Maintenance and declining mechanisms of endangered relict populations in moles

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In Mogera imaizumii, there are eight relict populations which are scattered to the southern Honshu, Shikoku, and Shodoshima, those being far from the main population of this mole distributing to the northern half of Honshu. In M.tokudae, relict populations are found at Mitsuke-Tochio and at Niitsu-Gosen where are situated in the range of M.imaizumii in the Echigo Plain. The following three types of isolating mechanisms were detected for these relict populations. a) Because of less suitable soil condition of habitats, the invasion of ecologically dominant species has been blocked and then inferior species could have maintained its range in these habitats. This case has been usually found at habitats on rocky mountain areas. b) Relict populations of ecologicallyy inferior species have been often maintained in habitats which are surrounded by barrier habitats unsuitable for dominant species. In this case, however, the former habitats are also suitable for the dominant species so that this species can easily exclude inferior species in the habitats when the dominant species could break the barrier. c) Rice fields which are the main habitats of Japanese moles have been altered to habitats unsuitable for larger moles, M.tokudae, under the plan for the basal improvement of agricultural fields. After the habitat alteration, the population of M.tokudae was sudivided by the invasion of smaller M.imaizumii into small isolated patches at the peripheral areas of the main distribution of M.tokudae in the Echigo Plain. The nucleotide sequences of the cytochrome oxidase subunit 1 gene indicated that relict populations of M.imaizumii from Shikoku, Shodoshima and Chugoku districts of Honshu constituted a closely related cluster. They showed relatively large differentiation rate from the Kii population which is rather close to Toyama and Ishikawa populations in Honshu.