A study of extinction patterns of 25 large mammal species in India finds that improving existing protected areas, creating new areas, and interconnecting them will be necessary for many species to survive this century.
The study, by a team of researchers from the United States and India, appears in the March 10 online edition of the British peer-reviewed journal, Proceedings of the Royal Society B. The team's analysis showed that forest cover and local human population densities are also key factors. Fostering greater human cultural tolerance for wildlife likewise will be critical.
The study examined extinction probabilities for a range of species. It looked at species considered endangered or critically endangered on the 2009 International Union for Conservation of Nature (IUCN) Red List of Threatened Species, including tigers, lions and elephants. And it looked at species of least concern, including jackals, wolves and other species.
"India's fragmented network of relatively small protected areas has high carrying capacities for large mammals," said Krithi K. Karanth, who conducted the study as part of her doctoral thesis at Duke's Nicholas School of the Environment. "But given the overall patterns of extinction estimated in our study, we need to create new areas, and connect them better, if many of the mammals are to persist into the future."
Karanth currently is a postdoctoral scientist at Columbia University. She also is a research associate of the Centre for Wildlife Studies in Bangalore, India.
To identify factors critical to the species' survival and estimate their extinction probabilities, she and her team collected 30,000 records, including hunting, taxidermy and museum records dating back to 1850. They divided India's geographical area into a grid with 1,326 individual local "cells" and entered the historical data into each cell. They then used occupancy estimation models, based on observations of more than 100 local wildlife experts, to infer the current occurrence of species in each cell.
Their analysis revealed that protected areas were associated with lower extinction probabilities for 18 species. Higher proportion of forest cover was associated with lower extinction of seven species. On the other hand, time elapsed since the last historical citing was associated with higher extinction probabilities of 14 species, and human population density in a cell was associated with higher extinction probabilities of 13 species.
One of the most important findings, Karanth noted, is that culturally tolerated species -- animals that humans perceive as nonthreatening or beneficial -- fared better overall.
Using both historical data and current occupancy estimation models allowed Karanth and her team to distinguish more clearly between when a species was truly absent or locally extinct in a cell, and when it likely still exists but hasn't been detected in recent surveys or field observations.
"Distinguishing between a species' absence and its simple non-detection is critical for accuracy," she said. "Failure to deal with non-detection results in underestimates of species occupancy and overestimates of local extinctions. This clouds our ability to determine the true impact of environmental and social factors on extinctions."
Karanth added that for conservation to succeed, policymakers and land managers must also take into account rapid changes in land use, climate, population growth and spread, and economic development now occurring in India and southern Asia.
Her co-authors on the study were Norman L. Christensen Jr., professor of ecology at Duke's Nicholas School; James D. Nichols and James E. Hines of the U.S. Geological Survey Biological Resources Division's Patuxent Wildlife Research Center; and K. Ullas Karanth of the Wildlife Conservation Society India Program and the Centre for Wildlife Studies in Bangalore.
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