Around the world, tropical forests are being chipped away and fragmented by agriculture, dams and other developments.
But how fast do species disappear from these forest fragments, and how soon must people act to stop extinction?
National University of Singapore (NUS) doctoral student Luke Gibson and his colleagues have been tracking islands in a drowned Thai forest, hoping to answer this question.
The Chiew Larn Reservoir in southern Thailand, midway between Ko Samui and Phuket, is a natural experiment. In 1987, it was formed by damming a river and flooding 165 sq km of forest, producing tiny islands, some smaller than a football field.
Twenty years ago, biologist David Woodruff of the University of California, San Diego, counted the small mammals such as moon rats (shrew-like jungle rats, native to and relatively common in South-east Asian tropical forests) on a dozen selected islands by trapping, tagging and releasing them.
Over the past few years, Mr Gibson and colleagues repeated the work.
They were startled by the sharp crash in the number of small mammal species on the islands.
And after just 25 years, the islands were dominated by Malayan field rats. These animals live in secondary forests and farmland, and were not on the islands when the dam was built, so they must have swum there.