Competition between Rodents in Successional Stages of Taiga Forests: Microtus agrestis vs. Clethrionomys glareolus

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Abstract
The field vole M. agrestis (L.) is a pronounced folivorous species while the bank vole C. glareolus (Schr.) is mixed granivorous-folivorous. Observations of field distributions nevertheless indicated competition. Possible mechanisms were elucidated by laboratory and enclosure experiments and the findings were tested on natural populations. Competition was pronounced with M. agrestis being generally dominant. C. glareolus reacted with withdrawal to the total number of M. agrestis present and not to any special category of the latter population. The presence of M. agrestis affected the distribution of C. glareolus between various habitats or microhabitats but the range size of the latter species was not changed. Experiments with removal of M. agrestis and subsequent return by C. glareolus showed that exploitation (scramble) competition is less important in present ecological time. M. agrestis must expel C. glareolus from grassland patches in taiga forest landscapes because otherwise its important forb resources are threatened as well as the nestlings. The latter threat will also come from granivorous species, and generally folivorous species in forest landscapes are larger than and dominant to sympatric granivorous and mixed granivorus-folivorous species.