Spatial structure of the spotted toad agama (Phrynocephalus guttatus guttatus, Agamidae) population in the conditions of overgrowth of semi-deserts in the Astrakhan region

The decrease in the number of many reptile species as a result of overgrowth of sandy deserts and semi-deserts is a widespread phenomenon in modern conditions. To understand the prospects of this process, it is necessary to study the mechanisms of population adaptation to changes in the biotope. Such a mobile and effective mechanism is, first of all, a change in the spatial structure of the population, the study of which does not cease to be relevant. The purpose of this study was to clarify the changes occurring in the spatial structure of the spotted toad agama, Phrynocephalus guttatus guttatus (Gmelin, 1789), and their relationship with the developing process of overgrowth of sandy semi-deserts in the Astrakhan region. The data were collected during the 2010-2014 and 2017-2019 field seasons. The place of research was a section of sandy semi-desert near the village of Dosang (46°54'08.7264"N, 47° 54'52.5312"E). In the work, standard methods were used: marking, sex and age determination, mapping of meetings and movements, identification of sedentary and migrating individuals. Investigation of overgrowth processes was based on the description of geobotanical sites. Statistical processing was carried out based on the Mann-Whitney U-test. Software consisted of a set of standard programs, Adobe illustrator and Yandex Map Constructor. The analysis of long-term studies of the spatial structure of the grouping allowed us to build a model of adaptation of the population to the reduction of characteristic habitats. At the initial stages of overgrowth of semi-fixed sands, there was a general increase in the mobility of animals, expressed in an increase in the number of individuals migrating in search of a suitable biotope. The reduction of the biotope caused the re-consolidation of the sedentary population of the grouping. This process occurred during the third and fourth seasons of research. Over-compaction was followed by a decrease in the rate of reproduction, manifested in a reduction in the number of immature individuals. As a result, the combination of factors led to a further decrease in the number of individuals (the fifth year of observations). The ongoing process of overgrowth and the reduction in the number for the tenth year of research resulted in the disintegration of the grouping into parts and a decrease in the population as a whole. The general decrease in the population was confirmed by observations in the adjacent territory and the almost complete disappearance of migrants in the grouping.