Thelion is the world'ssecond-largest big cat and serves as an apex land predator in Africa.[1][2]Thesaltwater crocodile is the largest living reptile and the dominant predator throughout its range.[3][4]Thegreat white shark (bottom) is one of the top marine predators; however, theorca (top) is known to prey upon them. Thus, great white sharks are not true apex predators. Despite coexisting the majority of the time, confrontations may occur in stressed environments when both species compete for limited resources.
Anapex predator, also known as atop predator orsuperpredator, is apredator[a] at the top of afood chain, without natural predators of its own.[6][7]
Apex predators are usually defined in terms oftrophic dynamics, meaning that they occupy the highesttrophic levels. Food chains are often far shorter on land, usually limited to being secondary consumers – for example,wolves prey mostly upon largeherbivores (primary consumers), which eat plants (primary producers). The apex predator concept is applied inwildlife management,conservation, andecotourism.
Apex predators have a long evolutionary history, dating at least to theCambrian period when animals such asAnomalocaris andTimorebestia dominated the seas.
Humans have for many centuries interacted with other apex predators including thewolf,birds of prey, andcormorants to hunt game animals, birds, and fish respectively. More recently, humans have started interacting with apex predators in new ways. These include interactions viaecotourism, such as with thetiger shark, and throughrewilding efforts, such as the proposed reintroduction of theIberian lynx.
Apexpredators affect prey species'population dynamics and populations of other predators, both in aquatic and terrestrial ecosystems. Non-native predatory fish, for instance, have sometimes devastated formerly dominant predators. A lake manipulation study found that when the non-nativesmallmouth bass was removed,lake trout, the suppressed native apex predator, diversified its prey selection and increased itstrophic level.[9] As a terrestrial example, thebadger, an apex predator, preys upon and also competes with thehedgehog, amesopredator, for food such as insects, small mammals, reptiles, amphibians, and the eggs of ground-nesting birds. Removal of badgers (in a trial investigatingbovine tuberculosis) caused hedgehog densities to more than double.[10] Predators that exert top-down control on organisms in their community are often consideredkeystone species.[11]
Apex predators can have profound effects on ecosystems, as the consequences of both controlling prey density and restricting smaller predators, and may be capable of self-regulation.[12] They are central to the functioning of ecosystems, the regulation of disease, and the maintenance of biodiversity.[13] When introduced tosubarctic islands, for example,Arctic foxes' predation ofseabirds has been shown to turngrassland into thetundra.[14] Such wide-ranging effects on lower levels of an ecosystem are termedtrophic cascades. The removal of top-level predators, often through human agency, can cause or disrupt trophic cascades.[15][16][17] For example, a reduction in the population ofsperm whales, apex predators with afractional trophic level of 4.7, by hunting has caused an increase in the population of the large squid, with trophic level over 4 (carnivores that eat other carnivores).[18] This effect, calledmesopredator release,[19] occurs in terrestrial and marine ecosystems; for instance, in North America, the ranges of all apex carnivores have contracted whereas those of 60% of mesopredators have grown in the past two centuries.[20]
Thewolf is both an apex predator and akeystone species, affecting its prey's behaviour and the wider ecosystem.
Because apex predators have powerful effects on other predators, herbivores, and plants, they can be important in nature conservation.[21] Humans have hunted many apex predators close to extinction, but in some parts of the world, these predators are now returning.[22] They are increasingly threatened byclimate change. For example, thepolar bear requires extensive areas ofsea ice to hunt its prey, typically seals, but climate change is shrinking the sea ice of the Arctic, forcing polar bears to fast on land for increasingly long periods.[23]
Dramatic changes in theGreater Yellowstone Ecosystem were recorded after thegray wolf, both an apex predator and akeystone species (one with a large effect on its ecosystem), was reintroduced toYellowstone National Park in 1995 as aconservation measure.Elk, the wolves' primary prey, became less abundant and changed their behavior, freeingriparian zones from constant grazing and allowingwillows,aspens, andcottonwoods to flourish, creatinghabitats forbeaver,moose, and scores of other species.[24] In addition to their effect on prey species, the wolves' presence also affected one of the park'svulnerable species, thegrizzly bear: emerging fromhibernation, having fasted for months, the bears chose toscavenge wolf kills,[25] especially during the autumn as they prepared to hibernate once again.[26] The grizzly bear gives birth during hibernation, so the increased food supply is expected to produce an increase in the number of cubs observed.[27] Dozens of other species, including eagles, ravens,magpies, coyotes, andblack bears have also been documented as scavenging from wolf kills within the park.[28]
Humans sometimes live by hunting other animals for food and materials such as fur, sinew, and bone, as in thiswalrus hunt in the Arctic, but humans' status as apex predators is debated.
Ecologists have debated whetherhumans are apex predators. For instance, Sylvain Bonhommeau and colleagues argued in 2013 that across the global food web, a fractional human trophic level (HTL) can be calculated as the mean trophic level of every species in the human diet, weighted by the proportion that that species forms in the diet. This analysis gives an average HTL of 2.21, varying between 2.04 (forBurundi, with a 96.7% plant-based diet) and 2.57 (forIceland, with 50% meat and fish, 50% plants). These values are comparable to those of non-apex predators such as theanchovy orpig.[29]
However, Peter D. Roopnarine criticized Bonhommeau's approach in 2014, arguing that humans are apex predators and that the HTL was based on terrestrial farming where indeed humans have a low trophic level, mainly eating producers (crop plants at level 1) or primary consumers (herbivores at level 2), which as expected places humans at a level slightly above 2. Roopnarine instead calculated the position of humans in two marine ecosystems, a Caribbean coral reef and theBenguela system near South Africa. In these systems, humans mainly eat predatory fish and have a fractional trophic level of 4.65 and 4.5, respectively, which in Roopnarine's view makes those humans apex predators.[b][30]
In 2021, Miki Ben-Dor and colleagues compared human biology to that of animals at various trophic levels. Using metrics as diverse as tool use and acidity of the stomach, they concluded that humans evolved as apex predators, diversifying their diets in response to the disappearance of most of the megafauna that had once been their primary source of food.[31]
Apex predators are thought to have existed since at least theCambrian period, around 500 million years ago. Extinct species cannot be directly determined to be apex predators as their behavior cannot be observed, and clues to ecological relationships, such as bite marks on bones or shells, do not form a complete picture. However, indirect evidence such as the absence of any discernible predator in an environment is suggestive.Anomalocaris was an aquatic apex predator, in the Cambrian. Its mouthparts are clearly predatory, and there were no larger animals in the seas at that time.[32]
Carnivoroustheropod dinosaurs includingAllosaurus[33] andTyrannosaurus[34] are theorized to have been apex predators, based on their size, morphology, and dietary needs.
Tiger sharks are popularecotourism subjects, but their ecosystems may be affected by the food provided to attract them.
Ecotourism sometimes relies on apex predators to attract business.[45][46] Tour operators may in consequence decide to intervene in ecosystems, for example by providing food to attract predators to areas that can conveniently be visited.[45] This in turn can have effects on predator population and therefore on the wider ecosystem.[45] As a result, provisioning of species such as thetiger shark is controversial, but its effects are not well established by empirical evidence.[45] Other affected apex predators includebig cats and crocodiles.[46]
The reintroduction of predators like thelynx is attractive to conservationists, but alarming to farmers.
In some densely populated areas like theBritish Isles, all the large native predators like the wolf, bear, wolverine and lynx have becomeextirpated, allowing herbivores such as deer to multiply unchecked except by hunting.[47] In 2015, plans were made to reintroducelynx to the counties ofNorfolk,Cumbria, andNorthumberland in England, andAberdeenshire in Scotland as part of therewilding movement.[48] The reintroduction of large predators is controversial, in part because of concern among farmers for theirlivestock.[48] Conservationists such as Paul Lister propose instead to allow wolves and bears to hunt their prey in a "managed environment" on large fenced reserves; however, this undermines the objective of rewilding.[48]
^Zoologists generally excludeparasites from trophic levels as they are (often much) smaller than their hosts, and individual species with multiple hosts at different life-cycle stages would occupy multiple levels. Otherwise they would often be at the top level, above apex predators.[5]
^However, humans had a network trophic level (NTL) of 4.27 in the coral reef system, compared to an NTL of 4.8 for theblacktip shark in the same system. Therefore, humans were not the topmost apex predator there.[30]
^Itstrophic level would be exactly 4 if the fish's prey were pure herbivores, higher if the prey were themselves carnivorous.
^Pace, M. L.; Cole, J. J.; et al. (December 1999). "Trophic cascades revealed in diverse ecosystems".Trends in Ecology and Evolution.14 (12):483–488.doi:10.1016/S0169-5347(99)01723-1.PMID10542455.
^Prugh, Laura R.; Stoner, Chantal J.; Epps, Clinton W.; Bean, William T.; Ripple, William J.; Laliberte, Andrea S.; Brashares, Justin S. (2009). "The Rise of the Mesopredator".BioScience.59 (9):779–791.doi:10.1525/bio.2009.59.9.9.S2CID40484905.
^Shipman, Pat (2015).The invaders : how humans and their dogs drove Neanderthals to extinction. Harvard University Press.ISBN978-0-674-73676-4.OCLC893897294.
^Rudstam, Lars G.; VanDeValk, Anthony J. (February 2004). "Cormorant Predation and the Population Dynamics of Walleye and Yellow Perch in Oneida Lake".Ecological Applications.14 (1):149–163.Bibcode:2004EcoAp..14..149R.doi:10.1890/03-5010.JSTOR4493527.providing the opportunity to study the effects of an increase of a top predator on an existing predator-prey system
^abMacdonald, Catherine; Gallagher, Austin J.; Barnett, Adam; Brunnschweiler, Juerg; Shiffman, David S.; Hammerschlag, Neil (2017). "Conservation potential of apex predator tourism".Biological Conservation.215:132–141.Bibcode:2017BCons.215..132M.doi:10.1016/j.biocon.2017.07.013.
^Jones, Lucy."The rewilding plan that would return Britain to nature". BBC. Retrieved6 June 2018.wolves, bears and lynx roamed the land. ... Humans chopped down the trees to make space for farms, and hunted the large animals to extinction, leaving plant-eaters to decimate the country's flora. Britain is now one of the few countries in the world that doesn't have top predators.
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