Spatial variation in population dynamics of Sitka mice in floodplain forests

Population dynamics and demography of the Sitka mouse, Peromyscus keeni sit kensis, were studied by mark-recapture live-trapping over a 4-year period i n four floodplain and upland forest habitats: old-growth Sitka spruce (Pice a sitchensis) floodplain; red alder (Alnus rubra) floodplain; beaver-pond f loodplain; and nearby old-growth Sitka spruce-western hemlock (Tsuga hetero phylla) upland forest. We did not find the expected source-sink population dynamics resulting from flood disturbance or between-habitat variation in f ood 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 consi stently,greater between replicate trapping grids within habitat types than between habitat types, and there was no year-to-year consistency in any dem ographic difference between replicates or habitat types. We conclude that f loodplain forests, per se, do not provide unique habitat for Sitka mice in either a strongly positive or negative sense compared with upland old-growt h forests.