Availability of resources, social demography and physiological stress in population of great gerbil (Rhombomys opimus) in conditions of peak and decline of density [Russian]

摘要

In southern Kyzylkum desert, Uzbekistan we studied the abundance of resources, composition of family groups, survival and dispersal rate from colonies (=isolated burrow systems) of the great gerbil during two years of high and low population densities. The influence of available resources at colonies and the composition and size of social groups on fecal corticosterone and testosterone levels in breeding males was examined. The relationship of corticosterone concentrations in breeding males, to composition of the social group and the allocation and abundance of resources showed that both social and environmental factors contributed to the amount of physiological stress. The relative role of environmental and social factors depends on conditions of the year and on population density. In the year of high population density (1999), the level of stress hormone (corticosterone) appeared to be more affected by availability of resources than by social condition, whereas in the year of population decline (2000), social factors played a predominant role. Up to now, it is unclear why the level of fecal corticosterone in breeding males in the spring was negatively correlated with the productivity of feeding resources that became available in summer and fall. We hypothesized that limited availability of those resources in the spring that are carried into the summer may play the role of a trigger, activating stress dependent regulation of reproduction. Survival of adult males was related to resource availability and corticosterone concentrations. We found survival of both sexes of gerbils was significantly influenced by productivity of succulent plants, the main feeding resource available in the drought summer period and not influenced by the rich spring vegetation. Availability of resources did not determine dispersal rate of gerbils from the family groups.