Factors affecting life and death in Serengeti cheetahs: environment, age, and sociality

We examined environmental and social factors affecting reproductive success across a 20-year data set of individually known cheetahs on the Serengeti Plains of Tanzania. Because cheetahs are seen infrequently and are not amenable to mark-recapture techniques, we devised a model to estimate time of death for individuals that disappeared from our records. We found that males had markedly lower survival than females. Recruitment was negatively affected by rainfall but positively affected by numbers of Thomson's gazelles, the cheetahs' chief prey. There was a negative association between recruitment and numbers of lions, demonstrating that the high rates of predation observed in previous studies have implications for the dynamics of cheetah populations. Recruitment was related to mother's age, peaking when she reached 6-7 years. Sociality affected survival in two ways. First, adolescents living in temporary sibling groups had higher survival than singletons, particularly males with sisters. Second, adult males living in coalitions had higher survival than singletons in periods when other coalitions were numerous, yet they had lower survival when other coalitions were rare. These results corroborate observations of enhanced prey capture by female adolescents and antipredator benefits for adolescents in groups, as well as competitive advantages for adult males in groups. Furthermore, our findings stress the importance of interactions between environmental and social factors in affecting reproductive success in mammals.