Human activity is slicing up forests worldwide, and it seems the resulting “islands” of vegetation can go into ecological meltdown much faster than thought
NO ANIMAL is an island. Mammals marooned on small islands or in isolated forest fragments are more vulnerable than anyone knew. A case study in Thailand suggests they can go extinct in just 25 years. This is worrying because ecosystems around the world are being diced up as human activities encroach.
When Thailand flooded a rainforest to build a dam in 1986, it created an opportunity to study how isolation affects mammal populations. Poking above the waters of the new Chiew Larn reservoir were 100 islands of tropical rainforest. William Laurance from James Cook University in Cairns, Australia, and colleagues identified 16 islands, varying in size from 0.3 to 56.3 hectares, and measured how quickly the small mammals there became extinct.
Five years after the flooding, the nine fragments under 10 hectares had lost almost all of their small mammals. Twenty years later, the larger islands had met the same fate. The only mammal left in any abundance was the Malayan field rat, an invasive species that had colonised the islands. The native species had declined so much — due to competition with the rats and inbreeding — that on many islands, researchers could only find a single individual (Science, doi.org/n2r).
“It’s a very striking and catastrophic decline of biodiversity,” says Laurance, and it emphasises the importance of linking habitats to create larger reserves.
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Mammals in fragmented forests die out within 25 years
Human activity is slicing up forests worldwide, and it seems the resulting “islands” of vegetation can go into ecological meltdown much faster than thought
NO ANIMAL is an island. Mammals marooned on small islands or in isolated forest fragments are more vulnerable than anyone knew. A case study in Thailand suggests they can go extinct in just 25 years. This is worrying because ecosystems around the world are being diced up as human activities encroach.
When Thailand flooded a rainforest to build a dam in 1986, it created an opportunity to study how isolation affects mammal populations. Poking above the waters of the new Chiew Larn reservoir were 100 islands of tropical rainforest. William Laurance from James Cook University in Cairns, Australia, and colleagues identified 16 islands, varying in size from 0.3 to 56.3 hectares, and measured how quickly the small mammals there became extinct.
Five years after the flooding, the nine fragments under 10 hectares had lost almost all of their small mammals. Twenty years later, the larger islands had met the same fate. The only mammal left in any abundance was the Malayan field rat, an invasive species that had colonised the islands. The native species had declined so much — due to competition with the rats and inbreeding — that on many islands, researchers could only find a single individual (Science, doi.org/n2r).
“It’s a very striking and catastrophic decline of biodiversity,” says Laurance, and it emphasises the importance of linking habitats to create larger reserves.