An apex predator, also known as an alpha predator or top predator, is a predator residing at the top of a food chain upon which no other creatures prey.[n 1] 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. The apex predator concept is commonly applied in wildlife management, conservation and ecotourism.
Food chains are often far shorter on land, with their apices usually limited to the third trophic level – for example, giant constrictor snakes, hyenas, varanid lizards, wolves, humans, or big cats preying mostly upon large herbivores. Most apex predators are hypercarnivores.
Effect on prey population dynamicsEdit
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 been known to devastate 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.
Effects on wider ecosystemEdit
Effects on wider ecosystem characteristics such as plant ecology have been debated, but there is evidence of a significant impact by apex predators. 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 – and, especially, recently – through human agency, can radically cause or disrupt trophic cascades.
A now commonly cited example of the effect of apex predators on an ecosystem is the dramatic changes in the Greater Yellowstone Ecosystem recorded after the gray wolf was reintroduced to Yellowstone National Park in 1995. Elk, the wolves' primary prey, became less abundant and changed their behavior, freeing riparian zones from constant grazing and allowing willows, aspens and cottonwoods to flourish, creating habitats for beaver, moose and scores of other species. In addition to their effect on prey species, the wolves' presence also affected one of the park's vulnerable species, the grizzly bear: emerging from hibernation, having fasted for months, the bears chose to scavenge wolf kills,:56 especially during the autumn as they prepared to hibernate once again.:90 The grizzly bear gives birth during hibernation, so the increased food supply is expected to produce an increase in the numbers of cubs observed. Dozens of other species, including eagles, ravens, magpies, coyotes and black bears have also been documented as scavenging from wolf kills within the park.
Keystone species are often apex predators, though there may be other species at the same trophic level. The first example to be described (by Robert Paine) was the relationship between the starfish Pisaster ochraceus and the mussel Mytilus californianus,
Keystone species thus do not have to be at the highest trophic level, but may have their own predators. Thus, sea stars are prey for sharks, rays, and sea anemones, while sea otters are prey for orca.
The status of homo sapiens as an apex predator has a complexity subject to various analyses for years.[quantify] The highly varied environments that human beings have lived in (and continue to live in) coupled with the similarly highly varied behaviors of human cultures towards animals make generalizations particularly difficult; though as omnivores that consume more plant matter than meat, humans have the organized ability to drive other species into extinction as well as threatened status vastly unlike any other animal. The topic has been explored in publications such as the Proceedings of the National Academy of Sciences and Scientific American, with disputed results.
Human tool use (especially firearms, but also clubs, spears, nets, and fishing gear) and collaboration with dogs make humans among the deadliest predators on Earth.
Wolves hunt in packs, often against prey much larger than themselves.
The tiger, like all cats a powerful predator, is one of the largest non-aquatic mammalian predators.
Electric eels use a powerful electrical shock to subdue prey and dissuade attack.
The whale shark, the world's largest fish, is a filter feeder with no natural predators.
The American alligator is top predator in the swamps of subtropical North America.
The honey badger is an aggressive predator capable of holding its own against snakes, big cats, bears, hyenas, dogs, and humans.
Driver ants in large swarms kill prey several hundred times their size. Their painful bites keep larger animals from attacking them.
The Eurasian brown bear is an adaptable omnivore.
Great white sharks are adaptable and sophisticated hunters.
Tyrannosaurus rex was one of the largest carnivorous dinosaurs, and could exert the largest bite force of any terrestrial animal.
Leopard seals take as prey other carnivores as large as penguins and seals.
Dogs may hunt in collaboration with humans.
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