Environmental filtering unveils differences in bird diversity patterns and underlying mechanisms in the Qilian Mountains

Aim The uplift of the Qinghai-Tibet Plateau provides an opportunity to understand the diversity patterns and their driving processes in high and low elevations regions of Qilian Mountains. However, the potential mechanisms leading to differences in multi-dimensional alpha diversity and beta diversity patterns between high and low elevation regions are unclear. Present study aims to investigate the response of bird communities respond to the overall elevation gradient and environmental factors drive different diversity patterns. Methods The wild bird surveys were conducted during both the breeding and migration season in the north (NSQM) and south slopes (SSQM) of the Qilian Mountains from 2021 to 2022. Turnover and nestedness patterns within bird communities across elevational gradients were investigated in three dimensions (taxonomic, functional, and phylogenetic). Alpha diversity and beta diversity were compared between the two regions (NSQM and SSQM) in different dimensions. And it was assessed the potential non-linear relationships with environmental variables. Results With the exception of nestedness, which predominates in bird functional beta diversity in the SSQM, turnover components dominated beta diversity in both the SSQM and NSQM. Bird diversities in three dimensions were significantly higher in the SSQM than in the NSQM, but has lower functional total beta diversity. Additionally, the predictive variables had different effects in the alpha and beta diversity of birds in different dimensions across different regions. Nighttime light and solar radiation were the most important factors in low elevation regions, while in high elevation region, slope and habitats are the most significant environmental variables. Conclusion Our study emphasizes the potential role of environmental filtering and the importance of environmental variables in driving bird communities. While increasing elevation enhances diversity in different dimensions of bird communities, habitat fragmentation in high elevation regions reduces functional dissimilarity among communities.