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- This article refers to the biology of Earth, for extraterrestrial biology, see Extraterrestrial life
Definition
In biology, an alien refers to an organism that is introduced into a foreign locale and subsequently becomes naturalized, as in the term alien species. Words with similar meaning in biology include exotic, adventive, introduced, and naturalized. These terms contrast with terms such as native, indigenous, and endemic.
Problems
Alien species can sometimes wreak havoc on their new ecosystem, since, in many cases, the local predators do not hunt them and so they will have no natural enemy. In some cases, people deliberately introduce the matching predator, with equally disastrous effects.
The introduction of alien species must therefore be prevented as much as possible. This can be difficult. For example, many marine species travel thousands of kilometers in the ballast water of ocean vessels, which are emptied at the destination port, leaving alien organisms in a place foreign to their species. As another example, people buy tropical animals and then discover that it is difficult to keep them and release them into the wild.
In recent years, tropical species have been moving to the north and south of their original habitat which is attributed to global warming.
See also
"Alien (biology)"