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Title: Grazing food web view from compound-specific stable isotope analysis of amino acids

Author
item CHIKARAISHI, YOSHITO - Japan Agency For Marine-Earth Science And Technology (JAMSTEC)
item Steffan, Shawn
item OHKOUCHI, NAOHIKO - Japan Agency For Marine-Earth Science And Technology (JAMSTEC)

Submitted to: Ecological Society of America (ESA)
Publication Type: Abstract Only
Publication Acceptance Date: 4/15/2013
Publication Date: 8/7/2013
Citation: Chikaraishi, Y., Steffan, S.A., Ohkouchi, N. 2013. Grazing food web view from compound-specific stable isotope analysis of amino acids [abstract]. Ecological Society of America (ESA). Paper No. COS 59-3.

Interpretive Summary:

Technical Abstract: Knowledge of the trophic position (TP) of organisms in food webs allows ecologists to track energy flow and trophic linkages among organisms in complex networks of ecosystems. Compound-specific stable isotope analysis (CSIA) of amino acids has been employed as a relatively new method with the high potential for accurate and precise estimates of the TP of organisms. This CSIA method is constructed based on contrasting isotopic fractionation during fundamental amino acid metabolisms between two common amino acids: glutamic acid (Glu) shows a significant 15N-enrichment (+8.0‰) whereas phenylalanine (Phe) shows little 15N-enrichment (+0.4‰), which is commonly occur both in aquatic and in terrestrial organisms. Recently, we have successfully established a general equation for the estimation of trophic position (TP) of organisms: TP = [('15NGlu – '15NPhe + ')/7.6] + 1, where ' represents the isotopic difference between glutamic acid and phenylalanine in aquatic algae (–3.4‰), and terrestrial C3 (+8.4‰) and C4 plants (–0.4‰). In this presentation, we demonstrate an application of this method for multiple species collected from coastal marine (a stony shore) and terrestrial (a fruit farm) environment, to obtain a fine view of grazing food web structure in the ecosystems. The isotopic composition of phenylalanine ranging from +3.5 to +8.7‰ for a stony shore and from +3.0 to +17.0‰ for a fruit farm represents much variation in the isotopic composition of primary producers at the bases of food webs. However, since this background variation is negated in the principle of this method, a small error (less than ~0.2 unit as 1 ') is accompanied with the TP estimated by the CSIA method. Based on the observed TP, we can present the trophic spectra for these species: 0.9-1.2 for macroalgae, 1.7-2.0 for gastropod and echinoid, 2.3-2.6 for crab, and 2.9-4.6 for fish in the coastal marine; and 1.0 for plant, 1.9-2.2 for caterpillar, bee, and butterfly, 2.9-3.1 for wasp and ladybug, and 3.5-4.0 for hornet in the terrestrial food webs. Thus a fine view of grazing food web structure in the ecosystems can be obtained from the accurate and precise estimation of TP for multiple species based on the CSIA method, which will be useful in better understanding of energy flow and trophic linkages (e.g., niche and function) among organisms in complex networks of ecosystems.