THE EFFECT OF SEEDLING AGE ON THE LIKELIHOOD OF HERBIVORY BY THE SLUG DEROCERAS-RETICULATUM

1. The effect of seedling age on the risk of predation by molluscs was investigated for three common grassland species by exposing uneven-aged seedling assemblages (monoculture and mixed species) to grazing by the slug Derocerus reticulatum in experimental trays in greenhouse conditions. 2. In monoculture, seedling age was found to influence significantly the risk of mollusc attack on both Senecio jacobaea and Taraxacum officinale. By contrast, the risk of attack on Veronica persica seedlings was unrelated to seedling age. 3. In a mixture of Taraxacum and Senecio seedlings, Taraxacum seedlings were not selected by slugs on the basis of age as they were in monoculture. Senecio seedlings in mixture with Taraxacum were generally grazed upon less than conspecifics in monoculture, although the effect of seedling age upon relative susceptibility to herbivory was broadly the same as in monoculture. 4, The results demonstrate that the timing of herbivory by molluscs can be crucial in determining the survivorship of a cohort of seedlings. The effects which seedling morphology, changes in seedling palatability with age, relative growth rates and pattern of association with neighbours have upon mollusc feeding behaviour are discussed, high-lighting the role molluscs play as an important selective force in plant communities.