Niche partitioning and seasonality may mediate coexistence of piranha species in Amazonian floodplain lakes

Unraveling factors that enable the coexistence of species occupying similar niches is a challenge in Ecology. In the Amazon basin, several piranha species (Serrasalmidae) co-occur in floodplain lakes, providing a model to understand how similar species manage coexisting. We employed a combination of classic and molecular stomach contents analysis, and stable isotope analysis to evaluate the use of resources and isotopic niche breadth among three co-occurring piranha species (Serrasalmus altispinis, S. maculatus, and Pygocentrus nattereri), and the influence of the hydrological cycle (low vs. high water) in resources partitioning. A higher diversity of prey and lower isotopic niches was found during low water, likely due to prey concentration. Cannibalism occurred in all three species, and although piscivores, these species feed on different trophic levels, with P. nattereri consuming omnivores, S. maculatus detritivores, and S. altispinis herbivores. Coexistence was mediated by changes in resource availability associated with the hydrologic cycle. Trophic niche overlap was higher during the high water compared to low waters due to high prey availability when lakes connect to river channels and floodplain forests. Here, we identified strategies used by piranhas to avoid competition under different environmental conditions. Understanding species interactions is fundamental to managing biodiversity conservation in a changing world.