Non-Native Species - Overview

Courtesy G.H. Rodda

by
Science Editor
Hiram W. Li
National Biological Service
Oregon Cooperative Fishery Research Unit
Oregon State University
Corvallis, OR 97331

Non-native Species
*Overview*
Introduced species evolved elsewhere and have been transported and purposefully or accidentally disseminated by humans. Many synonyms are used to describe these species: alien, exotic, non-native, and nonindigenous. The spread of non-native species during the last century has been unprecedented in Earth's history, with the speed and scale of these infestations more rapid than natural invasions. The spread of non-native species in human-disturbed habitats reflects a deterioration of the North American landscape.
Introduced species disrupt the functioning of native ecosystems upon which humans depend. Many non-native species become pests by rapidly dispersing into communities in which they have not evolved, and by displacing native species because of evolutionary mismatches. For example, non-native species contributed to 68% of the fish extinctions in the past 100 years, and the decline of 70% of the fish species listed in the Endangered Species Act (Lassuy 1994).
As several articles indicate, the economic cost incurred because of non-native species reaches millions, or even billions, of dollars. Non-native species damage agricultural crops and rangelands, contribute to the decline of commercially important fishes, spread diseases that affect domestic animals and humans, and disrupt vital ecosystem functions.
Some species that have become pests were first introduced to "create" a desired landscape; these non-natives include exotic game animals, fish, and decorative plants. Mack and Thompson (1982), for example, traced the widespread dissemination of 139 weedy, non-native plants in the United States to seed catalogues and the commercial seed trade of the 19th century. Similarly, feral (wild) domestic animals such as mustangs are a major problem on public lands, and sound management of such animals has been impeded by romantic images of America's past.
Accidental introductions through human travel is a theme repeated in several articles, indicating that cargo traffic (ship, air, land) is a major vector of non-native species and should be monitored as world trade increases. The zebra mussel (Dreissena polymorpha) is the most notorious hitchhiker, but introductions through ballast water are not isolated to the Laurentian Great Lakes. My colleagues and I recently found that 11 exotic benthic invertebrates have become established in Oregon estuaries. Similarly, dinoflagellates causing red tide toxins have spread into Australian waters through cargo traffic. The importation of raw logs from New Zealand and Siberia endanger Pacific Northwest forests through forest pests hitchhiking in the bark and wood (J. Lattin, Oregon State University, personal communication). It is clear that international cargo traffic must be monitored to reduce the spread of non-native species.
Although this section only briefly mentions disease, it may be one of the most important problems caused by non-native species. After Columbus landed in the New World, for example, 95% of the Native tribes became extinct because their people were susceptible to European microbes (Diamond 1992). Likewise, exotic diseases have devastated populations of aquatic organisms worldwide, killed many native trees, and exterminated much of Hawaii's avifauna. Non-native species are the primary vector for these diseases; for instance, the spread of fish diseases worldwide resulted from the unprecedented transfer of non-native fishes for hatchery production.
It is clear from the small sampling of articles here that changes caused by non-native species are widespread and profound. We present different case histories representative of a myriad of management problems today. New problems continually arise, however, because humans deliberately and accidentally release non-native species and encourage their invasion through massive disturbances of the landscape, thereby mitigating against native species' resistance to invaders by stressing native populations. These articles should make it clear that although non-native species are costly to manage, manage them we must.

References
Diamond, J. 1992. The arrow of disease. Discover 13 (10):64-73.	Lassuy, D.R. 1994. Aquatic nuisance organisms: setting national policy. Fisheries (Bethesda) 19(4):14-17. Mack, R.N., and J.N. Thompson. 1982. Evolution in step with few large, hooved mammals. American Naturalist 119:757-773.