Peculiarities of the Population Structure in the Settlement of the Secret Toad-Headed Agama Phrynocephalus mystaceus (Pallas, 1776) (Lacertilia: Agamidae) on the Sarykum Sandy Massif

The research results on the secret toad-headed agama (Phrynocephalus mystaceus mystaceus Pallas, 1776) population structure on the Sarykum sandy massif (N 43°00′23.9′′, E 47°14′04.3′′) are presented. The purpose of this study was to clarify features of the lizard population structure in the conditions of an island habitat: an isolated sandy area. The species’ settlement in Sarykum featured a very high population density, averaging 82.1 ind./ha, a relatively small average size of individual home ranges and their significant overlap within sexual groups, namely, 69.7 ± 33.32% for males, on average; 50.7 ± 35.92% for females; and 57.5 ± 39.41% between the home ranges of females with males, respectively. The overlap of home ranges within the group of young animals was significantly greater, 93.2 ± 12.9%. Another peculiarity of the settlement was the predominance of immature individuals in the sedentary part (1.7 : 1), whose 1- to 2-day sites moved around the territory of the settlement. The latter is probably connected with the desire of the young to gain a foothold in any part of the overpopulated territory. A flow of migrants equal to 25.7 ind./ha per week passed through the settlement territory, consisting in equal parts of sexually mature and immature animals. An incomplete overlap of the territories of females with those of males could be considered as a possible element of the abundance autoregulation mechanisms, which reduces the number of meetings of sexual partners. All specific features of the settlement are apparently connected with the island position of the population.