Abstract
Knowledge of the diet source and trophic position of organisms is fundamental in food web science. Since the 1980s, stable isotopes of light elements such as 13C and 15N have provided unique information on the food web structure in a variety of ecosystems. More recently, novel isotope tools such as stable isotopes of heavy elements, radioisotopes, and compound-specific isotope analysis, have been examined by researchers. Here I reviewed the use of compound-specific nitrogen isotope analysis of amino acids (CSIA-AA) as a useful dietary tracer in food web ecology. Its three key features—(1) offsetting against isotopic variation; (2) universality of the trophic discrimination factor; and (3) sensitivity to source mixing—were compared with conventional isotope analysis for the bulk tissue of organisms. These three advantages of CSIA-AA will allow future researchers to (1) estimate the integrated trophic position (iTP) of animal communities; (2) infer trophic transfer efficiency (TTE) in food webs; and (3) quantify contributions from different resources to animals, all of which are crucial for understanding the relationship between biodiversity and multi-trophic ecosystem functioning. Further development of trophic ecology will be facilitated by both methodological refinement of CSIA-AA and its application to a wider range of organisms, food webs, and ecosystems.
Highlights
Almost a century ago, Elton (1927) first explicitly defined the concept of the ‘food chain’, which is the simplest subset in a complex trophic network comprising numerous prey–predator relationships (Lindeman 1942; Hutchinson 1959)
The aim of this paper is to review the potential of the compound-specific nitrogen isotope analysis of amino acids (CSIA-AA) methodology for estimating trophic position’ (TP), and the diet sources of animals, with special emphasis on the physiological and ecological mechanisms of the trophic transfer
CSIA-AA does not need to characterize any diet source data to estimate the TP of the focal animal, because the TP value is represented as an offset between the d15N values of glutamic acid (d15NGlu), which increase considerably with trophic level’ (TL), and phenylalanine (d15NPhe), which remain unchanged during trophic transfer, in the animal (Table 1) (Chikaraishi et al 2009)
Summary
Almost a century ago, Elton (1927) first explicitly defined the concept of the ‘food chain’, which is the simplest subset in a complex trophic network comprising numerous prey–predator relationships (Lindeman 1942; Hutchinson 1959). The energy flow web puts more emphasis on biomass transfer and productivity in a trophic network (Thompson et al 2012). Over the past four decades, the d15N and d13C analysis has advanced greatly and has contributed to testing a number of ecological theories in food web science Most of these advances have important linkages with other disciplines, such as geochemistry and archaeology, where several new tools such as heavy element stable isotopes, radioisotopes, and compoundspecific isotopes, have recently emerged. The aim of this paper is to review the potential of the CSIA-AA methodology for estimating TP, and the diet sources of animals, with special emphasis on the physiological and ecological mechanisms of the trophic transfer. Only the three most critical features of both the methods in the context of food web science were highlighted, as follows
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