Invasive species are entirely a human-made phenomenon. As we developed the ability to transport ourselves around the world, we started carrying plants and animals along with us. Organisms from one part of the world were dropped in entirely new ecosystems devoid of competitors or predators and they took advantage of the situation by breeding and eating their way through their new homes.
Some of the most well-known invasive species were deliberate choices made by people hoping to provide food (in the case of the rabbits) or to control pests (the cane toads of Australia).
Other invasive species were established by accident, either by grabbing a ride on a passing ship (quagga mussels of the Great Lakes) or escaping from human captivity (Asian carp).
It's likely that most organisms that find themselves transported halfway around the world land in habitats to which they are not suited. Those organisms die a quiet death. In contrast, the plants and animals highlighted here were moved to environments that were a perfect fit. As a result, they have pushed out native species and, in some cases, have caused ecological havoc on the local ecosystem. These five invasive species are not going anywhere anytime soon. Shall we just admit that they have won the battle?
I, for one, welcome our new invasive overlords.
Glacier National Park in Montana closed all park waters to boats recently after finding larvae for the destructive quagga mussel. (Photo: U.S. Department of Agriculture [public domain]/flickr)
Quagga mussels are native to waters of the Ukraine’s Dnieper River, which dumps into the Black Sea. Over the years they have been picked up and transported part of the way around the world by large cargo ships running between the Black Sea and the Great Lakes, where they have spread to smothering proportions. There are enormous sections of the lakes bottoms that have been given over entirely to nothing but quagga mussels.
These mussels muscles out native species a number of ways. Most obvious is their propensity to cover every available inch of habitat, leaving no space for native species to eat, sleep, reproduce and die. Secondly, they are filter feeders and strip the waters of phytoplankton, depriving any other species a vitally important food source. Their filter feeding also results in abnormally clear waters that are favored by aquatic plants whose spread further impacts and disrupts ecosystems.
By now the quagga mussel has jumped beyond the Great Lakes and is becoming a threat to lakes and reservoirs all over the United States. "Since the 1980s freshwater zebra and quagga mussels have steadily advanced westward, transported on trailered boats," the National Park Service says. In fact, Glacier National Park in Montana recently closed all park waters to boats after finding larvae for the destructive mussel on a boat in Flathead Lake, which is just downstream from Glacier.
Basically, these mussels are winning.
The kudzu vine started in Japan and China and spread to parts of the U.S., Canada, Australia and New Zealand. (Photo: Galen Parks Smith [CC BY-SA 3.0]/Wikimedia Commons)
The kudzu vine is a native of Japan and China, where it enjoys a life of ecological balance, hemmed in by the other plant and animal species that it evolved alongside. It plays its biological part, fixing nitrogen out of the air and into the soil and helping to redistribute and diffuse nutrients and energy. The kudzu story would end there if it had stayed within its home range. Instead, the vine has taken on an almost mythological aura as it has spread and smothered a vast range of land in the southern United States, Canada, Australia and New Zealand. The fast-growing vine, in the absence of natural predators, blazes across forests, climbing and reaching for every bit of available sunlight. The leaves shade out and kill any native fauna unfortunate enough to be found underneath. This vine is a prodigious grower and its advance has yet to be stopped in any meaningful way. There are efforts underway to develop specialized herbicides to combat kudzu and some people are working on tasty ways to eat it, but for now, the vine marches on.
An American alligator and a Burmese python locked in a struggle to prevail in Everglades National Park. (Photo: Lori Oberhofer, National Park Service [public domain]/Wikimedia Commons)
The Burmese python evolved in the warm tropical waters of Southern and Southeast Asia, so it shouldn't be too surprising that they feel at home in the Florida Everglades. The large predator (they can grow up to 20 feet long) is a popular choice for pet snake enthusiasts and was slowly introduced to Florida by well-meaning but irresponsible owners who let them go free when they were no longer wanted around the house. These released snakes slithered into the Everglades and found the area to their liking. While they aren't completely without predation — they are known to battle alligators — they had enough of a free hand to rip through the natural web of Florida life. Populations of small mammals have dropped across the board. Some species have seen drops as high as 95 to 100 percent.
There are tens of thousands, if not hundreds of thousands, of Burmese pythons living in the Everglades. Hundreds of thousands of large, scary snakes living in dark, scary swampy water. Who's ready to wade in there and start taking them out? Anyone? It's hard to see how this story has a happy ending for anyone but the Burmese pythons.
Rabbits were introduced in Australia back in the late 1700s as a source of food. Enough rabbits escaped captivity to gain a foothold that they haven't let go of since. (Photo: Unknown [public domain]/Wikimedia Commons)
When you think about rabbits, it's likely that your mind springs to an image of a cute little fluffy bunny hopping through the forest and occasionally giving young children chocolates and jelly beans. Or maybe you think about a tasty roasted dish of rabbit and root veggies. Or maybe both.
But how about the image of rabbits as hungry invaders, advancing in never-ending waves of colonization? Rabbits, for as far as you can see, covering the proverbial horizon with their adorable twitchy little noses and their huge litters of fast-growing kits. Eating through everything. Eating, and having babies.
That's the story of the rabbits in Australia. They were introduced back in the late 1700s as a source of food. Enough rabbits escaped captivity to gain a foothold that they haven't let go of since. Australian newspapers were talking about the spreading scourge of rabbits in the 1800s and time has only allowed their advancement to spread. They are now firmly entrenched and have been blamed for the loss of innumerable native species. People have tried to stop the rabbits using fences, hunters, and poisoning but have not been able to do anything more than make small localized impacts that quickly get swallowed up by the rabbits' exponential growth.
Asian carp is a term that is used to collectively refer to a number of invasive species of carp that are now dominating many lakes, streams, and rivers in the United States. As their name implies, the different carp species are all native to Asia — China to be specific. They have been used in aquaculture for more than a thousand years and were originally imported to the United States to help clean wastewater generated by farmed catfish. Seasonal floods allowed enough of the carp to escape their containment ponds and they quickly spread along waterways, eating their way through local ecosystems. They have now been found in all but one of the Great Lakes as well as the Mississippi River and countless smaller rivers and streams.
Besides the direct impact they have on local ecosystems, many of the species that fall under the term "Asian carp" are extremely skittish fish. Any loud or sudden noise can spook them into swimming and jumping out of the air (as high as 10 feet). There are a plethora of videos of boaters being hammered by huge schools of leaping carp. On one hand, it's an effortless way to catch a fish for dinner, but on the other hand it's a brave soul who can stand up to a bombardment of fish that can weigh up to 100 pounds each and come at you from any direction at a high rate of speed.
Editor's note: This story has been updated since it was originally published in November 2013.