The “ecology of fear” emphasizes the potential role of predation risk in shaping large herbivore behaviour and the way they affect forest ecology. In this study we show how the presence or absence of predation risk by hunters, together with or in the absence of carnivores, affect the behaviour and ecological effects of Sitka black-tailed deer introduced to the islands of Haida Gwaii, (British Columbia, Canada) or native to coastal BC. Deer in risk-free population showed remarkable tolerance to human presence while deer exposed to severe culling in the recent past, exhibited more costly anti-predator behaviors (long flight initiation distances and long travel distances when fleeing; reluctance to consume foreign bait or to investigate baited traps; increased night-time foraging) and were more likely to use exposed habitats. Contrasts in hunting histories translated into dramatic variation in the nature, distribution and abundance of the understory vegetation deer depended on. The experimental translocation of unwary deer from an island without hunting to an island where culls had partially restored the vegetation, showed that the lack of costly anti-predator behaviors was not significantly affected by the presence of abundant and higher quality forage. We interpreted these results as evidence that the experience of risk was key in explaining the observed behavioral contrasts between deer populations with different risk histories. We strengthened this conclusion by analysing the proportion of stable isotopes in deer bone collagen to show that deer foraged less in the exposed intertidal zone when predation risk was higher. Our results provide novel insights into how predation risk affects ecological networks, ecosystem complexity and animal behaviour. By revealing the role of key species, they may enable better strategies for future ecosystem restoration.