The Alligator and the Python are competing for top predator. What affect can the introduction of a non-native species have on an ecosystem?

If a non native species got introduced then it would hurt the animals already there because there is no animals that are hunting it down. Also it would cause a imbalance in the food chain which can cause so animals to become extinct. If the animal is left unchecked then that animal can become the best in the food chain because nobody can get rid of it.