Die Nacktschneckengesellschaften in NW-Deutschland (Gastropoda: Milacidae, Boettgerillidae, Limacidae, Agriolimacidae, Arionidae): ein Ergebnis der NRW-Kartierung

Slug assemblages in NW Germany (Gastropoda: Milacidae, Boettgerillidae, Limacidae, Agriolimacidae, Arionidae): a result of the mapping survey of Northrhine-Westphalia. This survey provides information on inter-specific associations of slugs on a regional data base. Most of the data originate from the last ten years. In total, 25 slug species are known from the federal state Northrhine-Westphalia, Germany. A rough classification using two character species resulted in three groups. These groups correspond to habitat preferences, i.e. species that are regularly found together with Arion rufus usually occur in close-canopy forests and mid-successional stages, species that are regularly found together with Arion lusitanicus prefer open habitats to mid-successional stages, and the intermediate group inhabits either only midsuccessional stages, or all habitat types. This relation held true with the exception of one rare species, Deroceras agreste. This species was classified as intermediate based on the character species, but so far was only found in open habitats. This seemingly conflicting result is the outcome of a recent species turnover in open habitats. In some of the site, Deroceras agreste still co-occurred with Arion rufus, whereas in others the invasive species Arion lusitanicus had already established. In the last decades, Arion rufus has lost almost all sites in open habitats. Nowadays, it is mainly restricted to close-canopy forests that seem not to be invaded by Arion lusitanicus.