On the extinction of the intra-population group of the lizard Phrynocephalus mystaceus mystaceus (Pallas, 1776) in the overgrown semi-deserts of the Astrakhan region

Five-year observations of the intra-population grouping of the toad-headed agama Phrynocephalus mystaceus mystaceus (Pallas, 1776) were carried out in semi-deserts of the Astrakhan region. It showed a reduction in its number up to complete extinction in this territory. The main reason for the degradation of the grouping was the overgrowth of weakly fixed and semi-fixed sandy areas - a typical biotope for the species. The process of overgrowth is shown on the materials of the description of geobotanical sites, the projective cover of which significantly increased during the observation period. The nucleus of the intra-population group was composed of sedentary sexually mature individuals, and its stability was determined by attachment to the site of females that repeatedly met in the study area in successive seasons. Sedentary males and females disappeared from the territory at the same time. The experience of significant changes by the species grouping in the characteristic biotope for a lot of years was due to the influx of migrants passing through the studied territory. This mechanism is well known in mammals and insufficiently studied in reptiles. The flow of migrants mainly consisted of immature individuals, an age group with increased mobility, which usually serves the purpose of resettlement. The decrease in the influx of nomadic individuals, apparently related to the general decline in the number of species in the surrounding area, led, in the end, to the disappearance of the group.