Use of compound‐specific nitrogen isotope analysis of amino acids in trophic ecology: assumptions, applications, and implications

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 13 C and 15 N 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.