Occupancy modelling, which helps in separating true absence from non-detection of a particular species, was used in this study
Large terrestrial mammals are the most threatened taxa, and hence face a greater possibility of becoming extinct the world over — about 25 per cent of them are facing extinction, and 50 per cent are seeing their numbers declining. South Asian species are the most threatened.
A large-scale study of 25 mammals covering the entire country was taken up recently, and the results published on March 10 in the Proceedings of the Royal Society B journal. The study confirms most of the assumptions of the authors.
The paper concludes: “Overall, large-bodied, rare and habitat specialist mammals tend to have higher extinction probabilities.”
The main message is about the real importance of protected areas in conserving and protecting wildlife. “People are underplaying the importance of protected areas,” said Dr. K. Ullas Karanth.
“There has been a drift from recognising the importance of protected areas for some of the species [studied].” The survival of 18 species showed a strong link to the presence of protected areas. Stressing his point further, he said: “There is a need to expand the protected areas.”
Dr. Karanth is a senior conservation scientist with the Wildlife Conservation Society, New York, and the Director of the Centre for Wildlife Studies, Bangalore. He is also one of the authors of the paper.
The habitats of species like blackbuck, four-horned antelope, bear, wolf etc lie outside the protected areas. And for others like swamp deer, gaur, rhino etc, establishment of new protected areas is essential for their continued existence, the study found.
It was also predicted that presence of a forest cover would confer greater survival possibility. But the results only partially supported this — only seven of the 13 species studied showed a strong link. “Forest cover may not be an important determinant of extinction of other species,” notes the paper.
Explaining this, Dr. Karanth said: “Some animals essentially need forest cover for survival. But some animals like blackbuck and chinkara do not show strong dependency on forest cover.”
In general, they also found that living in higher elevation facilitated lower extinction probabilities. As expected, higher human density had negative fallout — 13 of the 25 species studied faced a danger of extinction. But three species (jackal, wild pig and blackbuck) that showed good adaptation capabilities were not affected by human density.
Cultural tolerance has played a great role in the survival of certain species. For instance, elephants are considered sacred and they are at least risk of extinction. The study found 8 other species escaping extinction for the same reasons. Blackbuck, chinkara and nilgai enjoyed greater cultural tolerance particularly in western India.
It was assumption that carnivores would be at a greater risk of extinction compared with herbivores turned out to be wrong. Local extinction rates were the same for both.
There are several reasons why this study stands out from the rest. To begin with, the whole of India was divided into a grid of 1326 cells; the average size of each cell being 2,818 sq. km. The baseline or the current presence of wildlife in a particular cell was created through a questionnaire sent to many experts, such as naturalists, foresters, wildlife experts, biologists etc. “So we have data from multiple experts and this helps in estimating correctly the probability of detection,” said Dr. Karanth. Data from multiple experts is like conducting replicate surveying in the case of field studies. This primary data was compared with multiple sources of historical data to arrive at the extinction risk.
The methodology used is also different.
“The real importance of the study is its methodology, especially for animal studies,” he said. The traditional method merely looks at the presence or absence of a particular species to determine if it has become extinct. “But this [traditional] methodology has a fundamental problem,” he said.
Lack of confirmation of presence of a species could either mean that it has become extinct or quite simply that its presence was not detected.
But the traditional method treats all non-detection as absence of the species. This leads to erroneous results – underestimation of the numbers/distribution.
But occupancy modelling, used in this study, helps in separating true absence from non-detection of a particular species. This makes the results more reliable.
Occupancy modelling is now increasingly being used for the last ten years in lieu of traditional method of looking at presence/absence of species. “This study will probably be the first one to use this methodology [occupancy modelling] on a large, country-wide scale,” he said.