Influência da conectividade hidrológica na dieta de peixes de pequeno porte que habitam regiões litorâneas de lagoas.

Abstract

Habitat connectivity can promote changes in the availability of food resources to fish, because it interferes directly in dispersal rates of organisms, thus playing a key role in the distribution patterns of their prey. In this context, we used two fish species, one invertivorous (Moenkhausia bonita) and another algivorous (Serrapinnus notomelas), to test the following predictions: i) species diet differs significantly between isolated lakes, while in connected lakes food composition is more similar; ii) the trophic niche breadth of the species is smaller in isolated lakes. Fish were sampled in the dry season in lakes connected to the main channel of the Paraná River and isolated lakes distributed in the floodplain. To test the prediction i, we applied a Permutational Multivariate Analysis of Variance (PERMANOVA). For prediction ii, differences between connected and isolated lakes were tested using two measures of trophic niche breadth: the food items richness in the diet and the average centroid distance, from the permutation analysis of multivariate dispersions. Moenkhausia bonita consumed essentially insects in the connected lakes and most of the items were consumed by all populations. In isolated lakes, the species consumed microcrustaceans and insects. Most of the populations were dominated by one food item. Serrapinnus notomelas consumed filamentous algae and aquatic higher plant in both groups of lakes. In most diets there were dominance of different resources. Thus, the diet of both species differed significantly between all isolated populations, and in majority of the connected ones. The trophic niche breadth of the invertivorous species was significantly higher in the connected lakes, while the algivorous species showed no significant difference. The first prediction was partially supported, suggesting that in spite of the greater dispersion between the connected lakes, it is possible to increase the similarity of the diets, these lakes also have environmental heterogeneity, possibly associated to the differences in composition of aquatic macrophytes, which provide different food resources. The greatest trophic niche breadth for M. bonita in isolated lakes can be associated to dispersion that enable the great species richness, while in isolated lakes the environmental stability and restricted area lead to the dominance of certain taxa. However, the second prediction was not supported by S. notomelas, probably because its food resources (periphyton) are more influenced by macrophyte composition than by connectivity. Therefore, although connectivity promotes an increase in food items richness and similarity of diet, species selection is highly influenced by local environmental conditions and the feeding habit of each species.