When you hear the term “non-native species”, what comes to your mind? For me, I think of a dangerous, aggressive, and foreign animal, one that displaces native biodiversity and damages the local ecosystem.
However, do they deserve such a harsh reputation? Before we make any judgement, let’s address some terms we commonly see.
| Non-native species | A species that has been intentionally or unintentionally introduced beyond their native range. This is inclusive of “any component of such species…that possess the potential to survive and proliferate”1. |
| Invasive species | A native or non-native species that has been established and threatens biodiversity and human health, alters the ecological balance, and causes economic loss. |
| Alien invasive species | An invasive species that is non-native. |
Until recently, I’ve foolishly assumed that “non-native species” and “invasive species” can be used interchangeably. Following this common misconception is the failure to distinguish between introduced species that cause harm from those that are harmless, leading to just about all non-native species to be harshly criticised.
Some cases rightfully have a bad reputation, such as the red-eared slider in Singapore. The red-eared slider is included in the list of “100 of the World’s Worst Invasive Alien Species”2. Originally from south-eastern United States, the sliders were first introduced into Singapore as exotic pets3 .
Many buyers are unaware of the potential size these animals can grow to and when they become too big and too much to take care of, many irresponsibly release them directly into Singapore’s reservoirs3. In fact, it was probably because so many sliders were released that the initial population could be established4! These generalist terrapins easily adapted to life in our freshwater ecosystems4, enabling them to now flourish in Singapore.
But now, the ecological balance is disrupted, threatening native wildlife. The red-eared slider is an aggressive competitor for food and space compared to the native terrapin species4. What’s more, a female red-eared slider can produce up to a dozen eggs, meaning it can possibly out-breed the native Malayan box turtle which only lays two eggs each time3.
This is just one example of how alien invasive species contribute to biodiversity loss. When they are not regulated, invasive species can out-compete and endanger native species.
Introduced =/= Invasive
However, as we learnt above, not all introduced species are invasive. Non-native species can contribute to biodiversity conservation by acting as replacements for extinct species5. In addition, they provide ecosystem services and are predicted to evolve into endemic taxa overtime5. For example, the Aldabra tortoise (Aldabrachelys gigantea), a close relative of the extinct giant tortoise, was brought over to the island of Ile aux Aigrettes to recover the island’s threatened ebony forest6. Aldabra tortoises supported the dispersal of native plants’ seeds islandwide through consumption and excretion6. Researchers reported that the ebony forest is steadily restoring6. This highlights the importance of non-native species in the restoration of ecological balance.
Nothing is black or white. We shouldn’t simply generalise that non-native species are either all good or all bad. We should always look at the context: which species and environment we are observing! For instance, zebra mussels can affect their ecosystem in many ways, depending on the circumstances. In Lake Michigan, zebra mussels are deemed harmful as they poisoned thousands of birds while in Lake Ontario, zebra mussels have improved water turbidity which benefited the marine ecosystem6.
The Cost of Prejudice
Although the majority of the non-native species are harmless or even generate positive effects7 , there is a prevailing prejudice towards non-native species. Effects of this unnecessary hatred can be seen in Scotland where local farmers and fishers shot down every Tay beaver in sight, believing they are invaders that disrupt agricultural activities and serve as possible vectors of disease8 , when they actually boost the ecosystem9.
Raising awareness regarding the distinction between non-native and invasive is a crucial step forward during the sixth mass extinction (you can read more about this here). Misconceptions hinder the advancement and enforcement of policies for the effective management of non-native and invasive species10. So, before we start hating all non-native species, we should always do our own research on a particular species’ ecological role in a localised context.
Adapted from https://blog.nus.edu.sg/awholenewworld/ by Goh Lixuan
Cover photo of Clementi Forest