Seasonal assembly mechanisms of wintering waterbird communities in isolated lakes within an intensive agricultural landscape

Understanding how community assembly vary across seasons is critical for wetland biodiversity conservation, especially in fragmented, human-dominated landscapes. Yet, most studies overlook fine-scale seasonal dynamics that influence species distribution. Here, we examined wintering waterbirds across 18 isolated lakes embedded in intensively managed agricultural landscape of the Dongting Lake Basin, a key node along the East Asia–Australasian Flyway. Using monthly surveys spanning two consecutive winters (November 2023–March 2025) and a multidimensional β -diversity framework encompassing taxonomic, functional, phylogenetic dimensions, combined with null model analyses, we revealed pronounced stage-specific shifts in assembly mechanisms. Taxonomic and phylogenetic diversity patterns were consistently shaped by stochastic dispersal and neutral processes throughout the wintering season. In contrast, functional diversity exhibited marked seasonal dynamics: deterministic assembly processes, particularly niche differentiation, peaked in mid-winter (December–January), likely driven by intensified interspecific competition associated with seasonal resource decline. Functional β -diversity was dominated by nestedness, indicating selective loss of functional traits in disturbed lakes, with spatial distance–decay relationships in functional structure emerging only during this mid-winter period. These findings highlight how seasonal resource dynamics and habitat isolation interact to restructure waterbird communities at multiple ecological scales. Based on these findings, we recommend implementing seasonal protection measures during mid-to-late winter when functional diversity peaks and subsequently declines, enhancing habitat connectivity to facilitate dispersal among isolated lakes, and incorporating functional diversity metrics into wetland monitoring programs to detect early signs of functional homogenization.