The authors tested their model by sampling tiger and prey populations in 11 ecologically distinct sites in India – from grasslands to dry forests – over an eight-year period, with teams of biologists walking more than 4,200 miles to count prey animals, and setting hundreds of camera traps over 8,600 days of effort. Densities of ungulate prey such as deer, antelopes, wild cattle and wild pigs ranged from a low of 5.3 animals per square kilometer in Meghat Reserve, to more than 63 per square kilometer in Pench Reserve. The model predictions matched the measured tiger densities ranging between 3.2 to 16.8 tigers per 100 square kilometers.
According to WCS scientist Dr. Ullas Karanth, the lead author of the study, the rigorous methods and extensive field component of this study set it apart from most population ecology research, which is often carried out on smaller animals in laboratories.
"When it comes to macro-ecological studies on far-ranging landscape species like tigers and their prey, the biological, statistical and practical problems involved have proved too daunting in the past, compelling scientists to draw weak inferences, usually based on secondary data," said Dr. Karanth. "We tackled this problem head-on by immersing ourselves for eight years in the secret world of the tiger."
"Our results confirm that decline of wild tigers is primarily driven by prey-depletion caused by human hunters," Karanth added. "Conservationists should direct their concerns at reducing such negative human impacts." WCS's conservation efforts to save tigers in India and throughout their range are featured in "Tiger Mountain," a new exhibit that opened at the Bronx Zoo last May.
Proceedings of the National Academy of Sciences