Fewer tiger subspecies, better protection?

The compilation and detailed analysis of the most comprehensive dataset for tigers ever assembled allowed scientists from the German Leibniz Institute for Zoo and Wildlife Research (IZW), National Museums Scotland, the Selandia College in Denmark and the Natural History Museum of Denmark in Copenhagen to carry out a critical evaluation of the nine putative tiger subspecies. They found that most of these subspecies were much more similar to each other than previously known. Only two tiger subspecies could be clearly distinguished: The "Sunda tiger" (Panthera tigris sondaica), formerly from Sumatra, Java and Bali and the "Continental tiger" (Panthera tigris tigris) from mainland Asia. From the perspective of conservation, the northern population of the "Continental tiger" (Amur tiger) should be treated as a distinct conservation management unit from the southern populations, since it is adapted to different environmental conditions.

For the first time multiple trait datasets of the six living and three extinct tiger subspecies described so far were compared. The morphology of more than 200 tiger skulls as well as the coloration and stripe patterns of more than 100 tiger skins were compared with molecular genetic data and ecological and life history traits. The results did not support the distinction of nine subspecies previously described for tigers. Only the Sunda tiger from the islands of Sumatra, Java and Bali could be clearly and unambiguously distinguished from populations of the Continental tiger. These detailed analyses also lend further support to the idea that there was a massive population decline of tigers after the super-eruption of the Toba volcano on Sumatra about 73,000 years ago. Tigers may have only survived in a single refugium in South China, from where all modern tigers then originated.

Worldwide there is significantly more concern about and money spent on the conservation of tigers than on any other individual wildlife species. However, fewer than 4,000 tigers roam around the forests of Asia -- a historically low number. For the tiger to survive at all, these small and shrinking populations require active conservation management. The discovery that only two tiger subspecies exist paves the way for new conservation management options in that global protection efforts can now be implemented more flexibly and effectively.

"A classification into too many subspecies -- with weak or even no scientific support -- reduces the scope of action for breeding or rehabilitation programmes. For example, tiger populations in South China and Indochina have been reduced to such low numbers that -- if each continue to be classified as separate subspecies -- they would likely face extinction," explained Dr Andreas Wilting from the IZW, the leader of the study. The new tiger classification allows for the combined conservation management of these populations and the Malaysian and Indian tiger, as all four populations from the southern part of continental Asia can now be managed as a single conservation unit. "The results of our collaborative research offer an exciting, pragmatic and more flexible approach to tiger conservation. Now we can plan the restoration of wild tiger populations with confidence, knowing that there is a sound scientific underpinning to tiger taxonomy," says Andrew Kitchener from National Museums Scotland.

The main goal of worldwide conservation efforts is to double the tiger populations by 2022. For this purpose, all remaining individuals are essential for the long-term survival of the tiger. The resulting high genetic diversity will ensure that tigers have sufficient adaptability to cope with future environmental changes and the challenges of new pathogens. The new study provides the scientific basis for a practical and effective tiger recovery.

The Leibniz Institute for Zoo and Wildlife Research (IZW) investigates the vitality and adaptability of wildlife populations in mammalian and avian species of outstanding ecological interest that face anthropogenic challenges. It studies the adaptive value of traits in the life cycle of wildlife, wildlife diseases and clarifies the biological basis and development of methods for the protection of threatened species. Such knowledge is a precondition for a scientifically based approach to conservation and for the development of concepts for the ecologically sustainable use of natural resources.