Origin and biogeography of the beetles (Coleoptera) of the Galápagos Archipelago, Ecuador

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Abstract
The Galápagos Archipelago is a model system for estimating the dynamics of biotic dispersal to, evolutionary differentiation in, and ecological structuring of oceanic islands. The islands, 800–1000 km west of the coast of Ecuador, have been available for terrestrial colonization for about 3 million years. After 150 years of sporadic study, the beetle fauna is still poorly known, but at least 54 families, 214 genera, and 366 species are present. Comparatively few families (10) contain endemic genera (13) that may represent early colonizations. Species flocks occur in usually flightless members of seven genera. Adaptive radiation, as seen in Darwin's finches, is evident in three genera of tenebrionids. The species are 24% native (i.e., they have naturally dispersed from Central or South America), 67% being endemic to one or more islands, and 9% have been introduced by man. Virtually nothing is known of the bionomics of the species. The fauna of 335 native and endemic species is estimated to have originated from at least 257 successful ancestral colonizations. Over 3 million years this is an average rate of one successful colonization every 11 700 years, and 1.4 new species per ancestral colonization. Most of the colonists reached the islands either through the air as "aerial plankton" (60%) or by rafting on oceanic flotsam (39%) from Central or South America. Extinctions were more prevalent in "glacial-arid" periods, and colonizations more prevalent in "interglacial-humid" periods. The rate of species introduction has increased with human visitation and colonization. The factors suppressing species proliferation in Galápagos beetles, compared with those in other insular areas, seem to be as follows, in probable order of importance: lack of strong ecological diversity, proximity to mainland areas, proximity of main islands to each other, geological youth, and recent development of a more suitable (wetter) climate. An appendix presents new beetle records for the islands. Lobopoda brunneipennis Campbell (Alleculidae) is placed in synonomy under Lobopoda galapagoensis Linell.

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