|Exotic plants and animals disturb ecosystems
The "purple plague" is still sold as a popular ornamental and garden plant
I stroll down
the outdoor garden aisle lined with beautiful flowering
perennials. One especially catches my eye: Delicate purple flowers swirl
elegantly around a majestic three-foot stalk, a dramatic beauty known as
purple loosestrife. At home, my curiosity piqued, I scale the Internet for
information on this garden perennial. What I find astounds me. At the
Canadian site on biodiversity I discover that this
same plant is also known as the "purple plague." Introduced from Europe,
this misplaced killer drowns out native vegetation, destroys habitat, and
reduces biodiversity in all 48 of the contiguous states. Yet the "purple
plague" is still sold as a popular ornamental and garden plant.
Distinguishing between good and bad is not always easy
loosestrife illustrates a situation common to many non-indigenous, or exotic, species. "Distinguishing between 'good' and 'bad' [non-indigenous species] is not always easy," states a recent report of the Office of Technology Assessment (OTA). "Some species produce both positive and negative consequences, depending on the location and perceptions of the observers."
In some cases, answers seem clearcut. Except for hunters, there are few fans of wild pigs, for example. But rarely is controlling exotic species a cut and dry issue. Many of the species that natural resource managers are frantically trying to eradicate, wildlife lovers and humanitarians are just as frantically fighting to protect.
The red fox, exotic to most of California, arouses such mixed feelings. Introduced in the 1870's for hunting and fur trapping, this species has invaded over 1/3 of the Golden State. According to Ron Jurek, wildlife biologist from the California Department of Fish & Game, introduced red foxes cause drastic changes in native ecosystems, decimating populations of native birds, mammals, lizards, and snakes, including several endangered species.
Yet eradication of red foxes is riddled with controversy. Despite being a documented threat to endangered and threatened species, trapping these pretty critters elicits a strong reaction from wildlife lovers and humanitarians. Trapped foxes are killed since there are no alternatives for relocation. Sterilization, another option, has proven ineffective. The result is that people who should be on the same side, fighting for wildlife conservation, are battling each other.
Often an ecological domino effect starts when you introduce exotics into an area already suffering from the loss of quality habitat. Jurek tells of an example: In San Diego County, many of the natural areas remaining are those canyons too steep or inaccessible to build on. In the smaller canyons, there are no coyotes left because they require large intact areas for their home range.
"When the coyotes go, you see a coincidental loss of quail and other ground-nesting birds," says Jurek. Without coyotes to keep them in check, possums, feral cats, and red foxes explode in population size, resulting in unnaturally high levels of predation on native birds and small mammals.
Humans are the ultimate exotic species
At the same
time, no one wants to see an explosion of rats and mice either, which these middle-predators, albeit exotic, help to control. The bottom line is that there are no easy answers. As with many other exotics, the red fox is now part of delicate ecosystems, many of which have had the balance already tilted by human meddling on a grand scale.
Humans are, of course, the ultimate exotic species. Our chainsaws and pesticides, fences and fossil-fuel engines do far more damage than any other species. Our intrusions into the wild domains causes us to view natives like coyotes as pests that must be eliminated, or larger and stronger animals like bears as threats to our safety. In the March 26th election, Californians will once more vote on mountain lion hunting, with supporters pointing to the two people killed last year as just cause. The vote is expected to be close; native or not, the general public has little sympathy for creatures that have the advantage over us.
But although almost all ecosystem invasions are caused by humans, we're sometimes innocent confederates. The native cowbird originally followed herds of buffalo and later cows, seeking worms and grubs from freshly disturbed soil. But as colonists cleared for crops -- and later, subdivisions -- the cowbird happily followed the people instead. As a result, the cowbird is now found far from its midwestern origins, and has upset ecosystems throughout the West and Canada.
What are the implications of releasing alien species into our native wildlands?
the implications of releasing alien species into our native wildlands? Competition for food and space is heightened, and "background" predation rates are elevated. Ultimately, exotic species displace natives, reducing biodiversity and hampering ecosystem integrity. "Alien plant invasions wreak havoc on the health of our forests," says Faith Campbell, Natural Resources Defense Council (NRDC) specialist.
"We are trading a diverse assemblage of native species (which have lived here at least since the last ice age) for a smaller number of exotic species which are not in balance with the ecosystem," according to Doug Yanega of the University of Illinois Entomology Department.
Despite growing controversy and concern over exotics, releasing non-indigenous species is nothing new. Exotics have been introduced, both intentionally and accidentally, since humans begun travelling the globe.
But as horse and wagon gave way to rail, car, and plane, the number of introductions increased dramatically. When Europeans first colonized the New World, they were homesick for the flora and fauna of their native land, and brought along scores of wildlife species.
One well-known example is that of house sparrows and starlings. These species were successfully introduced to North America by a lover of Shakespeare's plays. He wished to have all the critters mentioned in the plays present in the New World.
The pattern repeated as California was colonized by whites, particularly after the completion of the railroad. Game animals were introduced for hunting, trout and other sport fish were brought for angling. Even the possum came to California as an import in the 1870's, carried by a homesick farmer from Missouri.
Other species came accidentally; a seed tagging along in a foreign traveller's luggage, an ant colony transported in ship ballast -- the list goes on. A current worry is a one-eyed water flea from Africa, which threatens the food chain on which fish depend. It has been found in several Texas lakes and midwestern rivers, where it is moving towards the Great Lakes.
The introduction of exotics has reached such dramatic proportions that it has been termed "biological pollution"
most of these introductions perish, unable to survive in conditions different from their homeland, others establish small populations, persisting but not flourishing. And still others -- a small percentage but significant in their impact -- become firmly established. These species become "biological invaders," spreading at alarming rates, uncontrolled by the predators, parasites, and competitors that kept them in check in their native habitat.
What makes one species a successful invader while others fall by the wayside? This question evokes intense interest among ecologists. There are generally two views. One is that an invader's success depends upon the environment itself. Ecosystems "stressed" by human alterations are more susceptible. The other view is that invasion depends more upon the organism; species able to adapt to a variety of habitats or environmental conditions are typically more successful invaders.
Regardless of the reasons why a particular exotic becomes successful in a non-native land, the introduction of exotics has reached such dramatic proportions that it has been termed "biological pollution." According to Michael Rust, entomology professor at UC Riverside, two non-indigenous insect species are brought to the U.S. every 60 days. Insect pests cost California alone $1 billion annually, and over 50% of all crop losses are due to introduced insects.
Increased awareness of exotic pests is one reason for the new Center for Exotic Pest Research, a team venture of UC Davis and UC Riverside. A major focus of the center is research on the Mediterranean Fruit Fly, which has cost California $117 million over the past four years. Control of the fruit fly is also controversial; concerned citizens frown upon broadscale pesticide application, and pesticide regulation is stricter than ever. The alternatives to chemical pesticides -- including biotechnology -- bring their own controversies.
California is particularly susceptible to alien species invasions, insect and otherwise, because of its warm climate, large size, and variety of habitat types. Additionally, California's proximity to the Pacific Rim, border with Mexico, extensive agriculture and wide variety of crops make the Golden State even more vulnerable. According to Rust, there is growing concern that the recently enacted North American Free Trade Agreement (NAFTA) will increase the number of exotic species imported into the country. Florida researchers are already watching the spread of the aquatic soda apple, believed to come from Mexico and a potent threat to the fragile biological diversity of the Everglades.
The number and impact of exotics are chronically underestimated
isn't more being done about species introductions? "The number and impact of harmful [non-indigenous species] are chronically underestimated, especially for species that do not damage agriculture, industry, or human health," according to the Office of Technology Assessment (OTA).
The federal government has never had a good plan to battle exotic species. It's difficult to say which agency is responsible. "[T]he Federal Government places only a few piecemeal constraints on the importation of fish, wildlife, and their diseases. Tens of thousands of different species (most of the world's fauna, excluding insects) potentially could be legally imported into the United States."
The Animal Plant Health Inspection Service (APHIS) under the USDA (United States Department of Agriculture) oversees one aspect of the problem, that of bringing exotics in from other countries. The fact that APHIS falls under the jurisdiction of the USDA brings its own problems. According to the OTA report, APHIS pays little attention to species that don't threaten agricultural areas and "new imports are considered safe unless proven otherwise."
The Lacey Act, which regulates interstate species introductions, has been widely criticized for being simultaneously too loose and too strict. Originally passed in 1900, the Act was amended in 1981. As it stands, the Lacey Act keeps a not-so-critical eye on a short list of "injurious" species. The Act is too strict in that it is much too difficult to add new species to the list. But the law is unclear about how to enforce interstate transport of plants and animals, and gives no clue about how to handle a biological "emergency" or how to prevent problems from getting out of hand.
Conflicting state laws do not help define the problem either; a species welcome in one state may be illegal on the other side of the state line. California has an almost neurotic fear of ferrets, and is the only state besides Hawaii to ban an animal that most see as a harmless, loveable pet.
Yet many innovative ideas have been placed on the table regarding the control of exotics:
With a climate similar to CA, New Zealand is a shining example of exotic control
is one success story in managing exotic species. With a climate very similar to California's, according to Jurek, New Zealand is also prone to biological invasions. Innovative policies in recent years have resulted in a highly effective system of prevention.
New Zealand's comprehensive program for controlling species introductions includes treating 100% of arriving aircrafts with insecticide, inspecting incoming passengers, luggage, and merchandise, tracking imports using a state-of-the-art computer system, and garnering public support for scientific surveys and species monitoring. New Zealand has adopted a "user pays" approach which covers costs of inspection, scientific analysis, and enforcement.
The United States has not been so lucky. Introductions to the U.S. are not slowing, and their impact is only beginning to be addressed seriously. "Most people just take exotics for granted now," says Yanega, "[w]hat the long-term effects of this loss of biodiversity will be, we simply can't predict."
Wendee Holtcamp received her M.S. in Wildlife Ecology from Texas A&M University, with her Master's research on the effect of an exotic species. She currently owns GreenDesign, Web Design for Environmental & Socially Responsible Organizations.
Albion Monitor March 10, 1996 (http://www.monitor.net/monitor)
All Rights Reserved.
Contact firstname.lastname@example.org for permission to reproduce.
All Rights Reserved.
Contact email@example.com for permission to reproduce.