ARS | Publication request: Trophic spectra reveal the community structure of a terrestrial system

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: November 2, 2011
Publication Date: February 27, 2012
Citation: Steffan, S.A., Chikaraishi, Y., Bosak, E., Horton, D.R., Ohokouchi, N., Jones, V. 2012. Trophic spectra reveal the community structure of a terrestrial system [abstract]. 2012 Ocean Sciences Meeting. Paper No. AO323.

Technical Abstract: Recent advances in compound-specific isotopic ratio analysis (CSI-AA) have allowed researchers to measure trophic fractionation of 15N in specific amino acids, namely glutamic acid and phenylalanine. These amino acids have proven useful in food web studies because of the wide and consistent disparity in their respective fractionation tendencies. This discrimination at the molecular level allows glutamic acid to reflect the trophic position of a consumer, while phenylalanine represents the background signature of 15N in the plants at the base of the food web. In controlled feeding trials, we used CSI-AA to confirm the accuracy of the Chikaraishi C3-plant equation for trophic levels 1 through 4. We then collected wild arthropods from an old-field site, and each specimen was analyzed using both the Chikaraishi method and the conventional bulk-15N method. Regression analysis characterized the relationship between these two methods, allowing us to convert bulk-15N values into trophic level estimates (among the many specimens not analyzed via CSI-AA). This approach facilitated greater sample sizes and thereby permitted investigations of population- (trophic spectra) and community-scale parameters.