The loss of genetic diversity may not play as large a role in the demise of threatened and endangered animals as conservation biologists once believed, according to a study of wild cheetahs in Africa by researchers from the University of California, Davis, and The Game Conservancy. "The central paradigm in conservation biology over the last decade is that genetics are critically important in determining the fate of small populations," said zoologist Tim Caro, a UC Davis associate professor who has studied cheetahs for 14 years. "In the face of massive species losses and with limited time and resources, we should redirect efforts toward addressing ecological rather than genetic problems to stop populations from declining." Of 125 newborn cheetah cubs followed in the study, only 36 survived their first two months, and just six lived past their first year to adult independence, according to the report published in the Jan. 28 issue of the journal Science. This mortality rate is extremely high among mammals, but the most significant factor was that 73 percent of cub deaths were due to predation by lions. A few cheetah cubs died from bush fires or being abandoned by mothers, but only two could have died from factors indirectly related to genetic problems. Until now, biologists have focused on genetic factors as the key reason small populations of wild animals have been dwindling, in some cases to zero. Inbreeding in small populations, for example, could eventually lead to extinction as a result of fewer births or increased susceptibility to disease. Also, biologists have reasoned, the smaller gene pool could limit the long-term opportunities for a population to evolve and adapt. Although scientists have not found a strong empirical link between genetic factors and extinctions, the plight of cheetahs has been used to provide persuasive circumstantial evidence. For reasons that are not understood, cheetahs have an astonishing lack of genetic variation among individuals. In captivity, cheetahs reproduce slowly and may be prone to disease. A case study of 42 captive cheetahs in Oregon documented that nearly one-half succumbed to a type of disease believed to have raced through the population because its genetic uniformity offered no opportunity for resistance. In the wild, cheetahs live at a low population density compared to carnivores of similar size, a situation that also could be interpreted as a consequence of their impoverished genetics. In support of their argument, Caro and co-author Karen Laurenson, a postdoctoral researcher with The Game Conservancy in England, cite other studies that suggest relatively genetically uniform cheetah populations can show individual variability in response to viruses and other infectious agents. Caro and Laurenson suggest that the cheetahs' poor reproductive performance in captivity might be due to inappropriate social conditions, bad timing of mating and other nongenetic reasons. Finally, the authors note that predators, not genetic homogeneity, appear to be the most likely cause of low population density among cheetahs in the wild when they live with other large carnivores. Counterintuitively, cheetahs may fare poorly in the national parks set up for their protection because of the high density of lions and spotted hyenas that thrive there, Caro said. "Genetic considerations are clearly important in the management of captive populations but may only be relevant to free-living populations in limited circumstances because they impact populations on a slower time scale than environmental problems," Caro and Laurenson wrote in their paper. The most immediate threats to small wild populations are posed by humans, according to the researchers, who listed problems such as poaching, habitat fragmentation, decimation by exotic species, and pollution. Witnessing secretive predation in the wild is extremely difficult and has only been observed as a result of 20 years of intensive observations by Caro and others of the cheetahs in the Serengeti National Park, Tanzania. The Science report is the latest in a series of publications from this population. Such comprehensive long-term studies of animal populations are now yielding sophisticated data on mating systems, ecological interactions and, increasingly, issues of significance to conservation.