The habitats of the land snail Cepaea nemoralis (L.) on downland and their ecogenetic significance

Population densities of adult Cepaea nemoralis (L.) were estimated for nine chalk grassland sites on the South Downs. Estimates of cover, species composition and height of vegetation were also obtained. The density of C. nemoralis was positively associated with Bromus erectus cover, and negatively with Festuca spp. cover. This finding, confirmed by an earlier survey, suggests that the density of C. nemoralis in chalk grassland is directly or indirectly governed by mammalian grazing pressure, and not by the availability of suitable food. Intensely grazed downland is an unsuitable, or at best a marginal habitat for C. nemoralis. This conclusion is discussed with particular reference to ‘area effects’ in the shell character polymorphism, often found in downland populations of C. nemoralis.