Population structure of alien and native species of land snails in the conditions of the south of the Central Russian upland

The spread of a species beyond its natural range begins with the introduction of individuals into a new territory and the reproduction of the invader population. One of the key aspects of the invasion process is the interaction of an invading species with native one. Over the past ten years, populations of the alien land snail Xeropicta derbentina have been discovered in several locations in the Belgorod region within urbanized biotopes. One of these populations inhabits the biotope together with an indigenous land snail that has similar ecological requirements - Caucasotachea vindobonensis. During the mollusk activity season in 2022 and 2023, a study of the demographic structure and spatial organization of the populations of X. derbentina and C. vindobonensis was carried out in the south of the Belgorod region using the quadrant sampling method. It was revealed that the density of both populations is quite high, reaching its highest values in early to mid-summer. In all months of observation, with the exception of May 2023, significant differences in the population densities of X. derbentina and C. vindobonensis were revealed. At the same time, the population density is higher in the invasive species and averages 19-28 individuals/m2 in June-July. Nevertheless, the indicators obtained for C. vindobonensis are not critical for this species: in May-July, the average density is 4-12 individuals/m2. These values are consistent with our previous research and other studies. The spatial structure of both populations is predominantly of a random type, which may be due to the uniformity of conditions in the study area and the lack of interactions between species. We also did not detect any spatial cross-correlation between the two populations. The data obtained indicate the absence of a negative impact of the invader on the native species in the territory we studied.