Niche Dynamics of Deer Mice in a Fragmented, Old-Growth-Forest Landscape

Peromyscus oreas and P. maniculatus were non-randomly distributed across macrohabitats (including continuous old-growth forests, old-growth corridors, old-growth fragments, and clearcuts) of the Olympic National Forest, Washington. At this landscape scale, population densities of P. oreas were significantly higher in old-growth sites, particularly continuous forest and corridors, while densities of P. maniculatus were highest in clearcuts. At a finer scale, niche breadths measured across local habitats (within each macrohabitat) were broadest in preferred macrohabitat of each species. The potential importance of interspecific interactions was reflected in an inverse correlation between densities of the two species across all sites, niche segregation at the landscape (between macrohabitat) and local scales, and by the relatively high densities of P. oreas in forest fragments that lacked P. maniculatus . Relative densities of the two species combined were nearly as high in corridors as they were in continuous old-growth, and were nearly double that found in fragments and clearcuts. Given the importance of these rodents as prey for other vertebrates, including the endangered northern spotted owl ( Strix occidentalis caurina ), maintaining stands of continuous old-growth and forested corridors should remain a priority for conserving diversity of native forest communities.