Research press release




人間が改変した地形で、生息域の利用可能性が既に低下しているものは、ほぼ手付かずの生態系よりも生物多様性減少のリスクが高いと考えられているが、分断された生態系の一部で予想外の回復力が見られる。今回、Matthew Bettsたちの研究グループは、保全活動を実施すべきなのは手付かずの生態系なのか分断された生態系なのかを突き止めるため、全世界の森林減少と19,432種の脊椎動物の絶滅リスクに関する大規模なデータセットを評価した。


Bettsたちは、生物多様性の減少リスクが特に高い地域の一部(例えば、ボルネオ島、アマゾン中部、コンゴ盆地)を特定し、現在のペースで森林が減少すると、これらの地域に生息する121~219種の脊椎動物(例えば、Mendolong bubble-nest frogとMentawi flying squirrel)が今後30年間で絶滅危惧種になってしまうと予測している。現在のところ正式に保護されているのは、これらの地域の17.9%に過ぎず、脆弱性が低いと考えられている地域で動物種の絶滅リスクが実際には高くなっていることが明確に示されたとBettsたちは結論づけている。

Intact ecosystems suffer greater biodiversity losses as a result of deforestation than those that have already been damaged or altered, according to a report in Nature this week. The study assesses the effects of deforestation in intact and human-modified landscapes on the extinction risk of over 19,000 vertebrate species worldwide, and identifies hotspots for extinction risks. The findings suggest that novel conservation efforts to protect intact forest landscapes are needed to prevent a new wave of extinctions.

Human-modified landscapes that have already experienced reductions in habitat availability are thought to have a higher risk of biodiversity loss than ecosystems that are largely intact, but some fragmented ecosystems have been shown to be surprisingly resilient. To determine whether conservation efforts should be directed towards intact or fragmented ecosystems, Matthew Betts and colleagues assess large datasets of global forest loss and extinction risk in 19,432 vertebrate species. As expected, deforestation substantially increases the odds of a species being threatened with extinction. However, the risks are disproportionately higher in relatively intact landscapes than in already fragmented landscapes. For example, for every 1% rise in deforestation, the increased threat of extinction was over 10% higher in species from areas with high levels of forest cover (90%) than their counterparts in habitats with average forest cover (57%).

The authors find that some of the regions where biodiversity is at a particularly high risk include Borneo, the central Amazon and the Congo Basin. They predict that over the next 30 years, between 121 and 219 species in these regions (such as the Mendolong bubble-nest frog and the Mentawi flying squirrel) will become threatened with extinction under current rates of forest loss. Only 17.9% of these regions are currently formally protected, highlighting that areas considered to be of low vulnerability are actually at high risk of suffering species extinctions, the authors conclude.

doi: 10.1038/nature23285

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