Meeting Abstract
The recent pattern of replacement of populations of the native banana slug (Ariolimax columbianus) by the invasive terrestrial slug Arion rufus on San Juan Island, Washington state, USA, may be due to differences in susceptibility to desiccation rather than direct competition. While both species are poikilotherms, the native species is endemic, so it is likely even more sensitive to environmental changes. Recent years have been aberrantly hot and less humid. Field collections examining the level of hydration of different subpopulations of these two species indicated some small differences. However, in general both the hydration levels and the evaporation response of the two species of slugs to maintenance at different temperatures was surprisingly similar, and elevating maintenance temperature by 10oC did not necessarily increase the amount of evaporation. Therefore, it appears unlikely that physiological differences in susceptibility to desiccation are the main factors driving the recent differences in population dynamics. Alternative hypotheses, such as competition for food or shelter, should be investigated.
