title: Polar bears make little use of terrestrial food webs: evidence from stable-carbon isotope analysis.
abstract: The mean stable-carbon isotope ratios (δ13C) for polar bear (Ursus maritimus) tissues (bone collagen -15.7‰, muscle -17.7‰, fat -24.7‰) were close to those of the same tissues from ringed seals (Phoca hispida) (-16.2‰, -18.1‰, and -26.1‰, respectively), which feed exclusively from the marine food chain. The δ13C values for 4 species of fruits to which polar bears have access when on land in summer ranged from -27.8 to -26.2‰, typical of terrestrial plants in the Arctic. An animal's δ13C signature reflects closely the δ13C signature of it's food. Accordingly, the amount of food that polar bears consume from terrestrial food webs appears negligible, even though some bears spend 1/3 or more of each year on land during the seasons of greatest primary productivity.
authors.affiliation: Department of Fisheries and Oceans, Freshwater Institute, 501 University Crescent, R3T 2N6, Winnipeg, Manitoba, Canada.
authors.forename: M A
authors.initials: MA
authors.lastname: Ramsay
authors.affiliation: Department of Zoology, University of Manitoba, R3T 2N2, Winnipeg, Manitoba, Canada.
authors.forename: K A
authors.initials: KA
authors.lastname: Hobson
keywords: Arctic food web; Fasting; Polar bears; Ursus maritimus; δ13C