Scale Invariant Patterns of Life History Strategies of Riverine Mussels Are Shaped by Hydrological Factors

ABSTRACT Understanding how ecological patterns and processes scale across space is essential for predicting biodiversity structure, particularly in riverine systems where hierarchical networks and directional flow generate nested environmental gradients that influence community assembly. We examined how flow regime structures freshwater mussel life history strategies—opportunistic, periodic and equilibrium—across nested spatial scales in the Colorado River basin, Texas, USA, a system spanning strong hydrological and climatic gradients and supporting diverse but imperilled mussel assemblages. Using abundance data from 480 sites paired with long‐term hydrological records, we explicitly tested whether hydrological drivers of life history composition were consistent among sub‐basins, tributaries and mainstems. Three dominant hydrological gradients structured mussel assemblages across spatial scales: flow variability (e.g., annual discharge coefficient of variation), flow stability (e.g., sustained summer flows and high‐pulse duration) and low‐flow disturbance (zero‐flow days). Equilibrium (i.e., longer lived, slower growing) species were consistently associated with stable hydrological regimes, whereas opportunistic (i.e., shorter lived, faster growing) species were most strongly linked to low‐flow disturbance and periodic species (somewhat intermediate traits) increased in abundance with greater flow variability. Together, these patterns reveal a scale‐invariant, hydrology‐driven filtering process in which similar components of the flow regime structure life history composition across nested spatial scales. We present a conceptual model linking spatial position, flow regime and life history composition, illustrating how hydrological gradients determine the dominance of different life history strategies. This framework integrates trait‐based theory with hydrological scaling. More broadly, this framework highlights the value of trait‐based approaches for revealing general ecological rules that transcend taxon and ecosystem type, offering a transferable foundation for forecasting biodiversity change and ecosystem function in the Anthropocene.