Unraveling the impact of drought on waterbird community assembly and conservation strategies.

Drought-induced changes in lakes and wetlands, crucial habitats for migratory waterbirds, can greatly affect their foraging and habitat utilization. These changes lead to a decline in waterbird species richness and may cause shifts in community assembly from phylogenetic and functional trait perspectives. However, a gap remains between ecological mechanistic research about these changes and conservation applications. Here, we investigated the drought-induced phylogenetic and functional changes in waterbird community assembly over the past two decades in two lakes of the Yangtze River basin. Additionally, we explored conservation strategies to address the requirements of waterbirds during droughts. Results showed that drought modified the hydrological and phenological characteristics of waterbird habitats, leading to a decrease in waterbird species richness. As drought severity increased, species that were sensitive to drought exhibited higher degrees of similarity compared to the local species pool, leading to more divergent community assembly patterns. The mean values of body mass, tarsus length, bill length, and Evolutionary Distinctiveness (ED) of waterbirds in both lakes increased significantly under high drought stress conditions. Dabbling birds and small waders, which rely on habitats most susceptible to drought-induced changes, were the primary habitat preference groups affected. Additionally, the diversification of phylogenetic and functional community assembly in waterbirds and their associated conservation requirements indicated that effective conservation measures for waterbirds must be diversified and tailored to the specific requirements of different waterbird species, thereby preventing the loss of ecosystem functions and services. Conservation strategies should also be adaptive by incorporating periodic evaluations and adjustments to respond to environmental pressures and thus ensuring sustained effectiveness. In conclusion, as drought severity increased, functional and phylogenetic trait differences between species became more significant. Therefore, conservation measures must be diversified, tailored, and adaptive to effectively respond to the changes in waterbird community assembly.