Effectiveness of roadside verges as dispersal corridors for small ground-dwelling animals: A simulation study

Linear landscape elements are supposed to be suitable as dispersal corridors, and therefore are considered as possible solutions to mitigate the negative effects of fragmentation of more natural areas in agricultural landscapes. In the Netherlands certain road verges may offer good opportunities to connect heathland fragments. With the help of a simulation program and parameters estimated from field observations, we tested several concepts of road verge construction for their suitability as a dispersal corridor for carabid beetles with poor dispersal capacities. In broad road verges, long dispersal distances occur more frequently than in narrow ones. Losses of individuals to the adjacent areas are less in broad verges, leaving more individuals to continue dispersal. Only if these losses are fully compensated by reproduction, road verges may be dispersal corridors over more than a few hundred metres. Broader sites at the road verge, within reach of the next local population, can slightly increase the chance of long dispersal distances along the verge. The three species studied differ in their capacities to use the road verge as a corridor, mainly depending on their rates of movement, their response to the verge borderline, and their ability to reproduce in the narrow strip.