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Published in Winter 2000-2001
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Super invaders spreading fast
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Increased trade is accelerating the spread of species over the globe, contributing to decreased biological diversity and costing North America millions of dollars. In response, CEC explores cooperative strategies to curb invasive species, as described by Randy Westbrooks and William Gregg.
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A global biological invasion is now taking place.
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Photo: James E. Appleby, University of Illinois
The woodboring Asian Ionghorned beetle (Anaplophora glabripennis) probably hitchhiked to North America in packing crates from China. It has been found devouring hardwood trees in New York City and Chicago. If it spreads, it could be economically devastating.
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Thousands of species, from microbes to mammals, are being moved around the world by people—deliberately, and accidentally as hitchhikers in cargo and baggage.
Invasive species are plants, animals or other living things that are introduced into an ecosystem in which they did not evolve and in which normally no natural enemies limit their reproduction and spread. Their biological characteristics, such as fast growth or prolific reproduction, enable them to invade new habitats. Fortunately, only about one percent of all ‘exotic’ or alien species that find themselves in new settings become invasive.
Early invaders
From early European colonization through the 19th century, most biological invaders in North America were introduced, either accidentally or intentionally, from Europe and western Asia. For example, plants were brought to the New World to be cultivated in settlers’ gardens or arrived by accident as seeds on their boots or in their baggage. Early invaders include such well-known species as kudzu (Pueraria lobata), starlings (Sturnus vulgaris), house sparrows (Passer domesticus), the boll weevil (Anthonomus grandis) and dandelion (Taraxacum officinale). These species were previously unknown in North America.
North America has a huge range of climates and habitats that provide conditions suitable for establishment of invasive species (see map of North America’s ecoregions in this issue). It is estimated that at least 6,600 free-living species of terrestrial, freshwater, and marine organisms of foreign origin have become established in the United States and Canada since the beginning of European settlement. The domesticated forms of many non-native species, such as rice, wheat and soybeans, benefit society and are part of our everyday lives, of course. But introductions are increasing and causing untold harm.
Introductions increasing
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Photo: S. van Mechelen, University of Amsterdam
The zebra mussel (Dreissena polymorpha), a mollusk the size of a thumbnail, probably first arrived in North America in the ballast water of cargo ships from the Black Sea in the late 1980s. By 2002, it will cost some $5 billion in damages to shipping and power plants in North America.
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Increased global trade and travel has accelerated the natural movement of plants and animals around the globe, increasing the number of free-living exotics. Species arrive in containers, cars, or soil. They are released inadvertently with ballast water from ocean ships. They are introduced intentionally for such purposes as landscape restoration and controlling pests, and to provide game animals, sport fish, ornamental plants, algae, and pets. Some of these escape to the wild and establish themselves in new habitats, harming or even eliminating native species, or homogenizing the structure and diversity of terrestrial and aquatic ecosystems.
Ecologists now regard invasive species as the second most important threat to biodiversity, after habitat loss and degradation. They are a major or contributing cause of declines in 49 percent of all endangered species in the United States. Purple loosestrife (Lythrum salicaria) is threatening some species designated as endangered in both Canada and the United States. It has been spreading at a rate of 1,150 hectares a year, taking over wetland habitat from native plants and depriving waterfowl and other species of food sources.
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Photo: Bernd Blossey, Cornell University
Purple loosetrife, (Lythrum salicaria) which was introduced from Europe in the mid-1800s as a garden ornamental, has invaded wetlands throughout eastern North America and is still being planted in some areas in spite of its reputation as an invasive plant.
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When aquatic weeds such as this replace native species, their dense colonies can also impair navigation, water-based recreation and flood control, degrade water quality, hasten the filling of lakes and reservoirs and depress property values.
Many other newcomers are fundamentally changing ecosystems and food webs, and threatening the productivity of agriculture and other industries that depend on living resources. Introduced weeds, for example, interfere with crop and livestock production and are costly to control. In total, invasive species cost the US economy about $138 billion per year in damages to the environment, agriculture, industries, and human health, including control costs.
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Photo: Joel Simmons, Portland State University
The nutria (Myocastor coypus), a rat-like mammal native to South America and first brought to Louisiana to be bred for its fur, has invaded the eastern seaboard of the United States. Prolific breeders, Maryland's nutria population is up from 150 in 1968 to about 50,000 today. They have devastated wetland habitat for rare native species such as the bald eagle and eliminated crab and oyster nurseries. And their digging has allowed salt water to invade swamps and wetlands, damaging vegetation.
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In recent years, as trade with the Southern Hemisphere has increased, more invaders from the South have appeared. Examples include Africanized honey bees (Apis mellifera Adansonii) that spread from Brazil northward into Mexico and the United States; the floating fern giant salvinia (Salvinia molesta) from Brazil; as well as the Australian paperbark tree (Melaleuca quinquenervia) that has invaded south Florida.
In the future, with increasing human travel and trade, we are likely to see many new invaders from all parts of the world. The growing trade between North America and countries, such as China and Russia, which have many climates and habitats similar to those on this continent, is particularly likely to facilitate new invasions on both sides. At the same time, growing commerce within North America is increasing the risk of spreading one country’s established invaders to the others.
What can be done?
There are three lines of defense in preventing the world movement and introduction of invasive species. The first includes inspections and controls at borders and ports. Rapid response is the second, and costly control actions involving some combination of mechanical, chemical, and biological methods is the third line of defense. Effective laws and regulations, appropriate funding, the involvement of industry, public awareness and support and research are equally important strategies. Since about 85 percent of all invasive plants and almost all invasive vertebrates are intentionally introduced, prevention through screening imported plants and animals for invasiveness at entry points is increasingly viewed as the most cost effective strategy.
A role for CEC
CEC is testing a methodology to predict the probable vulnerability of North American habitats to invasions. It enables scientists to match habitats in which a particular species thrives with similar habitats in North America that may be suitable for the species’ establishment. This may be a useful tool for rapid assessment of a species' invasiveness, the pathways to watch and the probable vulnerability of habitats in North America to invasion. CEC previously supported the development of this method through the North American Biodiversity Information Network (NABIN) as a way to help predict habitats suitable for migratory birds. Through NABIN, a huge, worldwide, Internet-based repository of biodiversity information is being developed by connecting biodiversity databases across the continent and beyond. Facts on the spread of invasive species, and their management, taxonomy, and impacts will eventually be available.
The project is being closely coordinated with a pilot project to develop an invasive species information system for the Western Hemisphere through the Inter-American Biodiversity Information Network, which involves the participation of experts from the three NAFTA countries.
Early in 2001, CEC will sponsor a workshop on ways to prevent pathways for exchange of coastal and freshwater invasive species across our international boundaries. A CEC background paper will summarize what we know about the pathways, trends, impacts, and factors in aquatic invasions; discuss how each government is coping with the problem; and provide a possible scenario for North America.
The workshop will build on an international review of pathways and vectors for invasive species, sponsored in 1999 by the Global Invasive Species Program. CEC can encourage international agencies and organizations concerned with global trade and the environment to give greater attention to invasive species in their policies, and more support for increasing the capacity of all countries in preventing invasions. Global cooperation mush balance regional efforts. Many invasive species have yet to find a home in North America. We do not know how many, nor what their impacts may be. However, the devastating effects of invaders that have already arrived should be sufficient to sound the alarm. The wisdom of the adage, "an ounce of prevention is worth a pound of cure," must inform our thinking and our policy.
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William Gregg 
Randy Westbrooks 