An invasive species is an introduced species that expands into a new habitat and causes environmental or economical damage. Invasive species are a growing threat to ecosystems around the world, with potentially devastating consequences for biodiversity, agriculture, and human health. These organisms, often introduced unintentionally, spread and outcompete native species, altering the natural balance of an ecosystem.
Invasive Species Definition
There are multiple ways of defining an invasive species for different scientists, policymakers, and countries. The USDA defines an invasive species as “an alien species whose introduction does or is likely to cause economic or environmental harm or harm to human health”. The EU considers an alien species as a plant or animal that is accidentally or intentionally released into a region where it does not normally occur, reproduces, and has serious negative consequences for that environment. Once established, invasive species can displace native species, disrupt ecological processes, alter ecosystem functions, and cause economic losses.
Invasive vs Non-Native
A non-native species is one which does not naturally occur in an environment. Not all non-native species are invasive, even if they displace native organisms. For example. most food crops are not native to where they are grown. Without human oversight, most of these species would not expand into new territory and threaten the ecosystem. Similarly, some non-native plants grown in gardens are invasive, while others are not.
Invasive Species Examples
There are numerous examples of invasive species around the world. In the United States, one well-known example is the Burmese python, which was introduced to the Florida Everglades through the pet trade. The python has become established and preys on native species, including birds, mammals, and reptiles. In Australia, the cane toad was introduced in the 1930s to control agricultural pests. Now, the cane toad is itself a major pest, poisoning native species that prey on it. In Europe, the zebra mussel was introduced through ballast water from ships, and has since spread rapidly, clogging water intakes, disrupting ecosystems, and causing economic losses.
Here is a list of some invasive species examples:
- Feral cat (worldwide)
- Burmese python (Florida, US)
- Cane toad (Australia)
- Zebra mussel (European and North American lakes and rivers)
- Purple sea urchin (kelp forests off the California coast)
- Quagga mussel (Great Lakes of North America, European rivers and lakes)
- Asian carp (North America)
- Emerald ash borer (North America)
- Feral swine (worldwide)
- Hemlock woolly adelgid (North America)
- Sirex woodwasp (North America)
- Asian long-horned beetle (North America)
- Louisiana crawfish (Europe)
- American bullfrog (Europe)
- Canada goose (Europe)
- European rabbit (Australia)
- Red fire ants (Australia)
- Kudzu vine (US and other places)
- Leafy spurge (North America)
- Cheatgrass (Great Basin of North America)
- Garlic mustard (North America)
- Bufflegrass (North America)
- Japanese knotweed (North America)
- Acacia (Europe, South Africa)
- Lantana (Hawaii)
- Grape caulerpa (Europe)
- White-nose syndrome fungal pathogen (North America)
- Dutch elm disease (Europe and North America)
List of Causes of Invasive Species
The introduction and spread of invasive species is often the result of human activities. Some common causes of invasive species include:
- Intentional introductions for agriculture, horticulture, or recreation
- Accidental introductions through shipping, transportation, or trade
- Natural range expansion due to climate change or other environmental changes
- Release of exotic pets or plants into the wild
- Use of non-native species for biocontrol of pests or other invasive species
- Failure to properly manage and control invasive species populations
Traits Common to Invasive Species
While there is no single trait that defines an invasive species, there are several characteristics that make an organism more adaptable to new environments. These include:
- Rapid growth and reproduction rates
- High dispersal abilities, such as wind or waterborne seeds
- Broad ecological tolerances, allowing them to adapt to new environments
- Lack of natural predators or diseases in their new environment
- Competitive abilities that allow them to outcompete native species
- Ability to alter ecosystem functions or processes
Positive and Negative Effects
Invasive species can have both positive and negative effects on the environment, economy, and human health. Some of the positive effects of invasive species include:
- Providing new food sources or resources for native species
- Contributing to ecosystem services, such as soil fertility or nutrient cycling
- Providing economic benefits, such as new sources of food or medicine.
However, the negative effects of invasive species often outweigh the positive effects. Some of the negative effects of invasive species include:
- Displacing native species, leading to declines in biodiversity
- Altering ecosystem functions and processes, such as nutrient cycling and water flow
- Causing economic losses, such as crop damage or infrastructure damage
- Causing harm to human health, such as through the spread of disease or allergies
How to Control Invasive Species
Controlling invasive species can be challenging, but there are several methods that can be used. One common method is physically removing the invasive species from the environment. For example, removing plants can be done by hand, using tools such as shovels or rakes, or through the use of machinery such as tractors or excavators. Physical removal is effective for small infestations, but too labor-intensive and costly for larger areas.
Another method of controlling invasive species is through the use of chemical treatments. Herbicides kill invasive plants, while pesticides control invasive insects or animals. However, these chemicals can have negative impacts on the environment, including harming non-target species and contaminating water sources.
Biological control is another method of controlling invasive species. This involves introducing natural predators, parasites, or diseases that control or reduce the population of the invasive species. Biological control can be effective, but it requires extensive research to ensure that the introduced species will not harm non-target species. Careful monitoring is also necessary to prevent unintended consequences, such as the introduced species becoming invasive itself.
- Davis, Mark A.; Thompson, Ken (2000). “Eight Ways to be a Colonizer; Two Ways to be an Invader: A Proposed Nomenclature Scheme for Invasion Ecology“. Bulletin of the Ecological Society of America. Ecological Society of America. 81 (3): 226–230.
- Ehrenfeld, Joan G. (2010). “Ecosystem Consequences of Biological Invasions”. Annual Review of Ecology, Evolution, and Systematics. 41 (1): 59–80. doi:10.1146/annurev-ecolsys-102209-144650
- Fei, Songlin; Phillips, Jonathan; Shouse, Michael (2014). “Biogeomorphic Impacts of Invasive Species”. Annual Review of Ecology, Evolution, and Systematics. 45 (1): 69–87. doi:10.1146/annurev-ecolsys-120213-091928
- Primtel, David (2005). “Update on the environmental and economic costs associated with alien-invasive species in the United States”. Ecological Economics. 52 (3): 273–288. doi:10.1016/j.ecolecon.2004.10.002
- Williams, J. D. (1998). “Non-indigenous Species”. Status and Trends of the Nation’s Biological Resources. Reston, Virginia: United States Geological Survey. ISBN 978-0-16-053285-6.