Elevational patterns and assembly processes of multifaceted bird diversity in a subtropical mountain system

Abstract Aim Mountain systems harbour disproportionate biodiversity on Earth. However, the mechanism underlying community assembly along elevational gradients remains unclear due to the complexity of environmental constraints and biotic interactions. Birds play a crucial role in mountain system and are sensitive to environmental changes, making them an ideal taxon for exploring diversity patterns and the underlying assembly processes. We aimed to identify the elevational patterns of multifaceted bird diversity and explore how different ecological processes drive community assembly. Location A 2600 m elevational gradient on the eastern margin of the Qinghai–Tibetan Plateau. Methods We identified the elevational patterns and assembly processes of alpha‐ and beta‐diversity in the taxonomic, phylogenetic, and functional dimensions. We compared the multidimensional beta‐diversity components and assessed the response of beta‐diversity to variations in elevational and environmental distances. Finally, we examined the roles of spatial and environmental factors in structuring the diversity patterns. Results We observed bimodal elevational patterns across species richness, phylogenetic diversity, and functional diversity but distinct community structures in terms of mean pairwise phylogenetic, and functional diversity. We detected a linear decline in phylogenetic and functional diversity with increasing elevation after controlling for the confounding effect of species richness. We documented relatively high taxonomic and phylogenetic total beta‐diversity, but low functional total beta‐diversity. Turnover dissimilarity contributed much more to total beta‐diversity than nestedness‐resultant dissimilarity. The elevational patterns of standardised measures indicated that competition exclusion and environmental filtering jointly shaped the community assembly process. In general, mean annual temperature, annual precipitation, and area significantly influenced the majority of diversity measures. Conclusions Our results revealed incongruent community structures across phylogenetic and functional diversity. Additionally, our results indicated that species with similar ecological performances or distinct lineages may exhibit convergent adaptations to cold and dry environments. These findings provide insights into the mechanistic understanding of the community assembly process and assist in conservation planning in mountain systems by integrating multifaceted diversity across different dimensions.