Abundance of mega-carcasses does not profoundly affect trends in the population dynamics of a facultative scavenger predator and its prey

Abstract

AbstractThe interplay between facultative scavenging and predation has gained interest in the last decade. The prevalence of scavenging induced by the availability of large carcasses may modify predator density or behaviour, potentially affecting prey. In contrast to behavioural mechanisms through which scavenging affects predation, the demographic effects of facultative scavenging on predator and prey populations remain poorly studied. We used the semi-natural experimental opportunity in Hwange National Park, Zimbabwe, where contrasted management measures (culling and artificial supply of water) have led to fluctuations in elephant carrion abundance, to identify the consequences of facultative scavenging on the population dynamics of a large mammalian carnivore, the spotted hyaena (Crocuta crocuta), and its prey. Using a 50-year dataset and Multivariate Autoregressive State Space models, we estimated hyaena and prey densities over four time periods contrasted in carrion availability. Hyaena and prey population dynamics had similar trends within periods (increased prey density is generally accompanied by an increased hyaena density) and these trends differed across periods (increases in some periods and decreases in other). These results are consistent with an effect of management measures on prey and hyaena population dynamics. We rather hypothesise a predominance of bottom-up mechanisms, although some subtle patterns could be interpreted as consequences of changes in predation pressures following increases or decreases in scavenging opportunity. We discuss why signals of prey and predator population dynamics decoupling are less likely to be observed in system with a high diversity of prey such as African savannas and why inputs of mega-carcasses as pulsed resources hardly impacted top-down relationships on the long run. This study represents a first investigation of the long-term effects of carrion pulses, whose frequency may increase with climate changes, on the classical predator-prey coupling for large mammals.