Systematics and zoo geography of bembidion 1. the bembidion carlhi and bembidion erasum groups of western north america coleoptera carabidae bembidiini

Erwin, T.L.; Kavanaugh, D.H.

Entomologica Scandinavica Suppl (15): 33-72


Accession: 006574511

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The genus Bembidion, with its hundreds of described species whose cumulative ranges nearly cover terrestrial Earth, is an indicator of past geographic and climatic events. This paper, the 1st in a series, provides a monographic treatment of 2 species groups of Bembidion of western North America. New study methods are adapted to this purpose and old methods are modified where necessary. Data are gathered and organized in such a way that a base is established for a future comprehensive phylogenetic and zoogeographic study of the genus. Two Casey names, B. brumale and B. vacivum, are synonymized with B. castum. Ten species in 2 groups are fully discussed: B. erasum, B. osculans, B. pseudoerasum, B. sequoiae, B. castum, B. disjunctum and 4 newly-named species [B. carlhi, type locality Steamboat Creek (at Steamboat Falls, 410 m), Douglas County, Oregon [USA]; B. lindrothellus, type locality Little Boulder Creek (Haines Highway Mile 31.5), Alaska; B. lummi, type locality Friday Harbor, San Juan Island, San Juan County, Washington; and B. chintimini, type locality Mary's Peak (8 miles west of Philomath, 1220 m), Benton County, Oregon]. Their cumulative range extends from southern Alaska to southern California and from the Pacific coast east to Colorado; most species are fairly widespread within that range. Dot maps illustrate the range of each taxon. A phylogenetic analysis based on 26 characters and their respective states demonstrates relationships among B. erasum group taxa, thereby providing grounds for recognition of 4 spp. subgroups. A cladogram is provided. Based on cladistic relationships and present ranges, a zoogeographic analysis suggests the following: the B. erasum species group arose in western North America no earlier than Miocene time, in association with general cooling trends and contemporary orogenic events, and is presently restricted to that region. Four included subgroups evolved sequentially, the first (the B. osculans subgroup) perhaps as early as Late Miocene, the last (the B. erasum subgroup) during Illinoian time. All extant species appear to have differentiated in Pleistocene or post-glacial time; and present distributions demonstrate a high incidence of sympatry which reflects widespread past dispersal of species and species groups.