title: Rescaling the trophic structure of marine food webs.
abstract: Measures of trophic position (TP) are critical for understanding food web interactions and human-mediated ecosystem disturbance. Nitrogen stable isotopes (δ(15) N) provide a powerful tool to estimate TP but are limited by a pragmatic assumption that isotope discrimination is constant (change in δ(15) N between predator and prey, Δ(15) N = 3.4‰), resulting in an additive framework that omits known Δ(15) N variation. Through meta-analysis, we determine narrowing discrimination from an empirical linear relationship between experimental Δ(15) N and δ(15) N values of prey consumed. The resulting scaled Δ(15) N framework estimated reliable TPs of zooplanktivores to tertiary piscivores congruent with known feeding relationships that radically alters the conventional structure of marine food webs. Apex predator TP estimates were markedly higher than currently assumed by whole-ecosystem models, indicating perceived food webs have been truncated and species-interactions over simplified. The scaled Δ(15) N framework will greatly improve the accuracy of trophic estimates widely used in ecosystem-based management.
authors.affiliation: Great Lakes Institute for Environmental Research, University of Windsor, 401 Sunset Avenue, Windsor, ON N9B 3P4, Canada.
authors.forename: Nigel E
authors.initials: NE
authors.lastname: Hussey
authors.forename: M Aaron
authors.initials: MA
authors.lastname: Macneil
authors.forename: Bailey C
authors.initials: BC
authors.lastname: McMeans
authors.forename: Jill A
authors.initials: JA
authors.lastname: Olin
authors.forename: Sheldon F J
authors.initials: SF
authors.lastname: Dudley
authors.forename: Geremy
authors.initials: G
authors.lastname: Cliff
authors.forename: Sabine P
authors.initials: SP
authors.lastname: Wintner
authors.forename: Sean T
authors.initials: ST
authors.lastname: Fennessy
authors.forename: Aaron T
authors.initials: AT
authors.lastname: Fisk
mesh_terms: D000818:Animals; D001110:Arctic Regions; D005399:Fishes; D020387:Food Chain; D008954:Models, Biological; D009587:Nitrogen Isotopes; D009792:Oceans and Seas; D013019:South Africa
chemical_list: D009587:Nitrogen Isotopes
keywords: Discrimination; fish; food webs; marine; shark; stable isotopes; trophic level; trophic position