"In avoiding extinction, it pays to be promiscuous," says Justin Brashares of the University of British Columbia in Vancouver, who presents this work in the June issue of Conservation Biology. "This study is the first to show a strong link between social behavior and risk of extinction in mammals."
Most studies of risk factors for extinction are based on natural extinctions through the ages but other risk factors may be at play in today's world, where the extinction rate is unnaturally high due to overhunting, habitat fragmentation and other disturbances caused by people. Knowing which species are particularly sensitive to these disturbances would help conservationists figure out how to save them. Since 1970, more than half of the mammal populations in Ghanian reserves have become locally extinct. "This shocking loss of abundance and local diversity is occurring throughout Africa," says Brashares.
To help identify the risk factors for modern extinctions, he analyzed the extinctions and persistences of large mammals in six reserves in the savannas of Ghana, where the mammals have been censused monthly for more than 30 years and 78 local extinctions have been documented. Brashares assessed the extinction risk of nine traits (including population isolation, harem size, abundance and how much people like to eat them) in 41 mammal species (9 primates, 24 ungulates and 8 carnivores).
After accounting for the effect of reserve size, Brashares found that two of the factors studied correlated with local extinctions in the Ghanian reserves. The first is population isolation, which is not surprising because this was previously known to be a risk factor for natural extinctions.