Flow intermittence shapes fish metacommunity variability in a Neotropical ecoregion

Drying River Networks (DRNs) comprise intermittent reaches that cease to flow or dry, and these networks are becoming more prevalent with ongoing climate change. However, their distribution, constituent species, and ecological processes remain underexplored in the Neotropics, limiting our ability to predict future scenarios for freshwater biodiversity. Drying is a strong environmental filter, leading to low α-diversity at intermittent reaches as taxa lacking adaptations to resist and recover from drying are lost. Additionally, because drying creates a complex mosaic of lotic and lentic habitats that change through time, β-diversity (variability in community composition) is high in intermittent reaches. To explore these dynamics, we analyzed the influence of local and regional factors on the spatio-temporal variability of a fish metacommunity in the Chocó Biodiversity hotspot in Northwestern Ecuador. Fish α-diversity was lower in intermittent reaches during both seasons, while temporal β-diversity was higher at perennial reaches. Distinct fish assemblages were indicative of intermittent and perennial reaches, with community composition being stable in intermittent reaches but more variable in perennial reaches. Lastly, metacommunity analysis suggests that environmental filtering was the primary community assembly process, with species being replaced along the environmental gradient of the river network. Physical distance was important in structuring communities but only for fish species with low dispersal abilities, indicating that for these species, dynamics may be controlled by hydrological connectivity. Our findings suggest that variability in fish communities results from seasonal intermittence and species-specific habitat preference, partially confirming previous hypotheses regarding the determinants of fish diversity in DRNs.