We reviewed the history of studies and conservation efforts related to terrestrial mammals in the central and southern Ryukyu Archipelago in Japan, covering six orders, 11 families, 20 species, and six subspecies, with 77% endemic and 62% of species classified as threatened. The most significant feature is that phylogenetically ancient species have survived alongside humans, who have inhabited the islands for approximately 30 000 years. This coexistence is unique to this region and not found in other parts of Japan, making it a globally rare phenomenon. In 2021, four islands in the region were designated as Natural World Heritage Sites, marking a conservation milestone, although challenges remain. Island biodiversity is crucial to global biodiversity because of its high endemism. Island biology provides an essential biogeographical perspective to understand evolution and shape conservation strategies. The region has become a focal point of interest due to its unique biota and distinctive island ecosystems. We concluded that a comprehensive re-evaluation of the islands is essential, focusing on biogeography, ecology, and species interactions. Conservation measures should be tailored to each island by incorporating insights from ethnography, sociology, and economics. It is our responsibility to protect the region's endangered species and the biodiversity for future generations.
Published online 2 April, 2025; Print publication 30 April, 2025
It is estimated that there are approximately 341 000 islands on Earth, with around 22 000 islands larger than 1 km2 and about 319 000 islands smaller than 1 km2, collectively covering a total area of 9 959 553 km2, and making up nearly 7.4% of the Earth's land area (Sayre et al. 2019). These islands comprise oceanic islands (i.e., volcanic islands), atolls, and continental islands (islands on a continental shelf and continental fragments) (i.e., islands that originated from a continental plate but are now isolated from the ocean). These islands are estimated to maintain an 19% of bird species, 17% of rodent species, 17% of flowering plant species, and 27% of human languages (Tershy et al. 2015).
Island biodiversity is immensely important to global biodiversity because of its high endemism of living organisms. Island biology is an important biogeographical approach to understand ecology, evolutionary biology, and a strategy for conservation of biotas on islands surrounded by oceans (Kueffer et al. 2016). It has now been recognized that both historical and ecological biogeographic approaches are necessary to fully understand and explain the pattern of island biodiversity (Feldhamer et al. 2020).
The islands of the Ryukyu Archipelago in Japan, which consist of continental islands from the Eurasian Continent and oceanic islands, are biologically important because of their unique biogeographic history and endemic flora and fauna. Continental islands of the Ryukyu Archipelago were considered to have once been a part of the edge of the Eurasian Continent during Middle Miocene and were later divided into the islands of the Ryukyu Archipelago, consisting of the North Ryukyus, Central Ryukyus, and South Ryukyus, by channels and straits, since the Late Miocene to early Pleistocene (Government of Japan 2019; van der Geer et al. 2021). In the terrestrial mammals, dwarf mammoths, Mammuthus sp. and several deer (e.g., Muntiacus sp., and Cervus sp.) first inhabited the islands of the Ryukyu Archipelago during Pleistocene, and only small mammals, later migrants, have survived to date, such as the spiny rat, Tokudaia spp., the Ryukyu long-furred rat, Diplothrix legata (Thomas, 1906), and the Amami rabbit, Pentalagus furnessi (Stone, 1900), in the Central Ryukyus (van der Geer et al. 2021). Palaeolithic humans and the Ryukyu wild boar, Sus scrofa riukiuanus Kuroda, 1924, arrived on the Central Ryukyus and inhabited the area alongside those mammals present since the latest Pleistocene (37 000–13 000 years ago). During the similar period, the Iriomote cat, Prionailurus bengalensis iriomotensis (Imaizumi, 1967), and the extinct Miyako roe deer, Capreolus tokunagai (Otuka, 1941), the extinct Miyako island rat, Rattus miyakoensis (Kawaguchi et al., 2009), and the reed vole, Microtus fortis (Büchner, 1889), now extinct on the island, arrived on the South Ryukyus (Kawamura et al. 2016; van der Geer et al. 2021). For the unique ecosystems on each island constructed with a complex biogeographic history, the four islands of the Ryukyu Archipelago—Amami-Oshima, Tokunoshima, Okinawa, and Iriomote Islands—were listed as a UNESCO Natural World Heritage Sites in 2021 (UNESCO 2021).
In this review, we aimed to outline the island's history, including human history of the Ryukyu Archipelago, followed by summarizing research, and conservation efforts conducted to date on these islands, utilizing the latest studies and information of native and non-native insular terrestrial mammals. Our focus was particularly on the islands of the “central and southern Ryukyu Archipelago”, which include the Central and South Ryukyus, as well as the Senkaku and Daito Island Groups, excluding the North Ryukyus. The unique mammalian fauna of the central and southern Ryukyu Archipelago is globally distinct and will serve as a specific case study in island biogeography.
Note that the term “Japanese mainland” used in this review refers to the region including Honshu, Kyushu, and Shikoku, but excluding Hokkaido due to historical and zoogeographical differences. The scientific names of terrestrial mammals and other species, including the author and publication year, are primarily presented in the section on the transition of taxonomic nomenclature and in the relevant sections of the review. Additionally, the terminology related to invasion science in this review follows the recent proposal by Soto et al. (2024). Part of this topic was also discussed in Japanese by Izawa and Yamada (2023).
Location of the Ryukyu Archipelago
The Ryukyu Archipelago is situated in a zoogeographical zone that separates the Old North Region from the Oriental Region. The archipelago lies in an oceanic region between the southern end of Kyushu Island in Japan and Taiwan, spanning approximately 1200 km (Fig. 1). It comprises more than 900 islands, including approximately 70 inhabited by humans (Government of Japan 2019). This region, located between 20° and 30° north latitude, is characterized by a rare subtropical oceanic climate, influenced by warm Kuroshio Current and monsoons, which result in annual precipitation exceeding 2000 mm.
As a result, it is one of the few places in the world where rainforests exist in the subtropical zone (Government of Japan 2019). In the mountainous forests of the region, evergreen broadleaved forests have developed in the humid subtropical climate. The dominant tree species in the upper canopy include mainly oaks (e.g., Castanopsis sieboldii and Lithocarpus edulis), Ryukyu pines, Pinus luchuensis, and laurel trees (Lauraceae). The forest is also home to a diverse range of plant species, such as tree ferns (Cyathea species), Lasianthus species, some Ardisia species, strangler figs (Ficus species), and palm trees (Arecaceae). Additionally, cloud forests and mountain stream vegetation have developed in the high mountainous areas. These forests, including those in the mid and low mountainous areas with similar species, are referred to as subtropical rainforests and are crucial for the wildlife in the region (Government of Japan 2019).
The nomenclature of the islands and regional divisions in this review follows the conventions outlined by Toyama (2014), which are based on the natural sciences, including geography, geology, and biology. Specifically, the entire region along the Ryukyu Archipelago includes island groups such as the “Osumi Island Group,” “Tokara Island Group,” “Amami Island Group,” “Okinawa Island Group,” “Sakishima Island Group” which encompasses the “Miyako Islands” and “Yaeyama Islands,” as well as the “Senkaku Island Group” and “Daito Island Group” (Fig. 1).
Island formation and characteristics of terrestrial mammalian fauna
The Ryukyu Archipelago is located at the intersection of the Eurasian Plate and the Philippine Sea Plate (Fig. 1). Geological processes, such as the subduction of the Philippine Sea Plate beneath the Eurasian Plate in the Ryukyu Trench, led to the formation of these islands during the Late Miocene and subsequent periods (Machida et al. 2001; Kimura 2002; Hase 2010; Iryu and Matsuda 2010; Government of Japan 2019). Furthermore, as a continental island, the Ryukyu Archipelago has undergone historical cycles of intermittent separation from and connection to the Eurasian Continent through deformation and formation of land bridges, respectively, resulting in the development of a unique biota and ecosystems in the Ryukyu Archipelago (Kizaki and Oshiro 1980; Motokawa 2000, 2017; Oshiro 2002; Ota 2002, 2012; Otsuka 2002; Sato 2017; Watanabe et al. 2023).
Fig. 1.
Island groups and main islands of the Ryukyu Archipelago including the Senkaku Island Group and the Daito Island Group [based on Toyama (2014) and Japanese Government (2019) and modified from Izawa and Yamada (2023), using Google Earth]. The Ryukyu Archipelago is divided into three regions: North Ryukyus (from the Osumi Strait and Tokara Strait), Central Ryukyus (from Tokara Strait to the Kerama Gap), and South Ryukyus (from the Kerama Gap to the Yonaguni Strait). The depths of Tokara Strait and Kerama Gap are both over 1000 meters under sea with widths of 50 km each. Four islands, including sites designated as Natural World Heritage, are marked with an asterisk. The names of each island are as follows: Amami-Oshima, Amami-Oshima Island; Tokunoshima, Tokunoshima Island; Okinawa, Okinawa Island; Ishigaki, Ishigaki-jima Island; Iriomote, Iriomote Island; Miyako, Miyako-jima Island, Uotsuri, Uotsuri-jima Island; Minami Daito, Minami Daito-jima Island; and Kita Daito, Kita Daito-jima Island.

The Ryukyu Archipelago is subdivided into “North Ryukyus” between the Osumi Strait and the Tokara Strait, “Central Ryukyus” from the Tokara Strait to the Kerama Gap, and “South Ryukyus” from the Kerama Gap to the Yonaguni Strait (Fig. 1). Each region has a distinct historical trajectory and forms unique terrestrial mammalian communities. The depths of the Tokara Strait and the Kerama Gap exceed 1000 m, and their widths are approximately 50 km, geologically dividing the Ryukyu Archipelago. Biogeographically, the former is known as the Watase Line, and the latter as the Hachisuka Line.
Due to differences in the timing of continental connections and separations, distinct terrestrial mammalian assemblages have developed, especially in the central and southern Ryukyu Archipelago compared to those in the North Ryukyus, which are more similar to those of Kyushu Island, as shown in Table 1 (although data on the North Ryukyus are not presented here). Notable characteristics of the current mammalian fauna in the region include five key aspects: high diversity, high endemism, close relationships with biogeographical distribution patterns of the Indomalayan ecozone, a scarcity of large-sized mammals, and absence of top predatory mammals in the food chain—except on Iriomote Island in the South Ryukyus, where the Iriomote cat inhabits (Table 1). The island's structure, which poses challenges for medium- to large-sized mammals to immigrate and establish themselves across islands, may contribute to their lower diversity compared to continental or larger islands in other regions. Nevertheless, the central and southern Ryukyu Archipelago, representing approximately 20% of the total terrestrial mammal species in Japan, demonstrates high diversity when considering the area ratio (0.7% of Japan). The endemic rate of species and subspecies, defined as the proportion of native species that exist only in a specific area, ranges from 67% to 77% of the native species in each island of the Central Ryukyus, and Ishigaki-jima and Iriomote-jima Islands of the South Ryukyus (Table 1). This high endemic rate is a major distinguishing feature of the region. When compared with the other four continental island areas in the subtropics (cf. 27% in Taiwan, 30% in Cuba, 30% in Jamaica, and 18% in the islands of the Gulf of California), the high level of endemism of the central and southern Ryukyu Archipelago is remarkable (Government of Japan 2019). The other three characteristics—high diversity, biogeographical distribution patterns of the Indomalayan ecozone, and absence of top predatory mammals—are closely linked to region's complex geological history and island nature.
The earliest history of human colonization and key historical events leading to the Modern era
The history of human habitation in the central and southern Ryukyu Archipelago dates back to approximately 30 000 years during the Paleolithic era (see the later section). Furthermore, significant human activities have shaped the islands, including the cultivation of sugarcane, Saccharum officinarum since the 17th century, intensified upland cultivation, forest utilization, and modern-era forestry practices for pulp production. Consequently, the original pristine natural environment has been replaced by secondary natural environments and forests with minimal primary habitats (Toyama 2016; Yoneda 2016, 2017). Despite intensified development during the Meiji period (1868–1912) and later, it is noteworthy that these regions did not experience widespread species extinctions, except for bats (see the later section).
In the following, Okinawa Island Group and Sakishima Island Group, and Amami Island Group are explained separately due to differences in history and administration in each area.
Okinawa Island Group and Sakishima Island Group
Human remains known as “Yamashita Cape People” were discovered in the Yamashita limestone cave in Naha City, Okinawa Island, and were estimated to be around 37 000–32 000 years old, making them the oldest human bones in Japan (Watanabe 1970; Takamiya et al. 1975). Contemporary bones have also been found in the southern part of Okinawa Island, with Sakitari Cave yielding evidence of settlements and the world's oldest fishhooks (Fujita et al. 2016). “The Minatogawa Man,” discovered between 1967 and 1969, is believed to date back approximately 18 000–16 000 years, exhibiting similarities to the Jomon people and Neolithic people of the continent (e.g., Suzuki and Hanihara 1982; Hokama 1986; Asato and Doi 1999; Tsujino et al. 2010). The recorded history then jumps to the shell mound period, approximately 6000 years ago, characterized by natural gathering activities. Settled villages were established approximately 3000 years ago (Asato and Doi 1999; Hayaishi 2011; Pearson 2013; Shinoda and Adachi 2017).
During this era, forests thrived on islands such as Miyako-jima Island, hosting diverse fauna, as suggested by fossils and archaeological sites, and human activities appeared to have significantly altered the natural environment, including the animal populations (Matsuoka 2000; Pearson 2013; Nakamura and Ota 2015; Watanabe et al. 2023).
Subsequently, after passing through the Gusuku period, the Ryukyu Kingdom was established in 1429. The kingdom unified the Amami Island Group and the Yaeyama Islands, expanding its dominion. Although the Amami Island Group later came under the control of the Satsuma Domain (now Kagoshima Prefecture) in 1609, the Ryukyu Kingdom persisted until its collapse in 1879 because of the Ryukyu Disposition by the Japanese government. It was then settled as Okinawa Prefecture.
During the pre-modern era, deforestation for construction and shipbuilding rapidly progressed in ancient Ryukyu, and reforestation efforts have been documented (Tawada 1972). As the early modern era unfolded in the 1600s, industrial development was pursued, leading to further rapid degradation of the forest environment. This continued until the mid-1700s, when the “Somayama” system (forest policy regulations regarding forest management and use) established by the kingdom was implemented, focusing on sustainable management (Nakama 2011).
Table 1.
Terrestrial mammals inhabiting the main islands of the central and southern Ryukyu Archipelago, their endemism to the region, and their conservation status

However, as mentioned above, since Okinawa Prefecture was established in 1879, resurgence of deforestation activities has increased. Newspaper articles from that time expressed concern over the deforestation of forests in the northern part of Okinawa Island (called Yanbaru or Yambaru for the area's name) (Nakama 2011). Unfortunately, there is no record detailing how these changes affected the biodiversity in the area.
Okinawa Island became a battleground during the ground operations in World War II in 1945. Many lives and towns were lost, and forests in the central and southern parts disappeared. This wartime destruction significantly affected the current distribution of the flora and fauna. Post-war reconstruction efforts have led to the overuse of forests and their excessive development. Construction of logging roads, large-scale logging, and dams continued until the 1980s. Similar trends have been observed in the Miyako Islands, Yaeyama Islands, and other areas. The islands in Okinawa Prefecture, along with the Amami Island Group in Kagoshima Prefecture, were placed under U.S. military administration after the war, and the islands in Okinawa Prefecture were returned to Japanese administration in 1972 (see below about the Amami Island Group). During this period, “the 1953 Land Acquisition Act” resulted in the seizure of lands within the Okinawa Prefecture for military use. Nowadays, nearly 15% area of Okinawa Island is occupied by U.S. military bases (Okinawa Prefectural Office 2024).
Amami Island Group
In prehistoric times, evidence of human settlement in the Amami Island Group dates back over 30 000 years, as confirmed by the discovery of the “Aira Tanzawa Volcanic Ash” deposit layers from a volcanic eruption 30 000 years ago in the Kasari area of Amami City on Amami-Oshima Island and Isen Town on Tokunoshima Island. Below these layers, remnants of human activity suggest human habitation in the Amami Island Group 30 000 years ago (Hisashi et al. 2021). Artifacts from this period include bones of the Amami rabbit and the Ryukyu wild boar, suggesting that humans used these animals as food (Takamiya et al. 2016; Takamiya 2017, 2021; Toizumi 2018). The beginning of the “Jomon period,” i.e., the beginning of the shell mound period in Amami Island Group, is now estimated to be around 14 000 years ago, much earlier than previously thought (7000 years ago) (Hisashi et al. 2021; Takamiya 2021). During the equivalent of the “Yayoi period” on the Japanese mainland, when rice cultivation extended south to the Tokara Islands, the Amami Island Group relied on fishing and gathering, engaging in remote trade of large shellfish (e.g., Conus literatus, Strombus latissimus, and Turbo marmoratus) for ornamental purposes, extending to Kyushu and the Kansai region of the Japanese mainland, as well as overseas areas in East Asia.
In the early modern period, under the rule of the “Satsuma Domain” (current Kagoshima Prefecture) from 1609, the Amami Island Group underwent significant industry and human life changes through government policy (Hisashi et al. 2021). Large-scale cultivation of sugarcane plantations and the shift to black sugar production began in 1747. During this period, forests were extensively utilized for development of agricultural land, rice paddies, sugarcane fields, and for firewood.
After the end of the U.S. occupation of Japan (1945–1953) following World War II, the Amami Island Group was returned to Japan in 1953 and “Amami Islands Reconstruction Special Measures Law” was enacted in 1954 and is still ongoing to address regional disparities and promote various reconstruction and development projects, including continued basic infrastructure development, industrial growth, tourism, cultural promotion, and human resource development (Hisashi et al. 2021). During this period, land and forest development, flood control, and coastal development have intensified. Particularly, as a result of annual logging accumulation, more than 90% of the forests on Amami-Oshima Island had been logged in total, mainly for pulp chip material, during Japan's period of high economic growth (approximately between 1955 to 1985), significantly affecting local wildlife (Sugimura 2002). Today, many forests logged during this period have reached an age suitable for utilization, leading to the resumption of logging activities.
The earliest natural history records leading to the Modern era
The central and southern Ryukyu Archipelago has been recognized internationally—by countries such as China, the United States, and European nations—as a biologically valuable region since ancient times (7th century), particularly after a period of increased interactions, especially during the early modern period (18th century). This recognition is attributed to exchanges with China and visits by whaling ships, as described in detail later. Both international and domestic researchers from various research fields have visited the region for research purposes. Visiting scholars have preserved numerous valuable records, including the discovery of new species.
In the following, Okinawa Island Group and Sakishima Island Group, and Amami Island Group are explained separately as previous section.
Okinawa Island Group and Sakishima Island Group
Records of Okinawa Island's natural environment during the Ryukyu Kingdom era were described predominantly by foreign visitors. The earliest consolidated record of Ryukyus is found in the 7th century's “Zuisyo Ryukyukokuden” (Document of Ryukyu Kingdom on Geography, Flora and Fauna, and Other Subjects) published in China in 629 (Iki 2021). However, even when considering the fossil documentation found in later years, some of these records often differ from the present biological descriptions in Okinawa Island. The “Ryukyu Koku Yurai Ki” (Documents on Origin of the Ryukyu Kingdom) compiled by Ryukyu Kingdom in 1713, describes the origin of livestock and the introduction of the Kerama deer, Cervus nippon keramae (Kuroda, 1924), from the Satsuma Domain (current Kagoshima Prefecture) during 1628–1644. The document contains particularly valuable information, and also notes the native Ryukyu wild boar (Hokama and Hateruma 1997). The Japanese scholar Hakuseki Arai's “Nantoshi” (A History of the Southern Islands) (Arai 1719) and Xu Baoguang's “Chuzan Denshinroku” (Geography of Ryukyu) documented in China (Xu 1721) provided more specific records of flora and fauna, including the Yaeyama flying fox, Pteropus dasymallus yayeyamae Kuroda, 1933, dugongs, Dugong dugon (Müller, 1776), and Kerama deer. Occasional mentions of monkeys appear, supported by the discovery of bones of the Yakushima macaque, Macaca fuscata yakui (Kuroda, 1940), excaved in the Shurijo Castle of the Ryukyu Kingdom in Naha City on Okinawa Island. However, the Yakushima macaque is endemic to Yakushima Island in the North Ryukyus. Therefore, the Yakushima macaques were artificially brought from outside of Okinawa. Notably, the “Ryukyu Koku Shiryaku” (Documents of the Ryukyu Kingdom on Geography, History, and Other Subjects) published in China in 1756, mentioned the Kerama deer and a monkey whose species name was unidentified (Harada 2003). In the 1850s, Matthew C. Perry, an American naval officer who visited Okinawa Island in 1853–1854, and Charles Wright, a botanist, and William Stimpson, a zoologist, also visited in 1854–1855 by the North Pacific Exploring and Surveying Expedition recorded the flora and fauna of Okinawa Island (Perry 1856a, 1856b; Vasile et al. 2005; Goto 2017).
Shozaburo Watase (1862–1929), who was a professor of the University of Tokyo and the namesake of the Watase Line, a biogeographic line, made significant contributions to biogeography. However, he was also notable for his involvement in introducing the small Indian mongoose, Urva auropunctata (Hodgson, 1836), to Okinawa Island in 1910. Other noteworthy persons were Hyojiro Orii (1883–1970), a representative bird and mammal specimen collector who provided specimens to the British Museum, and to Yoshimaro Yamashina (1900–1989), an ornithologist, and Nagamichi Kuroda (1889–1978), an mammalogist (Motokawa and Maeda 2002). Orii's collected specimens, documented in the “Ryukyu and Osumi Islands Collection Journal (1921)” and “Ryukyu Collection Journal (1936)”, serve as valuable historical records for understanding the habitats of organisms during that time (Saito and Takehara 2013a, 2013b). Dedicating a species name to Hyojiro Orii, such as Orii's flying fox, P. d. inopinatus Kuroda, 1933, and Orii's shrew, Crocidura orii Kuroda, 1924, are also present.
When discussing Okinawa's biodiversity, a geological perspective is essential. The first geological survey of the Ryukyu Archipelago was conducted by the expedition of the American Squadron led by Matthew C. Perry in 1853 and by the North Pacific Exploring and Surveying Expedition led by John Rodgers in 1854 (see above). During the post-war American occupation, detailed geological maps were created by the U.S. Geological Survey (e.g., Flint et al. 1959). Records of animal fossils began with Hikoshichiro Matsumoto (1887–1975), covering the deer fossils, Cervus astylodon (Matsumoto, 1926), on Okinawa and surrounding islands (Hasegawa et al. 1973; Hasegawa 1980, 2012). Mitoshi Tokuda (1906–1975), initiated discussions of the geological history of the Okinawa Islands based on fossil analyses (Tokuda 1941). Subsequent discoveries, such as the fossils group at the Minatogawa River Fisher site on southern Okinawa Island and the Pinzaabu remains on Miyako-jima Island, have contributed to discussions on the origin of the fauna in the Ryukyu Archipelago (e.g., Hasegawa 2012; Hasegawa et al. 2018; Kawamura et al. 2016; Watanabe et al. 2023).
Amami Island Group
The first documented appearance of animals from Amami-Oshima Island was found in the folkloric book “Nanto Zatsuwa” (Ethnography of Amami-Oshima Island) (Nagoya ca. 1855), which details the flora, fauna, and customs of Amami-Oshima Island during the author's stay on the island from 1850 to 1855, in the late Edo period (1853–1868). This publication includes mentions of mammals such as the Amami rabbit, the Ryukyu long-furred rat, the Ryukyu wild boar, the musk shrew, Suncus murinus (Linnaeus, 1766), the Erabu flying fox, P. d. dasymallus Temminck, 1825, the dugong, and an unspecified species of rat. Livestock is also recorded. Among them, the Erabu flying fox is no longer found consistently on these islands now, though some records on a dead body, some individuals, and observation records were known both on Amami-Oshima and Tokunoshima Islands (Funakoshi 2017).
There was limited dissemination of information about the Amami Island Group to the Western world from the late Edo period to the early Meiji period (19th century). However, during the second expedition (1854–1855) by the North Pacific Exploring and Surveying Expedition (see above), the researchers visited Amami-Oshima, Kakeroma-jima, and Kikai-jima Islands. Plant specimens were collected, marking the first global dissemination of this information (Hamada 1993; Vasile et al. 2005; Goto 2017).
Articles by Ludwig Doederlein (1855–1936), a foreign lecturer and German zoologist at the University of Tokyo, detailing the geology, geography, flora, fauna, and customs of Amami-Oshima and the Kakeroma-jima Islands during his visit in 1880, was published in the mid-Meiji period (Doederlein 1881a, 1881b). Following this, visits by German horticulturists, plant merchants, researchers, and travelers also increased (Kreiner and Tabata 1992). Doederlein noted the presence of mammals such as wild boars, rabbits, rats, and bats but mentioned the absence of deer and carnivores on the islands. Furthermore, based on the distribution of plants, amphibians, and reptiles, he suggested that the boundary between the Old Northern and Oriental zoogeographic regions lies between Amami-Oshima Island and Kyushu Island (Doederlein 1881a, 1881b).
A review of subsequent and recent major research on terrestrial mammals
Here, we describe the main research topics related to each taxonomic group with a focus on endemic mammals in the central and southern Ryukyu Archipelago. By reviewing researches on these mammals, combined with the geographic history and human activities mentioned above, we highlight the characteristics of the region.
Overall, in the central and southern Ryukyu Archipelago, there are six orders, 11 families, and 26 species, including six subspecies, of native terrestrial mammals (Table 1). The number of endemic mammals is 20, including three relict endemic genera (Tokudaia, Diplothrix, and Pentalagus), resulting in a high endemic rate of 77% in the region. Sixteen of these species, i.e., 62% of native species, are listed as threatened species in the region, Critically Endangered (CR), Endangered (EN), and Vulnerable (VU), in the Red Lists of Japan (Ministry of the Environment 2020), and seven high-ranking species out of the 640 mammal species evaluated in the Evolutionarily Distinct and Globally Endangered (EDGE) Species List are recognized in the region. The EDGE is the first global conservation initiative to specifically focus on threatened species based on the IUCN Red List status that represent a significant amount of unique evolutionary history (Isaac et al. 2007; Gumbs 2023; EDGE Team 2024) (Table 1). The number of species on each island in the region is proportional to its area (Fig. 2). In particular, the Central Ryukyus, which were the first to become isolated from the continent for an extended period, have a higher number of species. Additionally, the percentage of non-chiropteran (bat) species out of the total number of species on the islands (excluding Uotsuri-jima Island due to the unknown habitat status of chiropteran species, see below) is also higher in the Central Ryukyus (Fig. 2). Furthermore, the characteristics of the mammalian fauna in the Central Ryukyus include evolutionarily distinct lineages of relict genera of rodent and lagomorph species, with an absence of top predatory mammals in the food chain, while the South Ryukyus are home to feline species found on a very small island (Table 1). Therefore, it can be said that the unique mammalian fauna in the central and southern Ryukyu Archipelago developed through different relationships with the continent over geological eras and the evolution of endemic species. Additionally, in this section, we describe research on six nonnative mammals (Table 2) and related human conflict issues.
Fig. 2.
Species-area relationships for native terrestrial mammals in the central and southern Ryukyu archipelago. Values in parentheses represent the area of the islands and the percentage of non-chiropteran species out of the total number of species on the islands (excluding Uotsuri-jima Island due to the unknown habitat status of chiropteran species). The names of each island are as follows: Amami-Oshima, Amami-Oshima Island; Tokunoshima, Tokunoshima Island; Okinawa, Okinawa Island; Ishigaki, Ishigaki-jima Island; Iriomote, Iriomote Island; Miyako, Miyako-jima Island, Uotsuri, Uotsuri-jima Island; Minami Daito, Minami Daito-jima Island; and Kita Daito, Kita Daito-jima Island. The area of Amami-Oshima does not include those of Kakeroma-jima, Uke-jima, Yoro-jima Islands, and other small islands around Amami-Oshima Island.

Eulipotyphla
Four Eulipotyphla species are distributed in the Central Ryukyus, the South Ryukyus, and the Senkaku Island Group (Table 1). The number of endemic species among the four species is three, and the endemic rate is 75% in the region.
The Watase's shrew, Crocidura watasei Kuroda, 1924, is now considered a valid species based on karyotype differences, is endemic to the Central Ryukyus, and is thought to be a sister species to the Horsfield's shrew, C. horsfieldii (Tomes, 1856), which is common in South Asia (Motokawa et al. 1996; Hutterer 2005; Ohdachi et al. 2006; Motokawa 2015a). The species is listed as Near Threatened (NT) on the Red List of Japan (Ministry of the Environment 2020) (Table 1). The ecology of the Watase's shrew, such as reproduction, diet, habitat, and behavior, has been studied (e.g., Motokawa et al. 1996; Motokawa 2015a).
The Orii's shrew, C. orii Kuroda, 1924, is endemic to the Central Ryukyus and its closely related sister species has not yet been identified (Ohdachi et al. 2006; Motokawa 2015b). Although the Orii's shrew was previously thought to be a subspecies of the dsinezumi shrew, C. dsinezumi (Temminck, 1842), which is common in the Japanese mainland, morphological and genetic analyses have confirmed that it is an independent species (Motokawa 1998, 2003; Hutterer 2005; Motokawa 2015b). The species is listed as EN on the Red List of Japan (Ministry of the Environment 2020) (Table 1). There have been few studies on the life history of Orii's shrews partly because of their status as an endangered species.
The musk shrew, Suncus murinus (Linnaeus, 1766), on the islands in the Central and South Ryukyus was thought to be native, while populations in Kyushu were considered non-native, and its original range is estimated to have extended across Afghanistan, India, China, Taiwan, and continental and peninsula Indomalayan region (Hutterer 2005; Motokawa 2015c). A recent phylogenetic and population genetic analysis revealed that the population on the Ryukyus Islands expanded from Vietnam and southern China about 3300 years ago, likely in relation to human migration, with repeated immigration to the Ryukyu Islands in more recent years (Ohdachi et al. 2024).
The Senkaku mole, Mogera uchidai (Abe, Shiraishi & Arai, 1991), was first described by Hisashi Abe (Abe et al. 1991) as Nesoscaptor uchidai Abe, Shiraishi & Arai, 1991, based on a specimen of a young female collected in Uotsuri-jima Island in 1979 (Shiraishi and Arai 1980). However, Masaharu Motokawa reclassified it as Mogera uchidai (Abe, Shiraishi & Arai, 1991), recognizing that it is closely related to the insular mole, M. insularis (Swinhoe, 1863), from Taiwan, based on the morphological analysis and is thought to be distributed only on Uotsuri-jima Island (Motokawa et al. 2001; also see Yokohata 2015 for the species account). The species is listed as CR on the Red List of Japan (Ministry of the Environment 2020) (Table 1).
Challenges to obtain biological characteristics remain for species with limited available specimens, such as Orii's shrew (approximately ten specimens) (Abe 2005) and the Senkaku mole (only one specimen) (Abe et al. 1991; Motokawa et al. 2001; Yokohata 2015). However, due to the difficulty of accessing its habitat on Uotsuri-jima Island, information about its population size and the current status is still lacking, and further research is needed.
Chiroptera
A total of 13 species, including four subspecies, of Chiroptera are distributed in the Central Ryukyus, the South Ryukyus, and Daito Island Group (Table 1). The ten species and subspecies are endemic among these 13 species and subspecies, and the endemic rate is 77% in the region.
The Ryukyu flying fox, Pteropus dasymallus Temminck, 1825, has been confirmed on the islands in the North, Central, and South Ryukyus, as well as Senkaku and Daito Island Groups, and on islands in Taiwan and Philippines (Kinjo and Nakamoto 2015). In Japan, four subspecies have been classified (Yoshiyuki 1989; Maeda 1996; Simmons 2005; Kinjo and Nakamoto 2015); the Erabu flying fox, P. d. dasymallus, Kuroda, 1933, on the islands of the Osumi and the Tokara Island Groups of the North Ryukyus, the Orii's flying fox, P. d. inopinatus, Kuroda, 1933, on the Okinawa Island Group, the Yaeyama flying fox, P. d. yayeyamae Kuroda, 1933, on the islands of the South Ryukyus, and the Daito flying fox, P. d. daitoensis, Kuroda, 1921, on the islands of the Daito Island Group. In Taiwan, the Formosan flying fox, P. d. formosus Sclater, 1873, is classified (Sclater 1873). This species also occurs on the northern islands of the Philippines, but its taxonomic status is unclear. Recent molecular studies have revealed differences among the subspecies (Chen et al. 2021; Taki et al. 2021). The Daito flying fox is listed CR on the Red List of Japan (Ministry of the Environment 2020), as well as Endangered Species of Wild Fauna and Flora, and National Natural Monument (Table 1). Research on the distribution and ecology of the Ryukyu flying fox has primarily focused on the Orii's flying fox (e.g., Nakamoto et al. 2011, 2012, 2016). In recent years, research has been conducted on the Daito flying fox, an oceanic island subspecies, examining its relationship with the unique island environment and its conservation (Izawa et al. unpublished). Additionally, temporal changes in the geographic distribution of the Ryukyu flying fox across the islands of the Ryukyu Archipelago have been explored (Nakamoto 2017). The habitat status of the Ryukyu flying fox on Uotsuri-jima Island in the Senkaku Island Group, as observed in the 1953 survey; however, since then and up to the present, it remains unknown due to inaccessibility to the island, and further research is needed (Takara 1954; Nakamoto 2017).
The Okinawa flying fox, Pteropus loochoensis Gray, 1870, was recorded only from Okinawa Island; however, its taxonomic status remains uncertain, and it is considered to be extinct (Kinjo 2015). Three or four specimens collected from Okinawa Island in the 19th century, but there have been no further records of collection or observation since it was described, and the details are completely unknown (Gray 1870; Yoshiyuki 1989; Maeda 1996; Simmons 2005; Kinjo 2015; Nakamoto 2023). There are two possible explanations: it may have become extinct shortly after the type specimens were collected, or the location where the specimen was collected may have been recorded incorrectly.
The Okinawa little horseshoe bat, Rhinolophus pumilus Andersen, 1905, is endemic to the Okinawa Island Group and, formerly, to the Miyako-jima Island in the Sakishima Island Group (Sano and Armstrong 2015b). However, the subspecies of this bat, the Miyako little horseshoe bat, R. p. miyakonis Kuroda, 1924, which was found only on Miyako-jima Island, is now considered extinct, with no specimens collected since the last four specimens were lost in a fire (Yoshiyuki 1989; Maeda 1996; Kinjo 2015; Sano and Armstrong 2015b; Sano and Tamura 2023). The Yaeyama little horseshoe bat, R. perditus Andersen, 1918, is endemic to the islands in the Sakishima Island Group, and the Orii's little horseshoe bat, R. cornutus orii Kuroda, 1924, is an endemic subspecies of the Amami Island Group (Sano and Armstrong 2015b; Sano and Tamura 2023). The Orii's little horseshoe bat is a subspecies of the Japanese little horseshoe bat, R. cornutus Temminck, 1834, which is endemic to and widely distributed across Japan (Sano and Armstrong 2015a). The three Rhinolophus species, R. pumilus, R. perditus, and R. cornutus, have been considered synonyms of R. cornutus and there are low levels of sequence divergence among them in molecular analyses (Li et al. 2006; Sano and Armstrong 2015a). The Okinawa little horseshoe bat and the Yaeyama little horseshoe bat have been proposed as subspecies or separate species, with ongoing taxonomic discussions (Simmons 2005; Sano and Armstrong 2015a, 2015c). Challenges regarding habitat status and taxonomic positioning remain for species with limited available specimens, such as the extinct Okinawa flying fox. The Okinawa little horseshoe bat is listed as EN on the Red List of Japan (Ministry of the Environment 2020), and Endangered Species of Wild Fauna and Flora. The Yaeyama little horseshoe bat is designated as VU on the Red List of Japan (Ministry of the Environment 2020). The Orii's little horseshoe bat is EN on the Red List of Japan (Ministry of the Environment 2020), and Endangered Species of Wild Fauna and Flora (Table 1).
The lesser leaf-nosed bat, Hipposideros turpis Bangs, 1901, is endemic to islands of the Yaeyama Island Group and is a distinct species from those found in Thailand and Vietnam, as analyzed through morphological and genetic studies (Simmons 2005; Thong et al. 2012; Sano and Diaz 2015). Populations of the lesser leaf-nosed bat on Hateruma and Yonaguni Islands of the Yaeyama Island Group are listed as a Local Population (LP) on the Red List of Japan (Ministry of the Environment 2020), as well as Endangered Species of Wild Fauna and Flora, and are ranked 328th by EDGE Team (2024) (Table 1).
The Japanese pipistrelle, Pipistrellus abramus (Temminck, 1984), is widely distributed across East Asia, including southern Ussuri, China, Taiwan, Korea, Vietnam, Myanmar, India, and Japan, with populations in the Central and South Ryukyus (Simmons 2005; Kawai 2015a).
The Japanese large-footed bat, Myotis macrodactylus (Temminck, 1840), is widely distributed across East Asia, including eastern Siberia, southern Sakhalin, and Japan, with populations in the North Ryukyus and on Amami-Oshima and Tokunoshima Islands in the Central Ryukyus (Sano and Ishida 2015).
A new species of small bat, the Yanbaru Myotis, M. yanbarensis Maeda & Matsumura, 1998, was discovered in 1996 (Maeda and Matsumura 1998). The Yanbaru Myotis is endemic to Amami-Oshima and Tokunoshima Islands, and the northern part of Okinawa Island in the Central Ryukyus, and is closely related to the frosted Myotis, M. pruinosus Yoshiyuki, 1971, endemic to the Japanese mainland, and is also grouped with the Burmese whiskered Myotis, M. montivagus (Dobson, 1874), from Malaysia and the hairy-faced Myotis, M. annectans (Dobson, 1871), from Thailand (Maeda and Matsumura 1998; Kawai et al. 2003; Simmons 2005; Kawai 2015b, 2015c). The species is listed as EN on the Red List of Japan (Ministry of the Environment 2020), as well as Endangered Species of Wild Fauna and Flora, and is ranked 147th by EDGE Team (2024) (Table 1).
The East-Asian little bent-winged bat, Miniopterus fuscus Bonhote, 1902, is endemic to mainly Amami-Oshima, Tokunoshima, and Okinawa Islands in the Central Ryukyus, and Ishigaki and Iriomote Islands in the South Ryukyus (Simmons 2005; Sano 2015a). The species is listed as EN on the Red List of Japan (Ministry of the Environment 2020), and Endangered Species of Wild Fauna and Flora (Table 1).
A new species of small bat, the Ryukyu tube-nosed bat, Murina ryukyuana Maeda & Matsumura, 1998, was discovered in 1996 (Maeda and Matsumura 1998). The Ryukyu tube-nosed bat is endemic to Amami-Oshima and Tokunoshima Islands, and the northern part of Okinawa Island in the Central Ryukyus (Simmons 2005; Kawai 2015d). The species is listed as EN on the Red List of Japan (Ministry of the Environment 2020), as well as Endangered Species of Wild Fauna and Flora, and is ranked 346th by EDGE Team (2024) (Table 1). Studies have been conducted on the ecology of the species (e.g., Funakoshi et al. 2019; Preble et al. 2021a, 2021b). Ongoing research anticipates the further discovery of new species and their records as noted below.
The Oriental little free-tailed bat, Tadarida latouchei Thomas, 1920, is known from China, Laos, Thailand, and Japan, and in Japan a single specimen has been collected since 1969, from each of Kuchinoerabu-jima in the North Ryukyu, and Amami-Oshima and Yoron-jima Islands in the Central Ryukyus (Sano 2015b; Funakoshi 2023). The species is considered clearly distinct based on morphological characteristics from the European free-tailed bat, T. teniotis (Rafinesque, 1814), and the East Asian free-tailed bat, T. insignis Blyth, 1862, which is distributed across China, Korea, the Ussuri region, Taiwan, and Japan (Funakoshi and Kunisaki 2000; Simmons 2005). The species is listed as Data Deficient (DD) on the Red List of Japan (Ministry of the Environment 2020) (Table 1).
Because Chiroptera species are volant, they sometimes stray into areas during typhoons or when transported in cargo. In recent years, the Chinese pipistrelle, Hypsugo pulveratus (Peters, 1871), which is distributed across southeastern China, Taiwan, Thailand, Laos, and Vietnam, has been found on Amami-Oshima Island (Funakoshi et al. 2022), and the black-bearded tomb bat, Taphozous melanopogon Temminck, 1841, which is distributed in Southeast Asia, has been found on Okinawa Island (Kobayashi et al. 2022). However, it is unclear whether the populations of these species have become established in the central and southern Ryukyu Archipelago.
Rodentia
Six Rodentia species were distributed on the Central Ryukyus and Senkaku Island Group (Table 1). The number of endemic species among the six species is four, and the endemic rate is 67% in the region.
Many islands in this region remain insufficiently surveyed, and ongoing research has revealed new insights, such as the division of the genus Tokudaia into three species and other findings (e.g., Endo and Tsuchiya 2006; Terao et al. 2022; also see Iwasa 2015a, 2015b, 2015c; Jogahara 2016).
The Amami spiny rat, Tokudaia osimensis (Abe, 1933), was first described by Yoshio Abe (Abe 1933) based on specimens from Amami-Oshima Island and initially classified Rattus jerdoni osimensis Abe, 1933. However, Mitoshi Tokuda (Tokuda 1941) later demonstrated that this form was distinct from R. jerdoni found in India and that its cranial and dental characteristics were more similar to those of Apodemus than Rattus, and proposed a new genus, Acanthomys osimensis (Abe, 1933). Subsequently, Nagamichi Kuroda (Kuroda 1943) established the genus Tokudaia and classified Tokudaia osimensis (Abe, 1933) within it. In contrast, David H. Johnson (Johnson 1946), based on his new specimens collected from the northern part of Okinawa Island, classified this form under a different genus, Tokudamys osimensis osimensis (Abe, 1933), and proposed a new subspecies, Tokudamys osimensis muenninki Johnson, 1946. However, Ellerman and Morrison-Scott (1951) reorganized the classification using Kuroda's genus Tokudaia, recognizing the Amami spiny rat as the subspecies Tokudaia osimensis osimensis (Abe, 1933), while the Okinawa spiny rat was classified as Tokudaia osimensis muenninki (Johnson, 1946). Finally, Musser and Carleton (1993) reclassified the Amami spiny rat as Tokudaia osimensis (Abe, 1933), and the Okinawa spiny rat as T. muenninki (Johnson, 1946), recognizing each as a distinct species, and this classification has been maintained since then (Kawamura 1989; Kaneko and Murakami 1996; Kaneko 2001; Musser and Carleton 2005; Kaneko 2006). The Tokudaia species found on Tokunoshima Island was confirmed in 1977, and Hideki Endo and Kimiyuki Tsuchiya (Endo and Tsuchiya 2006) described it as a new species, named the Tokunoshima spiny rat, T. tokunoshimensis Endo & Tsuchiya, 2006. The relict genus Tokudaia is thought to have diverged from the allied genus Apodemus and other species of the Murinae lineage in the Late Miocene, Okinawa spiny rats diverged from the ancestral lineage ca. 2.5 Mya and Tokunoshima spiny rats and Amami spiny rats branched from the lineage ca.1 Mya (Sato and Suzuki 2004; Murata et al. 2012; Kinoshita et al. 2025). The Amami spiny rat, which is endemic to Amami-Oshima Island, is listed as EN on the Red List of Japan (Ministry of the Environment 2020), as well as Endangered Species of Wild Fauna and Flora, National Natural Monument, and is ranked 79th by EDGE Team (2024) (Table 1). The Okinawa spiny rat, which is endemic to the northern part of Okinawa Island, is listed as CR on the Red List of Japan (Ministry of the Environment 2020), as well as Endangered Species of Wild Fauna and Flora, National Natural Monument, and is ranked 29th by EDGE Team (2024) (Table 1). The Tokunoshima spiny rat, which is endemic to Tokunoshima Island, is listed as EN on the Red List of Japan (Ministry of the Environment 2020), as well as National Natural Monument, Endangered Species of Wild Fauna and Flora, and is ranked 75th by EDGE Team (2024) (Table 1). The variations in karyotypes and unique sex chromosomes have been reported across the three Tokudaia species, revealing a novel sex-determination mechanism that was first identified in mammals (e.g., Murata et al. 2012; Kuroiwa 2015; Terao et al. 2022). Morphological discrimination between the Amami spiny rat and the Okinawa spiny rat (Kaneko 2001), captive breeding experiments on Amami spiny rats (Shinohara et al. 2013; Ministry of the Environment 2017), rediscovery of survival and historical distribution, foods, and behavior of Okinawa spiny rats (Yamada et al. 2010; Kudaka and Kudaka 2017b; Yasuda et al. 2017; Kotaka et al. 2021) and the survey on the distribution of Tokunoshima spiny rats (Jogahara et al. 2020) have been carried out.
The striped field mouse, Apodemus agrarius (Pallas, 1771), was first recognized in 1970 and confirmed in 1979 by the capture of two individuals on Uotsuri-jima Island in the Senkaku Island Group (Shiraishi and Arai 1980). This species is widely distributed across Eurasia, from Western Europe to Lake Baikal, and from the Amur River in the east to China, Korea, Taiwan, and Uotsuri-jima Island in Japan (Iwasa 2015d). However, due to the difficulty of accessing its habitat, information about its population size and the current status is still lacking, and further research is needed (Shiraishi et al. 1977; Shiraishi and Arai 1980). The species is listed as CR on the Red List of Japan (Ministry of the Environment 2020) (Table 1).
The Ryukyu long-furred rat, Diplothrix legata (Thomas, 1906), is a monospecific genus and endemic to Amami-Oshima and Tokunoshima Islands, and the northern part of Okinawa Island (Iwasa 2015e; Jogahara 2016). The original description of the Ryukyu long-furred rat was provided by Oldfield Thomas (Thomas 1906) based on a specimen collected by Alan Owston from Amami-Oshima Island as Lenothrix legata Thomas, 1906, because of its similarity to the gray tree rat, L. cana Miller, 1903, found on Sumatra Island in Indonesia. However, Thomas (1916) revised the genus to Diplothrix legata (Thomas, 1906) after comparing it with specimens of Indian species collected in British Sikkim in India. The species name was later supported by researchers such as Kuroda (1940) and Tokuda (1941). Although Ellerman (1941) and Ellerman and Morrison-Scott (1951) proposed Rattus legatus (Thomas, 1906), subsequent examinations by researchers such as Misonne (1969), Musser and Boeadi (1980), and Kawamura (1989) identified it as Diplothrix legata (Thomas, 1906), a name that is currently used (Musser and Carleton 1993, 2005; Kaneko and Murakami 1996; Kaneko 2006). The relict genus Diplothrix is thought to have diverged from the Rattus group more recently than Tokudaia diverged from the Apodemus group, and its lineage was established by at least the beginning of the Pleistocene (Suzuki et al. 2000; Kinoshita et al. 2025). The species is listed as EN on the Red List of Japan (Ministry of the Environment 2020), as well as Endangered Species of Wild Fauna and Flora and National Natural Monument (Table 1). Surveys of fossils and archeological records from the Holocene and the 11th to 15th centuries, aimed at elucidating the historical distribution of the species in the Central Ryukyus, have been conducted (Nakamura 2018). Genetic diversity (Okano et al. 2015; Kinoshita et al. 2025), morphology (Okano and Onuma 2015; Iwasa et al. 2020; Kubo et al. 2025; Nakanishi et al. 2025), ecological characteristics and role in forest ecosystems (Nago et al. 2019; Kobayashi et al. 2022: Higashi and Kobayashi 2023, 2025; Yamato et al. 2024) have been investigated. Food habits in the northern part of Okinawa Island (Kudaka and Kudaka 2017a; Kobayashi et al. 2025; Kubo et al. 2025), and food habits and some mating behaviors on Amami-Oshima Island (Makino 2020) have been revealed. Distribution surveys have been conducted in the northern part of Okinawa Island (Taniguchi et al. 2019) and Tokunoshima Island (Jogahara and Koshimoto 2017).
The Ryukyu mouse, Mus caroli Bonhote, 1902, is found only on Okinawa Island in Japan, but it is widely distributed across Southeast Asia, including Taiwan, Hainan, southern China, Malaysia, Vietnam, and Sumatra Island in Indonesia (Iwasa 2015f). The population of this species on Okinawa Island is thought to have recently invaded and may be non-native, based on morphological and genetic analyses compared to populations from Taiwan and other regions, as well as fossil records, although M. musculus has been found in the Holocene in the South Ryukyus (Motokawa et al. 2003; Shimada et al. 2007; Kawamura et al. 2016; Nishioka et al. 2016).
Lagomorpha
One species of Lagomorpha, the Amami rabbit, Pentalagus furnessi (Stone, 1900), is distributed on the Amami-Oshima and Tokunoshima Islands in the Central Ryukyus (Table 1). The species is endemic, and the endemic rate is 100% in the region.
The original description of the Amami rabbit was made by Witmer Stone (Stone 1900) as Caprolagus furnessi Stone, 1900, based on specimens collected by William H. Furness and Hiram M. Hiller on Amami-Oshima Island in 1896. Later, Marcus W. Lyon (Lyon 1904) reorganized the classification of the family Leporidae, creating a new genus for the Amami rabbit as Pentalagus furnessi (Stone, 1900), because the specimen had only five upper cheek teeth and lacked a third upper molar. Since then, the species has been classified under a monotypic genus (Hoffmann and Smith 2005; Yamada and Cervantes 2005; Yamada 2015; Yamada 2017). Molecular phylogenetic analyses revealed that the relict genus Pentalagus and its allied genera were thought to have diverged from each other ca. 9.44 Mya and its timing is also likely to be consistent with the paleogeographic explanation that the Central Ryukyus had been a part of the Eurasian Continent during the Middle Miocene but became separated from the continent since the Late Miocene to early Pleistocene (Yamada et al. 2002; Matthee et al. 2004; Government of Japan 2019; Kinoshita et al. 2025). Fossils of the genus Pliopentalagus have been found in the Yangtze River Basin in Anhui Province in eastern China on the Eurasian Continent, dating from 6 Mya to 3 Mya (Tomida and Jin 2002), and Pliopentalagus okuyamai Tomida & Takahashi 2023, collected in Mie Prefecture in the Japanese mainland dating from 3 Mya to 2.5 Mya (Tomida and Takahashi 2023; Tomida et al. 2024), and fossils of the genus Pentalagus on Okinawa Island dating from 1.7 Mya to 1.3 Mya and 0.4 Mya (Ozawa 2009), and fossils of present species on Tokunoshima Island probably dating to 0.03–0.018 Mya (Tomida and Otsuka 1993) have been discovered. The species is listed as EN on the Red List of Japan (Ministry of the Environment 2020), as well as Endangered Species of Wild Fauna and Flora and National Natural Monument, and is ranked 69th by EDGE Team (2024) (Table 1).
The first research on the distribution, ecology, and population status of the Amami rabbit on Amami-Oshima Island was conducted to designate the National Natural Monument, a year after the enactment of the “Historical Sites and Natural Monuments Protection Act” in 1919 (Uchida 1920). Over 40 years later, from 1963 to 1992, observations of captive individuals and outdoor surveys were conducted by Yamato Village Elementary and Junior High School on Amami-Oshima Island (e.g., Kirino 1977; Hiragi et al. 2024). Observations of nests, fecal distribution, and parasite research were carried out by the Medical Institute on Amami-Oshima Island of the University of Tokyo (e.g., Suzuki 1985). Researches on rearing and reproduction in captivity was also carried out in a laboratory and a zoo (Matsuzaki et al. 1989; Sako et al. 1991).
Distribution changes and population fluctuations (Sugimura and Yamada 2004; Seki et al. 2023; Ministry of the Environment unpublished), home range (Yamada et al. 2000), food habits (Asari and Kimoto 2022; Suetsugu and Hashiwaki 2023; Kubo et al. 2025), genetic analyses (Yamada et al. 2002; Ohnishi et al. 2017; Ando et al. 2018; Kinoshita et al. 2025), and morphology and growth (Hayashida et al. 1967; Otsuka et al. 1980, 1981; Hayashi et al. 2025; Gunji et al. 2025) have also been investigated mainly on Amami-Oshima Island and also Tokunoshima Island. Research on reproduction based on sensor camera surveys has revealed the detailed maternal behavior from prebirth to near the period of independence for offspring on Amami-Oshima Island (Suzuki and Oumi 2017b; Hamada and Mizuta 2020).
Carnivora
One subspecies of Carnivora, the Iriomote cat, Prionailurus bengalensis iriomotensis (Imaizumi, 1967), is distributed only on Iriomote Island of the South Ryukyus (Table 1). The Iriomote cat is endemic subspecies to the island and the endemic rate is 100% in the region.
Discovered by the animal literature writer Yukio Togawa in 1965, it was officially described as a new species by Yoshinori Imaizumi in 1967 (Imaizumi 1967). Initially it was considered a felid with a single genus and independent species as Mayailurus iriomotensis Imaizumi, 1967, because it was judged to maintain ancient traits. However, its taxonomic status has changed with the development of molecular genetic techniques and the accompanying revision of the classification of the Felidae as a whole. It has been classified as a separate species, first as Felis iriomotensis (Imaizumi, 1967) and Prionailurus iriomotensis (Imaizumi, 1967) (e.g., Wurster-Hill et al. 1987; Leyhausen and Pfleiderer 1994, 1999; Wozencraft 1993, 2005), and then subsequent taxonomic revisions now classify it as Prionailurus bengalensis iriomotensis (Imaizumi, 1967), endemic to Iriomote Island, and a subspecies of the mainland leopard cat, P. bengalensis (Kerr, 1792) (e.g., Masuda et al. 1994; Suzuki et al. 1994; Masuda and Yoshida 1995; Johnson et al. 1999; O'Brien and Johnson 2007). Twelve subspecies of the mainland leopard cat have been recorded, and more recently, the mainland leopard cat has been split into two species: the mainland leopard cat (including the subspecies Iriomote cat) and the Sunda leopard cat, P. javanensis (Desmarest, 1816) (Kitchener et al. 2017). The mainland leopard cat is widely distributed across the southeast Eurasian Continent, including India, Myanmar, Thailand, Indochina, China, Korea, and Japan, while the Sunda leopard cat is found in the Sunda Islands of Southeast Asia, including Sumatra, Borneo, and others (Kitchener et al. 2017). A review of the subspecies has been proposed (Patel et al. 2017), but this is currently under discussion. Processes of changes in taxonomy and relationships with fossil species are summarized in Nakanishi (2023) and Takahashi et al. (2023).
Since its discovery in 1965, the Iriomote cat has attracted international attention for both academic and conservation purposes. The IUCN Red List of 2018 designates it as a critically endangered subspecies; it is a rare occurrence, as it typically operates at the species level and is rarely specified at the subspecies level. In the IUCN Red List of 2021, the mainland leopard cat including the Iriomote cat was listed as Least Concern (LC) because of their wide distributions and stable population trends. However, an assessment report stated that “for the islands Iriomote and Tsushima in Japan and for Taiwan, the population sizes of the mainland leopard cat are supposed to be very small” (Ross et al. 2015; Ghimirey et al. 2023). The Iriomote cat is listed as CR on the Red List of Japan (Ministry of the Environment 2020), as well as Endangered Species of Wild Fauna and Flora, National Natural Monument (Table 1).
Following the discovery in 1965, research on Iriomote cat was undertaken by Tetsuo Takara of the Faculty of Agriculture at the University of the Ryukyus (Imaizumi and Takara 1971). Further ecological studies and conservation efforts were led by Sadao Ikehara of the Faculty of Science and Engineering (later the Faculty of Science) at the University of the Ryukyus. Research primarily centered on the University of the Ryukyus and Kyushu University has focused on habitat utilization, social structure, distribution, diet, behavior, ecology, and morphology, revealing the Iriomote cat's adaptation to life on a small island, specifically Iriomote Island, and its unique ecological traits among the world's felids (e.g., Watanabe et al. 2003; Watanabe and Izawa 2005; Nakanishi and Izawa 2015, 2016; Izawa and Nakanishi 2018; Doi and Izawa 2023; Tobe et al. 2024).
Artiodactyla
One subspecies of Artiodactyla, the Ryukyu wild boar, Sus scrofa riukiuanus Kuroda, 1924, is distributed and endemic subspecies to the Central and South Ryukyus (Table 1). The endemic rate is thus 100% in the region.
The Ryukyu wild boar was first described as S. leucomystax riukiuanus, Kuroda, 1924. However, the species name was later changed to scrofa, along with other species, due to synonyms across North Africa, Eurasia, South Russia, China, and other regions (Ellerman and Morrison-Scott1951; Grubb 1993). The Ryukyu wild boar is thought to be different from the Japanese wild boar, S. s. leucomystax (Temminck, 1842), common in the Japanese mainland, and other East Asian wild boars, based on morphological and DNA analyses (e.g., Imaizumi 1973; Watanobe et al. 1999; Endo et al. 2002; Kodera 2015; Yamada et al. 2018). Although the subspecies is genetically close to wild boars in Eastern Asia, the origin of the current subspecies is thought to be natural dispersal prior to its introduction by prehistoric humans (Ishiguro et al. 2008; Yoshikawa et al. 2016). Population of the Ryukyu wild boar on Tokunoshima Island is listed as LC on the Red List of Japan (Ministry of the Environment 2020) (Table 1).
Food habits, population fluctuation, and resource utilization by humans have been studied on Amami-Oshima and Iriomote-jima Islands, and the northern part of Okinawa Island (e.g., Handa 2000; Ishigaki et al. 2007; Ebihara 2009; Shimada et al. 2024). However, concerns regarding genetic introgression from the domestic pig, S. s. domesticus are likely to arise on the islands of the region, and further research is required (Watanobe et al. 2002; Tsuboi et al. 2011; Murakami et al. 2014; Takahashi et al. 2019). Predation of eggs of sea turtles (e.g., Caretta caretta and Chelonia mydas) and agricultural damage by the species have been reported, and concerns are growing regarding the impact on the ecosystem due to the increasing numbers of Ryukyu wild boars on some islands of the region (Sasai et al. 2016; Okinawa Prefectural Office 2020; Kagoshima Prefectural Office 2022).
Non-native mammals
Several non-native mammals, including the black rat, Rattus rattus (Linnaeus, 1758), the dog, Canis familiaris Linnaeus, 1758, the domestic cat, Felis catus Linnaeus, 1758, the Japanese weasel, Mustela itatsi Temminck, 1844, the small Indian mongoose, Urva auropunctata (Hodgson, 1836) [it was first recognized as the small Asian mongoose, Herpestes javanicus (Geoffroy Saint-Hilaire, 1818), and later classified to H. auropunctatus (Hodgson, 1836), but all Asian mongooses were later assigned to the genus Urva (Veron et al. 2007; Patou et al. 2009; Veron and Jenning 2017)], and the goat, Capra hircus Linnaeus, 1758, have been confirmed on various islands in this region, as shown by the six species listed in Table 2 (Ministry of the Environment 2021). Although other nonnative mammals, e.g., the European rabbit, Oryctolagus cuniculus (Linnaeus, 1758), and the Japanese wild boar, are temporarily found on some islands, only the species confirmed to have been established are shown in Table 2.
In non-native mammals, intensive research has been conducted on mongoose invasion in the northern part of Okinawa Island and on Amami-Oshima Island (Yamada et al. 2009; 2015; Ikeda and Yamada 2011; Ogura and Yamada 2011). Reproduction and morphology of mangooses and their food in the northern part of Okinawa Island (Ogura et al. 1998; 2001; 2002), the effects of mongooses on native species and the improvements of the mongoose eradication program on Amami-Oshima Island (Yamada 2002; Watari et al. 2008; Fukasawa et al. 2013a; Watari 2019), and the restoration of Amami spiny rat, Ryukyu long-furred rat, Amami rabbit, and other species on Amami-Oshima Island (Fukasawa et al. 2013b; Watari et al. 2013; Ministry of the Environment unpublished) have been studied. On the other hand, Okinawa spiny rat and Ryukyu long-furred rat in the northern part of Okinawa Island have also been monitored by the mongoose control program (Ministry of the Environment unpublished). The history of the mongoose introduction by humans from Okinawa Island to Amami-Oshima Island, and from Okinawa Island to Kagoshima City in Kyushu, was revealed through genetic analysis (Sato et al. 2023).
Table 2.
A summary of non-native mammals inhabiting the main islands of the central and southern Ryukyu Archipelago, which have already established themselves and are of concern due to their potential major impact on ecosystems

Research on invasive Japanese weasels has also been carried out regarding their diet and impact on native species in Miyako-jima Island, Minami Daito-jima Island, and Zamami Island (Sekiguchi et al. 2002; Kawauchi et al. 2018; Kobayashi et al. 2022).
Research has been conducted on actual condition of feral goats and their impact on environment. Due to inaccessibility to the island, surveys, such as aerial photography, were conducted on Uotsuri-jima Island of the Senkaku Island Group (Yokohata and Yokota 2000; Yokohata 2003; Yokohata et al. 2003, 2009; Takiguchi 2015), and research has also been conducted on Amami-Oshima Island (Watari 2016).
Additionally, studies have been conducted on the predation effects of free-ranging dogs on Amami-Oshima Island (Nakano and Murai 1996; Watari et al. 2007), as well as evaluations of predation by free-ranging domestic cats and surveys involving residents in the northern part of Okinawa Island, and on Amami-Oshima and Tokunoshima Islands (e.g., Jogahara et al. 2003; Izawa 2015; Shionosaki et al. 2015; Shionosaki 2016; Mameno et al. 2017; Suzuki and Oumi 2017a; Maeda et al. 2019; Kazato et al. 2020; Kobayashi et al. 2020; Qi et al. 2022). The identification of hair from native species for food habit analysis and DNA analysis of non-native carnivores on the bodies of endangered species have been studied and carried out in the northern part of Okinawa Island (Asato and Izawa 2020; Ministry of Environment unpublished).
Infection with Toxoplasma gondii, its definitive host being felines, including domestic cats, has been confirmed in an Amami spiny rat, Amami rabbit, invasive mongooses on Amami-Oshima Island, and invasive black rats and free-ranging domestic cats on Tokunoshima Island (Kubo et al. 2013; Tokiwa et al. 2019; Ito et al. 2020; Shoshi et al. 2021; Okada et al. 2022). Furthermore, infection with T. gondii has also been confirmed in livestock, such as pigs and goats, as well as in wild animals including black rats, musk shrews, Ryukyu wild boars, mongooses, and free-ranging domestic cats on Okinawa Island and the Yaeyama Islands (Kyan et al. 2013, 2021).
Roadkill, rehabilitating animals, and agricultural damage prevention caused by native mammals
Roadkill of endangered species by vehicles also occurs in this region. Particularly on islands, roadkill frequently occurs on roads that pass through or close to the habitats of endangered species. Research is being conducted on the environmental conditions of these incidents to develop preventive measures to protect Amami rabbits, Amami spiny rats, and other animals on Amami-Oshima Island (Hiragi et al. 2017; Asari and Fujiki 2020; Asari et al. 2020; Suzuki 2023), Ryukyu long-furred rats and Okinawa spiny rats in the northern part of Okinawa Island (Tamanaha et al. 2017; Miyamoto et al. 2021; Tamanaha and Watari 2023; Maruta et al. 2024), and Iriomote cat on Iriomote Island (Izawa et al. 2009; Yamamoto and Uchino 2023).
Researches on rehabilitating injured or sick individuals of endangered species that are primarily affected by roadkill or predation, such as the Ryukyu long-furred rat, the Okinawa spiny rat, the Amami rabbit, the Iriomote cat, and others, have been conducted (e.g., Nakaya et al. 2017; Ministry of the Environment unpublished).
Research has been conducted on using fences as a measure to prevent intrusion into farmland to mitigate agricultural damage. This includes damage to tankan orange Citrus tankan orchards, an important industry in the area, caused by the Amami rabbit on Amami-Oshima Island (e.g., Nakamura et al. 2023). Additionally, black rats, a non-native species, also cause damage to tankan oranges on Amami-Oshima Island (Yabe 1998). Although sugarcane and other agricultural products have been damaged by animals such as Ryukyu wild boars, Amami rabbits, and black rats, there has been little research on effective prevention methods. The only measures being implemented on agricultural sites are the use of rodenticides against black rats and the installation of fences or traps to control Ryukyu wild boars.
Outline of the history of conservation before and after the 1970's
We describe the national systems, policies, and conservation management, as well as academic initiatives, before and after the emergence of modern conservation in the 1970's, and outline the future conservation issues and challenges in the central and southern Ryukyu Archipelago.
National Natural Monuments and conservation of endangered species
Seven mammal species, including subspecies, in the central and southern Ryukyu Archipelago have been designated as National Natural Monuments by the Agency for Cultural Affairs of the Japanese Government (Table 1). The Amami rabbit was the first to be designated as a Natural Monument in 1921 (and was later elevated to a Special Natural Monument in 1963), and the spiny rat (genus Tokudaia) and Ryukyu long-furred rat were designated as natural monuments in 1972. The Iriomote cat was designated in 1972 and elevated as a Special Natural Monument in 1977, the dugong was designated in 1972, and the Daito flying fox was added in 1973.
The establishment of the Environmental Agency in 1971 and the reorganization of the Ministry of the Environment in 2001 by the Government of Japan marked the beginning of environmental administration at the national level. Since then, efforts have been made to commence and intensify the conservation and management of wildlife in the central and southern Ryukyu Archipelago. The international community has also directed attention to the central and southern Ryukyu Archipelago, leading to requests for the protection of wildlife and island ecosystems from organizations such as the World Wildlife Fund (WWF, established in 1961, and WWF Japan in 1971) and the International Union for Conservation of Nature (IUCN, established in 1948). These requests were based on surveys, including those for the Iriomote cat and Amami rabbit. The Government of Japan ratified the Washington Convention in 1980 to enhance domestic legislation. Subsequently, international conferences, such as the Convention on Biological Diversity (Earth Summit, 1992) and the Conference of the Parties to the Convention on Biological Diversity (Nagoya Summit, 2010) took place. These events provided opportunities for international understanding and cooperation, such as measures against the invasive mongoose on Amami-Oshima Island and the northern part of Okinawa Island under the “Invasive Alien Species Act (IAS Act),” enacted in 2005, aiming to prevent the harmful effects of invasive alien species (IAS) on the environment, human safety, and the agriculture, forestry, and fisheries industries, based on the list of the 100 of World's Worst Invasive Alien Species (Lowe et al. 2000).
The Ministry of the Environment enacted the “Act on the Conservation of Endangered Species of Wild Fauna and Flora” in 1994. At the first designation of endangered species, the Iriomote cat was listed in 1994, followed by the Daito flying fox and the Amami rabbit in 2004; the Amami spiny rat, Tokunoshima spiny rat, Okinawa spiny rat, and Ryukyu long-furred rat in 2016; and five small bat species (Ryukyu tube-nosed bat and Yanbaru Myotis in 2019, and Okinawa little horseshoe bat, Orii's little horseshoe bat, and East-Asian little bent-winged bat in 2020). In total, 12 species are listed (Table 1). The “Act on the Conservation of Endangered Species of Wild Fauna and Flora” includes provisions for individual protection and habitat conservation, along with the formulation of protection and breeding project plans. The Red List is an important indicator of conservation. After the IUCN published its first Red Data Book in 1966, the Japanese Ministry of the Environment issued a Japanese version in 1991 (Table 1). Subsequently, each prefecture, Okinawa and Kagoshima, created its own Red Data Book for their respective region. The first edition of Okinawa Prefecture's list was published in 1996, followed by revisions in 2005 and 2013. Considerations for the creation of the fourth edition are currently underway. The list included 22 mammalian species, including those categorized as LC or DD, were represented. The Kagoshima Prefecture's Red Data Book was published in 2003 based on surveys conducted from 1999 to 2002. The 2015 revised edition includes 15 species in the Amami Island Group, with no significant changes. According to the Ministry of the Environment's Red List, the Miyako little horseshoe bat was declared extinct in the 2020 edition owing to a lack of confirmation over a specific period. Following the Okinawa flying fox, this marks the second mammalian species to be declared extinct in the Central and South Ryukyus as mentioned in the previous section.
National parks and forest ecosystem protected areas
There are currently four national parks in the central and southern Ryukyu Archipelago. The Iriomote-Ishigaki National Park, established in 2007 with the incorporation of Ishigaki Island, was renamed from Iriomote National Park (established in 1972) to Iriomote-Ishigaki National Park and further expanded in 2016. Yambaru National Park, designated in 2016 and expanded in 2018, includes parts of the U.S. Marine Corps Northern Training Area's returned land. Kerama Islands National Park was established in 2014. While the national park mainly covers marine areas, it also includes conservation areas, such as the breeding sea areas of the humpback whale, Megaptera novaeangliae (Borowski, 1781), which migrates to the region annually. The Amami Islands National Park was designated in 2017. The Wildlife Conservation Centers of the Ministry of the Environment were established within these national parks. The Iriomote Wildlife Conservation Center was established in 1995, the Yambaru Wildlife Conservation Center was established in 1999, the Amami Wildlife Conservation Center was established in 2000, and the Tokunoshima Administration Office was established in 2013.
Another administrative agency involved in conserving endangered species at the national level is the Forestry Agency of the Ministry of Agriculture, Forestry and Fisheries. The Okinawa Forest Management Office, within the management of national forests, has designated “the Forest Ecosystem Protected Areas” (Iriomote Island in 1991 and the northern part of Okinawa Island in 2017), and the Kagoshima Forest Management Office, designated “the Forest Ecosystem Protected Areas” in national forests on Amami-Oshima and Tokunoshima Islands in 2013, implemented regulations for the conservation of highly diverse ecosystems. The monitoring and conservation of endangered species have also been conducted.
Natural World Heritage
The Natural World Heritage registration for “Amami-Oshima Island, Tokunoshima Island, Northern part of Okinawa Island, and Iriomote Island” was confirmed by the UNESCO on July 26, 2021 (UNESCO 2021). This marked Japan's fifth Natural World Heritage Site, following Shirakami-Sanchi (1993), Yakushima (1993), Shiretoko (2005), and the Ogasawara Islands (2011). The journey to registration of the central and southern Ryukyu Archipelago began in 1990 when the Nature Conservation Society of Japan included in their request to the government that the “unique biodiversity and habitats of the southwestern islands” should be considered candidates for World Heritage (Nature Conservation Society of Japan 1990). In 2003, the Ministry of the Environment and the Forestry Agency officially included this region as a candidate site for discussion. Subsequent preparations were made, and in-depth discussions aimed at preparing the nomination document began in 2013. The nomination document, aligned with Criteria IX (ongoing ecological or biological processes crucial for the evolution and development of ecosystems and species) and Criteria X (areas essential for biodiversity conservation), was submitted to UNESCO in 2017. During this period, the Yambaru National Park (2016), Amami Islands National Park (2016), and the Yambaru Forest Ecosystem Protected Area (2017) were newly designated as mentioned in the previous section. However, the nomination received an evaluation of “deferred registration” from IUCN. According to the evaluation, it did not meet the Outstanding Universal Value for the Criterion IX, citing issues such as the discontinuity of the recommended area owing to its enclave nature and the absence of returned lands from the U.S. Marine Corps Northern Training Area in the northern part of Okinawa Island. After a year of consideration following the integration of parts of discontinuity areas, the criteria were narrowed down to the Criteria X, and the recommended area was revised. The second nomination document was submitted in 2019. The World Heritage Committee was postponed during the 2020 COVID-19 pandemic. After twisting and turning, the final registration was achieved in 2021 (Fig. 3).
The four islands listed as Natural World Heritage Sites in Japan are home to 21 species of terrestrial mammals, 394 species of birds, 36 species of terrestrial reptiles, and 21 species of amphibians (note that the number of species is subject to change due to taxonomic revisions, and the figures mentioned here are based on the time of nomination) (Government of Japan 2019). Regarding endemism rates of species, including subspecies, on the four islands, terrestrial mammals accounted for 82%, birds for 48%, terrestrial reptiles for 87%, and amphibians for 86%, indicating high values (Government of Japan 2019). Among these, 20 species are internationally recognized as EDGE species (Isaac et al. 2007; Government of Japan 2019; Gumbs et al. 2023).
Countermeasures against invasive non-native mammals
Except for Iriomote Island, where the Iriomote cat lives, especially the Central Ryukyus, which originally lacked native predatory mammals, has faced significant threats to native wildlife and ecosystems from non-native mammals, such as mongooses, weasels, free-ranging domestic cats, dogs, and goats.
The mongoose control project, officially implemented by the Ministry of the Environment under “the Invasive Alien Species Act” enforced in 2005, was conducted on Amami-Oshima Island for nearly 30 years. The project has reduced the number of captured mongooses and the locations where they were trapped significantly (Ishii 2003; Fukasawa et al. 2013a; Hashimoto et al. 2016; Ministry of the Environment 2024). This reduction was achieved through various methods, including setting 30 000 traps per year, monitored by 300 sensor cameras per year, using three to 13 detection dogs annually, partially using rodenticides, and the Amami Mongoose Busters (about 40 members each year). On September 3, 2024, the Ministry of the Environment (2024) declared the successful eradication of mongooses on the island after confirming, based on two eradication probability evaluation models, that no mongooses had been captured by the traps or cameras, nor detected by the dogs, for six consecutive years since 2018, following 31 years of capturing a total of 32 645 mongooses.
Fig. 3.
Natural World Heritage Sites (NWHS), Buffer Zones (Buffer), and Surrounding Management Areas in Amami-Oshima Island, Tokunoshima Island, Northern Part of Okinawa Island and Iriomote Island [modified from Japanese Government (2019), and Izawa and Yamada (2023)]. Note: The white areas in the Northern Part of Okinawa Island indicate the U.S. Northern Training Area and others. NWHS, area of Natural World Heritage Site; Buffer, area of Buffer Zone; Island, area of whole island; U.S., the U.S. Northern Training Area; Area, total area of the three villages. The area of Amami-Oshima Island includes Kakeroma-jima, Uke-jima, Yoro-jima Islands, and other small islands around Amami-Oshima Island.

The recovery of native species, such as the Amami rabbit, Amami spiny rat, and Ryukyu long-furred rats, indicates substantial progress in achieving the initial conservation goals (Ministry of the Environment 2024). However, vigilance is required against the potential re-invasion into Amami-Oshima Island from Okinawa Island, where mongooses have been established since 1910 as mentioned previously. Mongoose control efforts in the northern part of Okinawa Island have also shown positive results through trapping, sensor cameras, and detecting dogs with mongoose busters similar to those on Amami-Oshima Island, and fences to prevent the invasion of mongooses. However, continued control efforts in the northern part of Okinawa Island, including the targeted area to the south, are necessary.
Introduction of the Japanese weasel from Japanese mainland in the 1960s and 1970s for rat control has resulted in their establishment on islands in the central and southern Ryukyu Archipelago (Masuda and Watanabe 2015; Yamada 2021). Some islands have initiated measures to control the Japanese weasel (Okinawa Prefectural Office 2020).
The issue of predation by free-ranging domestic cats on native species has become evident on most islands, including Amami-Oshima Island, Tokunoshima Island, and the northern part of Okinawa Island (see the previous section). Although measures to remove free-ranging domestic cats from endangered native species' habitats have been implemented, there is an increasing need for comprehensive efforts, including proper management and ownership of domestic cats, which act as source populations (Maeda et al. 2019; Ministry of the Environment 2018, 2023; Kazato et al. 2020). The free-ranging domestic cat issue has moved to a new phase in terms of invasive species management, highlighted by the “Invasive Alien Species' List to Prevent Ecological Damage” published by the Ministry of the Environment (2015), and as part of islands designated as Natural World Heritage Sites. Similarly, predation problems caused by free-ranging dogs have also emerged, demanding comprehensive solutions.
Additionally, there is a feral goat problem in the central and southern Ryukyu Archipelago. While goats have traditionally been a source of food for people in the region, their feralization has led to vegetation damage, erosion along coastal cliffs, intrusion into forests, and negative impact on endangered species and ecosystems (Yokohata et al. 2003, 2009; Watari 2016). Control measures for feral goats in the northern part of Okinawa Island and on Iriomote Island have been initiated (Okinawa Prefectural Office 2023).
Overall, effective control of non-native species and comprehensive management strategies are crucial for conserving native species and ecosystems in the central and southern Ryukyu Archipelago.
Contribution of the academic communities to conservation
Various domestic and international academic communities and organizations have expressed interest in conserving this region. Among them, the Mammal Society of Japan has made particularly significant contributions.
The Mammal Society of Japan regularly submits requests and opinions to the Ministry of the Environment, the Okinawa and Kagoshima Prefectural Offices, and other relevant authorities regarding conservation measures for endangered mammals and the management of non-native species. These submissions aim to support and collaborate with the administrative policies and local community initiatives to provide reliable expert opinions. The Mammal Society of Japan plays a crucial role in guiding conservation efforts in the natural environment of the central and southern Ryukyu Archipelago. A total of 16 key requests and opinions regarding conservation in the central and southern Ryukyu Archipelago were submitted by the Mammal Society of Japan. This number constitutes a significant portion (23%) of the total requests and opinions (71 items) submitted by the Mammal Society of Japan from 1993 to 2022, highlighting the region's conservation challenges and the important role that the academic community has played in guiding conservation efforts in this region.
Principal issues and challenges of conservation
A common understanding is that the entire Ryukyu Archipelago, consisting of over 900 islands stretching from southern Kyushu Island to Taiwan, constitutes a valuable island group in terms of island biodiversity, and its value is not confined to any single island (e.g., Ota 2002, 2012; Kinoshita et al. 2025). Regrettably, only four representative islands were selected from a regulatory perspective in the context of Natural World Heritage registration. Furthermore, conservation issues related to Natural World Heritage Sites include that protected areas are limited land areas, fragmented conditions, scarcity of public land, the existence of the U.S. Marine Crop training area, and human activities, such as population of Amami-Oshima, Tokunoshima, the northern part of Okinawa, and Iriomote Island, counted 61 256, 23 497, 10 039 and 2402, respectively, in 2016 (Government of Japan 2019) (Fig. 3). In addition, the IUCN requests more information and measures on 1) tourist management plan for mitigation of overuse, 2) reduction of road fatalities of endangered species [including but not limited to Amami rabbits, Iriomote cats, and Okinawa rails, Hypotaenidia okinawae (Yamashina and Mano, 1981)], 3) river restoration options and dam removals to secure and enhance the integrity of aquatic ecosystems, 4) potential threats and mitigations to registered property from logging/timber extraction activities in buffer zones, and 5) monitoring implementation and information utilization based on comprehensive management plans and monitoring plans, which include the maintenance status of endangered species, reduction and improvement in human-induced impacts, decrease in invasive species, sustainable use in tourism, and understanding of the impact of climate change and disasters (UNESCO 2021).
However, the designation of the Ryukyu Archipelago as a Natural World Heritage Site marked a significant historical turning point and milestone, offering a valuable opportunity to share the region's geological, natural, and human history. By sharing these aspects among island groups, various fascinating features of the Ryukyu Archipelago are expected to unfold in the future. Historically, opportunities for mutual exchange and information sharing have been limited due to differences in administrative regions and among universities, research institutions, and organizations. However, the scope of sharing is expanding through the World Heritage Site platform, and efforts to address various issues are expected to progress.
Conclusion
The Ryukyu Archipelago, renowned for its globally significant natural environment and endemic species, has garnered attention as a biodiversity hotspot. The distinctive characteristic of the natural environment in this region is succinctly described as “diversity” and “endemism” which have become crucial keywords. Furthermore, the most notable feature of this region is that phylogenetically ancient mammal species have survived, and humans have been colonized here for the past approximately 30 000 years, coexisting with these species to this day and ensuring their continued existence. Such a region does not exist in other parts of Japan, and it is a globally rare phenomenon (Takamiya et al. 2016; Sato 2017; Takamiya 2017, 2021; van der Geer et al. 2021).
Although the unique characteristics of the islands contribute to their scientific value, research efforts have been directed mainly toward a few key species and islands. Consequently, comprehensive research on certain islands and species is lacking. There is concern that research efforts may disproportionately focus on registered Natural World Heritage Sites. Although the Natural World Heritage designation in 2021 is limited to the four islands under the World Heritage system, it is the consensus of the entire research community that the Ryukyu Archipelago, as an entire island group from southern Kyushu to Taiwan, has academic value (Government of Japan 2019). It is imperative to re-evaluate the entire Ryukyu Archipelago to advance research on biogeographical challenges, the characteristics of individual islands, biological communities, and the ecology of endemic species.
Biological research on the Ryukyu Archipelago has not only contributed to elucidating the taxonomy, ecology, and morphology of individual species, but has also contributed to establishing an ideal foundation for island biology research. Each island in the Ryukyu Archipelago, including many islands, has a different geological history and environment, which are mutually related to each other in the past and present (e.g., Ota 2002, 2012; van der Geer et al. 2021; Kinoshita et al. 2025). This can be considered a field of natural experiment. Understanding this region requires integration with geological fields. Since the first edition of “The Theory of Island Biogeography” was published in 1967 by MacArthur and Wilson (MacArthur and Wilson 2001), many studies have focused on “island” (e.g., Ota 2002, 2012; Gunji et al. 2025; Hayashi and Kubo 2025; Hayashi et al. 2025; Kinoshita et al. 2025; Kubo et al. 2025). Now, the development of new theories in the field of island biology, focusing on the evolution and adaptation of individual species with “islands” as a key concept, has begun on the Ryukyu Archipelago. These include topics such as ecosystem evolution, interspecific relationships, and changes and adaptations in response to climate change. The Japanese Archipelago is a collection of small islands from a global perspective and is considered a treasure house of biodiversity (Motokawa 2017; Sato 2017). We believe that various island theories can be disseminated worldwide from the study of the Ryukyu Archipelago, which is a typical island in terms of island biodiversity.
Simultaneously, this region hosts numerous endangered species, i.e., 62% of mammal species are classified as endangered (CR, EN, and VU) on the Japan's and IUCN's Red Lists (see Table 1). The conservation of the ecosystems of each island and each endangered species also requires an island perspective. In the field of island biology, it has been suggested that a small population size and small habitat area can lead to extinction. Specific factors related to conservation may also reflect the island's uniqueness. For example, the introduction of native species from one island to another can also threaten the uniqueness of the island, because the genetic structure of even the same species can sometimes differ from island to island. Furthermore, invasion of non-native species becomes an even greater threat to the uniqueness because the island's ecosystem is simple and vulnerable. In addition, the islands of the Ryukyu Archipelago have a long history of human settlement, and each island has a different human environment (history, industry, culture, customs, and other factors); therefore, it is necessary to consider conservation measures for each island. Information from ethnography, sociology, economics, and other fields is also required. It is our responsibility to conserve highly endangered wildlife species and to preserve the biodiversity of this region for future generations.
This collective effort aims to reveal novel insights into the interconnectedness among and unique evolutionary adaptations on the islands. The achievements of research and conservation efforts in the Ryukyu Archipelago will contribute to our understanding of island mammals and island biology. We hope that this review and special articles featured in this issue will be helpful for future studies and conservation efforts.
Acknowledgments:
We would like to thank Drs. Mugino O. Kubo, Shoji Hayashi, and Shun Kobayashi for their planning and management of this special issue. We would like to express our gratitude to the anonymous reviewers who provided useful comments and thorough reviews of the manuscript, covering a wide range of themes. We sincerely appreciate Drs. Tatsuo Oshida and Shingo Miura for their help, and Mr. Daisuke Nagaosa, Ms. Kumi Maruyama, Drs. Sota Niiyama, and Akira Sano for providing their information. We would also like to extend our thanks to Dr. Naomi Doi for her advice on the part related to the human history of the Ryukyu Islands, which is outside our area of expertise. We also thank Editage ( www.editage.jp) for English language editing. We would like to express our sincere gratitude to them. This study was financially supported by JSPS KAKENHI (grant no. 23K05910).
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