What Is an Invasive Species? - Definition and Examples

By Cristina Pérez Simón, Biologist and medic. August 24, 2022
What Is an Invasive Species? - Definition and Examples

We often refer to nature's ecosystems as being in a delicate balance, but this estimation can be misleading. While science does its best to understand how these ecosystems might change under the influence of certain new developments, nature itself often finds ways to adapt which are extraordinary and unexpected. For example, there are massive changes from which an ecosystem is able to stabilize and recover. Conversely, there are seemingly small changes to an ecosystem which can have devastating effects. Introducing an invasive species can be one such devastating effect.

At AnimalWised, we ask what is an invasive species? To answer the question, we provide a definition of invasive species, as well as examples of how they can affect various ecosystems.

You may also be interested in: Umbrella Species Definition and Examples

Definition of invasive species

Knowing what is an invasive species will help us to know how they affect different ecosystems. According to the International Union for Conservation of Nature (IUCN), an ‘invasive alien species’ is a species that establishes itself in a natural or semi-natural ecosystem or habitat, becoming a threat to native its biological diversity. Acting as agents of change, they do so by overpopulating an area

Invasive species are those capable of successfully reproducing and forming self-sufficient populations in an ecosystem that is not their own. When this happens, we say they have naturalized. This can have very unfortunate consequences for native species and we look at the common consequences below.

Some introduced exotic species are not capable of surviving and reproducing on their own. In these cases, they end up disappearing from the ecosystem and do not endanger native biodiversity. In this case, they are not considered invasive species, merely an introduced alien species.

Origin of invasive species

Throughout history, human beings have made great migrations across Earth. In doing so, they often take with them various species for varying reasons. Often it is to help them survive, as is the case of bringing animals for food or work. It may also be due for anthropological or scientific discovery. They may even do so unwittingly. While it is not the only cause, transoceanic shipping and exploration greatly increased the number of invasive species.

The globalization of trade that has taken place over the last century has exponentially increased the introduction of species. The introduction of an invasive species is known to have various causes, including:

  • Accidental: animals which hide in various forms of transport form one ecosystem to another.
  • Pets: it is depressingly common for people who buy pets to get tired of them or be unable to take care of them, so they decide to release them into an ecosystem which is not their own. They may even do so with good intentions, but they do not take into account the endangerment of said ecosystem.
  • Aquariums: the discharge of water from aquariums in which there are exotic plants or small animal larvae has led to the invasion of rivers and seas by many species.
  • Hunting and fishing: both the rivers and mountain ranges are full of invasive animals released by hunters, fishermen and even official animal administrations. This is often to provide game or even as a food resource for other wildlife.
  • Gardens: both in public and private gardens, ornamental plants are grown that are very dangerous invasive species. Some of these species have come to displace native forests.
  • Agriculture: with few exceptions, plants grown for food are not usually invasive plants. However, during transport, seeds and arthropods may be accidentally introduced. This is the case with many adventitious grasses (weeds).
  • Conservation: while very rare, it is possible a species is introduced in order to aid an ecosystem (such as introducing predators to cull another invasive species), only for this new species to also become invasive.

If you want to know more about the consequences of using exotic species as pets, we recommend our related article on animals that should not be pets.

What Is an Invasive Species? - Definition and Examples - Origin of invasive species

Consequences of introducing invasive species

The consequences of the introduction of invasive species are not immediate. They are observed after their introduction has been given the time to affect the ecosystem. Some of these consequences are:

  • Extinction of species: invasive species can end the existence of the animals or plants they consume. This is usually because they are not adapted to their type of predation or the voracity of the new species. In addition, they compete for resources (food, space, etc.) with native species, displacing them and causing their disappearance.
  • Alteration of the ecosystem: as a consequence of their activity, they can alter the food chain, natural processes and the functioning of habitats and ecosystems.
  • Disease transmission: alien species carry pathogens and parasites from their places of origin. Native species have never lived with these diseases, so they often suffer a high mortality rate as they have no natural defense against them.
  • Hybridization: some introduced species may breed with other indigenous species or breeds. As a consequence, the native variety may disappear, reducing biodiversity.
  • Economic consequences: many invasive species become crop pests, decimating crops in the process. Others adapt to living in human infrastructure, such as pipes, causing economic losses and other problems to human communities.

Invasive species can have the devastating effects of endangering other animal and plant species. Learn more with the 10 animals most in danger of extinction.

Examples of invasive species

There are already thousands of invasive species around the world. They all have varying methods of invasion and the consequences of their introduction depends on the specific ecosystem. Here we look at some common exampls of invasive species:

Nile perch (Lates niloticus)

These huge freshwater fish were introduced into Lake Victoria (Africa). In a short time, they caused the extinction of more than 200 endemic fish species due to their predation and competition. Activities derived from its fishing and consumption are also believed to be related to the eutrophication of the lake and the invasion of the common water hyacinth (Eichhornia crassipes).

Rosy wolfsnail (Euglandina rosea)

Also known as the cannibal snail, the rosy wolfsnail was introduced to some Pacific and Indian islands as a predator of another invasive species, the giant African land snail (Achatina fulica). This had been introduced as a food resource and pet in many countries, until it became an agricultural pest. As expected, the wolfsnail not only consumed the giant African land snail, but also wiped out many indigenous species of gastropods.

Caulerpa (Caulerpa taxifolia)

Caulerpa is probably the most damaging invasive plant in the world. It is a tropical algae that was introduced into the Mediterranean in the 1980s, probably as a result of the discharge of water from an aquarium. Currently, it is found throughout the western Mediterranean, where it is a threat to native grasslands, where many animals breed.

Kudzu (Pueraria)

Also known as Japanese arrow root, kudzu is a perennial vine which has various plants in the genus Pueraria. This invasive species is well known in parts of North America where its ability to grow rapidly has meant the plant has taken over various ecosystems. Some estimate it can develop at a rate of 150,000 acres per year. It was originally encouraged as a way to reduce soil erosion, without realizing how invasive it would prove to be.

Eastern grey squirrel (Sciurus carolinensis)

One of the most well-known invasive species in countries such as the United Kingdom, this squirrel species has visibly taken over red squirrel populations in many countries. While they are both similar animals, the Grey squirrel is larger and it is believed to be a better competitor for food and other resources. This has led to the decline of ed squirrel populations to the extent that some legal measures have been introduced to slow their rate of growth.

However, it is also possible red squirrels are less able to tolerate habitat destruction at the hands of human interference and their population decline may also be related to disease. For this reason, it is important to note there are very complicated reasons for invasive species to be successful, so we need to bear in mind various factors.

What Is an Invasive Species? - Definition and Examples - Examples of invasive species

If you want to read similar articles to What Is an Invasive Species? - Definition and Examples, we recommend you visit our Facts about the animal kingdom category.

  • Lowe, S., Browne, M., Boudjelas, S., & De Poorter, M. (2004). 100 of the most harmful Invasive Alien Species in the world. A selection from the Global Invasive Species Database. Invasive Species Specialist Group (IESG), Species Survival Commission (SSC) of the World Conservation Union (IUCN), 12pp. First edition, in English, Aliens 12 (2000).
  • Capdevila, L., et al. Invasive Alien Species. Diagnosis and bases for prevention and management. General Directorate for Biodiversity, Ministry of the Environment. Madrid.

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