Fragmentation Explained!

If you take a look a map of Singapore’s natural habitats such as the one from the Singapore Biodiversity: An encyclopaedia of the natural environment and sustainable development1, you might notice something glaringly obvious. Our natural habitats are generally small and isolated from each other with large patches of urban landscape between them (the white space!). This is known as habitat fragmentation and it poses a threat to biodiversity through a number of different ways.

Firstly, fragmentation reduces the amount of habitat available to organisms1. This poses a problem as it restricts the resources available to them and prevents them from crossing over to other habitat fragments to mate, resulting in in-breeding. So why is in-breeding bad for biodiversity? In-breeding is a problem because little genetic diversity in each fragment could possibly result in the accumulation of non-desirable genetic traits. Thus, the survivability of the population would be reduced.

Also, with little genetic diversity, populations are less able to adapt to changes in their environment like new pathogens. Unfortunately, Bukit Timah Nature Reserve (BTNR) proves to be a good case study of the damages of habitat fragmentation1. In the past, BTNR was connected to the larger Central Catchment Nature Reserve (CCNR) but from 1983 to 1986, the Bukit Timah Expressway (BKE) was constructed and it isolated BTNR1. As a result of this, the population of banded leaf monkeys (Presbytis femoralis) that used to live in BTNR was unable to survive1 with the last surviving member recorded to have died in October 1987. To make things worse, there were also many records of animals that got run over when they attempted to cross the expressway1.

A banded leaf monkey. Image source: http://www.wildsingapore.per.sg/discovery/factsheet/bandleafmonkey.htm
Roadkill found along Mandai Road near Bukit Timah Expressway, 11 June 2001. Image source: http://www.wildsingapore.per.sg/discovery/factsheet/leopardcat.htm

On top of the isolation that is caused by fragments, there is another phenomenon known as “edge effect” caused by fragmentation2.  Edge effect occurs as fragmentation increases the amounts of “edge” a habitat has and this edge tends to have differing physical conditions compared to the habitat interior2. For example, in forest habitats, the edge would tend to receive more light and stronger winds resulting in increased temperature and reduced humidity compared to the forest interior2. Certain animals may not be able to adapt to these habitats and as such have their habitat range even further restricted to only the forest interior, possibly resulting in local extinctions.

Fortunately, steps have been taken to mitigate the effects of fragmentation. One of these measures is the construction of the Eco-Link@BKE, a ecological corridor over the BKE meant to allow wildlife to pass through. The Eco-Link@BKE was completed last year and plants were planted on it to simulate a forest habitat to encourage animals to cross it. With luck, this ecological corridor would allow animals that were isolated in CCNR like the lesser mousedeer (Tragulus kanchil) to expand their range into BTNR. References

  1. Ng, P. K. L., Corlett, R., & Tan T. W. H. (2011). Singapore biodiversity: An encyclopaedia of the natural environment and sustainable development. Singapore: Didier Millet in association with Raffles Museum of Biodiversity Research
  2. Chattjea, K. (2014). Edge effects and exterior influences on Bukit Timah Forest, Singapore. European Journal of Geography, 5(1).

Words by: Lee Juin Bin

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