Are roads barriers to dispersal in the land snail Arianta arbustorum?

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Abstract
The effect of road width on dispersal in the land snail Arianta arbustorum was examined by recording displacements of marked individuals during one activity season (3 months) in central Sweden. For two sites, a paved road (8 m wide, low traffic density) and an unpaved track (3 m wide), the snails' movements were largely confined to roadside verges. The snails followed the vegetation belts; the average displacements ranged from 1.5 to 4.9 m at different sites. Several snails covered large distances, the maximum recorded being 14 m. Despite these long-distance dispersers, only one of the recaptured snails crossed the paved road and two crossed the track, indicating that the road and, to a minor extent, the track acted as dispersal barriers. By contrast, an overgrown path (0.3 m wide) did not influence the snails' movement. Our results suggest that snail populations separated by paved roads with high traffic densities may be isolated from each other.