What are invasive species?
Invasive species are exotic species which can cause damage to the biodiversity of their ecosystem. Unlike the indigenous species, the exotic species is not naturally existent in the area : it has been introduced.
This introduction is due to the action, on purpose or not, of men : globalization of transport, exotic plants trade market…
Fragilized or artificialized ecosystems also foster the development of invasive species : a healthy ecosystem is able, generally speaking, to regulate their harmful effect, whereas in a poor or fragilized ecosystem, the invasive species develops more easily and threatens the indigenous species. Islands are particularly endangered par invasive species, because of the relative isolation of their ecosystem ; it is also the case for artificialized areas like canals.
Did you know?
Some species can even become invasive in their native habitat !
This phenomenon is caused by human activity, which modified the balance of the habitat. For instance, wild boars now have a facilitated access to food thanks to agriculture, and their population is not naturally regulated anymore because men eradicated their predators (wolves, bears). Therefore, they become dangerous for their own environment because of their increased number.
Competing for space
The grey squirrel, introduced in Europe from America at the beginning of the XXth century, reduced the living area of the red squirrel, which could lead to its extinction.
Predating indigenous species
The New Guinea flatworm, introduced in Europe and America, feeds on snails and earthworms. But these animals are necessary to renew soils.
The caulerpa taxifolia, (also known as « the killing seaweed »), originally from Australia and eastern Africa, colonizes larger and larger parts of the Mediteranean Sea. However, it can’t be eaten by herbivores, because it is toxic.
Farmed red-legged partridges were released in forests in order to be hunted. But it led to hybridation with wild partridges, which are now endangered.