Variation in 15 N and 13 C values of forages for Arctic caribou: effects of location, phenology and simulated digestion. Academic Article uri icon


  • RATIONALE: The use of stable isotopes for dietary estimates of wildlife assumes that there are consistent differences in isotopic ratios among diet items, and that the differences in these ratios between the diet item and the animal tissues (i.e., fractionation) are predictable. However, variation in isotopic ratios and fractionation of 13 C and 15 N values among locations, seasons, and forages are poorly described for arctic herbivores especially migratory species such as caribou (Rangifer tarandus). METHODS: We measured the 13 C and 15 N values of seven species of forage growing along a 200-km transect through the range of the Central Arctic caribou herd on the North Slope of Alaska over 2years. We compared forages available at the beginning (May; n=175) and the end (n=157) of the growing season (September). Purified enzymes were used to measure N digestibility and to assess isotopic fractionation in response to nutrient digestibility during simulated digestion. RESULTS: Values for 13 C declined by 1.38 with increasing latitude across the transect, and increased by 0.44 from the beginning to the end of the season. The range of values for 15 N was greater than that for 13 C (13.29 vs 5.60 ). Differences in values for 13 C between graminoids (Eriophorum and Carex spp.) and shrubs (Betula and Salix spp.) were small but 15 N values distinguished graminoids (1.871.02 ) from shrubs (-2.872.93 ) consistently across season and latitude. However, undigested residues of forages were enriched in 15 N when the digestibility of N was less than 0.67. CONCLUSIONS: Although 15 N values can distinguish plant groups in the diet of arctic herbivores, variation in the digestibility of dietary items may need to be considered in applying fractionation values for 15 N to caribou and other herbivores that select highly digestible items (e.g. forbs) as well as heavily defended plants (e.g. woody browse). Published in 2017. This article is a U.S. Government work and is in the public domain in the USA.

published proceedings

  • Rapid Commun Mass Spectrom

altmetric score

  • 4.25

author list (cited authors)

  • Vansomeren, L. L., Barboza, P. S., Gustine, D. D., & Syndonia Bret-Harte, M.

citation count

  • 3

complete list of authors

  • Vansomeren, Lindsay L||Barboza, Perry S||Gustine, David D||Syndonia Bret-Harte, M

publication date

  • May 2017