ORIBATID MITES OF THE GALAPAGOS-ISLANDS - FAUNISTICS, ECOLOGY AND SPECIATION

The results from investigations on oribatid mites of the Galgpagos arc hipelago during 10 years are presented. Samples were taken on all larg er and most smaller islands of the archipelago, as well as in all vege tation zones and some special habitats such as grass or cactus litter and fumaroles. A total of 202 oribatid species belonging to 64 familie s were encountered; among them 81 species are new to science. The Orib atida occur from the littoral zone to the summit of the volcanoes. Div ersity and abundance increases from the arid to the moister zones at h igher elevations. Most species prefer moist habitats at medium to high er elevations of the islands, in some parts reaching remarkably high a bundances (in the Scalesia zone of Santa Cruz approximately 18 000 ind ividuals m(-2)). The species richness of an island depends on the alti tude and number of available habitats rather than the area of the isla nd. Many oribatid species on the Galapagos Islands have a wide biogeog raphical distribution. The majority originate from the Central and Sou th American mainland, but several Pacific and even Holarctic elements were also found. In comparison with the species composition of the adj acent mainland, the oribatid mite fauna of the Galapagos Islands can b e regarded as disharmonic. Sea surface transportation has been proved at least between the islands, which also applies to oribatid species l iving at higher elevations. Long distance dispersal can be assumed to be mainly hydrochorous. The oribatid fauna of the littoral and arid ve getation zones is presented in detail. Some species even inhabit such extreme habitats as warm fern litter in fumaroles or hot volcanic soil s. Others were mainly found in or near a,ori cultural areas, suggestin g human introduction. Striking distribution patterns within the archip elago are discussed. The distribution of endemic forms in the genera A eroppia, Scapheremaeus, Schleoribates and Cultrobates indicates both s peciation on different islands, as well as speciation on the same isla nd by occupying different habitats. Exp Appl Acarol 22: 373-409 (C) 19 98 Chapman & Hall Ltd.