Intra- and Interspecific Influences on Age at First Reproduction and Fecundity in the Land Snail Balea perversa

The influences of conspecific density and of presence of a competitor (the land snail Chondrina clienta) on both age at first reproduction and reproductive output in the rock-dwelling land snail Balea perversa were evaluated in a laboratory experiment. Since adult size of B. perversa decreases with increasing density of conspecfics, fecundity was also examined for size-dependence. Age at first reproduction of B. perversa was positively correlated with time to complete shell growth. Both increased with density of conspecifics, indicating intraspecific competition. By contrast, the presence of C. clienta did not influence the age at first reproduction of B. perversa. However, both fecundity (number of young produced per adult snail during the experiment) and reproductive rate (number of young produced per 100 days of adult life) in B. perversa were negatively affected by increased density of conspecifics and by the presence of C. clienta, indicating intra-and interspecific influences. No relationship was found between shell size of B. perversa and number of young produced. This suggests that the reduced fecundity of B. perversa was caused by conditions experienced during adulthood rather than by the smaller adult size as a result of growth under crowded conditions.