Data from: Individual growth as a non-dietary determinant of the isotopic niche metrics

1. Quantitative analytical approaches for isotopic niche analysis in the trophic diversity studies are proliferating rapidly; however, the assumptions behind the isotopic niche applications are rarely tested. One of the main assumptions is independence of the niche metrics and physiological status of the animals. The aim of this experimental study was to test the relationship between growth and Layman’s metrics of isotopic niche in consumers eating the same food but in different quantities and growing at different rates. 2. Based on research indicating that individual variability in isotopic fractionation increases under suboptimal conditions, I hypothesized that a group of consumers originating from the same population and exposed to food limitation would have greater estimates of the niche breadth and diversity as a result of higher inter-individual variability in growth rate and stable isotope signatures than in non-limiting feeding conditions. This hypothesis was tested using Baltic mysids Neomysis integer fed isotopically uniform diet under laboratory conditions and analyzing individual growth and stable isotope signature in concert. 3. As hypothesized, mysid growth rate was a significant negative predictor of most niche metrics. These effects were related to both increased inter-individual variability and higher trophic fractionation in malnourished animals, whereas in actively growing mysids lower fractionation was observed together with lower values for niche size, isotopic range and trophic diversity. 4. These findings challenge how we interpret the intrapopulation isotopic variance and evaluate isotopic evidence of individual specialization and call for integrated approaches for isotopic niche and growth assessment.1. 营养多样性（trophic diversity）研究中用于同位素生态位（isotopic niche）分析的定量分析方法正快速涌现，但同位素生态位应用背后的核心假设却极少得到验证。其中一项关键假设为生态位指标（niche metrics）与动物生理状态相互独立。本实验研究的目的，是检验摄食相同食物但摄入量不同、生长速率各异的消费者，其生长情况与莱曼同位素生态位指标（Layman’s metrics）之间的关联。 2. 已有研究表明，亚最优条件下个体间同位素分馏（isotopic fractionation）的差异会增大。基于此，本研究提出假设：相较于食物充足的投喂条件，来自同一种群且受食物限制的消费者群体，因生长速率与稳定同位素特征（stable isotope signature）的个体间差异更高，其生态位宽度（niche breadth）与生态位多样性的估计值会更大。本研究通过在实验室条件下投喂同位素均质日粮的波罗的海糠虾（Baltic mysids *Neomysis integer*），同步分析个体生长状况与稳定同位素特征，对该假设进行了验证。 3. 正如研究假设所示，糠虾的生长速率对多数生态位指标具有显著的负向预测作用。该效应与营养不良个体的个体间差异增大以及更高的营养级分馏（trophic fractionation）有关；而在快速生长的糠虾中，则观察到分馏程度更低，同时生态位面积、同位素范围与营养多样性的数值也更低。 4. 上述研究结果对我们解读种群内同位素变异以及评估个体特化的同位素证据的方式提出了挑战，并呼吁采用整合化方法开展同位素生态位与生长状况评估。