Demography and Resource Use by Microtine Rodents near Toolik Lake, Alaska, U.S.A.

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Abstract
Five species of microtine rodents occurred in tundra near Toolik Lake, Alaska, but only tundra voles (Microtus oeconomus) and singing voles (M. miurus) were widespread and abundant. The relative abundance of these two species in different habitats corresponded to the availability of their preferred food items in each habitat. Tundra voles reached their highest densities (50 ha-1) in low, wet habitats dominated by rhizomatous monocotyledons and primarily ate monocotyledons. Singing voles reached similar densities in more mesic habitats that contained relatively high availability of dicotyledons and horsetails and mostly ate dicotyledons and horsetails. Although resource use differed, the demographies of the two species were remarkably similar. Both species of voles began breeding in the spring before snowmelt was complete and were still breeding when the first heavy snows occurred in autumn. However, tundra voles began breeding a few weeks earlier than singing voles, and singing voles had slightly larger litters than tundra voles (an average of 8.4 vs. 7.1 for adults, respectively). Population fluctuations appeared to be synchronous in the two species, which suggests control of their densities by similar environmental factors. The differences in food preference and habitat use suggest that competitive interactions between these species are weak and unlikely to be a major factor influencing their abundance.