Mollusc grazing and seedling survivorship of four common grassland plant species: The role of gap size, species and season

Two experiments conducted in spring and autumn 1992 examined the effect of mollusc grazing and gap size on seedling survivorship for four common grassland species (Plantago lanceolata, Ranunculus acris, Senecio jacobaea and Taraxacum officinales) sown into artificially created gaps in plots in a grassland sward. Molluscs were excluded from half the plots by application of molluscicide. The intensity of mollusc grazing was greatest in autumn, although mollusc grazing in the spring experiment also reduced seedling survivorship. A close relationship between seedling identity, season and survivorship was found. All four species were adversely affected by the presence of molluscs, although Senecio jacobaea populations were only affected in the spring and Plantago lanceolata in the autumn. While gap size significantly influenced seedling survivorship, this factor had no effect upon mollusc feeding behaviour. The relative importance of seedling palatability, morphology and seasonal changes in mollusc herbivory is considered and the role of molluscs as a selective force in determining the species composition of grassland communities is discussed.