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Native, exotic and invasive species

By Scott Shalaway

The origin of species, whether they are native, exotic and/or invasive, is a hot topic in conservation today. So hot that the summer 2012 issue of The Wildlife Professional magazine is devoted entirely to it. The Wildlife Professional is one of the publications produced by The Wildlife Society (www.wildlife.org), an organization of wildlife biologists (including me).

In the past I have addressed this problem with columns on everything from bullfrogs and emerald ash borers to feral hogs and cats. But sometimes the terminology gets confusing.

Native species are those that naturally occur in a defined geographic area.

Box turtles, brook trout, eastern bluebirds, and white oaks are all native to the Eastern U.S. Thus, all are natives. Generally, conservation favors native species.

Exotic species are those that have intentionally or accidentally been introduced to areas where they do not naturally occur. Asian multicolored lady beetles were introduced to control other insect pests. Emerald ash borers arrived accidentally on ships via the Great Lakes. And some, such as the pythons plaguing Florida's Everglades, arrived via the exotic pet trade.

The list of exotic species in North America is long and includes many that have been in place so long they almost seem native. The large green praying mantis, for example, is native to China, though there are more than a dozen mantids native to North America. Red foxes, house sparrows, European starlings, and honeybees came from the Old World. And I'm sure multiflora rose and autumn olive seemed like good ideas when they were introduced more than 60 years ago as "living fences."

More recent introductions of exotic species that have gone wrong include pythons in the Everglades where they eat herons, alligators, and deer; zebra mussels that clog pipes in the Great Lakes; and brown tree snakes in Guam that have eliminated 15 of 16 native bird species.

The movement of exotic species is not simply a one-way problem from elsewhere to North America. Gray squirrels in England came from U.S. stock, and raccoons imported to Japan for the pet trade in the 1970s have become a serious pest.

Exotic species are not by definition "bad," though many earn that status by competing fiercely with native species. House sparrows and starlings battle bluebirds and other native cavity-nesters for nest sites. On the other hand, gardeners love praying mantises because they eat many injurious insects.

Invasive is a term used when the exotics become so successful they harm the environment, human health and/or the economy. In Louisiana, for example, millions of nutria, a semi-aquatic rodent native to Argentina, damage thousands of acres of wetlands each year.

In Illinois, Asian carp have invaded the state's rivers. Known as the big fish that jumps into boats and sometimes strikes boaters, these carp now make up more than 60 percent of the fish biomass in the Illinois River. Population surveys have found that as many as 2,800 can live in each mile of some rivers.

Perhaps the worst examples of invasive, exotic species are the rats that reached oceanic islands on shipwrecks. About half of the many extinctions of birds and reptiles on ocean islands are attributable to rats.

But wildlife need not be exotic to be invasive. Even native species can become pests. Too many white-tailed deer destroy forest ground cover and sapling trees. They kill about 200 people annually in deer-vehicle collisions. And insurance companies expect about 1.5 million deer-vehicle collisions annually that cost more than a billion dollars in claims. And let's not forget Canada geese. They damage vegetation in parks and on golf courses, and when struck in flight, they can take down airliners.

Even bullfrogs, native to eastern and central U.S. states, wreak ecological havoc. They have been introduced throughout the West, presumably to harvest them for their tasty legs. But they are ravenous predators that eat anything they can swallow -- turtles, snakes, birds, other frogs and even recently hatched alligators. In Arizona, bullfrogs eat the federally threatened Chiricahua leopard frog.

Like it or not, wildlife affects us all. And often its negative effects can be attributed to invasive, exotic species.

Send questions and comments to Dr. Scott Shalaway, 2222 Fish Ridge Road, Cameron, WV 26033 or by email at sshalaway@aol.com.

 

 


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