They attack the planet on all fronts: on land, in the sea, and in the air, non-native species are crowding out native populations and disrupting ecosystems all over the world.
In most instances, the invasion is the inadvertent result of human activity. As people and goods travel around the world, plants and animals are unintentionally transported from one place to another. Imported fruit served as the means of transportation for Ceratitis capitata, or the Mediterranean fruit fly — known commonly as the medfly — from Europe to California in the 1980s, where an infestation wreaked havoc on the agricultural industry. Accidentally transported to Guam after World War II, Boiga irregularis (the brown tree snake) was responsible for the extirpation of over 50% of the island’s native breeding birds, as well as several species of native bats and lizards.
At other times, purposeful decisions have disrupted the local environment in unanticipated ways. Neovison vison, commonly known as the American mink, escaped from fur farms in South America and the United Kingdom in the mid-1950s; the carnivore, with no local natural predators, decimated populations of ground nesting birds and small mammals. In recent years, some aquarium owners in the United States have dismantled their fish tanks and released tropical aquarium lionfish, which are native to the Pacific and Indian Oceans, into nearby tropical saltwater. With no natural predators in the Atlantic Ocean, the venomous lionfish have significantly upset the bioversity of edible fish.
Methods to eradicate invasive species such as these have centered on forced removal by humans — for example, catching and killing the lionfish, or the use of poisons to control mink and snakes. Efforts to provide barriers to invasion include extensive searches of ships entering foreign ports, and pesticide application to airplanes and — in some countries — airline passengers. Nine countries currently require aerosol spraying of all inbound flights while passengers are onboard, and other countries mandate spraying when flights originate from certain countries. These approaches,however, have been of limited effect, and have carried their own disruptive and disturbing elements into the environment.
Increasingly, scientists have been addressing non-indigenous species more creatively; they have conditioned groupers to enjoy eating lionfish and to become an Atlantic Ocean predator, and employed the insect Muscidifurax raptor to consume the Mediterranean fruit fly in areas outside of its native range. But scientists concur that early detection and long-term monitoring of non-native species is the best means to control ecosystem balance.
Several countries have established data systems to track the pattern and rate of expansion of species outside of their native ranges. In June 2015, an extensive review lauded the implementation of a system in Belgium, where collaboration between scientists and policy makers has allowed for the development of ways to target invasive alien species. Composed of scientists, policy makers, and other stakeholders, the government-sponsored group encourages cooperation, information exchange, and dissemination of information. With an information system called Harmonia, it is possible to assess the potential for an invasive species to spread and colonize natural habitats, as well as to evaluate the extent of adverse effects on native species and on native ecosystems. For evaluation, species are assigned a score which is available to all, and which then allows for an organized approach in targeting removal or containment. A dynamic system, Harmonia permits new research and information to be quickly accounted for and disseminated.
Efforts to establish broader information systems have, as yet, been unsuccessful. The European Alien Species Information Network is less than comprehensive, and in the United States — where the Department of the Interior contends that the country is “under siege” by more than 6,500 non-indigenous species — 17 different centers conduct research for designated ecoregions.
Yet some people assert that environmentalists are being unnecessarily alarmist. “Understandable love of the local, the native and the familiar — of an imagined pristine environment before humans showed up — too often becomes fear and hatred of the foreign and the unfamiliar,” claims environmental consultant Fred Pearce. While certain ecologists see the introduction of the European honeybee Apis mellifera (brought to North America in the 1600s) as a disaster, others value the major role the insect plays in pollination.
With the increase of global travel and trade, and the world’s changing climate making new habitats available to many plants and animals, boundaries between species are more difficult to preserve. Whether alarmist or prudent, isn’t it time to focus on an international database of aliens?
“Ecosystems—Invasive Species Program.” United States Geological Survey, U.S. Department of the Interior. 2015.
Fraser, Elaine J., et al. “Range expansion of an invasive species through a heterogeneous landscape—the case of American mink in Scotland.” Diversity and Distributions, A Journal of Conservation Biogeography. vol. 21. Issue 8. 888-900. August 2015.
Lehtinienmi, Maiju, et al. “Dose of Truth—Monitoring marine non-indigenous species to serve legislative requirements.” Marine Policy. vol. 43. 26-35. April 2015.
“Management and Control of the Venomous Lionfish.” Vone Research, Inc. 2010.
McGee, Bill. “Should fliers worry about pesticide spraying on planes?” USA Today. 13 May 2015.
Pala, Christopher. “As Lionfish Invade, Divers Defend Threatened Ecosystems.” Science. 343.6171. February 2014. Web. 4 May 2015.