Reevaluating trophic discrimination factors (Δδ13C and Δδ15N) for diet reconstruction

IF 7.1 1区 环境科学与生态学 Q1 ECOLOGY Ecological Monographs Pub Date : 2022-04-06 DOI:10.1002/ecm.1525
Ryan B. Stephens, Andrew P. Ouimette, Erik A. Hobbie, Rebecca J. Rowe
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引用次数: 10

Abstract

Stable isotope analysis is increasingly being used to assess diet and trophic positions of animals. Such assessments require estimates of trophic discrimination factors (TDFs)—offset between the isotopic composition of diet and animal tissues—with imprecise applications of TDFs leading to biased conclusions in resource use. Because TDFs are unavailable for most species, ecologists often apply values from taxonomically similar species or use trophic step increases of approximately 1‰ for carbon (TDF-δ13C) and 3‰ for nitrogen (TDF-δ15N). Such practices may yield inaccuracies since TDFs vary greatly, even within a species. To better understand the factors that influence TDFs, we conducted a meta-analysis of TDF-δ13C and TDF-δ15N for mammals and quantified variation in relation to consumer type (herbivore, omnivore, carnivore) and diet source (C3-based, C4-based, marine-based, mixture). Additionally, to guide TDF choice, we used an isotopic data set of small mammal tissues and diet items to assess how predicted dietary contributions vary with TDFs estimated using (1) taxonomic relatedness, (2) consumer type and diet source, or (3) values derived from wild animals eating natural diets. Our meta-analysis revealed that metabolic routing and interactions between consumer class, dietary source, and the protein versus energy content of diets best explained variation in TDF-δ13C values (−1.5‰ to 7.3‰), whereas consumer class best explained variation in TDF-δ15N values (−0.5‰ to 7.1‰). Our test of methods to estimate TDFs indicated that ecologists should avoid relying on taxonomic relatedness when selecting TDF-δ13C because mixed-diet lab studies may produce misleading results for herbivores and omnivores. Additionally, field-derived estimates could help fill TDF gaps where diets within a consumer class are absent. Overall, we suggest that using standard TDF trophic step values should be abandoned, because feeding studies are often poor proxies for natural diets, particularly for herbivores and omnivores. Instead, we make recommendations on how to select TDFs, along with a range of TDF-δ13C and TDF-δ15N values depending on diet source, consumer class, and tissue type. Use of these more refined recommendations and TDF values in isotopic assessments will improve estimates of diets and trophic interactions in natural systems, leading to a better understanding of ecological interactions and communities.

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重新评估营养区分因子(Δδ13C和Δδ15N)以重建饮食
稳定同位素分析越来越多地被用于评估动物的饮食和营养地位。这样的评估需要对营养区分因子(tdf)进行估计——食物和动物组织的同位素组成之间的抵消——不精确的tdf应用会导致在资源利用方面得出有偏差的结论。由于大多数物种无法获得TDF,生态学家通常采用分类上相似的物种的值,或使用大约1‰的碳(TDF-δ13C)和3‰的氮(TDF-δ15N)的营养阶跃增加。这种做法可能会产生不准确的结果,因为即使在同一物种内,tdf也会有很大差异。为了更好地了解TDF的影响因素,我们对哺乳动物的TDF-δ13C和TDF-δ15N进行了荟萃分析,并量化了与消费者类型(草食、杂食、食肉)和饮食来源(c3型、c4型、海洋型、混合型)相关的变化。此外,为了指导TDF的选择,我们使用了小型哺乳动物组织和饮食项目的同位素数据集来评估预测的饮食贡献如何随着TDF的估算而变化,这些数据使用(1)分类相关性,(2)消费者类型和饮食来源,或(3)从食用自然饮食的野生动物获得的值。我们的荟萃分析显示,消费阶层、饮食来源和饮食中蛋白质与能量含量之间的代谢途径和相互作用最能解释TDF-δ13C值的变化(- 1.5‰至7.3‰),而消费阶层最能解释TDF-δ15N值的变化(- 0.5‰至7.1‰)。我们对估计TDF方法的测试表明,生态学家在选择TDF-δ13C时应避免依赖分类学相关性,因为混合饮食实验室研究可能会对草食动物和杂食动物产生误导性的结果。此外,实地估算可以帮助填补缺乏消费阶层饮食的TDF缺口。总的来说,我们建议放弃使用标准的TDF营养阶跃值,因为饲养研究通常不能很好地代表自然饮食,特别是对于草食动物和杂食动物。相反,我们根据饮食来源、消费者类别和组织类型,就如何选择TDF以及TDF-δ13C和TDF-δ15N值范围提出了建议。在同位素评估中使用这些更精确的建议值和总密度值将改进对自然系统中饮食和营养相互作用的估计,从而更好地了解生态相互作用和群落。
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来源期刊
Ecological Monographs
Ecological Monographs 环境科学-生态学
CiteScore
12.20
自引率
0.00%
发文量
61
审稿时长
3 months
期刊介绍: The vision for Ecological Monographs is that it should be the place for publishing integrative, synthetic papers that elaborate new directions for the field of ecology. Original Research Papers published in Ecological Monographs will continue to document complex observational, experimental, or theoretical studies that by their very integrated nature defy dissolution into shorter publications focused on a single topic or message. Reviews will be comprehensive and synthetic papers that establish new benchmarks in the field, define directions for future research, contribute to fundamental understanding of ecological principles, and derive principles for ecological management in its broadest sense (including, but not limited to: conservation, mitigation, restoration, and pro-active protection of the environment). Reviews should reflect the full development of a topic and encompass relevant natural history, observational and experimental data, analyses, models, and theory. Reviews published in Ecological Monographs should further blur the boundaries between “basic” and “applied” ecology. Concepts and Synthesis papers will conceptually advance the field of ecology. These papers are expected to go well beyond works being reviewed and include discussion of new directions, new syntheses, and resolutions of old questions. In this world of rapid scientific advancement and never-ending environmental change, there needs to be room for the thoughtful integration of scientific ideas, data, and concepts that feeds the mind and guides the development of the maturing science of ecology. Ecological Monographs provides that room, with an expansive view to a sustainable future.
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