| Summary: | The ecological distribution of small mammals (<200 g) was studied in the foothill tundra of the De Long Mountains in northwestern Alaska. Three species of shrews and five species of microtine rodents were trapped on 15 live-trapping grids during 1978 and 1979. Emphasis was placed on the three most abundant microtine species (Clethrionomys rutilus, Microtus oeconomus and M. gregalis). During late summer up to six species of small mammals were captured per habitat type which ranged from wet meadow through mesic shrubland to dry ridges. Following snowmelt most habitats contained only a single species and some contained none. Only four habitat types were continuously occupied by small mammals during both summers. Species diversity was variable among habitats. Most species of small mammals were captured on eight or fewer of the 15 trapping grids. Only Clethrionomys rutilus was captured on all grids. The number of habitats occupied by Clethrionomys rutilus increased from 4 to 14 as population densities increased. The number of habitats occupied by the other species seemed to be independent of population density. Average population densities for the microtines were low (<15/ha) and, for each species, varied according to habitat type. Only Clethrionomys rutilus populations demonstrated marked intra-annual fluctuations (3/ha to 37/ha).Key words: rodents, habitat, Alaska, populations, Clethrionomys rutilus, Micro oeconomus, Microtu gregalis Mots clés: rongeurs, habitat, Alaska, populations, Clethrionomys rutilus, Microtus oeconomus, M. gregalis
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