Invasive species
A species moved by people to a place where it does not naturally live, which then spreads and causes harm.
People constantly move plants and animals around the world, on purpose or by accident. Most of these non-native species cause no trouble, and many, such as tomatoes or farm cattle in the Americas, are useful. An invasive species is defined by two things together: it is not native to the ecosystem, and its arrival causes, or is likely to cause, harm to the environment, the economy or human health.
Invaders often succeed because they leave their natural checks behind. In a new land there may be no predators, parasites or competitors adapted to them, and plenty of food. With nothing holding them back, their numbers can grow exponentially. Sixty European starlings released in New York's Central Park in 1890 became more than 200 million across North America, where they compete with native birds such as bluebirds and woodpeckers for nesting holes. Rabbits in Australia and hippos in Colombia have followed similar paths.
The harm takes many forms: eating or outcompeting native species, spreading disease, damaging crops or changing whole habitats. Island species, which evolved without certain predators, are especially vulnerable.
Control is hardest once a species is established, so prevention and early detection matter most. Bringing in another species to control an invader can backfire too, if the newcomer finds easier prey.
A common misconception is that every introduced species is invasive. The label applies only when an introduction does harm.
Coming up in future stories
- Pablo Escobar's Hippos Are Taking Over Colombia 1980s–today · Magdalena River valley, Colombia