Using multiple tracers and directly accounting for trophic modification improves dietary mixing-model performance

作者：Brett M T; Eisenlord M E; Galloway A W E^*

来源：Ecosphere, 2016, 7(8): e01440.

DOI：10.1002/ecs2.1440

• Bayesian mixing model
• biomarkers
• dietary tracers
• fatty acids
• feeding trials
• herbivore
• Idotea wosnesenskii
• Special Feature: Biomarkers in Trophic Ecology
• stable isotopes

Stable isotope (SI) mixing models are one of the most common approaches used to infer resource pathways in consumers. However, SI-based analyses are often underdetermined, and consumer SI fractionation is often unknown. The use of fatty acid (FA) biomarkers in mixing models offers an alternative approach that can resolve the underdetermined constraint. A limitation to both methods is the considerable uncertainty regarding the "trophic modification" of dietary tracers, which occurs when consumers transform dietary resources into their own tissues. We tested the utility of SI and FA approaches for inferring the diets of the marine benthic isopod (Idotea wosnesenskii) fed various marine macroalgae in controlled feeding trials. Our analyses quantified how the accuracy and precision of Bayesian mixing models were influenced by the choice of algorithm (SIAR vs. MixSIR), trophic modification (assumed or known), and whether the model was under or overdetermined (seven sources and two vs. 26 tracers) for cases where isopods were fed an exclusive diet of one of the seven macroalgae. Using the conventional approach (two SI with assumed trophic modification) resulted in average model outputs, that is, the contribution from the exclusive resource =0.20 +/- 0.23 (0.00-0.79), mean +/- SD (95% credible interval), that only differed slightly from the prior assumption. This result was only somewhat improved by the use of measured trophic modification values for SI data. Using the FA-based approach with known trophic modification greatly improved model performance, that is, the contribution from the exclusive resource =0.91 +/- 0.10 (0.58-0.99). The choice of algorithm (SIAR vs. MixSIR) made a clear difference when trophic modification was known, and the model was overdetermined. In this case, SIAR and MixSIR had outputs of 0.86 +/- 0.11 (0.48-0.96) and 0.96 +/- 0.05 (0.79-1.00), respectively. When using FA biomarkers, going from two to seven tracers dramatically improved model performance (i.e., from 0.55 to 0.89, respectively), whereas going from 13 to 26 tracers only improved performance by 0.01. This analysis shows the choice and number of dietary tracers and the trophic modification assumption greatly influence the performance of mixing-model dietary reconstructions and ultimately our understanding of what resources actually support aquatic consumers.

• 出版日期2016-8