Maintenance and declining mechanisms of endangered relict populations in moles

在Mogera imaizumii，有8个遗存种群，它们分散在本州南部、四国和Shodoshima，这些种群远离本州北半部的鼹鼠主要种群。在M.tokudae中，位于越后平原M.imaizumii范围内的Mitsuke-Tochio和Niitsu-Gosen发现了遗存种群。在这些孑遗种群中检测到以下三种类型的隔离机制。a)由于生境土壤条件不适宜，生态优势种的入侵被阻断，劣势种得以在生境中保持活动范围。这种情况通常发生在落基山区的栖息地。b)生态劣势物种的孑遗种群往往维持在不适宜优势物种生存的屏障生境周围。然而，在这种情况下，原有的生境也适合优势物种，当优势物种能够突破屏障时，优势物种可以很容易地排除生境中的劣势物种。(3)农田基础改造计划已将田鼠的主要生境稻田改造为不适宜较大田鼠生存的生境。在生境改变后，越后平原上的野田鼠种群在其主要分布区域的外围被较小的野田鼠的入侵划分为小的孤立斑块。细胞色素氧化酶亚基1基因的核苷酸序列表明，来自本州四国、Shodoshima和Chugoku地区的m.i imaizumii残群构成了一个密切相关的群体。与本州富山种群和石川种群的分化率比较接近。

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.