From Wikipedia, the free encyclopedia

Functional extinction is the extinction of a species or other taxon such that:

1. it disappears from the fossil record, or historic reports of its existence cease;^[1]
2. the reduced population no longer plays a significant role in ecosystem function^[2]; or
3. the population is no longer viable. There are no individuals able to reproduce, or the small population of breeding individuals will not be able to sustain itself due to inbreeding depression and genetic drift, which leads to a loss of fitness.

In plant populations, self-incompatibility mechanisms may cause related plant specimens to be incompatible, which may lead to functional extinction if an entire population becomes self incompatible. This does not occur in larger populations.

In polygynous populations, where only a few males leave offspring, there is a much smaller reproducing population than if all viable males were considered. Furthermore, the successful males act as a genetic bottleneck, leading to more rapid genetic drift or inbreeding problems in small populations.

Under the IUCN Red List categories, a functionally extinct species that has had no recent sightings may be classified as critically endangered unless there is no reasonable doubt that the last individual has died, such as through extensive surveys. It is extinct in the wild if specimens remain in captivity but there is no reasonable doubt that the last wild specimen has died.

The Abingdon Island Tortoise (Geochelone nigra abingdonii), a subspecies of the Galápagos tortoise, has only one known surviving individual. This individual is named Lonesome George and is estimated to be 70-80 years of age (Galápagos tortoises may live to an age of 120-200 years or more), and is in good health.

The Western Black Rhinoceros (Diceros bicornis longipes) was tentatively declared as extinct by the World Conservation Union in July 2006 ^[3], after researchers failed to find the animal in its last known habitat. If any animals remain, they would be considered functionally extinct.

The Baiji (Lipotes vexillifer) was a freshwater dolphin found only in the Yangtze River in China. Although efforts were made to conserve the species, the population declined drastically in recent decades. It was declared "functionally extinct" after an expedition in late 2006 failed to find any in the river,^[4] the first extinction of a large mammal species in recent decades.

• Conservation genetics
• Mutational meltdown
• Small population size
• Extinction Vortex