Dispersal of a non-native land snail across a residential area is modified by yard management and movement barriers

Urban areas with residential yards (= domestic gardens) provide a diverse environmental mosaic characterized by high plant architectural and species diversity and variation in yard management practices among residents. For small, slow-moving taxa such as land snails, this mosaic provides an unplanned experiment to document dispersal patterns and conditions influencing this pattern. The snail Cornu aspersum is a Mediterranean-native that was likely introduced into a Norman, Oklahoma (USA) yard through the plant trade. Cornu spread across 16 residential yards (and up to 110 m) in a single block over a period of at least 6 years, moving in a diffusive dispersal pattern. Supplemental water (e.g., watered plant beds and ponds) combined with nearby shelters contributed to increased local density but may also result in targeted snail control. Although roads contributed to the species arrival, roads were barriers to short-term snail self-dispersal and the limited road crossing may have been human-mediated (e.g., snails carried on potted plants). Dispersal was limited across non-residential properties with expansive grass lawns and parking lots. Residential areas provide a good model system for examining factors associated with the spread of non-native species, especially for species having low mobility.