SPECIES EXTINCTION

In biology and ecology, extinction is the cessation of existence of a species or group of taxa, reducing biodiversity. The moment of extinction is generally considered to be the death of the last individual of that species (although the capacity to breed and recover may have been lost before this point). Because a species' potential range may be very large, determining this moment is difficult, and is usually done retrospectively.

A species becomes extinct when the last existing member of that species dies. Extinction therefore becomes a certainty when there are no surviving individuals that are able to reproduce and create a new generation. A species may become functionally extinctcia when only a handful of individuals survive, which are unable to reproduce due to poor health, age, sparse distribution over a large range, a lack of individuals of both sexes (in sexually reproducing species), or other reasons.

There are a variety of causes that can contribute directly or indirectly to the extinction of a species or group of species. Extinction of a species may come suddenly when an otherwise healthy species is wiped out completely, as when toxic pollution renders its entire habitat unlivable; or may occur gradually over thousands or millions of years, such as when a species gradually loses out in competition for food to better adapted competitors.

Humans have been transporting animals and plants from one part of the world to another for thousands of years, sometimes deliberately and sometimes accidentally. In most cases, such introductions are unsuccessful, but when they do become established as an invasive alien species, the consequences can be catastrophic. Invasive alien species can affect native species directly by eating them, competing with them, and introducing pathogens or parasites that sicken or kill them or, indirectly, by destroying or degrading their habitat.

Credits: Documental, la 2, animales en extinción

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