No abstract

Recent theoretical studies suggest that food webs are size-structured with top predators coupling different energy sources, but evidence for this hypothesis is still scarce, especially in highly diverse tropical rivers. Here, we explored the association between body size, trophic position, and the use of allochthonous and autochthonous basal production sources in the Volta Grande rapids of the Xingu River, a major clearwater tributary of the Amazon River, during the period prior to operation of the Belo Monte Hydropower Plant (BMHP). This section of the river contains a maze of channels with rocky shoals that support dozens of endemic fishes, mollusks and other aquatic taxa that may be impacted by flow regulation by the Pimental Dam located upstream. During the low-water season, we surveyed fish, crustaceans, mollusks, sponges, aquatic and terrestrial insects, zooplankton, and basal production sources to obtain tissue samples for analysis of stable isotope ratios of carbon (δ13C) and nitrogen (δ15N). Biomass of most aquatic organisms appears to be largely supported by riparian vegetation, highlighting the importance of the lateral connectivity between aquatic and terrestrial habitats. Unlike expected, we did not observe a gradual increase in coupling of energy pathways with increasing body size and trophic position. Findings provide a baseline for trophic ecology of this river under the natural flow regime for future impact assessments, and also indicated that more complex food web models, potentially including additional functional traits (e.g., gut length), are needed to describe resource and habitat use in highly diverse tropical ecosystems.

Recent theoretical studies suggest that food webs are size-structured with top predators coupling different energy sources, but evidence for this hypothesis is still scarce, especially in highly diverse tropical rivers. Here, we explored the association between body size, trophic position, and the use of allochthonous and autochthonous basal production sources in the Volta Grande rapids of the Xingu River, a major clearwater tributary of the Amazon River, during the period prior to operation of the Belo Monte Hydropower Plant (BMHP). This section of the river contains a maze of channels with rocky shoals that support dozens of endemic shes, mollusks and other aquatic taxa that may be impacted by ow regulation by the Pimental Dam located upstream. During the low-water season, we surveyed sh, crustaceans, mollusks, sponges, aquatic and terrestrial insects, zooplankton, and basal production sources to obtain tissue samples for analysis of stable isotope ratios of carbon (δ 13 C) and nitrogen (δ 15 N). Biomass of most aquatic organisms appears to be largely supported by riparian vegetation, highlighting the importance of the lateral connectivity between aquatic and terrestrial habitats. Unlike expected, we did not observe a gradual increase in coupling of energy pathways with increasing body size and trophic position. Findings provide a baseline for trophic ecology of this river under the natural ow regime for future impact assessments, and also indicated that more complex food web models, potentially including additional functional traits (e.g., gut length), are needed to describe resource and habitat use in highly diverse tropical ecosystems.

We report Pterygoplichthys pardalis introduction - a freshwater fish species from the Amazon river basin - in the Cauca river basin and in Salvajina and Calima dams, Colombia. Scope: We registered and taxonomically evaluated P. pardalis to verify its identification, seeking to avoid the elimination of native morphologically similar species. Methodology: Material deposited in some ichthyology collections was examined, evaluating 35 morphometric characters for identification following Armbruster’s keys. These results were compared with the available literature for Pterygoplichthys genus. Conclusions: This article reports some identification errors, mainly regarding Pterygoplichthys undecimalis, which actually correspond to P. pardalis. We also suggest two possible mechanisms that explain P. pardalis introduction into national basins: i) oversights during ornamental fish species trade and by their buyers, and ii) aquaculture projects that, seeking to “improve” regional economy, not take into consideration characteristics and suitability of the species they seek to promote. Finally, this article alerts about P. pardalis introduction in national basins and their possible effects on native species and ecosystems.