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Exotic Invasive Species: The Guests That Won’t Go Home

Originally appears in the Summer 2006 issue

My next-door neighbor likes to brag about her green thumb: everything she plants around her yard seems to grow like Jack’s beanstalk. She seldom pays for her landscaping plants, preferring instead to dig up trees and shrubs she finds growing along the creek or in a nearby field. Among her scavenged finds are mimosa, privet, honeysuckle, and multiflora rose. Unfortunately, the shrubs and trees that she finds growing in abundance in the wild are now also growing in abundance in my landscape beds! It seems these scavenged plants will grow just about anywhere. My neighbor has unknowingly become part of an enormous threat to biodiversity by propagating plants that are identified as “invasive exotic pests” in our region of the southeast.

By definition, an invasive exotic species is any species that is not native to that ecosystem, is capable of propagating itself, and whose introduction causes or is likely to cause economic or environmental harm or harm to human health.1 Invasive exotic pests are not only plants: animals, fungi, and microorganisms are also players in this threat to biodiversity. Invasive exotic pest species upset the balance in ecosystems in a variety of ways. Many have selective advantages over native species, such as faster growth and reproduction rates or more effective dispersal mechanisms. Some invasive plants come equipped with sharp spines, barbs, or stickers; some like to grow in dense clusters, crowding out other plants; and some taste bad to predators. Not being indigenous to the ecosystems in which they become established, they may have no native predators or competitors to limit their population size. Reproducing rapidly, spreading rampantly, out-competing native species, lacking predators, and being extremely difficult to control, invasive exotic species pose a threat to native biodiversity globally. Many also have devastating economic effects on natural systems and resource industries. In the U.S. alone, it is estimated that invasive exotic species are responsible for $138 billion in damages per year to forestry, fisheries, agriculture, and waterways.2

We have only begun to understand the complex interrelationships among living things, and sometimes these relationships are not apparent until a species is threatened or lost. Once ecosystem complexity is lost, it is very difficult to put it back. Teachers and students can play an important role in maintaining local biodiversity by learning about exotic species that are threatening the natural environment in the communities where they live. As stewards of the local environment, they can volunteer with local groups to remove exotics and restore native plant and animal populations. This article takes a closer look at invasive species and the impact these uninvited species have had on biodiversity.

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Kim Cleary Sadler is Assistant Professor of Biology at Middle Tennessee State University and the Assistant Director of the Center for Environmental Education. Special thanks to Karen Hargrove, Outreach Coordinator, MTSU Center for Environmental Education.