Spotted hyaena survival and density in a lion depleted ecosystem : the effects of competition between large carnivores in African savannahs

Abstract

Competition is considered an important factor for large carnivore population dynamics, but the manner in which interspecific competition impacts these species are not well understood. This lack of knowledge is due to the ongoing declines of large carnivores, the loss of intact large carnivore guilds, the complexity of competitive relationships and how they can be impacted by ecological and anthropogenic factors. In light of rapid declines of carnivore populations across the globe, understanding how interspecific competition limits large carnivores is an important component for the management and conservation of these species. Using data from 233 individuals in five clans and capture-recapture robust design models we estimated the survival and density of spotted hyaena in 5 clans in the Liuwa Plain, where their main competitor, the African lion was reduced to a single individual. We tested for the effects of settlements, prey density, competition with lions and hyaena clan size on the mean hyaena survival. The average population size during the duration of study was 151.2 + or = 5.9(SE) individuals. Population size fluctuated through time with the seasonal fluctuations of the main prey species, the blue wildebeest. Mean annual survival across all age classes was 0.93 (95%CI: 0.39 - 0.99). We found no detectable effects of variation in hyaena clan size, prey density, local variation in utilization by lions, or proximity to people on survival. We also estimated the densities of wildebeest, oribi and zebra, the main prey species for the carnivores in the system using distance sampling methods. We tested for the effects of variables in three classes: environmental (year, season, vegetation, grass height, burn, water presence), predation risk (hyaena density), and anthropogenic (distance to park boundary and settlements). Densities ranged from 6.2 - 60.8 individuals km superscript -2 for wildebeest, 1.1-14.5 individuals km superscript -2 for oribi, and 1.8-8.1 individuals km superscript -2 for zebra. Results reveal resource partitioning among ungulate species and indicate that predation risk and proximity to humans affect ungulate distributions with implications for managing migrations in the Greater Liuwa Ecosystem. They suggest that the maintenance of native prey populations allows coexistence between humans and large carnivores in Liuwa Plain National Park.