Landscape and habitat effects on functional and phylogenetic diversity and structure of bird communities in fragmented habitats within an urban landscape, Southwest China

Understanding how landscape and habitat characteristics shape species diversity and community structure in fragmented habitats offers insights into the impact of fragmentation on biodiversity. However, relying solely on taxonomic metrics is insufficient to reveal their effects; incorporating functional and phylogenetic dimensions, while accounting for the complex (direct and indirect) relationships between landscape and habitat characteristics, is essential for elucidating the mechanisms of community assembly. By investigating birds in 30 remnant woodlot patches (0.3–290.4 ha) within an urban landscape, Southwest China, during the breeding seasons from 2017 to 2023, we examined the influence of landscape characteristics (i.e., patch area, isolation, and shape index) and habitat characteristics (including habitat composition and woody plant richness) on their functional and phylogenetic diversity and structure. We recorded 80 bird species, with species richness per patch varying from 14 to 58. Both functional and phylogenetic diversity increased with patch area and woody plant richness but decreased with isolation, which was measured as the percentage of built-up area within a 500 m buffer surrounding patches. Bird communities in most patches showed a trend toward functional and phylogenetic clustering. Functional clustering intensified with increasing isolation but weakened with higher woody plant richness, while phylogenetic clustering weakened as the proportion of croplands increased. The results suggest that landscape and habitat characteristics jointly explain the fragmentation effects on functional and phylogenetic diversity and structure of bird communities, with environmental filtering and niche differentiation-based competition likely acting as context-dependent underlying mechanisms. These findings highlight the importance of protecting and restoring large habitat patches with greater plant richness, expanding green spaces, allotment gardens, or corridors, and minimizing the density of built-up areas across the landscape to maintain functionally or phylogenetically diverse communities in urban environments.