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Taxonomic and functional β-diversity patterns reveal random assembly rules in nearshore fish assemblages

Francisco Gerson Araújo*, Márcia Cristina Costa de Azevedo, Rafaela de Sousa Gomes-Gonçalves, Ana Paula Penha Guedes

*Corresponding author:

ABSTRACT: Evaluating β-diversity provides ecologists with a greater understanding of the processes that drive compositional variation of biological communities in ecosystems. The decomposition of taxonomic and functional β-diversity into their components of turnover (species replacement) and nestedness (species loss) was conducted for nearshore fish assemblages in four areas with different habitat characteristics in the southeastern Brazilian coast. We hypothesized that the environmental filtering process is occurring along a gradient of wave exposure, anthropogenic influences, sediment types and water physicochemical variables, inducing high taxonomic and functional β-diversity. Higher functional β-diversity compared to taxonomic β-diversity was found, which suggest that different species tend to play different functions indicating assemblages taxonomically and functionally distinct. Taxonomic and functional turnover presented similar values ​​and were both comparatively higher than nestedness, indicating the predominance of species replacement over species loss. β-diversity did not differ significantly from the null expectations of randomness, suggesting that there is no evidence of influences of environmental filtering in the assemblages. The high nestedness in the area where anthropogenic activities are more intense, suggests that only fish with the ability to tolerate harsh conditions can potentially settle there. We conclude that there is an environmental gradient that explains partially the differences in the components of functional β-diversity. However, species are functionally distinct and organized at random with no influences of environmental filtering because of the large unexplained part of the variation. This study helps to assess the impact of natural and human activities on the functional facets of biodiversity at the local scale.