title: Meta-analysis of amino acid stable nitrogen isotope ratios for estimating trophic position in marine organisms.
abstract: Estimating trophic structures is a common approach used to retrieve information regarding energy pathways, predation, and competition in complex ecosystems. The application of amino acid (AA) compound-specific nitrogen (N) isotope analysis (CSIA) is a relatively new method used to estimate trophic position (TP) and feeding relationships in diverse organisms. Here, we conducted the first meta-analysis of δ(15)N AA values from measurements of 359 marine species covering four trophic levels, and compared TP estimates from AA-CSIA to literature values derived from food items, gut or stomach content analysis. We tested whether the AA trophic enrichment factor (TEF), or the (15)N enrichment among different individual AAs is constant across trophic levels and whether inclusion of δ(15)N values from multiple AAs improves TP estimation. For the TEF of glutamic acid relative to phenylalanine (Phe) we found an average value of 6.6‰ across all taxa, which is significantly lower than the commonly applied 7.6‰. We found that organism feeding ecology influences TEF values of several trophic AAs relative to Phe, with significantly higher TEF values for herbivores compared to omnivores and carnivores, while TEF values were also significantly lower for animals excreting urea compared to ammonium. Based on the comparison of multiple model structures using the metadata of δ(15)N AA values we show that increasing the number of AAs in principle improves precision in TP estimation. This meta-analysis clarifies the advantages and limitations of using individual δ(15)N AA values as tools in trophic ecology and provides a guideline for the future application of AA-CSIA to food web studies.
authors.affiliation: Department of Ecology, Environment and Plant Sciences, Stockholm University, 10691, Stockholm, Sweden, jens.nielsen@su.se.
authors.forename: Jens M
authors.initials: JM
authors.lastname: Nielsen
authors.forename: Brian N
authors.initials: BN
authors.lastname: Popp
authors.forename: Monika
authors.initials: M
authors.lastname: Winder
mesh_terms: D000596:Amino Acids / Q000032:analysis / Q000378:metabolism*; D000818:Animals; D059001:Aquatic Organisms / Q000378:metabolism*; D017753:Ecosystem; D020387:Food Chain; D005766:Gastrointestinal Contents / Q000737:chemistry; D009584:Nitrogen / Q000032:analysis; D009587:Nitrogen Isotopes / Q000032:analysis; D011235:Predatory Behavior
chemical_list: D000596:Amino Acids; D009587:Nitrogen Isotopes; D009584:Nitrogen
references.citation: PLoS One. 2014 Jan 22;9(1):e85818
references.pmid: 24465724
references.citation: Biol Rev Camb Philos Soc. 2006 May;81(2):259-91
references.pmid: 16573844
references.citation: J Fish Biol. 2012 Jul;81(2):826-47
references.pmid: 22803737
references.citation: Biol Rev Camb Philos Soc. 2009 Feb;84(1):91-111
references.pmid: 19046398
references.citation: Proc Natl Acad Sci U S A. 2011 Jan 18;108(3):1011-5
references.pmid: 21199952
references.citation: Oecologia. 2003 Jul;136(2):169-82
references.pmid: 12802678
references.citation: Sci Rep. 2011;1:21
references.pmid: 22355540
references.citation: Oecologia. 2005 Aug;144(4):647-58
references.pmid: 16041545
references.citation: Ecol Evol. 2014 Jun;4(12):2423-49
references.pmid: 25360278
references.citation: PLoS One. 2012;7(11):e50133
references.pmid: 23209656
references.citation: Org Geochem. 1990;16(4-6):1115-28
references.pmid: 11540919
references.citation: Ecology. 2014 Jun;95(6):1674-83
references.pmid: 25039231
references.citation: J Anim Ecol. 2010 Sep;79(5):1132-41
references.pmid: 20629794
references.citation: PLoS One. 2012;7(7):e42024
references.pmid: 22848693
references.citation: Ecology. 2014 May;95(5):1285-93
references.pmid: 25000760
references.citation: PLoS One. 2013;8(3):e59651
references.pmid: 23527242
references.citation: PLoS One. 2012;7(5):e37403
references.pmid: 22666354
references.citation: Oecologia. 2014 Jul;175(3):911-22
references.pmid: 24719209
references.citation: Naturwissenschaften. 2004 Feb;91(2):90-3
references.pmid: 14991147
references.citation: PLoS One. 2014 Jun 02;9(6):e98087
references.pmid: 24887109