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Received: 17 Feb. 2017; Accepted: 16 May 2017
ABSTRACT
The physical structures of streams are subjected to intense changes throughout the seasons. Intense drought in dry periods has been frequent and potentially harmful to aquatic species. In this study, we tested whether the changes in the habitat structure of the streams during the dry period determine the organization of fish communities. Five streams in the Upper Tocantins River were studied in the dry and rainy seasons. The species were characterized by 13 functional traits based on morphological measurements. The descriptors of functional diversity were: mean pairwise functional distance of species in the community (MPD) and mean functionally nearest species distance (MNTD). We also calculated the standardized effect size for MPD and MNTD, an indicator of functional redundancy, and compared the observed patterns with those expected by chance. Streams differed between seasons with respect to environmental variables. Functional diversity in the rainy season did not differ from the pattern expected by chance for both metrics. While functional diversity in the dry season has not differed from the pattern expected by chance for SESmpd, a greater functional redundancy for SESmntd was found in this season. These results indicate that environmental changes in the streams during the dry season are important constraints for fish occurrence, preventing the occurrence of functionally original species. Therefore, a prospective scenario of dry-period intensification could result in functionally redundant communities, with functional homogenization of the regional species pool.
Keywords: ecomorphology, functional diversity, niche filtering.
RESUMO
Os riachos são submetidos a intensas mudanças na sua estrutura física ao longo das estaçães. Secas intensas nos periodos de estiagem tem sido frequentes e potencialmente deletérias para as espécies aquáticas. Neste estudo, testamos se as alteraçães na estrutura do hábitat dos riachos no periodo da seca determinam a organização das comunidades de peixes. Foram estudados cinco riachos pertencentes à bacia do Alto rio Tocantins, amostrados no período seco e chuvoso. As espécies foram caracterizadas por meio de 13 atributos funcionáis baseados em medidas morfológicas. Os descritores de estrutura funcional das comunidades foram: distãncia média entre pares de espécies da comunidade (MPD) e distãncia média da espécie funcionalmente mais similar na comunidade (MNTD). Também calculamos o tamanho do efeito padronizado para MPD e MNTD, uma medida de...