Page 52 - A bird’s-eye view of recreation - Rogier Pouwels

A bird's-eye view of recreation
1999). We categorized three types of suitability: optimal, sub-optimal and marginal habitat. In optimal habitats, densities can reach 60 breeding pairs per square kilometer (Cramp et al. 1998, Teixeira 1979). In sub-optimal habitats, the densities where set at 30 breeding pairs per square kilometer while in marginal habitats the densities where set at 15 breeding pairs per square kilometer. Because Skylarks forage within 300-350 meters of their nest (Cramp et al. 1988), all patches within 300 meters of one another belong to the same local population. The dispersal capacity of the Skylark is estimated at 10 kilometers and 90% of all dispersal events are assumed to remain within this distance (Pouwels et al. 2002). All patches in the study area lie within this threshold distance and form one metapopulation. The main parameters for reproduction, mortality and dispersal are based on Cramp et al. (1988) and Beintema (1995) (Table 2). Mortality rates and reproduction used by Topping et al. (2005) for Skylark are within the ranges set for high and low densities in METAPHOR.
For each scenario, 100 replica runs were generated. Results were collected between years 150 and 250. It is expected that after 150 years the metapopulation in METAPHOR achieves a balance (Vergeer 1997).
Table 2. Main yearly parameters for the Skylark in METAPHOR.
Parameter Probability mortality low densities 0.2 mortality high densities 0.4 standard deviation mortality 0.05 reproduction low density 0.75 reproduction high density 0.35 standard deviation reproduction 0.1 fraction of juveniles that disperse 0.7 fraction of adults that disperse 0.1
3.4.5 Recreation impact: linking MASOOR and METAPHOR
MASOOR and METAPHOR are linked by the impact of visitors on two model parameters: density and reproduction. In their study, Vos and Peltzer (1987) related the impact of recreation on birds to the number of people on a path at the tenth busiest day in the year (mostly a sunny weekend day in spring). The result of MASOOR is translated into this output. The number of visitors on each path was scaled to 4500 visitors for the total area (the estimated number on the tenth busiest day). This resulted in visitor densities per path segment per hour. The recreation impact is calculated by using buffer zones. The width of the disturbance zones depends on the visitor densities (Vos and Peltzer 1987, see Fig. 2).
50