The introduction and spread of invasive species is another major driver of species decline and ecosystem disruption. Invasive species are defined as non-native organisms whose introduction causes, or is likely to cause, economic or environmental harm, or harm to human, animal, or plant health. There are several mechanisms by which invasive species cause harm to native biodiversity, ranging from direct predation, competition for resources, and hybridization with native species to alteration of key ecosystem functions and structure. As an example, nutria (a large South American rodent) accelerates erosion and loss of wetlands through its burrowing activities, while cheat grass in the intermountain West is fueling loss of sagebrush habitat by altering natural fire regimes. Invasive species have been identified as the second leading threat to endangered species in the United States (Wilcove et al. 1998).
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Author
Bruce Stein, Ph.D., Chief Scientist and Associate Vice President
National Wildlife Federation