Diet, Trophic Plasticity and Niche Dynamics of Four Barbel Species Across Elevational and Seasonal Gradients in a Mediterranean Stream

Conservation and effective management of freshwater ecosystems require detailed insights into species-specific dietary strategies, resource partitioning and ecological interactions, including competition for shared resources. This study investigates seasonal dietary shifts within four barbel species (Atlantor reinii, Luciobarbus magniatlantis, Luciobarbus ksibi and Carasobarbus fritschii) in the Zat Basin (Morocco). The study's objective is to inform conservation and ecosystem management planning that should be considered for threatened species, such as A. reinii and L. magniatlantis. We evaluated feeding strategies and niche partitioning across species and seasons using stomach content analysis and alimentary indices, including Dietary Index (DI) and occurrence (OC). L. ksibi demonstrated the highest insect consumption (OC = 51.11%, DI = 0.84%). L. magniatlantis showed the most diverse animal prey composition, with the highest Mollusca occurrence (OC = 76.67%, DI = 0.59%), substantial insect intake (OC = 54.07%, DI = 1.43%) and significant Arachnida presence (OC = 60%, DI = 0.54%). A. reinii displayed the highest selectivity for insects (DI = 1.14%). C. fritschii exhibited moderate insect consumption (OC = 36.30%, DI = 0.88%) and an equal preference for Mollusca and Tubellaria (both OC = 53.33%, DI = 0.38% and 0.64%, respectively). NMDS analyses revealed partial dietary overlap among species, with A. reinii and C. fritschii exhibiting distinct clustering, while L. ksibi and L. magniatlantis displayed broader nutritional niches. Moderate-to-high dietary niche overlap, particularly between C. fritschii and L. ksibi, highlights the potential for significant competition for shared prey resources, which may intensify during periods of resource scarcity. This study highlights species-specific dietary flexibility, emphasising the importance of adaptive foraging strategies in conservation planning and the ecological resilience of freshwater fish in Mediterranean streams.