Ecology of the terrestrial snail (Brephulopsis bidens): age composition, population density and spatial distribution of individuals

Studies were carried out during the spring, summer and autumn seasons of 1974–1976 on a natural population of the terrestrial snail Brephulopsis bidens (Pulmonata: Enidae), located on a mountain in Crimea (USSR). The overall population was characterized by a high density (50.2–124.4 ind/m² in 1974, 61.3–162.5 ind/m² in 1975 and 27.8–157.3 ind/m² in 1976) and a strongly pronounced congregational tendency of snails. There was a significant correlation (r=087, P <O.O1) between the mean number and size of snail colonies on random 10 × 10 m areas during active season. The proportion of sexually mature snails reached maximum (70–80%) in autumn before the hibernation, and was minimal (about 25%) in the spring. The better winter survival of the pre‐adolescent snails (81.7%vs 56.3%) and their earlier emergence from the ground following hibernation, both explain the preponderance of young molluscs observed in the spring. Density and spatial distribution of individuals were subject to considerable seasonal and spatial variability. Seasonal variation of the active snails density in dry years seemed to depend on the amount of rainfall (r=0.93). Spatial distribution of the molluscs significantly correlated with humus as well as with the nitrogen and magnesium ion concentration.