Differing responses of native and non-native slugs (Mollusca: Gastropoda) to local vegetation structure and landscape composition in cool-temperate forested wetlands

Slugs are fungivores, herbivores, carnivores and decomposers that provide important ecosystem services and disservices in natural and disturbed habitats. Our aim was to estimate the effects of local vegetation structure (tree basal area and canopy openness) and landscape composition (land cover types) on the occurrence of native and non-native slugs in 13 cool-temperate forested wetlands across Nova Scotia, Canada. We collected 1437 slugs of eight species (five non-native species and three native species). The non-native Arion subfuscus and Arion fuscus were dominant, and together represented 84.3% of all the slugs collected. The native Deroceras laeve and the non-native Arion hortensis were also relatively common. Among Arion species A. subfuscus was positively associated with open wetlands within a 1000 m radius, whereas A. fuscus and A. hortensis were positively associated with road density within 250 and 750 m radii, respectively. The native species Deroceras laeve and Pallifera dorsalis did not respond to local vegetation and landscape composition. These findings suggest that forested wetlands across Nova Scotia are dominated by non-native Arion species that benefit from road systems and non-forested habitats in the surrounding landscape. The absence of effect on the native species D. laeve and P. dorsalis suggests these species can forage in multiple mainly forested habitats that were the dominant land use types in the studied landscapes. Such information is crucial to fill knowledge gaps and support priority actions for tackling biological invasions at appropriate spatial scales.