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June 2001
Myths of invasive species
Natasha Kassulke
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- All exotic species are invasive.
Over 85 percent of all exotic plants and animals are not a problem for agricultural, ecological or human health. Many simply exist with the native species so they aren’t considered invasive. Thousands of plants and animals have been introduced into North America without becoming a problem, however, there are certain characteristics that allow some species to spread out of control. If plants and animals were screened for potential impacts to native species, the problem of new weeds and pests would be greatly reduced.
- If it is pretty or beneficial it can’t be a problem.
Not true. Purple loosestrife is beautiful in bloom, but replaces other wetland plants. Reed canary grass was once widely planted to turn "worthless wetlands" into forage production areas for cattle. Now, a large percentage of the once biologically rich marshes and meadows in the state are largely blanketed by this one grass species that provides little useful wildlife habitat or forage.
- Biological controls are dangerous and the solution may become worse than the initial problem.
Not as true, today. While it is true that early experiments with biological controls sometimes turned out to be serious mistakes – introducing the mongoose to the Caribbean Islands to control the rat population is a key example -- in recent decades, federal regulations on biocontrol have become very strict. These regulations require extensive testing of any organism to be introduced to ensure that it doesn’t impact our native plant communities, forests or crops. The key is that the organism used for biocontrol must be specific to the target species otherwise it is not authorized for use.
- By the time you notice the spread of an exotic species, it is too late to control it.
True, in some cases. Some organisms, particularly those living in water, often are not detectable until their populations are quite high. But it is still possible to control the spread of an invading species if correctly done. Eradication may be possible only if an effective control effort is begun when a population is still small and the site is monitored for recolonization for many years.
 The Eurasian ruffe, a perch-like fish now found in lakes Superior and Huron, may spread to the other Great Lakes. They harm perch, whitefish and herring fisheries. © University of Wisconsin Sea Grant
- All aquatic plants are weeds.
Not true. In fact, there are hundreds of species of native aquatic plants that are critically important parts of a lake or river ecosystem. Currently, Wisconsin has only a few invasive aquatic plants – these are the ones that cause problems for boaters and anglers, as well as for fish and other plants. They receive the most attention because they are problematic.
- It is natural for plants and animals to move around. And since it is nature, it’ll all even out in the end.
Not true. Often, they don’t balance out. Ecosystems have evolved over hundreds of thousands of years with plants and animals moving around slowly, allowing the rest of the community to adapt to them. As humans move plants and animals around the globe, they purposefully leave behind the organisms that keep them in control in their homeland. Some of these introduced species find an ideal environment to spread without anything to keep them in check. Meanwhile, native species are being lost and ecosystem functions are altered.
- All exotic species are spread by "natural" mechanisms such as birds and the wind.
Not true in a majority of the cases. In fact, people are a major contributor to the spread of exotic species from purposely introducing carp to North America to unintentionally introducing zebra mussels via ballast water and transporting Eurasian water milfoil by recreational boaters and anglers.
- It only takes one mistake to cause an infestation.
Actually, most introductions of exotics fail, but the more times an exotic is introduced, the greater the chance it will eventually take to the system. That’s why natural resources managers agree that it is important to try to reduce the frequency of introductions.
Natasha Kassulke is Associate Editor of Wisconsin Natural Resources magazine.
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