Seasonal elevational patterns and the underlying mechanisms of avian diversity and community structure on the eastern slope of Mt. Gongga

Abstract Aim Mountain ecosystems harbour significant biodiversity across elevations and seasons. This biodiversity, however, is increasingly under threat from climate change and human land use. While much work has been done to characterize biodiversity in tropical mountains, far less is known about the environmental, seasonal and spatial factors that impact diversity and community structure in subtropical and temperate regions. Location Mt. Gongga, Sichuan, China: the eastern‐most peak in Asia above 7000‐m elevation and the main peak of the Hengduan Mountains. Method We examined elevational patterns and ecological variables underlying taxonomic diversity (TD), phylogenetic diversity (PD), functional diversity (FD) and community structure in birds on the eastern slope of Mt. Gongga between 1100‐ and 4400‐m elevation. We assessed biodiversity patterns between species with different elevational range sizes (small‐ vs. large‐ranged species) and between seasons (breeding vs. non‐breeding season). Results We recorded 230 bird species across seven field surveys. TD, PD and FD showed similar hump‐shaped elevational patterns in both seasons. In the breeding season, TD, PD and FD for small‐ranged species were highly correlated with climatic factors (mean daily temperature, seasonal temperature range) and vegetation factors (enhanced vegetation index), while large‐ranged species were correlated with spatial factors (mid‐domain effect). In the non‐breeding season, TD, PD and FD for all species groupings were positively correlated with climate factors. For small‐ranged species in both seasons, community structure was more overdispersed at low and high elevations, and more clustered at middle elevations. For large‐ranged species, community structure differed between seasons, showing a general trend towards clustering as elevations increase in the breeding season and trends towards overdispersion and/or evenness as elevations increase in the non‐breeding season. Conclusions We found that different factors shape elevational patterns of diversity for small‐ and large‐ranged species in the breeding season; small‐ranged species are shaped by climate and vegetation structure, while large‐ranged species are shaped by spatial factors. This difference is likely explained by differences in ecological niche breadth (physiological tolerance and/or habitat specialization) between small‐ranged species and large‐ranged species. In the non‐breeding season, however, when climate is seasonally harsher, we found that patterns of diversity for all range‐size groupings were driven by climatic factors. We also found that community structure generally becomes more overdispersed as resource availability decreases and environmental conditions become harsher, like at higher elevations and in the non‐breeding season, suggesting that competition for limited resources is important for shaping communities in seasonal environments. These findings highlight how avian diversity and community structure are dynamic across a local elevational gradient and seasonally, shifting across the annual cycle, which has implications for conservation strategies and land management.