Population limitation of a non-ruminant in a nutrient-poor ecosystem—predation rather than food

Abstract

Current theory predicts that plains zebra (Equus quagga) populations should be resource-limited. Long-term, detailed work in the Hwange ecosystem (Zimbabwe) on zebras and all their major predators provides empirical data to test this on a population that has been at a low density for at least 2 decades and is largely naturally regulated. Information on body condition is used as an indicator of resource use, and offtakes by the three major predators are estimated from a synthesis of data on densities and diets. This information leads to rejection of the expectations for resource limitation. Zebras provide a significant part of the diets of all the main predators and are important (11%) for the most abundant of these, spotted hyaenas (Crocuta crocuta). Using conservative values, we calculate that the three main predators, hyaenas, lions (Panthera leo), and leopards (Panthera pardus), kill some 17.5% of the zebra population. Given that this estimated offtake is of the same order of magnitude as maximum population growth (22.3% per year), we conclude that this population is likely to be limited by predation. Further work is needed to better understand the mechanisms by which the greater susceptibility of juveniles to predation in ungulates contributes to population limitation.