First data on population estimates and dispersal of Montenegrina subcristata – a field study at Virpazar, Montenegro

Abstract

Background. In this study a population of the rock dwelling terrestrial gastropod Montenegrina subcristata was monitored over one season and data about life cycle, population density and dispersal were gathered. Three study sites (A, B, C) near Virpazar, Montenegro were selected. Snails were categorized into three size classes. (1) The smallest juveniles were counted but not marked because of their tiny and dainty shell, middle sized snails (2) were marked with a dot and (3) larger subadults and adults were marked with an individual number. The sites were observed 25 times from April to October 2017. The study sites were equipped with data loggers to register microclimate data like temperature and humidity. Based on counts and recapture counts population estimates were calculated. Positions of the snails were recorded throughout the season and minimum distances between each two observations were calculated.Results. Small juveniles (not marked) were observed in high numbers at the beginning of the season and disappeared during summer. Site C had to be excluded from the calculations because snails nearly disappeared as early as the second visit. Population size estimations of sites A and B provided similar results for the beginning of the season, whereas for June the high estimates stood in high contrast to the number of observed snails in that period. Concerning "minimum distances" (MD; distance between two subsequent observations), the majority of MDs with a 1-week interval resulted in 0–0.1m. Yet, some individuals were more mobile, with sums of MDs over the season of up to 8.0 m. The sum of MDs over the season was on average 1.6 m (sites A+B).The temperature and humidity curves of the data loggers showed a seasonal pattern. The average temperatures of all three sites were rather similar. However, daily oscillations in temperature and humidity were high in some periods and differed between sites. In site C temperature and humidity extremes and fluctuations were pronouncedly higher, with the highest temperatures reaching more than 60 °C and relative humidity dropping each day below 3.7% in June.Conclusions. Dispersal ability is in general low but single individuals might cover distances of at least several meters over the season. Together with further observations we conclude that fluctuations of population size can be considerable and might be strongly influenced by climatic conditions. On the other hand, also population estimates may be influenced by climatic conditions. This study provided first hints to assess the potential of migration, local extinction and recolonization in Montenegrina and other rock dwelling snails.