Page 51 - A bird’s-eye view of recreation - Rogier Pouwels

3.4.3 METAPHOR
The main processes that determine the fate of a population are birth, death and
exchange (dispersal). METAPHOR simulates these processes. METAPHOR is a spatially
explicit, individual based model that simulates the dynamics of a metapopulation. A
simulation starts with a given number of individuals of different age classes and sex
categories in a specified number of patches. In the case study the simulations started
with each patch filled to carrying capacity. Carrying capacity is a linear function of
patch area, truncated to discrete numbers. METAPHOR follows the life history of each
individual. The first simulated event is formation of breeding pairs and reproduction,
followed by a mortality event. Individuals age and finally disperse through the
landscape. Reproduction and mortality are density dependent and stochastic 3 processes. The dispersal algorithm is spatially explicit (Verboom et al. 2001, Vos et al.
2001).
Each year, METAPHOR assesses the state of sub-populations, thus, the state of the metapopulation. The results are, for example, the persistence probability of the metapopulation and the mean densities in the sub-populations. METAPHOR can be used to simulate the effects of changes in landscape pattern as well as processes within the metapopulation. Because each individual is assigned to a specific location the model is able to translate local impacts (recreation disturbance) into results on the landscape level (persistence). METAPHOR is a flexible tool that can easily be adjusted to meet the requirements of new applications.
Comparable models are ALEX (Possingham & Davies 1995), ALMASS (Topping et al. 2003) and RAMAS (Akçakaya 2000), which all have in common that they can be used for population viability analysis (PVA, see Brook et al. 2000) and differ in the exact formulation of density dependence, population structure, and dispersal algorithms. METAPHOR has detailed and realistic algorithms for these features, but lacks the interaction between species that characterizes ALMASS.
3.4.4 Parameters METAPHOR case study
In the case study, we used the model for evaluating the persistence of the Skylark (Alauda arvensis). The Skylark breeds in open vegetation without shrubs or trees (Topping et al. 2005, Beintema et al. 1995). Species density is directly correlated with the presence of more open landscapes (Van ‘t Hoff 2001). These conditions were used to select suitable vegetation types from a local land cover map (Van Til and Mourik
Linking ecological and recreation models
49