Simply being nonnative in an ecosystem does not mean that a species will become invasive. It must possess certain characteristics, such as those listed above “How Does a Species Become Invasive?”, that ideally suit it for colonization in a particular area. It also is possible for a species to be invasive in one ecosystem, but non-invasive in another. This can be due to a variety of factors, such as the presence of a predator species or less-than-ideal habitat conditions.
Read More: http://www.fs.fed.us/pnw/invasives/