Isotopic nitrogen in fecal fiber as an indicator of winter diet in caribou and muskoxen
Rapid Communications in Mass Spectrometry
- David D. Gustine, Perry S. Barboza, Jennifer Addison, Rachel Shively, Lola Oliver
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AbstractRATIONALE: The ratios of stable nitrogen isotopes (δ15N values) in excreta have been used to examine aspects of trophic and nutritional ecology across taxa. Nitrogen fractions in feces of herbivores include endogenous (e.g., sloughed intestinal cells, unresorbed digestive secretions, and microbial debris) and dietary sources. For animals such as large herbivores, that have diets and feces with high concentrations of indigestible ﬁber, endogenous 15N may constrain the use of fecal δ15N values to estimate dietary δ15N values and reconstruct diets.
METHODS: We compared two techniques (detergent and detergent-free) to isolate fractions of plant ﬁbers in the forages of caribou (Rangifer tarandus) and muskoxen (Ovibos moschatus); estimated the discrimination factors between the δ15N values of fecal ﬁber residues and of the diets of captive animals; and used the more effective isotopic tracer of dietary δ15N values to examine the relationships between the δ15N values of fecal residues and diet composition in several populations of wild caribou and muskoxen throughout North America in winter.
RESULTS: The detergent-based approach contaminated the fractions of plant ﬁbers in forages and feces with 14N, whereas the detergent-free method was a good proxy to estimate δ15N values of plant ﬁbers (r2= 0.92) and provided a better estimate of the fecal-ﬁber to diet discrimination factor for both species (caribou = 3.6‰; muskoxen = 2.8‰). In wild populations, the δ15N values of fecal ﬁbers reﬂected diet composition in muskoxen (adjusted R2= 0.43) but not caribou (adjusted R2= 0.06).
CONCLUSIONS: Contamination from detergent residues prohibited the use of detergent extraction in isolating forage 15N from endogenous 15N in the feces of herbivores. Although δ15N values in fecal ﬁbers can be used to track dietary δ15N values in wild herbivores, discrimination between fecal extracts and diet may vary with the contribution of endogenous nitrogen (N), and, therefore, residual endogenous 15N in feces may limit dietary reconstructions from fecal δ15N values for some large herbivores.
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- Journal Article
- Isotopic nitrogen in fecal fiber as an indicator of winter diet in caribou and muskoxen
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- Rapid Communications in Mass Spectrometry
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- John Wiley & Sons
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- New York, NY
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- Alaska Science Center
- 10 p.
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- Journal Article
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- Canada;Greenland;United States