| Budget Amount *help |
¥1,700,000 (Direct Cost: ¥1,700,000)
Fiscal Year 1990: ¥300,000 (Direct Cost: ¥300,000)
Fiscal Year 1989: ¥400,000 (Direct Cost: ¥400,000)
Fiscal Year 1988: ¥1,000,000 (Direct Cost: ¥1,000,000)
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| Research Abstract |
Through the examination of the geographic and stratigraphic distributions of these species we can trance the history of faunal migration caused by the climatic changes during Postglacial Period. The warm species can be grouped into three groups based on their ages of the first appearance and geographic distributions. None of the species has an intermediate distribution pattern. The tropical elements now living in the south of Kyushu or Taiwan appeared in southwest Japan at about 7,500 years B. P. and reached South Kanto at 6,500-5,500years B. P. . The subtropical species appeared as early as 9,000 years B. P. in south Kanto, which extended their distribution to northern Honshu at about 6,500-6,000 years B. P. In Hokkaido, the third group of warm species appeared at about 7,500 years B. P. in the Japan Sea and okhotsk sea coast, and 7,500 years B. P. along the Pacific coast. They are the warm temperate elements now widely living in the Japanese water except Hokkaido. They disappeared at around 4,000 years B. P. from Hokkaido.
The age of the maximum spread these warm elements indicates Hypsithermal Period, and is concluded to be at about 6,500 to 5,000 years B. P.. Species belonging to one group appeared throughout broad areas within a relatively short interval. This may suggest the shallow benthic species are able to spread immediately when a suitable environment is given. On the other hand, the age of disappearance differs among species, and is seemingly related to their different limits of tolerance to the environmental deterioration.
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