Much of the world's species diversity is located in tropical and sub-tropical ecosystems, and a better understanding of the ecology of these systems is necessary to help stem biodiversity loss and assess community- and ecosystem-level responses to anthropogenic impacts. In this study, we will examine how the interaction between two species, the peacock bass and piranha, may render the peacock bass more susceptible to commercial net fishing. We hypothesize that piranha restrict peacock bass to near-shore habitats, an area where they can be readily exploited by netters. In large-scale (~ca. 500m2) experimental areas, we will examine if peacock bass move into shallower water in the presence of piranha than they otherwise would. Further, we will examine if the behavioral response of peacock bass has cascading effects on lower trophic levels, that is, composition of prey fish assemblages are different when peacock bass are restricted to shallow water. Experimental manipulations will be combined with landscape-scale surveys to examine the distribution of peacock bass, piranha, and the dominant prey of these species. These data will be incorporated with extensive stomach content and isotope analyses, to provide detailed information of food web structure in a species-rich tropical river. By describing human impacts within a food web context, we endeavor to provide predictive power regarding a specific environmental problem, yet still allowing for generality that will broaden the theoretical foundations and applications of food web ecology.
