Window on Nature
By Lowell & Kaye Christie, F47246
Loss of habitat is the number-one threat to native creatures and biodiversity. The introduction of non-native plants and animals to a specific area or region comes in second. Whether these newcomers are called exotic, introduced, alien, or non-indigenous, many of these plants and animals have dramatically increased in numbers throughout much of North America — and they’re here to stay.
How did these exotics get here in the first place? Some came as uninvited guests aboard ships and airplanes. Others were imported or sold as pets. When they became too large or were otherwise unwanted, their owners released them in what they considered to be a “good home.” Non-native boa constrictors and pythons have even shown up in the Everglades. Sure, it’s a good home, until you consider the welfare of the native animals who fall prey to these large snakes.
Not all exotic plants and animals cause problems. Clearly, many of the plants that make our gardens beautiful aren’t native to North America. They’ve been imported. Our pets provide companionship, laughter, and only a few headaches, yet their ancestors came from foreign lands. The same goes for most of the food we eat. Unfortunately, these desirable species are but a small part of the total immigrants. The rest of the intruders can range from being innocuous to major pests.
Take house sparrows, for instance. English immigrants, homesick for the cheerful songs and chatter of these pretty little birds, imported a few, never dreaming that they would be fruitful and multiply to such an extent. Now they can be found throughout North America.
Starlings were introduced by an industrialist who was so devoted to William Shakespeare that he decided to bring to America all the birds mentioned by the Bard in his works. A little more than a century later they, too, have spread across North America and in far greater quantities than the aforementioned sparrows. Starlings live coast-to-coast and as far north as they can survive the cold.
Starlings are excellent mimics, but they have horrible voices. No one who has had to share a campground with a huge flock of raucous, raspy starlings would call them musical. Noise isn’t the only nuisance they create. Because of their omnivorous eating habits, starlings can be very destructive to both fruit and grain crops. They compete with cattle for livestock feed and can seriously impact poultry. Where will it end? It won’t. Starlings are here to stay.
Far more non-native bird species have been introduced to North America than other kinds of animals. Florida may hold the record for exotic wildlife. One census reports a total of 272 non-native species broken down into 196 types of birds; 30 types of mammals (including three monkey species); 42 types of reptiles; and four types of amphibians.
What may come as a surprise is that some of the smallest imports create the most trouble. One example is the unwelcome chestnut blight, a fungus that arrived from Asia in the early 1900s and dramatically swept the American chestnut from hardwood forests of eastern North America. The gypsy moth, imported in the 1860s to improve silk production, has caused great damage to numerous species of trees and plants. The zebra mussel appeared in the United States in 1988, and it already has spread throughout all the Great Lakes and into the Mississippi, Missouri, and Ohio rivers, to name a few. When zebra mussels become too numerous, other water species can’t compete for food. They also can clog pipes at power plants, public water works, and industrial facilities.
Non-native plants have had their own impact. Kudzu, originally from Asia, may be an attractive vine, but it has spread widely in the Southeast, to the disadvantage of indigenous plants. Purple loosestrife, found in the Northeast, has pretty flowers, but it is very aggressive and can grow anywhere. Mile-a-minute weed, a trailing vine imported from Asia for use in gardens, grows so rapidly that it can shroud shrubs and other vegetation from necessary sunlight. Damage or death is the result. The plant has prospered to the point where it is now making a pest of itself in Pennsylvania, Maryland, Delaware, West Virginia, New York, Virginia, Ohio, and the District of Columbia.
Water hyacinth, a beautiful plant used in garden ponds, is considered to be one of the worst aquatic weeds in the world. Why? It grows so rapidly that it can double in size every 12 days. An overgrowth of water hyacinth has been known to block waterways and interfere with humans’ enjoyment of activities like swimming, fishing, and boating.
Even some trees can become offensive. The salt cedar can outcompete native trees and shrubs in the desert Southwest by sucking up scarce water before the native species get it.
As for mammals, during a recent drive to Fresno, California, from our foothill abode, we spotted a feral hog lying dead on the roadside. Ranchers don’t raise hogs in that area, but these wild pigs appear to thrive everywhere but towns and cities. Originally, these pigs were released in various parts of North America for hunters who consider them attractive game. Unfortunately, the boars didn’t hang around in the hunt area very long; they struck out to colonize other areas. As their numbers continue to increase, their rooting habits destroy the habitats of smaller species, and their aggressive appetites deprive other species of food.
Then there is the African oryx. This antelope was first introduced into New Mexico for sport hunting, but the species multiplied more quickly than expected. The animal is especially adapted to desert life, and researchers believe the oryx will spread throughout the grasslands of southern New Mexico, Texas, and Mexico. The problem is that, except for hunters, few desert predators are equipped to handle a 400-pound animal wearing 3-foot-long horns.
Once an exotic species escapes from captivity/cultivation, it will spread until it is controlled by man; it reaches the limit of an acceptable climate; or, finally, reaches the edge of the continent.
But, cheer up — at least you don’t live in Guam. Nothing compares to the invasion of brown tree snakes on that island. After arriving there in 1940, the population of the poisonous snake increased to as many as 13,000 per square mile in some locations. In addition to being a nuisance, the snakes have eradicated many species of Guam’s native forest birds.