TROPICS Vol. 10 (1): 63-7L Issued May 30, 2000 Biogeography of Living Mammals in the Ryukyu Islands Masahanr MoToKAwA The Kyoto University Museum, Sakyo, Kyoto 606-8501, Japan ABSTRACT The faunas of the living non-volant mammals in the Ryukyu Islands are geographically different among northem, central and southem islands, and the Senkaku Group. The Tokara Gap and the Kerama Gap are recognized as important borders ofdistributional ranges, The northem Ryukyu species are the same as those on the main-islands ofJapan; probably they have been isolated only since the late Pleistocene. The central Ryukyu species include endemic elements that are considered as Miocene immigrants, The southern Ryukyu Islands has one endemic species, Prionailurus iriomotensis, which was possibly derived from the ancestral form ofP. bengalensis in the middle Pleistocene. The Senkaku Group has two species, of which lVesosc aptor uchidai is endemic to this island group at the generic level. This mole may be closely related to Mogera insularis in Taiwan. The second species, Apodemus agrarius, is a continental species and probably immigrated in the late Pleistocene, Key words: phylogeny / distribution / biogeography / Pleistocene / Miocene The Ryukyu Islands is a long archipelago, about 1200 km in length ranging between Kyushu and Taiwan (Fig. 1). It consists of approximately 150 islands (Mezaki, 1980). Seven island groups are usually recognized for this archipelago: osumi, Tokara, Amami, okinawa, Miyako, Yaeyama and Senkaku Groups (Fig. 1). In the Ryukyu Islands, several endemic species of mammals occur, making this archipelago an interesting and important region for the studies of evolution and conservation of mamrnals (Abe et al., 1994). Nevertheless, the origin and biogeography have been discussed for some remarkable species only (Kizaki & Oshiro, 1977). Herc,I discuss the distributional patterns of the Ryukyu living non- volant mammals and their biogeographical implications through a review of published data. The specific names follow Wilson & Reeder (1993) unless otherwise stated. Distribution data are taken from Abe et al. (1994), Motokawa (1996) and Funakoshi (1993). Five species, the house rut Rottus norvegicus, the black nt Rattus tanezurni, the house mouse Mzs musculus and the house musk shrew Suncus murinus in the Ryukyus, and the Japanese deer Cervus nippon in ttre Okinawa Group, are excluded from the present discussion, because they were possibly introduced with human activities (Kuroda, 1924; l+be et al.,1994). Distributions of the Ryukyu mammals are shown in Table 1. A total of 18 non-volant mammals are known from the Ryukyus, eight of which are endemic to this region. Based on distributional patterns, the Tokara Gap between northern and southern Tokara islands and the Kerama Gap between the Okinawa and the Miyako Groups are recognized as important barriers to dispersals for most Ryukyu mammals (see below). The mammal fauna of the Senkaku Group is different from those in 64 M. MOTOKAWA Fig. 1. The map of the Ryukyu Islands. the rest of the Ryukyus. Thus, the Ryukyu Islands is divided into four regions for the following discussion: northern, central and southern islands as divided by the Tokara and Kerama Gaps, and the Senkaku Group. Among the Ryukyu non-volant mammals, the wild boar Szs scrofa is widely distributed in the Palaearctic and Oriental regions including the Ryukyu Islands, the main-islands of Japan, Taiwan and continental China (Corbet & Hill, L992; Abe et al., 1994). In the Ryukyus, this species is recorded from Amamioshima and Tokunoshima of the Amami Group, Okinawajima of the Okinawa Group, and Ishigakijima and kiomotejima of the Yaeyama Group (Abe et al., 1994\. Such a distribution of this species is exceptional in that it includes both sides of the Kerama Gap. The Ryukyu populations of this species are characterized by smaller overall size and some unique morphological characters (Kuroda, 1924; Semba, 1964; Imaizumi, 1973). As a result, these populations are sometimes considered as a relict form deserving a distinct subspecies (as S. scrola riukiuana [see Kuroda, L924; Ellerman & Morrison-Scott, 19511) or even a full species status (as S. riukiuana [see Imaizumi, L9731). On the other hand, Semba (1964) supposed that the Ryukyu populations had originated from introduced domestic animals of ancient people in the Ryukyus. It is also possible that the hybridization occurred between the Ryukyu relic form and the inhoduced boar. As such, problems regarding the origin and taxonomic status of the Ryukyu wild boar are highly complicated and definitely need further intensive studies. NORTHERN RYUKYUS Seven species of mammals, the Japanese white-toothed shrew Crocidura dsinezumi, the Japanese large mole Mogera wogura (specific name following Motokawa & Abe [1996]), the Japanese monkey Macaca fuscata, the Japanese weasel Mustela itatsi, the Japanese deer Cerws nippon, the Japanese Biogeography of mammals in the Ryukyus 65 Table 1. Distribution of the non-volant terrestrial mammals in the Ryukyu Islands. Species Island groups and regions MI OS NT ST AM OK MY YY SK TW Soricidae Crocidura dsinezumi +++ Crocidura orii I + Crocidura watasei l'2 ++ Talpidae Mogera wogura 3 ++ Nesoscaptor uclidai I Cercopithecidae Macaca fuscata ++ Felidae P r ion ailur us ir iomo tens is 1'4 Mustelidae Mustela itatsi ++ Suidae Sus scrofa + ++++ Cervidae Ceraus nWon ++ Muridae Apodemus argenteus ++ Apodemus speciosus +++ Apodemus agrarius Diplothrix legata I ++ Tokudaia osimensis t + Tokudaia muenninki 7 + Mrts caroli + Leporidae Pentalagus furnessi 1 + Abbreviatio:rs for island groupj and rggions, MJ: main-islands of Japan; OS: Osumi Group; NT and ST: Tokara islands north and south of the Tokara Gap, respectively; AM: Amami Group; OK: Okina*a Group; MY: Miyako Group; W: Yaeyarna Group; SK: Senkaki Groirp; TW: Taiwan. 1, Endemic species of the Ryukyus; Specific names follow: 2, Motokawa ef al. (L996),3, Motokawa & Abe (19%) and {, Corbet & Hill (1992). small field mortse Apodemus argentew and the Japanese large field motse Apodemus speciosus, are recorded from the Osumi Group. Of these species, C. dsinezutni and A. speciosus are also recorded from the northern Tokara Group. All of these seven species in the northern Ryukyus are also distributed in the rnain-islands of Japan. Their distributional ranges in the Ryukyus are restricted to the north of the Tokara Gap. This strait is usually considered a border between the Palaearctic and Oriental faunal realms in the Ryukyus, and is often referred to as the "Watase's line" (Watas6, t9l2; Okada,1927). CENTRAL RYUKYUS The genera Diplothrix and Tohtdaia are endemic to Amamioshima and Tokunoshima of the Amami Group and Okinawajima of the Okinawa Group. The former genus is comprised of a single species D. legata and is often divided into two subspecies: D. l. legata for the Amami populations and D. l. M. MOTOKAWA okinavensis for the Okinawajima population. The latter genus includes three karyologically divergent species (Musser & Carleton, L993): T osimensis from Amamioshima, an undescribed species from Tokunoshima, and Z muennincki from Okinawajima. The leporid genus Pentalagas, consisting of one species P furnessi, and the soricid species Crocidura orii, are endemic to Amamioshima and Tokunoshima of the Amami Group. Pentalagus is considered to have diverged from the extinct genus Pliopentalagus; its extant closest relative may be the African genus Pronolagas (see Tomida, [1997]). Crocidura orii was originally described by Kuroda (L924) as a subspecies of C. dsinezumi, which is widely distributed in the main-islands of Japan. Later, Imaizumi (1961) gave it a separate species status C. orii, on the basis of a few morphological features. Most subsequent scientists still regarded C. orii as the closest relative to or a local variant of. C. dsineatmi (Abe et al., 1994), but recently Motokawa (1998a) demonstrated that a number of important morphological characters discriminate C. orii from C. dsinezumi. He suggested that the former is rather distant from the latter phylogenetically. Crocidura watasei is endemic to the Amami and the Okinawa Groups, occurring on 14 islands (Motokawa, 199Sb). This species was considered a subspecies of the Southeast Asian C. horsfieldii by many authors (e.g., Ellerman & Morrison-Scott, 1951; Abe et al., 1994). However, because it's chromosomal number Qn=26, Harada et al., L985) is distinct from that of C. horsfteldii (2n=38, Krishna Rao & Aswathanarayana, 1978), it is obvious that C. watasei is actually a separate species endemic to the central Ryukyus (Motokawa et al., 1996). Mus caroli is known only from Okinawajima of the Okinawa Group within Japan, though it is widely distributed in Southeast Asia and Taiwan (Musser & Carleton, 1993). The reason for such a range restriction of this species in Japan remains uncertain. Because this species is associated with cultivated fields (Abe et al., L994), it is probable that this mouse was introduced to the Ryukyus with human activities. SOUTHERN RYUKYUS In the Miyako Group, no native living mammals have been known. In the Yaeyama Group, two species, the Iriomote cat Prionailurus iriomotensis (specific name following Corbet & Hill [1992D from Iriomotejima, and the wild boar Szs scrofa from Iriomotejima and Ishigakijima are recorded' The former was originally described by Imaizumi (1967) as an endemic genus and species Mayailurus iriomotensis on the morphological basis. This cat was often considered as a relic of the Miocene immigrant (Kizaki &