Dynamics of bobak marmot’s habitat and population number in Ukraine in XX-XXI centuries. Dinamika areala i tchislennosti stepnogo sourka v Oukraine v XX-XXI bekakh. [Dynamique de l’habitat de la marmotte bobac et de sa population en Ukraine au XX-XXI siècle].

Résumé

At the beginning of XX century, marmot colonies in Europe had been preserved in Kharkov and Lugansk provinces, ??Rocky steppe??, south of the Voronezh province, and north-east of the Rostov province, as weIl as in the Chuvash Republic and Tatarstan. A factor that affects marmot population is direct or indirect anthropogenic influence. It includes hunting, poaching, grazing, and civil works. ln Ukraine, all open flat areas have been ploughed up and are under crops now. This, a number of specialists believe, has led to marmots' mortality. There is also an opinion that it is incorrect to conclude that ploughing up virgin steppes was the main reason for bobak to disappear from the steppes of Eastern Europe. According to D.I. Bibikov and A.V. Dezhkin (1988), ploughing up the virgin lands was one of the factors that contributed to its disappearance, while the main reason for that was said to be the hinting for bobaks. V. Lobkov (2003) believes that bobaks left the tlat areas for the guIlies to open a new habitat. The phenomenon of Europe's bobak revival in XX century, specialists explained, was due to improved protection and acclimatization in the former habitat (Abelentsev, 1975 et al.). Revival of marmot can be also explained by its protection and overall prohibition on hunting. But according to V.I. Mashkin (1993) and in our opinion, it was insufficient for its revival. During several decades European bobak acquired features non-peculiar to this species in terms of both ecology and etiology that explain European marmot's revival phenomena. Starting from 1960s, marmots from Velikoburluk district have begun to penetrate and live in alI neighbouring districts forming new centers of resettlement. At the end of XX century marmots habitat expanded 15-25 km in each 20 years. ln 1987, marmot population only in one Melovsk district made up 29,000 animals. A density of baibak population in this area made up 3-10 animals per one ha, sometimes reducing to one animal (in Melovoy GuIly), while growing in the others up to 15 animals per one ha (Glinyanniy gully) (Tokarskiy, 1988). The 1992 studies showed that compared to a period with maximum population (the beginning of 1980s - over 0.4 families per ha at 5.4 animals in one family, on the average) no redistribution of the area between families took place but reproduction decreased significantly (density -0.4 families per ha at 3.5 animals in one family). At the beginning of XXI century a population of this species decreased sharply in Ukraine. A sharp decrease in bobak population is also related to the changes of vegetation in the gullies. A major part of gully steppes underwent a strong depression. O. Grebenshikov (1973) singled out five stages of the depression. We can name one more stage; this is a stage of ruderal plants expansion. Only in the Velikoburluk district (the Kharkov province) number of cattle reduced 2.4 times during the last decade. This has a negative effect on bobak population. ln 2003-2004, the guIlies, where a cattle grazing was stopped, were so much overgrown with vegetation. Also, we can not ignore predators. When herbs grow too high, the young animals, particularly during the first months of life, become easy prey for foxes, polecats, dogs and wolf. And finally, ifs epizootics. Bobaks repeatedly died of rabbit-fever (for example, at the autumn 2004).