Not only native wildlife is at risk, but human health and economies are also suffering. The impacts of invasive species costs billions of dollars each year and many of our agricultural, commercial, and recreational activities depend on healthy native ecosystems.
We will take a look at what exactly makes up an invasive species, how they end up invading, the damage they do, and what we can do to promote and support healthy natural ecosystems.
What Is An Invasive Species?
An invasive species is an organism that is not indigenous, or native, to a particular area. To be considered invasive, a species must adapt to the new area easily, reproduce quickly, and harm property, the economy, or the native plants and animals of the region. Not all non-native species are invasive. For example, most of the food crops grown in the United States, including popular varieties of wheat, tomatoes, and rice, are not native to the region, but do not cause harm and therefore aren’t invasive.
How do invasive species invade?
Many invasive species are introduced into a new region accidentally. They may hitch a ride on a ship or vessel, or someone may carry it unknowingly in their belongings or even on their clothes. Zebra mussels, for example, are native to the Black Sea and the Caspian Sea in Central Asia. However, they were stuck to large ships that traveled to the Great Lakes in North America and there are now so many zebra mussels in the Great Lakes that they have threatened native species.
Some invasive species are brought to a new area on purpose for a variety of reasons. Someone might be interested in them as a pet or decorative display in their home. They could be introduced in hopes of being a type of pest control for a different unwanted species. Or many people and businesses import them, not considering the consequences they may have, and when they escape or a gust of wind spreads their seeds, there is no controlling where they end up. Even some scientists do not consider the lasting effect the introduced species can have or how fast they can breed. Before you know it their population is out of control.
For example, in 1949, five cats were brought to Marion Island, a part of South Africa in the southern Indian Ocean. The cats were introduced as pest control for mice. By 1977, about 3,400 cats were living on the island, and many of the local bird populations are now endangered. Cats, even though they have been domesticated, are harming native wildlife all over. European colonists have brought them over, and since then many people leave their cats outdoors, or unfortunately release them if they can’t take care of them anymore, and they are left to fend for themselves. Today, more than 100 million feral and outdoor cats function as an invasive species with enormous impacts. Every year in the United States, cats kill well over 1 billion birds. This stunning level of predation is unsustainable for many already-declining species like Least Tern and Wood Thrush.
An invasive species does not have to come from another country to harm local environments. Lake trout are native to the Great Lakes, but have been introduced to Yellowstone Lake in Wyoming for sport fishing and now compete with native cutthroat trout for habitat.
How do invasive species harm local environments?
Many invasive species thrive because they out-compete native species for food. They can be more aggressive and have different adaptations that allow them to thrive in their new ecosystem and take resources that native species need to survive. Bighead and silver carp are two large species of fish that escaped from fish farms in the 1990s and are now common in the Missouri River of North America. They feed on tiny organisms that float in the water called plankton, which many native fish also rely on for food, such as the paddlefish. The feeding cycle of the paddlefish is slower than that of the carp, and there are now so many carp in the lower Missouri River that paddlefish are not getting enough food, and their numbers are decreasing.
Many invasive species destroy the habitat where other native plants and animals live, making it harder for them to find food and shelter to survive. Nutria are large rodents native to South America. In the 1900s, ranchers brought them over to North America for the fur trade as they have coats similar to beavers and overhunting was causing beavers to almost disappear. When the fur market declined, many farmers and ranchers just released their nutria. Today, they are a major pest in the Gulf Coast and Chesapeake Bay regions of the United States. Nutria eat tall grasses and rushes which are vital to the regions' marshy wetlands by providing food, nesting sites, and shelter for many organisms. Nutria burrows also damage flood-control levees that protect low-lying areas, weaken the foundations of reservoir dams, buildings, and roadbeds, as well as erode the banks of streams, lakes, and ditches.
Some invasive species also harm the local economy. People have developed farming and hunting techniques specific to their area to help provide a way of life. Invasive species can overtake areas and ecosystems that have a trickling effect on how communities survive. Water hyacinth is a plant native to South America that has become an invasive species in many parts of the world. Many people have introduced this plant to their lakes, rivers, and waterways because of its pretty flowers, but the plant spreads quickly, often chokes out native wildlife. In Lake Victoria, Uganda, water hyacinth grew so thickly that boats could not get through it, and some of their ports that brought in goods and resources that the local economy had to be closed. Because water hyacinth prevents sunlight from reaching underwater, many local plants and algae could not grow which prevents fish from feeding and reproducing. Lake Victoria’s fishing industry also declined and forced many people to lose their main source of income.
How do we get rid of invasive species?
Governments, officials, and communities have used a variety of methods to try to eradicate invasive species. Most methods include chemical, mechanical, or biological control. For plants, the most common method is using selective herbicides to spray on affected areas or sometimes even being directly injected into the plants. The struggle with getting rid of harmful invasive species, is trying to also not damage the noninvasive plants and wildlife also found in that area. To eradicate the cats on Marion Island, they infected them with a virus.
Sometimes other species are introduced to help control an invasive species. In Australia, prickly pear cactus, which is native to the Americas, was growing out of control and destroying rangeland, where ranchers raised livestock. The government brought in cactus moth caterpillars to eat the cactuses as they are natural predators of the cactus. However, introducing insects can be dangerous, and sometimes, the insects also damage other plant species and become invasive species themselves.
Communities can also approach invasive species like an invading army. Officials at the Blackwater National Wildlife Refuge, in the U.S. state of Maryland, worked with hunters to eradicate the 8,500 nutria in the refuge. Hunters would track the nutria and wade into specific areas of the marsh during specific times of the year. The hunters set traps and moved across the refuge in a massive, coordinated, west-to-east movement and would shoot them on sight. The operation took two years, but nutria were eradicated from Blackwater National Wildlife Refuge, and the wetland is slowly recovering.
What can you do to help?
The best way to fight invasive species harming our areas, is to prevent them from occurring. The Nature Conservancy lists six easy ways to combat invasive species:
1. Make sure the plants you are buying for your home or garden are not invasive, and replace invasive plants with native ones instead! Contact your state's native plant society for a list of native plants, and talk to your local nursery staff to help choose better options.
2. When boating, make sure to clean your boat thoroughly before putting it into a different body of water.
3. Clean your boots before you hike in a new area to make sure you don’t have any hitchhiking seeds or pathogens.
4. Don't take home any animals, plants, shells, firewood, or food from different ecosystems. Fruits and vegetables, plants, insects and animals can carry pests or become invasive themselves.
5. Never release pets into the wild. If you plan to own an exotic pet, do your research and plan ahead to make sure you can commit to looking after it for its entire life.
6. Volunteer at your local park, refuge, or other wildlife area to help remove invasive species. Most parks also have native species restoration programs.
You can also check out this Homeowner’s Guide to Preventing the Introduction and Spread of Invasive Species which gives great tips and answers common questions.
National Invasive Species Awareness Week is taking place February 22-26, 2021. The North American Invasive Species Management Association (NAISMA) is putting on free webinars all week where you can learn more. Check out their scheduled talks here. You can also follow on social media and share what you learned using #NISAW or #invasivespecies.