There are about 500 Amur tigers currently surviving in the wild, but the effective population accounts for genetic diversity. BBC reports that the tiger has a very low diversity, which means that any disease or rare genetic disorders will probably be passed on to the next generation. A more diverse genetic population would increase the tiger's chance of survival -- it would be able to "cancel out" diseases and disorders with healthy genes.
The Amur tiger is the largest cat in the world. It once lived across China, Korea, and Russia, until the early 20th Century, when human settlements, habitat loss, and poaching drove the cats to near extinction. By the 1940's, less than 30 individual tigers survived in the wild -- this has now led to a "genetic bottleneck," destroying the Amur tiger gene pool. The results of this are seen today in the tiger's lack of genetic diversity.
Not just Amur tigers are at risk of extinction. The World Wildlife Fund reports that climate change may be shrinking tigers' habitat by 96%. Bengal tigers are shrinking in size due to stress over environmental changes. The WWF goes so far as to state that if no action is taken, tigers may become extinct in the next 12 years.
This past November, a summit was held focused on saving tigers from extinction. The summit's biggest news? It was probably that Leonardo DiCaprio survived a plane accident and still managed to attend. But also at the summit, countries agreed to double the tiger population by 2022 and crack down on poaching and illegal trade of tiger parts. It is an uphill battle, but one worth fighting.