Invasive alien species have invaded and affected native biota in almost every ecosystem type on Earth, and have affected all major taxonomic groups¹. In economic terms, the costs of invasive alien species are significant. Total annual costs, including losses to crops, pastures and forests, as well as environmental damages and control costs, have been conservatively estimated to be in the hundreds of billions of dollars and possibly more than one trillion². This does not include valuation of species extinctions, losses in biodiversity, ecosystem services and aesthetics.

The Millennium Ecosystem Assessment concluded that the relative impact of invasive alien species on biodiversity has varied across biomes, and that for all biomes, the impact is either steady or increasing as follows³:

^{1 IUCN (The World Conservation Union). 2000. IUCN Guidelines for the Prevention of Biodiversity Loss Caused by Alien Invasive Species. Prepared by the Species Survival Commission Invasive Species Specialist Group, and approved by the 51st Meeting of the IUCN Council. Gland, Switzerland.}

^{2 Pimentel, D., S. McNair, J. Janecka, J. Wightman, C. Simmonds, C. O’Connell, E. Wong, L. Russel, J. Zern, T. Aquino, T. Tsomondo 2001. Economic and environmental threats of alien plant, animal, and microbe invasions. Agriculture, Ecosystems and Environment 84 (2001) 1–20.}

^{3 Millenium Ecosystem Assessment. 2005. Ecosystems and human well-being: biodiversity synthesis. World Resources Institute, Washington, DC.}