Résumé
Predators influence prey populations not only through predation itself,
but also indirectly through prompting changes in prey behaviour. The
behavioural adjustments of prey to predation risk may carry nutritional
costs, but this has seldom been studied in the wild in large mammals.
Here, we studied the effects of an ambush predator, the African lion
(Panthera leo), on the diet quality of plains zebras (Equus quagga) in
Hwange National Park, Zimbabwe. We combined information on movements of
both prey and predators, using GPS data, and measurements of faecal crude
protein, an index of diet quality in the prey. Zebras which had been in
close proximity to lions had a lower quality diet, showing that
adjustments in behaviour when lions are within short distance carry
nutritional costs. The ultimate fitness cost will depend on the frequency
of predator–prey encounters and on whether bottom-up or top-down forces
are more important in the prey population. Our finding is the first
attempt to our knowledge to assess nutritionally mediated risk effects in
a large mammalian prey species under the threat of an ambush predator, and
brings support to the hypothesis that the behavioural effects of predation
induce important risk effects on prey populations.