Functionally redundant communities do not show differences in the main environmental drivers of different diversity metrics

We investigated which environmental variables of floodplain lakes act as potential drivers of fish assemblages and how they explain the variation in taxonomic and functional diversity of the community. We evaluated the taxonomic richness, functional dispersion (the distribution of species abundances with different traits) and redundancy (how similar the species are) of fish communities from six floodplain lakes of the upper Paraná River floodplain, evaluating whether they respond to the same set of predictor variables. We predict that the variation in taxonomic richness will be explained by limnological variables that express the characteristics of the water and the functional variation by variables that express the physical structure of the habitat. We sampled limnological and habitat structural variables and fish communities of each floodplain lake in a span of 14 years. Functional diversity was evaluated from six functional traits. The three diversity indices were used as response variables in Generalized Linear Mixed Models (GLMMs), while environmental variables were used as predictor variables. Taxonomic richness was best explained by total phosphorus, water transparency, depth and water level, while functional dispersion was explained by water level. Functional redundancy was explained by the water transparency variable. Our results show that taxonomic and functional diversity metrics may have environmental predictors in common, but the taxonomic richness is more predictable depending on the environmental gradient than the functional diversity. Besides, the floodplain lakes showed high functional redundancy. This may suggest that in functionally redundant communities, the main drivers of different diversity metrics do not differ.