A class of organisms that have grown in the same place for a long time, evolved over a certain period of time, produced adaptability to this place, and had a certain degree of impact on the environment here (not to be ignored) is called local species. Alien species refers to the spread from another place to this place in some way, relative to local species. Invasion of alien species means that alien species come to a certain place through certain channels. Because there is no restriction, their growth in this place is not restricted, which affects the growth and reproduction of some creatures in this place, thus affecting the ecosystem in this area and making the system unbalanced (that is, the resistance and stability of this system are reduced). It means that human beings intentionally introduce non-native species from other places for a certain purpose.