THE INSECT FAUNA OF THE PACIFIC NORTHWEST COAST OF NORTH AMERICA: PRESENT PATTERNS AND AFFINITIES AND THEIR ORIGINS

Abstract

AbstractThe insect fauna of the Pacific Northwest Coast is diverse and rich in endemic forms. Nine different elements are recognized in the fauna, including (1) restricted coastal, (2) coast-centred, (3) Great Basin, (4) Rocky Mountain, (5) trans-American, (6) Holarctic, (7) trans-Beringian, (8) Alaskan, and (9) introduced elements. Elements (6), (7), and (8) are generally restricted to the northwestern portion of the coast; and representation of Rocky Mountain elements (4) increases in three major steps from south to north along the coast—at the Puget Lowland/Fraser River valley, the Prince Rupert area, and the Kenai Peninsula, respectively. Patterns of vicariance among sister taxa in the carabid beetle genus Nebria demonstrate relationships which, together with analyses of other faunal elements, show that the fauna of glaciated portions of the Coastal region has greatest affinity with faunas of southern coastal areas, less affinity with those of southern interior areas, and least affinity with faunas of northern areas. Areas of local endemism within the region include the Aleutian Archipelago, the southeastern Alaskan Panhandle, the Queen Charlotte Archipelago, the Olympic Peninsula/Vancouver Island, the northern Cascade Range, the Klamath Mountains system, and the Sierra Nevada. The extant coastal insect fauna has evolved from a widespread northern Tertiary fauna, elements of which were isolated in several separate refugia during Pleistocene glaciations. The northern two-thirds of the region has been recolonized in postglacial time from both coastal and interior refugia south of the Cordilleran and Laurentide ice sheets. Local endemism in the region reflects survival and differentiation of a few forms in small coastal refugia; but survivors from these refugia, as well as those from the Yukon/Beringian refugium, have generally been unable to extend their ranges to other parts of the Coastal region following deglaciation.