Seasonal Dynamics of Benthic Macroinvertebrate Community Assembly in a Subtropical Monsoon-Driven Mountain Stream

Seasonal variation in community assembly influences biodiversity patterns, yet its dynamics under monsoon-driven hydrology remain underexplored in subtropical mountain streams. We applied the Elements of Metacommunity Structure (EMS) framework and variation partitioning to assess seasonal shifts in benthic macroinvertebrate communities across dry, normal, and wet phases in a subtropical monsoon-driven mountain stream. Assembly patterns transitioned from Quasi-Clementsian (dry season) to Clementsian (normal flow) and Nested structure (wet season). Deterministic environmental filtering-mediated by water temperature, dissolved oxygen, conductivity, water depth, and flow velocity-dominated during dry and intermediate phases. Conversely, stochastic dispersal (mass effects) prevailed during high-flow monsoon periods, driven by enhanced connectivity. By quantifying the hierarchical balance between deterministic and stochastic drivers, our study advances understanding of how hydrological seasonality structures metacommunities. These findings underscore the importance of integrating intra-annual hydrological variability into stream biodiversity assessments and management frameworks.