Alpha predator

An apex predator, also known as an alpha predator or top predator, is a predator at the top of a food chain, with no natural predators. Apex predators are usually defined in terms of trophic dynamics, meaning that they occupy the highest trophic levels and serve as keystone species, vital to their ecosystems. One study of marine food webs defined apex predators as those feeding at trophic levels above four. Food chains are often far shorter on land, usually limited to the third trophic level – for example, wolves prey mostly upon large herbivores. The apex predator concept is applied in wildlife management, conservation and ecotourism.

Apex predators affect prey species' population dynamics. Where two competing species are in an ecologically unstable relationship, apex predators tend to create stability if they prey upon both. Inter-predator relationships are also affected by apex status. Non-native fish, for example, have sometimes devastated formerly dominant predators. One lake manipulation study found that when the non-native smallmouth bass was removed, lake trout, the suppressed native apex predator, diversified its prey selection and increased its trophic level.

Apex predators have "profound" effects on ecosystems, as the consequences of both controlling prey density and restricting smaller predators, and may be capable of self-regulation. When introduced to subarctic islands, for example, Arctic foxes' predation of seabirds has been shown to turn grassland into tundra. Such wide-ranging effects on lower levels of an ecosystem are termed trophic cascades. The removal of top-level predators, often through human agency, can radically cause or disrupt trophic cascades.

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