Preliminary findings of a study by the Wildlife Institute of India (WII) suggest that the density of tigers in the Sunderbans may have reached the carrying capacity of the mangrove forests, leading to frequent dispersals and a surge in human-wildlife conflict.
Prey, eat, breed
Availability of food and space is the primary factor that determines how many tigers a forest can hold. And often, food is space for the tiger.
While they are known to establish vast ranges — the male in particular strives to control multiple females with typically smaller ranges — how far a tiger will range is determined by the abundance of prey in its forest.
In the Terai and Shivalik hills habitat — think Corbett tiger reserve, for example — 10-16 tigers can survive in 100 sq km. This slides to 7-11 tigers per 100 sq km in the reserves of north-central Western Ghats such as Bandipur, and to 6-10 tigers per 100 sq km in the dry deciduous forests, such as Kanha, of central India.
The correlation between prey availability and tiger density is fairly established. There is even a simple linear regression explaining the relationship in the 2018 All-India Tiger report that put the carrying capacity in the Sunderbans “at around 4 tigers” per 100 sq km.
A joint Indo-Bangla study in 2015 pegged the tiger density at 2.85 per 100 sq km after surveying eight blocks spanning 2,913 sq km across the international borders in the Sunderbans. “Low density of tigers in the Sundarbans is an inherent attribute of the hostile mangrove habitat that supports low tiger prey densities,” it said.
The ongoing WII study indicates a density of 3-5 tigers in the Sunderbans. Given that 88 (86-90) tigers were estimated in 2,313 sq km of the Sundarbans in 2018, the population has been close to its so-called saturation point in the mangrove delta for some time.
Conflict: cause or effect
The consequence, as classical theories go, is frequent dispersal of tigers leading to higher levels of human-wildlife conflict in the reserve peripheries. But, experts say, carrying capacity and conflict may also pose a chicken-and-egg conundrum.
While physical (space) and biological (forest productivity) factors have an obvious influence on a reserve’s carrying capacity of tigers, what also plays a crucial role is how the dispersal of wildlife is tolerated by people — from the locals who live around them to policymakers who decide management strategies.
While this not-so-discussed social carrying capacity assumes wider significance for wildlife living outside protected forests, it is an equally important factor in human-dominated areas bordering reserves where periodic human-wildlife interface is inevitable. More so when different land uses overlap and a good number of people depend on forest resources for livelihood.
Imagine a 1,000 sq ft terrace apartment. In theory, it can accommodate, say, 20 people at 50 sq ft per person. Put in place some furniture — think roads, traffic, encroachment — and that capacity will fall. It will slide further if no one is allowed to step out in the common terrace where they are targeted by hostile neighbours who consider them a threat.
That’s how potential carry capacity may shrink in a reserve. Perceived conflict can squeeze the tiger’s domain, which the animal is bound to overstep from time to time, leading to further conflict with no immediate winners.
The way ahead
Artificially boosting the prey base in a reserve is often an intuitive solution but it can be counter-productive. While tackling external factors, such as bushmeat hunting, is necessary to ease pressure on the tiger, the government’s policies have discouraged reserve managers from striving to increase tiger densities by artificial management practices of habitat manipulation or prey augmentation.
To harness the umbrella effect of tigers for biodiversity conservation, experts say, it is more beneficial to increase areas occupied by tigers. For many, the prescription is to create safe connectivity among forests and allow tigers to disperse safely to new areas. But though vital for genes to travel and avoid a population bottleneck, wildlife corridors may not be the one-stop solution for conflict.
First, not all dispersing tigers will chance upon corridors simply because many will find territories of other tigers between them and such openings. Even the lucky few that may take those routes are likely to wander to the forest edges along the way. Worse, the corridors may not lead to viable forests in reserves such as Sunderbans, bounded by the sea and villages.
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Little choice
While it has never been easy to share space with wildlife, particularly carnivores, the contours of conflict largely depend on the local perception of animals. It ranges from minding one’s own business based on the assurance gathered over generations that, left alone, animals rarely pose physical danger, to mobilising demand for removal at sight.
However, as several studies have shown, removing tigers or any wildlife cannot eliminate the chances of future interface as another lot invariably turns up. The remedy, experts say, lies in smarter land use to minimise damage and adequate incentives to promote acceptance of wildlife.
Generous compensation policies can take care of the financial cost of losing livestock or crops, or wasted man hours when a workplace is avoided due to a passing tiger. Besides, the percolation of financial benefits of having charismatic wildlife in the neighbourhood can also nudge some towards better tolerance.
Ultimately, it is the people of the Sunderbans who will decide how many tigers can be accommodated in their neighbourhood. In a landscape squeezed in by climate change, rising sea level and salinity, their future is nearly as precarious as the tiger’s. It is for the policymakers to give them enough reasons to make a balanced choice.