An apex predator, also known as an alpha predator, super predator, top predator or top-level predator, is a predator residing at the top of a food chain upon which no other creatures prey. Apex predators are usually defined in terms of trophic dynamics, meaning that apex-predator species occupy the highest trophic level or levels and play a crucial role in maintaining the health of their ecosystems. One study of marine food webs defined apex predators as greater than trophic level four. The apex predator concept is commonly applied in wildlife management, conservation and ecotourism.