Linking foraging behavior to population density: An assessment of GMM models for Dall sheep

We adapted Owen-Smith's general growth-metabolism-mortality (GMM) model to estimate the abundance of a population of Dall sheep (Ovis dalli dalli) in the southwest Yukon, Canada. Estimated sheep densities using the GMM approach (18–32 sheep/km2) approximated long-term aerial survey data (20.2–29.6 sheep/km2) when biologically realistic levels of parameter variation were introduced. Sheep population growth rate based on the GMM model was most sensitive to the metabolic conversion of forage into sheep biomass, rate of vegetation attrition, and mortality rate during winter. Model estimates may be improved with better estimates of metabolic conversion of forage into sheep body mass, vegetation attrition, incorporation of inter-annual variability, and stratification by sex and age classes. Overall, GMM models using mechanistic physiological and behavioral information may provide a complimentary approach to aerial censuses for estimating ungulate population abundance.