From a metacommunity perspective, patterns of β‐diversity emerge from the interplay between spatial and environmental processes. For obligate aquatic dispersers, river network constraints can be reflected in diversity patterns. Here, we aimed to determine the effects of environmental heterogeneity and spatial connectivity on β‐diversity components. We sampled fish assemblages in 21 sites across a longitudinal gradient. Beta‐diversity for taxonomic and functional composition among sites was decomposed into its turnover and nestedness components. We investigated whether environment was more important to functional β‐diversity and spatial factors had a higher contribution to dissimilarity in species composition. Further, we tested whether environmentally homogeneous sites with higher spatial connectivity showed lower compositional changes. We found that spatial factors were more important for taxonomic β‐diversity, whereas environment explained functional dissimilarity among habitats. Although environment and spatial factors contribute to total β‐diversity, they explained different components: while environment explained a higher portion of turnover, spatial factors were related to nestedness. The effects of mere spatial isolation and directional connectivity differed for species and functional β‐diversity and for the components of β‐diversity. Including directionality in spatial connectivity enabled the explanation of a higher proportion of variation of total species β‐diversity and its turnover. Our results suggest that niche and spatial processes may influence differently taxonomic and functional β‐diversity components. Thus, habitat filtering was the primary mechanism affecting functional diversity and species turnover, whereas spatial connectivity drove species nestedness.

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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.

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An intensively debated issue in ecology is whether the variations in the biodiversity patterns of different biological groups are congruent in space and time. In addition, ecologists have recognized the necessity of accounting for both taxonomic and functional facets when analysing spatial and temporal congruence patterns. This study aimed to determine how the cross-taxon congruence of taxonomic and functional beta diversity varies across space and time, using data from four floodplains at a continental scale. Our general hypothesis was that the congruence between aquatic biological groups, either taxonomic or functional, would decrease with the “between-group” functional distance. Also, we examined how congruence patterns varied across spatial and temporal scales by focusing on how the cross-taxon relationships differ among Brazilian floodplains and between dry/wet periods. Our study comprised information on eight biological groups from the four largest Brazilian river-floodplain systems, and cross-taxon congruence was assessed using Procrustes analysis. Our results show how detailed analyses can reveal different patterns of cross-taxon congruence, and partially support the hypothesis that the strength of cross-taxon congruence is negatively related to between-group functional distance.

Our objective was to evaluate the effectiveness of protected areas (PAs) in the Paraná-Paraguay basin on multiple facets of ichthyofauna, both currently and in future climate change scenarios, based on reaching the 17% of conserved terrestrial and inland water defined by Aichi Target 11. Analyses were carried out vis-à-vis a distribution of 496 native species, modeling for the present and for the future, and in moderate and pessimistic scenarios of greenhouse gases. We calculated species richness, functional richness, and phylogenetic diversity, overlapping the combination of these facets with the PAs. The results indicate that the current PAs of the Paraná-Paraguay basin are not efficient in protecting the richest areas of ichthyofauna in their multiple facets. While there is a larger overlap between PAs and the richest areas in phylogenetic diversity, the values are too low (2.37%). Currently, the overlap between PAs and areas with larger species richness, functional richness, and phylogenetic diversity is only 1.48%. Although this value can increase for future projections, the values of the indices decrease substantially. The relevant aquatic environments, biological communities, and climate change should be considered as part of the systematic planning of PAs that take into consideration the terrestrial environments and their threats.