The Potential for Seed Dispersal by the Banana Slug (Ariolimax columbianus)

Abstract

We observed wild banana slugs (Ariolimax columbianus) eating fruits of several Pacific Northwest plant species. Slime trails and direct observations indicated that slugs are capable of reaching the fruits of many wild plants. This motivated us to test the hypothesis that slugs may act as seed dispersers, provided that they defecate viable seeds. We fed captive slugs the fruits of Rubus spectabilis, R. discolor, Vaccinium ovatum, V. parvifolium, Gaultheria shallon and Disporum smithii to determine the effects of slug ingestion on seed germination. At least some seeds of each species germinated after the fruits were consumed by the slugs, but the effects on germination were species-specific. Seeds of Rubus spectabilis were less likely to germinate after passage through the guts of slugs, and we found significant evidence that the two fruit color morphs reacted differently over time. Disporum smithii seeds did not statistically differ in germination behavior between treatments, although the trend suggested possible germination enhancement following rasping of the seeds by slugs. All other species of seeds tested germinated following consumption by slugs, but results could not be tested statistically. Gut passage times of R. discolor seeds were determined (x̄ = 25.4 h, se = 3.6 h). We conclude that despite the short distances slugs are likely to disperse seeds, their generalist habits and ubiquity suggest that they may have complex and ecologically significant effects on seed dispersal in Pacific Northwest forests.