Environmental heterogeneity drives the distribution of copepods (Crustacea: Copepoda) in the Amazon, Araguaia, Pantanal, and Upper Paraná floodplains.

Environmental heterogeneity influences the physiology and behavior of organisms, leading to alterations in populations, communities, and ecosystems. This study was designed to evaluate the effect of the spatial and temporal limnological heterogeneity on the distribution of copepods in the Amazon River floodplain, Araguaia River floodplain, Pantanal floodplain, and Upper Paraná River floodplain. We performed dispersion homogeneity tests (PERMIDISP) to analyze the limnological heterogeneity, a Generalized Linear Mixed Model (GLMM) to test the relationship between limnological heterogeneity and species distribution, and a Canonical Correspondence Analysis (CCA) to analyze which limnological variables explain the variation in the community composition. In our study, we observed higher environmental heterogeneity during dry periods, especially in the Amazon floodplain. The Amazon showed the highest species richness (the total number of species that occurred in each floodplain), with endemic species, also the highest abundance of individuals, especially during dry periods, which was possibly due to the biogeography, the size of the basin, and the heterogeneity of the environments. The Pantanal presented the second highest species richness and showed the highest species richness and abundance of individuals during rainy periods. The distribution of copepods was highly correlated with environmental heterogeneity. The species were mainly related to temperature, nutrients, and depth.

Predation by an omnivorous fish and food availability alter zooplankton functional diversity: a microcosm approach.

Studies considering the functional traits of organisms, populations, and communities functional indices increase the understanding of many factors on ecosystem functioning. Here, we analyze the predation effect (by fish) on zooplankton functional diversity and the effects of biomass and density of periphytic algae on zooplankton feeding type trait and body size. We expect that intense predation by fish on zooplankton leads to higher values of zooplankton functional diversity and that food resource will be positively related to the abundance of zooplankton trait and body size. For that, microcosms were established (T1- fish-absence, and T2- fish-presence, both with periphytic algae as food). We observed that fish presence decreased zooplankton functional diversity through modifications in the availability of nutrients and algae, through the middle-out effect. We also observed that body size had a negative relationship with the food resource, reaffirming that high food availability in subtropical lakes is linked to small-bodied zooplankton. The raptorial copepods covariate positively with the periphytic algae, which was an alternative food resource and, in this case, the main form of carbon input into the system. In this study, omnivorous fish reduced zooplankton functional traits, which can alter the energy stock and energy flow in aquatic ecosystems.