There were significant effects of both plant and snail density on total above-ground biomass and mean plant biomass with no evidence of interaction. There was a significant interaction between plant and snail density in influencing variation in plant size. Variability in plant size was higher at high plant density. At this density, herbivory had very little effect on plant size variability, perhaps because the primary effect of snails was to reduce plant density slightly. At low plant density, a high level of herbivory increased plant size variability by reducing the size of some plants while not affecting the largest individuals. -from Author