Bangladesh Sundarbans won't have Bengal Tigers in 50 yrs over habitat loss

The Sundarbans in south-coastal Bangladesh is the world's largest surviving mangrove ecosystem, spanning over 6,000 sq km.

Bengal tigers could vanish from the Bangladesh Sundarbans in the next 50 years--by 2070--as a combination of climate change and rising sea levels threatens their last remaining habitats, says a new study by a team of researchers from Bangladesh and Australia, published in the journal Science of the Total Environment.

The Sundarbans in south-coastal Bangladesh is the world’s largest surviving mangrove ecosystem, spanning over 6,000 sq km, and “the last stronghold” of the Bengal tiger, a species that is particularly adapted to living in this environment. Situated on the lower Ganges-Brahmaputra delta, up to 70% of the Sundarbans area is less than one metre above sea level, meaning rising water levels pose a significant threat to the low-lying tiger habitats. Meanwhile, climate change effects such as changing weather patterns, heatwaves and extreme weather events are likely to have an even greater impact, the study says.

Using computer simulation models based on two climatic scenarios developed by the Intergovernmental Panel on Climate Change (IPCC), coupled with projected sea level rise in the area, the researchers have assessed the future suitability of the Sundarbans region for tigers.

“While this is preliminary analysis, we can conclude that the largest population of Bengal tigers is in an area where a combination of actors including climate change and human encroachment could both contribute to the decimation of habitats,” William Laurence, distinguished research professor at James Cook University and co-author of the study, told IndiaSpend.

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The global tiger population is currently estimated at just under 4,000, with an illegal trade in tiger parts, hunting and habitat loss having culled the population by 96% from 100,000 in 1990, the study says. Three of the eight sub-species of tiger have already become extinct, with the remaining five species currently either ‘endangered’ or ‘critically endangered’.

As global temperatures rise and melting polar ice raises sea levels, the influx of salinated sea water can make it harder for certain plants to grow, subsequently decreasing the availability of certain food types. The Sundarbans’ spotted-deer population, a key food source for the Bengal tiger, is likely to be affected as the tree leaves on which it feeds begin to disappear. As resources become scarce, tigers are more likely to stray into human settlements in search of food, increasing the chance of tiger-human conflict.

The loss of the world’s largest mangrove ecosystem also raises concerns for human populations and other animal species. Mangroves are an effective water regulation system, preventing shoreline erosion that also act as a shelter belt against cyclones and tsunamis. Villages surrounded by mangroves experienced less loss of life and capital during the 2004 tsunami, than those that were not, according to this 2005 Annamalai University study.

Tigers confirmed as 6 subspecies: Why it's big deal for their conservation

The lack of genetic and morphological differences between mainland tigers could allow them to be managed as single subspecies.

During my time as a zookeeper I had the privilege of working with both Sumatran and Amur tigers. If they did not both have stripes, you would think they were different species altogether.

The Sumatran tiger is the smallest alive today. At around 100kg, it’s “only” about the weight of a large adult male human. It is suited to the warm and wet forests of the Indonesian island of Sumatra, which is reflected in its smaller size and short, dark rusty orange coat which has many thin black stripes to conceal it in dense vegetation from their prey.

The Amur – or Siberian – tiger is much larger, averaging around 170kg (though there are historic reports of males clocking in at 300kg or more) and is now found mainly one corner of far-eastern Russia. It has a thicker but relatively pale coat, with sparse dark brown stripes, which enables it to survive in freezing and snowy winters.

Tiger experts have long debated what such differences mean scientifically. Should the biggest of the big cats be divided into various subspecies, or are all tigers simply “tigers”?

It’s an issue with serious implications for conservation. About 3,500 or so tigers remain in the wild, in just 7% of their former range. And if those tigers are all the same, or if even most of them are the same, then saving individual populations matters slightly less – and tigers can be moved around to assist breeding in the wild.

Traditionally, eight subspecies were considered to exist. They are the two already mentioned, plus the Bengal tiger, found mainly in India, the Indochinese, the South China tiger and then three extinct subspecies: the Bali (extinct in the 1940s) and Javan (80s), both closely related to surviving tigers on nearby Sumatra, and the Caspian tiger from Central Asia which went extinct in the 1970s.

As genetic techniques evolved, a 2004 study found there was little genetic diversity among tigers, but enough to support the separation of subspecies. It also suggested that Indochinese tigers living on the Malayan peninsular were different enough to those living further north to warrant a ninth subspecies: the Malayan tiger.

These ideas were contested by a group of researchers in 2015, who argued that the relative lack of variation among the mainland Asian subspecies and large overlaps in their shape, size and ecology meant that all tigers from India to Siberia or Thailand should be considered the same subspecies. The researchers called for just two recognised subspecies: the continental tiger, and the Sunda tiger, found on the various Indonesian islands.

However the various subspecies are classified, one of the consistent findings is that tigers follow Bergmann’s rule: a principle in zoology which states that animals within the same overall species will tend to be larger in colder environments and vice versa. The Amur tiger, for instance, benefits from the fact that larger animals are better at retaining heat as they have a smaller surface area relative to their overall mass... Read More

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