title: Environmental and physiological influences to isotopic ratios of N and protein status in a Montane ungulate in winter.
abstract: Winter severity can influence large herbivore populations through a reduction in maternal proteins available for reproduction. Nitrogen (N) isotopes in blood fractions can be used to track the use of body proteins in northern and montane ungulates. We studied 113 adult female caribou for 13 years throughout a series of severe winters that reduced population size and offspring mass. After these severe winters, offspring mass increased but the size of the population remained low. We devised a conceptual model for routing of isotopic N in blood in the context of the severe environmental conditions experienced by this population. We measured δ15N in three blood fractions and predicted the relative mobilization of dietary and body proteins. The δ 15N of the body protein pool varied by 4‰ and 46% of the variance was associated with year. Annual variation in δ15N of body protein likely reflected the fall/early winter diet and winter locations, yet 15% of the isotopic variation in amino acid N was due to body proteins. Consistent isotopic differences among blood N pools indicated that animals tolerated fluxes in diet and body stores. Conservation of body protein in caribou is the result of active exchange among diet and body N pools. Adult females were robust to historically severe winter conditions and prioritized body condition and survival over early investment in offspring. For a vagile ungulate residing at low densities in a predator-rich environment, protein restrictions in winter may not be the primary limiting factor for reproduction.
authors.affiliation: United States Geological Survey, Alaska Science Center, Anchorage, Alaska, United States of America.
authors.forename: David D
authors.initials: DD
authors.lastname: Gustine
authors.affiliation: Institute of Arctic Biology, Department of Biology and Wildlife, University of Alaska Fairbanks, Fairbanks, Alaska, United States of America.
authors.forename: Perry S
authors.initials: PS
authors.lastname: Barboza
authors.affiliation: United States Geological Survey, Alaska Science Center, Anchorage, Alaska, United States of America.
authors.forename: Layne G
authors.initials: LG
authors.lastname: Adams
authors.affiliation: Environment and Natural Resources Institute, University of Alaska Anchorage, Anchorage, Alaska, United States of America.
authors.forename: Nathan B
authors.initials: NB
authors.lastname: Wolf
mesh_terms: D000413:Alaska; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D001823:Body Composition; D003080:Cold Temperature; D004044:Dietary Proteins / Q000378:metabolism; D005260:Female; D009584:Nitrogen / Q000097:blood* / Q000737:chemistry; D011156:Population Density; D011157:Population Dynamics; D012044:Regression Analysis; D012053:Reindeer / Q000033:anatomy & histology / Q000378:metabolism* / Q000502:physiology; D012098:Reproduction; D012621:Seasons; D012914:Snow
chemical_list: D004044:Dietary Proteins; D009584:Nitrogen
references.citation: Am Nat. 1998 Sep;152(3):367-79
references.pmid: 18811445
references.citation: J Anim Sci. 2001 May;79(5):1085-92
references.pmid: 11374528
references.citation: Physiol Biochem Zool. 2005 Sep-Oct;78(5):819-27
references.pmid: 16096984
references.citation: PLoS One. 2011;6(6):e21357
references.pmid: 21731715
references.citation: Proc Natl Acad Sci U S A. 2002 Apr 2;99(7):4413-8
references.pmid: 11930002
references.citation: Physiol Biochem Zool. 2006 May-Jun;79(3):628-44
references.pmid: 16691528
references.citation: Ecology. 2008 Mar;89(3):829-37
references.pmid: 18459345
references.citation: Ecology. 2009 Feb;90(2):348-55
references.pmid: 19323218
references.citation: Biol Rev Camb Philos Soc. 2009 Feb;84(1):91-111
references.pmid: 19046398
references.citation: Ecology. 2009 Jul;90(7):1981-95
references.pmid: 19694145
references.citation: Ecology. 2013 Aug;94(8):1815-27
references.pmid: 24015525
references.citation: Nutr Res Rev. 1999 Jun;12(1):25-54
references.pmid: 19087445
references.citation: Br J Nutr. 1972 Jan;27(1):177-94
references.pmid: 5059380
references.citation: Am Nat. 2010 Oct;176(4):414-23
references.pmid: 20735260
references.citation: Physiol Biochem Zool. 2010 Jul-Aug;83(4):687-97
references.pmid: 20497043
references.citation: Ecol Appl. 2010 Jan;20(1):251-62
references.pmid: 20349845
references.citation: Physiol Biochem Zool. 2006 May-Jun;79(3):534-49
references.pmid: 16691519
references.citation: Ecology. 2008 Jun;89(6):1675-86
references.pmid: 18589531
references.citation: Oecologia. 2001 Apr;127(2):230-238
references.pmid: 24577654
references.citation: Oecologia. 2009 Aug;161(2):421-32
references.pmid: 19488787
references.citation: Ecology. 2010 Jul;91(7):2034-43
references.pmid: 20715626
references.citation: Ecology. 2006 Jan;87(1):95-102
references.pmid: 16634300
references.citation: Ecology. 2014 Apr;95(4):882-96
references.pmid: 24933808
references.citation: Oecologia. 2001 Jan;126(1):30-41
references.pmid: 28547435
references.citation: Physiol Biochem Zool. 2008 Nov-Dec;81(6):835-55
references.pmid: 18702605