A small, medium-sized and large mammal species

In the simulations for these mammal species we varied the maximum size (carrying capacity) of the populations on either side of the road, and the percentage of mixing, i.e. the percentage of the total number of animals in the population that take part in the exchange across the road. As indicator for population performance, we used the percentage of time that the target area was occupied by a population. A population is here defined as at least one adult male and one adult female. The simulations were initiated at 75% of carrying capacity and cover 200 years. Occupation of the target area was monitored between year 100 and 200. For each scenario, differing in population size of the target area and source area and differing in mixing percentage, 100 simulations were run.

A toad and salamander species

In the simulations for these amphibian species we varied the maximum size (carrying capacity) of the population, the fraction of migrating animals that successfully get across the road and the fraction of migrating animals that get killed in traffic, despite the road mitigation measures. As indicator for population performance, we used the percentage of survival after hundred years, based on 1000 simulations. A population is here defined as at least one adult male and one adult female.

Although the model simulations will never exactly reflect reality due to model assumptions, they do provide a first indication whether your road mitigation measures are, in terms of population persistence, on the right track or not. The model assumptions should always be considered when interpreting the model output. Therefore, it is recommended to discuss any outcome of the Road Mitigation Calculator with an ecologist before it is implemented in a road planning project.