Stable Isotope Analysis in Food Web Reconstruction

Abstract

Stable isotope analysis of carbon (δ13C) and nitrogen (δ15N) in consumer and basal resource tissues provides a time-integrated, cost-effective framework for reconstructing food web structure, estimating trophic positions, and quantifying dietary niche breadth and overlap in ecological communities. This study applied multi-isotope Bayesian mixing models (MixSIAR) and stable isotope Bayesian ellipses (SIBER) to reconstruct food web structure and quantify
trophic niche partitioning in three temperate freshwater food webs (Loire River, France; Rhine River, Germany; Aare River, Switzerland) across seasonal gradients (spring, summer, autumn), sampling 2,842 individuals from 48 consumer species and 18 basal resource categories. Isotope biplot analysis revealed a mean trophic range of 4.8 +- 0.6 trophic levels across the three river systems, with invertebrate drift feeders occupying trophic positions 2.2-2.8 and apex piscivores (brown trout Salmo trutta, pike Esox lucius) reaching trophic positions 4.4-4.8. SIBER analysis showed significant seasonal contraction of trophic niche ellipses in summer (mean SEAC reduced by 34.2 +- 8.4% relative to spring), consistent with dietary specialisation during peak resource availability. MixSIAR dietary source modelling identified aquatic macroinvertebrates as the dominant dietary source for 38 of 48 consumer species (mean contribution 62.4 +- 14.2%), with terrestrial subsidies contributing significantly (> 20%) to 14 species. Cross-system comparison
revealed significant differences in food web metrics (trophic range, basal resource δ13C spread, piscivore isotopic niche width) between the three rivers, correlated with catchment land use intensity (r■ = -0.84, p = 0.002 for trophic niche width vs. agricultural land cover %). These results demonstrate the power of stable isotope approaches for comparative food web ecology and provide baseline food web data for river bioassessment under the EU Water Framework Directive.