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Diet Quality and Intake Requirements of Adult Female Caribou of the Denali Herd, Alaska

R. D. Boertje
Journal of Applied Ecology
Vol. 27, No. 2 (Aug., 1990), pp. 420-434
DOI: 10.2307/2404291
Stable URL: http://www.jstor.org/stable/2404291
Page Count: 15
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Diet Quality and Intake Requirements of Adult Female Caribou of the Denali Herd, Alaska
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Abstract

(1) This paper incorporates empirical, derived, and theoretical values of diet digestibility, dry matter intake requirements (DMI), diet nutrient content, and nitrogen (N) and phosphorus (P) balance in a summary of the nutrient regime of well-nourished adult female caribou (Rangifer tarandus granti) of the Denali herd. This study provides a baseline framework for comparisons with other herds, and discusses the utility and advantages of estimating intake requirements when investigating caribou-range relationships. (2) Estimated apparent dry matter digestibility (ADMD) of seasonal forages weighted by diet composition indicated that the ADMD of diets was high and varied little (60-70%) by season. A technique for predicting ADMD of seasonal diets was demonstrated assuming cell contents were 98% digestible, hemicelluloses were 35-61% digestible and the remaining small fractions of cells were indigestible. (3) Derived DMI requirements (ME required - ME of the diet) were 86, 104, 104, and 74 g kg-0.75 day-1 during spring, summer, autumn and winter, respectively. Spring and summer derived intake rates were similar to spring and summer intake rates of oesophageal-fistulated reindeer. Proposed changes in the energy model (Boertje 1985a), diet composition (Boertje 1984), and ADMD of individual forages (Boertje 1981) can easily be reflected in DMI requirements. (4) Derived values predict that caribou consuming a lichen-dominated diet are in a negative phosphorus balance and probably a negative nitrogen balance. Pregnancy and survival rates indicate caribou are well adapted to this winter diet. Dietary Ca, K, and Mg are likely to be adequate all the year round. Caribou of the Denali herd frequented mineral licks in spring and summer, probably to supplement Na-deficient forage. (5) Future comparisons of DMI requirements with empirical measurements of nutritional status and related demography are recommended as the most appropriate and practical approach to developing reliable predictors of caribou nutrition limitation. Conventional appraisals of caribou nutritional status, based on lichen abundance, are deemed inadequate.

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