Imagine that humans were a species facing extinction, and every week one household in your country died out. Terrible, right? Now imagine that all the states in the USA became independent islands, and now one household in each newly formed island country died out each week. How long would you expect to survive in the latter?
Although humans are not a species facing immediate extinction, the scenario discussed above has become an analogy directly translated into reality for small mammals native to tropical forests. Luke Gibson and his colleagues have published research with evidence that forest fragmentation is having detrimental impacts among small mammalian species in tropical forests by significantly accelerating their extinction rates.
Previous research on forest fragmentation has shown that in large size fragmentations around 1000 hectares, bird species have an estimated 50 years before they face extinction.
Gibson was able to take this finding based on populations of beaks and feathers, and apply it to the hairy, lactating beings of Southern Thailand.
The study focused on 16 islands ranging up to 56 hectares. Now located on the Chiew Lam Reservoir, these islands were a few selected from the hundreds of forest islands that were created years ago by a large flood that fragmented what once was remembered as a vast forest.
Within 5-7 years of fragmentation, islands less than 10 hectares proved home to only 1-3 original small mammal species. Within 25 years of observation after fragmentation occurred, nearly all 16 islands were clear of native small mammalian species. This time frame was noticeably decreased from the 40 years observed for the 1000 hectare fragment.
Going back to the human analogy, assuming that one household is exterminated every week in each state, you probably have a longer chance of survival in Texas compared to small states like Rhode Island. This fact has been found in forest fragmentations as well.
From data analysis, researchers were able to find a strong positive correlation between species richness and area of the forest fragment. The mammal population found in larger areas was able to push extinction a little further.
Now let’s say that you are a resident of Rhode Island, and alongside the one household per week rate of extermination, a large population of Canadian immigrants were taking all your jobs and eating all your food. How long would you survive then?
Malayan field rats were the one exception to small mammalian extinction in these fragmented forests. These rodents are not native species to the forest, but rather were invasive species that inhabited nearby villages. With fragmentations, the forests became more vulnerable to invasive species infestations, destabilizing native mammal populations – taking their jobs and their food.
Conservation biologists world wide have been acting to estimate the extinction debt of such endangered forest species for years, but with this recent study, it just might be that the problem is a lot worse than we could have imagined.
Most numerical estimates are made under the assumption that deforestation is happening to contiguous forest areas – but clearly we see that this isn’t the case. We aren’t dealing with the US here. We are dealing with little United States Islands – the divided states of America, with misery and extinction for all.
We must learn to step aside from the notorious environmental culprit we call deforestation and look into such blatantly obvious habitat fragmentation issues that are eating away our tropical biodiversity.
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.