Human- and risk-mediated browsing pressure by sympatric antelope in an African savanna

Abstract

Human activity shapes landscape heterogeneity, which can influence where and how species interact. In African savannas, human-mediated changes to woody cover affect perceptions of risk and foraging decisions by large herbivores. Through cafeteria-style feeding trials, we presented two common, browsing ungulates (Guenther's dik-dik [Madoqua guentheri] and impala [Aepyceros melampus]) with branches from four tree species that varied in their relative investment in mechanical and chemical defenses. We conducted trials in habitats that were perceived as risky to either dik-dik (i.e., open habitat) or impala (i.e., bushland habitat). We found that dik-dik preferred to eat thorny trees low in tannin content within bushland habitats, while the larger-bodied impala preferred tannin-rich but thorn-less branches within open habitats. Risk-induced habitat use homogenized browsing pressure in the lower canopy, but increased heterogeneity in browsing pressure in the upper canopy. In addition, plant defenses neutralized the effects of risk, and foraging height on browsing pressure. Our results demonstrate how foraging experiments—typically the basis for field studies on species coexistence—can be extended to make inferences about consumer-resource dynamics in human-modified landscapes.