RATIONALE Determining the flow of energy from primary producers to higher trophic levels in complex systems remains an important task for ecologists. Biomarkers can be used to trace carbon or energy sources contributing to an organism's tissues. However, different biomarkers vary in their ability to trace carbon sources based on how faithfully they transfer between trophic levels. Comparing emerging biomarker techniques with more commonly used techniques can demonstrate the relative efficacy of each in specific systems. METHODS Two common biomarker techniques, fatty acid analysis (FAA) and bulk stable isotope analysis (SIA), and one emerging biomarker technique, compound-specific stable isotope analysis of amino acids (CSIA-AA), were compared to assess their ability to characterize and quantify basal carbon sources supporting the seaside sparrow (Ammodramus maritimus), a common salt marsh species. Herbivorous insect and deposit-feeding fiddler crab biomarker values were analyzed as proxies of major terrestrial and aquatic basal carbon sources, respectively. RESULTS All three biomarker techniques indicated that both terrestrial and aquatic carbon sources were important to seaside sparrows. However, FAA could only be evaluated qualitatively, due to a currently limited understanding of trophic modification of fatty acids between primary producer and this consumer's tissues. Quantitative stable isotope (SIA or CSIA-AA) mixing models predicted nearly equal contributions of terrestrial and aquatic carbon sources supporting seaside sparrows, yet estimates based on CSIA-AA had greater precision. CONCLUSIONS These findings support the use of CSIA-AA as an emerging tool to quantify the relative importance of basal carbon sources in salt marsh consumers. Integrating multiple biomarker techniques, with their differing benefits and limitations, will help to constrain models of carbon and energy flow in future ecosystem studies.

中文翻译：

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多种生物标志物方法支持使用氨基酸的化合物特定的稳定同位素分析来定量盐沼消费者中基础碳源的使用。

理由对于复杂的系统来说，确定从初级生产者到更高营养级别的能量流仍然是生态学家的一项重要任务。生物标记物可用于追踪有助于生物体组织的碳或能源。但是，不同的生物标志物根据其在营养水平之间的迁移忠实程度来追踪碳源的能力也有所不同。将新兴的生物标志物技术与更常用的技术进行比较，可以证明每种方法在特定系统中的相对功效。方法两种常见的生物标记技术，即脂肪酸分析（FAA）和本体稳定同位素分析（SIA），以及一种新兴的生物标记技术，即氨基酸的化合物特异性稳定同位素分析（CSIA-AA），进行了比较，以评估它们表征和量化支持常见的盐沼物种海边麻雀（Ammodramus maritimus）的基础碳源的能力。分别以草食性昆虫和摄食提琴蟹的生物标志物值作为主要陆地和水生基础碳源的代理进行了分析。结果三种生物标记技术均表明陆生和水生碳源均对海边麻雀很重要。但是，由于对初级生产者和该消费者组织之间脂肪酸的营养修饰的了解有限，因此只能对FAA进行定性评估。定量稳定同位素（SIA或CSIA-AA）混合模型预测，支持海边麻雀的陆地和水生碳源的贡献几乎相等，然而，基于CSIA-AA的估算具有更高的精度。结论这些发现支持将CSIA-AA用作量化盐沼消费者基础碳源相对重要性的新兴工具。整合多种生物标记技术及其各自的优点和局限性，将有助于在未来的生态系统研究中限制碳和能量流的模型。