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Tiger Subspecies


How many tiger subspecies

Extracts from the outstanding book:
Tiger - The Ultimate Guide by Valmik Thapar
CDS Books, 2004, p 17 - 21

Andrew Kitchener, Curator of Mammals and Birds at the National Museum of Scotland, conducted recent research that has led to the reclassification of tiger subspecies. He is also involved in long-term research into the effects of captivity on the morphology of cats and other mammals. He is a member of the Cat Specialist Group of IUCN, the World Conservation Union.

TIGER SUBSPECIES

  • Asian Panthera tigris tigris
    Mainland Asia, from India through Indochina, China and as far north as the Russian Far East

  • Sunda Island Panthera tigris sondaica
    Sumatra, Java, Bali, Borneo

  • Caspian Panthera tigris virgata
    Western Asia

Tiger Subspecies

"Within any given subspecies, there is variation in size and coloring from individual to individual, and there is often overlap in morphology between subspecies, but the tiger has adapted to cope with the different habitats, climates and available prey. The most northerly animals are generally larger, paler, and have thick, shaggy coats to cope with the cold, while the southern animals, which live in dense jungle and intense heat, are smaller, darker, and have shorter fur.

Until recently, tigers were divided into eight subspecies, often with country-specific names. Andrew Kitchener pioneered the research that led to the reduction in the number of tiger subspecies from eight to three.

Many animals have very wide geographical distributions. Nor surprisingly, as climate and habitats vary throughout their ranges, the local populations of a species may express this variation in several ways. Sometimes a species' morphology changes gradually over its geographic distribution so that at the extremes of their range animals may look completely different. This is known as a cline, and even though individuals on the opposite ends of a cline may look very different, it is inappropriate to regard them as belonging to different subspecies. There is always gene flow throughout the geographic range, albeit tempered by natural selection for particular morphotypes of perhaps reflecting a pattern of broad hybridization between two populations that differentiated previously in isolation. Sometimes local populations are separated from one another by geographical barriers, such as a river or a mountain range, and they differ in their appearance such that at least 75 percent of one population can be distinguished from 100 percent of the other. In such a case, it is possible to recognize two distinct subspecies or geographical races, which can be given different names. Finally, in many cases, local populations of morphologically different animals may meet but have a narrow hybrid zone between the two, where animals of mixed appearance occur. Therefore. there is always some limited gene flow between most subspecies. Again, these can be classified as separate subspecies if they conform to the 75 percent rule. In these last two cases, although local populations have been isolated or may continue to be isolated from one another, there has been insufficient differentiation between the populations for a new species to have evolved. However, reality is not that simple.

Although each animal species and subspecies has its own scientific name, science was often not involved in determining their distinctiveness. Many scientific names date back to between the late eighteen and early twentieth centuries and are often based of a single or a few specimens. For example, Coenraad Temminck described the Amur and Javan tigers as distinct species in 1844, based on the length of the fur on a handful of specimens. Of course, he could not have known how tigers varied in between (or even if there were any), as no samples were available to him. However, the two tigers he had from the extremes of their geographical range were so different that he decided they must be different species.

Despite the tens, if not hundreds, of thousands of tigers that have been killed during the last two hundred years, sadly very few are preserved in the world's natural-history museums. This means that some local populations of tigers are barely available for mammalogists to study - for example, there are fewer than ten Bali and possibly only thirty to forty Javan tigers. Moreover, we do not have a good geographical spread of specimens, so that it may be difficult to decide where one supposed tiger subspecies ends and another begins. In the north of China, there is even a historical gap in the tiger's distribution between the so-called South China and Amur tigers, which probably reflects a local extinction caused by the early development of civilization in this region and its demand for tigers for use in traditional Chinese medicine.

By applying modern molecular and morphological studies to the specimens we have available, it is possible to gain some insight into the variation throughout the tiger's range. A preliminary morphological study suggested that the ground color of the fur and the number of flank stripes were more variable within supposed subspecies than between them.  There was also a clinal variation in the size of the skull in male tigers, with those of northern tigers in Russia and India the largest and those of the equator in Sumatra the smallest. Interestingly, male Javan tigers were significantly bigger that Sumatran males; this size variation probably reflects either the effects of temperature on body size (i.e., Bergmann's rule, where bigger bodies retain their heat better than smaller ones and so are found further north where it is cooler, and vice versa) or the productivity of the environment, allowing for different potentials for body growth or adaption to different-sized prey. Females on the mainland did not vary in size, although those of the Sunda islands (which include Sumatra and Java) were smaller. A molecular study also suggested little difference between supposed tiger subspecies, although a later study suggested that Sumatran tigers should be recognized as a distinct species; this study, however, relied heavily on zoo-bred tigers, which were closely related to one another and likely to be genetically similar.

The problem with all modern studies of tiger taxonomy is that the sample sizes are likely to be small and do not reflect the former distribution of the species, so it may be difficult to arrive at unambiguous conclusions. Therefore, it may be more appropriate to carry out biogeographical studies, which provide insight into how a species was distributed before human interference and how this has changed over time as climate and habitats varied, as in the ice ages. By correlating known tiger distribution records with environmental factors that are thought to be important to tigers, such as habitat, precipitation, snow depth, and temperature, it is possible to create a model of the tiger's original distribution. This indicates that all mainland populations were once contiguous with one another during warm climatic periods, such as the one we are in now. Looking back in time to the coldest period of the last ice age, about twenty thousand years ago, we see that tigers were pushed south by colder global temperatures and a southward shift in their key habitats, but again mainland populations were contiguous, except for the Caspian tiger, which was isolated in perhaps two areas. The ice ages resulted in a fall in sea levels, which allowed mainland and Sunda Island tigers to meet each other, encouraging gene flow between populations. In theory, Sumatran tigers ought to be hybrids between the mainland and Sunda Island forms, except that a volcano in northern Sumatra intervened seventy thousand years ago (which is another story). So whether the world is hot or cold, there has always been some potential for considerable gene flow between so-called tiger subspecies. However, Caspian and Sunda Island tigers did experience periods of isolation during the ninety or so glacial cycles (as these climatic oscillations are known) in the last two million years, and they are morphologically distinct enough to be recognized as subspecies. Some we can conclude that it is most likely that there were originally three tiger subspecies: The Asian tiger, Panthera tigris tigris, which occurred from India through Indochina and China as far north as the Russian Far East; the Sundra Island tiger, Panthera tigris sondaica, which was originally found on Sumatra, Java, Bali and Borneo; and the Caspian tiger, Panthera tigris virgata, which occurred in western Asia. However, this is unlikely to be the last word of the subject, as new methods and approaches are applied to the little we have left of living and museum tigers".

Extinct Tigers

"The world's current total population of tigers represents five of the original eight subspecies into which the tiger was divided: The Amur (Panthera tigris altaica), the Bengal (Panthera tigris tigris), the Indo-Chinese (Panthera tigris corbetti), the South China (Panthera tigris amoyensis) and the Sumatran (Panthera tigris sumatrae) tigers. The first four are now classified as the Asian tiger (Panthera tigris tigris), the last as the Sunda Island tiger (Panthera tigris sondaica). In fact, no South China tigers have been seen in the wild since the 1980's, although there are records of pugmarks and of prey killed by tigers. They may already be extinct, or a few may still be roaming the forests.

Of the original eight subspecies, at least three are now extinct. Little is known of these populations beyond a handful of rare photographs and museum specimens left in existence today. The Caspian, also known locally as the Hyrcanian of Turan tiger, once roamed across Turkey, Iran, Iraq, Afghanistan, Mongolia, and the central Asiatic area of Russia. Much of this habitat was quite arid and therefore unique to this tiger subspecies. The Caspian also differed from other tigers in that it followed prey, such as boars, on their migrations instead of holding territories all year around as the other tigers do. (Having said this, there is some evidence that some Amur tigers also followed prey migrations, until these were disrupted by over hunting.) The demise of the Caspian tigers began in the early twentieth century, when Russian government ordered its army to kill them in order to free up land for cultivation. The soldiers soon pushed the last remaining tigers into the mountain forests, where they found life more difficult. The last certain sighting of a Caspian tiger was in the 1950'. Although it is now extinct, it is still regarded as one of the three subspecies - the West Asian tiger - according to the new classification.

The Balinese tiger, from the island of Bali in Indonesia, was the smallest subspecies, being only half the size of the Amur or Siberian tiger. It was dark with many thin stripes, much like the Sumatran and Javan tigers. As it was confined to a tiny island and suffered from speedily increasing human populations, the Balinese tiger was the first to go extinct. It had vanished by the early 1930's.

The JAvan tiger was, as the name suggests, found solely on the island of Java, which at 132 000 square kilometers (51 500 square miles) is just over one quarter the size of Sumatra. The Javan looked much like the Sundra Island tiger of today, with thin dark stripes, which were often double-looped. Another distinctive feature was its long cheek whiskers. Until the early nineteenth century, Javan tigers were common, but like the Caspian they were exterminated as people continued to expand their agricultural lands. As Java became exceptionally densely populated, the Javan tiger, not surprisingly, became the most recent extinction, sometime in the 1970's. Both the Javan and the Balinese tigers are regarded as a part of the Sunda Island subspecies in the new classification.

There are sporadic reports of all three extinct tigers being spotted in the wild, but none has been professionally validated or backed up with photographic or other hard evidence. It is assumed that most of these possible sightings were of leopards or other big cats".

Tigers Today

Extracts from the outstanding book:
Tiger - The Ultimate Guide by Valmik Thapar
CDS Books, 2004, p 17

"Today there are an estimated five thousand to seven thousand tigers living in the wild, spanning eighteen countries, from the snowy Russian Far East to the sweltering dense jungles of Sumatra. Tigers are incredibly versatile animals, living in temperatures that range from -33°C (-28°F) in the northern extreme of their range to 50°C (122°F) in the southern parts, and altitudes ranging from sea level to more than three thousand meters (ten thousand feet). Not only do temperatures and altitude vary greatly, so, of course, does vegetation, from tropical evergreen and deciduous forests of southern Asia to the coniferous, scrub oak, and birch woodlands of Siberia. Tigers also thrive in the mangrove swamps of the Sundarbans, the dry thorn forests of northwestern India, and the tall grass jungles at the foot of the Himalayas. They need only dense vegetative cover, sufficient large ungulate prey, and access to water to survive."

 

 

 

 

 

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