Predators and management influence adult sex ratio of ungulate communities: Synergies and challenges for contemporary conservation

Abstract

Adult sex ratio (ASR) is important for the ecology, behaviour and life histories of large ungulate populations. ASR, however, varies considerably in wild populations, with driving factors not fully understood. Predation is one possible driver and can alter the ASR of prey species via direct and indirect mechanisms. In the absence of predators, management may also alter ungulate ASR via sex-biased animal removal. Here, we utilised a wildlife reserve divided into two sections, but with comparable environments and ungulate communities. One section hosts lions (Panthera leo) with no management-driven wildlife offtakes, while the other has cheetah (Acinonyx jubatus), wild dogs (Lycaon pictus) and management periodically removes ungulates. To assess the impacts of these differences on ungulate ASR, we surveyed 12 ungulate species (body mass: 10–2000 kg) that co-occur in both sections, revealing that five ungulate species exhibited statistically significant differences in ASR between sections. Predators exerted contrasting direct effects on prey ASR: lion generally displayed a bias towards killing male prey individuals, cheetah had a weak female bias in smaller prey species, and wild dog displayed no general pattern across species. A meta-analysis of sex-biased predator mortality in 53 ungulate populations across Africa broadly supported our findings. Lion appeared to further elicit indirect changes to herding and sexual segregation behaviours in larger-bodied ungulate species, but we found limited evidence for changes in ungulate nutrition or body condition. In the section without lions, wildlife management annually removed ~10%–20% of larger-bodied ungulate populations, with a mild bias towards male individuals. This intervention somewhat replicated the direct effects of natural lion predation on ungulate ASR. Management removals did not, however, stimulate the same behavioural effects in ungulate populations as lions. Synthesis and applications. Predators and management can influence ungulate adult sex ratio (ASR) through multiple pathways, with important implications for breeding system evolution and population dynamics. Given many landscapes are defaunated of natural predators, we demonstrate the importance of incorporating sex-biased wildlife management into contemporary conservation plans. Where management attempts to replicate the effects of ‘missing’ predators, efforts should be made to monitor ungulate ASR and synergistically complement existing predator guilds.