Environmental heterogeneity explains species turnover but not nestedness in upper Paraná River fish assemblages.

Oscar Peláez, Filipe Manoel Azevedo, Carla Simone Pavanelli


Aim: the stretch between Porto Primavera Reservoir and the transition zone of the Itaipu Reservoir still remains without impoundments and conserve some of its natural conditions. Due to the importance of that region for protection of aquatic communities in the upper Paraná River basin we aimed to answer two questions: 1) whether tributaries and main channel of the Paraná River contribute differently to fish diversity, and 2) whether dissimilarity in species composition is explained by environmental gradients. Methods: 22 sites were sampled between 2013 and 2015. Hill numbers were used to compute the effective diversity expected for tributaries and Paraná River proper. Then, Non-metric Multidimensional Scaling analysis and partition of beta diversity were used to describe variation in species composition among sites. To examine the relationships between species composition variation and environmental variables we used distance-based linear models. Results: 74 species were captured, 32% of these species are non-native for the upper Paraná River basin. Some of these species were restricted to different habitats contributing to variation in species composition. Hill numbers showed a trend for tributaries have a higher diversity than Paraná River sites. Dissimilarity in species composition was driven mainly by species turnover. Total beta diversity and species turnover were related to environmental variables (conductivity and turbidity), while beta diversity due to changes in species richness had not relation with environment. Conclusions: species diversity and composition of fish assemblages in the upper Paraná River can be related to environmental gradients. Overall, our results suggested that Paraná River tributaries contribute for environmental heterogeneity, therefore to maintain a high diversity and variation in species composition. For that reason, we strongly recommend preserving highly heterogeneous habitats in the region.


species diversity; Hill numbers; beta diversity; environmental gradient; dbRDA

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