⏳ Estimated Reading Time: 13 - 15 minutes

Explain the environmental problems associated with invasive species and strategies to control them.

Nonnative vs. Invasive Species: What's the Difference?

A long, slender worm with a light brown body is winding across a rough asphalt surface. The head of the worm has a distinctive shovel-shaped head, which is similar to the head of a hammerhead shark. — **While running outside my home in Gainesville, Georgia, I saw this hammerhead worm. It is considered invasive and preys on earthworms.**

Exotic or alien species are species that have been introduced into an area from somewhere else, often a different country, either accidentally or intentionally. As an example, Burmese pythons have invaded the Florida Everglades and authorities suspect that the invasion was caused by people releasing pet pythons into the closest “natural” habitat, whether it is the species’ natural habitat or not.

The moving of species has occurred throughout history. Most people, in fact, cannot distinguish between native and nonnative species. For example, almost 1/3 of the plants in Massachusetts are alien or introduced, which amounts to about 725 species. Sixty-six of those introduced species are invasive and actively causing problems. In Georgia, the following species are actually non-native, but they've been there so long, we don't even realize they aren't native:

fallow deer
greenhouse frog
joro spider
nine-banded armadillo

Invasive species are exotic species that thrive, spread, and eliminate native species. They are a major cause in driving native species to extinction and are responsible for 39% of all extinctions since 1600.

It is important to understand that not all non-native species are invasive. Non-native species become invasive once they start growing out of control in an ecosystem. Invasive species cause problems for organisms that are native to the area. Non-native non-invasive species do not cause problems in their new environments. The species listed above are non-native, but also non-invasive.

Even though exotic species can sometimes be beneficial, they are considered invasive when they threaten native species.

Essential Knowledge

Invasive species are species that can live, and sometimes thrive, outside of their normal habitat. Invasive species can sometimes be beneficial, but they are considered invasive when they threaten native species.

Characteristics of Invasive Species

A dense growth of green foliage with various shades of green leaves from different plants and trees intertwined, creating a lush and vibrant natural tapestry. — **Kudzu is an invasive plant that was widely planted in the 1930s for soil erosion control. It has since caused problems, especially in the southeastern United States.**

Invasive species can take over niches previously occupied by native species and disrupt food chains. Invasive species are usually generalists, have many offspring, and usually exhibit characteristics of r-selected species.

These two characteristics allow them to out-compete many native species making them a true nuisance and danger to the stability of the new ecosystem.

Explore the tabs below to refresh yourself on the characteristics of r-selected species. Choose an invasive species from the list under "Effects of Invasive Species" and think about how that species has each of the characteristics below:

🪳 Adapted to Unstable and Unpredictable Environments (click to reveal)

r-strategists are adapted to unstable and unpredictable environments, where they can quickly exploit new resources and produce many offspring.

🦎 Small Body Size (click to reveal)

r-strategists have a small body size because they do not face competition and unpredictable environmental conditions often cause mass mortality, so smaller body size is preferred over larger body size among r-strategists.

PS - can you imagine an elephant having 100 babies at once?

🦐 Short Lifespan (click to reveal)

A short lifespan is beneficial for r-strategists because it allows them to reproduce quickly and exploit new resources before they are depleted or become too competitive. A short lifespan also reduces the risk of predation, disease, and senescence (getting old).

🐞 Many Offspring (click to reveal)

By having many offspring in a short time, r-strategists increase their chances of survival and adaptation in unpredictable environments.

🪼 Low Recruitment (click to reveal)

Low recruitment is beneficial for r-strategists because it reduces the competition and predation pressure on their offspring. By producing many offspring and leaving their survival to nature, r-strategists can ensure that some of them will find suitable habitats and resources to grow and reproduce. Low recruitment also allows r-strategists to maintain a high population growth rate and adapt to changing environmental conditions.

Invasive species outcompete native species in an area. Usually in ecosystems, niches, or an organism’s specific place in the environment, are very well-defined. This means that any disruption to the area will disrupt the niches in the ecosystem. Since the invasive species have no natural predators, there are no predators of the invasive to keep the population of the invasive in check. So, invasive can grow out of control, eating the prey, or taking the habitat of native organisms.

These species have no native predators and are usually generalists, which means they can eat a wide variety of foods, and their population numbers are not regulated by any predators, they can cause extensive economic and environmental harm to an area. For example, some non-native plants are difficult for herbivores to eat and can keep energy from passing up the food chain. Kudzu doesn't have any native predators in Georgia, but goats have been used to eat kudzu and help manage its growth.

Essential Knowledge

Invasive species are often generalist, r-selected species and therefore may outcompete native species for resources.

Effects of Invasive Species

Aquaculture, the farming of shellfish, seaweed, and fish, produces 1/3 of all of the seafood consumed worldwide. Unfortunately, aquaculture species can escape and hybridize with native species or displace native species.

Invasive species can be the leading cause of local extinctions and can cause over 130 billion dollars per year in damages. Learn more about some notable invasive species below. Have you seen any of these before? I bet you've seen at least one of them!

Zebra Mussel (click to reveal)

A zebra mussel on a rock — **Zebra mussels are small mollusks with a zig-zag pattern on their shells.**

When and where did it come from?

Zebra mussels are native to the lakes of southern Russia and Ukraine. They likely arrived in the Great Lakes in the 1980s via ballast water discharged by large ships from Europe. The first established population was discovered in 1988 at Lake St. Clair, which straddles the border between the U.S. and Canada.

Where is it found?

Zebra mussels have spread rapidly throughout the Great Lakes region and into the large rivers of the eastern Mississippi drainage. They have also been found in Texas, Colorado, Utah, Nevada, and California. They are now present in many waterways across the United States.

What problems has it caused?

Zebra mussels outcompete native mussel species, foul pipes in water treatment plants, power plants, and other industries that pull water from infested lakes, decrease property values and recreational use of affected lakes and beaches, and damage boats, docks, and marinas by attaching to these surfaces in large numbers.

Kudzu (click to reveal)

A lush green landscape dominated by dense kudzu foliage. — **Kudzu vines grow quickly and can completely cover ecosystems.**

When and where did it come from?

Kudzu is native to Asia, specifically regions in Japan and China. Kudzu was first introduced to the United States from Japan in 1876 at the Centennial Exposition in Philadelphia. It was later widely planted in the 1930s for soil erosion control.

Where is it found?

Today, kudzu covers an estimated 7,400,000 acres in the southeastern United States, particularly in states like Alabama, Georgia, Tennessee, Florida, North Carolina, South Carolina, and Mississippi. It has also been found as far north as Nova Scotia, Canada, and in all five boroughs of New York City.

What problems has it caused?

Kudzu can overgrow and suffocate native plants, trees, and entire ecosystems, posing challenges for agriculture, forestry, and property management due to its rapid growth and difficult removal. In addition, the weight of the vine can break trees, branches, and buildings, causing further ecological and structural damage.

Kudzu can also emit isoprene and nitric oxide, which combine with nitrogen in the air to form ozone, a harmful air pollutant.

Feral Pigs (click to reveal)

A group of wild boars, including adults with dark grey to brown bristly fur and smaller, striped piglets, foraging on a grassy path surrounded by green foliage. — **Each dot on the map is an Argo float that moves with the ocean currents.** **Dots suddenly appearing in a line, represent new floats being deployed (float movement over a 6-month period in 2005)**.

When and where did they come from?

Feral pigs are not native to the Americas. They originally came from the Eurasian super-continent. They were first brought to the United States in the 1500s by early explorers and settlers as a source of food. Free-range livestock management practices and escapes from enclosures led to the establishment of feral swine populations within the United States.

Where are they found?

Feral pigs have expanded dramatically from their native range and are currently found on every continent except for Antarctica. As of 2019, feral pigs have been reported in 35 out of 50 states in the United States.

What problems have they caused?

Feral pigs have caused extensive damage to crops and fields by feeding, rooting, and trampling crops. They can also disrupt habitats, damage archaeological sites, and prey on native species. They are responsible for an estimated $2.5 billion worth of damage in the U.S. each year.

Feral pigs can carry at least 30 diseases and nearly 40 types of parasites that may affect people, pets, livestock, and wildlife. Some diseases, such as pseudorabies, are fatal to cats and dogs that may be exposed from direct contact with a feral swine carcass.

Hydrilla (click to reveal)

Hydrilla plants filling a waterway to where water is no longer visible. — **Hydrilla can reproduce from very, very small fragments, making it very hard to control.**

When and where did it come from?

Hydrilla is native to the Eastern Hemisphere, with U.S. strains possibly originating in Asia. Some sources specify that the dioecious form of hydrilla originated from the Indian subcontinent, and the monoecious form originated from Korea. It was introduced to North America in the early 1950s by an aquarium plant dealer who discarded it into a canal near his business in Tampa, Florida. It was imported into the United States from Asia for use in aquariums and likely introduced into the wild near Tampa and Miami, Florida.

Where is it found?

Hydrilla can be found on all continents except Antarctica and South America. It is most common in Middle Eastern countries, Southeast Asia, Northern and Eastern Australia, and the Indian subcontinent. In the United States, hydrilla has become established from Florida to Connecticut and west to California and Washington, with the most severe occurrences in the Gulf and South Atlantic States.

What problems has it caused?

Hydrilla forms dense mats that crowd out native species, impede irrigation, and disrupt boating. It can clog intake structures at power plants, water supply facilities, and other industries near infected waterways. Hydrilla can reproduce from very small fragments, making it difficult to control and easy to spread.

European Starlings (click to reveal)

A starling bird perched on the ground, showcasing its iridescent black plumage with speckles of white and hints of green and purple shimmering in the light. — **Starlings were intentionally released in the United States by a Shakespeare superfan.**

When and where did they come from?

European Starlings are native to the UK, Europe, large parts of Asia, and North Africa. In the late 19th century, an entrepreneur named Eugene Schieffelin introduced 100 European Starlings in Central Park, New York City. Schieffelin was a Shakespeare enthusiast and aimed to bring all bird species mentioned in Shakespeare’s works to North America.

Where are they found?

European Starlings are now widespread in North America, from Alaska to Florida and northern Mexico.

What problems have they caused?

European starlings cause significant agricultural damage when they forage on crops and outcompete native bird species. They are noisy, which is a nuisance to homeowners and building managers. Roost sites can be messy, posing health risks.

Cane Toad (click to reveal)

A large brown toad with bumpy skin is being held in a person’s hand, showcasing the toad’s size relative to human hands. — **Cane toads have highly toxic skin.**

When and where did it come from?

Cane toads are native to South and Central America. In Australia, they were introduced in 1935 to control pest beetles in sugar cane crops. In the United States, they were first introduced to Florida in 1936.

Where is it found?

In Australia, they have spread well beyond Queensland into coastal New South Wales, the Northern Territory’s Top End, and the Kimberley region of Western Australia.

In the Americas, they are found from the Rio Grande Valley in South Texas to the central Amazon and southeastern Peru, and some continental islands near Venezuela.

What problems has it caused?

Cane toads are highly toxic and have devastated populations of native predators, such as crocodiles and snakes. Their toxic skin is particularly dangerous to dogs.

They also outcompete native species for food.

Green Mussel (click to reveal)

A close-up image of several green-shelled mussels with a glossy texture, clustered together. — **Green mussels have been migrating northward since their introduction in Tampa in 1999.**

When and where did it come from?

Green mussels are originally from the Indo-Pacific region, including the coasts of Southeast Asia, India, and the Persian Gulf. They were first observed in the Caribbean in 1990 and later along the coast of Venezuela in 1993. The first known occurrence of green mussels in the United States was in Tampa Bay, Florida, during the summer of 1999.

Where is it found?

In the United States, their known distribution is limited to Florida, including Tampa Bay, and from Clearwater south to Boca Grande in the Gulf of Mexico. They have also been found along the Atlantic Coast from Palm Beach County northward.

What problems has it caused?

Green mussels displace native species and, like the zebra mussel, clog the intakes of power plants and other industrial facilities that take water from infected waterways. They can increase the drag on boat hulls and growth on floating buoys can cause them to sink.

They also accumulate high concentrations of toxins and heavy metals, making them unsafe to eat.

Domestic Cats (click to reveal)

A grey cat with faint stripes sitting on a branch, looking directly at the camera with a focused expression. — **Cats are so prevalent that we hardly realize that they are not native to most places in the world.**

When and where did they come from?

Domestic cats were originally bred from wild cats in the Near East approximately 10,000 years ago. Cats were introduced to the United States by European colonists. The number of domestic cats has tripled in the past 40 years.

Where are they found?

Cats inhabit all continents except Antarctica. Cats are responsible for the extinction of several mammals, reptiles, and at least 33 bird species globally.

What problems have they caused?

Cats threaten native wildlife abundance and diversity, especially ground-nesting species. Cats kill billions of animals each year, including birds, mammals, reptiles, and insects.

They can also serve as vectors for diseases.

Lionfish (click to reveal)

A lionfish swimming underwater, identifiable by its distinctive red and white zebra stripes, elongated fin rays, and an array of venomous spiky fins. — **Grey's Reef National Sanctuary holds a Lionfish fundraising event in Savannah every year, where local chefs prepare invasive lionfish.**

When and where did it come from?

Lionfish are native to the warm tropical waters of the Indo-Pacific region, including the Indian and South Pacific Oceans. They were first detected along the Florida coasts in the mid-1980s. It is believed that they may have been introduced to Atlantic waters through the aquarium trade or accidental release, possibly during Hurricane Andrew in 1992.

Where is it found?

Lionfish have since spread extensively and are now found along the southeast coast of the U.S., the Caribbean, the Gulf of Mexico, and as far as the Mediterranean Sea. Their range continues to expand, posing a threat to various marine ecosystems.

What problems has it caused?

Lionfish compete for food with native predatory fish such as snappers and groupers. They also prey on herbivorous species that are essential for controlling algae growth on coral reefs, lionfish indirectly contribute to the degradation of reef ecosystems.

Controlling Invasive Species

Controlling invasives and loss of native species costs around $137 billion annually in the United States.

There are three main methods used for control of invasive species - biological, mechanical, and chemical.

Images of Mnemiopsis and Beroe comb jellies. Both jellies are transparent with comb rows of cilia down their bodies. — **The story of** **Mnemiopsis and Beröe in the Black Sea is a success story of biological control of an invasive species**.

Biological Control: involves the use of natural enemies, such as predators, parasites, or pathogens, to control invasive species populations. The goal is to introduce or enhance the population of these natural enemies in the environment where the invasive species are present. For example, Mnemiopsis leidyi is a species of comb jelly native to Atlantic coastal waters. It was introduced into the Black Sea in the 1980s, where it had no natural predators and voraciously consumed zooplankton, almost collapsing the food web in the Black Sea. In response, Mnemiopsis's natural predator, Beröe ovata was introduced to the Black Sea. Beröe has helped reduce the Mnemiopsis population in the Black Sea. This specific example was a success, but we need to be cautious when introducing new species to control invasives. The intentionally introduced species can sometimes cause more problems than the initial invasive.
Chemical Control: Chemical control includes the application of pesticides, herbicides, fungicides, and insecticides to manage invasive species. These substances can effectively reduce or eliminate invasive populations but must be used carefully to avoid harm to non-target species and the environment. Chemical control can be expensive and may raise concerns about environmental health and safety.

An informational graphic about the invasive ‘Air Potato’ plant, providing details on the plant’s growth, characteristics, and methods for removal and disposal. — *The University of Florida has spent significant funds educating the public about the air potato*.

Mechanical Control: Mechanical control involves physical actions to remove or destroy invasive species. This can include mowing, hoeing, tilling, girdling, chopping, and constructing barriers. It also encompasses manual efforts like hand-pulling, digging, and mulching. Mechanical control is often labor-intensive and may be used in combination with other methods for greater effectiveness. For example, in Florida, there is an invasive plant known as the air potato. Many cities in Florida host an annual Great Air Potato Round Up, where residents would come together to remove air potatoes from natural areas.

Each of these methods has its advantages and limitations, and they are often used in combination to achieve the best results in managing invasive species.

Essential Knowledge

Invasive species can be controlled through a variety of human interventions.

AP Exam Tip

You should know the characteristics of invasive species and how they can cause environmental, societal, and economic damages.

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