No abstract

Spotted hyenas (Crocuta crocuta) are large mammalian carnivores, but their societies, called 'clans', resemble those of such cercopithecine primates as baboons and macaques with respect to their size, hierarchical structure, and frequency of social interaction among both kin and unrelated group-mates. However, in contrast to cercopithecine primates, spotted hyenas regularly hunt antelope and compete with group-mates for access to kills, which are extremely rich food sources, but also rare and ephemeral. This unique occurrence of baboon-like sociality among top-level predators has favoured the evolution of many unusual traits in this species. We briefly review the relevant socioecology of spotted hyenas, document great demographic variation but little variation in social structure across the species' range, and describe the long-term fitness consequences of rank-related variation in resource access among clan-mates. We then summarize patterns of genetic relatedness within and between clans, including some from a population that had recently gone through a population bottleneck, and consider the roles of sexually dimorphic dispersal and female mate choice in the generation of these patterns. Finally, we apply social network theory under varying regimes of resource availability to analyse the effects of kinship on the stability of social relationships among members of one large hyena clan in Kenya. Although social bonds among both kin and non-kin are weakest when resource competition is most intense, hyenas sustain strong social relationships with kin year-round, despite constraints imposed by resource limitation. Our analyses suggest that selection might act on both individuals and matrilineal kin groups within clans containing multiple matrilines.

To investigate how anthropogenic activity might affect large carnivores, we studied the behaviour of spotted hyenas (Crocuta crocuta) during two time periods. From 1996 to 1998, we documented the ecological correlates of space utilization patterns exhibited by adult female hyenas defending a territory at the edge of a wildlife reserve in Kenya. Hyenas preferred areas near dense vegetation but appeared to avoid areas containing the greatest abundance of prey, perhaps because these were also the areas of most intensive livestock grazing. We then compared hyena behaviour observed in 1996-98 with that observed several years earlier and found many differences. Female hyenas in 1996-98 were found farther from dens, but closer to dense vegetation and to the edges of their territory, than in 1988-90. Recent females also had larger home ranges, travelled farther between consecutive sightings, and were more nocturnal than in 1988-90. Finally, hyenas occurred in smaller groups in 1996-98 than in 1988-90. We also found several changes in hyena demography between periods. We next attempted to explain differences observed between time periods by testing predictions of hypotheses invoking prey abundance, climate, interactions with lions, tourism and livestock grazing. Our data were consistent with the hypothesis that increased reliance on the reserve for livestock grazing was responsible for observed changes. That behavioural changes were not associated with decreased hyena population density suggests the behavioural plasticity typical of this species may protect it from extinction.

Interspecific competition among carnivores is an important determinant of predator population dynamics, and it may also affect lower trophic levels. Whereas considerable research has focused on effects of interspecific competition on threatened carnivore populations, here we examine the effects of interspecific competition on the most abundant large carnivore in Africa, the spotted hyena Crocuta crocuta. Specifically, we compared two populations of spotted hyenas to examine the sources of variation in fitness, including effects of competition with lions Panthera leo. Hyenas living in Amboseli National Park and the Masai Mara National Reserve, Kenya, were monitored from 2003 to 2005 and 1988 to 1992, respectively. Females reproduced at significantly higher rates in Amboseli, due to shorter lactation periods, though neither juvenile survival nor litter size differed between populations. Differences in reproduction were estimated to result in 24% greater lifetime reproductive success among Amboseli than among Mara females. We then tested alternative ecological hypotheses to explain these differences in fitness measures between populations. We found little support for hypotheses suggesting that population differences were due to variation in prey availability or dispersion, or to intraspecific competition either within or between hyena groups. Our results were most consistent with the hypothesis that population differences were due to variation in interspecific competition with lions. Hyenas in Amboseli lived at lower lion density, enjoyed higher rates of food intake despite less abundant prey, and scavenged more food from lions than did Mara hyenas. Our results indicate that competition with lions operated primarily via food competition, rather than direct killing, to generate the fitness differences.