What are introduced species? How are they a threat to biodiversity?
Answers
Invasive species cause more damage than some pollutants. Almost half of the native species in America areendangered because of invasive species. Compared to other threats to biodiversity, invasive introduced species rank second only to habitatdestruction, such as forest clearing.
An introduced species (alien species, exotic species, non-indigenous species, or non-native species) is a species living outside its native distributional range, but which has arrived there by human activity, either deliberate or accidental. Non-native species can have various effects on the local ecosystem.
Introduced species can devastate populations by disrupting the food chain, predator-prey dynamics and by outcompeting native species. They are particularly devastating on islands as islands are often home to ground dwelling birds due to the lack of mammalian predators. For example, when humans have moved to islands they often bring cats for companionship, however the ground dwelling birds will not have evolved to cope with mammalian predators and so may go extinct.
Grey squirrels in the UK are a well known example, they were introduced and are more resilient than the native red squirrels. Red Squirrel populations have declined rapidly as grey squirrels have outcompeted them for resources.
Introduced species are not always animals, they can be plants too. In the 19th Century prickly pears (a species of cactus) were introduced to Tenerife for agriculture and they are very resilient plants that can grow in all manner of conditions. The plants grew abundantly and use up the natural resources needed by the native plants.