Invaders All Around Us!

I was enjoying lunch at a hawker centre when I heard a familiar, shrill sound near my feet. A few seconds later, a Javan myna, hopped onto my table and eyed my food curiously. Not wanting to share my yummy meal, I quickly gobbled it up, thinking ‘Wow, these birds are becoming increasingly common’. Javan mynas have adapted to urban environments and can be found in many public spaces. However, did you know that these animals are not native?

So how do we differentiate native and introduced species? A native species is found naturally in that region. An introduced animal does not originally live there. It was brought to that area by humans, who may have released them into the wild, or unwittingly transported these hitchhikers during travel. An introduced animal may then be considered invasive when they cause harm to the environment or to native animals.

How do invasive animals or plants cause harm?

When a new animal is brought to an area, it is unfamiliar to the animals there, and it would not have any natural predators. The animal multiplies quickly without a predator keeping its numbers low. Invasive animals are often generalists – they do not have specific requirements, but can thrive in a range of environments. This means they can do better than the native animal would in a short time. Thus, invasive animals often cause the decline of native animals.

Invasive plants, like animals, adapt easily to new environments. They grow quickly, covering vast areas of forest floors or water bodies in a short time, smothering native plants. Areas where invasive plants are abundant often leads to a reduction in plant biodiversity.

Many common animals and plants in Singapore are, in fact, not native. What were their journeys here? Our first culprit is the food thief that I mentioned earlier – the Javan myna.

Which bird have you seen before?
Javan myna photograph by: Lip Kee / CC BY-SA 2.0

Which bird do you see more commonly? The Javan myna is indeed more common than the Common myna (before you roll your eyes at the irony, let me explain why). The Javan myna is native to Indonesia and was first brought to Singapore in the 1920s, via the pet trade. These birds made their way into the wild by escaping, or pet release.

The Common myna, on the other hand, is a native bird and therefore used to be more common. However, as the Javan myna is more easily adaptable to urban environments – they even build their nests behind air-con ducts! – it has driven the Common myna to less urban areas. This is how an introduced animal, being more readily adaptable, can cause the decline of its native counterpart. But the Javan myna is not our only foreign invader.

Which lizard is more commonly found?
Changeable lizard photography by: Alan Tan Keng Hoe / CC BY 2.0
Green crested lizard photography by: Lip Kee / CC BY-SA 2.0

How many of you are guilty of calling this animal a chameleon? This is a Changeable lizard, also capable of changing its colour for camouflage. The changeable lizard is native to Thailand and Malaysia and has made its way to Singapore in the 1980s. It has since been widespread and has outcompeted our native green-crested lizard. Like the Javan myna, the changeable lizard is highly adaptable to urban areas, unlike the Green-crested lizard, which can only be found in forested areas.

After a jog in Bishan Park one day, I chanced upon a pink clump growing on a rock near the water. Thinking that it looked suspiciously like a sea cucumber, I went closer to investigate. I found out that these were eggs of the Golden apple snail.

The golden apple snail is named so, because of its gold-green shell that looks like a golden apple. Yup, I hear you, biologists are not very creative when it comes to naming species. A freshwater snail, it lays its eggs in clusters, which can range from 100 to 1000 eggs, on plants or rocks above the water, to decrease chances of predation. The snail eggs contain a toxin, further protecting them from being eaten.

The golden apple snail (Pomacea canaliculata) has made a long journey here from South America. It was brought to Singapore via the pet trade and is now unfortunately found in many reservoirs and parks such as Lower Pierce Reservoir and Bishan Park. It has outcompeted our native apple snail, Pila scutata, that can only lay about 100 eggs in a cluster. Elsewhere, the golden apple snail is causing economic losses too – by destroying agriculture such as rice. Pretty aggressive for a seemingly innocent creature, huh.

Red-eared slider photography by: Maksym Kozlenko / CC BY-SA 4.0

Have you ever kept a terrapin before and happily called it a turtle? This animal is the Red-eared slider. Its home range is in the southern United States, and (as you have guessed by now) came to Singapore by the pet trade. These creatures are quite cute when they are small, but what happens when they get too big? Sadly, many often release them into the wild.

You may think that releasing a pet into the wild is an act of kindness, but you are causing more harm, for both the animal and the environment. A released pet may not know how to fend for itself, or as we have seen, an introduced animal would cause the decline of a similar native species. In this case, our native Malayan Box Terrapin is becoming increasingly rare because of the slider’s rapid proliferation.

Although these animals are not presently listed as invasive,we do know that they cause substantial harm to the ecosystem. This is why releasing pets – any pet – does more harm than good. ‘Operation No Release’ is organised by NParks annually in May, where volunteers visit parks and reservoirs to raise awareness about the dangers of releasing animals into the wild. Besides harm to the environment, pet release is also against the law.

The rapid proliferation of the water hyacinth leads to the covering of entire surfaces of water bodies.

The Water hyacinth (Eichhornia crassipes) is an aquatic plant with beautiful purple flowers. It seems harmless at first sight. After all, how much harm can a plant, a relatively immobile thing, cause the environment, right? Well, you would be surprised.

The water hyacinth is native to the Amazon river basin. It was first brought to Singapore from Hong Kong in the 1890s but was confined to a private garden. It was soon introduced to Botanic Gardens, and later made its way into reservoirs. In the 1970s, water hyacinths became a huge problem at the Kranji Reservoir, as hundreds of water hyacinths would clog the waterways. Moreover, since it was a reservoir, the use of herbicides was banned, hence officers had to physically remove the hyacinths by boats. These mounds of water hyacinths were then transported to pig farms to be used as fodder.

Due to its extremely quick reproduction, the water hyacinth is able to swiftly cover rivers and reservoirs within a short period of time. With the entire water surface covered by hyacinths, they block sunlight and oxygen from reaching submerged plants. The water hyacinth also takes up a lot of nutrients, hence depleting nutrients for other aquatic plants. Water hyacinth overcrowding can drastically reduce biodiversity in the water body.

In fact, the water hyacinth is so pervasive that it is listed in ‘Top 100 Invasive Alien Species’ list by the International Union for the Conservation of Nature (IUCN). See, we told you it was a rebel.

The leaves and fruits of the Koster’s Curse plant are covered with fine hairs.
Koster’s curse photography by: Forest & Kim Starr / CC BY 3.0

Have you ever seen a plant with hairy leaves? How about hairy berries? ‘Koster’s curse’, also known as hairy clidemia (Clidemia hirta) is one such plant. Its leaves are covered with soft hair, and so are its small, dark blue fruits. In Singapore, it can be found along forest edges, and parks such as Kent Ridge Park.

But who is Koster, you may ask, and why did he curse? Well, Koster was the man who accidentally introduced this plant to coffee plantations in Fiji, between 1880 – 1886. The plant grew rapidly and destroyed the plantations and caused damage to neighbouring coconut plantations as well. Even today, this plant is causing damage to many forests across the world. It quickly occupies gaps in the forest undergrowth, preventing native plants from regenerating, and forms thickets that smother other vegetation. This is another notorious plant that has made its way into IUCN’s Invasive Species List.

The next time you are at a hawker centre and an annoying myna eyes your lunch, or spot other invaders, remember that it is human actions that have brought it here. Yes, humans are the leading cause of many current environmental problems, but we are also capable of becoming something much more powerful: the solution.

Written by Beatriz Fernandez
Designed by Toh Bee Suan

References

  1. https://www.nparks.gov.sg/biodiversity/wildlife-in-singapore/invasive-alien-species
  2. https://www.ecologyasia.com/verts/lizards/changeable_lizard.htm
  3. https://web.expasy.org/spotlight/back_issues/100/
  4. https://www.straitstimes.com/singapore/environment/tracking-non-native-animal-species-here
  5. https://iucngisd.org/gisd/100_worst.php

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