The shrinking ark: patterns of large mammal extinctions in India

1. What they did

Large mammals are among the most threatened animals in the world, and those of South Asia are among the most endangered. The authors asked how much India’s large mammals have disappeared from places where they once lived, and what helps them survive: protected areas, forest, high ground, fewer people, or people who tolerate them.

• Past. They gathered more than 30 000 historic records of mammals from museums, taxidermists, gazetteers, hunting journals and natural history journals, mostly from 1860 to 2000. They chose 25 large mammals with 64 to 3606 reliable records each and mapped them onto a grid of 1326 cells covering India (each about 2800 km²).
• Present. For every cell where a species had once been recorded, they asked more than 100 wildlife experts whether they had detected the species there during the previous year (to 2006). Experts were told that a reported detection had to be certain and based on direct evidence, and that a non-detection would not be read as absence.
• Analysis. They used occupancy models, which allow for animals being present but missed, to estimate the probability that each species had gone locally extinct in each cell. They tested how this was linked to time since the historic record, protected areas, forest cover, elevation, human population density and cultural tolerance, and compared species by body size, diet, habitat and rarity.

2. What they found

How much has been lost

• Estimated local extinction over 100 years ranged from 0.14 (jackal) to 0.96 (lion). Other high values were swamp deer (0.90), mouse deer (0.81), Nilgiri tahr (0.71), tiger (0.67), wild buffalo (0.66), wild dog (0.62) and gaur (0.60). Lower values included wild pig (0.25), wolf (0.25), nilgai (0.29), blackbuck (0.33) and sambar (0.34).
• The longer ago a species was recorded in a cell, the more likely it had since disappeared there, for 14 species.

What helped species persist

• Protected areas: linked with lower extinction for 18 species, especially large carnivores and forest-dwelling mammals.
• Forest cover: linked with lower extinction for seven species. For species of open habitats, which have seen intensive land-use change, forest cover alone did not appear to ensure survival.
• Elevation: higher ground was linked with lower extinction for eight species.
• Human population density: more people was linked with higher extinction for 13 species. Wild pig, jackal and blackbuck were unaffected, as predicted; chinkara and nilgai, predicted to be unaffected, were not.
• Cultural tolerance: species did better where people tolerate them, especially nilgai, chinkara and blackbuck in western India, and also several other species.

Which species are most at risk

• Large-bodied species mostly had higher extinction, except elephants, which are culturally tolerated. Smaller species living at naturally low densities (mouse deer, Nilgiri tahr) were also at high risk.
• Habitat generalists (leopard, jackal, wild pig) had lower extinction than habitat specialists (Nilgiri tahr, brown bear, rhino, swamp deer).
• Contrary to prediction, herbivores (0.25 to 0.90) and carnivores (0.14 to 0.96) had similar extinction ranges.

3. What they concluded

• All 25 large mammals have had substantial local extinction across India over the past century. Large-bodied, rare and habitat specialist mammals tend to be most at risk.
• Protected areas are critical for reducing local extinction of most of India’s large mammals. Species living mostly outside protected areas (such as blackbuck, nilgai, chinkara, sloth bear, jackal and wolf), and species with only a tiny part of their former range protected (such as tiger, elephant, lion and wild dog), will need new protected areas and connections between existing ones.
• Because the analysis used large grid cells, stronger links may exist at the finer scales where human–wildlife conflict and conservation action happen.
• The results should be considered against rapid changes in land use, climate, human population, culture and economic growth in India and southern Asia.

6. Other technologies, skills or innovations

• Combining centuries of museum, taxidermy and hunting records with present-day expert reports to rebuild where species used to live and estimate where they have been lost.
• Occupancy modelling that accounts for imperfect detection, using repeated reports from several experts per cell as replicate surveys.
• Estimates standardized to 50 and 100 years ago, so cells with records from different periods could be compared.
• A “cultural tolerance” covariate grouping Indian states by their historic hunting, diets and reverence for wildlife.

7. Implications for conservation (from the paper)

• Many species need new protected areas and better connections between India’s small, fragmented reserves (average under 300 km²) if they are to persist.
• Regional development plans for dams, mines, highways and industry could use these occupancy patterns to reduce harm and avoid further shrinking and fragmenting of mammal ranges.
• Conservation policy needs to take account of changes in land use, climate, human population, culture and economic growth.