Univ. Lille, Univ. Littoral Côte d'Opale, CNRS, IRD, UMR 8187 Laboratoire d'Océanologie et de Géosciences, Lille, France.
EMH, Centre Atlantique, Ifremer, Nantes, France.
PLoS One. 2022 Feb 7;17(2):e0263454. doi: 10.1371/journal.pone.0263454. eCollection 2022.
Stable isotope ratios are used to reconstruct animal diet in trophic ecology via mixing models. Several assumptions of stable isotope mixing models are critical, i.e., constant trophic discrimination factor and isotopic equilibrium between the consumer and its diet. The isotopic turnover rate (λ and its counterpart the half-life) affects the dynamics of isotopic incorporation for an organism and the isotopic equilibrium assumption: λ involves a time lag between the real assimilated diet and the diet estimated by mixing models at the individual scale. Current stable isotope mixing model studies consider neither this time lag nor even the dynamics of isotopic ratios in general. We developed a mechanistic framework using a dynamic mixing model (DMM) to assess the contribution of λ to the dynamics of isotopic incorporation and to estimate the bias induced by neglecting the time lag in diet reconstruction in conventional static mixing models (SMMs). The DMM includes isotope dynamics of sources (denoted δs), λ and frequency of diet-switch (ω). The results showed a significant bias generated by the SMM compared to the DMM (up to 50% of differences). This bias can be strongly reduced in SMMs by averaging the isotopic variations of the food sources over a time window equal to twice the isotopic half-life. However, the bias will persist (∼15%) for intermediate values of the ω/λ ratio. The inferences generated using a case study highlighted that DMM enhanced estimates of consumer's diet, and this could avoid misinterpretation in ecosystem functioning, food-web structure analysis and underlying biological processes.
稳定同位素比率被用于通过混合模型在营养生态中重建动物的饮食。稳定同位素混合模型的几个假设是至关重要的，即消费者与其饮食之间的稳定的营养辨别因子和同位素平衡。同位素周转率（λ及其对应的半衰期）影响生物体同位素掺入的动态和同位素平衡假设：λ涉及实际同化饮食与个体尺度上混合模型估计的饮食之间的时间滞后。当前的稳定同位素混合模型研究既不考虑这种时间滞后，也不考虑同位素比率的动态。我们使用动态混合模型（DMM）开发了一个机制框架，以评估 λ 对同位素掺入动态的贡献，并估计在传统静态混合模型（SMM）中忽略饮食重建中的时间滞后所引起的偏差。DMM 包括来源的同位素动态（表示为 δs）、λ 和饮食切换频率（ω）。结果表明，与 DMM 相比，SMM 会产生显著的偏差（高达 50%的差异）。通过在等于同位素半衰期两倍的时间窗口内对食物源的同位素变化进行平均，可以在 SMM 中大大减少这种偏差。然而，对于 ω/λ 比值的中间值，偏差仍将持续（约 15%）。使用案例研究生成的推论表明，DMM 增强了消费者饮食的估计，这可以避免在生态系统功能、食物网结构分析和潜在的生物过程中产生误解。
