Filtros ambientais, similaridade limitante e diversidade funcional de peixes Gymnotiformes em dois rios Amazônicos

Abstract

Using an approach that combines the species’ functional atributes with null models can help us better understand the distribution patterns and mechanisms that potentially affect the cooccurrence of species. If the ecological processes or "assembly rules" involved in the formation of species assemblages are dependent on spatial scale, it is expected that such mechanisms have different effects at local and regional scales. Understanding the relationship between ecological processes and the spatial scale at which they act is a challenge for ecologists. In this context, this study evaluated the relative importance of environmental filtering and limiting similarity as structural mechanisms of assemblages of electric fishes (Gymnotiformes) in two Amazonian river channels with different limnological characteristics and at different spatial scales. Through benthic seine collections in the Madeira and Trombetas rivers, we obtained information on the taxonomic diversity of these assemblages in addition to measuring environmental variables in each river (temperature, conductivity, depth, transparency, dissolved oxygen, turbidity and pH). All species were characterized functionally by ecomorphological analysis. Significant differences in functional identity (i.e. Community weighted mean; CWM) between the assemblages of the Madeira and Trombetas rivers indicate that environmental factors likely limit the occurrence of certain functional attributes on a regional scale. Moreover, when comparing observed patterns of functional diversity with null models at the local level (i.e. within each drainage), we noted that none of the two mechanisms of assembly is clearly predominant although there was some influence of similarity limiting on the assemblages of the Trombetas River. These results suggest that environmental filters should be more important for the distribution of Gymnotiformes species in Amazonian river channels at larger spatial scales, especially at the regional scale. They also, however, stress the importance of the dependent relationship between ecological processes and spatial scale. This study expands our knowledge of functional diversity patterns and assembly rules for fish assemblages in a relatively unknown system.