Essay from the year 2006 in the subject Biology - Ecology, grade: A, University of Bremen (Center of Marine Tropical Ecology), course: Essay for M.Sc. course, language: English, abstract: In the first part, this essay aims at providing a rough overview about the most important topics in the literature dealing with alien invasive species. This overview tries to answer questions about the general biology of alien invasive species and the existence of a perfect invader. However, some ecosystems seem to be more susceptible to invasion than others do. General assumptions are that the tropics are less invasible than temperate regions and that islands are more vulnerable than continental areas. An alien species must complete three stages of human-mediated spreading which are transportation, introduction and establishment in order to become invasive. An alien invasive species might then have positive or negative impacts. Either it adds to the species richness or it has detrimental effects on the ecological, economical or human health sector. However, sophisticated treatments are available to prevent several means of introduction. The second part of this essay will provide a critical evaluation about the literature reviewed. There still exists a great deal of uncertainty and variety of opinions within publications. The need of increased prevention of introductions and collaboration are conclusions that can be drawn. Furthermore, public awareness has to be raised and a clear definition of terms is a must. Finally, it is important to recall that many alien species are responsible for human well-being by providing food and aesthetics.