Protecting ecosystems from non-native species has been a priority among ecologists and conservationists since at least the 1980s. Horror stories such as the Burmese python slithering around the Everglades swallowing endangered birds, the Asian carp decimating native fish populations in the Great Lakes, or kudzu taking over just about everything are, in fact, worrisome. But do all non-natives deserve a bad rap? Aren’t ecosystems dynamic by nature? Mark Davis says biologists and government officials need to be more careful about assigning blame. Daniel Simberloff argues that preventing invasions is better than trying to address them later.
by Mark Davis
Mark Davis is the DeWitt Wallace Professor and Chair of Biology at Macalester College, St. Paul, MN. He is the author of Invasion Biology (Oxford U Press, 2009).
For 25 years, the American public has been inundated with horror stories involving non-native species. Think: snakehead, kudzu, Asian carp. This has largely been the result of selective communication from scientists and a media that too often have been more than eager to promote these stories without engaging in any critical analysis or research of their own. Usually provided with just a single perspective, the public largely accepted the idea that non-natives, as a group, are noxious and undesirable.
In fact, this is anything but true. Non-native species are just species. Like native species, some of them produce effects we like, some produce effects that we don’t like, and most are comparatively benign. Have some introduced species caused changes that most everyone would agree have been very harmful? Absolutely. By killing timber trees, gypsy moths and the emerald ash borer have caused, and continue to cause, enormous economic damage to the United States. Introduced pathogens that threaten human health are also clearly harmful species. At the same time, the danger posed by non-native species as a group often has been exaggerated and misrepresented. For example, ecologists and conservationists often describe non-native species as the world’s second greatest extinction threat, despite the fact that existing data shows this clearly not to be the case. It is true that introduced species can and have caused many extinctions in insular environments such as oceanic islands and freshwater lakes. But they have caused very few extinctions on continents or in marine systems. In fact, the primary regional biodiversity effect of introduced species is to increase species diversity. Due to the introduction of thousands of plant species, the United States has approximately 20 percent more wild plant species than it did 500 years ago.
by Daniel Simberloff
Daniel Simberloff is the Nancy Gore Hunger Professor of Environmental Studies at the University of Tennessee. He is editor-in-chief of Biological Invasions and senior editor of the Encyclopedia of Biological Invasions (University of California Press, 2011).
Obviously not all non-native species deserve a bum rap. Invasion biologists have long known this and worked hard to determine which species to try to keep out and, failing that, which to manage at low densities and which to ignore, given the limited funds available. But the idea that resources are squandered fighting harmless species is a straw man argument. Hundreds of non-native species – including many that initially seemed innocuous – have caused staggering ecological, economic, and public health damage. The only logical policy is to work hard to prevent their entry in the first place and, if unsuccessful, to find them quickly and eradicate or limit them before management becomes impossible. A small group of critics brandishing groundless arguments and catchy sound bites can get a lot of attention and impede control efforts and the research that underpins them. But they cannot make the many problems go away.
At least four factors should make us cautious about any introduced species, and about not acting when we see a small, seemingly innocuous population of some non-native. First, even widely used risk assessments to determine which plants to allow in – such as the Australian Weed Risk Assessment adopted not only in Australia but also in several other countries – are far from infallible. Some species judged likely to be harmless turn out to be problematic. The number of surprising ways introduced species can cause trouble is enormous. For example, pupae of flies introduced in the American West to control spotted knapweed (which they failed to do) provided a food bonus for overwintering deer mice, greatly increasing their populations with myriad possible follow-on effects.
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