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Invasive Species

Introduction to Invasive Wildlife

Non-native species collage (Images courtesy of
Wikimedia and Oregon Department of Fish and Wildlife)

"To have a fighting chance at controlling them, we have to know where they are and how many of them there are," Jim Gores, former Invasive Species and Wildlife Integrity Coordinator at ODFW

An "invasive species" is defined as a species that is 1) non-native (or alien) to the ecosystem under consideration and 2) whose introduction causes or is likely to cause economic or environmental harm or harm to human health. Invasive species are any species or other viable biological material that enters an ecosystem beyond its historic range, including any such organism transferred from one country into another. Invasive non-native species (also known as introduced, foreign, alien, and immigrant species) include both exotics and transplants.

Control of invasive wildlife species is one of the Six Key Conservation Issues of statewide concern in the Oregon Conservation Strategy.

The spread of non-native invasive 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.

Invasive 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).

Invasive species can be plants, animals, and other organisms (e.g., microbes). Human actions are the primary means of invasive species introductions. One study estimates that the total costs of invasive species in the United States amount to more than $100 billion each year. Invasive species impact nearly half of the species currently listed as Threatened or Endangered under the U.S Federal Endangered Species Act.

The Oregon Invasive Species Council maintains the most current list of the Top 100 most invasive species in Oregon. The list is categorized by type of invader, such as micro-organisms, aquatic plants, fish, mammals and others.

USDA Forest Service. Pacific Northwest Region. Invasive Species Links and Contact. Includes lists of governmental and non-governmental sites.