TWS Position Statement: Invasive and Feral Species

Invasive and feral species present unique challenges for wildlife management. The Wildlife Society defines an invasive species as an established plant or animal species that causes direct or indirect economic or environmental harm within an ecosystem, or a species that would likely cause such harm if introduced to an ecosystem in which it is non-indigenous as determined through objective, scientific risk assessment tools and analyses.  Feral species are those that have been established from intentional or accidental release of domestic stock that results in a self-sustaining population(s), such as feral horses (Equus ferus), feral cats (Felis catus), or feral swine (wild pig, Sus scrofa) in North America.  Feral species are generally non-indigenous and often invasive.

Whereas invasive species are typically non-indigenous, not all non-indigenous species are perceived as invasive. For example, species introduced as biological control agents and some naturalized wildlife species, provide significant economic benefits while not resulting in significant or perceived harm to native ecosystems. Similarly, some indigenous species can be perceived as invasive when population increase or range expansion beyond historical levels disrupt ecosystem processes, resulting in economic or environmental harm. Determination of an invasive species can vary across regions based on the presence of local economic or environmental harm.

The extent to which invasive and feral species harm indigenous species and ecosystems can be difficult to determine, and few laws and policies deal directly with their control. Many invasive and feral species are wrongly perceived as natural components of the environment and some have the support of advocacy groups who promote their continued presence in the wild. Invasive and feral species may negatively affect public trust resources, including indigenous and naturalized wildlife, which are managed by government agencies for society’s benefit.

Effects of invasive and feral species on the natural world and their economic costs to society are increasing. Some known effects of these species include negative impacts to biological diversity, ecosystem productivity, environmental integrity, wildlife health, human health and safety, and property.  Impacts vary widely depending on species and ecosystems affected. Negative effects of invasive and feral species on indigenous wildlife populations occur through direct competition, predation, habitat alteration and/or degradation, disease transmission, and diversion of conservation funds for control and research efforts. Many invasive and feral species also exhibit high reproductive potential and minimal natural regulation in the ecosystems in which they become established.

Cumulative impacts of invasive and feral species can be substantial. Resources are limited in all ecosystems and introduction of invasive and feral species to systems where indigenous species are already stressed can have significant negative effects.  Even after control and/or removal of invasive and feral species, recovery of ecosystems can take considerable time and may require direct management efforts, depending on type, intensity and duration of disturbance.

The policy of The Wildlife Society regarding invasive and feral species is to:

  1. Promote maintaining indigenous biological diversity and ecosystem integrity and function. Oppose introduction or maintenance of invasive species and feral species that threaten the survival of indigenous species.  Land and resource management agencies should place primary emphasis upon management needs of indigenous wildlife and plants and resist efforts to sustain invasive and feral species on public or private lands.
  2. Acknowledge that some introductions of non-indigenous species have contributed to conservation and society’s appreciation for wildlife or have been used as biological control agents
  3. Encourage programs to monitor invasive and feral species to inform and target future management strategies, especially those that include the key elements of early detection, rapid response, containment of spread, and eradication where possible.  Support sharing technical data and cooperation among agencies and other partners to manage invasive and feral species.
  4. Encourage and support increased funding for scientific research by public and private agencies and organizations to control, minimize, or eliminate negative impacts of invasive and feral species.
  5. Support cost-effective control and/or eradication programs for invasive and feral species that exhibit timely results without sustaining or causing additional ecosystem harm.
  6. Encourage the enactment, expansion, and enforcement of laws and regulations focused on eradicating and controlling the spread of invasive and feral species, and the introduction of harmful wildlife pathogens carried by non-indigenous species.
  7. Urge strict control of known invasive and feral species in livestock and agricultural industries to prevent their accidental escape into the wild and consequent negative impacts.

See also The Wildlife Society’s related fact sheets and statements: feral cats, feral horses, feral swine, Standing Position on Fertility Control

Approved by Council October 2016. Expires October 2021.

Invasive and Feral Species Position Statement pdf