Adapt or perish? Flexible habitat selection by an endangered and dispersal-limited fish under variable flow conditions and invasive crayfish competition

Abstract Mediterranean freshwaters are renowned for their high level of fish endemism, but at least 250 species are threatened with extinction due to climate change, biological invasions, habitat loss and fragmentation. Our research focuses on the behavioural plasticity of dispersal-limited fish as a mechanism to cope with human-driven environmental changes, using an endemic and endangered benthic species as a model, the Southern Iberian spined-loach Cobitis paludica . We collected a seven-year dataset on microhabitat selection in a regulated river invaded by the exotic red swamp crayfish Procambarus clarkii and investigated habitat selection patterns under fluctuating flow scenarios and crayfish presence, using a combination of univariate (Kruskal–Wallis test) and multivariate (GAM) analyses. Our findings showed that C. paludica changed habitat selection patterns across years with differing flow conditions. The species selected deeper habitats with embedded, coarser substrates and presence of aquatic vegetation under low-flow conditions but showed higher preference for finer substrates with little embeddedness when flow increased. This behavioural flexibility may serve as a buffering mechanism against the increasing environmental degradation; however, our results also showed that C. paludica avoided positions with crayfish presence, indicating that P. clarkii may be displacing the spined-loach to suboptimal microhabitats, potentially through competitive exclusion.