Resource use by omnivorous fish: Effects of biotic and abiotic factors on key ecological aspects of individuals

Abstract

AbstractResource use by organisms is mainly influenced by factors such as the morphology of individuals and the diversity and abundance of resources. For omnivores, the influence of these factors is more complex, as they have a morphology adapted to access different trophic levels, and any change in the environment can affect the quality or availability of resources. The aim of this study was to evaluate the effect of biotic and abiotic factors on the use of resources by omnivorous fish. We analysed the diet of 107 individuals of Astyanax lineatus in headwater streams in the Pantanal plateau, Brazil. We analysed the influence of body size and the characteristics of streams on the dietary composition, proportion of allochthonous items, trophic niche width and trophic position of individuals. These alimentary parameters were mainly influenced by body size and environmental variables, such as stream vegetation cover, flow, dissolved oxygen and conductivity. Allochthonous resources were more important to the diet of our model fish. We observed that larger individuals are more specialists than medium‐sized individuals and the trophic position decreases with increasing body size. Basically, three factors may have contributed to these results: large supply of carbon‐rich resources; morphology adapted for the consumption of larger, harder and carbon‐rich foods; and the interaction of increased body size and the high temperatures in the Neotropical region that can increase the demand for carbon for energy production.