The extinction of species has been documented ever since about the year 1600. With a percentage of 36%, invasive alien species are considered to be one of the key causes for a biodiversity loss. A pertinent example for a major decimation of existing species due to invasive alien species is the vast diminution of the bird population on the Pacific Island Guam caused by the accidental carry-over of the brown tree snake during the Second World War. The complete eradication of a New Zealand bird species (Bush Wren) caused by one single cat serves as another relevant example for a biodiversity loss due to invasive alien species. Despite the fact that the possibility of a biodiversity loss due to invasive alien species is generally accepted, the actual impact these invasive species have on the ecosystems and biodiversity of the biotopes into which they were introduced, is being debated.