A key assumption in trophic position (TP) estimation using stable isotope analysis is that consumers are in isotopic equilibrium with their resources. Here, we assess the degree to which time-varying resource dynamics and isotope incorporation rates of consumers influence consumer TP estimates across multiple trophic levels and aquatic ecosystems. We constructed a first-order kinetics model to explore consumer stable isotope incorporation rates and modeled the effect on TP calculations using bulk and compound-specific stable isotope data from previous experimental and observational studies. We found TP estimates of higher trophic level consumers are less accurate than lower trophic level consumers when applying bulk stable isotope analysis (BSIA) and using particulate organic matter as the stable isotope baseline. The accuracy of TP estimates depended on the time-varying dynamics of the stable isotope baseline. Tertiary consumers had the highest TP estimation error, and this error was not eliminated by sampling tissues with fast incorporation rates (i.e., blood) in the tertiary consumer. Compound-specific stable isotope analysis (CSIA) of individual amino acids was more accurate in estimating TP for all consumers and ecosystems compared to BSIA. Our analysis confirms that consideration for the dynamic nature of stable isotope ratios is necessary for accurate TP estimates. Finally, we show how first-order kinetics models can provide a useful framework for integrating prey and consumer incorporation rates in stable isotope studies to improve TP estimates.

中文翻译：

---

动态资源和稳定同位素掺入率对水生消费者营养位估计的影响

使用稳定同位素分析进行​​营养位置 (TP) 估算的一个关键假设是消费者与其资源处于同位素平衡。在这里，我们评估了随时间变化的资源动态和消费者的同位素掺入率对多个营养级别和水生生态系统的消费者总磷估计的影响程度。我们构建了一个一阶动力学模型来探索消费者稳定同位素掺入率，并使用来自先前实验和观察研究的批量和化合物特定稳定同位素数据模拟对 TP 计算的影响。我们发现，当应用批量稳定同位素分析 (BSIA) 并使用颗粒有机物作为稳定同位素基线时，较高营养级消费者的 TP 估计不如较低营养级消费者准确。TP 估计的准确性取决于稳定同位素基线的时变动态。第三级消费者的 TP 估计误差最高，并且该误差并不能通过在第三级消费者中采样具有快速掺入率的组织（即血液）来消除。与 BSIA 相比，单个氨基酸的化合物特异性稳定同位素分析 (CSIA) 在估算所有消费者和生态系统的 TP 方面更加准确。我们的分析证实，考虑稳定同位素比的动态性质对于准确的总磷估算是必要的。最后，我们展示了一阶动力学模型如何提供一个有用的框架，将猎物和消费者的掺入率整合到稳定同位素研究中，以改进 TP 估计。