Distribution patterns of waterbirds and their driving factors in Ramsar sites of China

Most internationally important wetlands in China hold irreplaceable value for waterbird conservation. However, systematic understanding remains lacking regarding the multi-dimensional spatial patterns of waterbird diversity in these wetlands and their underlying driving mechanisms. Based on waterbird species checklists from 80 internationally important wetlands across China, this study analyzed the spatial distribution patterns of waterbird diversity along three major geographical gradients, longitude, latitude, and elevation, and their driving mechanisms. The results showed that species richness exhibited a significant increasing trend with rising longitude (p<0.001); phylogenetic nearest-neighbor structure and functional structure significantly tended toward clustering with increasing longitude (p<0.001), indicating significantly enhanced environmental filtering in high-longitude eastern regions; phylogenetic structure was significantly regulated by the latitudinal gradient (p<0.001), with high-latitude areas displaying a complex pattern characterized by the coexistence of overall phylogenetic structure divergence and close-relative clustering. Along the elevational gradient, species richness significantly decreased with increasing elevation (p<0.001), whereas phylogenetic and functional diversity significantly increased with rising elevation (p<0.001), with community structure shifting from a clustered state at low elevations to a divergent state at high elevations. Temperature factors such as mean annual temperature (bio1) and isothermality (bio3), along with wetland area, were identified as core driving factors influencing waterbird diversity distribution patterns, with explanatory power exceeding 20% in diversity models (adjusted R²=0.23-0.42), among which mean annual temperature (bio1) contributed the most to species richness. This study reveals significant differences in waterbird community assembly mechanisms across spatial gradients: phylogenetic clustering at low elevations is dominated by environmental filtering, whereas phylogenetic overdispersion at high elevations may result from niche differentiation and competitive exclusion. These findings can provide a scientific basis for formulating differentiated conservation strategies and guiding habitat restoration practices for waterbird diversity in China.