The Invasion of Native Ecosystems

What is an invasive species?

An invasive species is an organism that is not native to an area that becomes problematic because it outcompetes native species for the resources needed to survive. In addition to competition for resources, invasive species may target native species as a host or food source. Some commonly discussed examples of invasive species in the United States are the emerald ash borer, purple loosestrife, zebra mussels, and pythons. As you can see, these examples are all from different families of organisms: insects, plants, and animals can all be considered invasive if they endanger the success of native organisms and environments. Because invasive species tend to thrive and grow quickly in an area, they easily change the structure of a natural ecosystem.

In the case of plants, invasive species can overtake an area and eliminate native species by outcompeting them for resources like sunlight, water, nutrients, and space. Aquatic invasive plants cause additional challenges by overtaking waterways, lakes, and ponds, inhibiting their use for commercial and recreational purposes, as well as changing the environmental structure by capturing the sunlight that would normally reach deeper waters.

aquatic invasive
Aquatic invasive plants can quickly overtake waterways

The introduction of non-native species can have far-reaching effects and can quickly become out-of-control. This has been seen with the emerald ash borer, which is an invasive beetle that uses ash trees as a host. Adults drill into the wood of ash trees to lay their eggs, which then hatch into larvae that feed on the inner bark, in the process killing the ash tree. Natural reproduction of ash trees is not rapid enough to help these

Adult Emerald Ash Borer

populations recover, and the progression of the forest ecosystem replaces these trees with smaller shrubs and brush that can survive in the understory. Rapid declines in ash populations foreshadow the possible extinction of this tree, all caused by an invasive beetle.



How did these invasive species get here?

In terms of aquatic invasive species like zebra mussels and some aquatic plants, these species were unintentionally and unknowingly brought to North America in the ballast of or attached to ships coming from other parts of the world. When these ships arrived in eastern North America, the species were introduced to new bodies of water and soon thrived when having the opportunity to inhabit new environments.

Zebra mussels grow densely on underwater surfaces and are about the size of a fingernail, but can reach 2 inches.

Similarly, unwanted insects and other animal species can be brought here in shipments of goods and raw materials from other parts of the world. For example, emerald ash borer was brought to North America in shipments of wood.

Invasive species are often introduced unknowingly, however in the case of many invasive plants, species are introduced to new places for use in ornamental landscape plantings. At the times of introduction, it was not anticipated that these species would become invasive, and they were sold to homeowners across the country. An excellent example of this is purple loosestrife, a plant with beautiful purple flowers that you may have seen while driving along highways or in other natural areas. This plant was used in landscaping for many years until it was discovered to be growing wild in natural areas. Once the negative effects of this and other ornamental plants were seen, their use in landscape plantings was discouraged. Unfortunately, in many cases of invasive plants we are still working to eradicate these species from natural areas, prevent their spread to unaffected regions, and encourage the regrowth of native plant species.

Purple Loosestrife

A major source of invasive animal species is the accidental or intentional release of exotic pets.  A common case of this is the intentional release of pet pythons that have grown too large to easily keep as pets. These pythons and other such animals interfere with natural ecosystem dynamics and the balance of food chains. While invasive pythons thrive primarily in places like the everglades, other species of amphibians, reptiles, and fish have become invasive in many native ecosystems.

In some places, it seems like the battle against invasive species is a lost cause, but there are things that we can do to prevent further damage by invasive species.

The easiest thing that can be done by all is the prevention of the future spread of these species. For example, if you have a boat that you use on public waters, the best thing to do is to take advantage of the boat cleaning stations located at most docking points. Why is this important? While your boat is in Lake X, an invasive plant or animal may become attached to it, and then next time when you visit Lake Y or Lake Z, you could easily and unknowingly be responsible for the infection of that body of water with this invasive species that had not yet been introduced there. Even if the species already exists in all of the bodies of water that you visit, you can help to reduce the problem by cleaning your boat at the washing stations provided to remove any invasive hitchhikers.

In the case of invasive insects, like the emerald ash borer, you can adhere to restrictions on the transport of firewood when you are heading off on your camping trips. In most states, parks prefer that you do not bring your own firewood and that you do not transport firewood across state lines. Because invasive insects may be living within the firewood that you use, you could easily transport them to a new area where they’ve not yet been introduced.

Even though invasive species already exist in the US, their spread across the country can be much slower if we pay close attention to our role in introducing them to new areas. We can also aid in this effort by joining initiatives to combat the spread of invasive plants and restore native species. Many areas have local preservation groups who work to eliminate invasive plants in native environments. Even when hiking, you may see signs asking for your help to pull up specific invasive plants that you might come across. While these efforts can help to contain invasive species, it will not stop the problem from eventually spreading on its own. So what are scientists doing to help reduce the threat from invasive species?

While many scientists are also on the front lines of manually removing invasive species from native environments, they are also working to develop innovative solutions to these problems. A good example of this is the effort to prevent landscape plants from becoming new invasive species. This is done by breeding ornamental plants that are sterile, which means that they cannot produce the seeds that would form new plants, therefore preventing these plants from spreading to unintended areas near the landscape where they’ve been planted.

Scientists are also working to counter invasive insect species. Recently, several states have approved the release of parasitic wasps to control the spread of emerald ash borer. A wasp will lay her eggs inside a beetle larva and upon hatching, the wasp larvae eat the beetle larva. This interaction occurs in nature between wasps and many insect species and is an effective biological control of pests. Read this brief article for more details about this wasp release project.

The issue of invasive species is not only nationwide, but worldwide.

Species that are native to the Americas have become invasive in Europe, Africa, Asia, and Australia, just as species from these continents have proven troublesome here in the Americas. The challenges brought about by existing invasive species have illustrated the importance of monitoring human activities that contribute to this problem, however, there is always a chance that new species will be introduced. To counter our existing invasives, do your part by cleaning your boat, using local firewood, planting native plant species, and taking appropriate responsibility for exotic pets; and if you’re interested, join a local invasive plant removal task force!

For more information, check out these links or ask about invasive species and plant removal efforts at your local extension office.

More on Invasive SpeciesEmerald Ash BorerInvasive Ornamental Plants Release of Exotic Pets



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