Biogeography of Hawaiian Collembola: The simple principles and complex reality

Abstract

Abstract We estimate that over 90% of Collembola species now living in the Hawaiian islands have been recorded, but the distribution of the fauna on individual islands is less well known. The relative number of species on the different large islands, except for Hawaii, is similar to that of most other groups of organisms. It appears that most species of Collembola could find suitable conditions on most islands; the subgenus Entomobryoides may be an exception. Endemicity appears to be related to age of the region, to habitat type, and perhaps to altitude. The Hawaiian fauna appears to have been recruited primarily from North America and temperate Asia, with tropical southeast Asia providing a smaller component; Western North America appears to be the main source for exemic species, and temperate Asia for the ancestors of endemic forms. Modes of immigration are uncertain, but ocean transport seems most likely for endemies of North American and Oriental origin, especially mobile members of the Entomobryidae and Sminthuridae; bird and/or wind transport may also have played a role. Although it is possible that most exemic species of Collembola are anthropochore, this remains in question. A much higher fraction of families of Collembola than of insects are represented in Hawaii. Much of the original native fauna has probably become extinct; the rate of extinction may have been declining during this century, and the remaining endemic species may be generalists which are relatively tolerant of altered conditions; the same is probably true of successfully introduced exemic species, whose rate of extinction has been low. Most exemic species were probably introduced before the middle of the century, and perhaps much earlier. There appears to be a low rate of speciation of Collembola in Hawaii in comparison to insects or even flowering plants; only Entomobryidae, Sminthuridae, and (to a lesser extent) Neanurinae provide evidence of endemic radiation. The dispersal patterns of different groups among the islands are dissimilar, and human transport may have been unequally important for different families. Compared with the fauna of other parts of the world, the % of different families represented of the Hawaiian endemic fauna appears to resemble Latin America, perhaps because of ecological similarity, while the insular structure may be responsible for greater similarity of the exemic fauna with that of Japan and Macaronesia in this respect.