When a plant, animal, or microbe is found in an ecosystem outside of its natural geographic range, it is broadly referred to as a non-native species. This term is the direct answer to what a living thing not normally found in an ecosystem is called. The presence of such a species is always a result of human activity, whether the introduction was intentional or accidental. The consequences of their arrival can range from benign to catastrophic.
Defining the Terminology: Non-Native and Alien Species
The scientific and policy communities use several terms interchangeably to describe organisms existing outside of their native range, including non-native, alien, exotic, and non-indigenous species. These terms denote that the species arrived in the new location through human actions, bypassing natural barriers that would have otherwise prevented dispersal. Introduction can happen through intentionally importing plants for landscaping or crops for agriculture.
Accidental introductions are equally common, often occurring when species “hitchhike” on global trade routes. For instance, insects may travel in wood packing materials, or aquatic organisms may be transported in the ballast water tanks of large ships. These terms are purely geographical and do not imply whether the species causes harm. Many food and ornamental plants in the United States are non-native species that cause no ecological issues.
The Difference Between Introduced and Invasive
It is important to recognize the difference between an introduced species and one that is labeled invasive. An introduced species, synonymous with non-native or alien, simply refers to a species living outside its native range due to human activity. The majority of non-native species do not become problematic; they may establish small populations or fail to thrive in the new environment.
An invasive species is formally defined as an alien species whose introduction causes or is likely to cause economic or environmental harm, or harm to human health. This distinction means all invasive species are non-native, but only a small fraction ever become invasive. The transition to an invasive species happens when an organism successfully establishes, spreads rapidly, and negatively impacts the new ecosystem.
Why Invasive Species Cause Harm
Once established, invasive species cause harm through several distinct ecological mechanisms, often leading to a widespread decline in native biodiversity. One common impact is intense competition for limited resources such as sunlight, water, or food. Invasive plants may grow faster and taller than native flora, effectively shading them out and preventing their growth.
Invasive animals often act as novel predators, preying on native species that have not evolved defenses against them. This can decimate local populations, such as the Burmese python’s impact on mammal and bird populations in the Florida Everglades. Furthermore, invasive organisms can introduce new diseases or parasites to which native species have no natural immunity, leading to widespread mortality.
The ecological disruption also carries a substantial economic burden, costing governments and industries billions of dollars annually. For example, the zebra mussel clogs water intake pipes and structures at power plants and water treatment facilities, costing an estimated $500 million each year in the Great Lakes region for control and maintenance. Invasive species can also fundamentally alter habitats, such as changing soil chemistry or increasing the frequency of wildfires, creating an environment unfavorable to native life.
Management and Mitigation Strategies
The most effective strategy for dealing with invasive species is prevention, which is also the most cost-efficient approach. Prevention involves regulatory measures, such as monitoring shipping pathways and inspecting imported goods, to stop the introduction of new non-native organisms. This proactive stance prevents the enormous ecological and financial costs associated with established invasions.
When prevention fails, the next line of defense is early detection and rapid response (EDRR). EDRR programs quickly identify new populations of non-native species and immediately deploy resources to eradicate them. This rapid action is far more effective than trying to manage a widespread infestation.
For species that are already established, control and management strategies are necessary to mitigate their ongoing harm, often involving a combination of techniques:
- Mechanical control, such as manual removal or mowing.
- Chemical control, using targeted herbicides or pesticides.
- Biological control, which introduces a carefully tested natural enemy to suppress the invasive population.
The choice of method depends heavily on the specific organism, the affected ecosystem, and the feasibility of achieving long-term population reduction.