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.
