Topic – Invaders!

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When you hear the word invaders, you might think of armies marching in to take over new territory. Would you be surprised to learn there are invaders in Canada right now? The invaders are not armies of humans—they are plants and animals known as invasive species.

Kudzu is an invasive Japanese vine found in some parts of the United States

What is an invasive species?

A species of animal or plant that begins to live and reproduce in an area where it has not lived before is called an alien species. When an alien species causes problems for living things that were already in the area, it is called an invasive species.

How do invasive species cause problems?

An ecosystem is made up of all the living things in a particular place. We say an ecosystem is balanced when all the living things in it can get what they need to survive over time. There is land where plants are able to grow. There are enough plants to feed animals in the ecosystem that eat plants. There are enough animals for predators to eat. A balanced ecosystem is a healthy ecosystem.

Eastern grey squirrels are considered one of the top 100 invasive species in the world

Now, imagine that a new type of plant—an alien species—starts to grow in the ecosystem. None of the animals in the ecosystem eat this plant, so it starts to spread quickly and cover more and more land. There is less and less land for plants that have always lived in the ecosystem (called native plants). Soon, animals that eat native plant species begin to die because they cannot get enough food. As these animals die, predators that eat these animals will also die from lack of food. The ecosystem is no longer balanced because all the living things in it cannot get what they need to survive. Just one invasive species can have negative effects on many living things in an ecosystem.

Not every alien species is considered an invasive species. Some alien species do not cause any problems in an ecosystem. Only alien species that spread throughout an ecosystem and cause an ecosystem to become unbalanced are called invasive species.

How do invasive species start living in new ecosystems?

The Emerald Ash Borer is an invasive species in Canada that kills living ash trees

Invasive species are found all across Canada. How did they get here? Human activity is responsible for bringing many alien species into our country. Humans can bring an alien species into a country intentionally (on purpose) or unintentionally. Some of these alien species can become invasive species.

There are several reasons why people might intentionally bring an alien species into Canada. Alien plant species might be brought into the country for farmers or gardeners to grow. Alien animal species might be brought in to sell as unusual pets that will live in people’s homes. If these species start to live and reproduce in places where they were not intended to live, they might become invasive species.

Zebra mussels, an invasive species from Europe and Asia, came into Canada in ballast water.

Alien species that are brought into a country unintentionally are often secret “hitchhikers”—people have no idea they are bringing an alien species into the country. Every day, people and goods coming from all over the world arrive in Canada. Insects may be inside the wood of a crate carrying goods. Ballast water is seawater kept in the bottom of a cargo ship to help keep it steady. When a ship from overseas reaches its destination in Canada, it lets out the ballast water. Marine animals from another country may be in the ballast water. Zebra mussels, an invasive species from Europe and Asia, came into Canada in ballast water. These mussels are now an invasive species found in all of the Great Lakes.

How does Canada try to control invasive species?

Canada has laws that make it illegal to bring into the country certain alien species that could become invasive. However, it is impossible for government officials to check every piece of cargo that comes into the country to see if it contains an alien species that could become an invasive species. It is also hard to predict which alien species could become invasive species. Canada’s main focus is on controlling invasive species that are already here, in order to limit how much damage they do to ecosystems.

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