Estrutura, ocupação e competição na assembleia de peixes de riacho da Bacia do Alto Paraná

Abstract

Aquatic ecology has been extensively studied in some large basins due to the intense economic activity developed. However, certain ecological patterns have been underexplored. Understanding the influential factors of these patterns can reveal an initial picture of the ecological processes (both natural and anthropogenic) that are affecting species distribution. Thus, we aimed to identify the main factors determining the distribution patterns of fish in the Alto Paraná. Firstly, we evaluated the spatial effect at two different scales and the environmental effect on the fish assemblage, controlling for a potential effect of dams on species distribution. Secondly, we tested the effect of abundance, niche position, niche breadth, distribution position, distance to the nearest river, body size, origin (exotic and native), and commercial character (commercial and non-commercial) on the fish occupancy patterns. Thirdly, we assessed whether elevation, stream order, environmental heterogeneity, human disturbance, and exotic richness affected the competition patterns between native-exotic species. The results indicated that purely spatial factors at a broad scale explained more than the environment, while, in turn, the environment explained more than the purely spatial processes at a fine scale to the fish assemblage. Furthermore, we observed that abundance, body size, and origin (exotic and native) explained the species occupancy. Furthermore, stream order and exotic richness have affected the competition patterns between native and exotic species. Our results suggest that the isolation among sub basins may explain the strong influence of spatial factors on a broad scale in the fish assembly of the region. Additionally, our findings indicate that processes such as the rescue effect or source-sink dynamics may be structuring species occupancy. Finally, our results imply that the competition patterns between native and exotic species are environmentally structured.