Abstract. Overexploitation, habitat destruction and a changing climate threaten populations of the Roman snail (Helix pomatia Linnaeus, 1758), which has led to a high protection status in Germany. Vertebrate and invertebrate predators, including parasites and facultative parasitoids, further cause pressure on populations. Given the conservation concern for H. pomatia and its rarity in the study region (Cottbus, Germany), we studied how predators and facultative parasitoids utilize H. pomatia shells with a focus on non-invasive field methods. As previous studies indicated that shell size may affect prey selection by predators, morphometric traits were measured in eight subpopulations. We identified the total number and percentage of H. pomatia shells that showed external attack marks by predators and internal utilization marks by Diptera pupae and related those utilization patterns to the morphometric traits of shells. A large proportion of the shells in local subpopulations showed signs of external attack and internal utilization, and both utilization forms were positively correlated. External attacks by predators were more frequent in larger shells and internal utilization by Diptera was more common in shells with higher body density. These results suggest a considerable pressure by predators and potential facultative parasitoids on H. pomatia populations in the study area. Future research should focus on the relationship between snails from the family Helicidae and flies from the genus Discomyza. Conservation programmes should consider abiotic habitat conditions together with potential trophic interactions to maximize the success of conservation strategies.

中文翻译：

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贝壳的形态特征决定了德国东部罗马蜗牛的外部攻击和内部利用标记

摘要。过度开发、栖息地破坏和气候变化威胁着罗马蜗牛的种群（Helix pomatia Linnaeus，1758），这导致了德国的高度保护地位。脊椎动物和无脊椎动物捕食者，包括寄生虫和兼性寄生蜂，进一步对种群造成压力。鉴于对 H. pomatia 的保护问题及其在研究区域（德国科特布斯）的稀有性，我们研究了捕食者和兼性寄生蜂如何利用 H. pomatia 壳，重点是非侵入性现场方法。由于先前的研究表明外壳大小可能会影响捕食者对猎物的选择，因此在八个亚群中测量了形态特征。我们确定了 H. pomatia 贝壳显示出捕食者的外部攻击标记和双翅目蛹的内部利用标记，并将这些利用模式与贝壳的形态特征相关联。当地亚种群中很大比例的贝壳表现出外攻和内利用的迹象，两种利用形式呈正相关。在较大的贝壳中，捕食者的外部攻击更为频繁，而双翅目在身体密度较高的贝壳中的内部利用更为常见。这些结果表明，捕食者和潜在的兼性寄生蜂对研究区的 H. pomatia 种群造成了相当大的压力。未来的研究应集中在螺旋科蜗牛与飞蝇属的苍蝇之间的关系上。