Interspecific competition plays a major role in organizing biological communities. Competition can involve direct (e.g. aggression) or indirect (e.g. avoidance) interactions, and can influence the behaviour, distribution and fitness of interacting species. Competition appears to be common among marine and terrestrial snail species, but the potential role of interspecific competition in the structure of terrestrial slug communities remains poorly known. This study examined whether competition between two terrestrial slug species, Geomalacus maculosus and Lehmannia marginata, contributes to the abundance of each species in a modified habitat (commercial conifer forest) in Ireland. Geomalacus maculosus is an EU-protected species but was probably an ancient introduction to Ireland, whereas L. marginata is unprotected but is native and widespread. A negative association was observed between the abundances of each species in field plots, sampled fortnightly over a 19-month period. The presence of other slug species and some environmental variables also influenced the abundances of L. marginata and G. maculosus. Behavioural experiments found no evidence of direct aggressive interactions between G. maculosus and L. marginata. However, L. marginata exhibited an aversion to G. maculosus mucus trails, suggesting an indirect mechanism of competition. Conversely, G. maculosus behaviour was not modified by the presence of L. marginata mucus. Results from field and laboratory studies together suggest that both species may compete in modified habitats. To our knowledge, these results provide the first experimental evidence of a negative long-term association between sympatric slugs, and the first evidence that mucus trails can act as a mechanism of interspecific interference competition in slugs.

中文翻译：

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欧盟保护的克里弹头GeoGeomalacus maculosus与爱尔兰原生树弹头Lehmannia marginata之间的干扰竞争迹象

种间竞争在组织生物群落中起主要作用。竞争可能涉及直接（例如侵略）或间接（例如避免）相互作用，并且可能影响相互作用物种的行为，分布和适应性。竞争似乎在海洋和陆地蜗牛物种中很普遍，但是种间竞争在陆地虫群落结构中的潜在作用仍然知之甚少。这项研究调查了两种陆生species物种（Geomalacus maculosus和Lehmannia marginata）之间的竞争是否有助于爱尔兰改良栖息地（商业针叶林）中每种物种的丰度。斑是受欧盟保护的物种，但可能是爱尔兰的古老引进，而缘缘乳杆菌没有受到保护，但是本土的且分布广泛。在19个月的周期中每两周采样一次的田间样地中，每个物种的丰度之间都存在负相关。其他物种的存在和一些环境变量也影响了L. marginata和G. maculosus的丰度。行为实验发现没有证据表明斑线兰和边缘线虫之间有直接的积极相互作用。然而，边缘乳杆菌对斑纹粘菌径迹表现出厌恶，表明存在竞争的间接机制。反过来，边缘乳杆菌的存在并不能改变黄斑霉菌的行为。野外研究和实验室研究的结果共同表明，这两种物种可能在改良的栖息地中竞争。据我们所知，这些结果提供了同胞之间长期负相关的第一个实验证据，以及粘液踪迹可以作为trail中种间干扰竞争的机制的第一个证据。