Invasive Species
An invasive species is any species ( vegetable , animal or from another biological kingdom ) that has been introduced, intentionally or casually, into an ecosystem other than that of its origin , where it has been able to establish itself and proliferate uncontrollably.
As there are no natural mechanisms that regulate their population in the new ecosystem , such as potential predators or pathogens (viruses, bacteria, parasites, etc.), the invasive species becomes a pest .
Alien species that are successful in invading a new location are usually generalist species . This means that their diet is varied or that they can survive in a wide range of environmental conditions. Consequently, these species have a great capacity for adaptation and colonization of new environments, where they manage to reproduce and grow populationally.
With globalization , the flow of transport of objects, animals, plants and human beings around the world has facilitated the introduction of invasive species in places where they would not otherwise have reached naturally. This has caused serious problems worldwide, such as the displacement of native species , the alteration of the physiognomy of a region, or the spread of new diseases.
The introduction of invasive species is the second cause of biodiversity loss worldwide.
How does a species become invasive?
The process of biological invasion consists of three stages:
- Transport stage , where a species is transported from its place of origin to a new territory. From that moment the species is classified as exotic. However, how invasive species reach new territories is a complex issue, although most species are deliberately moved, some specimens are accidentally transported, such as weeds whose seeds can be harvested with commercial seeds or even rats. and insects that stay on board ships and planes.
- Settlement stage , occurs when the exotic species finds favorable conditions to survive and reproduce in the new ecosystem, so that it can form populations. In this instance the species has naturalized.
- Propagation stage , occurs when the naturalized species has a propagation capacity greater than that of the ecosystem’s own species, a fact that leads to the alteration of the environment. Now the species is considered invasive.
Consequences of invasive species
As we have indicated at the beginning, the great consequence of biological invasions is the loss of biological diversity . In this other article you can learn more about the Causes and consequences of the loss of biodiversity .
You must probably be wondering what damage invasive species cause to biodiversity. The establishment of invasive species causes, first of all, the displacement of native species , mainly when the invasive species uses the resources of the native species but with greater efficiency. They also cause alterations in the interaction networks between species, since it is common, for example, for invasive plant species to compete with native ones for pollinators and dispersers in the ecosystem. In addition, we cannot ignore the possibility that the invaders bring with them diseases or pests to which they are resistant, but not the local biodiversity.
The most invasive species in the world
In the world there is a large number of species that have invaded and modified different environments. Some have had a greater impact on biodiversity and human activities than others .
In 2004, the Invasive Species Specialist Group compiled a list of one hundred of the world’s most damaging invasive alien species. This group is part of the Species Survival Commission of the World Conservation Union (IUCN).
Among the species with the greatest invasive potential are the water hyacinth, the common carp, the zebra mussel and the European rabbit, among others.
Water hyacinth
The water hyacinth (Eichhornia crassipes) is a species native to the Amazon basin (Brazil), in South America , which today is found in more than 50 countries distributed on all continents (except Antarctica).
It was introduced as a decorative plant and as a source of food for livestock . Its seeds were also accidentally dispersed by adhering to the hulls of ships.
Because it grows so fast, water hyacinth has become one of the worst weeds: it clogs rivers, makes it difficult for animals to live in the water , and prevents sunlight and oxygen from entering freshwater bodies. and reach other plants. This reduces the biodiversity of freshwater bodies.
Kudzu
Kadzu ( Ppueraria montana var. lobata) is a leguminous plant native to East Asia, Australia, and some islands in the Pacific Ocean. It was introduced to North America, South Africa, and Europe as a decorative plant and to control soil erosion.
However, being a fast-growing aggressive vine, it chokes out other plants and changes the appearance of the landscape , even growing on abandoned houses and vehicles. In addition, it is home to other invasive species considered pests, such as soybean rust and kudzu bugs.
common carp
The common carp ( Cyprinus carpio) is a freshwater fish native to Asia and Eastern Europe. Currently, it is one of the most widespread species in the world. It has been introduced as a pet, for food, for sport fishing, and to remove algae and plants from ponds and sewage lagoons, among other reasons.
Because it reproduces rapidly, is resistant to varied environmental conditions, and feeds on aquatic vegetation and plankton, it affects many native species and fisheries.
zebra mussel
The zebra mussel ( Dreissena polymorpha ) is a species native to eastern Europe and western Russia. It reached the rest of Europe and North America accidentally, transported by ballast water (the water that ships contain to maintain their balance during navigation) and the ships’ hulls.
By feeding on plankton and reproducing rapidly, it has displaced many native species that compete for the same food . In addition, it clogs filters and water intake pipes, which affects industrial, agricultural and urban supplies.
Something similar occurs with the golden mussel ( Limnoperna fortunei ) in South America.
cane toad
The cane toad ( Rhinella marina ) is an amphibian native to much of the Americas. It was introduced in different countries around the world (for example, Australia, Spain, Cuba, Egypt and Japan) in order to control insect pests of different crops, such as sugarcane.
Being skilled competitors for food and breeding grounds, they have displaced many native amphibians . In addition, they secrete a toxic substance that is deadly to domestic and wild animals.
chick starling
The common starling ( Sturnus vulgaris) is a bird native to Europe, Asia, and North Africa. It was introduced to North America, South Africa, Australia, and New Zealand to control insect pests and to be traded as a pet.
Individuals of this species gather in large flocks that feed on fruits and grains, causing severe agricultural damage. In addition, they are aggressive and crowd out native bird species by competing for food and nest sites .
european rabbit
The European rabbit ( Oryctolagus cuniculus) is a species native to southern Europe and northern Africa. It was introduced to all continents (except Asia and Antarctica) to be traded mainly as food.
The overpopulations of this rabbit are due to their high speed in reproducing and their effective competition for food and shelter . This, added to the fact that they favor the increase of natural predators (such as cats and foxes), has displaced many native species. In addition, they cause significant soil erosion.
amphibian chytrid fungus
The amphibian chytrid fungus (Batrachochytrium dendrobatidis) is a fungus native to South Africa that has been introduced to most of the world, except Asia. The commercialization of the African clawed frog ( Xenopus laevis ) is thought to have caused the dispersal of this species.
This fungus causes a mycosis or infection on the skin of frogs, toads and salamanders that is lethal . In addition, it can disrupt skin respiration and alter the immune responses of these vertebrate animals. So it is one of the main causes of the global decline of amphibians.
asian longhorn beetle
The Asian longhorn beetle ( Anoplophora glabripennis ) is native to Asian countries, such as China, Japan, and Korea. It was introduced to North America and Europe as a result of the shipments (by sea) of logs and wooden packaging.
This insect reproduces quickly and feeds on a layer between the bark and the log of the trees. In doing so, it makes large tunnels in the wood that weaken them and make it difficult for nutrients to be transported within the trunk . This threatens a large number of urban trees and has economic and ecological consequences.
small indian mongoose
The small Indian mongoose ( Herpestes auropunctatus ) is native to southern Asia. It was introduced to the rest of Asia, Central America, and northeastern South America to control pests of rats and snakes. Above all, it has invaded many tropical islands.
This mammal is a general carnivore, that is, it has a very varied diet. This has caused several species of birds, amphibians, reptiles and mammals to be in danger of extinction (such as the Jamaican petrel, the hawksbill turtle, the pink dove and the Amami rabbit)). In addition, it transmits rabies and leptospirosis to humans.
North Pacific starfish
The North Pacific sea star ( Asterias amurensis ) is native to the waters surrounding Russia, China, Japan, and Korea. However, it has found its way to many other parts of the world, such as the coasts of Australia, via ballast water, by adhering to boats and fishing vessels, and by trade in fish .
This echinoderm feeds on a wide variety of prey, supports different temperatures and salinity conditions, and reproduces quickly. This affects many native species, such as the spotted handfish, and economic activities, such as salmon farming and oyster production.
Managing the problem of invasive species
Possible solutions to the problem of invasive species are not easy to find, since once the species has established itself, it is difficult to eradicate. Despite this, there are some management strategies :
- In principle, constant monitoring of ecosystems is done to achieve early detection.
- Then the control of the invasive populations, that is, reduce the abundance of the species and limit its distribution.
- Lastly, mitigation is done. That is, using strategies that do not aim at managing the invasive species, but rather at the resource that you want to conserve.
However, the best strategy is prevention, since avoiding the introduction of exotic species , which can later become invasive, is less expensive than other management strategies.
