[Factors of stress in a local population of water vole].

Physiological mechanisms of stress have a multiple influence on the implementation of the adaptive capacity of individuals. From this perspective, analysis of factors determining the stress level of animals in changing environment acquires important ecological and evolutionary significance. In the paper the results are presented of long-term studies carried out at a site of irrigative channel being populated by water voles every year. The results show that high stress level of males is observed in connection with shortages of environmentally significant resources--food and sexual partners. An activation of adrenocortical function due to resources deficit is formed as a result of exacerbation of intraspecific competition that occurs at both low food supply and reducion in proportion of females in the local population. The effects of these factors are mediated through changes in spatio-ethological structure of the studied populations which are manifested in increased overlapping of individual home ranges. Food supply and lack of females have different effects on the level of glucocorticoids in resident and nonresident males. These results indicate that social interactions in water vole is the real stress factor even when total population is significantly depleted, which in North Baraba occurs when territory watering is reduced and suitable summer habitats are not plenty enough.