Modeling Population Dynamics of Mountain Sheep

Our objective is to review approaches for modeling the population dynamics of mountain sheep populations (bighorn [ Ovis canadensis ] and thinhorn [ Ovis dalli ]) to identify applications that can assist management, including harvesting. The approach to modeling mountain sheep populations depends on the questions and potential applications of the modeling results, but model reliability ultimately depends on the availability of data. Demographic models, specifically structured population models, are used to synthesize data on vital rates and project future population size and composition for mountain sheep. Basic models for demography that assume exponential growth models are inadequate for modeling sustainable yield. Yet, complexity can be built into a model with vital rates as functions of population density, animal performance metrics, vegetation, and environmental variables. The interaction with vegetation that leads to animal performance can replace the need for density dependence, but would require detailed plant-herbivore interactions that are seldom available. Nevertheless, characterization of foodscapes or measures of habitat quality can be combined with density dependence in vital rates. Applied population models will always require a balance between realism (model complexity) and model simplicity so that parameters can be estimated with statistical reliability.