Exotic plants: It is not all bad

Throughout my final year, I had the opportunity to examine a exotic butterfly host plant species, Aristolochia tagala, as part of my FYP. As I dug up literature on this specific host plant species, I came across an interesting tidbit, the common birdwing (which is the only native butterfly species listed under Appendix II of CITES and is listed as vulnerable under the Singapore Red Data Book) relies entirely on A. tagala as its only host plant in Singapore. The only known native species of Aristolochia in Singapore is Aristolochia jackii, which is locally extinct. It is hypothesized that the local common birdwing population survived due to the switch from A. jackii to A. tagala. Therefore, the conservation and survival of the common birdwing population here in Singapore is heavily dependent on the cultivation of an exotic host plant species.

The planting A.tagala in forested areas to support the birdwing population may not be an option to conserve the common birdwing population. NParks actively removes exotic species from forested areas in Singapore and discourage the planting of exotics near forested areas. Therefore, A. tagala is almost exclusively found in cultivated green spaces. This may not be ideal as the common birdwing is a forest adapted species. This provide a conservation dilemma for decision makers which they have to balance not actively introducing an exotic host plant species into forested areas and the conservation of a common birdwing in Singapore.

A possible strategy that could implement is the reintroduction of A. jackii back into Singapore using individuals from other countries. This may allow more extensive planting throughout Singapore. However, using individuals from other countries may have complications due to genetic differences between sub-species that was in Singapore and other countries. In addition, it is uncertain whether the common birdwing will actively switch back to its native host plant species.

In my opinion, exotic plants often have a negative association with biodiversity, which many people view exotics as harmful and detrimental to native biodiversity. In many cases, that might be true. However, this is a good example which the introduction of an exotic ornamental plant species may have prevented the local extinction of a native butterfly species.

 

References

Davison, G. W., Ng, P. K., & Ho, H. C. (2008). The Singapore red data book: Threatened plants & animals of Singapore. Nature Society.

Jain, A. (2016). Ecology and conservation of butterflies in a transformed tropical landscape (Doctoral dissertation).

National Parks Board. (2014) Invasive Alien Species. Retrieved from https://www.nparks.gov.sg/biodiversity/wildlife-in-singapore/invasive-alien-species (accessed 7 April 2019).

Tan, H., & Khew, S. K. (2012). Caterpillars of Singapore’s Butterflies. National Parks Board.

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