From The Ecological X-Files: Proof That Aliens Are Destroying Endangered Species

July 15, 1998

The most comprehensive assessment ever made of threats to vanishing species in the US has found that alien species are behind the disappearance of nearly half of the imperiled species in the United States. Alien species are plants and animals that are not native to a given region, but which have been brought there by people. Some are brought there accidentally aboard ships or planes; others are intentionally released. Once in these new areas, they can increase in numbers and displace native species from their habitats.

The study, jointly prepared by scientists from the Environmental Defense Fund (EDF), The Nature Conservancy, and the Smithsonian Institution, appears as the cover story in the August issue of BioScience, to be released on Friday (7/17). Only habitat loss ranks as a more serious threat, affecting 85% of our vanishing species, while alien species affect 49%. Alien species rank well ahead of pollution (24%), overharvest (17%), and disease (3%) as threats to biodiversity. Agriculture and commercial development are identified as the two most widespread causes of habitat loss for wildlife, affecting 38% of imperiled species, followed by commercial development (35%) and water development (30%).

“Alien invasion is the least recognized threat to wildlife today. People understand that habitat destruction and pollution are harmful to wildlife. But they don’t realize that alien plant and animal species are everywhere, growing in our forests and grasslands, swimming in our lakes and rivers, and driving native species to the brink of extinction,” said EDF senior ecologist Dr. David S. Wilcove, lead author of the peer-reviewed article.

The article, “Quantifying Threats to Imperiled Species in the United States,” ranks the threats to 1,880 rare species and subspecies of birds, mammals, reptiles, amphibians, fishes, mussels, butterflies, beetles, dragonflies, other invertebrates, and plants.

“Simply protecting habitats from further development won’t do the trick for most of our endangered species. We need to control invasive, alien plants and animals that are degrading the remaining habitats. That takes time and money,” said Wilcove. “Tax credits and direct grants are needed for landowners who agree to manage their properties in ways beneficial to endangered species, including controlling harmful alien species.”