Clinic for Zoo Animals, Exotic Pets and Wildlife, Vetsuisse Faculty, University of Zurich, Winterthurerstr 260, 8057 Zurich, Switzerland.
Oecologia. 2012 Aug;169(4):939-53. doi: 10.1007/s00442-012-2274-3. Epub 2012 Feb 17.
Stable isotope analysis of consumer tissues document patterns of resource use because data are linearly related to isotope compositions of their source(s) (i.e., food, water, etc.). Deviations in parameters estimated for these relationships can arise from variations in consumer tissue-diet spacing (Δ(TS)) and the level of isotopic heterogeneity in the source(s). We present a set of simple hypotheses that distinguish between the effects of Δ(TS) and source isotope heterogeneity. The latter may arise via mixed diets, during tissue turnover, or by isotopic routing of dietary components. We apply these concepts to stable carbon and nitrogen isotope relationships between gut contents and body tissues of large mammal herbivores from mixed C(3)/C(4) South African savannas and test predictions based on the compound- and/or time-specific data archived within each material. Predicted effects of source isotope heterogeneity are readily detected in carbon isotope relationships between materials representing different time periods or comprising bulk versus protein-only diet components. Differences in Δ(TS) of carbon isotopes across mammal herbivore species with very different feeding niches (and diet isotope compositions) are likely to be small or non-existent in these habitats. Variations in Δ(TS) estimated for nitrogen isotopes are much greater, leading to inconsistencies that cannot be explained by diet or trophic level effects alone. The effects of source heterogeneity on isotopic relationships generate numerical artefacts that have been misinterpreted as variations in Δ(TS). We caution against generalized application of hypotheses based on assumptions of source isotopic homogeneity, even for single diets commonly used in laboratory studies. More careful consideration of how heterogeneity affects consumer-diet relationships is needed for many field and laboratory systems.
消费者组织中稳定同位素的分析记录了资源利用的模式，因为数据与它们的来源（如食物、水等）的同位素组成呈线性关系。这些关系中估计参数的偏差可能来自消费者组织与饮食的间隔（Δ（TS））和来源（同位素异质性）的变化。我们提出了一组简单的假设，可以区分Δ（TS）和来源同位素异质性的影响。后者可能是由于混合饮食、组织更新或饮食成分的同位素路由而产生的。我们将这些概念应用于混合 C(3)/C(4)南非草原大型食草动物的肠道内容物和身体组织之间的稳定碳和氮同位素关系，并根据每种材料中存档的复合和/或特定时间的数据来测试预测。在代表不同时间点的材料或包含大量蛋白质饮食成分的材料之间的碳同位素关系中，很容易检测到来源同位素异质性的预测影响。在这些栖息地中，具有非常不同的觅食生态位（和饮食同位素组成）的哺乳动物食草动物的碳同位素Δ（TS）差异可能很小或不存在。氮同位素估计的Δ（TS）变化大得多，导致不能仅用饮食或营养水平效应来解释的不一致。来源异质性对同位素关系的影响产生了数字伪影，这些伪影被误解为Δ（TS）的变化。我们警告不要根据来源同位素均匀性的假设来推广应用，即使是在实验室研究中常用的单一饮食也是如此。需要更仔细地考虑异质性如何影响消费者饮食关系，这对于许多现场和实验室系统都是必要的。
