Meeting Abstract
As nocturnal detritivores, slugs have a large, but often unrecognized, role in nutrient cycling within many ecosystems. The banana slug (Ariolimax columbianus) is the second-largest terrestrial slug in the world and had no comparably-sized competitors in its evolutionary history until Arion rufus was introduced from Europe within the last century. Transect surveys over the past four summers on San Juan Island, Washington state, indicate that the relative frequency of these two slug species is shifting dramatically in some locations, with the invasive species becoming much more common than the native banana slug, perhaps in part due to impacts of drought. These two species (even the invasive species from different microhabitats) have similar food preferences and general feeding rates. While the slugs’ catholic diet on relatively common foods may reduce competition, they both demonstrated a very strong preference for particular moist food items that are ephemeral and patchily distributed. This preference may indicate that particularly limited resources, especially for moisture in dry seasons, produce intense competition, and that the invasive species is a superior competitor to the native species in accessing these ephemeral, patchy, important food resources.
