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Ecologists have long relied on niche theory to describe the ecology of a species as a whole, by treating individuals as ecologically equivalent (Bolnick et al., 2003). However, the niche of a species can vary as a result of a variation in the population's niche width or a variation in the individual's niche breadth (Abbey-Lee, Gaiser,

Habitat complexity is recognized to mediate predator–prey relationships by offering refuge or not. We investigated the availability of planktonic microcrustaceans and the diet of a planktivorous fish (Hyphessobrycon eques) at different levels (low, intermediate and high) of aquatic macrophyte biomass. Sampling was carried out in a river with low flow speed, located in a Neotropical floodplain. We collected fish and microcrustaceans in macrophyte stands with variations in biomass. There were no differences in microcrustacean density in the water among the levels of macrophyte biomass, but microcrustacean richness and diet composition of H. eques differed. Microcrustacean richness and trophic niche breadth of the planktivorous fish were higher in high biomass stands. There was high consumption of a small cladoceran species in low macrophyte biomass, which was replaced by larger species, such as copepods, in intermediate and high biomass. Thus, the selection of some species was different among the biomass levels. These results suggest that plant biomass plays an important role in the interaction between fish and microcrustaceans, and prey characteristics such as size, escape ability and energy value make them more or less subject to predation by fish according to habitat structuring.

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the effects of sublethal SCA concentration on aquatic organisms. In this study, we evaluated the behaviour of a piscivorous (Hoplerythrinus unitaeniatus) and an invertivorous (Moenkhausia forestii) fish species, after a short-term (24 h) exposure to a sublethal concentration of SCA (0.8 g L −1 ). We hypothesized that the outcomes of predator-prey interaction would change when the players are subjected to sublethal SCA concentration. Our findings revealed that neither the behaviours of predator and prey fish species nor the outcome of their interactions was changed by the exposure to sublethal SCA concentrations, suggesting that their behavioural traits were not particularly sensitive to SCA. However, we emphasize that (i) other predatory and anti-predator behavioural traits could be affected by SCA even at under 0.8 g L −1 concentration and (ii) higher concentrations of SCA and/or long-term exposure may trigger profound changes in the behaviour of predator and prey fish species. Our findings are worrisome because there are new public policies to expand sugarcane production in Brazil, with the possibility of continuing burning sugarcane crops across the country. This will increase the input of SCA into aquatic systems, generating more prominent and pervasive negative impacts than those evaluated in this study.

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