Spatial and temporal variation in stream fish assemblages of Guiraí River Basin, Upper Paraná Basin

Abstract

This paper aims to characterize the fish assemblages and to quantify the importance of spatial and temporal variations on the organization of stream fish assemblages of Guiraí River Basin, Upper Paraná River Basin. The samples were taken every two months in seven streams, from October 2006 to August 2007. To examine these data, we used analysis such as cluster, similarity, variance, canonical correspondence and regression tree. We collected 64 species and the spatial variations of the assemblages were more evident than the temporal ones. The most important variables in determining the occurrence of the species were altitude of the region, stream width and depth and water velocity. This result indicates there is an interaction of regional factors (altitude) with local ones (depth, velocity and width) to define the species composition of each stream. The turnover in species composition was significantly influenced by stream depth and altitude. The differentiation on richness and species composition between upper and lower sites should allow richness increment at regional level (hydrographic basin), decreasing the niches overlap and maintenance of sub-populations (for wide-distributed species) which should to resist more to the antropic action over the habitat structure.