Pacific Rim National Park supports a variety of marine and terrestrial wildlife. Healthy wildlife populations depend primarily upon the protection of habitat. As areas outside the park become progressively altered by the activities of man, habitats within the park become important benchmarks of environmental change. Wildlife plays an increasingly important role as an indicator of healthy ecosystems.
The present assemblage of wildlife is believed to have established itself within the last 10,000 years. During the early stages of the last deglaciation, mainland animals were able to invade Vancouver Island. A lowering of sea levels and consequent narrowing of the channels that separated Vancouver Island from the mainland enabled several species to cross. Subsequent isolation of Vancouver Island contributed to the evolution of subspecies different from those on the nearby mainland. Saltwater barriers are effective obstacles to the movement of some mammal populations. Distinct subspecies of cougar, mink and wolf suggests that these mammals have been resident on the island, and separate from mainland species, for quite some time.
Species diversity is reduced at each stage of isolation from the mainland. This is particularly true of mammals. For example, the coastal mainland of British Columbia has 48 native land mammal species; Vancouver Island has just 18, while the Broken Group Islands unit of the park has only 10 species. The introduction of new species since the post-glacial resurgence of sea levels has been attributed to animals rafting or swimming across channels, or deliberate and accidental introduction by man.