4 Aug 1998
Endangered cheetah populations in Africa have a staggeringly high rate of infant mortality: Just 5% of cheetah cubs survive to adulthood. This has led to proposals to stop predators from killing the cubs. But a new computer model, described in the August issue of Conservation Biology, indicates that deaths among adults pose a potentially graver threat, in part because female cheetahs can maintain a stable population by conceiving again soon after losing their litters. As a result, the authors urge ecologists to focus their efforts on protecting adult cheetahs from poaching and habitat loss.
About 10,000 cheetahs still sprint across African plains, largely in Namibia and on the Serengeti plateau. The rate of cub deaths--among the highest for a large predator--has prompted some researchers to propose raising cheetahs in enclosures or culling lions and hyenas, the main threats to newborns. However, such efforts would be hard, intrusive, and expensive. Moreover, field biologists found in the last decade that female cheetahs apparently have evolved to counteract the losses of their cubs by becoming fertile again within a few months. Some conservation biologists reasoned that protecting adults might therefore be more productive, but they lacked evidence.
The new model provides that support. Biologist Kevin Crooks of the University of California, Santa Cruz, and his colleagues divided cheetahs into six age ranges and devised equations that related the survival rates of each group--as measured in the field--to overall population growth. The longevity of adults, they found, was by far the most critical factor. "Working with ranchers outside of national parks to reduce human-cheetah conflicts may be the best way to conserve the population," Crooks says.
Geneticist Stephen O'Brien, a cheetah expert at the National Cancer Institute in Bethesda, Maryland, agrees with the model's main conclusion. "Infant mortality, although it sounds dramatic, pretty much influences just what happens in a given year," he says. O'Brien notes that even though cheetahs show genetic signs of inbreeding, the result of a population bottleneck in the past, the key limiting factor today may be habitat loss. He remains "cautiously optimistic" that current conservation efforts to manage habitats and educate landowners will help the cheetah endure.