Whilst there is still no news from Sumatra, Oll is hard at work looking at the Forteana of that strange island...Sumatra’s land animals have been genetically isolated since sea levels rose between 12,000 and 6,000 years ago. As a result of this the fauna of the island is quite unique with many distinct and rare subspecies being found on the island. Some species and subspecies like the Sumatran rhinoceros are, although critically endangered and very rare indeed, found on the mainland as well as Sumatra itself, but others are found just on the island, having evolved there after the island became cut off from the mainland. One of those endemic subspecies is the Sumatran tiger,
Panthera tigris sumatrae.
The Sumatran tiger is the smallest subspecies of tiger in the world, with males measuring an average of 2.4 metres in length compared to the 3.5-metre-length reported in some Siberian tigers (
Panthera tigris altaica). There are a number of reasons why a comparatively small size has proved an evolutionary advantage for the Sumatran tiger; their smaller size makes movement and hunting easier in the dense forests that formed their habitat, for one. Another reason the Sumatran tiger is smaller than that of their Siberian counterparts is that, according to Bergman’s rule, when a species is widely distributed, larger sizes will tend to be present in colder climates and smaller sizes will be seen in warmer climates. This is certainly true of tigers, which show smaller average size and weight the closer one gets to the equator. A smaller size will tend to mean a higher surface area to volume ration facilitating heat loss through the skin, which is useful in warmer climates.
The advantages to being smaller in dense forest outweigh the disadvantages but the small size of the Sumatran tiger also presents problems that they might not have to deal with were they larger like the Siberian tiger. One of these problems is, being smaller they might seem more attractive as prey themselves but due to markings mimicking the look of eyes on the back of their ears, predators approaching the tigers from behind are often fooled into thinking it is facing towards them and larger.
Another adaptation to their habitat exhibited by the Sumatran tiger subspecies is webbing between their toes, which makes them fast swimmers in comparison to most of their prey. This is particularly useful if hunting in or near water as the tigers, with their webbed feet, will easily be able to out-swim most other mammals, especially those with hooves; should their prey enter the water they will be able to catch up with it or get to the bank quicker. Should the prey be of a manageable size they may even kill it while still in the water.
Despite being very well adapted to their environment the numbers of Sumatran tigers are very low and they are a critically endangered species. Estimates of their numbers range from 500 according to a 1998 survey and 300 according to a 2008 survey. If both surveys are accurate this means that the tiger’s population has crashed by almost 50% in only 10 years, giving a very bleak outlook for the continued survival of the species. Even if the species were to recover its numbers almost half of its genetic diversity has been wiped out; that can include resistance to various diseases and amplify the instance of various genetic disorders amongst the surviving population. On the other hand, other species of big cat like cheetahs (
Acinonyx jubatus) show a very low genetic diversity thought to have been caused by similar potentially catastrophic population crashes, but their species have survived to the present day. The Sumatran tiger’s current problems have similar causes to the problems that have also caused the near extinction of the Sumatran rhinoceros (
Dicerorhinus sumatrensis): habitat destruction and poaching. Habitat destruction caused by deforestation (often by the palm oil industry) has meant that there is less food available for the tigers' regular prey and therefore in turn less prey and that there are less places to hunt or raise cubs in safety. Deforestation and human encroachment has also made it easier and more likely for humans to encounter the tigers. This can have advantages, such as when the shy animal was caught on film in the wild for the first time a few years ago, but these pale into insignificance when compared to the disadvantages.
The worst of these is that the creature becomes easier for poachers to catch. Tiger body parts are popular in Chinese medicine and fetch a high price on the black market, often being turned into other products like wine or powders, which idiots who put the rest of their countrymen to shame actually believe increase virility, prolong life or can be cures for syphilis or other STDs. Because they are harder to locate than Sumatran rhinos and have a much larger range tigers are harder to protect in nature reserves and the fact that often the whole body will be taken when a poacher murders a tiger makes it difficult to be sure of the impact of poachers on this shy animal without regular population surveys, so poaching can go unchecked.
Whilst there is still no news from Sumatra, Oll is hard at work looking at the forteana of that strange island...
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