The human-caused introduction of non-native species into an environment can have drastic biological and economic effects. However, of the multitude of species either purposefully or accidently transported from one location to another, only a small percentage of them become established in the new environment and are able to spread.

Factors influencing the success or failure of invasions is of both practical and theoretical interest. Basic knowledge of community and ecosystem structure, species competition, and population/dispersion dynamics can be used to not only prevent and control harmful exotics, but also better select species for planned introductions, such as in biocontrol.

The purpose of this page is to give a short overview of invasion theory. All information contained here is synthesized from other sources .

A lot of the factors contributing to the success or failure of a species in a new environment are intuitive. For instance, if you wanted to introduce some species to a new region, would you choose ones that are slow growing with long generational times or fast-growing ones which reproduce quickly? Would you rather place your species in an environment with its predators present or absent? These are examples of the two most overriding influences on invasion success--characteristics of the species and characteristics of the invaded habitat. Actually, it is the strong interaction between these two variables that will determine the success of a new organism in a particular habitat. Of course, chance will also play a role in whether a particular species will establish after a particular introduction. The "innoculation rate" (the number of species or individuals transported and given the opportunity for establishment) will have a general overall effect on the number of species that become established.

It is important to remember that there are no hard rules for invasion success and that the given attributes are only generalizations. In fact, controlled experiments investigating invasion theory are often incorrect in their predicted outcome. Usually the species-community interactions are more complex than first realized.

For links dealing with exotic species:

• Extensive list assembled by Dr. Ray Newman for a seminar on exotic species.
• Nonindigenous Aquatic Species -- large resource by USGS