India’s tiger story is a globally acclaimed conservation model but the rising population of big cats is beginning to pose uncomfortable questions in the face of growing conflict. Though uniform benchmarks do not apply to diverse tiger landscapes, wildlife scientists and forest managers are willing to take a fresh look at “carrying capacity” — a phrase that evokes unease among conservationists.
Notwithstanding the sentiments it may provoke, many tiger-rich states, including Karnataka, have begun expressing the need to redefine carrying capacity. In fact, carrying capacity will be one of the topics at the upcoming Global Big Cat Alliance summit, scheduled for February 9–12 in Bandipur and Nagarhole Tiger Reserves in Karnataka.
In the Tigers, Co-predators and Prey in India 2018 report released by the Ministry of Environment, Forests and Climate Change (MoEFCC) and Wildlife Institute of India (WII), prey-based carrying capacity for tigers was defined. The calculation of tiger density (per 100 sq km) was derived using a formula: (-0.377 ± 0.36) + (0.143 ± 0.01) × (tiger prey density per sq km).
Based on the formula, researchers noted that the tall-grass Terai and Shivalik Hills habitats achieved the highest tiger densities -- 10 and 16 tigers per 100 sq km. In central India, the calculated density was 6–10 tigers. The north-central Western Ghats recorded densities of 7–11 tigers, while the southern Western Ghats consistently recorded lower densities, with upper limits around 2–3 tigers. The carrying capacity in the Sundarbans was around 4 tigers per 100 sq km. Researchers also noted that the hills of the Northeast had extremely low tiger densities (less than 1 per 100 sq km).
There research team had a caveat: Tiger reserve managers should not strive to increase tiger densities beyond landscape upper limits through artificial habitat manipulation or prey augmentation, as this could be detrimental to co-predators and prey populations. The scientific recommendation was to expand the area occupied by tigers rather than increase density.
“This caveat mentioned in the report holds good even now. Conservation measures have increased tiger populations but landscapes have not expanded. Pressure on forests has intensified. Therefore, there is a need to redefine carrying capacity and make it more region-specific rather than rely on a uniform standard,” a senior WII researcher said.
In some habitats, the tiger’s prey base has changed. In Sariska, 60 per cent of dependence is on domestic prey. Along forest boundaries in Karnataka, it exceeds 70 per cent. A similar pattern is seen with lions in Gujarat and leopards across India, the researcher added.
Dr Vishnupriya Kolipakam, scientist and faculty member at WII, said carrying capacity serves as a baseline to understand how much pressure a forest can sustain. Co-predators and ungulates are equally important, she said.
“Our camera trap images and studies show that 7–8 tigers share a 10 sq km area, against the standard norm of each tiger requiring at least 10 sq km as territory. This is one of the prime reasons for rising conflict,” said a senior Karnataka forest department official. Officials from other tiger states agree. Addl PCCF (wildlife), Karnataka, Bishwajit Mishra said a team has been constituted to prepare a carrying capacity report. Data is being compared with other states.