Deforestation is one of the most significant factors to species extinction in well-known biodiversity hotspots, mainly tropical forests. However, recent research has found evidence to support that it is forest fragmentation that is accelerating the rate of extinction in resident species, especially small mammals.
Past studies have shown that large fragments of forests around 1000 hectares in size had native avian species extinctions projected at around a time frame of 50 years, a period long enough for conservation efforts to be drafted to reduce the predicted decrease in biodiversity.
Luke Gibson and his colleagues were able to expand this theory in a recent study extending this idea onto small mammalian populations occupying 16 of the fragmented lands of the Chiew Lam Reservoir in Southern Thailand.
This newly published study has found that virtually all native mammalian species had gone extinct on forest fragmentations less than 56 hectares in size after just 25 years of isolation.
After 5 to 7 years of fragmentation, 3 of the islands sized 10 to 56 hectares had showed a quantity of small mammalian species very close to the number found on the nearby mainland. On smaller fragments smaller than 10 hectares, less than 3 species of native mammals were found after equal time periods of isolation.
After 25 years of isolation, the extinction rates observed on the fragmented forest islands was significantly higher than that observed on mainland forests.
With statistical analysis, it has been found that species richness showed a strong positive correlation with fragmentation area.
From this study, Gibson and his colleagues have presented a hypothesis relating heightened extinction rates with the introduction of invasive species.
Forest fragmentation may hold a high leverage on extinction rates because such breakdown of habitat makes it more susceptible to invasive species.
In this study, despite the decrease in all small, native mammalian species, the Malayan field rat population continued to increase.
Occupation by such species caused a rapid extinction of small native mammalian communities in the fragmented regions in the Chiew Lam Reservoir because the invasive species caused a destabilizing effect for such mammals.
After a few years, the invasive rodent species had dominated the native mammalian populations and had pushed them to extinction.
Forest fragmentation may be beneficial conservation efforts when it comes to improving habitat connectivity in areas where much of its natural flora has gone extinct. However, fragmentation has proven to be detrimental to the mammalian population in various forests worldwide.
Conservation biologists have been predicting extinction rates in regards to deforestation for ages, but those numbers may be greatly underestimated. Most of these rate predictions are developed under the assumption that the forests are contiguous.
With forest fragmentation as another devastating factor, the dangers of extinction severely increased.
In order to sustain biodiversity, especially for small mammals occupying such areas of tropical forests, sustaining large blocks of contiguous habitats is a must. Conservation efforts must not only be focused on slowing down deforestation, but also in prohibiting fragmentation of such habitats.
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. 30 Sept. 2013.