Description of the Property
Description of the Property
The nominated property is a terrestrial serial site covering 42,698 ha comprised of five component parts in four regions, Amami-Oshima Island, Tokunoshima Island, and the Northern part of Okinawa Island in the Central Ryukyus, and Iriomote Island in the South Ryukyus. The islands of the Central and South Ryukyus are members of the Ryukyu Chain at the southern tip of the Japanese archipelago. Influenced by the Kuroshio Current and the subtropical high-pressure system, the nominated property has a warm and humid subtropical climate and is covered mainly with evergreen broadleaved subtropical rainforests.
The nominated property is the best representative of the Central and South Ryukyus that contain the richest biota in Japan, one of the world’s biodiversity hotspots. The nominated property has a large number of species in many taxonomic groups. The property also supports many threatened species and species endemic to the Central and South Ryukyus, and the proportions of those species are high. Further, various examples of evolution of endemic species, especially many examples of relict and/or evolutionarily distinct species, are found in the nominated property.
These features of the biodiversity of the nominated property are all interrelated and derived from the geological history of the Central and South Ryukyus as continental islands. Reflecting its long history of separation and isolation, the terrestrial creatures went through various evolutionary processes and formed unique biota, as observed in many examples of endemic species in non-flying terrestrial vertebrate groups and plants. Also, the Central and South Ryukyus have differences in their patterns of speciation and endemism.
Thus, the nominated property is of overall high global irreplaceability for the protection of unique terrestrial species including many endemic and globally threatened species, and contains the most important and significant natural habitats for in-situ conservation of the unique and rich biodiversity of the Central and South Ryukyus.
The nominated property is of overall high global irreplaceability for the protection of unique terrestrial species
The four regions containing the nominated property, which together cover less than 0.5% of Japan’s land area, support a large proportion of the fauna and flora in Japan. For example, there are 1,819 vascular plants, 21 terrestrial mammals, 394 birds, 36 terrestrial reptiles and 21 amphibians. As a whole, around 57% of the terrestrial vertebrates of the Biodiversity Hotspot of Japan, including 44% of species endemic to Japan as well as 36% of globally threatened vertebrates in Japan, are living in the four regions containing the nominated property. The number and proportion of threatened species are also large in the nominated property, including 95 globally threatened species.
Among those species listed on IUCN Red List of Threatened Species, the Amami rabbit (Pentalagus furnessi) lives on Amami-Oshima and Tokunoshima Islands and is the only species in its genus, with no close relatives anywhere in the world. Okinawa rail (Gallirallus okinawae), which lives in the Northern part of the Okinawa Island, is one of the non-flying rails that are known to be vulnerable to extinction. Spiny rats form an endemic genus consisting of three species (Tokudaiada osimensis, T. tokunoshimensis, T. muenninki) endemic to each of the three regions of the nominated property in the Central Ryukyus. Iriomote cat (Prionailurus bengalensis iriomotensis) only inhabits Iriomote Island, “the world’s smallest island where wildcats live”.
Also, there are abundant examples of diverse speciation and endemic species in the nominated property. For example, 188 species of vascular plants and 1,607 insect species are endemic. Especially, rates of endemism among terrestrial mammals (62%), terrestrial reptiles (64%), amphibians (86%), and inland water crabs (100%) are high. Among these endemic species in the nominated property, there are as many as 20 species identified as Evolutionarily Distinct and Globally Endangered (EDGE) species, including the Okinawa spiny rat (Tokudaida muenninki), Ryukyu black-breasted leaf turtle (Geoemyda japonica), and Kuroiwa’s ground gecko (Goniurosaurus splendens) that are ranked in the Top 100 EDGE species.
The species richness, large number and high proportion of threatened species and endemic species, and diverse examples of speciation and unique evolution, are all interrelated and have resulted from the geological history of the Central and South Ryukyus that formed as continental islands. The Ryukyu Chain was part of the Eurasian Continent until the middle Miocene, but it became separated and formed an archipelago of small islands through the development of the Okinawa Trough and three deep straits. The terrestrial creatures there became isolated on small islands and went through the unique processes of evolution. For this reason, in the Central and South Ryukyus, many examples of endemic species are clearly shown in non-flying terrestrial vertebrate groups and plants that were not able to cross the straits with ease.
Ryukyu Chain’s ancient geography and biological trends (Estimates)
A: Before middle Miocene (Before around 12 Ma)
The current Ryukyu Chain including the nominated site was apparently located on the eastern margin of the Eurasian Continent and shared a common terrestrial biota.
B: Late Miocene to early Pleistocene (around 12 to 2 Ma
(1) The Okinawa Trough started to expand and separated Central and South Ryukyus from the continent. During late Miocene (around 12 to 5 Ma), the Tokara Strait and Kerama Gap were formed, which separated Central Ryukyus and its neighboring land area, including Kyushu, North Ryukyus, and South Ryukyus. This resulted in the isolation of terrestrial biotas, such as the Amami rabbit, spiny rats, ground geckos, habu vipers, tip-nosed frogs, and inland water decapod cructaceans.
(2) In the Pliocene (around 5 to 2.6 Ma), the South Ryukyus was separated from the continent, which resulted in the isolation of its terrestrial biotas, such as the Yaeyama yellow-margined box turtle, Kishinoue’s giant skink, Sakishima habu viper, and tip-nosed frogs.
C: Early Pleistocene to present (around 2 Ma onwards)
(1) The terrestrial organisms that shared ancestor species with those on the Central Ryukyus became extinct gradually on the continent, leaving a relict and endemic terrestrial biota in the Central Ryukyus.
(2) Sea level changes associated with climate changes (glacial-interglacial cycles) caused repeated connections and separations among neighbouring islands. As a consequence, these islands’ biological distribution was fragmented and island-specific speciation was accelerated in the Central Ryukyus and South Ryukyus.
(3) As relative species of the Iriomote cat and Ryukyu wild boar are distributed in the continent, it is thought that these specie have entered the South Ryukyus from the continent by crossing the sea when the sea level lowered during a glacial period and the distance between the South Ryukyus and the Eurasian Continent was shortened to a minimal level (around 0.09 to 0.05 Ma).
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