Every species plays its part in an ecosystem, creating a perfect balance. Introducing a species or exterminating one could throw off that balance, causing devastating results. For example, an eagle, a snake, a rat, and a grasshopper. The leaves are eaten by grasshoppers. The grasshoppers are eaten by rats. The rats are eaten by snakes. The snakes are eaten by eagles. Let's say that you decide to kill off the grasshoppers. The balance would be thrown off. Because there's no animal or insect to eat the grass, the grass will grow and grow and grow. Since the grasshopper was also a food source for the rats, the the rats will most likely start to die out because they have no grasshoppers to eat. Same goes with the snakes, since the rats die off, the snakes die too cause they have no rats to eat. Same with the eagle. Introducing a species will, in a way do the same thing as well. Introducing a species will cause a new demand for food and space, effecting an ecosystem. For example, there's a forest. The forest is a home to many animals, especially the birds that live in the trees. Let's say you decide to place wood eating bugs in that forest. Their food source would be the trees, the very home of those birds. If they start eating all the trees, then the birds would have to home to go to, the habitat of other animals may also be destroyed, all because the balance of an ecosystem was thrown off. I hope this helps!
