Environmental heterogeneity explains species turnover but not nestedness in fish assemblages of a Neotropical basin

Oscar Eduardo Peláez,Carla Simone Pavanelli,Filipe Manoel Azevedo

doi:10.1590/s2179-975x8616

Oscar Eduardo Peláez, Carla Simone Pavanelli + Show 1 more

Open Access

https://doi.org/10.1590/s2179-975x8616

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Abstract

Abstract Aim: Heterogenous environments can contribute to maintain biodiversity. Traditionally beta diversity studies have focused on determining the effect of environmental variables on the total dissimilarity of species composition. However, decomposing beta diversity in species replacement and nestedness could give new insights on mechanisms affecting spatial patterns of biodiversity. We aimed to answer two main questions about spatial patterns of fish diversity in a Neotropical basin: 1) whether some regions contribute differently to fish diversity, and 2) whether species turnover and nestedness are explained by environmental gradients. Methods Sampling sites in the main channel and tributaries of the Upper Paraná River were sampled between 2013 and 2015. We partitioned beta diversity and tested the relationship of turnover and nestedness with environmental variables. Results 74 species were captured. Some of these species were restricted to different sites, contributing to variation in species composition. Hill numbers showed a trend for higher diversity in the tributaries than in Paraná River sampling sites, and the partition of beta diversity revealed that species replacement drove dissimilarity in species composition. Only total beta diversity and turnover were related to environmental variables, mainly conductivity and turbidity. Conclusions Species diversity and composition of fish assemblages in the Upper Paraná River could be related to environmental gradients. Overall, our results suggest that Paraná River tributaries contribute to increase environmental heterogeneity, and hence to maintain a high diversity and variation in species composition. For that reason, we strongly recommend preserving highly heterogeneous habitats in the region.

Highlights

Beta diversity is defined as the variation in the identities of species among sites (Heino et al, 2015)
Hill numbers showed a trend for higher diversity in the tributaries than in Paraná River sampling sites, and the partition of beta diversity revealed that species replacement drove dissimilarity in species composition
Our results suggest that Paraná River tributaries contribute to increase environmental heterogeneity, and to maintain a high diversity and variation in species composition

Summary

Introduction

Beta diversity is defined as the variation in the identities of species among sites (Heino et al, 2015). Over the past decade the variation in species composition was recognized as being a result of species replacement (turnover), and of the contribution of differences in species richness among sites (nestedness). It was proposed that measures of beta diversity based on dissimilarity could be partitioned to account for these two components of variation in species composition: dissimilarity among sites derived from species replacement and dissimilarity derived from nestedness (Baselga, 2010). The relationship between beta diversity and environmental heterogeneity depends on the spatial scale and dispersal rates. A stronger environmental control on species composition is expected at intermediate spatial scales, where dispersal is neither too high to mask the effects of environmental variables (Heino et al, 2015) nor too low for the differences in species composition to be related to historical processes (e.g. Villéger et al, 2013). A high nestedness could show that sites with high species richness should be a priority for conservation (Gianuca et al, 2017)

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