DIVERSIDADE DE PEIXES DE RIACHOS EM ÁREAS DE CERRADO: COMPOSIÇÃO, ESTRUTURA E INTEGRIDADE DE HABITATS.

Abstract

As a natural system, rivers and streams are important for the conservation of biodiversity because they harbor a great diversity of species formed from spatial and temporal variations that include the environment, the species, the interactions between the species and the environment, besides the historical and geographical conditions. Understanding the causes of this variation is an important issue to understand how biodiversity is structured throughout space. In order to test the hypothesis that there are differences in the composition and structure of the ichthyofauna between watersheds, due to the differences in the internal habitat and due to changes in the supply of allochthonous materials, we use a regularly standardized sampling method to characterize the margins and the inner part of the streams in the watersheds of the rivers Alpercatas, Itapecuru, Munim and Preguiças between the years of 2012 and 2015. We used a similarity analysis (ANOSIM) to verify the existence of spatial differences in the composition and abundance of fish species between the basins. To compare abundance we use the rank of abundance. Diversity was compared through rarefaction curves. The patterns in the trophic composition between the watersheds were evaluated with the abundance data of the species for each trophic guild through a coordinate analysis (PCoA). The multicollinearity among predictor variables was calculated using the Spearman correlation. In order to analyze the effects of the predictor variables on the response variables (richness and abundance of species) in each basin, we used multiple linear regression and the generalized linear model. A total of 4,048 individuals belonging to seven orders, 27 families and 68 species were collected. The species composition among the basins was similar between Alpercatas and Itapecuru and between Munim and Preguiças. In the basins of Itapecuru, Alpercatas and Preguiças there was a predominance of omnivorous individuals, whereas in the Munim basin there was a predominance of herbivorous individuals. Regarding local factors, the richness and abundance of the species was influenced by the depth and width of the channel in the Alpercatas basin and by the temperature of the dissolved oxygen and water in the Itapecuru basin. The abundance of the species was influenced by the flow velocity and the water temperature in Munim. In the Preguiças basin, the depth of the canal was the most important variable for the richness and abundance of the species. To cover the soil, areas with cultivation presence presented lower richness and abundance of species in the Itapecuru basin. Whereas, in the Munim areas with pasture presence presented greater wealth and abundance of species. The results obtained in this work suggest that even if more drainage systems share a greater number of species, a certain portion of these species may be restricted to a river basin or may have difficulties in dispersing to other basins. On the other hand, some species seem to adapt well to the different conditions imposed by the environment, since changes in soil cover were reflected in the trophic composition of the species favoring the occurrence of omnivorous individuals. In addition, the effect of local factors (depth, channel width, water temperature, dissolved oxygen and soil cover) in each of the studied watersheds shows that the habitat structure plays an important role in structuring the fish community.