Spread of Invasive Species
Spread of Invasive Species

Invasive species (also referred to as exotic, alien, or non-native species) are defined by the U.S. Fish and Wildlife Service as “infiltrators that invade ecosystems beyond their historic range”(NWRS, 2006). When introduced to a new habitat where they happen to be particularly fit for survival, invasive species quickly dominate the naturally occurring wildlife and throw the ecosystem out of balance.

For instance, zebra mussels have invaded waterways around the United States and clogged up pipes that deliver water to municipalities, farms, and factories, costing billions of dollars in economic disruption. Trout populations in the Great Lakes have declined precipitously after sea lamprey arrived and began feeding heavily on them (Greg, et al.). Since its discovery in a Washington, DC pond in 1942, an aquatic plant called Eurasian water milfoil has spread all over the country and pushed out native vegetation, thus impeding water flow and depriving many waterfowl of a proper diet.

In July 2002 snakehead fish were discovered in Maryland. Snakehead fish are a voracious family of fish species that can survive out of water for three days, reproduce quickly, and eat nearly any small animal they come across (NAS, 2008). The findings have sparked great environmental concern and an effort to eradicate snakefish.

More recently, according to the New York Times (October 7, 2006), “Asian carp have infested the rivers flowing into the Mississippi” to such an extent that fishermen can no longer leave their fishing nets in the river overnight. The carps have proven to be a nuisance, as they tend to leap near passing boats to such an extent that “being hit by fish [is] a normal occupational hazard now” (Vaughn, 2006).

The U.S. Forestry Service reports that in the United States invasive plant species already cover over 100 million acres and are spreading at a rate of 14 percent per year (Bodner). One agriculture monitoring organization noted that a new invasive species moves into the San Francisco Bay area every 12 weeks (NatureServe, 2012). In order to mitigate the effects of invasive species in the United States, the National Invasive Species Council (NISC) released a national invasive species management plan in 2008, which will be effective until 2012 (NISC, 2008).

Of the 1,200 domestic plant species recognized as weeds by the Weed Science Society of America, 65 percent are non-native to the United States.The U.S. Department of Agriculture (USDA) says that invasive plants force farmers to spend billions on pesticides and, according to the Weeds Science Society of America, cause an annual $34.7 billion (est. 2007) loss in American agricultural productivity and wildlife (Garhan, 2007).

According to United Nations Environmental Program, the total annual cost of invasive species (plant and animal) to the world economy is $1.4 trillion dollars, which constrains UN Millennium Development goals on poverty (Steiner, 2009). Because invasive species reproduce quickly, take resources from native plants, and are hard to eliminate, there are huge losses in biodiversity related to the increased introduction of nonnative species into societies. Increased travel, immigration, and international trade have made it more difficult to manage these alien species and have inflated the number of species entering societies.

Farmers and fisherman in developing countries, dependent on the survival of their crops, accrue costs for the damage wrought by invasive insects or plants that clog lakes and waterways. The introduction of the water hyacinth into Lake Victoria in 1990 has caused major difficulties in Uganda. The way the plant grows is “affecting shipping, reducing fish catches, hampering electricity generation and human health.”

The spread of invasive species has occurred for hundreds of years as a consequence of human activity, both intentional and unintentional. As noted above, however, this spread is emerging as a pressing problem now because in a globalized world where more people and goods travel all over the planet, it is common for wildlife species to be transported with them.

Another example of an invasive species is the corn rootworm, the major pest to corn in the United States. This pest was accidentally introduced to the Balkans through American military transport during the Bosnia conflict (Smith, 2012). Likewise, insects, rodents, and fish get trapped in cargo containers and are carried to new ecosystems. Sometimes, owners of aquariums dump non-native fish in a local pond or owners of exotic pets release them into the wild.

In 2010 and 2011 the brown marmorated stink bug, an invasive species, was seen in record numbers in the mid-Atlantic region. These insects caused major economic damage to fruit and vegetable crops. The species is known to particularly cause damage to apples, apricots, pears, and tomatoes which are staples in certain regions of the area. This insect has no natural predator and can survive the harsh winters of the region by taking shelter in homes. Their numbers fell in 2012, however, as a harsh winter killed off many that were kept outdoors. Still, the control of the stink bug is a top priority for the Department of Agriculture and they are considering possibility of introducing its native predator, a parasitoid wasp, into the U.S. by 2013 (EPA, 2012).

Questions for Discussion

The Burmese python were brought to households in Florida as pets. Once they got too big and hard to feed, many households let them go into the wetlands. Now the native wildlife in the Everglades is threatened because the pythons are multiplying and have no natural predator.

How do you solve this problem? What can you do to prevent similar problems in the future?

A program does not yet exist to combat the invasive species problem, but the World Conservation Union and parties to the Convention on Biological Diversity have recently begun working on a global initiative for that purpose. To date, the invasive species phenomenon has been addressed most attentively at the national level. In the United States, the Lacey Act restricts the importation, acquisition, transportation, and possession of wildlife deemed injurious to human activity and wildlife resources.

The National Invasive Species Act, passed in 1996, established a comprehensive framework to research, regulate, and combat the spread of aquatic nuisance species, in particular the zebra mussel. In 1999, President Clinton signed an executive order creating the Invasive Species Council to oversee all efforts nationally. Invasive species are likely to be a persistent and escalating problem in the future all over the world, with UNEP describing this issue as the second-most important threat facing wildlife, after loss of habitats.

The problems faced by animals in a globalized economy exemplify themes that arise repeatedly throughout this Issue in Depth. In the case of international trade in animals, governments have agreed on an international treaty to cover legal trade in animals, but the illegal trade remains lucrative, and domestic protection of animals within countries’ borders has so far escaped international concern. Meanwhile, international non-governmental organizations have rallied private citizens to oppose trade in wildlife.

In the case of invasive species, governmental efforts to protect animals have so far proceeded only domestically, with, for example, U.S. laws to prevent their spread, but have not yet produced any international strategy. As with other environmental problems, the balance between international concern and domestic sovereignty, coordinated government action versus inter-government disputes, environmental concern and economic interest on the one hand and cultural values on the other, has yet to be clearly drawn.

1 National Wildlife Refuge System.
2 Greg, et al.
3 Nonindigenous Aquatic Species.
4 Tom Vaughn and Deborah Weisberg.
5 Bodner.
7 National Invasive Species Management Plan
8 Weed Science Society of America
9 Garhan.
10 Steiner
11 Smith “US Pushes its Agenda, and Its Pest, on Europe.”

Youtube clip: http://www.youtube.com/watch?v=-V5513w1XSk


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