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United States Department of Agriculture

Agricultural Research Service

Research Project: CRANBERRY GENETIC IMPROVEMENT AND INSECT PEST MANAGEMENT Title: Amino acid isotopic analysis in agricultural systems

Authors
item Steffan, Shawn
item Chikaraishi, Yoshito -

Submitted to: National Meeting of Entomological Society Of America
Publication Type: Abstract Only
Publication Acceptance Date: June 18, 2013
Publication Date: November 11, 2013
Citation: Steffan, S.A., Chikaraishi, Y. 2013. Amino acid isotopic analysis in agricultural systems [abstract]. National Meeting of Entomological Society Of America. Paper No. 1435.

Technical Abstract: A relatively new approach to stable isotopic analysis—referred to as compound-specific isotopic analysis (CSIA)—has emerged, centering on the measurement of 15N:14N ratios in amino acids (glutamic acid and phenylalanine). CSIA has recently been used to generate trophic position estimates among animal species; however, the validity of such estimates is dependent on the consistency of the trophic enrichment factor (TEF). To address whether the TEF may scale with trophic level, we created model communities with discrete trophic groups (a basal resource, strict herbivores, strict predators, and predators of strict predators), and used CSIA to analyze the organisms representing these trophic levels. We then tested the method using wild specimens from a terrestrial ecosystem. We provide the first evidence that the TEF remains consistent across a wide range of trophic levels. Based on these findings and previous studies in aquatic and marine systems, the TEF (+7.6 ‰) appears to be a universal, non-scaling enrichment factor. Employing this parameter within formulae for trophic position estimation, we derived highly accurate estimates of animal trophic positions. These estimates permitted the assembly of trophic hierarchies, revealing the highest trophic position (5.07) and thus longest food chain ever measured with verifiable accuracy. Our findings suggest that CSIA facilitates extremely accurate measurement of animal trophic positions. Such trophic position estimates will allow bio-control researchers to accurately characterize the lifetime trophic tendencies/spectra of bio-control agents.

Last Modified: 10/20/2014
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