Meeting Abstract
The invasive terrestrial slug Arion rufus was introduced to San Juan Island, WA, within the last century and represents a novel potential competitor to the native banana slug Ariolimax columbianus as no other local pulmonate attains such a size. Building on past findings, we investigated the feeding rates and preferences of these two species. Both species (regardless of size class) preferred mushrooms (Agaricus bisporus) to pathfinder (Adenocaulon bicolor), sword fern (Polystichum munitum), and lichen (Usnea sp.). However, when mushrooms were oven-dried and lichen was super-hydrated, both species of slugs switched their preference to the lichen, suggesting that moisture and texture are more important here in dictating food choice than are nutrients and taste. Mushrooms in both the local forested areas and grasslands are typically scarce, patchily distributed, with a small biomass compared to common local plants, and so may represent an important limited resource that might promote inter- and intra-specific competition. Additionally, we observed the effects of temperature (5°C, 10°C, and 20°C) on feeding rates (consuming spinach leaves and stinging nettles, in separate experiments) in both species of slugs. Surprisingly, despite the fact that slugs are ectothermic, we found no evidence of increased feeding rates with increasing temperature across this range. Again, moisture levels, which differed slightly across our chambers, may be more important than temperature. These considerations may be critical in predicting how these terrestrial slugs may respond to impending climate changes.
