What’s the difference between
non-native and invasive species?

Non-native or exotic refers to species that do not naturally occur in an ecosystem. Invasive species are plants or animals that aggressively establish themselves in an ecosystem at the expense of its native species and natural functions. 

Most exotic species introduced into North America do not become invasive. Many of the species our civilization relies upon such as wheat, barley and rice are exotic but not invasive. Some exotic species, like the nutria, giant reed and zebra mussel, have become grave threats to natural habitats in the Chesapeake Bay region. 

Occasionally an aggressive native species (such as the double-crested cormorant in the Chesapeake), can be invasive, especially in a stressed or disturbed ecosystem.

Invasive species damage our ecosystem by competing for resources native species need to survive, sometimes choking out natives entirely. They are one of the greatest threats to native biological diversity.

Once they are established, controlling the spread of invasive species is expensive and difficult, and complete eradication is usually impossible.  Therefore, prevention plays a critical role in avoiding their introduction and spread.  Ship ballast water, released pets and international packing material have all been pathways for introductions of invasive exotic species, but intentional human release, usually in an effort to ‘improve’ nature, are the single largest cause. 

- Jonathan A. McKnight
Associate Director for Habitat Conservation
Maryland Department of Natural Resources

Photo of double-crested cormorant
courtesy of John White.

 For more information:
Invasive & Exotic Species of Maryland
 

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