Alaska Department of Fish and Game
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Native species are organisms living within their historic distributional range; this is the term that applies to the vast majority of fish, wildlife, and plant species in Alaska. By contrast, a nonnative species is one that is found outside its previously observed range. Such a species is typically one that has been introduced to the new environment, either intentionally or accidentally, by human activity.
Nonnative organisms are referred to by many different names, including nonindigenous, introduced, exotic, alien, and transplants. These terms are commonly used interchangeably to refer to species occurring outside their historic native range.
Effects on the Environment
People intentionally move certain kinds of organisms from place to place, as in when we bring pets with us to a new town, or conduct fish stocking or animal transplant programs. These movements of species are generally considered benign, since no adverse effects to the environment are expected. Indeed, humans have come to depend on many nonnative plants and animals that, once introduced, offer agricultural, horticultural, recreational, and subsistence benefits or commercial value to society.
In other cases, an introduced species causes, or has the potential to cause, harm to their new environment or the economy. As such they are deemed to be “invasive” species. We apply terms to nonnative species differently depending on the magnitude of the impacts they exert on the ecosystem to which they are introduced.
Living in Balance: What makes a Species “Invasive”?
Native organisms living in their native ecosystem develop a natural balance with other species in the same environment. For example, the complex web of food-intake-and-energy-output dynamics, and predator-prey relationships, dictates that no one native species overpopulates an area or totally depletes resources needed for the ongoing existence of other species. A system of checks and balances is at work.
When nonnative species are introduced to stable environments they can adapt to the conditions of the ecosystem and fill a niche. This may happen, for example, with some of the species expected to expand their range northward with a warming climate.
However, the introduction or arrival of a nonnative species may instead upset the natural balance, resulting in harmful changes to structure and function of the ecosystem. It is only the aspect of being harmful to native species and ecosystems that earns a nonnative plant or animal the “invasive species” designation.