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The proposed property consists of Amami-Oshima Island, Tokunoshima Island, the northern part of Okinawa Island and Iriomote Island. The area which demonstrates Outstanding Universal Value for inscription on the World Heritage List is to be limited, in the light of scientific research and studies, only to these four islands.
As the result of the these islands’ long isolation, this property shows a series of speciations in various terrestrial lineages of the islands and the state of relict endemisms. This identified area is currently harbour diverse fauna and flora that are characterized by high proportions of endemic and rare species.
The proposed property is an area that offers outstanding examples of speciation and phylogenetic diversification of terrestrial organisms at various stages through varying extents of geographic isolation. Not only have numerous endemic species emerged through relatively recent vicariance events, but also a large number of relict species that have no close relatives on the Japanese mainland or Eurasian Continent occur on this property.
Furthermore, because these four islands are located between the tropical and warm–temperate zones, their current fauna and flora include not only representatives of long-standing subtropical lineages but also those of East Asian temperate lineages and South East Asian and Oceanian tropical lineages. Moreover, the high proportion of endemic and threatened species in this area indicates that they deserve a major conservation focus. The proposed property encompasses a set of important, essential habitats for these species.
Criterion (ix): The terrestrial organisms occurring in the proposed property likely had broad continental distributions. In the course of the area’s conversion to islands separated from the continent, the terrestrial organisms isolated on each island, with its distinctive environment, have evolved in various unique directions. This has been enhanced by the effects of population fragmentation.
In particular, on Amami-Oshima Island, Tokunoshima Island and the northern part of Okinawa Island, a number of terrestrial organisms with limited ability to disperse across the sea, such as non-volant tetrapods, have been isolated from their continental relatives since no later than the Early Pleistocene (between 2 and 1.7 million years ago). This, along with the subsequent extinction of the relatives in surrounding areas, despite the survival of many of the insular representatives to the present because they have been protected from recently emerging predators and competitors, has made the region the centre of relict endemism. Such relict species are generally characterized by prominent geographical and genetic gaps from extant sister populations in other areas. Prominent faunal representatives of such relict endemisms on Amami-Oshima Island, Tokunoshima Island and the northern part of Okinawa Island include the Amami rabbit Pentalagus furnessi; the Long-tailed giant rat Diplothrix legata; three spiny rat species of the genus Tokudaia; the Amami jay Garrulus lidthi; the Black-breasted leaf turtle Geoemyda japonica; Kuroiwa’s ground gecko Goniurosaurus kuroiwae; Anderson’s crocodile newt Echinotriton andersoni; and Namiye’s frog Limnonectes namiyei. Floral representatives include Arisaema heterocephalum (Araceae), Viola amamiana (Violaceae), Polystichum obae (Dryopteridaceae), Platanthera sonoharae (Orchidaceae) and Solenogyne mikadoi (Asteraceae . The Amami rabbit is estimated to have diverged from the other extant members of the family Leporidae in the Middle Miocene (about 10 million years ago). Since then, it seems to have evolved a suite of distinctive ecological traits while maintaining its largely primitive morphological features. There are no other extant congeners at all, thus making the rabbit endemic to Amami-Oshima Island and Tokunoshima Island at the generic level.
On the proposed property, speciations and phyletic divergences are still ongoing at various stages among island populations with close historical affinity. As a result of genetic differentiation in each lineage through geographic isolation caused by insularization of the region, there are numerous cases of between-island in-situ speciation and sub-speciation. Typical example is a group of tip-nosed frogs that has differentiated into four species in this property. Two subspecies of Kuroiwa’s ground geckos are distributed in Tokunoshima Island and the northern part of Okinawa Island. The high frequencies of occurrence of endemic taxa among the amphibians and terrestrial reptiles on the proposed property deserve particular attention. 33 species of endemic terrestrial reptiles and 18 species of endemic amphibians, are found on the four islands. About 121 plant species are endemic to the four islands.
Speciation and further diversification of a number of evolutionary lineages at these islands have therefore supposedly been enhanced. Indeed, many endemic species occur on these islands, most likely as a result of geohistorical processes in the region that involved the initial isolation of insular populations from their continental relatives and subsequently repeated vicariance and secondary sympatry among the former. Moreover, several islands harbour taxa that represent the stage of relict endemism as a result of long insular isolation from the formidable predators or competitors that started to prevail on the continent after the islands became isolated. This is particularly true for Amami-Oshima Island, Tokunoshima Island and the northern part of Okinawa Island in which relict species are particularly frequent because of the islands’ long isolation. These aspects of the proposed property collectively constitute an outstanding example of the effects of long-standing geohistorical processes on speciation and phylogenetic diversification of terrestrial organisms.
Fossil evidence indicates that on Amami-Oshima Island, Tokunoshima Island and the northern part of Okinawa Island there have been no, or have long been no endothermic vertebrates such as carnivorous mammals and large-bodied resident birds of prey to occupy the position as the top predators in the indigenous food web. Instead, the biotic community of this region is characterized by a high frequency of relict species (see above) and constitutes a unique food web in which a few large-bodied snakes occupy the top predator position.
Criterion (x): The proposed property contains important habitats for a large number of internationally recognized threatened species that are listed on the IUCN Red List. Furthermore, the islands provide diverse instances of neo- and relict endemism that are most explicitly represented by non-volant, inland-water-dependent taxa such as amphibians, the dispersal ability of which across the ocean is very limited by physiological constraint. From the global point of view, therefore, this property can obviously be regarded as among the most important areas for biodiversity conservation.
These islands contain irreplaceable habitats for more than 30 terrestrial species listed on the IUCN Red List in the Vulnerable (VU), or higher, threatened categories. These include the Iriomote leopard cat Prionailurus bengalensis iriomotensis (IUCN Red List 2012: critically endangered, CR), Amami rabbit (endangered, EN), Okinawa spiny rat Tokudaia muenninki (CR), Amami spiny rat Tokudaia osimensis (EN), Tokunoshima spiny rat Tokudaia tokunoshimensis (EN), Long-tailed giant rat (EN), Okinawa rail Gallirallus okinawae (EN), Okinawa woodpecker Dendrocopos noguchii (CR), Amami jay (VU), Black-breasted leaf turtle (EN), Yaeyama yellow-margined box turtle Cuora flavomarginata evelynae (EN), Kuroiwa’s ground gecko (EN), Anderson’s crocodile newt (EN), and Utsunomiya’s frog Odorrana utsunomiyaorum (EN). They also include two sibling Odorrana species, namely the Okinawa Ishikawa’s frog Odorrana ishikawae and the recently described Amami Ishikawa’s frog Odorrana splendida, which are still listed as one species (Ishikawa’s frog Odorrana ishikawae (EN)) on the IUCN list. Most of the threatened species seen in the four islands are endemic to the area at the generic, specific, or subspecific level. Furthermore, a characteristic mixture of East Asian, South East Asian, and Oceanian floral elements can be seen on the islands, reflecting the climatic conditions and various historical processes of dispersals. The proposed property accounts for less than 1% of the whole land area of Japan, yet it accommodates about 17% of the nation’s endangered vascular plants. This area is therefore of the utmost importance for the conservation of Japan’s endangered plants.
Integrity: The proposed property contains distinctive island ecosystems that reflect its geological history and the effects of the warm, humid climate. These ecosystems contain examples of well-preserved processes of evolution on islands, and they provide habitats for internationally important endangered species. The proposed area also contains diverse and endemic animal and plant species and a sufficient area of subtropical forest to ensure these species’ survival. The site not only covers all of the elements that constitute the outstanding universal value described above; it also has an area of sufficient size to maintain its values.
In addition, relevant organizations are working together on measures to counter alien species. This includes pest control and eradication projects that are based on the Invasive Alien Species Act and aim to conserve the unique island ecosystems, including their threatened faunal and floral elements.
Of the Nansei Islands, which include the proposed property, Yakushima has already been inscribed on the World Heritage List as a natural property. However, with the formation of the Tokara Strait, which is currently deeper than 1,000 m, Yakushima was separated from this property by the time of the Early Pleistocene (between 2 and 1.7 million years ago). In contrast, the strait between Yakushima and Kyushu Island of the mainland Japan, is no deeper than 100 m, so it is almost certain that Yakushima and Kyushu were connected through eustatic sea-level lowering by 120 to 140 m during the latest glacial period about 20,000 years ago, and that various terrestrial organisms such as deer and macaques migrated freely between the two islands. For this reason, the biota of Yakushima has very close affinity with that of Kyushu, being an almost complete subset of the latter. Yakushima was inscribed on the basis of criteria (vii) and (ix), with its outstanding universal value for extensive, successive vertical plant distributions ranging from coastal vegetation dominated by subtropical elements up to a cold temperate bamboo grassland at the central peaks, together with its natural landscape characterized by abundant huge Japanese cedar trees, including those that are thousands of years old.
In contrast, the marked universal value of the proposed area lies primarily in its offering a number of outstanding examples of speciation at various stages in terrestrial organisms, as enhanced by their isolation on these islands. The value of the area is further strengthened by the fact that the area accommodates many endangered endemic species by having habitats suitable for them. It is therefore obvious that the area deserves high priority for preservation in terms of not only evolutionary biology but also biodiversity conservation. Thus, the source of value of the proposed property is completely different from that of Yakushima.
In the biogeographical classification of the whole World of Udvardy (1975), the four islands and Yakushima were assigned to the Palaearctic realm but to different Provinces and Biomes. As mentioned above, it is currently obvious from the presence of many relict species that the property consisting of Amami-Oshima Island, Tokunoshima Island, the northern part of Okinawa Island and Iriomote Island were separated from the other island groups of the Nansei Islands and adjacent continent at least by the time of the Early Pleistocene (between 2 and 1.7 million years ago). Also, the terrestrial biota of the proposed property clearly differs from that of the Palaearctic realm, with the boundary being located along the Tokara Strait.
In Japan, there is another subtropical island group, the Ogasawara Islands, which was inscribed as a natural World Heritage on the basis of criterion (ix). The Ogasawara Islands feature ongoing evolutionary processes in oceanic island ecosystems—in particular speciation through adaptive radiation in land snails and plants—as outstanding universal values. For this reason, the ecological process of the Ogasawara Islands differs completely from that of the proposed property where there is neo- and relict endemism of biota as a result of separation during the process of formation of the islands.
Existing World Heritage islands that lie at similar latitudes as this property, that have been inscribed on the basis of criterion (ix), and that have geohistorical relationships with adjacent continents include Alejandro de Humboldt National Park (Cuba), the Islands and Protected Areas of the Gulf of California (Mexico), Coiba National Park and its Special Zone of Marine Protection (Panama), and the Lagoons of New Caledonia: Reef Diversity and Associated Ecosystems (France). Unlike in the case of the proposed property, however, for none of these others is it explained under criterion (ix) that the property provides a clear example of the processes of speciation and diversification of various evolutionary lineages and production of many endemic species, including relicts, during the formation of the current island assemblage through isolation and the repetition of separation and reunion among the component islands.
Other tropical or subtropical islands that may have significant geohistorical relationships with adjacent continents but are nevertheless not inscribed on the World Heritage List include the Caribbean Islands. The Caribbean Islands are the islands at the boundary of the North American Plate, the Caribbean Plate, and the South American Plate; they consist of the Bahama Islands, Greater Antilles, and Lesser Antilles. Each of these island assemblages has unique ecosystems and biodiversities as a result of their processes of land formation. New findings have recently been reported in regard to the relationship between island formation in the Caribbean Islands and the origin and separation of the biota there. These findings suggest that animals dispersed across the sea in an age more recent than was presumed from the islands’ geological history, although the academic dispute continues.
On the other hand, because of its background conditions, this property serves as a plain model of the history of island formation and evolutionary diversification of biota, and the history of their formation have been studied in detail. The proposed property is therefore the only such area that can be used, at least to a certain extent, to present the relationships between geological and biological history in a scientific and concrete manner.