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Connected forest corridors is key to save tigers, says study

Isolation could drive tigers to extinction by 2100

There was once a time when tigers roamed the expanse of Asia--from Turkey in the west to the eastern coast of Russia, featuring in many legends and folklores. They once stood for royalty and prosperity. Fast forward to today, these magnificent cats have dwindled in numbers and have lost 93% of what once used to be their home, over the last century alone. While 5,000 to 7,000 tigers roamed the wild in 1998, they are reduced to just about 3500 individuals -- a 50% decline in last three decades! Unsurprisingly, tigers are now an endangered species on the International Union for Conservation of Nature (IUCN) Red List. In a recent study by researchers at the National Center for Biological Sciences, Wildlife Conservation Trust, FERAL and University of Montana, have examined genetic diversity of tigers in India to identify the importance of connected forest corridors to future populations and minimize their risk of extinction in the coming century.

India was once home to a sprawling tiger population. By the end of 19th century, between 50,000 to a lakh tigers were thought to have populated the subcontinent. Even today, the country is home to nearly 65% of the world’s wild tigers. India has identified priority areas called Tiger Conservation Landscapes (TCLs) in historical tiger ranges to save what is left. The TCLs are 40 in number, vary in size and each one is big enough to conserve at least five tigers. However, tigers cross vast landscapes, and about 35% of India’s tigers are estimated to be living outside these protected areas. Since most of these protected areas are sandwiched between dense human settlements, agricultural lands and highways with high traffic density, they are increasingly being disconnected from each other, restricting the movements of animals. And that is a problem, say the researchers of the present study.

“Understanding how different species are impacted by landscape features like roads and agriculture is important to develop conservation strategies that ensure survival of multiple species into the future”, says Ms. Prachi Thatte, a researcher from NCBS, who led this study, talking about the importance of the study published in Elsevier’s journal Biological Conservation.

The researchers conducted the study in central India, in eleven tiger reserves and other potential areas in the state of Maharashtra, Madhya Pradesh and Chhattisgarh.  Expanding cities are resulting in encroachments of these forests for building houses, roads and railways. For example, the national highway 7, that cuts across one such protected area used by tigers as a corridor for movement, is being widened. These developments result in fragmentation of protected areas, restricts the movement of tigers between such areas, isolates small populations leading to inbreeding, low genetic variation and an increase in susceptibility to diseases.

The researchers collected tiger scats in central India, within and outside protected areas, to measure genetic variation  and genetic exchange between populations/areas. The genetic data was also used to infer how different landscape features like roads and railway lines affect connectivity. Using both, genetic data and the inferred effect of landscape variables, they simulated the possible changes in genetic diversity, connectivity and the probability of extinction under various development scenarios in the year 2100.

The results of the study show that today, human settlements and roads with high traffic restrict tiger movement the most. In the future, due to rapid urbanisation, this would worsen, reducing the genetic diversity of tigers in the area. Stepping-stone corridors -- forest area where protection is ensured -- that facilitate movement of tigers would also be insufficient to maintain the current genetic diversity. Although they contribute to 10% higher genetic variation and between 6% to 86% lower extinction probability when compared to areas without these corridors. Large areas of forest have been used for mining, which could lead to 22% higher chance of extinction for the neighboring tigers.

“We found that tiger numbers in small populations fluctuate over years much more than in large populations. The ratio of number of males to females (sex ratio) in the population also fluctuates in small populations. This contributes to the extinction risk of these populations”, says Ms. Thatte, on the findings of the study. 

So, what would help these tigers survive the risk of extinction? “It is important that the Central Indian landscape is managed as a network of Protected Areas inter-connected with corridors. We need informed development plans that consider biodiversity and connected wildlife populations in addition to human development goals”, opines Ms. Thatte. “Protected areas are not currently disconnected, as shown by the genetic data in our study. There is movement of individuals between several of them. Our future simulations suggest that stepping stone corridors are the best way maintain connectivity and also sustain the tiger population increase into the future”, she adds.

This study stresses on the importance of conservation planning on the management of land use and tiger populations. By keeping a close eye on vulnerable tiger populations, the species, as well as it’s landscape can be protected.