The Bali Tiger (Panthera Tigris Balica) Now Extinct

On the brink

The Amur, or Siberian, tiger once lived across a wide geographical area, reaching from northern China, the Korean Peninsula, to the southern regions of eastern Russia. Expanding human settlements in the early 20th century led to hunting and habitat loss, and to the near extinction of this largest of the tiger subspecies (and therefore the largest big cat), with a 90% reduction in population numbers from across its range. By the 1940s between only 20 and 30 individuals survived – this extreme reduction in numbers led to a genetic ‘bottleneck’, when the gene pool of the tiger was severely reduced (i.e. the diversity of alleles was reduced as the number of tigers and the genetic diversity they represented was decimated).

A recent report has suggested that the effective population size of the Amur tiger is now fewer than 14 individuals. Although approximately 500 Amur tigers survive in the wild, the genetic diversity these represent is therefore only equivalent to a handful of tigers. Very low genetic (i.e. allele) diversity (see textbook page 176) means that the remaining populations are vulnerable to diseases or rare genetic disorders, and a reduced likelihood that the subspecies will survive into the future. Scientists from Russia, Spain and Germany examined DNA samples from 15 wild Amur tigers – their results suggested a relatively recent genetic bottleneck, which the wild populations have not recovered from. The subspecies is therefore on the brink of extinction.

Tiger subspecies

Tigers (Panthera tigris) are divided into subspecies depending on geographical region. A subspecies is a sub-division of a species whereby different subspecies can in theory breed together to produce fertile offspring (as opposed to different species which cannot do this). There were once eight subspecies, all native to Asia:

· The Bali tiger (Panthera tigris balica) – now extinct

· The Bengal or Indian tiger (Panthera tigris tigris)

· The Caspian tiger (Panthera tigris virgata) – now extinct

· The Indo-Chinese tiger (Panthera tigris corbetti)

· The Javan tiger (Panthera tigris sondaica) – now extinct

· The Siberian or Amur tiger (Panthera tigris altaica)

· The South China or Amoy tiger (Panthera tigris amoyensis)

· The Sumatran tiger (Panthera tigris sumatrae).

For more information on each of these subspecies see the Tiger Foundation website.

The extinction of the Bali, Caspian and Javan tigers have all occurred in the last 60 years, through hunting, competition for food with humans, illegal trade, habitat loss and fragmentation.

In the early part of the 20th century as many as 100,000 tigers roamed the diverse habitats of Asia, from forests and swamps to open tundra. Now, overall, there may be as few as 3,200 tigers left in the wild, with all subspecies threatened with extinction.

Virtually all countries which contain tigers have laws in place to protect them, although enforcement and success varies from country to country. One of the main threats to tigers in the wild is the trade in body parts – e.g. for medicinal purposes in East Asian countries, and the illegal trade in skins, claws and teeth. The trade in tigers and their parts is prohibited from commercial international trade by the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), an international treaty that includes over 160 member countries (see textbook page 211).

For more information on the conservation status (textbook page 194) for the Amur tiger see the IUCN Redlist status.

A new subspecies?

Analysis of mitochondrial DNA from tigers across Asia shows that all tigers share a common ancestor that lived between 72,000 and 108,000 years ago. Geographical separation and diversity of habitats led to tigers evolving into the eight known subspecies. Adaptations of each subspecies, e.g. geographical, location, size, and stripe patterns, relate to their distinct habitat relative to the other subspecies. Even though any subspecies can in theory interbreed with any other, spatial separation means that the inability of different subspecies to encounter each other makes hybrid populations difficult to realize.

A recent report also used tiger DNA from throughout Asia to show that traditional subspecies groupings are reflected by genetic patterns. The only discrepancy was found in Malaysian tigers which are grouped in the subspecies Panthera tigris corbetti. The difference in genetic makeup led scientists to propose a new subspecies – Panthera tigris jacksoni, named after tiger conservationist Peter Jackson. Whilst not actually increasing the number of tigers in the wild, this new discovery does highlight how research can further broaden our knowledge of biodiversity and how best to conserve it.

Discussion points

1 How could the genetic techniques discussed in this worksheet be used to help conserve tigers?

2 What does the discovery of a new tiger subspecies tell us about tiger conservation?

3 The different groups of tigers are not different species, but subspecies of the same species. If all subspecies can in theory interbreed, does it matter if one subspecies is lost?

Suggested answers

1 Genetic techniques could be used to trace the origins of tiger parts confiscated from the black market. Tiger parts could be not only traced back to specific subspecies, but also to specific populations.

2 Whereas before the populations of Malaysian tigers would have been seen as a subpopulation of the Indochinese tiger, now they must be seen as a subspecies in their own right. There is a need to conserve the new distinct subspecies – through habitat protection and strict enforcement of conservation laws.

3 Each subspecies has distinct features such as body size and stripe pattern, and these adaptations help the various groups to survive in their different habitats. Although conservation tends to focus on the conservation of individual species, the evolution of subspecies over long periods of time makes these subspecies unique and irreplaceable, and therefore equally worthy of conservation.