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thinking about ecosystems

Imagine you have a small piece of land, like an island. It's sandy and there are lots of plants and animals, beautiful birds and insects. The island is an ecosystem (but there are ecosystems within it as well).

Imagine what would happen if you changed something about the island. For example, what would happen if you cut down all the trees? Or what would happen if you built a factory that emitted polluting gases? Or what would happen if you decided to introduce big cats to the island? All of those things would change the ecosystem.

For example, if you cut down the trees, some of the birds and animals who lived in trees would need to find new places to live. Living things that needed shade from the sun would have to find shade somewhere else, or they might even die out (that's called 'becoming extinct!').

For example, before humans arrived in New Zealand, estuaries were usually surrounded by forests. Forests provided shade for all the plants and animals who needed it. When humans arrived and cleared a lot of the forests, it changed a huge number of ecosystems. Land and water creatures had to adapt to their new environment, move on, or die.

If, say, a rare bug became extinct on your island, what would happen to the animal that only eats this kind of rare bug? And what about the next animal up the food chain? One seemingly tiny change in your ecosystem could wipe out the whole island!