The Last Siberian Tigers

Another day brings another fascinating report from BBC Earth, but this one has absolutely gut-wrenching news about the future of Siberian tigers:

Researchers have estimated that the effective population size of the Amur(Siberian) tiger has now dropped to just 35.

You may remember that we talked about effective population size in regards to genetic bottlenecks and the endangered cheetah a few months ago - the effective population size of a population is the theoretical number of individuals that it would take to represent all the genetic possibilities left in a species.

This is used as an indicator of the genetic diversity and health of a population, and is crucial in determining the vulnerability of a population, since groups of animals that have very similar genes are susceptible to catastrophic disease outbreaks and the damages of inbreeding.

In the case of the Amur tiger, this is readily apparent - while it would take just 35 tigers to represent the genes left in the population, there are approximately 500 tigers left in the wild, with nearly that many still living in zoos.

That’s shocking - even in other endangered species, the ratio is often about 1 to 10. The fact that the Siberian tiger’s genetic diversity has dropped below that is a sobering sign that these tigers are extremely vulnerable, and that their future is very bleak.

However, it gets even worse: the breeding population left in the wild seems to be naturally split into two distinct geographic regions, meaning that there is an even smaller number of genes being shared.

“In actuality, it seems that Amur tigers are residing in two, fairly independent populations on either side of the development corridor between Vladivostok and Ussurisk, further lowering the effective size for each from 26 to 28 for Sikhote-Alin and 2.8 to 11 for Southwest Primorye.”

If action is not taken, and quickly, it is hard to imagine that this population will be able to remain stable for very long, and is a tragic reminder of the lasting impacts of overhunting and environmental damage.