Homoptera (Insecta) in Pacific Northwest grasslands. Part 2 - Pleistocene refugia and postglacial dispersal of Cicadellidae, Delphacidae and Caliscelidae

Abstract

Biogeographic analysis suggests that 241 Cicadellidae, 33 Delphacidae and I Caliscelid are restricted to grasslands in the Pacific Northwest. Nearly half of these (120 or 44%) are endemics. This grassland endemic fauna is third only to those of the prairies and desert grasslands. Of these, only six taxa probably postdate retreat of continental glaciers. The present distribution of the older taxa indicates that this fauna are descended from nine main glacial-era refugia (in descending order of importance): (1) east slopes of the Cascade Range, from Washington state to southern Oregon; (2) Columbia basin including Palouse hills of Washington and canyons of western Idaho; (3) south-facing slopes on the Rocky Mountains of Montana and western Wyoming; (4) the headwaters of the Snake River and south-facing slopes north of the Snake River in southern Idaho; (5) east of the Coast Range of Oregon; (6) edges of glacial Lake Missoula in western Montana; (7) a periglacial grassland near the ice front in Alberta; (8) the mountains of south-central Oregon; and (9) the coast of the Queen Charlotte Islands. Additional refugia might have been in the mountains of Colorado, Utah, eastern Arizona, and eastern Wyoming, where there are an additional 22 endemics, Postglacial warming brought grasslands and their endemic insects to British Columbia on the islands of the Strait of Georgia, to the East Kootenay valley and to the upper Fraser River of BC. Faunal exchanges have occurred across at least nine mountain passes on the continental divide. Three of these passes still provide continuous grassland connections between the prairies and the intermontane grasslands, yet not more than 14 slow-moving prairie species have surmounted any one pass.