Economic and environmental threats of alien plant, animal, and microbe invasions

Over 120,000 non-native species of plants, animals and microbes have invade d the United States, United Kingdom, Australia, South Africa, India, and Br azil, and many have caused major economic losses in agriculture and forestr y as well as negatively impacting ecological integrity. Some introduced spe cies, like corn (Zea may L.), wheat (Triticum spp.), rice (Oryza sativa L.) , plantation forests, domestic chicken (Gallus spp.), cattle (Bos taurus), and others, are beneficial and provide more than 98% of the world's food su pply. Precise economic costs associated with some of the most ecologically damaging alien species are not available. Cats (Felis cattus) and pigs (Sus scrofa), for example, are responsible for the extinction of various animal species, however, it is impossible to assign monetary values to species fo rced to extinction. The estimate is that nun-native species invasions in th e six nations are causing more than US$ 314 billion per year in damages. (C ) 2001 Elsevier Science B.V. All rights reserved.