8.1: What is Extinction?
The term “extinct” has several nuances in conservation biology, and its meaning can vary somewhat depending on the context:
Over ninety-nine percent of recent extinctions have been caused by human activities.
- A species is globally extinct when no individuals of that species remains alive anywhere in the world. The bluebuck (Hippotragus leucophaeus, EX) has been globally Extinct since the last individual was shot around 1800 (Kerley et al., 2009).
- Four (possibly seven) species of cycad (Encephalartos spp.)—ancient seed plants that were dominant in the age of the dinosaurs—are currently considered extinct in the wild; in other words, they exist only in cultivation; in captivity; or another human-managed situation (IUCN, 2019).
- A species is locally extinct, also called extirpated, when it is extinct in a part of its historic range but can still be found elsewhere in the world. Cheetahs (Acinonyx jubatus, VU) once roamed throughout much of Africa, but are now extirpated in over 90% of their historical range (Durant et al., 2017).
- A species is ecologically extinct (also called functionally extinct) if it persists at such low numbers that its role in an ecosystem is negligible. Africa’s vultures are ecologically extinct over much of their range and thus unable to remove diseased carcasses from the environment, posing both an ecological and socio-economic hazard (see Box 4.4).