Padrões de diversidade da comunidade de peixes ao longo de um gradiente longitudinal de um Rio Subtropical

Abstract

Understanding species distribution patterns and the influence of habitat structure on distribution patterns is extremely relevant for future management and conservation actions. The Uruguay River is subject to several disturbances, however, it presents a freeflowing segment of 950 km in its middle section, offering a mosaic of hydrogeomorphic patches, being an opportunity to understand the patterns of fish diversity in lotic corridors of the La Plata Basin. . In this sense, the present study aimed to investigate the role of environmental heterogeneity and spatial distance in the longitudinal patterns of species diversity and functional traits. A total of 48 field trips were carried out seasonally between the periods of May 2017 and February 2018 (Year 1) and May 2018 and February 2019 (Year 2), in six sampling sites, covering a stretch of 450 km of extension. The present study showed a total of 80 species for Year 1 and 76 species for Year 2 (gamma diversity). Local richness (alpha diversity) ranged from 46 to 71 species. The taxonomic and functional beta diversity for the two sampling periods showed high values, with contributions from turnover and nesting components. In this set of taxa, many presented small size and sedentary behavior, however, we also captured large and migratory fish, with the orders Characiformes, Siluriformes and Cichliformes being the most abundant. The high values of β-diversity observed revealed that each environment, with its set of hydrogeomorphological particularities, allows the structuring of unique assemblages in the main channel of the Uruguay River, clearly showing the importance of the irregularities of the channel mosaic for the ichthyofauna. The results obtained in this study emphasize the need to better understand the ichthyofauna of the river systems that are still preserved and the factors that drive the patterns of their diversity. This information will make it possible to predict the losses of diversity and help in the elaboration of more effective management and conservation plans, thus minimizing future anthropic disturbances.