The tiger (Panthera tigris) is the largest cat species, most recognisable for their pattern of dark vertical stripes on reddish-orange fur with a lighter underside. The largest tigers have reached a total body length of up to 3.38 m (11.1 ft) over curves and have weighed up to 388.7 kg (857 lb) in the wild. The species is classified in the genus Panthera with the lion, leopard, jaguar and snow leopard. Tigers areapex predators, primarily preying on ungulates such as deer and bovids. They are territorial and generally solitary but social animals, often requiring large contiguous areas of habitat that support their prey requirements. This, coupled with the fact that they are indigenous to some of the more densely populated places on Earth, has caused significant conflicts with humans.
Tigers once ranged widely across Asia, from Turkey in the west to the eastern coast of Russia. Over the past 100 years, they have lost 93% of their historic range, and have been extirpated from southwest and central Asia, from the islands of Java and Bali, and from large areas of Southeast and Eastern Asia. Today, they range from the Siberian taiga to open grasslands and tropical mangrove swamps. The remaining six tiger subspecies have been classified as endangered by IUCN. The global population in the wild is estimated to number between 3,062 and 3,948 individuals, down from around 100,000 at the start of the 20th century, with most remaining populations occurring in small pockets isolated from each other, of which about 2,000 exist on the Indian subcontinent.[4] A 2016 global census estimated the population of wild tigers at approximately 3,890 individuals.[5][6] Major reasons for population decline include habitat destruction, habitat fragmentation and poaching. The extent of area occupied by tigers is estimated at less than 1,184,911 km2(457,497 sq mi), a 41% decline from the area estimated in the mid-1990s. In 2016, wildlife conservation group at WWF declared that world’s count of wild tigers has risen for the first time in a century. [7]
Tigers are among the most recognisable and popular of the world’s charismatic megafauna. They have featured prominently in ancientmythology and folklore, and continue to be depicted in modern films and literature. They appear on many flags, coats of arms, and asmascots for sporting teams. The tiger is the national animal of Bangladesh, India, Malaysia and South Korea.
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Taxonomy and etymology
In 1758, Linnaeus described the tiger in his work Systema Naturae and gave it the scientific name Felis tigris.[3] In 1929, the British taxonomist Reginald Innes Pocock subordinated the species under the genus Panthera using the scientific name Panthera tigris.[8]
The word Panthera is probably of Oriental origin and retraceable to the Ancient Greek word panther, the Latin word panthera, the Old French word pantere, most likely meaning “the yellowish animal”, or from pandarah meaning whitish-yellow. The derivation from Greekpan- (“all”) and ther (“beast”) may be folk etymology.[9]
The specific epithet, tigris, as well as the common name, tiger, come from the Middle English tigre and the Old English tigras (a plural word), both used for the animal.[10] These derive from the Old French tigre, itself a derivative of the Latin word tigris and the Greek wordtigris. The original source may have been the Persian tigra meaning pointed or sharp and the Avestan tigrhi meaning an arrow, perhaps referring to the speed with which a tiger launches itself at its prey.[11]
Evolution
Tiger phylogenetic relationships
Restoration of Panthera zdanskyi, an extinct relative whose oldest remains were found in northwest China, suggesting the origins of the tiger lineage
The tiger’s closest living relatives were previously thought to be the lion, leopard and jaguar, all of which are classified under the genus Panthera. Genetic analysis indicates that the tiger and thesnow leopard diverged from the other Panthera species about 2.88 million years ago, and that both species may be more closely related to each other than to the lion, leopard and jaguar.[12][13]
The oldest remains of an extinct tiger relative, called Panthera zdanskyi or the Longdan tiger, have been found in the Gansu province of northwestern China. This species is considered to be a sister taxon to the extant tiger and lived about 2 million years ago, at the beginning of the Pleistocene. It was smaller than the modern tiger, being the size of a jaguar, and probably did not have the same coat pattern. Despite being considered more “primitive“, the Longdan tiger was functionally and possibly ecologically similar to its modern cousin. As Panthera zdanskyi lived in northwestern China, that may have been where the tiger lineage originated. Tigers grew in size, possibly in response to adaptive radiations of prey species like deerand bovids which may have occurred in Southeast Asia during the early Pleistocene.[14]
The earliest fossils of true tigers are from Java, and are between 1.6 and 1.8 million years old. Distinct fossils are known from the early and middle Pleistocene deposits in China and Sumatra. A subspecies called the Trinil tiger (Panthera tigris trinilensis) lived about 1.2 million years ago and is known from fossils found at Trinil in Java.[15]
Tigers first reached India and northern Asia in the late Pleistocene, reaching eastern Beringia (but not the American Continent), Japan, andSakhalin. Fossils found in Japan indicate the local tigers were, like the surviving island subspecies, smaller than the mainland forms, an example of insular dwarfism. Until the Holocene, tigers also lived in Borneo, as well as on the island of Palawan in the Philippines.[16]
The tiger’s full genome sequence was published in 2013. It and other cat genomes were found to have similar repeat composition and an appreciably conserved synteny.[17]
Subspecies
There are 10 recognised tiger subspecies. One, the Trinil, became extinct in prehistoric times. The remaining subspecies all survived at least into the mid-20th century; three of these are also considered extinct. Their historical range in Bangladesh, Siberia, Iran, Afghanistan, India, China, and southeast Asia, including three Indonesian islands, is severely diminished today. The modern subspecies are:
| Subspecies | Description | Image |
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| Bengal tiger(P. t. tigris), also called the Indian tiger | Lives in India, Nepal, Bhutan, and Bangladesh, and is the most common subspecies. In 2011, the total adult population was estimated at 1,520–1,909 in India, 440 in Bangladesh, 155 in Nepal and 75 in Bhutan.[18] In 2014, the population in India was estimated at 2,226,[19]163–253 in Nepal and 103 in Bhutan as of 2015.[20] It lives in alluvial grasslands, subtropical and tropical rainforests, scrub forests, wet and dry deciduous forests, and mangroves. It is the second-largest of the surviving subspecies. Males attain a total nose-to-tail length of 270 to 310 cm (110 to 120 in) and weigh between 180 to 258 kg (397 to 569 lb), while females range from 240 to 265 cm (94 to 104 in) and 100 to 160 kg (220 to 350 lb).[21][22] In northern India and Nepal, the average is larger; males can weigh up to 235 kilograms (518 lb), while females average 140 kilograms (310 lb).[23] Coat colour varies from light yellow to reddish yellow with black stripes.[24]
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| Indochinese tiger (P. t. corbetti), also calledCorbett’stiger | Is found in Cambodia, China, Laos, Burma, Thailand, and Vietnam. In 2010 the total population was estimated at about 350 individuals.[25]Their preferred habitat is forests in mountainous or hilly regions.[21] Males average 108 inches (270 cm) in total length and weigh between 150–195 kg (331–430 lb), while females average 96 inches (240 cm) and 100–130 kg (220–290 lb).[26]
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| Malayan tiger (P. t. jacksoni) | Exclusively found in the southern part of the Malay Peninsula. Was not considered a subspecies in its own right until a 2004 genetic analysis showed that they are distinct in mtDNA and micro-satellite sequences from the Indochinese subspecies.[27] As of 2014 the total population is estimated at fewer than 500 individuals,[28] though a new report from September that year estimated it at between 250 and 340 individuals.[29] Males range in total length from 190–280 cm (75–110 in) and weigh between 47.2 to 129.1 kg (104 to 285 lb), while females range from 180–260 cm (71–102 in) and 24 to 88 kg (53 to 194 lb).[30]
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| Siberian tiger (P. t. altaica), also known as theAmur tiger | Inhabits the Amur–Ussuri region of Primorsky Krai and Khabarovsk Krai in far eastern Siberia, with the exception of a small population in Hunchun National Siberian Tiger Nature Reserve in northeastern China, near the border of North Korea.[31][32] In 2005, there were 331–393 adult and subadult Siberian tigers in the region, with a breeding adult population of about 250 individuals. As of 2015, there an estimated population of 480-540 individuals in the Russian Far East.[33][34][35] It is the largest subspecies and ranks among the largest felids ever to have existed. Males have a head and body length of between 190–230 cm (75–91 in) and weigh between 180 to 306 kg (397 to 675 lb), while females average 160–180 cm (63–71 in) and 100 to 167 kg (220 to 368 lb). Tail length is about 60–110 cm (24–43 in).[21] Compared to other subspecies, Siberian tigers have thicker coats, paler hues, and fewer stripes in dark brown instead of black.[24][36][37]
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| South China tiger (P. t. amoyensis), also known as the Amoyor Xiamen tiger | Is the most critically endangered subspecies of tiger, and one of the 10 most endangered animals in the world.[37] Despite unconfirmed reports and some evidence of footprints, there has been no confirmed wild sighting in over 25 years, leading experts to consider it “functionally extinct”, with the entire known population of roughly 65+ individuals held in captivity.[38][39] It is the second-smallest subspecies. Males range in total length from 230–260 cm (91–102 in) and weigh between 130 to 180 kg (290 to 400 lb), while females range from 220–240 cm (87–94 in) and 100 to 110 kg (220 to 240 lb). The South China tiger is considered to be the most ancient of the tiger subspecies and is distinguished by a particularly narrow skull, long muzzle nose, rhombus-like stripes and vivid orange colour.[37]
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| Sumatran tiger (P. t. sumatrae) | Found only on the island of Sumatra, and is thus the last surviving of the three Indonesian island subspecies. Listed as a distinct subspecies as of 1998, when genetic testing revealed the presence of unique genetic markers, and is critically endangered.[40] As of 2014 the wild population is estimated at between 400 and 500, seen chiefly in the island’s national parks.[41][42] It is the smallest of all living tigers. Males range in total length from 220 to 255 cm (87 to 100 in) and weigh between 100 to 140 kg (220 to 310 lb), while females range between 215 to 230 cm (85 to 91 in) and 75 to 110 kg (165 to 243 lb).[21] Their reduced size is an adaptation to the thick, dense forests and smaller prey in their native habitat. This subspecies also has the darkest coat, with more narrowly spaced stripes and a longer mane and beard.[36][37]
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| Subspecies | Description | Image |
|---|---|---|
| Bali tiger (P. t. balica) | Was limited to the Indonesian island of Bali. Had a weight of 90–100 kg (200–220 lb) in males and 65–80 kg (143–176 lb) in females.[43] Bali tigers were hunted to extinction; the last Bali tiger, an adult female, is thought to have been killed at Sumbar Kima, West Bali, on 27 September 1937, though there were unconfirmed reports that villagers found a tiger corpse in 1963.[44] The Bali tiger is reported to have had some spots in between its stripes.[37]
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| Caspian tiger (P. t. virgata), also known as the Hyrcanian tiger or Turan tiger | Was found in the sparse forest habitats and riverine corridors west and south of the Caspian Sea and east through Central Asiainto the Takla-Makan desert of Xinjiang, and had been recorded in the wild until the early 1970s.[45] The Siberian tiger is the genetically closest living relative of the Caspian tiger.[46]
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| Javan tiger (P. t. sondaica) | Was limited to the island of Java, and had been recorded until the mid-1970s.[47] Javan tigers were larger than Bali tigers; males weighed 100–141 kg (220–311 lb) and females 75–115 kg (165–254 lb).[48] After 1979, no more sightings were confirmed in the region of Mount Betiri.[49] An expedition to Mount Halimun Salak National Park in 1990 did not yield any definite, direct evidence for the continued existence of tigers.[50]
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An analysis of craniodental and pelage morphology, ecology, and molecular biology of the tiger subspecies indicates that they have many traits in common and that the genetic diversity between them is low. The authors of this analysis suggest to group the Bengal, Indochinese, Malayan, South China, and Siberian tiger subspecies to the Continental tiger Panthera tigris tigris; and the Sumatran, Javan and Bali tiger subspecies to the Sunda tiger Panthera tigris sondaica. This classification is intended to facilitate tiger conservation management, both regarding breeding programmes in zoos and future translocations in the wild.[51] The classification is criticised by several geneticists, who maintain that the currently recognised nine subspecies can be distinguished genetically.[52]
Hybrids
Lions have been known to breed with tigers (most often the Amur and Bengal subspecies) to create hybrids called ligers and tigons. Such hybrids were once commonly bred in zoos, but this is now discouraged due to the emphasis on conservation. Hybrids are still bred in private menageries and in zoos in China.[53]
The liger is a cross between a male lion and a tigress.[54] Because the lion sire passes on a growth-promoting gene, but the corresponding growth-inhibiting gene from the femaletiger is absent, ligers grow far larger than either parent. They share physical and behavioural qualities of both parent species (spots and stripes on a sandy background). Maleligers are sterile, but female ligers are often fertile. Males have about a 50% chance of having a mane, but, even if they do, their manes will be only around half the size of that of a pure lion. Ligers are typically between 10 and 12 feet in length, and can weigh between 800 and 1,000 pounds or more.[54]
The less common tigon is a cross between a lioness and a male tiger.[55] Because the male tiger does not pass on a growth-promoting gene and the lioness passes on a growth inhibiting gene, tigons are often relatively small, only weighing up to 150 kg (350 lb), which is about 10–20% smaller than lions. Like ligers, they have physical and behavioural traits from both parental species, and males are sterile. Females are sometimes fertile and have occasionally given birth to litigons when mated to a lion.[53]
Description
Though similar to a lion’s, the lower jaw structure is a reliable indicator of the species.
Tigers have muscular bodies with powerful forelimbs, large heads and long tails. The pelage is dense and heavy; colouration varies between shades of orange and brown with white ventral areas and distinctive vertical black stripes, whose patterns are unique to each individual.[21][56] Their function is likely for camouflage in vegetation such as long grass with strong vertical patterns of light and shade.[56][57] The tiger is one of only a few striped cat species; it is not known why spotted patterns and rosettes are the more common camouflage pattern among felids.[58] The tiger’s stripes are also found on the skin, so that if it were to be shaved, its distinctive coat pattern would still be visible. They have a mane-like heavy growth of fur around the neck and jaws and long whiskers, especially in males. The pupils are circular with yellow irises. The small, rounded ears have a prominent white spot on the back, surrounded by black.[21]These false “eyespots”, called ocelli, apparently play an important role in intraspecies communication.[59]
The skull is similar to that of the lion, though the frontal region is usually not as depressed or flattened, with a slightly longer postorbital region. The skull of a lion has broader nasal openings. However, due to variation in skulls of the two species, the structure of the lower jaw is a more reliable indicator of species.[60] The tiger also has fairly stout teeth; the somewhat curved canines are the longest among living felids with a crown height of up to 90 mm (3.5 in).[21]
The oldest recorded captive tiger lived for 26 years. A wild specimen, having no natural predators, could in theory live to a comparable age.[61]
Size
A Siberian tiger, one of the tallest subspecies, together with the Bengal tiger are considered the largest living felids.
Tigers are the most variable in size of all big cats, much more so than lions.[62] The Bengal and Siberian subspecies are the tallest at the shoulder and thus considered the largest living felids, ranking with the extinct Caspian tiger among the biggest that ever existed.[63] An average adult male tiger from Northern India or Siberia outweighs an average adult male lion by around 45.5 kg (100 lb).[62] Males vary in total length from 250 to 390 cm (98 to 154 in) and weigh between 90 to 306 kg (198 to 675 lb) with skull length ranging from 316 to 383 mm (12.4 to 15.1 in). Females vary in total length from 200 to 275 cm (79 to 108 in), weigh 65 to 167 kg (143 to 368 lb) with skull length ranging from 268 to 318 mm (10.6 to 12.5 in).[64] In either sex, the tail represents about 0.6 to 1.1 m (24 to 43 in) of total length.[21]
Body size of different populations seems to be correlated with climate—Bergmann’s rule—and can be explained by thermoregulation.[21] Large male Siberian tigers can reach a total length of more than 3.5 m (11.5 ft) over curves and 3.3 m (10.8 ft) between pegs, and can weigh up to 306 kg (675 lb). This is considerably larger than the weight of 75 to 140 kg (165 to 309 lb) reached by the smallest living subspecies, theSumatran tiger. At the shoulder, tigers may variously stand 0.7 to 1.22 m (2.3 to 4.0 ft) tall.[43] The current record weight in the wild was 389 kg (858 lb) for a Bengal tiger shot in 1967.[63][65]
They are a notably sexually dimorphic species, females being consistently smaller than males. The size difference between males and females is proportionally greater in the larger tiger subspecies, with males weighing up to 1.7 times more than females.[66] Males also have wider forepaw pads than females, enabling gender to be told from tracks.[66]
Colour variations
A well-known allele found only in the Bengal subspecies produces the white tiger, a colour variant first recorded in the early 19th century and found in an estimated one in 10,000 natural births. Genetically, whiteness is recessive: a cub is white only when both parents carry the allele for whiteness.[67] It is not albinism, pigment being evident in the white tiger’s stripes and in their blue eyes.[56] The causative mutation changes a single amino acid in the transporter proteinSLC45A2.[68]
White tigers are more frequently bred in captivity, where the comparatively small gene pool can lead to inbreeding. This has given white tigers a greater likelihood of being born with physical defects, such as cleft palate, scoliosis(curvature of the spine), and strabismus (squint).[67] Even apparently healthy white tigers generally do not live as long as their orange counterparts. Attempts have been made to cross white and orange tigers to remedy this, often mixing with other subspecies in the process.[69]
Another recessive gene creates the “golden” or “golden tabby” colour variation, sometimes known as “strawberry”.Golden tigers have thicker than usual light-gold fur, pale legs, and faint orange stripes. Few golden tigers are kept in captivity; they are invariably at least part Bengal. Some golden tigers carry the white tiger gene,[70] and when two such tigers are mated, they can produce some stripeless white offspring. Although a “pseudo-melanistic” effect—wide stripes that partially obscure the orange background—has been seen in some pelts, no true black tigers have been authenticated, with the possible exception of one dead specimen examined in Chittagong in 1846. These wholly or partially melanistic tigers, if they exist, are assumed to be intermittent mutations rather than a distinct species.[71][72] There are further unconfirmed reports of a “blue” or slate-coloured variant, the Maltese tiger. However, while some felids do exhibit this colouration as a solid coat, there is no known genetic configuration that would result in black stripes on a blue-gray background.[71]
Distribution and habitat
Historical distribution
In the past, tigers were found throughout Asia, from the Caucasus and the Caspian Sea to Siberia and the Indonesian islands of Java, Bali and Sumatra. Fossil remains indicate tigers were also present in Borneo and Palawan in the Philippines during the late Pleistocene andHolocene.[73][74]
During the 20th century, tigers became extinct in western Asia and were restricted to isolated pockets in the remaining parts of their range. They were extirpated on the island of Bali in the 1940s, around the Caspian Sea in the 1970s, and on Java in the 1980s. This was the result of habitat loss and the ongoing killing of tigers and tiger prey. Today, their fragmented and partly degraded range extends from Indiain the west to China and Southeast Asia. The northern limit of their range is close to the Amur River in southeastern Siberia. The only large island they still inhabit is Sumatra.[1] Since the beginning of the 20th century, tigers’ historical range has shrunk by 93%. In the decade from 1997 to 2007, the estimated area known to be occupied by tigers has declined by 41%.[2][75]
Tigers can occupy a wide range of habitat types, but will usually require sufficient cover, proximity to water, and an abundance of prey. Compared to the lion, the tiger prefers denser vegetation, for which its camouflage colouring is ideally suited, and where a single predator is not at a disadvantage compared with the multiple felines in a pride.[56] A further habitat requirement is the placement of suitably secluded den locations, which may consist of caves, large hollow trees, or dense vegetation.[61] Bengal tigers in particular live in many types of forests, including wet, evergreen, and the semievergreen of Assam and eastern Bengal; the swampy mangrove forest of the Ganges Delta; the deciduous forest of Nepal, and the thorn forests of the Western Ghats. In various parts of their range they inhabit or have inhabited additionally partially open grassland and savanna as well as taiga forests and rocky habitats.
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