Chapada Diamantina differ among the nature of diversity indices, with richness-dependent taxonomic, phylogenetic, and functional indices being more strongly associated with elevation and current climatic, whereas richness-independent indices did not exhibit clear patterns. Our results highlight the importance of current climate in shaping spatial variation in bird diversity across tropical mountain systems and provide a baseline for assessing potential responses of montane bird assemblages to future environmental change.