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Aim: Gradients of environmental heterogeneity perform a strong influence on the distribution of organisms and determine differences in composition, where more physically complex habitats harbor greater species richness than those simpler. We took as assumptions that differences in environmental requirements of taxa promote distinct distribution patterns which are carried through to community nestedness. Therefore, we hypothesized that more heterogeneous sites hold more nested, richer and abundant communities than those less heterogeneous ones. Methods We analyzed Chironomidae occurrence of 29 floodplain lakes, through one-year-surveys. Analyses of variance were performed to test differences among data. To test our hypothesis, we calculated correlations between the gradients of environmental heterogeneity and Chironomidae metacommunity. Results Highest values in all Chironomidae attributes were recorded in general to the floodplain lakes from Paraná System, mainly in September. Positive correlation between all Chironomidae attributes (i.e, richness, density, Biodiversity score and NODF index) both with PCA scores and variation coefficient values supported our initial hypothesis about the importance of environmental heterogeneity in metacommunity assembly. Conclusions We have demonstrated how differences in environmental heterogeneity promote the nestedness in floodplain lakes and the importance of more heterogeneous places in supporting richer and more abundant communities in species. Such results contribute to future studies on composition and richness of Chironomidae community in other kind of environments. Nested distribution suggests that, despite the existence of floodplain lakes including most of the Chironomidae richness, considering the dispersal ability of species and environmental requirements, there is a strong interaction between all environments of the area. Therefore, areas that have locations with different patterns of richness and composition are critical to maintaining the diversity of the group at the landscape level.

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.

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Habitat complexity may stabilize consumer–resource interactions and reduce the probability of invasion in aquatic habitats. We tested the hypotheses that (i) higher habitat complexity reduces resource consumption independently of grazer species, but that (ii) invasive grazers have a greater influence on decreasing resources independently of habitat complexity. We performed an experiment using artificial substrates to simulate different complexity levels. We evaluated Melanoides tuberculata (O.F. Müller, 1774) and Aylacostoma chloroticum Hylton Scott, 1954 consumption of specific algal groups and the interaction between habitat complexity and grazer species. Moreover, we evaluated grazer activity on the different substrates during the experiment. The results support only the first hypothesis and indicate lower resource consumption on complex substrates compared with simpler substrates. Additionally, the effect of the grazing of the invasive species on taxon richness was greater in simplified than in complex habitats. The grazing activity on the substrate suggests a relationship between resource exploitation and habitat complexity in which the invasive grazing species visited the simple habitat less frequently. However, the effects of invasive grazers on food resources were higher on the simple substrate. The effects of grazing activity on food resources depend on the interaction between habitat complexity and grazer species. In this way, the introduction of an invasive species may have negative impacts on the structure and function of periphytic communities, mainly in simplified aquatic ecosystems.