Impacts of predators on prey populations are incurred not only through mortality inflicted, but also from how the risk of mortality affects the behaviour, spatial distribution and resource access of potential prey species. This risk is governed by exposure to predators and vulnerability following encounters. Behavioural responses to reduce risks have ramifying consequences for habitat partitioning, regional distributions and local impacts of herbivores on vegetation. These consequences are reviewed for carnivore-ungulate assemblages in African savanna ecosystems. Vigilance serves multiple functions,