Abstract
Abstract The aim of this study was to determine the food webs structure of a large Patagonian river in two river sections (Upstream and Midstream) and to evaluate isotopic overlap between native and introduced species. We used stable isotope analyses of δ15N and δ13C and stomach content. The Upstream section had a more complex food webs structure with a greater richness of macroinvertebrates and fish species than Midstream. Upstream basal resources were dominated by filamentous algae. Lake Trout were found to have a higher trophic position than all other fish species in that area although, the most abundant fish species, were Rainbow Trout. Depending on the life stage, Rainbow Trout shifted from prey to competitor/predator. In the Midstream section, the base of the food webs was dominated by coarse particulate organic matter, and adult Rainbow Trout had the highest trophic level. Isotopic values changed among macroinvertebrates and fish for both areas. The two most abundant native and invasive species — Puyen and Rainbow Trout — showed an isotopic separation in Midstream but did not in Upstream areas. The presence of invasive fish that occupy top trophic levels can have a significant impact on native fish populations that have great ecological importance in the region.
Highlights
Species invasion and habitat degradation represent major threats to biodiversity (Vitousek, 1990; Clavero, García-Berthou, 2005; Gallardo et al, 2016)
Debris was constituted by dead macrophytes and Coiron sp. grasses. Both macrophytes and benthic visual algae cover were very low along the two sections (< 1.5-3% and < 4-5%, respectively), with algae patches being in the Upstream section and macrophytes in the Midstream section
The present research is the first study of food webs in the Santa Cruz River, a river that is about to change due to damming without information regarding the trophic structure and with poor information about the influence of introduced species on aquatic food webs
Summary
Species invasion and habitat degradation represent major threats to biodiversity (Vitousek, 1990; Clavero, García-Berthou, 2005; Gallardo et al, 2016). Fish can have an important effect at the individual, population, community, and ecosystem level (Simon, Townsend, 2003; Tagliaferro et al, 2014a; Buoro et al, 2016). Changes in the ecological structure of communities by introducing species can directly modify the flow of energy and matter in the ecosystem (de Ruiter et al, 1995; Chapin III et al, 2000) or indirectly modify abundance or species traits (Power et al, 1996; Milardi et al, 2016). A reduction in native top predators could generate an increase in prey populations and deplete basal resources, generating a cascade of ecological effects (Chapin III et al, 2000; Shelton et al, 2016). A reduction in native species or the presence of nonnative assemblages can produce novel species interactions that have not co-evolved (Hobbs et al, 2006; Tagliaferro et al, 2014a) and could lead to a system with unstable ni.bio.br | scielo.br/ni
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