I don't know if I'll help much, but if your looking for real world examples...An introduced species, like a species that is brought into an ecosystem can greatly disrupt it's balance. I live in Oregon and on the Pacific cost their is a species of crab I think called the chinese red rock. They were introduced to the area and are killing off the native species of crab. Normally their are regulations and a crab has to be a certain size before you can keep it. With the red rock you can keep every one you catch because of the effect they are having on the ecosystem.
Other than this idea I'm not really sure what the question is asking?