Responses of Fish Trophic Guilds to Dams in Neotropical River Systems: A Systematic Meta-Analytic Review

Abstract

In Neotropical river systems, dams promote profound physical and biological changes by disrupting longitudinal connectivity, altering flow regimes, and modifying nutrient and energy pathways. These transformations have the potential to reshape the trophic organization of fish assemblages. Here, we conducted a systematic review and multilevel meta-analysis to evaluate the effects of river impoundment on species richness within trophic guilds across upstream (control), reservoir, and downstream (intervention) river stretches. Following the PRISMA guidelines, we screened 2428 records from four scientific databases and grey literature, of which 26 studies met the eligibility criteria for quantitative synthesis. Overall, no consistent differences in trophic guild richness were detected between upstream reference stretches and reservoir or downstream stretches. However, meta-regression analyses showed that latitude explained variation in trophic guild richness within reservoir stretches, whereas reservoir area was the only significant predictor in downstream stretches. Although significant residual heterogeneity remained, these results indicate that trophic responses to river impoundment are strongly context dependent and influenced by environmental conditions operating at different spatial scales. Overall, our findings indicate that river impoundment does not consistently alter trophic guild richness across Neotropical river systems but instead promotes context-dependent ecological responses, providing new insights into the functional organization of fish assemblages and supporting conservation and management strategies for dammed rivers.