Kueffer, C., Fischlin, A. & Filli, F., 2001. An Individual-based Model of the
Summer Energy Budget of Red Deer (Cervus elaphus L.) in the Swiss
National Park. Ms. submitted to J. Nature Conservation, 39pp.
While the estimation of the carrying capacity of red deer (Cervus elaphus L.) in the Swiss National Park until now was based on seasonal mean phytomass productivity, we present a new approach which accounts for seasonal changes in the vegetation and the physiology of red deer during a growing season.
Our approach roots in an individual-based simulation model of the foraging behavior during the growing season in the Swiss Alps (May - October). The model assumes that red deer physiology and behavior lead to a maximization of energy intake during summer to compensate for winter weight losses. Maximal daily energy intake is constraint by the time needed for grazing plus forage digestion. We used a Michaelis-Menten functional response to parameterize the grazing. Digestion is a function of forage quality and is formulated as an exponential decay of rumen fill. A vegetation model calculates phytomass quantity as logistic growth. Phytomass quality (crude protein and fiber content) decreases linearly with the increasing phytomass quantity. Vegetation consists of four vegetation types: subalpine grassland, subalpine meadows, alpine meadows, and subalpine forest.
Our modeling of the interaction between red deer and vegetation helped us to identify critical temporary conditions during the growing season: For instance the demand supply ratio was most critical in spring. The non-linearity of the functional response was found to be crucial for any reliable estimation of the carrying capacity.