No abstract

Aim Floodplains are among the most biologically diverse systems in the world, where hydrological regime is recognized as crucial to structure aquatic communities. We predicted that i) structure of benthic metacommunity is nested in the drought and random in the flood season in a Neotropical floodplain. We expected to find ii) environmental homogenization during the flood season which may disrupt the nested pattern. Moreover, we identified habitats of high taxa richness of benthic invertebrates and characterized them by habitat type and fluvial systems. Methods We sampled benthic invertebrates from 36 habitats in the Upper Paraná River floodplain. We tested nestedness using NODF index and evaluated the environmental variability using the multivariate homogeneity of group dispersions (PERMDISP), separately for flood and drought periods. Results The environmental variability was lower during the flood. We found a nested distribution among benthic invertebrates in both flood and drought periods. The highest species richness values were recorded in small and unconnected lakes from Paraná fluvial system and some rivers and secondary channels, independent of the fluvial system. Chironomidae, Oligochaeta and Ostracoda were the most frequent taxa and were recorded in all habitats. Conclusion The nested distribution of benthic invertebrates is a consistent pattern for this metacommunity because its distribution was not disrupted by floods that homogenize limnological conditions and increase the connectivity among habitats. We also found that habitats with high taxa richness were both lotic and lentic in the three fluvial systems. Our findings emphasize that different habitats in different subsystems sustains the richness of the benthic invertebrates metacommunity in the Upper Paraná River floodplain over time.

Aim This study aimed to investigate the diet of seven species of fish that consume predominantly benthic macroinvertebrates, and the availability of these organisms in the environment. We analyzed the occurrence of trophic segregation between species and the correlation between the abundance of macroinvertebrates in the diet and in the environment. Methods Fish and macroinvertebrates were sampled in three streams of the Pirapó River basin (Upper Paraná River - Brazil). Differences in diet composition between species were tested using a multivariate permutation analysis of variance (PERMANOVA). A Spearman Correlation was performed to test the relation between the abundance the macroinvertebrates consumed and those available in the environment. Results All species mainly consumed aquatic insect, and significant interspecific variations in diet composition were found for most of them. For five out of the seven species of fish analyzed no significant correlation was detected between the abundance of macroinvertebrates in the environment and in the diet. Conclusions The results showed that most of the species segregate and their diets are not positively correlated with the abundance of preys in the environment, indicating that the most consumed macroinvertebrates were not the most abundant in the environment. These results suggest that the fish species select the macroinvertebrates, and that the morphological and behavioral characteristics of both predators and prey are important in feeding fish from streams.