Data from: Functional connectivity in replicated urban landscapes in the land snail (Cornu aspersum)

Urban areas are highly fragmented and thereby exert strong constraints on individual dispersal. Despite this, some species manage to persist in urban areas, such as the garden snail, Cornu aspersum, which is common in cityscapes despite its low mobility. Using landscape genetic approaches, we combined study area replication and multi-scale analysis to determine how landscape composition, configuration, and connectivity influence snail dispersal across urban areas. At the overall landscape scale, areas with a high percentage of roads decreased genetic differentiation between populations. At the population scale, genetic differentiation was positively linked with building surface, the proportion of borders where wooded patches and roads appeared side-by-side and the proportion of borders combining wooded patches and other impervious areas. Analyses based on pairwise genetic distances validated the isolation-by-distance and isolation-by-resistance models for this land snail, with an equal fit to least-cost paths and circuit-theory-based models. Each of the 12 landscapes analyzed separately yielded specific relations to environmental features, whereas analyses integrating all replicates highlighted general common effects. Our results suggest that urban transport infrastructures facilitate passive snail dispersal. At a local scale, corresponding to active dispersal, unfavorable habitats (wooded and impervious areas) isolate populations. This work upholds the use of replicated landscapes to increase the generalizability of landscape genetics results, and shows how multi-scale analyses provide insight to scale-dependent processes.

城市区域具有高度的生境破碎化特征，因此会对个体扩散施加极强的限制作用。尽管如此，仍有部分物种能够在城市区域存续，例如庭园蜗牛（Cornu aspersum）——尽管其移动能力较弱，却在城市景观中极为常见。本研究采用景观遗传学（landscape genetics）方法，结合研究区域重复采样与多尺度分析，探究景观组成、配置及连通性如何影响蜗牛在城市区域内的扩散过程。在整体景观尺度下，道路占比高的区域会降低种群间的遗传分化水平。在种群尺度上，遗传分化水平与建筑用地占比、林斑与道路相邻的边界比例，以及林斑与其他不透水区域相邻的边界比例呈正相关关系。基于成对遗传距离的分析验证了该陆生蜗牛的距离隔离（isolation-by-distance）与阻力隔离（isolation-by-resistance）模型，且其与最小成本路径（least-cost paths）及基于电路理论（circuit-theory）的模型拟合程度相当。对12个景观分别开展的独立分析均得到了与环境特征相关的特异性关联，而整合所有重复采样的综合分析则揭示了普遍存在的共性效应。本研究结果表明，城市交通基础设施可促进蜗牛的被动扩散；而在对应主动扩散的局域尺度上，不适生境（林斑与不透水区域）会导致种群间的隔离。本研究证实了采用重复景观设计可提升景观遗传学研究结果的普适性，并阐明了多尺度分析如何为尺度依赖的生态学过程提供研究视角。