Seasonal variation of microhabitat distribution of the polymorphic land snail Cepaea nemoralis

We studied the seasonal variation of microhabitat distribution of the land snail Cepaea nemoralis over a 3-year period in a population at Dansville, New York. Stratified random quadrat sampling was used to determine snail densities and environmental variables in each month. The plant cover of each quadrat was estimated by a modified Daubenmire measure. Canonical correlation analysis was used to investigate the relationship between the morph density and the environmental variables. Significant relations existed between snail morphs and environmental variables in 8 of the 13 months analyzed. Temperature and rainfall are two important factors affecting such relations. In hot and dry summer months, morphs had a stronger canonical correlation with the environmental variables than in cool and wet months. Food and shelter were important in determining distribution over habitats of the snail. Food was primarily responsible for snail distribution over habitats in the early summer. As the weather became hot and dry, the importance of shelter became more evident. Both banded and unbanded morphs tended to be associated strongly with sheltered microhabitats in hot dry seasons.