LINKING MOOSE POPULATION AND PLANT-GROWTH MODELS WITH A MOOSE ENERGETICS MODEL

Selective foraging by large mammals can change ecosystem properties su ch as plant species composition, nutrient cycling rates, and soil fert ility. These changes, in turn, alter the availability of forage and co uld affect the relative efficiencies of foraging strategies used by th ese animals. We used a simulation model to predict how alternate forag ing strategies affected the net annual energy balance of moose (Alces alces), moose density, and distribution of browse across the landscape . The model simulates the spatial distribution of vegetation in an 8-h a landscape of 1-m(2) cells with seasonal changes in the energetic nee ds of free-ranging moose and plant phenology. The energetics model was integrated with a moose population model and a plant-growth model for long-term simulations. Changes in bite density in each feeding statio n are predicted with height and biomass logistic curves modified by a quadratic response to browsing. We tested foraging strategies using ra ndom, fractional, and marginal value theorem (MVT) algorithms on lands capes with a range of bite densities and differing spatial distributio ns. Small-scale disturbances (that is, treefall gaps) were required to maintain browse supply and prevent moose population extinction under all foraging strategies. Populations using a fractional stopping rule survived the 100-year simulations because moose browsed across much of the landscape and did not overbrowse patches with high bite density. Populations using random and MVT stopping rules became extinct in abou t 25 and about 50 years, respectively. Moose using a random stopping r ule were in negative energy balance because travel time was high and t he net energy intake rate was low on an annual basis. Moose using the MVT stopping rule were initially in positive energy balance, but as th e high-density browse patches were overbrowsed and low-density unbrows ed patches grew out of reach, bite density decreased, and energy balan ce became negative in subsequent years. Thus, the foraging strategy us ed by individual moose resulted in creation of landscapes that strongl y affected browse density, browse distribution, moose population densi ty, and moose survival.