During the period that the reserve has been in existence, a considerable changes of steppe vegetation has taken place. The area of virgin soil has decreased from 427 square kilometers (Kurdiuk, 1974) to 110 square kilometers. Some reservoirs and new settlements have been built, and some areas have been planted with trees and bushes. Maintenance of the virgin soil area has also gradually changed. Till 1966 only 15.62 square kilometers were strictly protected. Other areas were used as cattle pasture or for hay mowing (Drogobych, 1995). Since then a conservation regime has been established for the whole area. After a sharp decrease of the Citellus pygmaeus Pall. (1778) population due to cessation of grazing, Mustela eversmanni Less. (1827) which was ecologically tightly linked to it, became very rare (Reut & Polishchuk, 1988). At the same time Meles meles L. (1753) appeared, probably because of the extension of strict protection to the whole reserve. This species begun to be noted in 1987 (Semenov & Reut, 1989; Polishchuk, 1995), having been absent from earlier lists of the reserve (Brauner, 1928; Ivanenko, 1938; Ivanenko, 1955; Vedenkov & Karpachevska, 1977). Strict protection has had little effect on populations of Vulpes vulpes L. (1758) and Mustela nivalis L. (1766), as the high ecological plasticity these species enjoy enables them to survive even in agricultural areas. But the absence of disturbance on the preserved steppe makes this territory most favourable for them. Irrigation of areas adjacent to the reserve, and an increase in forest plantations and parks within Askania-Nova town has caused some species which are unusual for steppe land to penetrate the reserve, notably Martes foina Erx. (1777) and Mustela putorius L. (1758). Martes foina has been known for Askania-Nova since the 1950s (Ivanenko, 1955; Vedenkov & Karpachevska, 1977). At present it is a permanent inhabitant of settlements, and the arboretum and bird park. Mustela putorius is mentioned in almost all lists of Askania-Nova vertebrates (Brauner, 1928; Ivanenko, 1938; Ivanenko, 1955; Vedenkov & Karpachevska, 1977) but there are no reliable recent records of this species. Since 1968 sporadic visits to Askania-Nova of Nyctereutes procyonoides Gray (1834) have been noted (Vedenkov & Karpachevska, 1977) but this species is not a permanent resident of the reserve.