Ecologists are battling one another over the value of nonnative species. Last month, Mark Davis and colleagues argued in Nature that experts and laypeople are committing a naturalistic fallacy when it comes to favoring native species over nonnative or invasive species. Just because plants and animals are considered native doesn't mean they deserve special protection over nonnative species, especially in light of the fact that climate change and other environmental pressures are rapidly reducing many species' options, argued Davis, a biologist at Macalester College in St. Paul, Minnesota. Among the examples he gave of bias against nonnatives were bans by the Agriculture Department on introduced honeysuckle, which he said assist bird populations and aid the spreading of native berry-producing plants.
The piece has provoked a contentious debate and a petition of 141 scientists who have opposed the piece. Daniel Simberloff, an ecologist at the University of Tennessee, Knoxville, writes today on behalf of the signatories that Davis and his colleagues were attacking strawmen in their letter. "[M]ost conservation biologists and ecologists do not oppose non-native species per se -- only those targeted by the Convention on Biological Diversity as threatening 'ecosystems, habitats or species,'" he wrote. "There is no campaign against all [nonnative] introductions."
Davis wrote that biologists and wildlife managers ignore the fact that some nonnative species wind up benefitting their new homes, such as the tamarisk shrubs that were introduced to the American Southwest from Eurasia and Africa and now are the preferred nesting grounds of the endangered southwestern willow flycatcher. "Tamarisks ... arguably have a crucial role in the functioning of the human-modified river-bank environment," Davis wrote. "Yet between 2005 and 2009 alone, the US Congress authorized US$80 million to support ongoing tamarisk control and eradication." Simberloff counters that biologists do recognize those benefits, but emphasize control over them nonetheless, as some environmental impacts don't manifest until decades after a species' introduction.
Military metaphors of waging war against invasive species have "convey[ed] the message that introduced species are the enemies of man and nature," wrote Davis, adding that such rhetorical tactics drive scientists' and the public's distaste for them.
But "[b]ias against non-native species is not xenophobic—it has a sound scientific foundation," writes Andrei Alyokhin, an entomologist at the University of Maine, Orono. Introduced species can decimate local populations, leading to population bottlenecks and undercutting local species' genetic diversity, he says. And two scientists from the Chinese Academy of Sciences, argue today that invasion ecologists don't have the luxury of time to wait and see whether species will be harmful because once the species settle in, they're harder to extirpate.
"Invasion ecology is making real progress with defining impact and characterizing risk," write Julie Lockwood of Rutgers University, Martha Hoopes of Mount Holyoke College, and Michael Marchetti of California State University, Chico. "Let's not throw up our hands in despair just yet."