Long-term demography of spotted hyena (Crocuta crocuta) in a lion-depleted but prey-rich ecosystem

Interspecific competition has strongly shaped the evolution of large carnivore guilds. In Africa, the lion (Panthera leo) and spotted hyena (Crocuta crocuta, hereafter hyena), exert direct and indirect competitive impacts on each other and on subordinate guild members. The impacts of competition on demography are complex and not well-understood.  With carnivore guilds now ubiquitously impacted by humans, disentangling effects of interspecific competition and other drivers of hyena demography is important.

Western Zambia’s Greater Liuwa Ecosystem (GLE) provides a unique natural experiment where lions were functionally eliminated from the system. Hyenas are the apex predator, with an abundant prey base, and low levels of human-hyena conflict. We measured GLE hyena survival and density, using mark-recapture models fit to ten years of data from 663 known individuals in 11 clans.   

GLE hyena densities were high, though slightly lower than other wildebeest-dominated systems, and stable over 10 years. Survival rates were high for all age-sex classes, and higher than other systems with high lion density, suggesting the possibility of competitive release from lion competition.

These findings provide insights into long-term hyena demography in the absence of their top competitor, but with an abundant prey base. As humans continue to alter ecosystems and fundamental ecological relationships such as interspecific competition, altered dynamics such as competitive release are likely to be widespread and should be a focus of future research.  

Methods
Over a time period of 9 years (2010 - 2019) of year-round monitoring, a combination of stratified random sampling and opportunistic sightings was used to observe 663 individually known hyenas. We binned sightings of each individual into 2-month bins and created capture histories for each individual. 

We then used Bayesian statistical methods to fit Cormack-Jolly-Seber and closed-capture models of age-sex specific survival, reproduction and population densities per season.