Deterministic niche dynamics drive zooplankton community assembly in megacity river networks: biotic interactions outweigh environmental filtering in winter

Zooplankton play pivotal roles in aquatic ecosystems, yet the mechanisms by which species interactions shape their community structure remain poorly understood, particularly in urbanized river networks. Here, we investigated the assembly processes of zooplankton communities across 44 sites in Shanghai’s megacity river network during winter. Using canonical correspondence analysis (CCA) and variance partitioning analysis (VPA), we identified water temperature (WT), Secchi depth (SD), and pH as significant environmental drivers, albeit with limited explanatory power (11.10%). Neutral community model (NCM) analysis revealed that deterministic niche processes dominated community assembly, emphasizing the critical role of biotic interactions. Co-occurrence network analysis further identified 29 keystone species, predominantly generalist rotifers (58.62%), which exhibited broad niche breadth and strong competitive traits (e.g. pollution resistance and omnivory). High modularity (0.55) and interspecific competition (18.67% niche overlap > 0.5) indicated structural instability within the community. These findings highlight the interplay of environmental filtering and species interactions in shaping urban zooplankton communities, offering insights for biodiversity conservation and ecological monitoring in anthropogenically impacted aquatic systems.