Isotopic trophic discrimination factors (Δ13C, Δ15N) and its potential determinants along a subtropical macroinvertebrate food chain

Abstract

To estimate trophic discrimination factors (TDFs) for stable isotopes of carbon and nitrogen (Δ13C and Δ15N) accurately, specific studies are needed for each species or taxonomic group, because the use of general TDFs values for all animals obtained from the literature represents an important bias in isotopic modelling. Values of Δ13C and Δ15N were estimated in an aquatic food chain (periphyton-Chironomini-Perithemis sp.), in a subtropical region of South America, under experimental conditions and using two approaches: i) Traditional arithmetic equation and ii) Bayesian inference from mixing models. In addition, determinants of TDFs variation related to diet quality were evaluated. We report the values of Δ13C and Δ15N for Chironomini when feeding on periphyton (1.12 ± 1.31‰ and 0.92 ± 1.94‰ for C and N, respectively using the arithmetic equation) and for Perithemis sp. when feeding on Chironomini (0.65 ± 1.52‰ and 0.90 ± 1.08‰ for C and N, respectively according to the arithmetic equation), obtaining similar results using Bayesian inference. We did not find effects of diet quality on Δ13C and Δ15N values; although we highlight that unexpectedly, the taxonomic composition of the periphyton strongly affected the isotopic values of C and N. These reported values improve the accuracy of isotopic modeling for subtropical aquatic macroinvertebrates in future food web research.