How small can a population be and still survive? © Getty Images

How small can a population be and still survive?

In 2014 the International Union for Conservation of Nature (IUCN) identified that around 4568 species are critically endangered.

Asked by: Auriol Matthews, Twickenham


We often hear of species being on the brink of extinction, with reported remaining numbers from several thousand to a few dozen. But their fate depends on whether they can be protected from three key threats. The most potent threat is environmental, such as changes in food and water supplies. The other two are disease and the emergence of a new predator. Populations below 10,000 can be quickly wiped out by such challenges.

Below a few hundred, species become vulnerable to genetic inbreeding, while species with fewer than around 50 members can be wiped out by otherwise normal blips in birth and death rates. Even then, their fate is not sealed: conservation efforts have rescued species such as the whooping crane of North America, which in the 1940s numbered fewer than 23 individuals.


Subscribe to BBC Focus magazine for fascinating new Q&As every month and follow @sciencefocusQA on Twitter for your daily dose of fun science facts.