Invasive species are the stock villains of conservation biology, disrupting ecosystems and throwing native populations into disarray. But in certain cases, they're actually quite beneficial, and perhaps it's time to recognize that.

In California, for example, native butterflies feed on non-native plants. In Puerto Rico, alien trees help restore abandoned pastures to a condition suitable for native plants. Even the much-maligned zebra mussel helps filter toxins from lakes.

"We predict the proportion of non-native species that are viewed as benign or even desirable will slowly increase over time," write ecologist Martin Schlaepfer of the State University of New York and colleagues in a paper published Feb. 22 in Conservation Biology.

According to Schlaepfer's group, biologists are often biased against invasives, and decline to notice or report instances of beneficial invasions.

They support their unorthodox perspective by reviewing dozens of papers on plants and animals introduced, accidentally or otherwise, outside their historical ranges. A variety of underappreciated invasive roles are described: providing ecosystem services, replenishing human-damaged regions, and generally helping to sustain some semblance of natural health even as many ecosystems struggle to survive.

Schlaepfer and colleagues admit to a certain bias of their own. "Negative roles listed here are not exhaustive and include only those that directly oppose the listed positive roles," they write. "Many of the non-native species listed have other negative effects on conservation objectives."

Their goal, however, isn't to do a conclusive analysis of the pros and cons of invasives, but to encourage a more open-minded consideration of benefits – and not just cost – for species often described in militarized, even xenophobic terms.

After all, many now-beloved native creatures were once invasives. Among them are dozens of honeybee species introduced to North America since the 16th century. Far from declaring war on bees, people now worry that these invading aliens might vanish.

Image: Thomas Bresson/Flickr.

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Citation: "The Potential Conservation Value of Non-Native Species." By Martin Schlaepfer, Dov Sax and Julian Olden. Conservation Biology, published online Feb. 22, 2011.