Diet quality and intake requirements of adult female caribou of the Denali herd, Alaska.
Abstract
Empirical, derived, and theoretical values of diet digestibility, DM intake requirements (DMI), diet nutrient content, and nitrogen and phosphorus balance are used in a summary of the nutrient regimen of well-nourished adult female caribou (Rangifer tarandus granti) of the Denali herd, Alaska, USA. A baseline framework for comparisons with other herds is provided, and the utility and advantages of estimating intake requirements when investigating caribou-range relations are discussed. Estimated apparent DM 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. Derived DMI requirements (ME required/ME of the diet) were 86, 104, 104, and 74 g/kg0.75 daily 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. Changes in the energy model, diet composition, and ADMD of individual forages can easily be reflected in DMI requirements. Derived values predict that caribou consuming a lichen-dominated diet are in negative P balance and probably negative N balance. Pregnancy and survival rates indicate caribou are well adapted to this winter diet. Dietary calcium, potassium and magnesium are likely to be adequate all the year round. Caribou of the Denali herd frequented mineral licks in spring and summer, probably to supplement sodium-deficient forage. 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, seem to be inadequate.