PARENT SESSION

Population Ecology 3 -- Session Chair: Winston Smith-- Van Duzer Theater

ECOLOGICAL CORRELATES OF MICROHABITAT USE AND DENSITY OF CLETHRIONOMYS GAPPERI WRANGELI AND PEROMYSCUS KEENI MACRORHINUS IN SOUTHEASTERN ALASKA. Winston P. Smith¹, Scott M. Gende² and Jeffrey V. Nichols¹. ¹ USDA Forest Service, Pacific Northwest Research Station, Forestry Sciences Laboratory, 2770 Sherwood Lane - Suite 2A, Juneau, Alaska, United States; ² National Park Service, Glacier Bay Field Station, 3100 National Park Road, Juneau, Alaska, United States.

ABSTRACT- We studied the Keen′s mouse (Peromyscus keeni macrorhinus) and the Wrangell Island red-backed vole (Clethrionomys gapperi wrangeli) in rainforest of the Alexander Archipelago during 1998-2000 to obtain the first quantitative estimates of habitat relations in southeastern Alaska. We trapped 1-ha grids and assessment lines with live traps during spring and autumn to compare population density and microhabitat use among gap-phase old growth (GP), multi-cohort old growth (MC), pre-commercially thinned young (23 yr-old) growth (YG), and peatland mixed-conifer (PM) forests. For both species, populations in 1998 were higher than 1999-2000 and we analyzed microhabitat use in those periods separately. Habitat distribution and microhabitat use varied with density. Both species used microhabitats randomly in 1998, but were highly selective in 1999-2000. Correlates of microhabitat use varied between seasons and among habitats, but vole captures were most often positively correlated with the percent cover of deciduous shrubs in the understory. Microhabitats used by mice had less moss cover on the forest floor, but in GP were directly related to the probability of capturing a vole. Population density of vole and mouse populations during both seasons was directly related to the amount of decayed down wood in the understory. During spring, the population density of Keen's mouse explained 62% of the variation in vole density, whereas vole density explained 89% of the variation in mouse density. Our results support earlier studies that concluded P. keeni populations in southeastern Alaska flourish in a variety of habitats, but departed from the general view that C. gapperi populations achieve their highest densities in late-seral coniferous forests. Unlike populations elsewhere in northwestern North America, voles in southeastern Alaska may be able to persist in habitats where the canopy has been removed. Peatland mixed-conifer forest likely contributes little to breeding populations of C. gapperi or P. keeni and thus is unlikely to mitigate any impacts of broad-scale clearcut logging of more productive old-growth forests.

KEY WORDS: Clethrionomys gapperi wrangeli, habitat relations, temperate rainforest, Peromyscus keeni macrorhinus