Влияние выпаса на пригодность местообитаний для степного сурка (Marmota bobak Müll.) на северо-востоке украины. Effect of cattle pasture on the suitability of habitats for the steppe marmot (Marmota bobak Müll.) in North-Eastern Ukraine [Effet du pâturage du bétail sur la convenance des habitats pour Marmota bobak Müll.) dans le nord-est de l'Ukraine].

Résumé

These investigations were made at a stationary site (about 90 km to northeast of Kharkov). The animal counting showed that the highest density of steppe marmot is observed on the territories occupied by pastures. Thus the maximum density of 1.9 ± 0.2 fam/ha (n=7) is characteristic for the territory of an intensive grazing and drops to a minimum of 0.3±0.1 fam/ha (n=7) in the area without any pastures. The density in the territory of moderate grazing equals 0.8±0.1 fam/ha (n=7). All the above data were obtained for the stationary site in the period of 1990-1996.The mean value of total terraneous phytomass on the territory without pastures is more than 3 times that of the plots with intensive one. This difference is by 87% due to the fact that in the plots of the first type there is an abundance of Poaceae, Cyperaceae, Juncaceae and dead plants (of the present and past years) that is, a phytomass, almost fully rejected by marmots. The comparison of the species phytomass used as fodder (preferred species and moderately eaten ones) showed that the difference in the mean terraneous phytomass values of forage species at the plots under study is insignificant. In habitats without pastures as well as in those with a high degree the phytomass of species used as fodder is considerably higher equaling 127 g/m2. At the same time the proportion of forage species in the total phytomass significantly varies for the plots compared (27, 86 and 73 % respectively) because of a considerable difference in the phytomass of species not eaten by animals.Capture-bred animals (a male and a female) from the living collection of marmots at the Biological station of Kharkov State University wee used in experiments. The maximum intake rate measured during cage feeding a diet abundant in the preferred fodder was 7.3±0.2 g/min (n=5) for the female and 10.9±0.2 g/min (n=8) for the male. The observations on the foraging of the same animals in natural environment on the territories with different plant group proportions showed that the intake rate expressed in percent of the maximum one varies within one and the same period from 59% at the plots where Polygonum aviculare L. predominates (intensive grazing) to 9% with Fragaria viridis Duch. Domination (a territory without any grazing or haymaking).Pasture availability leads to a diminishing in vegetation cover diversity and to the disappearance of the microgroups of low nourishing value for the steppe marmot. The vegetation cover of the territories with pasture availability is represented by two main microgroups, the best foraging quality possessing the mezophite group on the territory of moderate grazing (or hay-making) due to a high proportion of Fabaceae whereas on the intensive pasture territory vegetation of dry ecotope is a highest value as fodder (because of the predomination Artemisia austriaca Jacq., Achillea submillefolium Klok. et Krytzka, Plantago media L. and Taraxacum officinale Webb ex Wigg.).The specificity in foraging behavior of marmots is connected with a relative plant accessibility which plays an important role and may be expressed in the proportion of the phytomass of forage species (or vise versa in that of dead plants and the species rejected by animals) in the total phytomass. The investigations performed permit to conclude that the high proportion of nor eaten species and dead plants (for similar mass of forage plants) diminishes the accessibility to forage plants and worsens forging conditions for marmots. Providing during the whole activity season a high accessibility of forage plants for the steppe marmot, cattle pasture improves foraging resources for them. Probably this fact, among others, explains a high marmot density in plots with pastures on their territory.