What is an invasive species?
An "invasive species" is defined as a species that is:
1) nonnative to the ecosystem under consideration
2) whose introduction causes or is likely to cause economic or environmental harm or harm to human health. (Executive Order 13112).
Species that have been introduced, or moved, by human activities to a location where they do not naturally occur are termed nonnative, exotic, alien, and nonindigenous. Conversely, "native" describes a species living in an area where it is found naturally. A nonnative species is not necessarily harmful, in fact the majority have beneficial purposes. When a nonnative species invades lands or waters —particularly natural communities— causing ecological or economic problems, it is termed invasive. The terms harmful exotic species, plant pest, pest plant and nonindigenous aquatic nuisance species are all groups of nonnative invasive species.
Over the past 200 years, several thousand foreign plant and animal species have naturalized the United States. About one in seven have become invasive, leading to problems that cost the United States more than $138 billion each year according to figures provided by Cornell University.
Common vertebrate invasive species in Minnesota include European starlings, round goby, ruffe, and common carp. Less common species found in the wild include Eurasian collared-doves, mute swans, and white perch. Additionally, numerous invertebrate invasive animals have become established in the state such as zebra mussels, spiny water fleas, rusty crayfish.
Several aquatic and terrestrial plants have invaded Minnesota . The most well known and problematic aquatic plants include Eurasian watermilfoil, curly-leaf pondweed, and purple loosestrife that have invaded lakes, rivers, and wetlands. Many terrestrial invasive plants are problematic for agriculture and the environment. Garlic mustard and European buckthorn species are woodland invaders. Spotted knapweed and leafy spurge are grassland invaders.
Invasive Insects/Plant Pests
Invasive insects, such as gypsy moth, emerald ash borer, Asian longhorned beetle, exotic bark beetles, and Khapra beetle.
Effects of Invasive Species
Many invasive species clearly impair biological diversity by causing population declines, species extinctions, shifts in predator–prey dynamics, shifts in species niches, changes in habitat, and reductions in ecosystem complexity.
In 1993, the Congressional Office of Technology Assessment reported that devastating invasions of plants, insects, aquatic invertebrates, pathogens, and other organisms have changed ecosystems and permanently diminished the biological diversity associated with them. Examples of these in the United States and its territories include: melaleuca (a wetlands tree), gypsy moth, spruce bark beetle, zebra mussel, larch canker, chestnut blight, and the brown tree snake.
Conservation experts have found that in the United States invasive plant infestations cover 100 million acres (an area twice the size of Delaware) and are spreading at a rate of 14 percent per year. Past studies have also revealed that the San Francisco Bay has been invaded by a new exotic species on the average of once every 15 weeks.
Movement and Pathways
Naturally occurring movement of species into and within the United States is uncommon. Most invasive species arrive in association with human activities or transport. Species can be brought into the country and released intentionally or unintentionally through the international movement of people, commodities, and their conveyances.
Many species enter the United States each year as contaminants of commodities. Agricultural produce, nursery stock, cut flowers, and timber can harbor insects, plant pathogens, slugs, and snails. Weeds continue to enter the United States as seed contaminants. Plant pathogens sometimes arrive as unintended contaminants of plant materials.
Fish and shellfish pathogens and parasites have been introduced unintentionally into the United States on infected stock destined for aquaculture. Crates and containers can harbor snails, slugs, mollusks, beetles, and other organisms.
Military cargo transport may unintentionally bring in invasive species. Ballast water used to stabilize ships that is discharged when cargo is loaded or unloaded has historically introduced numerous unwanted aquatic species.