We expanded the island biogeography paradigm to test whether mammalian communities of the heavily fragmented temperate rain forests of the Olympic Peninsula were influenced by local environmental conditions, biogeographic factors (fragment area and isolation) and characteristics of the surrounding landscape.
We used live-trapping, sign surveys and infra-red triggered cameras to compare distributions of non-volant mammals among fragments and between fragments and other principal landscape components (continuous old-growth, riparian corridors, second-growth forest and clearcuts).
Of the 24 species of non-volant mammals detected during our studies, 18 occurred in at least one fragment.
Species richness of old-growth mammals was not significantly correlated with fragment area or isolation, per se, but was significantly and positively correlated with the amount of old-growth fragments and old second-growth (41–159 years) in the surrounding landscape (r2 = 0.95, P < 0.005).
Distributions of three old-growth dependent species [shrew-mole (Neurotrichus gibbsii), Douglas squirrel (Tamiasciurus douglasii) and Trowbridge shew (Sorex trowbridgii)] were significantly associated with local environmental conditions within the fragment, with geographical isolation from continuous old-growth and riparian corridors, and with the amount of old-growth and old second growth in the adjacent matrix.