INVASIVE SPECIES

Related OREGON EXPLORER Info

• Invasive wildlife species
• Introduction to invasive wildlife
• Learn about the worst invaders in Oregon
• Invasive bird, fish, and mammal species
• Invasive plant species

Next to habitat loss, invasive species pose the greatest threat to the survival of native biota in the United States, and many other areas of the world.

Invasive species are those plants, animals, and microbes not native to a region that, when introduced either accidentally or intentionally, out-compete native species for available resources, reproduce prolifically, and dominate regions and ecosystems. Because they often arrive in new areas unaccompanied by their native predators, invasive species can be difficult to control. Left unchecked, many invasives have the potential to transform entire ecosystems, as native species and those that depend on them for food, shelter, and habitat disappear.

Below you can find information about native plants and their importance to ecosystems, along with examples of some non-native wildlife species of concern in Oregon's Coast Range.

For more information, visit the Oregon Invasive Species Councils Invasive Species webpage listing the 100 most dangerous invasive species to Oregon.

See the Oregon Wildlife Explorer for more information on invasive wildlife. The Oregon Wetlands Explorer provides additional information on invasive species.

Invasive Wildlife Species

• Virginia Opossum (Didelphis virginiana)
  • The Virginia opossum is a native species in North America east of the Rocky Mountains in Central America. Nonnative opossums also occur in western Washington, coastal California, and southwestern British Columbia.
  • The opossum was first introduced in Oregon in Umatilla County., between 1910 and 1921, and in Clatsop County. in the 1920s. These animals were originally held as pets and novelties, and escaped from captivity or were intentionally released. Populations are now established throughout the Willamette Valley, other inland valleys, and along the entire Pacific Coast.
  • Although relatively short-lived, opossums are very adaptable, have high birth rates, are opportunistic omnivores, and will eat practically anything available. These traits make opossums very successful in colonizing new areas.
  • The impact of opossums preying upon native invertebrates, small mammals, amphibians, reptiles, and ground nesting birds, nestlings and eggs is of concern.
• Nutria (Myocastor coypus)
  • Nutria are large rodents naturally found in South America. Nutria have been widely introduced throughout the world for fur-farming purposes.
  • Nutrias in Oregon were first introduced when an unknown number escaped from a fur farm in Tillamook County. during a flood in 1937. Currently, nutria can be found in much of the western Oregon along the coast and in the interior valleys from the Columbia River to Coos and Klamath counties, and counties that border or include the Snake and Malheur rivers.
  • Nutria are herbivores and can eliminate certain species of native muskrats for food and places to live. There is also anecdotal evidence where nutria become abundant, muskrats become rare or disappear.
  • Nutria are an economic liability when their burrowing activity damages dams and dikes and their feeding activity damages new plantings and crops.
• Bullfrog (Rana catesbeina)
  • The bullfrog is the largest frog in North America and is native to eastern North America. Bullfrogs were first introduced to Oregon in the 1920s to provide frog legs for the West Coast market. The frog leg industry declined in the 1930s, but the bullfrogs remain.
  • The bullfrog is highly adaptable to a number of aquatic habitats and is an opportunist that will eat anything it can catch and swallow. Because of the voracious appetite of the bullfrog, there is concern about the effect they are having on several rare or declining species in the Pacific Northwest including the spotted frog (Rana pretisoa), Western Pond turtle (Clemmys marmorata) and Oregon chub (Oregonichthys crameri).
  • In Oregon, areas with an abundance of bullfrogs have few or no turtle hatchlings or other frog species. This same pattern occurs between bullfrogs and other amphibian and reptile species in several other western states where the bullfrog has been introduced.

Sources

Compiled by John Ame, Science Writer (2007)

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