Conserving waterbird diversity in fragmented agricultural wetlands: The roles of habitat heterogeneity and positive species associations in community persistence

Agricultural expansion has caused rapid wetland loss globally, yet small isolated lakes within farmland remain critical but undervalued habitats for migratory waterbirds. Understanding how communities assemble in these fragmented systems is essential for developing evidence-based conservation strategies and advancing ecological theory. We surveyed waterbirds across 18 isolated lakes in the Dongting Lake basin (2022–2025) and applied hierarchical modeling of species communities (HMSC) to disentangle environmental, trait-based, phylogenetic, and biotic drivers of assembly. Habitat heterogeneity strongly influenced community structure, with open-water extent, disturbance distance, and vegetation area as key predictors. Species responses varied, but a strong phylogenetic signal indicated niche conservatism. Positive residual associations dominated (82% of significant species pairs), a pattern more consistent with shared responses to unmeasured environmental gradients or migratory co-aggregation than with direct facilitation. Predictive accuracy differed among functional guilds, with herbivores more predictable than carnivores, reflecting differences in resource stability. These findings show that small but structurally complex wetlands embedded in agricultural matrices can retain substantial conservation value, indicating that habitat structural complexity at the patch scale partially mitigates the ecological consequences of wetland fragmentation. Integrating traits, phylogeny, and species associations within joint models offers a powerful framework for understanding community assembly and guiding wetland conservation globally.