The Concept of Subspecies
Subspecies is the lowest rank under the biological classification just after species and it refers to the populations that are distinguishable on the basis of size, shape, and other physical characteristics and are capable of interbreeding.
The concept of species and subspecies was first given by Darwin in his book ‘Origin of Species’ but it does not describe the process of why and how speciation Ernst Mayr an American Evolutionary biologist has given the concept of subspecies and explained how and why species and subspecies originates.
According to Merriam- Webster dictionary “Subspecies is a category in biological classification that ranks immediately below a species and designates a population of a particular geographic region genetically distinguishable from other such populations of the same species and capable of interbreeding successfully with them where its range overlaps theirs”.
Subspecies of Tigers
Tiger is one of the most adoptable cats and is found in different types of habitats. Tiger habitat ranges from semi-arid zones of North Western India to snow-clad mountains of Eastern Himalayas, from Tropical Evergreen forests of South and South East Asia to dry deciduous forests of Central India, and from Mangrove forests of Sundarbans to the Siberian boreal & Taiga forests. This adaptation helped the tigers to distribute widely in most of the available habitats.
During the glacial period when land connections were exposed, tigers and other animals have taken advantage and colonized different areas. During this period forested areas were shrunk due to the cold climate and grassland expanded. The glacial period ends with an approaching warmer period when the sea level rises and all the land connection gets submerged, which resulted in the species being isolated from other population which during the course of time has evolved with certain unique features suitable to their environment. This has created a concept of subspecies in tigers.
Read more about the different subspecies of tigers.
Two Subspecies theory
In 2015 a study done by scientists and researchers from Leibniz Institute for Zoo and wildlife research has found that only two subspecies of tigers exists against the earlier belief of 6 extant subspecies. They have investigated the differences in these subspecies by comparing skull measurements, fur pattern genetics and ecology.
They have collected the data from various sources which includes museum specimens of extinct subspecies and already published data. When they have analyzed the data on different traits they found little evidence to support the theory of nine subspecies.
On the basis of their findings they have proposed two subspecies theory with the given details:
- Sunda Tigers: This subspecies includes Sumatran Tigers, and extinct subspecies of Bali and Javan Tigers.
- Continental Tigers: Except the subspecies included in Sunda tigers all other subspecies are comes under this subspecies. Royal Bengal tiger also comes under this category.
Nine subspecies theory
Traditionally it was believed that eight species of tigers survived once on the earth. Later in a 2004 study, it was found that Indo-Chinese tigers living on Malayan Peninsula are different enough to those living in the north to be a ninth subspecies: the Malayan Tiger. The same study has suggested that tigers have little genetic diversity but enough to differentiate them in subspecies.
As discussed above a study in 2015 suggested that there are only two subspecies of tigers exist which was accepted by some and rejected by others, later researchers from China and USA in 2018 have proved through molecular genetic analysis that there are six living and three extinct subspecies of tigers. They have done whole genome sequencing of 32 voucher specimens which reveals six clades of tigers.
Though ecological and morphological analysis reveals little distinction, the identification of different extant and extinct subspecies of tigers requires genomic analysis. The research team has identified multiple genomic regions that show the adoptive divergence of the subspecies.
Like all other animals tigers also follow Bergmann’s rule which states that animals within the same species tend to be larger in colder environments and smaller in warm regions of the tropics. The Amur tigers are the largest among subspecies because they live in colder environments and Sumatran is the smallest because they live in tropical hot and humid environments. The following are the subspecies of tigers recognized by the molecular genetic study:
Extant Subspecies
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Bengal Tiger (Panthera tigris tigris)
Bengal Tiger is a type specimen for various subspecies, they are the most studied and most numerous subspecies. They are found in Indian Subcontinent (India, Nepal, Bhutan, and Bangladesh).
According to the latest census, their number in India is 3,167, the highest among all other subspecies. They represent more than 70% wild tiger population of the world. Though they are doing much better than other subspecies but still IUCN has given them ‘Endangered’ status.
In terms of size, they come second to the Amur Tiger and only a slight difference between both subspecies has been found except for the thick furs in Amur Tigers. They are highly adaptable and found in different habit types like tropical deciduous forests, mangrove forests, temperate forests, etc.
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Amur Tigers (Panthera tigris altaica)
Amur Tigers are also known as Siberian, Manchurian, and Ussurian tigers. They are the largest in terms of their size and body fur. The male Amur Tiger can grow up to 3.5 meters and weigh of 306 Kilograms. Females are smaller and can attain 8.5 feet in length and about 100 to 170 Kilograms in weight.
Their fur is paler in comparison to other subspecies so they can get merged easily in their habitat. Earlier they were found in an expensive range in Siberia, the Russian Far East, North East China, and Korea. Now 95% population of Amur Tigers is found in Far-Eastern Russia where the Amur River forms a border with China. That is why they are known as Amur Tigers. A small population also lives in North East China.
In the first half of the 1900s, they were relentlessly persecuted as pests by the Russian Army. After conducting a survey in 1940 Russian scientists raised an Alarm on their status which suggests only 20-30 individuals were left in the wild. In 1947 the government have taken action and this subspecies was legally protected under the stringent law. With this protection, their population has recovered which led the IUCN to downlist its status from critically endangered to endangered. Their population as per the most recent estimate is 580 individuals which is a conservation success story.
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South China Tiger (Panthera tigris amoyensis)
South China Tiger is the world’s most endangered tiger, it was found in Central and Eastern China. After more than thirty years of extensive survey, it was declared extinct in the wild. They are the most recent tiger subspecies going extinct after Javan Tigers.
They are given the status of Critically Endangered by IUCN. It is said that till 1950 there were 4,000 South China tigers roamed in the forests of China but at the same time government of China declared them as pests and was killed indiscriminately by hunters and wildlife traders.
South China Tiger is the most ancient Tiger Subspecies and it is believed that all other subspecies are descendent from it. It was most important for China as it is the only subspecies of tiger endemic to China.
The captive population of this subspecies is numbered 178 in 2018 (88 female, 89 male) distributed across 15 zoos in China and one private reserve in South Africa.
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Sumatran Tiger (Panthera tigris sumatrae)
Sumatran tigers are found in the Indonesian Island of Sumatra. They are one of the most endangered tiger subspecies in the world and hence categorized as critically endangered by IUCN red list.
The dwindling population of this subspecies is attributed to illegal hunting. The Indonesian government has imposed a strict law with tough provisions of jail and heavy fines. But still they are hunted for trophy and illegal trade despite all the conservation efforts.
They are the smallest among all the extant subspecies of tigers almost the size of an adult leopard or Jaguar. The average length of the male Sumatran Tiger from head to tail is 2.4 meters and can weigh not more than 120 kilograms, while females are average 2 meters and weigh 90 kilograms. They also have the darkest, broadest, and most closely spaced stripes. Unlike Amur tigers, they also have stripes on their forelegs.
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Indochinese Tiger (Panthera tigris corbetti)
This subspecies is named after the British Hunter Conservationist Jim Corbett. Indochinese tigers are found in Cambodia, Laos, Myanmar, and Thailand. They were also found in Vietnam, Cambodia Laos and China but functionally they are extinct in these past range countries. Thailand is the only country in their range that have viable breeding population which is as per last estimate is 189 individuals. In Myanmar there is a single population of 20 individuals remain. In 2016 they were declared extinct in Cambodia. In Myanmar they were so common that until 1931 they were considered as pest and license and reward has been given to kill them due to which thousands of individuals has been killed.
This tiger is smaller than Royal Bengal Tiger with narrower and shorter stripes but larger than the Sumatran Tigers. The males are on an average are 3 meters in length and 180 kilogram in weight, females are shorter and measure 2.4 meters and weighing approximately 115 kilograms.
Very less studies has been done on them, they live in hilly and mountainous region which makes them inaccessible for researchers and scientists.
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Malayan Tiger (Panthera tigris jacksoni)
In 2004 scientists found that Indochinese tigers living on the Malayan peninsula are different than those living in other parts and countries. Further studies have led them to identify this as a separate subspecies. Malayan tigers are the smallest continental tigers but larger than the Sumatran Tigers.
Malayan tigers were once also found in Singapore forests but they were hunted and killed by government-paid bounties when forests were cleared for plantation. The last wild tiger of Singapore was shot dead in 1930.
The subspecies name Jacksoni was given to honor Peter Jackson, former chair of the IUCN cat specialist group. They are listed as endangered in IUCN red list.
In Peninsular Malaysia and the Southern tip of Thailand, they are found in tropical and subtropical moist broadleaf forests.
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Extinct Subspecies of Tiger
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Bali Tiger (Panthera tigris balica)
Bali tigers is the first tiger subspecies to go extinct in modern history. They were hunted down by Dutch Colonial Hunters. The last Bali tiger was shot in 1937. They were last recorded in Western Bali in the late 1930s as per the IUCN.
They were the smallest tigers about the size of a leopard. Their fur was short and dark yellowish with few black stripes compared to other tigers. Some even had black spots among the stripes. The reason for their extinction is hunting, habitat loss and loss of pray base.
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Javan Tiger (Panthera tigris sondaica)
Javan Tigers inhabited the Indonesian island of Java and went extinct in the late 1970s. They were last recorded from Java’s Meru Betiri National Park in 1976 and most likely disappeared from rest of the island in 1940s. The reason for their extinction is same as Bali tiger. They were smaller on average but larger than the neighboring Bali Tigers.
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Caspian Tiger (Panthera tigris virgata)
They were found in the sparsely forested habitat and riverine corridors of west (Turkey) and South (Iran) of the Caspian Sea and west through Central Asia into the Takla Makan desert of Xinjiang, China according to IUCN. They were evolved to live near rivers and lakes on the edges of dry desert environments. They once populated the largest geographical range of any tiger subspecies.
The Caspian tiger was one of the biggest tigers ever to live which makes them the largest cat ever to roam on Earth. Caspian tigers were very similar genetically to Amur tigers. It suggested that they are developed from a common ancestor in the recent past.
The extinction of this subspecies can be attributed to the loss of pray, hunting and habitat loss.
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