Spatial Variation in Population Dynamics of Sitka Mice in Floodplain Forests

Population dynamics and demography of the Sitka mouse, Peromyscus keeni sitkensis, were studied by mark-recapture live-trapping over a 4-year period in four floodplain and upland forest habitats: old-growth Sitka spruce (Picea sitchensis) floodplain; red alder (Alnus rubra) floodplain; beaver-pond floodplain; and nearby old-growth Sitka spruce-western hemlock (Tsuga heterophylla) upland forest. We did not find the expected source-sink population dynamics resulting from flood disturbance or between-habitat variation in food resources. We found significant between-year differences (P < 0.05) in population densities, age and sex ratios, survival rates, growth rates, and movements. Within-year differences in all demographic variables were consistently greater between replicate trapping grids within habitat types than between habitat types, and there was no year-to-year consistency in any demographic difference between replicates or habitat types. We conclude that floodplain forests, per se, do not provide unique habitat for Sitka mice in either a strongly positive or negative sense compared with upland old-growth forests.