Some Distribution Patterns of Pacific Island Faunae

Abstract

THIS paper concerns problems in the zoogeography of Pacific islands, based primarily on two families of insects, and notes comparisons with patterns in some other groups of animals. Some of the views here expressed are based on uncompleted research and are thus tentative. The insects of Pacific islands are too insufficiently known for one to draw comprehensive conclusions on the basis of distribution, so only preliminary deductions can be made. The insect faunae of the various island groups are quite unequally known. For instance, those of Hawaii, Samoa, Marquesas, and New Caledonia are moderately to fairly well known, whereas those of Tonga, New Hebrides, and others have hardly been investigated. Extensive collections from Micronesia are now being studied at the Bishop Museum. Large collections from Fiji and Southeastern Polynesia, also at the Bishop Museum, have only been studied in small part. Furthermore, the rich source areas of the Solomons, New Guinea, and the Philippines, or regions to the westward, are imperfectly known. Among the studies of insect distribution made so far, widely conflicting views have been expressed. Mayr (1941a, b) has given an excellent discussion of the distribution in Polynesia of birds, the best known group of animals, and has modified the outlines of the Polynesian Subregion. Mayr's outline differs from that accepted by most entomologists, and my early impression was that insect distribution would dictate conclusions other than those reached by Mayr. However, on analyzing distribution in the groups under study, my tentative outlines are not greatly different from Mayr's, as far as Polynesia is concerned. Further studies of insect distribution in the area will determine how correct Mayr may be in assuming that tropical land birds are as adequate indicators of insular zoogeography as are other groups of terrestrial animals. In this discussion the following assumptions or facts are taken as basic to an understanding of the distribution of terrestrial organisms on Pacific islands, but space will not be taken for elaboration of each point. (See Mayr, 1941b; Usinger, 1941; Zimmerman, 1942, 1948; Baker, 1951; Gressitt, 1954.) 1. All outlying Pacific islands (except Galapagos, Juan Fernandez, New Zealand, and islands near New Zealand) belong to the Oriental Region and not to the Australian Region, although there is conspicuous New Zealand influence in New Caledonia, and New World and Holarctic influence in Hawaii. The entire area (Fig. 1) may be termed the Polynesian Subregion, though more accurately it is a tapering fringe of the Papuan Subregion with overlapping influence from the Philippine Subregion and other areas. Within Polynesia, Hawaii and New Caledonia may each be assigned to a division of its own, and the rest to the division Polynesia proper, consisting of the subdivisions Micronesia (Bonin, Mariana, Caroline, Marshall, and Gilbert Islands), Eastern Melanesia (Santa Cruz, New Hebrides, and Fiji), Central Polynesia (Tonga, Samoa, Ellice, Phoenix Islands, etc.), and Southeastern Polynesia (Marquesas, Society, Tuamotu, Mangareva, Austral, Cook Islands; Rapa, and Easter Island). These subdivisions are not strict zoogeographical areas, but are