Conservation value of roadside verges for stenotopic heathland Carabidae: corridors or refugia?

Abstract

It has been shown that, in The Netherlands, sandy roadside verges may aid the survival of stenotopic Carabidae associated with open habitats such as heathland and sandy grassland. It is suggested that roadsides serve as ‘corridors’ linking heathland fragments, thus maintaining a metapopulation structure, which helps avoid regional extinction. However, a counter-argument is that verges encourage dispersal into unsuitable habitats, and function as ‘sinks’ in which individuals die without reproducing. The stenotopic species recorded from roadside verges but not in adjacent open habitats all had high powers of dispersal. The least successful dispersers were found only in open habitats and in verges closely connected to them. From this, the conclusion that verges function as corridors can be drawn. We reinterpret these data to suggest that stenotopic species were breeding on the roadside verges, and that they acted as refugia rather than corridors. We also present evidence from a roadside verge in the Breckland region of East Anglia, England. We show that many stenotopic species breed on the verge, which thus functions as a refugium. For Carabidae dependent on early successional habitats, survival may be more likely on disturbed roadside verges than on nature reserves in the absence of regular management disturbance.