Trophic Shifts in a Native Predator Following the Introduction of a Top Predator in a Tropical Lake

Some of the most dramatic and well-studied impacts of introduced predators involve their ecological effects on native prey communities. However, how native predators respond to introduced predators has received less attention. Here, we examined the potential impacts of an introduced predatory fish (Cichla monoculus, the peacock bass) on the diet and trophic ecology of a native predator (Hoplias microlepis) in Lake Gatun, Panama. We used stomach content analysis and stable isotope analysis to quantify the dietary niche of both species in sympatry, and of the native predator in the presence vs. absence of the peacock bass. We found that in the presence of the peacock bass, H. microlepis had a more diverse diet and a wider (five-fold) isotopic niche, relative to where it occurred alone. Specifically, H. microlepis, which were predominantly piscivorous in the absence of peacock bass, broadened their diet in the invaded Lake Gatun to include invertebrates and scavenged fish, the latter comprising 26% of its diet. Scavenged fish consisted of C. monoculus and Oreochromis niloticus (Nile tilapia) remains, both heavily harvested, non-native species in Lake Gatun, whose scraps are often thrown back into the lake by fishers. We suspect that these human-mediated food subsidies may lead to indirect facilitative interactions between introduced and native species in this system.