Drivers of fish trophic guild composition in lakes of the Upper Paraná River floodplain

In freshwater ecosystems, flood pulses, the degree of connectivity between environments, and the vegetation mosaic are among the main variables affecting environmental structure at the landscape scale. At a finer scale, local limnological conditions seem to be more important for structuring river fish assemblages. However, rather than exerting isolated effects, these limnological characteristics can have combined impacts on the environment. We evaluated the main drivers of the spatial structuring of fish trophic guilds in the littoral zone of lakes in the Upper Paraná River floodplain (UPRF) and determined the relative importance of limnological conditions, spatial distance, and riparian vegetation. We sampled fish and limnological variables in June, September, and December of 2011, and classified the fish species into trophic guilds. We used variation partitioning analysis to assess the influence of the three sets of predictors and distance-based redundancy analysis to visualize the position of samples, as described by the composition of trophic guilds in multivariate space. The distribution of trophic guilds was mainly influenced by limnological variables, i.e., conductivity, chlorophyll a, and pH, in periods of low water. Spatial and riparian vegetation predictors, despite being low, also influenced the distribution because limnological variables and riparian vegetation of the UPRF have a well-defined spatial structure due to differences between rivers. The lakes with Class III riparian vegetation (dominated by tree species) supported most of the trophic guilds, including insectivores. This indicates that allochthonous materials, even when they occur in smaller proportions, contribute to the structuring of fish communities in periods of low water.