Maintenance and declining mechanisms of endangered relict populations in moles

今泉摩氏鼹鼠有8个残遗种群，分布于本州南部、四国和小豆岛，与分布于本州北方的主要种群相距甚远。在M.tokudae中，在越后平原的M.imaizumii范围内的Mitsuke-Tochio和Niitsu-Gosen发现了残留种群。在这些孑遗种群中检测到以下三种类型的隔离机制。a）由于生境的土壤条件不太适宜，生态优势种的入侵被阻挡，从而使劣势种得以在这些生境中维持其活动范围。这种情况通常在岩石山区的栖息地发现。B）生态劣势种的残遗种群通常维持在被不适合优势种生存的屏障生境所包围的生境中。然而，在这种情况下，以前的栖息地也适合优势种，这样，当优势种可以打破屏障时，优势种可以很容易地将劣势种排除在栖息地之外。c）根据农田基础改良计划，日本鼹鼠的主要栖息地稻田已被改造成不适合大型鼹鼠（M.tokudae）的栖息地。在生境改变后，在越后平原的主要分布区的外围，由于今泉野螟的入侵，种群被分割成孤立的小斑块。细胞色素氧化酶亚基1基因的核苷酸序列分析表明，日本四国、小豆岛和中国的今泉美蚊孑遗种群构成了一个密切相关的类群。它们与本州的富山和石川居群比较接近，从纪氏居群分化率较高。

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.