Invasive Species Aren't Always the 'Boogeyman,' Biologists Say

Non-native species can have some devastating effects, but that’s not always the case.

Brown trout swimming
Brown trout.

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From wild rabbits to zebra mussels, Asian carp to kudzu, many invasive species have caused harm to the ecosystems where they’re introduced. 

Although sometimes they arrive accidentally, often they are brought in to “fix” another problem. The red fox, for example, was released in Australia to deal with the wild rabbits which earlier settlers had brought with them to remind them of home.

But not all of these non-native species have negative impacts, a new review article suggests. Most research focuses on the negative effects instead of considering a more balanced approach.

Brown University biologist Dov Sax says he was first interested in the topic while studying eucalyptus trees that were planted in California’s Bay Area. The trees are originally from Australia, but many have been planted in California since the 1800s.

In some of his early research, Sax showed that eucalyptus woodlands in the state support as many species as native oak woodlands. Eucalyptus trees have become important in helping to conserve monarch butterflies and many eucalyptus forests are now protected because they provide a habitat to monarchs.

“The particular article that I just published was motivated by concern that too many scientists are continuing to ignore the benefits that non-native species provide,” Sax tells Treehugger. “Non-native species (including the subset labeled as "invasive') really can cause large problems, but if we only focus on those problems (and ignore the benefits) then we risk making bad policy decisions.”

The paper was published in the journal Trends in Ecology and Evolution.

Real Costs for People and Nature

Sax and his co-authors suggest a framework for considering the benefits of non-native species with nature-based values including relational, instrumental, and intrinsic values.

They agree that non-native species can have some devastating effects, but that’s not always the case.

“Some invasive species really do cause ecological harm or economic costs. Agricultural pests result in a loss of productivity (and more expensive food). Some invasives have caused species extinctions, particularly on remote oceanic islands,” Sax says. “These are real costs for people and nature. These costs are well documented in the scientific literature and well reported by the media. Consequently, people are aware of these real-world examples.”

In contrast, he says, the benefits of non-native species aren’t well studied, so there’s little attention paid to them by the media and people are mostly unaware of their beneficial effects. “It's not like there's some inherent trade-off: Non-natives aren't the boogeyman," said Sax in a statement.

The researchers cite many examples of these positive effects.

Earthworms, for example, aren’t native to most of the midwestern United States but have been widely introduced. They are important for traditional and organic farming and increase farming productivity by an average of about 25%, Sax points out, which offers an impressive economic benefit and leads to lower food prices.

Brown trout were introduced to New Zealand where they now contribute to the economy and recreational activities.

“New Zealand has been impacted negatively by many invaders,” Sax says. “But the trout in New Zealand are highly valued and they've adapted policies and legislation to help make the trout populations sustainable for the long-term.”

He also says that in some parts of the world, introduced fish like this become the mainstay of fisheries that support local economies.

“All of the examples above are cases where the non-native species in question are ‘wild’ in that they survive with direct human interventions,” Sax says. “Our article mentions, but does not specifically cover, the case of domesticated species (such as tomatoes, corn, goldfish, and dogs), which are the cornerstone of our global civilization. It is highly likely, for example, that whatever you had for breakfast this morning was from non-native, domesticated species.”

View Article Sources
  1. Scroggie, Michael P., et al. “Invasive Prey Controlling Invasive Predators? European Rabbit Abundance Does Not Determine Red Fox Population Dynamics.” Journal of Applied Ecology, vol. 55, no. 6, 2018, pp. 2621–2631., doi:10.1111/1365-2664.13253

  2. Alves, Joel M., et al. “A Single Introduction of Wild Rabbits Triggered the Biological Invasion of Australia.” Proceedings of the National Academy of Sciences, vol. 119, no. 35, 2022,

  3. Sax, Dov F., et al. “Valuing the Contributions of Non-Native Species to People and Nature.” Trends in Ecology & Evolution, 2022, doi:10.1016/j.tree.2022.08.005

  4. Brown University biologist Dov Sax

  5. Van Groenigen, Jan Willem, et al. “Earthworms Increase Plant Production: A Meta-Analysis.” Scientific Reports, vol. 4, no. 1, 2014, doi:10.1038/srep06365

  6. "'Non-Native Species Aren’t the Boogie Man.' Brown Biologist Calls for More Balanced View." Brown University.