Invasive species are one of the leading causes of global biodiversity loss. They can damage native habitats, spread diseases, cause extinctions and leave massive clean-up bills in their wake. But what exactly are they?
An invasive species is commonly defined as any living organism that is not native to an area that causes economic harm, environmental harm or is damaging to human health. Not all introduced species are invasive. In fact, they can sometimes be beneficial. For example, common foods such as potatoes and tomatoes come from plants that were introduced to the rest of the world from the Americas. An introduced species is only considered to be invasive if it causes harm.
Invasive species can usually survive in a variety of environmental conditions. When introduced to a new environment, they can quickly crowd out native species and take over resources such as food and water. They often lack predators, competitors or parasites in their new home. This means that the populations of invasive species can grow rapidly without natural enemies to keep them in check. In many cases, native species have not evolved natural defenses against the new invader, making them easy prey.
Human Influence
Invasive species are almost always spread by human activity. For example, the increase in tourism and trade has meant people and goods can move all over the planet. They often take invasive species with them, whether accidentally or intentionally.
Early explorers were responsible for the introduction of many invasive species, such as dogs (Canis familiaris), cats (Felis catus), pigs and rats. Norway rats (Rattus norvegicus), also called brown rats, originated in China. They spread throughout the Pacific islands during the 18th century by stowing away on ships. They damage ecosystems by eating native species and spreading deadly diseases. Invasive feral pigs (Sus scrofa) live on the United States' Hawaiian islands. They are thought to be descended from domesticated pigs (Sus domesticus) that early Polynesian settlers brought with them for food. Feral pigs dig up large areas of vegetation, spread invasive plant species and contribute to soil erosion.
In some cases, government officials have encouraged the introduction of invasive species. For example, the Asian plant kudzu (Pueraria montana var. lobata) was introduced to the United States during the 1876 World's Fair in Philadelphia, Pennsylvania. In the 1930s, the government encouraged people in the southern United States to plant the fast-growing vine. They hoped this would prevent soil erosion. But the kudzu quickly grew out of control, earning it the moniker "the vine that ate the South."
Other times, invasive species were introduced as ill-advised attempts at biocontrol. For example, the cane toad (Bufo marinus), native to South and Central America, was introduced to Australia in the 1930s. It was hoped the toad would control pests in sugar cane plantations. Unfortunately, the plan backfired, and the cane toads became pests themselves. The oversized toad is famously toxic and can be deadly to predators who try to eat it.
Invasive Species Are World Travelers
Today, we have a better understanding of the repercussions of moving plants and animals outside their natural habitats. We now take measures to prevent spreading organisms beyond their ecosystems. Nonetheless, we continue to spread invasive species around the globe through trade and travel at an alarming rate.
For example, the brown tree snake (Boiga irregularis), native to Australia and Indonesia, has caused the extinction of endemic bird species in the South Pacific U.S. territory of Guam. It has also caused widespread power outages by climbing electrical lines. It is thought to have arrived there in the 1950s by hitching a ride in military aircraft and cargo. In Hawai'i, officials are on high alert to stop the brown tree snake from spreading to the islands so it doesn't cause damage.
Meanwhile, in the U.S. Florida Everglades, Burmese pythons (Python bivittatus) are causing trouble. These snakes make popular pets but grow to be incredibly large. Owners have released them into the wild, such as the Everglades, to get rid of them. Because the Burmese python has no natural predators in Florida, the population has thrived. They prey on local birds, mammals, and even alligators. They even interbreed with local snakes to form a super-resilient hybrid.
Similarly, species of lionfish that are native to the South Pacific and Indian Ocean have quickly spread throughout the Atlantic Ocean, Gulf of Mexico, and the Caribbean Sea. It's thought that a number of separate events have caused the spread of lionfish. As their name suggests, lionfish are fierce and prey on native fish species. They cause economic damage to fisheries and put coral reef ecosystems at risk.
What Can Be Done?
When it comes to invasive species, prevention is the best strategy. Most countries have strict rules about what can and cannot be brought across their borders. Education is also important.
Some innovative approaches to managing current populations of invasive species include turning invasive plants into paper. Other examples include hunting Burmese pythons to eliminate them and serving invasive fish species, such as lionfish, as a delicacy (complete with the catchy slogan, "If you can't beat 'em, eat 'em").
Whether by accident or design, human activities have been the leading cause of invasive species introductions throughout history. But we can also be part of the solution.
So the next time you are in Florida, why not try a lionfish fillet? And whatever you do, do not release your pet Burmese python into the wild.
