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This lesson focuses on a group of organisms called invasive species. You’ll learn what makes a species invasive and see some examples of invasive species. You’ll also discover why invasive species are considered a problem and explore the impacts they have on the environment, the economy and on humans.

What Is an Invasive Species?

Think about all of the plants and animals you encounter in a day.

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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.

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.

Invasive Species and Human Health

Besides harming the environment and other animal and plant species, some invasive species are also known to cause harm to human health.

Invasive plants can increase the severity of respiratory allergies due to the exposure to new pollen types. Some invasive plants also have saps and resins that can cause skin irritations. Invasive animals can be harmful to human health because some possess toxins and venoms that could cause serious health problems if passed to humans. A major concern about invasive species such as rodents, mosquitoes and ticks is that they can transmit deadly pathogens to humans in their new environment. Normally, the diseases transmitted by invasive species are not common in the new environment, and this can cause delayed or incorrect diagnosis and possibly increase the likelihood of mortality.

An example of an invasive species that has caused harm to humans in recent years is the West Nile virus. The virus is native to Africa and was accidentally introduced to the United States in 1999. It infects birds and mammals, including humans, and is passed between individuals by mosquitoes. Since its introduction, the virus has spread throughout most of the United States, and in 2012, there were more than 1,100 cases.

What to Do About Invasive Species

Unfortunately, once a non-native species invades an environment, it is very difficult and expensive to get rid of.

In the case of water-bound invasive species, agencies set up hull checks to ensure that boats are not transporting an invasive species on the hull of their boat. Large cargo ships need to release their ballast water, water stored in the ship to help them float, which can carry invasive species in it. Programs are being put in place to treat this water for invasive species before it is released.Invasive plant species, while also problematic, are a bit easier to deal with than water-bound invasive species.

The largest concern with these species is how they spread. Typically, birds and other organisms eat the seeds or leaves of the invasive plant and allow further invasion by transporting their seeds somewhere else. The big question becomes how to kill an invasive plant without killing all the native plants around it. Kudzu is an invasive vine that grows rapidly, up to a foot a day, and quickly kills off surrounding plants by covering them and eliminating their access to sun. The best way to kill kudzu? Goats.

The goats eat the kudzu faster than it can grow, eliminating massive patches of it without harming other species. This is also preferable to the other common way to get rid of invasive plants, which is burning.

Lesson Summary

An organism that lives in an environment where it is not typically found is called a non-native. A non-native species is considered invasive if it can cause harm to the economy, the environment or to human health. Invasive species can be plants, animals or even microbes. The majority of invasive species intruded upon their new environment as a direct cause from human action, and because they typically do not have any natural predators where they invade, they quickly spread.While there are thousands of invasive species worldwide, they all cause harm to the environment they invade, either directly killing native species, or indirectly harming them by out-competing them for resources, or by bringing disease into the ecosystem.

Regardless of how they affect the species within the ecosystem they invade, any changes to an ecosystem can have drastic effects on the ecosystem as a whole.Another issue with invasive species is the potential to harm humans. Invasive species can bring new allergens, which affect our respiratory system, or new toxins or venoms that humans cannot fight against. Unfortunately, eradicating an invasive species is a lengthy, costly process. While all invasive species pose significant problems to the environment and to the economy, invasive species on land are a bit easier to eradicate than invasive species in water.

Learning Outcomes

After this lesson, you’ll be able to:

  • Define non-native and invasive species
  • Describe three ways that invasive species can cause harm
  • Identify examples of invasive species and the harm they cause
  • Explain why eradicating an invasive species is a difficult task

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