Influence of the riparian zone phytophysiognomies on the longitudinal distribution of fishes: evidence from a Brazilian savanna stream

The structure and composition of a fish community in a tributary stream of the Aquidauana River, located in the plateau region of the Paraguay River basin, central west Brazil are described, with special attention to the differential effects of the phytophysiognomies of the Cerrado (a tropical savanna), which are predominant in riparian zones all along their longitudinal gradient. A total of 1,166 individuals belonging to 44 species were captured. Similarity analyses of composition and abundance showed two groups: upstream reaches (R1 and R2) and downstream reaches (R3, R4 and R5), which presented 85.8% of the average dissimilarity. Although physical habitat and physicochemical descriptors varied along the longitudinal gradient of the Correntes stream, shoreline vegetation was the most important environmental feature predicting fish structure and composition. The Mantel test revealed a correlation between shoreline vegetation structure and fish composition and quantitative structure of the fish community (R > 0.65; p < 0.04). This relationship is driven by the prevalence of species occupying microhabitats associated with shoreline vegetation in contact with water in upstream reaches. Structural differences in shoreline vegetation along the longitudinal gradient correspond to the phytophysiognomic dichotomy observed in the Correntes stream, where riparian vegetation is made up of wet grassland upstream and of gallery forest downstream; this reinforces the importance of the phytophysiognomic heterogeneity of the Cerrado in maintaining ichthyofauna diversity.