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Title: High-resolution food webs based on nitrogen isotopic composition of amino acids

Author
item CHIKARAISHI, YOSHITO - Japan Agency For Marine-Earth Science And Technology (JAMSTEC)
item Steffan, Shawn
item OGAWA, NANAKO - Japan Agency For Marine-Earth Science And Technology (JAMSTEC)
item ISHIKAWA, NAOTO - Japan Agency For Marine-Earth Science And Technology (JAMSTEC)
item SASAKI, YOKO - Japan Agency For Marine-Earth Science And Technology (JAMSTEC)
item TSUCHIYA, MASASKI - Japan Agency For Marine-Earth Science And Technology (JAMSTEC)
item OHKOUCHI, NACHIKO - Japan Agency For Marine-Earth Science And Technology (JAMSTEC)

Submitted to: Ecology and Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/15/2014
Publication Date: 6/1/2014
Publication URL: https://handle.nal.usda.gov/10113/60231
Citation: Chikaraishi, Y., Steffan, S.A., Ogawa, N.O., Ishikawa, N.F., Sasaki, Y., Tsuchiya, M., Ohkouchi, N. 2014. High-resolution food webs based on nitrogen isotopic composition of amino acids. Ecology and Evolution. 4(12):2423-2449.

Interpretive Summary: In the traditional approach to trophic position estimation using bulk '15N values of organisms, the wide variability in the trophic enrichment factor coupled with substantial background heterogeneity in the isotopic composition of consumers often causes significant uncertainty in the mapping of food web structure. The methods and preliminary data we present here demonstrate that '15N analysis of individual amino acids can potentially attend to background heterogeneity while simultaneously allowing accurate and precise estimation of the trophic position of organisms. Part of the accuracy of the method derives from the consistency and non-scaling of the trophic 15N-enrichment factor when the '15N values of glutamic acid and phenylalanine are analyzed. As predicted by theory and early empirical work, the trophic structures evident in the marine and terrestrial systems we studied are highly indicative of multichannel omnivory: a number of the animal species were distributed between integer trophic levels. Impact Statement: By accommodating background heterogeneity and demonstrating the constancy of trophic enrichment, our work allows food web researchers to accurately characterize virtually any consumer’s place in its food chain. Doing so reveals how a species will influence primary productivity, which in agricultural terms, represents crop production. This information will transform how food webs are assembled and analyzed.

Technical Abstract: Food webs are known to have myriad trophic links between resource and consumer species. However, since the difficulties associated with characterizing the trophic position of organisms—particularly omnivores and higher-order consumers—have remained a major problem in food web ecology, our knowledge on the trophic structure of food webs is often obscured. To better understand the trophic linkages and energy flow in complex networks of ecosystems, analysis of the stable nitrogen isotopic composition of amino acids has been suggested as a relatively new tool to provide accurate and precise estimates of the trophic position of organisms in aquatic and terrestrial ecosystems. In the present study, we employ this method to estimate the trophic position of a total of 200 samples from 39 species in coastal marine (a stony shore) and from 38 species in terrestrial (a fruit farm) environments, in order to provide a high-resolution view of the respective communities. In the coastal marine ecosystem, we observed the trophic position (TP) for macroalgae (0.8-1.2), gastropods (1.7-2.1), echinoids (1.8-2.0), oyster (2.4), crustaceans (2.3-4.0), and various fish species (2.7-4.7). In the terrestrial ecosystem, the trophic position was quantified for plant species (0.7-1.3), herbivorous insects (1.8-2.3), paper wasps (2.8-3.3), ladybugs (2.9-3.2), ant (3.0), mantis (3.2), and hornets (3.5-4.1). Thus, based on the trophic position from the nitrogen isotopic composition of amino acids, we are able to present a highly resolved image of the trophic structure in the food web, which is critical for revealing key elements of the trophic niches while illuminating the functional diversity of animal communities in complex ecosystems.