tailieunhanh - Kangas - Ecological Engineering - Principles and Practice - Chapter 7

7 Exotic Species and Their Control The invasion of ecosystems by exotic species is a major environmental problem that has become widely recognized (Culotta, 1991; Mack et al., 2000; Malakoff, 1999). This phenomenon is occurring globally and causing changes to ecosystems, along with associated economic impacts. | 7 Exotic Species and Their Control INTRODUCTION The invasion of ecosystems by exotic species is a major environmental problem that has become widely recognized Culotta 1991 Mack et al. 2000 Malakoff 1999 . This phenomenon is occurring globally and causing changes to ecosystems along with associated economic impacts. The most important issue with the invasion of exotics is the replacement of native species in terms of either reduction of their relative abundance or in the extreme their outright extinction. Associated costs to human economies from the invasion of exotics include losses of value derived from the natives they replace direct damages caused by them and expenditures for control programs directed at exotics Pimentel et al. 2000 . The invasion of exotic species occurs because of introduction by humans either intentionally or unintentionally. Of course intentional introductions are undertaken in an effort to add a useful species to an ecosystem and there are positive examples of this action such as the introduction of honey bees as a pollinator for crop species. Problems arise however when intentionally introduced species take on unintended expanded and negative roles in ecosystems or when this occurs with unintentional introductions. Perhaps because it is an environmental problem caused by excessive growth or biology gone wrong the invasion of exotics has become sensationalized by environmentalists and the news media with seemingly good reason. This situation is reflected in titles of news stories about exotics such as Unstoppable Seaweed Becomes Monster of the Deep Simmons 1997 and other evocative descriptions such as the Frankenstein effect Moyle et al. 1986 and the need to consider exotics as guilty until proven innocent Ruesink et al. 1995 Simberloff and Stiling 1996 . A further example is the announcement of America s Least Wanted Table which is a list of the dirty dozen of the country s worst exotics according to the Nature Conservancy Flack and .

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