Dynamics of ungulate populations are shaped by the climatic conditions and/or density-dependent causes, due to e.g. resource overexploitation. In absence of any top-down control, ungulate populations tend to fluctuate considerably, and this is only exacerbated through environmental fluctuations (Clutton–Brock and Coulson, 2002). High densities often result in lowering of body condition, and may adversely affect fecundity and age at first reproduction. Individual body size is an important determinant of survival, both in juveniles and adults, especially under extreme environmental conditions. A combination of highly dense populations and rough weather, e.g. in the form of snow or delayed growing season, inevitably results in substantial population die-offs. Subsequently, lowered pressure on the resource will ensure growth in body size, increased survival and population growth. With this model we explore the life history of individual horses, exploitation of a seasonal resource and dynamics of the whole population. We explicitly model energy acquisition through resource grazing and milk intake (for foals), and energetic costs of metabolism, growth, gestation and lactation. In addition, a certain probability and duration of snow cover can be tested with the model. Under snow conditions, both resource intake by individual horses and resource growth are stopped. The model is inspired by and largely parameterized based on the Konik horse population in the nature reserve in The Netherlands.
This is a companion discussion topic for the original entry at https://www.comses.net/codebases/4031/releases/1.3.0/