The Role of Microhabitat and Water Level in Regulating the Small-Scale Distribution, Seasonal Abundance and Overwintering Success of the Protected Snail Vertigo moulinsiana in a Natural Wetland

ABSTRACT Despite the high taxonomic diversity, wide distribution and important ecosystem functions of snails, their ecology remains obscure, and this can hamper their conservation. Overwintering in the studied population of Vertigo moulinsiana is effective enough to allow the majority of it to survive. The population dynamics of V. moulinsiana is specific, where the summer boom in a suboptimal habitat covering a small area (wet patches of sweet grass) can determine the snail's range over much larger areas. Our results suggest that humidity could have been the major factor governing population increase. The summer boom is caused by juveniles appearing in very large numbers during this period, thus the peak height is mostly influenced by the considerable susceptibility of juveniles and eggs to desiccation. The limiting influence of humidity is evident in the unequal spatial distribution of individuals: the wetter the substrate, the greater the abundance of snails. As a consequence, the boom may be spatially regulated and only occurs in wet habitats, even though the snail actually occupies a much larger area. Our results indicate that this V. moulinsiana population does not follow typical models constructed for vertebrates or other animals with high dispersal abilities, like the Ideal Free Distribution (IFD) model, and requires a specific approach. Its specific spatiotemporal pattern should be taken into account during monitoring surveys and conservation actions.