Effect on Ecosystem

The biggest effect of exotic species is on the ecosystem. Earlier, there is a lot of mention about balance in the ecosystem. This means that there is the right amount of each of the species in the system for it to survive. There is a right amount of predators for prey, and right amount of plants for the animals to eat. This ‘right amount’ is the balance that we refer to in an ecosystem.

balance

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Negative effect

When a new species is introduced, the balance is disrupted. If the new species is a predator, then the population of the prey will decrease as there are more predators now, including the native ones. If the introduced species is a herbivore, then the amount of plants will decrease. New species also compete with native species for land, water, and food. If the introduced species is stronger than the native ones, they could replace the native species in the ecosystem. Foreign species may also carry diseases that can harm the native species.

In Singapore, there are many species that are not native. As mentioned before, the rock pigeon is an ‘Alien species’. It doesn’t originate from Singapore, and is known to be one of the top 100 invasive species in the world. Currently, it is one of the top 10 most abundant species of bird in Singapore, which I am sure most of you have seen looking for food in flocks in urban areas. These pigeons are a threat to our native birds, as they compete for food, water and (to some extent) territory. If the rock pigeon is left unmanaged, there is a likely possibility that our native birds will be pushed to extinction.

Similarly, the introduced changeable lizard has pushed the native green crested lizard to the forest. Such invasive species are a real threat to our native species.

Changeable lizard:

changeable-lizard

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Positive effect

However, the same point above can also be seen as a positive effect. Sometimes, introduced species helped to regain balance in the ecosystem by altering the population of some of the native species. For example, the ecosystem may have originally not been in balance, with one or two overpopulated species. To solve this problem, species can be introduced to reduce the population.