Erecting barriers against invastions
Erecting barriers against invastions
What can be done to stem the tide of bioinvasions? For one, before intentionally introducing an exotic, it would be helpful to thoroughly analyze potential risks and trade-offs of the introduction. However, biologists cannot predict with certainty the invasive potential of any given plant, animal, or microbe [13]. For this reason, a few nations such as New Zealand -- where 47 percent of the flora is already exotic [14] -- have adopted the precautionary principle, banning importation of all exotic species except for a few clean-list species that are known to be benign. In contrast, most nations, if they have any import restrictions at all, use a dirty-list concept, only denying import of known problem pests or weeds [15].
In the case of unintentional introductions, the first line of defense is a system of quarantines and regulations designed to limit the free flow of species through trade, transport, aquaculture, agriculture, forestry, game farming, horticulture, the pet trade, recreation, tourism, and travel [16]. Strengthening these barriers will not be easy in light of potential conflicts with treaties such as the General Agreement on Tariffs and Trade (GATT) that promote fewer, rather than more stringent, restrictions on international trade [17].
Yet, some steps are already underway. The 156-nation International Maritime Organization has been developing regulations to control ballast water discharge, which is the source of many exotic species in coastal estuaries [18]. In the interim, several countries have acted individually to protect their own waters from invasions. In the Great Lakes bordering the United States and Canada, mandatory controls on ballast water releases from commercial shipping have been in place since 1990, in reaction to the invasion of the zebra mussel [19]. More recently, the United States has extended voluntary ballast water controls to other U.S. ports, requesting that ships filter or exchange their ballast water at sea before entering port [20]. Chile and the port of Haifa, Israel, have also instituted mandatory ballast water requirements, and Australia has a program to control ballast water releases as well [21] [22].
Other strategies to deal with the larger issues of invasions of both aquatic and terrestrial ecosystems are taking shape at an international level. These strategies include computerized databases of information on known harmful invasives in various regions that can serve as an early warning system for other nations. Other approaches include a global assessment of the status of invasions -- such as the land area dominated by exotic plants -- as well as techniques for rapid and regular reassessment of the extent of bio-invasions [23] [24]
| Bird Populations Are Under Siege Worldwide | |
| Threatened Birds as a Percentage of Total Known Avian Species
Approximately 11 percent of all known bird species are threatened with extinction. Habitat fragmentation or loss is the principal factor in this decline, but harvesting for food and trade and competition from nonnative species are important as well. |
|
 |
|
| Source: World Resources 1998-99 Data Table 14.2.
Note: Data for map taken from mid-range projections, Water Resources Vulnerability Index I, Conventional Development Scenario for 2025. | |
References and notes
13. H.A. Mooney and J.A. Drake, "Biological Invasions: A SCOPE Program Overview," in Biological Invasions: A Global Perspective, SCOPE 37, J.A. Drake et al., eds. (John Wiley & Sons Ltd., Chichester, U.K.,
14. Vernon H. Heywood, "Patterns, Extents, and Modes of Invasions by Terrestrial Plants," in Biological Invasions: A Global Perspective, SCOPE 37, J.A. Drake et al., eds.
(John Wiley & Sons Ltd., Chichester, U.K.,
15. Michael J. Bean, "Legal Authorities for Controlling Alien Species: A Survey of Tools and Their Effectiveness," 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), pp. 204-210.
16. Thorbjorn Berntsen, "Opening Speech," 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. 8.
17.
18. 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. 101.
19. U.S. National Research Council Committee on Ship's Ballast Operations, Stemming the Tide: Controlling Introductions of Nonindigenous Species by Ships' Ballast Water (National Academy Press, Washington, D.C., 1996), pp. 59-60.
20. The White House Office of the Press Secretary, "Statement by the President," October 26, 1996.
21. National Academy of Sciences, Stemming the Tide: Controlling Introductions of Nonindigenous Species by Ships' Ballast Water, National Research Council Committee on Ship's Ballast Operations of the National Academy of Sciences (National Academy Press, Washington, D.C., 1996), p. 59.
22. Australian Quarantine and Inspection Service (AQIS), "Australian Ballast Water Management Strategy," AQIS. (June 6, 1997).
23. Harold A. Mooney, "The SCOPE Initiatives: The Background and Plans for a Global Strategy on Invasive Species," 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), pp. 30-33.
24. Michael N. Clout and Sarah J. Lowe, "Reducing the Impacts of Invasive Species on Global Biodiversity: The Role of the IUCN Invasive Species Specialist Group," 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), pp. 34-38.
