Anthropogenic Disturbance Shapes Native-Alien Community Patterns Across Urban-Rural Gradients in a Neglected Invertebrate Model System.

Land snails represent a diverse yet understudied group of organisms, with new species continuously being described. However, numerous extinctions have recently occurred, largely due to the introduction of alien counterparts. Urbanisation and habitat disturbance are well-known to promote the spread of opportunistic and alien species, but their effect on alien land snails has seldom been investigated. This research aimed to test whether alien snails' presence and abundance can be influenced by proximity to roads, water sources and human structures, as well as the site size and the presence of native species. Snail populations were surveyed in eight woodland sites across Oxfordshire, U.K., using systematic quadrat sampling. Species identification was based on morphological characteristics, complemented by molecular analyses for taxonomically ambiguous taxa. A total of 24 species (grouped in 23 taxa) were identified, including five aliens. The results indicate that alien snails are more prevalent in smaller and disturbed areas, with their abundance decreasing with increasing distance from roads. The presence of native species appears to exert biotic resistance against invasions, particularly in larger and less disturbed sites. These results highlight the critical role of human activities in shaping land snail communities, evidencing that roadsides can act as important corridors for alien species dispersal. In contrast, larger rural sites, with richer native communities, provide biological resistance against invasions. Given the growing trends of urbanisation and habitat alteration, future conservation strategies should focus on mitigating anthropogenic disturbances and preserving larger, interconnected natural areas to support native biodiversity and limit biological invasions.