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A Invasive species are among the leading threats to the native wildlife of most countries, with approximately 42 percent of endangered species at risk from them. Invasive species can be any kind of organism—for example, a mammal, amphibian, fish, insect, or plant—that is not native to an ecosystem. Often, they reproduce and spread with great speed. Contrary to popular belief, a plant or animal classified as an invasive species does not necessarily originate in another country. For example, lake trout are native to the Great Lakes of North America but are considered an invasive species in Yellowstone Lake in Wyoming because they compete with native cutthroat trout for habitat.
B When a new species is introduced into an ecosystem, native wildlife may struggle to compete with it for food and other resources. Invasive species can change the food web in an ecosystem by destroying or replacing native food sources while providing little or no food for local wildlife. In extreme cases, the invader may prey on the native species. Above all, invasive species threaten biodiversity in many habitats. For instance, the climbing plant species kudzu (which is native to East Asia) can easily replace a habitat that had a wide range of plants with a monoculture consisting solely of kudzu, as has started to happen in the southeast of the USA.
C The phenomenon is not an exclusively modern one. Humans have always transferred a variety of species from one region to another, but the development of rapid means of transportation has increased the frequency of such introductions. Aquatic organisms can be shipped across the oceans, while insects can easily get into the wooden crates that are transported around the world in this way. In addition, climate change has enabled some invasive plant species to colonize new areas. Other invasive species include pets such as snakes or turtles, which are intentionally set free into the wild.
