While disappearing tiger populations have been a cause of major worry, analysis now shows that tigers have survived better in larger protected areas across all habitat types in the country. The researchers focused their analysis on a tropical dry forest as such forest areas constitute the largest habitat for tigers.

The examination of historic range areas for tigers by the research team shows that populations are disappearing at a faster rate in these forests – 64 per cent sites suffering local extinction in 100 years – than in any other suitable habitat in India. The reason: home ranges of all breeding radio-collared tigers extended beyond the protected area boundary and were exposed to “edge effects” that exist at the periphery and outside. Explaining further, the researchers said that since edge effects not only include organised poaching, but also “more chronic retaliatory killing”, such “high exposure to human-caused mortalities” may be responsible for the loss of tiger population.

They research said for long-ranging species such as tiger, size of the protected area is an important factor, but in India, the average size of protected areas is relatively small – 367.74 ± 365.22 square km – and even smaller in tropical dry forest. “On an average, protected areas in tropical dry forests are relatively small (366.92 ± 422.12 square km) and the average size of protected areas from where tigers have disappeared in this habitat in the last 100 years is even smaller,” said the research team from Ashoka Trust for Research in Ecology and the Environment, Bengaluru, Nature Conservation Foundation, Mysuru, among others from organisations in Delhi, Dehradun, Bandhavgarh, USA and South Africa.

“In several countries around the world, the size of protected areas is often insufficient to hold viable populations of species, especially those that have large space-requirements. In India, a network of forty eight tiger reserves has been established specifically for the conservation of tigers and their habitat. Despite this, India has witnessed local extinctions of at least two tiger populations – from the Sariska Tiger Reserve in 2004 and from the Panna Tiger Reserve (PTR) in 2009. Both fall in the tropical dry forest habitat. These extinctions underline the urgency for a better understanding of the minimum ecological requirement to manage a viable tiger population in this habitat. Our analysis suggests that in addition to the size of the protected area, certain forest habitats might be more vulnerable than others,” said the findings published in “Biological Conservation”.

Field studies were conducted in PTR between 1996 and 2005 to monitor tiger movement via radio telemetry. The researchers attempted to locate each radio-collared tiger at least once every three to four days at different hours during night and day to evenly cover the 24-hour period. “Our analysis of past trends indicates that tigers have survived better in larger protected areas in tropical dry forest. But the probability of survival even in protected areas as big as Panna Tiger Reserve (543 square km) is barely more than 40 per cent and worryingly almost 85 per cent of the protected areas in this habitat type are smaller than PTR,” they said. Further, the research team observed that because of the large space requirement of tigers in tropical dry forest, even the relatively large PTR was able to only partially protect a population of just seven to eight breeding females within its boundary.

“The near continuous presence of researchers, and intensive radio-tracking and monitoring of all the tigers may have provided additional security to the breeding females. When this was curtailed, poaching hit these individuals,” they said.

The researchers said that since Panna Tiger Reserve is isolated and lacks connectivity, the small breeding tiger population was not able to withstand this poaching pressure. “The local extinction of tigers due to poaching from PTR in 2009 and Sariska Tiger Reserve in 2004, both tropical dry forest habitats, underlines the serious threats that small populations face when they are exposed to edge-effects,” said the authors.