Species living in rainforest fragments could be far more likely to disappear than was previously assumed, says an international team of scientists.
In a study spanning two decades and published on 27 September in the journal Science, the researchers witnessed the near-complete extinction of native small mammals on forest islands created by a large hydroelectric reservoir in Thailand.
The study is considered important because forests around the world are being rapidly felled and chopped up into small island-like fragments. “It’s vital that we understand what happens to species in forest fragments,” said Antony Lynam of the Wildlife Conservation Society (WCS). “The fate of much of the world’s biodiversity is going to depend on it.”
The study was motivated by a desire to understand how long species can live in forest fragments. If they persist for many decades, then this gives conservationists a window of time to create wildlife corridors or restore surrounding forests to reduce the harmful effects of forest isolation. However, the researchers saw native small mammals vanish with alarming speed, with just a handful remaining — on average, less than one individual per island — after 25 years.
“There seemed to be two culprits,” said William Laurance of James Cook University in Australia. “Native mammals suffered the harmful effects of population isolation, and they also had to deal with a devastating invader — the Malayan field rat.” In just a few years, the invading rat grew so abundant on the islands that it virtually displaced all native small mammals. The field rat normally favours villages and agricultural lands, but will also invade disturbed forests.
“This tells us that the double whammy of habitat fragmentation and invading species can be fatal for native wildlife,” said Lynam. “And that’s frightening because invaders are increasing in disturbed and fragmented habitats around the world.”