Ecological determinants of survival and reproduction in the spotted hyena

Abstract

Large carnivores play a key role in the structuring and dynamics of many ecosystems, yet the factors influencing dynamics of carnivore populations themselves are often poorly understood. Spotted hyenas (Crocuta crocuta) are the most abundant large carnivores in many African ecosystems. We describe demographic patterns in a population of spotted hyenas observed continuously for 15.5 years, and assess the effects of per capita prey availability, interspecific competition, rainfall, anthropogenic disturbance, and disease on 2 key determinants of population dynamics: reproduction and survival. Annual reproduction, survival of juveniles (i.e., recruitment to adulthood), and mortality of adults varied among years of the study. Per capita prey availability and group size both had positive effects on reproduction, whereas interspecific competition with lions had a negative effect. Competition with lions and rainfall both had negative effects on survival of juveniles. We suggest that the negative effect of rainfall on survival may be mediated by increased rates of human-carnivore conflict during periods of heavy rain, although human population size did not influence survival or reproduction directly. Disease had no substantial effect on this hyena population, despite occurrence of at least 2 disease outbreaks among sympatric carnivores during the study. By focusing on demographic processes that determine population growth (i.e., survival and reproduction), this study highlights the importance of both top-down and bottom-up forces acting on populations of large carnivores. These findings also add to a growing literature suggesting that interspecific competition may be more important than previously recognized in the dynamics of populations of large carnivores. © 2009 American Society of Mammalogists.