Comparative demography of Clethrionomys rutilus in taiga and tundra in the low Arctic

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Abstract
Winter mortality of C. rutilus may be more severe in tundra than in taiga, and in winters with unfavorable rather than favorable conditions during establishment or ablation of the snow cover or in the subnivean environment during midwinter. Vole mortality was higher in the tundra (90-95%) than in the taiga (55-75%), in accordance with this prediction, but year to year differences in snow conditions were not necessary determinants of winter survival during the 4 yr of the study. Subnivean breeding was never detected. The onset of summer breeding was related to the time of snow melt, and a late spring was followed by a low rate of maturation of young-of-the-year females and small spring-to-fall increase in numbers. Few young of either sex matured in 2 of 3 summers in the taiga; about half the females and 1/3 of the males matured each year on the tundra. Litters were significantly larger on the tundra and spring sex ratios were female biased. Reproductive output was high on the tundra, which would offset high winter losses. Intraspecific wounding was related to density and maturity except that on the tundra many immature young had bites. No superannual fluctuation was apparent on the tundra.