The rate of extinction threatening to engulf south-east Asia this century could be a "catastrophic" 20%, scientists say.
"
We expect more and more species will go downhill
"
Caroline Pollock, IUCN
They base their warning on the example of Singapore, where key habitats have shrunk by 95% since 1819.
The scientists say it is the unprecedented rate of habitat loss that now threatens so many species.
South-east Asia is one of the Earth's most important biodiversity "hotspots".
The scientists, from Singapore, Japan and Australia, report their findings in the journal Nature.
They found "substantial rates of documented and inferred extinctions, especially for forest species", with butterflies, fish, birds and mammals all affected.
The authors say: "Observed extinctions were generally fewer, but inferred losses often higher, in vascular plants, phasmids (stick and leaf insects), decapods (crustaceans), amphibians and reptiles.
Global impact
"Forest reserves comprising only 0.25% of Singapore's area now harbour over 50% of the residual native biodiversity."
They think the rate at which habitats are disappearing is so great that south-east Asia will lose up to two-fifths of all its species over this century, at least half of them endemic species found nowhere else on Earth.
They used both historical and modern checklists of species occurring in Singapore to estimate how many had become extinct, in relation to large-scale habitat loss, since the British arrived in 1819.
Since then more than 95% of the estimated 540 square kilometres of original vegetation has been entirely cleared. Less than 10% of the remaining 24 sq km of forest is primary growth.
The authors also used checklists from nearby peninsular Malaysia to deduce the possible species composition of Singapore in 1819, compensating for probably incomplete extinction records.
The overall loss of biodiversity, they calculated, was at least 28% - 881 of 3,196 recorded species.
Butterflies, freshwater fish, birds and mammals lost 34-43% of all species. About a quarter of all vascular plants, freshwater decapods and phasmids have disappeared.
On the slide
But there seem to have been comparatively fewer extinctions of amphibians and reptiles. Total local extinction rates, the authors say, could be as high as 73%.
They say their lists of surviving species include several long-lived ones whose populations are too small to survive in the long term, like the white-bellied woodpecker, the banded leaf monkey and the cream-coloured giant squirrel.
They say: "These 'living dead' taxa will almost certainly become extinct in the coming decades."
Forest birds have fared worse than open-habitat species: since 1923, 61 of the 91 known forest-dependent birds have disappeared.
The authors say rapid and large-scale habitat destruction was undoubtedly the predominant cause of Singapore's extinctions.
But hunting may also have been important: Singapore's last tiger was shot in 1930.
They describe the prospects for its surviving species as "bleak", with 77% classified as threatened by IUCN-The World Conservation Union.
Quart in a pint pot
With the few remaining protected nature reserves occupying only 0.25% of the island's total land area, they worry at how much biodiversity is packed into so small a space.
On Singapore's lessons for south-east Asia, they note a projected overall deforestation rate of 74% for the region by 2100.
They conclude: "We predict the overall loss of 13-42% of regional populations due to the effects of deforestation in south-east Asia by the end of the present century, at least half of which are likely to represent global species extinctions."
Caroline Pollock, of IUCN's Red List programme, told BBC News Online: "The projected loss for south-east Asia is very high, but it's not really a surprise.
"We're finding increasing numbers of species are being assessed as threatened, and we expect more and more species will go downhill."
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