Intra- and Interspecific Effects of Population Density on Growth and Activity in Some Helicid Land Snails (Gastropoda: Pulmonata)

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Abstract
Growth-rates and activity of juveniles of the land snails Cepaea nemoralis (L.) and C. hortensis (Mueller) in the laboratory were inversely related to density in the range of 1-8 snails/box of 1000 cm2 internal surface area. Single C. nemoralis in boxes of 125 cm2 surface area were more active, and grew faster, than 8 in 1000 cm2 boxes. The influence of other snails or their products is therefore an important part of the effect. Interspecific density effects for Cepaea could not be distinguished from intraspecific effects at the combination of densities investigated. The activity of C. nemoralis and C. hortensis, and possibly of Helix aspersa (Mueller) is reduced in boxes pretreated with mucus trails of the same species. The activity of C. hortensis is reduced by pretreatment with C. nemoralis mucus. H. aspersa mucus has no effect on the activity of Cepaea. Chromatography reveals close similarity in the mucus of C. nemoralis and C. hortensis and that of H. aspersa is distinct. The possibility of growth inhibiting pheromones in snail mucus is discussed in relation to the population dynamics of the species and to the results of other studies.