Meta-analysis of amino acid stable nitrogen isotope ratios for estimating trophic position in marine organisms
- 1.9k Downloads
Estimating trophic structures is a common approach used to retrieve information regarding energy pathways, predation, and competition in complex ecosystems. The application of amino acid (AA) compound-specific nitrogen (N) isotope analysis (CSIA) is a relatively new method used to estimate trophic position (TP) and feeding relationships in diverse organisms. Here, we conducted the first meta-analysis of δ15N AA values from measurements of 359 marine species covering four trophic levels, and compared TP estimates from AA-CSIA to literature values derived from food items, gut or stomach content analysis. We tested whether the AA trophic enrichment factor (TEF), or the 15N enrichment among different individual AAs is constant across trophic levels and whether inclusion of δ15N values from multiple AAs improves TP estimation. For the TEF of glutamic acid relative to phenylalanine (Phe) we found an average value of 6.6 ‰ across all taxa, which is significantly lower than the commonly applied 7.6 ‰. We found that organism feeding ecology influences TEF values of several trophic AAs relative to Phe, with significantly higher TEF values for herbivores compared to omnivores and carnivores, while TEF values were also significantly lower for animals excreting urea compared to ammonium. Based on the comparison of multiple model structures using the metadata of δ15N AA values we show that increasing the number of AAs in principle improves precision in TP estimation. This meta-analysis clarifies the advantages and limitations of using individual δ15N AA values as tools in trophic ecology and provides a guideline for the future application of AA-CSIA to food web studies.
KeywordsCompounds-specific isotope analysis Food webs Trophic enrichment factor Trophic ecology
This study received financial support from the German Science Foundation (DFG) under the project number WI 2726/2-1. This work was also partially supported by the National Science Foundation under grant number OCE-1041329 (to B. N. P. and Jeffrey C. Drazen). This is SOEST contribution number 9284. The authors would like to thank Alfred Burian, Karen Arthur, Yoshito Chikaraishi and one anonymous reviewer for constructive comments that helped improve the manuscript. We are thankful to authors of previous publications of marine δ15N AA values which made data compilation for this manuscript possible. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of our funding sources.
- Chikaraishi Y, Ogawa N, Ohkouchi N (2010) Further evaluation of the trophic level estimation based on nitrogen isotopic composition of amino acids. Earth, life, and isotopes. Kyoto University Press, Kyoto, pp 37–51Google Scholar
- Froese R, Pauly D (2012) Fishbase http://www.fishbase.org
- Hynes H (1950) The food of fresh-water sticklebacks (Gasterosteus aculeatus and Pygosteus pungitius), with a review of methods used in studies of the food of fishes. J Animal Ecol 36-58Google Scholar
- Lorrain A et al (2014) Nitrogen isotopic baselines and implications for estimating foraging habitat and trophic position of yellowfin tuna in the Indian and Pacific Oceans. Deep Sea Res Part II Topical Stud Oceanogr 113:188–198. doi. 10.1016/j.dsr2.2014.02.003
- Martínez del Rio C, Wolf BO (2005) Mass-balance models for animal isotopic ecology. In: Physiological and ecological adaptations to feeding in vertebrates pp 141–174Google Scholar
- R Development Core Team (2014) R: a language and environment for statistical computing. R Foundation for Statistical Computing, ViennaGoogle Scholar