Changes in the spatial structure of the Eremias arguta Deserti population in semi-deserts of the Astrakhan region

Materials on the spatial structure of the lizard Eremias arguta deserti (Gmelin, 1789) were collected in the sandy semi-deserts of the Astrakhan region during the 2017-2019 field seasons. Three-year studies at the level of intra-population grouping show a gradual reduction in the population size from season to season. During the mating season, the spatial structure of the grouping is first transformed from a system of overlapping individual plots of males and females (2017) into a system of isolated territories of sexual partners (2018), and then into a small grouping of isolated home ranges of females (2019). This is due to the fact that lizards are dispersed in the area of decreasing inherent open biotopes. The decrease is also typical for the nomadic part of the grouping, which confirms the general decline in the population in the surrounding area. The group is gradually ceasing to reproduce, as evidenced by the absence of immature individuals in all spring seasons and a decrease in the number of current year’s young at the end of summer 2018 compared to the same period in 2017. The main reason for the described process of population degradation is a change in the biotope characteristic of the species - the overgrowth of sand massifs, which has been observed in recent years in many areas of desert and semi-desert ecosystems. Observations show that the negative consequences of biotope overgrowth are the deterioration of conditions for movement and communication. The measurement of the projective cover and plant species diversity of phytocenosis, carried out on sample geobotanical plots in 2011, 2014 and 2017, indicates that the territory is being transformed into steppe. The main reason for steppification is the increase in total precipitation over the past decade from 2010 to 2019. The latter is confirmed by a positive correlation between the increase in the projective cover and the total amount of precipitation over this period.