Don’t Judge Species On Their Origins
The concept of nativeness was first outlined by the English botanist John Henslow in 1835. By the late 1840s, botanists had adapted the terms native and alien from common law to help them distinguish those plants that composed a ‘true’ British flora from artefacts.
Over the next century, many botanists and a few zoologists described and studied introduced species without being aware that others were doing the same. By the time the British ecologist Charles Elton wrote his famous 1958 book The Ecology of Invasions by Animals and Plants, some 40 scientists had published descriptions of non-natives, but no consensus had been reached on the desirability of intervening when alien species were introduced.
It wasn’t until the 1990s that ‘invasion biology’ became a discipline in its own right. By this point, partly fuelled by Elton’s book, proponents of biodiversity preservation and ecological restoration commonly used military metaphors and exaggerated claims of impending harm to help convey the message that introduced species are the enemies of man and nature.
Certainly, some species introduced by humans have driven extinctions and undermined important ecological services such as clean water and timber resources. In Hawaii, for instance, avian malaria—probably introduced in the early 1900s when European settlers brought in song and game birds—has killed off more than half of the islands’ native bird species. Zebra mussels (Dreissena polymorpha), originally native to the lakes of southeast Russia and accidentally introduced to North America in the late 1980s, have cost the US power industry and water utilities hundreds of millions (some say billions) of dollars in damage by clogging water pipes.
But many of the claims driving people’s perception that introduced species pose an apocalyptic threat to biodiversity are not backed by data. Take the conclusion made in a 1998 paper that invaders are the second-greatest threat to the survival of threatened or endangered species after habitat destruction. Little of the information used to support this claim involved data, as the original authors were careful to point out. Indeed, recent analyses suggest that invaders do not represent a major extinction threat to most species in most environments—predators and pathogens on islands and in lakes being the main exception. In fact, the introduction of non-native species has almost always increased the number of species in a region.
The effects of non-native species may vary with time, and species that are not causing harm now might do so in the future. But the same is true of natives, particularly in rapidly changing environments.
Nativeness is not a sign of evolutionary fitness or of a species having positive effects. The insect currently suspected to be killing more trees than any other in North America is the native mountain pine beetle Dendroc- tonus ponderosae. Classifying biota accord- ing to their adherence to cultural standards of belonging, citizenship, fair play and morality does not advance our understand- ing of ecology. Over the past few decades, this perspective has led many conservation and restoration efforts down paths that make little ecological or economic sense.