U.S. Department of Agriculture: Animal and Plant Health Inspection Service


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Witmer, G.W., W.C. Pitt, and J.C. Beasley. 2018. Introduction. pgs. 1-4. In: W.C. Pitt, J.C. Beasley, and G.W Witmer, editors. Ecology and Management of terrestrial vertebrate invasive species in the United States. CRC Press, Boca Raton, FL. 403 pp.


U.S. government work.


Vertebrate species have been introduced to almost all parts of the world for thousands of years. Within the United States and its territories alone, over 1000 vertebrate species have been introduced since the early sailing ships explored the world. This includes at least 86 species of mammals, 127 species of birds, 126 species of reptiles, 53 species of amphibians, and over 673 species of fish (Witmer and Fuller 2011). Many of these species were native to the United States, but were moved to novel regions, often unintentionally or intentionally by humans. While invasive vertebrates have been introduced to all parts of the world, in this book, we focus on introduced terrestrial vertebrates in the United States and its territories, and the intention is to provide an overview of the complexity and challenges associated with managing invasive species within the United States. Often, the management of invasive species and the prevention of new species becoming established is largely a function of the regulatory framework established within a specific country. In this book, although historical management successes and failures are discussed, the focus is on current effective management options and potential future developments to minimize the effects of invasive species and prevent their spread into new areas.

Although plants and animals have been introduced into new areas for centuries, the increased volume of worldwide trade and transportation has accelerated the rate of species introductions over the last 150 years. Animals are introduced for many reasons, both purposeful and accidental. Intentional introductions include both legal and illegal activities such as the production of food and fur, work animals, sport hunting opportunities, companion animals, aesthetics, pets, pet trade propagation, religious purposes, and pest control. Accidental introductions occur because of stowaways in transport vehicles, hitchhikers or stowaways in or on other commodities, escapees, and, in some cases, because of range expansion of a species, often facilitated by human activities and land use. For example, a tropical storm is thought to have brought the cattle egret Bubulcus ibis to North America (Florida initially) from the Caribbean islands after they had crossed the Atlantic Ocean from Europe and Africa. However, it may have been agricultural land use that allowed its subsequent rapid range expansion westward across North America. Likewise, habitat fragmentation stemming from anthropogenic land use has facilitated the expansion of coyotes (Canis latrans) across the Eastern United States and far south into Central America over the last several decades, reaching areas where the species formerly did not occur.

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