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ABSTRACT Flow intermittency is expanding across river networks, transforming perennial streams into newly drying habitats and exposing macroinvertebrate communities to novel selective pressures. Understanding the mechanisms governing community reorganisation under these transitional conditions is essential for predicting ecological responses to climate‐driven drying. Using long‐term hydrological modelling combined with trait‐based analyses along a continuous intermittency gradient, we tested four mechanistic hypotheses addressing taxonomic filtering, trait–state‐specific responses, the role of cumulative trait–state advantages and dimension‐specific functional reorganisation between resistance and resilience dimensions. Richness declined while Simpson diversity increased with drying, indicating strong but selective environmental filtering (H1). Only specific drying‐related trait states increased in representation, revealing differential responses across resistance‐ and resilience‐related states (H2). The number of drying‐related trait states did not consistently enhance taxon performance; instead, intermediate and functionally coherent combinations were favoured (H3). Functional richness and redundancy exhibited asymmetric trajectories between the two survival dimensions, highlighting differences in how resistance‐ and resilience‐related strategies reorganise under increasing intermittency (H4). These findings demonstrate that emerging flow intermittency restructures communities through selective trait–state filtering and the dominance of optimal, rather than cumulative, survival strategies. The asymmetric functional trajectories between resistance and resilience dimensions reveal early‐stage functional vulnerability in newly drying systems, providing a mechanistic foundation for intermittency‐aware bioassessment tools under climate‐driven drying.