What Is an Invasive Species? - Definition, List & Effects

Lesson Transcript
Instructor: Laura Enzor

Laura has a Master's degree in Biology and is working on her PhD in Biology. She specializes in teaching Human Physiology at USC.

Invasive species are non-native organisms that cause harm to the community or components of the ecosystem where they were transferred. Learn about invasive species, their examples, and their effects on ecosystem balance and human health, and explore what actions should be done when dealing with invasive species. Updated: 09/02/2021

What Is an Invasive Species?

Think about all of the plants and animals you encounter in a day. Of these organisms, do you have any idea how many of them are originally from your location or how many have been transplanted from some other place?

Plants and animals that have been transplanted from one location to another are often referred to as non-natives. Although some non-native organisms mesh very well with their new environment and do not do any harm, others can have serious effects on their new home. These organisms are known as invasive species due to their intrusive nature. Under United States federal law, invasive species are defined as species that are non-native to the ecosystem under consideration and whose introduction causes economic harm, environmental harm or harm to human health.

Invasive species can include plants, animals and other organisms, such as microbes. They are found in every type of habitat on Earth, including human homes. The number of invasive species has increased in past decades due to the rapid growth of worldwide transportation. As new technologies made it easier for humans to travel around the world, they also made it easier for invasive species to move around the world. Some invasive species are transplanted to a new environment by accident, such as species that get into boats and travel across the ocean unnoticed. Other invasive species are transplanted on purpose by humans who travel and want to bring something from their travels back home or plant flowers or bushes because they like the way they look. No matter how an invasive species gets to its new environment, it is likely a direct result of human action.

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Invasive Species Examples

Around the world, invasive species take on different shapes and sizes and invade all types of habitats. Every ecosystem imaginable has at least one example of an invasive species. Some of the more publicized invasions in the United States include the zebra mussel into freshwater lakes, the sea lamprey into the Great Lakes, lionfish into the Atlantic Ocean and Gulf of Mexico and the plant Kudzu into the south.

There are, unfortunately, hundreds of other invasive species examples in the United States and around the world. According to the United States Fish and Wildlife Service, there are over 50,000 species in the United States that are non-native, and over 4,300 of those are invasive! In fact, invasive species are considered such a problem that in 1999, the White House formed the National Invasive Species Council (NISC), whose primary purpose is the detection and eradication of invasive species.

Effects of Invasive Species

The effects of invasive species can be divided into three different types: harm to the physical environment, harm to other species and harm to human health. In terms of harming the physical environment, many invasive species change their new environment and make it less inhabitable for others. Other common effects of invasive species on the environment include altering nutrient availability, water quality and the flow of water. Some invasive species also affect their new environment by increasing the risk of erosion because the invasive species do not hold the soil as well as native species. In 2011, the United States spent $100 million on invasive species prevention and land restoration due to the harm caused by invasive species on the environment.

Invasive species can also damage human structures as well. In the case of the zebra mussel, these mussels attach to the hulls of ships and inside water pipes. This is a process known as biofouling. Just like when you get a clog in your drain, the presence of hundreds, sometimes thousands, of mussels can either clog the pipe entirely or dramatically decrease the amount of water flowing through it. In the case of boats, it increases the drag, or how fast they can go, which increases the amount of fuel they consume. Biofouling of ships also causes erosion of the hull of the ship. In the United States, almost six billion dollars a year is spent on the treatment and prevention of biofouling!

Invasive Species and Ecosystem Balance

Invasive species can cause harm to other species that inhabit the environments they invade. Recall that ecosystems are delicately balanced; one small change has drastic effects on the ecosystem as a whole. The normal balance of an ecosystem can be altered when an invasive species is introduced because they can directly or indirectly affect native species, thereby changing the flow of energy in the system.

Invasive species can directly kill native species by feeding on them and immediately reducing the population. Invasive species indirectly affect native species because they are new to the environment they invade and not preyed upon. Therefore, their population numbers quickly rise, and they can push out species that are native to the area by out-competing them for food and space. Some invasive species harm native species because they bring with them toxins or parasites that the native species are not adapted to deal with.

An example of an invasive plant that has caused harm to both the environment and native species is purple loosestrife. Purple loosestrife is native to Great Britain, Central and Southern Europe, Russia, Japan, China and Southeast Asia. It was introduced to the East Coast of the United States in the 1800s for ornamental and medicinal uses and has since expanded its range to include at least 47 states and most of Canada. Purple loosestrife can easily adapt to any new environment and out-compete the native plant species. They often harm plant species by crowding them and by competing for water and resources. They also harm the environment because they fill in open water habitats and alter the availability of nutrients, which degrades the overall quality of the land.

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