Interspecific competition among terrestrial slugs

ABSTRACT Interspecific competition among terrestrial gastropods has previously been considered to have little effect on population dynamics and local distribution. Recent studies, however, demonstrate several cases in which interspecific competition plays a major role in structuring terrestrial gastropod communities. To explore the general importance of interspecific competition for the ecology of slugs, we conducted a semi-systematic literature review, synthesizing available peer-reviewed literature relating interspecific interactions to the following: (1) mortality and reproduction; (2) activity, movement, feeding and growth; and (3) habitat use and geographical distribution of slugs. To support the literature on slugs, we also reviewed literature on terrestrial snails. The body of available literature is relatively limited, but the effect of interspecific competition on survival, reproduction, movement and activity has clearly been demonstrated in laboratory experiments for different slug species. The occurrence of interspecific competition seems, however, to be species specific, and no negative effects due to the presence of heterospecifics have been reported for many of the species combinations investigated to date. Most of the studies demonstrating interspecific effects between slug species involved interference from a few aggressive species (mainly Limax maximus as the aggressor). In addition, several correlative studies have indicated that in terrestrial gastropods, habitat use and geographical distribution might be mediated by interspecific competition. Further, well-designed experiments are needed to explore the general importance of interspecific competition among slugs, potentially with a focus on interactions between invasive and native species, where the lack of a shared evolutionary history and niche separation may increase the intensity of competition. Such experimental studies may produce information that has implications for the conservation of native species, as well as for management of invasive pests, because interspecific competition may result in local extinction of vulnerable species and influence the possibility of non-native species establishing invasive populations in new areas.