The term big cat— which is not a biological classification — is used informally to distinguish the larger felid species from smaller ones. One definition of "big cat" includes the four members of the genus Panthera: the tiger, lion, jaguar, and leopard. Members of this genus are the only cats able to roar. A more expansive definition of "big cat" also includes the cougar, cheetah, snow leopard, and clouded leopard.
Despite enormous differences in size, the various species of cat are quite similar in both structure and behavior, with the exception of the cheetah, which is significantly different from any of the big or small cats. All cats are carnivores and efficient apex predators. Their range includes the Americas, Africa, Asia, and Europe.
The Sumatran tiger (Panthera tigris sumatrae) is a rare tiger subspecies that inhabits the Indonesian island of Sumatra. It was classified as critically endangered by IUCN in 2008 as the population is projected to be 441 to 679 individuals, with no subpopulation having an effective population size larger than 50 individuals, with a declining trend.
The Sumatran tiger is the only surviving member of the Sunda Islands group of tigers that included the now extinct Bali tiger and Javan tiger. Sequences from complete mitochondrial genes of 34 tigers support the hypothesis that Sumatran tigers are diagnostically distinct from mainland populations.