Ecologia trófica da ictiofauna e simpatria de espécies congenéricas no córrego da Lapa, bacia do Alto Paraná, estado de São Paulo, Brasil

Abstract

Streams and rivers are loctic environments characterized for a strong and unidirectional water flow. These environments in general have the light incidence partial or totally obstructed by the canopy of the riparian vegetation showing a high dependence of allocthonus organic inputs. The stream fishes are usually small sized, with reproductive strategies adapted to the unstable environment and have great trophic plasticity. The endemism is very common in this ictiofauna. The studies on trophic ecology and resources partitioning are important for the understanding of the community dynamics in the environment and the maintenance of the species. The Lapa Stream Watershed is located in the central region of the São Paulo State on area of basaltic cuesta relief. The surroundings of these streams are relatively well preserved and the main economic activities of the region are farming and ecotourism. This study was performed throughout four seasonal fish collections, carried out between April of 2002 and February of 2003 in the diurnal and nocturnal periods. Twelve collection stations were distributed in Lapa and Cantagalo Streams and in Passa Cinco River and sampling were made using cast nets, baited traps, sieves, and gill nets. The diet of 29 species were studied and it was found that insetivory was the main alimentary habit, followed by iliophagy - algivory and omnivory. The alimentary overlapping was high in several species pairs, but the habitat segregation occurred in some of them. The diet of three species altered along the upstream downstream gradient. The patterns of simpatry had been analyzed in three genera: Bryconamericus, Apareiodon and Astyanax and the food was the main resource partitioned among these species followed by the space resource. The results had shown that the micro basin is still well preserved, but that investments in the maintenance and recovery are necessary.