Premium
The biological basis for understanding and predicting dietary‐induced variation in nitrogen and sulphur isotope ratio discrimination
Author(s) -
Florin Scott T.,
Felicetti Laura A.,
Robbins Charles T.
Publication year - 2011
Publication title -
functional ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.272
H-Index - 154
eISSN - 1365-2435
pISSN - 0269-8463
DOI - 10.1111/j.1365-2435.2010.01799.x
Subject(s) - biology , protein quality , methionine , plant protein , limiting , sulfur , stable isotope ratio , nitrogen , amino acid , dietary protein , omnivore , flesh , δ15n , food science , zoology , biochemistry , δ13c , ecology , chemistry , physics , organic chemistry , quantum mechanics , mechanical engineering , engineering , predation
Summary 1. Accurately predicting isotope ratio discrimination is central to using mixing models to estimate assimilated diets of wild animals. This process is complicated when omnivores consume mixed diets because their discrimination is unlikely to be the weighted average of the various dietary constituents as occurs in current models. 2. We sought a basic understanding of how protein quality and quantity determine Δ 15 N and Δ 34 S in mammals and birds. Dietary protein is the primary source of both elements in many plants and animals. Low protein quality and high protein content have the potential to increase Δ 15 N by increasing protein turnover. 3. Protein quality, defined as the relative amount of the most limiting amino acid, accounted for 87–90% of the variation in Δ 15 N when mammals and birds consumed plant matter and mixed diets of plants and animals with protein of intermediate quality and quantity. However, foods containing relatively large amounts of high quality protein (i.e. vertebrate flesh) and foods with exceptionally low quality protein (e.g. lentils, Lens culinaris ) had disparate nitrogen discriminations relative to what would be predicted from protein quality alone. 4. Supplementation of plant and animal diets with nitrogen‐free carbohydrates and fats to reduce protein quantity did not reduce Δ 15 N in three plant‐based diets fed to laboratory rats, but reduced Δ 15 N in two of three meat diets with >50% protein. 5. Δ 34 S was weakly correlated with Δ 15 N ( R 2 = 0·48) but was highly correlated with dietary δ 34 S ( R 2 = 0·89). Because methionine, a sulphur amino acid, was the most limiting amino acid in all diets, sulphur should be highly conserved as indicated by the lack of any change in Δ 34 S when diets were supplemented with carbohydrates and fat to both provide additional energy and reduce protein content. 6. Predictive equations incorporating both protein quality and quantity accounted for 81% of the variation in Δ 15 N and offer the opportunity to create more realistic mixing models to accurately estimate assimilated diets for omnivores.