日本の植物絶滅速度は世界の2、3倍

日本列島の植物の保全は急務である。そのことを知らせる研究が報告された。
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日本列島の植物の保全は急務である。そのことを知らせる研究が報告された。日本で維管束植物(シダ、裸子、被子植物)の減少傾向が現状のまま続くとした場合、100年後までに370~561種の絶滅が起こる可能性があることを、国立環境研究所の角谷拓(かどや たく)主任研究員と九州大学大学院理学研究院の矢原徹一(やはら てつかず)教授らが示した。

植物1618種の絶滅リスクを分析した結果で、その絶滅速度は世界全体の維管束植物で推定されている値の2~3倍にも相当する。国立・国定公園の区域内と外で個体数の減少傾向を比較したところ、公園内では減少傾向が最大で60%程度改善されていることも確かめた。絶滅危機を警告する定量的な分析として注目される。

国立環境研究所、日本自然保護協会、徳島県立博物館、神奈川県立生命の星・地球博物館、神戸大学、岐阜大学、愛知教育大学、北海道大学、熊本大学、人間環境大学、横浜国立大学、琉球大学、東北大学、九州大学の植物学者を総動員した共同研究で、6月12日付の米オンライン科学誌プロスワンに発表した。

動物に比べて植物の調査は遅れがちだ。日本植物分類学会と環境省は、市民も含む調査員約500名の協力で、1994-1995年と2003-2004年に、維管束植物の個体数分布全国調査を実施した。全国を10km x 10kmの調査区(4473区)ごとに、調査員が絶滅危惧維管束植物種の個体数を記録した。10年間を挟んだこの2回の調査で、個体数の記録が得られたのは1618種に上った。研究グループは今回、この結果を基に、国内1618種の絶滅リスクを定量的に分析した。全国規模で植物の定量的な絶滅リスクを分析したのは世界で初めての試みという。

絶滅リスクを見る際、2つの情報を利用した。ひとつは第2回調査時(2003-2004年)の個体数(現存個体数)、もうひとつは2回の調査の間での個体数増減(10年あたりの個体数変化率)。個体数変化の平均的傾向が今後も変わらないと仮定して、将来10年ごとの個体数は、現存個体数に個体数変化率を繰り返し乗じて算定した。この計算をすべての種、すべての調査区で行い、種ごとに絶滅リスクを推計した。

解析の結果、100年後には370~561種の絶滅が起こると推定された。国立・国定公園に含まれる調査区では、個体数の減少防止確率が、公園外を0とした場合に、第一種特別地域で0.22、特別保護地区で0.62となっていた。多くの植物の絶滅を回避するためには、保護区の一層の拡充が求められることがはっきりした。

ただ、保護区の面積を増やすだけでは、絶滅リスクの低減の効果は限定的なこともわかった。国立・国定公園内で個体数減少が続く要因は、踏みつけや採集が主で、保護区を設置しても影響が軽減されないか、悪化する傾向さえみられた。日本全体では、開発が植物絶滅危機の最大の要因だった。

研究グループの矢原徹一九州大教授は「全国規模の定量的な植物絶滅リスクの分析は世界で初めてで、国際的に誇れる研究だが、日本の植物の絶滅危機は深刻であることがよりはっきりした。生物の保全効果を上げるためには、それぞれの保護区で、個体数を減少させている要因に応じて、きめ細かい管理が望まれる。将来予測を高めるには、個体数分布を把握する広域調査を継続的に実施する必要がある」と提言している。

Top 10 Endangered Species That Need Our Help
Asian Elephant(01 of10)
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Asian elephants (Elephas maximus) are currently listed as endangered on the IUCN Red List of Threatened Species, meaning they are \"facing a high risk of extinction in the wild.\"\r\n\r\nWorld Wildlife Fund estimates that there are between 41,410 and 52,345 Asian elephants in the wild.\r\n\r\nHuffPost blogger Wendy Diamond writes that besides deforestation and industrialization, landmines also threaten Asian elephants in the wild. The founder of an elephant park in Thailand claims he \"has known about 20 elephants who stepped on land mines and died\" since 1989.\r\n\r\nEfforts to raise awareness for elephants\' fragile status include Elephant Appreciation Day. (credit:David Lawson/WWF-UK)
Javan Rhino(02 of10)
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The Javan Rhinoceros (Rhinoceros sondaicus) is very close to extinction. There are believed to be as few as 40 left in the wild in Ujung Kulon National Park, Indonesia and none are currently in captivity. The IUCN Red List currently lists Javan rhinos as critically endangered.\r\n\r\nIn October, poachers killed the last remaining Javan rhino in Vietnam. Several were alive in the wild in Vietnam as recently as 2004.\r\n\r\nA survey of surviving Javan rhinos in Indonesia found that there are very few females in the population. (credit:WWF Greater Mekong)
Snow Leopard(03 of10)
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Snow leopards (Panthera uncia) are listed as endangered on the IUCN Red List. IUCN estimates that there are 4,080 to 6,590 snow leopards in the wild.\r\n\r\nA subspecies, the Amur leopard is critically endangered. Native to the Russian Far East and northern China, there are fewer than 50 left in the wild.\r\n\r\nIn July, cameras recorded snow leopards in 16 different locations in northeastern Afghanistan. (credit:Bruce W. Bunting/WWF-US)
Tiger(04 of10)
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Tigers (Panthera tigris) are listed as endangered on the IUCN Red List. According to WWF, there are as few as 3,200 tigers left in the wild.\r\n\r\nIn November, Interpol launched a campaign to save tigers in the 13 Asian countries where they still exist, reported the Associated Press. There were around 100,000 tigers in Asia in 1900. (credit:David Lawson/WWF-UK)
Irrawaddy Dolphin(05 of10)
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The Irrawaddy dolpin (Orcaella brevirostris), which is native to Southeast Asia, is listed as vulnerable on the IUCN Red List. The Mekong River subpopulation, however, is listed as critically endangered.\r\n\r\nAccording to WWF, there are only 85 of these dolphins left in Southeast Asia. The limited range of this animal along with killing by fisherman has left Irrawaddy dolphin populations in danger. (credit:David Dove/WWF Greater Mekong)
Vaquita(06 of10)
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The Vaquita (Phocoena sinus) is a small porpoise native to the Gulf of California. It is listed as critically endangered on the IUCN Red List.\r\n\r\nWWF estimates that there are around 245 vaquita left in the wild. They are most immediately threatened by \"entanglement in fishing gear.\" Fortunately, WWF helped authorities in Mexico to reduce bycatch of vaquita to a \"level that does not threaten the population\" by 2009. (credit:WWF-US/Eugene Lee)
Atlantic Bluefin Tuna(07 of10)
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Atlantic Bluefin Tuna (Thunnus thynnus) are listed as endangered on the IUCN Red List. According to WWF, they are threatened by overfishing.\r\n\r\nA report from October found that eastern Atlantic bluefin is traded at twice the amount catch quotas actually allow.\r\n\r\nIn August, it was reported that Mitsubishi executives planned to buy up tons of bluefin and freeze it to profit from impending population collapses. (credit:naturepl.com/Visuals Unlimited/WWF)
Mountain Gorilla (subspecies of Eastern Gorilla)(08 of10)
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The mountain gorilla (Gorilla beringei beringei), a subspecies of the eastern gorilla, is listed as critically endangered on the IUCN Red List.\r\n\r\nWWF explains that there are estimated to be about 786 individuals left in the two mountain gorilla populations near the Uganda-Rwanda-DRC and in a national park in Uganda. However, the two populations have grown by 14 and 12 percent, respectively, in the past decade.\r\n\r\nArmed conflicts and natural resource exploitation have been blamed for endangering the gorilla populations. (credit:Martin Harvey/WWF-Canon)
Sumatran Orangutan(09 of10)
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The Sumatran Orangutan (Pongo abelii) is listed as critically endangered on the IUCN Red List. According to WWF, they are the most endangered of the two orangutan species and there are about 7,500 Sumatran Orangutans left in the wild.\r\n\r\nNative only to parts of Sumatra, Indonesia, the orangutans are threatened by human agricultural and residential development.\r\n\r\nA recent study found that residents of Borneo killed at least 750 endangered orangutans in a one-year period. \"Born To Be Wild,\" a recent IMAX film, tells the story of caretakers who are raising orphaned orangutans. (credit:Peter Hofland/WWF-Canon)
Leatherback Turtle(10 of10)
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Leatherback turtles (Dermochelys coriacea) are listed as critically endangered on the IUCN Red List. According to WWF, there are about 34,000 nesting females left in the world and populations in the Atlantic are relatively stable. In the Pacific, however, there may be as few as 2,300 adult females. \r\n\r\nTheir wide geographical distribution and shallow dive depth means they are threatened by longline fishing operations, explains WWF. \r\n\r\nA study from September found that although the number of sea turtles killed in U.S. fisheries has declined by 90 percent since 1990, it may not be enough to sustain sea turtle populations.\r\n\r\nIn August, a 700-pound leatherback washed up on the shore at Montauk, New York. (credit:Jürgen Freund/WWF-Canon)