The effects of food and density on the nocturnal behaviour ofArion ater andAriolimax columbianus (Pulmonata: Stylommatophora)

Summary The effects of food supply and population density on the nocturnal behaviour ofArion ater andAriolimax columbianus were investigated. Density did not significantly affectA. ater's level of activity or short-term movement, resting, or feeding.A. columbianus was more active and moved, rested, and fed more frequently when slug density was high.A. ater foraged and rested more often, but fed less when good food was unavailable.Ariolimax's only response to the food regime was to feed more when good food was available. Seasonal changes in the level of activity and behaviour ofArion were evident, whereasAriolimax's activity and behavioural repertoire were not similarly affected.Arion ater's nightly activity appeared to be mainly food oriented, whileAriolimax columbianus seemed most responsive to slug density during its nocturnal activity periods.