Abstract
(1) Individual differences in the predicted foraging efficiency of forest-dwelling red deer Cervus elaphus L. are used to assess the consequences for population demography. (2) Analysis of the ontogeny of the incisor arcade and its allometry with body weight shows that growing animals experience restricted incisor breadth relative to weight during the transition from juvenile to mature dentition. (3) A model of bite dimensions predicts that yearlings, male calves and stags will have the greatest reduction in foraging efficiency when feeding on depleted resources. This is corroborated by observed patterns of seasonal weight loss. (4) Sex differences in growth strategy combined with the ontogeny and allometry of the incisor arcade may cause differential mortality between age and sex classes. It is suggested that population ecology and life-history theory should take greater account of natural selection on the juvenile phase.