The relationships in an ecosystem are very complex, and just one small change can have multiple effects. A keystone species is one that has a large effect on its ecosystem.
|Read more about Keystone Species, on the National Geographic site. When you're thinking about keystone species, think about the image on the right of the doorway. The keystone is the stone at the top of the arch. What happens to the rest of the arch when that stone is removed?||
Before moving on to invasive species, you need to understand native and non-native species. Native species normally live in a particular community. In that community they have a specific niche and natural predators, that keep their population in check.
Non-native species are species that migrate or are introduced into an ecosystem. In the new ecosystem these species do not have natural predators to keep their population in check. These are often referred to as invasive species because of the difficulty in controlling their population growth.