("Eating from the same plate": trophic niche overlap of two fish species from streams in the upper Tocantins river basin

Abstract

Phylogenetically close species use similar resources and can be potential competitors. However, in order to minimize interspecific competition, species may present strategies for sharing resources in space (among different habitats), in food consumption and in time (differences in the activity period). These differences can be decisive for the coexistence of species. In this work, we describe the diet and investigate the trophic niche overlap of two stream fish species in two hydrological periods in the upper Tocantins River basin. We describe species diets from stomach content analysis and determine feeding preferences with the Alimentary Importance Index (IAi) for both species. Knodus aff. chapadae and Hyphessobrycon heterorhabdus preferred to consume terrestrial and aquatic invertebrates during the two hydrological periods, although they consumed other types of food with plant or animal origin. Both species have a high trophic niche overlap, so they potentially compete for food. These results show that the coexistence between these small characids is mediated by divergence in other niche dimensions and not by differences in their diets. For these two species have a similar morphology and are phylogenetically close, it is possible that there is certain space-time segregation between these species, allowing for their coexistence. Over time, coexistence between these two species can be maintained by divergence in resource use. Alternatively, competitive exclusion may drive one species to local extinction.