Invasive species are a worldwide scourge – a nasty side effect of modern transportation technology and economic globalization. ~ The Week
An invasive species is a plant or animal introduced into an ecosystem which then has a disruptive effect by establishing itself as dominant, to the diminishment or exclusion of native species.
An introduced species may establish itself by using resources unavailable or untapped by natives, such as plants tolerating low-nutrient soils, or outcompeting indigenous animals that feed on the same food sources.
An invasive species tends to be successful when introduced into a habitat like the one in which it evolved. Amphibian introductions are particularly successful. When frogs and salamanders come into an area where a similar species exists, they are more, not less, likely to establish themselves. Darwin staunchly predicted otherwise.
Generalist species may rapidly adapt to their adopted home. Their tolerance for temperature and other variables gives them a head start.