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For species of small mammals in fragmented forest habitats as little as twenty five years could lead to extinction.
By studying forest fragments, on the Chiew Larn Reservoir in southern Thialand that were caused by a massive flood in 1986, researchers found that compared to surrounding, unfragmented habitats the extinction rate for small mammals in the fragmented areas was much higher.
They discovered this by selecting sixteen islands from the approximately one hundred islands that were formed after the flood. The islands ranged from .3 hectares to 56.3 hectares and all of the islands were not occupied by humans.
When the islands were surveyed five to seven years after fragmentation large islands, which are those from 10 hectares to 56 hectares, had been able to maintain seven to twelve species of small mammals, which is similar to the species richness found on the mainland. But the small islands, less than 10 hectares, were only able to sustain one to three species.
By the twenty fifth and twenty sixth years almost all native small mammal species were extinct on the sixteen forest fragmentation. As a control surrounding mainland habitats were also surveyed and no similar loss of diversity was found.
Oddly enough after the fifth and seventh years is was actually found that diversity loss occurred faster in the larger islands rather than the smaller islands. This can be explained by the fact that after the habitat was originally fragmented the larger islands maintained larger populations and higher species diversity.
Unfortunately not only did almost all native small mammal species go extinct on these fragmented island habitats, but an invasive specie of rat, Rattus tiomanicus, also took over the islands. There is also some evidence that Rattus tiomanicus is part of the reason than species went extinct so quickly in the island habitats because invasive have been shown to speed up the extinction process.
The idea of using small habitats as stepping stones to larger habitats is a fairly popular idea in population biology, but the fact that these habitats cannot always sustain species as well as the fact that they are vulnerable to being overrun by exotic species must be taken into account when efforts at conservation are made.
Gibson, Luke, Antony J. Lynam, Corey JA Bradshaw, Fangliang He, David Bickford, David S. Woodruff, Sara Bumrungsri, and William F. Laurance. “Near-Complete Extinction of Native Small Mammal Fauna 25 Years After Forest Fragmentation.”Science 341.6153 (2013): 1508-510. Science. 27 Sept. 2013. Web. 28 Oct. 2013.