SPATIAL-ORGANIZATION OF CYCLIC CLETHRIONOMYS FEMALES - OCCUPANCY OF ALL AVAILABLE SPACE AT PEAK DENSITIES

Density and spatial organisation of reproductive C. glareolus, C. rufo canus and M. agrestis females were studied in a coniferous forest in n orthern Sweden. Individually marked voles were live-trapped during a f ive-year period covering two cyclic peak years. During the first peak all three species were abundant, but during the second one only C. gla reolus was present. Breeding Clethrionomys females had exclusive range s both intra- and interspecifically, whereas Microtus females tended t o be randomly distributed in relation to both C. glareolus and conspec ific females. The individual Clethrionomys females remained fairly sit e tenacious during the entire breeding season, while Microtus females changed location markedly. The range size of C. glareolus females duri ng breeding was almost four times larger than that of C. rufocanus, wh ile range size of M. agrestis females tended to be intermediate. Both intra- and interspecific competition for space among reproductive fema les were likely to limit the size of the breeding population of C. gla reolus. The results indicated that breeding females of either C. glare olus alone, or the two Clethrionomys spp. together, occupied all space available during peak years.