Density variation in a natural population of the land snail Pomatias elegans (O. F. Müller, 1774) in a beech forest in Switzerland: A 15-year study

Population density is a key factor in ecological and evolutionary processes. Using a mark-release-recapture method, we examined the population density of the land snail Pomatias elegans (O. F. Müller, 1774) in a nature reserve with beech forest in northwestern Switzerland over a period of 15 years (2004–2018). To examine whether the population density of P. elegans is influenced by microhabitat characteristics, we recorded annually leaf litter cover, thickness of the leaf litter layer, and shrub cover in the study area and measured the shell height of all snails found. Recapture rate of marked P. elegans after 3–6 days averaged 48.1% (range 24.0–60.0%). Linear mixed model (LME) analysis revealed that recapture rate was reduced as the time between release and recapture increased. Furthermore, the recapture rate was negatively influenced by increasing leaf litter cover and positively affected by increasing shrub cover. Overall population density of P. elegans averaged 6.9 individuals/m2 over the entire study period, with an annual fluctuation between 2.8 and 16.8 individuals/m2. LME-analysis showed that the population density was positively influenced by the percentage of ground covered with leaves, but negatively affected by increasing thickness of the leaf litter layer and increasing shrub cover. Individual shell growth of marked snails found in two consecutive years showed that shell growth depends on the size of the animals. Individual shell growth is initially rapid and becomes progressively slower as the snails increase in size. Shell growth of large individuals is very low, suggesting that these snails have started reproductive activities.