Elevational Patterns of Avian Community Diversity in the Daba Mountains and Their Underlying Drivers

Mountain ecosystems serve as natural laboratories for studying biodiversity distribution along elevational gradients. This study was conducted at Hualongshan National Nature Reserve in the Daba Mountains, Shaanxi Province, using line transect surveys, mist-netting, and passive acoustic monitoring (PAM). We systematically examined the spatial variation and drivers of bird community diversity along the elevational gradient, integrating α and β diversity across taxonomic, functional, and phylogenetic dimensions. A total of 91 bird species from 8 orders and 33 families were recorded, among which breeding birds (84 species) were dominated by Oriental (55.95%) and Palaearctic (26.19%) species, reflecting significant transitional characteristics between the two realms. Alpha diversity exhibited a mid-elevation unimodal pattern, peaking at 1951~2250 m in the coniferous and broad-leaved mixed forest zone. β diversity decomposition revealed that taxonomic diversity was dominated by turnover, functional diversity by nestedness, and phylogenetic diversity by balanced contributions of both, indicating asynchrony among dimensions. Random forest models identified precipitation difference as the primary driver of taxonomic β diversity, while Enhanced Vegetation Index (EVI) difference dominated functional β diversity, revealing differentiated mechanisms by which water availability and vegetation productivity shape species composition and functional structure, respectively. Our findings highlight the asynchrony of multidimensional bird diversity, emphasizing that a single dimension cannot fully capture community assembly mechanisms, and provide theoretical and practical reference for mountain biodiversity conservation.