The Convention on Biological Diversity adopted at the 1992 United Nations environmental summit in Rio de Janeiro recognized this threat. The treaty calls on participating nations – as far as possible and as appropriate [to] prevent the introduction of, [to]control, or [to] eradicate those alien species that threaten ecosystems, habitats, or species – [5]. Participating nations are now exploring how to begin implementing this enormous task [6].
A biological conveyor belt
Burgeoning world trade poses a particular threat in terms of its potential to increase bioinvasions. Most species introductions are unintentional, and trade opens up major dispersal opportunities. Food- and waterborne disease organisms, agricultural pests and weeds, and other nuisance species hitchhike to new lands aboard ships, airplanes, and trucks, stowing away in shipping containers and packing materials or riding on nursery stock, unprocessed logs, fruits, vegetables, and seeds [7]. On any given day, for instance, some 3,000 aquatic species are moving around the globe in the ballast tanks of ships, a biotic conveyor belt that has already altered the ecological makeup of much of the world’s coastal waters [8].
Deliberate introductions of exotic plants and animals for commercial and agricultural purposes also can pose risks. The bulk of the diet of most of the world’s population comes from crop and livestock species that originated elsewhere [9], and land managers, agricultural scientists, and other sectors of society have clear economic incentives to continue importing exotic species for food, timber, horticultural, and other uses.
But these intentional imports do not always prove benign. The golden apple snail, which was introduced into Asia from South America in 1980 to be cultivated as a high-protein food source, has dispersed into the region’s rice paddies, where it feeds voraciously on rice seedlings, causing significant crop damage [10].
Of course, not all newly arriving species become problems, but those that do can cause not only biological damage but also economic damage. In the United States, roughly one fifth of 4,500 established exotic species cause serious economic or ecological harm. Estimates of economic losses, not including damage to native species or to ecological services, range up to several billion dollars per year in the United States alone [11]. In the Philippines, estimates of economic losses associated with the golden apple snail alone ranged from US$425 million to US$1.2 billion in 1990 [12].
References and notes
5. James T. Carlton, “Invasions in the World’s Seas: Six Centuries of Reorganizing Earth’s Marine Life,” in Proceedings of the Norway/UN Conference on Alien Species, The Trondheim Conferences on Biodiversity, July 1-5, 1996, O.T. Sandlund et al., eds. (Directorate for Nature Management/Norwegian Institute for Nature Research, Trondheim, Norway, 1996), p. 100.
6. O.T. Sandlund et al., eds., Proceedings of the Norway/UN Conference on Alien Species, The Trondheim Conferences on Biodiversity, July 1-5, 1996 (Directorate for Nature Management/Norwegian Institute for Nature Research, Trondheim, Norway, 1996).
7. Jeffrey A. McNeely, “The Great Reshuffling: How Alien Species Help Feed the Global Economy,” in Proceedings of the Norway/UN Conference on Alien Species, The Trondheim Conferences on Biodiversity, July 1-5, 1996, O.T. Sandlund et al., eds. (Directorate for Nature Management/Norwegian Institute for Nature Research, Trondheim, Norway, 1996), p. 53.
8. James T. Carlton, “Invasions in the World’s Seas: Six Centuries of Reorganizing Earth’s Marine Life,” in Proceedings of the Norway/UN Conference on Alien Species, The Trondheim Conferences on Biodiversity, July 1-5, 1996, O.T. Sandlund et al., eds. (Directorate for Nature Management/Norwegian Institute for Nature Research, Trondheim, Norway, 1996), p. 100.
9. Jeffrey A. McNeely, “The Great Reshuffling: How Alien Species Help Feed the Global Economy,” in Proceedings of the Norway/UN Conference on Alien Species, The Trondheim Conferences on Biodiversity, July 1-5, 1996, O.T. Sandlund et al., eds. (Directorate for Nature Management/Norwegian Institute for Nature Research, Trondheim, Norway, 1996), p. 53.
10. Rosamond Naylor, “Invasions in Agriculture: Assessing the Cost of the Golden Apple Snail in Asia,” Ambio, Vol. 25, No. 7 (1996), p. 443.
11. Peter Jenkins, “Free Trade and Exotic Species Introductions,” in Proceedings of the Norway/UN Conference on Alien Species, The Trondheim Conferences on Biodiversity, July 1-5, 1996, O.T. Sandlund et al., eds. (Directorate for Nature Management/Norwegian Institute for Nature Research, Trondheim, Norway, 1996), p. 145.
12. Rosamond Naylor, “Invasions in Agriculture: Assessing the Cost of the Golden Apple Snail in Asia,” Ambio, Vol. 25, No. 7 (1996), p. 443.
