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  Loss of Biodiversity Due to Non-native species

Cat eating a bird  House cats in Wisconsin alone may kill 19 million songbirds each year, according to a University of Wisconsin study by Stanley Temple and John Coleman

Non-native species are a major cause of biodiversity loss around the world. When a species is brought to a new area accidentally or on purpose it may compete with native species for food, sunlight, shelter, space, or other special features of the habitat. It may also prey on native species that have not evolved defenses against the new predator.

The house cat is an example of a very hardy and adaptable predator that has established wild populations wherever it has been released. Birds that nest on the ground and small mammals are particularly at risk.

Non-native species can also carry diseases and parasites to which the native species have little or no immunity. Europeans brought smallpox, tuberculosis and other human and livestock diseases to the American continents. A succession of epidemics swept through South, Central, and North America, drastically reducing the populations of Native Americans who had little or no immunity to the "old world" diseases.

The brown tree snake, brought accidentally to Guam following World War II, is an incredible example of an exotic species that took over a new area because it had no natural predators or diseases. The snakes have exterminated native species of birds and small mammals on Guam and now threaten Hawaii and other islands. The snakes slither unseen into airplanes and are transported across the ocean to new habitats.


Find out about
non-native species in your area


Where did they come from?

How do they change the local ecosystems?

Do they compete with or prey on native plants or animals?

Is anything being done to reduce their impact?



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