Regional diversity of insects in the Pacific Northwest

Abstract

Provincial and state records for a sample of insect groups from British Columbia, Idaho, Oregon, and Washington show that this region, here termed "the Pacific Northwest", contains about 29% of North American insect diversity, a level that can be extrapolated to suggest that about 26,000 reported species occur in the region. Nearly half of these species are widely distributed in North America. Many species are more-or-less broadly western; 13% of all species essentially are confined to the Pacific Northwest, although some of them occur otherwise only in California, which contains many Pacific Northwestern species, especially in the north. Most of the fauna of British Columbia occurs also in the United States part of the region, and one-third of the species confined in Canada to British Columbia occur also in Idaho, Oregon or Washington. Despite these overall trends, there are wide differences among families and among genera, reflecting the diverse ranges, origins and ecological relationships of the different groups. Detailed studies that would more fully explain the differences are limited, even for groups of North American insects that are taxonomically better known. Nevertheless, the simple but feasible analysis of state and provincial records presented here provides useful indexes of regional occurrence, and indicates groups in the region that are of particular interest.