Not so Apex Predator: Food Web Dynamics in a Freshwater Stream Dominated by Mesopredators

Abstract We investigate the impact of apex predator absence on the food web structure and ecological balance of freshwater stream ecosystems at the Salto Morato Natural Reserve, Brazil. Despite the absence of fish due to a natural barrier, species richness in upstream pools was not significantly affected, suggesting ecological balance. Detailed food web analysis revealed that the upstream food web has a higher proportion of top predators, predominantly predatory insect larvae, and lower complexity metrics compared to the downstream web. Our findings challenge the traditional concept of mesopredator release and highlight the unique dynamics of predator-less ecosystems, emphasizing the need for tailored conservation strategies for such fragile environments.