Predation
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Ecology
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Predation is a biological interaction in which one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill the host) and (which always does, eventually). It is distinct from Scavenger on dead prey, though many predators also scavenge; it overlaps with Herbivore, as Seed predation and destructive are predators.
Predation behavior varies significantly depending on the organism. Many predators, especially , have evolved distinct hunting strategy. Pursuit predation involves the active search for and pursuit of prey, whilst ambush predation instead wait for prey to present an opportunity for capture, and often use stealth or aggressive mimicry. Other predators are opportunism or omnivore and only practice predation occasionally.
Most obligate carnivores are specialized for hunting. They may have acute senses such as eye, hearing, or olfaction for prey detection. Many predatory animals have sharp or to grip, kill, and cut up their prey. Physical strength is usually necessary for large carnivores such as to kill larger prey. Other adaptations include stealth, endurance, intelligence, social behaviour, and aggressive mimicry that improve hunting efficiency.
Predation has a powerful selective effect on prey, and the prey develops anti-predator adaptations such as warning colouration, and other signals, camouflage, mimicry of well-defended species, and defensive spines and chemicals. Sometimes predator and prey find themselves in an evolutionary arms race, a cycle of adaptations and counter-adaptations. Predation has been a major driver of evolution since at least the Cambrian period.
Definition
There are other difficult and borderline cases. are small animals that, like predators, feed entirely on other organisms; they include and that consume blood from living animals, and that consume sap from living plants. However, since they typically do not kill their hosts, they are now often thought of as parasites.
, organisms that only eat organisms found already dead, are not predators, but many predators such as the jackal and the hyena scavenge when the opportunity arises. Among invertebrates, such as are both hunters and scavengers of other insects.
Seed predation is restricted to mammals, birds, and insects but is found in almost all terrestrial ecosystems.
Some plants, like the pitcher plant, the Venus fly trap and the sundew, are carnivorous and consume insects. Methods of predation by plants varies greatly but often involves a food trap, mechanical stimulation, and electrical impulses to eventually catch and consume its prey. Some carnivorous fungi catch using either active traps in the form of constricting rings, or passive traps with adhesive structures.
Many species of protozoa () and bacteria () prey on other microorganisms; the feeding mode is evidently ancient, and evolved many times in both groups. Among freshwater and marine zooplankton, whether single-celled or multi-cellular, predatory grazing on phytoplankton and smaller zooplankton is common, and found in many species of , , , , a diverse range of meroplankton animal larvae, and two groups of crustaceans, namely and . summarizes findings from many authors.
Prey distributions are often clumped, and predators respond by looking for patches where prey is dense and then searching within patches. Where food is found in patches, such as rare shoals of fish in a nearly empty ocean, the search stage requires the predator to travel for a substantial time, and to expend a significant amount of energy, to locate each food patch. For example, the black-browed albatross regularly makes foraging flights to a range of around , up to a maximum foraging range of for breeding birds gathering food for their young. With static prey, some predators can learn suitable patch locations and return to them at intervals to feed. The optimal foraging strategy for search has been modelled using the marginal value theorem.
Search patterns often appear random. One such is the Lévy walk, that tends to involve clusters of short steps with occasional long steps. It is a good fit to the behaviour of a wide variety of organisms including bacteria, honeybees, sharks and human hunter-gatherers.
One of the factors to consider is size. Prey that is too small may not be worth the trouble for the amount of energy it provides. Too large, and it may be too difficult to capture. For example, a mantid captures prey with its forelegs and they are optimized for grabbing prey of a certain size. Mantids are reluctant to attack prey that is far from that size. There is a positive correlation between the size of a predator and its prey.
A predator may assess a patch and decide whether to spend time searching for prey in it. This may involve some knowledge of the preferences of the prey; for example, can choose a patch of vegetation suitable for their aphid prey.
An extreme form of pursuit is endurance or persistence hunting, in which the predator tires out the prey by following it over a long distance, sometimes for hours at a time. The method is used by human and by Canidae such as African wild dogs and domestic hounds. The African wild dog is an extreme persistence predator, tiring out individual prey by following them for many miles at relatively low speed.
A specialised form of pursuit predation is the of . These very large marine predators feed on plankton, especially krill, diving and actively swimming into concentrations of plankton, and then taking a huge gulp of water and Filter feeder it through their feathery baleen plates.
Pursuit predators may be Social predator, like the lion and wolf that hunt in groups, or solitary.
Predators of different species sometimes cooperate to catch prey. In coral reefs, when fish such as the grouper and coral trout spot prey that is inaccessible to them, they signal to Giant moray, Humphead wrasse or . These predators are able to access small crevices and flush out the prey. have been known to help whalers hunt . ISBN R-105732-9.
Social hunting allows predators to tackle a wider range of prey, but at the risk of competition for the captured food. Solitary predators have more chance of eating what they catch, at the price of increased expenditure of energy to catch it, and increased risk that the prey will escape. Ambush predators are often solitary to reduce the risk of becoming prey themselves. Of 245 terrestrial members of the Carnivora (the group that includes the cats, dogs, and bears), 177 are solitary; and 35 of the 37 Felidae are solitary, including the cougar and cheetah. However, the solitary cougar does allow other cougars to share in a kill, and the coyote can be either solitary or social.
For Prey detection, predators have well-developed eye, olfaction, or hearing. Predators as diverse as and have forward-facing eyes, providing accurate binocular vision over a relatively narrow field of view, whereas prey animals often have less acute all-round vision. Animals such as foxes can smell their prey even when it is concealed under of snow or earth. Many predators have acute hearing, and some such as echolocating hunt exclusively by active or passive use of sound.
Predators including , birds of prey, and ants share powerful jaws, sharp teeth, or claws which they use to seize and kill their prey. Some predators such as and fish-eating birds like herons and cormorants swallow their prey whole; some snakes can unhinge their jaws to allow them to swallow large prey, while fish-eating birds have long spear-like beaks that they use to stab and grip fast-moving and slippery prey. Fish and other predators have developed the ability to crush or open the armoured shells of molluscs.
Many predators are powerfully built and can catch and kill animals larger than themselves; this applies as much to small predators such as and as to big and visibly muscular carnivores like the cougar and lion.
In size-selective predation, predators select prey of a certain size. Large prey may prove troublesome for a predator, while small prey might prove hard to find and in any case provide less of a reward. This has led to a correlation between the size of predators and their prey. Size may also act as a refuge for large prey. For example, adult elephants are relatively safe from predation by lions, but juveniles are vulnerable.
In aggressive mimicry, certain predators, including insects and fishes, make use of coloration and behaviour to attract prey. Female Photuris Firefly, for example, copy the light signals of other species, thereby attracting male fireflies, which they capture and eat. are ambush predators; camouflaged as flowers, such as , they attract prey and seize it when it is close enough. are extremely well camouflaged, and actively lure their prey to approach using an Fin ray, a bait on the end of a rod-like appendage on the head, which they wave gently to mimic a small animal, gulping the prey in an extremely rapid movement when it is within range.
The metaphor of an arms race implies ever-escalating advances in attack and defence. However, these adaptations come with a cost; for instance, longer legs have an increased risk of breaking, while the specialized tongue of the chameleon, with its ability to act like a projectile, is useless for lapping water, so the chameleon must drink dew off vegetation.
The "life-dinner" principle has been criticized on multiple grounds. The extent of the asymmetry in natural selection depends in part on the heritability of the adaptive traits. Also, if a predator loses enough dinners, it too will lose its life. On the other hand, the fitness cost of a given lost dinner is unpredictable, as the predator may quickly find better prey. In addition, most predators are generalists, which reduces the impact of a given prey adaption on a predator. Since specialization is caused by predator-prey coevolution, the rarity of specialists may imply that predator-prey arms races are rare.
It is difficult to determine whether given adaptations are truly the result of coevolution, where a prey adaptation gives rise to a predator adaptation that is countered by further adaptation in the prey. An alternative explanation is escalation, where predators are adapting to competitors, their own predators or dangerous prey. Apparent adaptations to predation may also have arisen for other reasons and then been co-opted for attack or defence. In some of the insects preyed on by bats, hearing evolved before bats appeared and was used to hear signals used for territorial defence and mating. Their hearing evolved in response to bat predation, but the only clear example of reciprocal adaptation in bats is stealth echolocation.
A more symmetric arms race may occur when the prey are dangerous, having spines, quills, toxins or venom that can harm the predator. The predator can respond with avoidance, which in turn drives the evolution of mimicry. Avoidance is not necessarily an evolutionary response as it is generally learned from bad experiences with prey. However, when the prey is capable of killing the predator (as can a coral snake with its venom), there is no opportunity for learning and avoidance must be inherited. Predators can also respond to dangerous prey with counter-adaptations. In western North America, the common garter snake has developed a resistance to the toxin in the skin of the rough-skinned newt.
Trophic transfer efficiency measures how effectively energy is passed up to higher trophic levels by predation. Each transfer decreases the available energy due to heat, waste, and the natural Metabolism that occur as predators consume their prey. The result is that only about 10% of the energy at a trophic level is transferred to the next level. This limits the number of trophic levels that an individual ecosystem is capable of supporting.
The elimination of wolves from Yellowstone National Park had profound impacts on the trophic pyramid. In that area, wolves are both keystone species and apex predators. Without predation, herbivores began to over-graze many woody browse species, affecting the area's plant populations. In addition, wolves often kept animals from grazing near streams, protecting the ' food sources. The removal of wolves had a direct effect on the beaver population, as their habitat became territory for grazing. Increased browsing on and along Blacktail Creek due to a lack of predation caused channel incision because the reduced beaver population was no longer able to slow the water down and keep the soil in place. The predators were thus demonstrated to be of vital importance in the ecosystem.
Cyclical fluctuations have been seen in populations of predator and prey, often with offsets between the predator and prey cycles. A well-known example is that of the snowshoe hare and lynx. Over a broad span of in Alaska and Canada, the hare populations fluctuate in near synchrony with a 10-year period, and the lynx populations fluctuate in response. This was first seen in historical records of animals caught by Fur trade for the Hudson's Bay Company over more than a century.
A simple model of a system with one species each of predator and prey, the Lotka–Volterra equations, predicts population cycles.
The Lotka–Volterra equations rely on several simplifying assumptions, and they are structurally unstable, meaning that any change in the equations can stabilize or destabilize the dynamics.
Many factors can stabilize predator and prey populations. One example is the presence of multiple predators, particularly generalists that are attracted to a given prey species if it is abundant and look elsewhere if it is not. As a result, population cycles tend to be found in northern temperate and subarctic ecosystems because the food webs are simpler. The snowshoe hare-lynx system is subarctic, but even this involves other predators, including coyotes, and great horned owls, and the cycle is reinforced by variations in the food available to the hares.
A range of mathematical models have been developed by relaxing the assumptions made in the Lotka–Volterra model; these variously allow animals to have geographic distributions, or to animal migration; to have differences between individuals, such as and an age structure, so that only some individuals reproduce; to live in a varying environment, such as with changing ; and analysing the interactions of more than just two species at once. Such models predict widely differing and often chaos theory predator-prey population dynamics. The presence of refuge areas, where prey are safe from predators, may enable prey to maintain larger populations but may also destabilize the dynamics.
The earliest predators were microbial organisms, which engulfed or grazed on others. Because the fossil record is poor, these first predators could date back anywhere between 1 and over 2.7 Gya (billion years ago). Predation visibly became important shortly before the Cambrian period—around —as evidenced by the almost simultaneous development of calcification in animals and algae, and predation-avoiding . However, predators had been grazing on micro-organisms since at least , with evidence of selective (rather than random) predation from a similar time.
Auroralumina attenboroughii is an Ediacaran crown-group (557–562 mya, some 20 million years before the Cambrian explosion) from Charnwood Forest, England. It is thought to be one of the earliest predatory animals, catching small prey with its as modern cnidarians do.
The fossil record demonstrates a long history of interactions between predators and their prey from the Cambrian period onwards, showing for example that some predators drilled through the shells of bivalve and gastropod molluscs, while others ate these organisms by breaking their shells.
Among the Cambrian predators were invertebrates like the with appendages suitable for grabbing prey, large compound eyes and jaws made of a hard material like that in the exoskeleton of an insect.
Some of the first jawed fish were the armoured and mainly predatory placoderms of the Silurian to Devonian periods, one of which, the Dunkleosteus, is considered the world's first vertebrate "superpredator", preying upon other predators.
developed the ability to fly in the Early Carboniferous or Late Devonian, enabling them among other things to escape from predators.
Among the largest predators that have ever lived were the theropod dinosaurs such as Tyrannosaurus from the Cretaceous period. They preyed upon herbivorous dinosaurs such as , and .
In biological pest control, predators (and parasitoids) from a pest's natural range are introduced to control populations, at the risk of causing unforeseen problems. Natural predators, provided they do no harm to non-pest species, are an environmentally friendly and sustainable way of reducing damage to crops and an alternative to the use of chemical agents such as .
Among poetry on the theme of predation, a predator's consciousness might be explored, such as in Ted Hughes's Pike. The phrase "Nature, red in tooth and claw" from Alfred, Lord Tennyson's 1849 poem "In Memoriam A.H.H." has been interpreted as referring to the struggle between predators and prey.
In mythology and folk fable, predators such as the fox and wolf have mixed reputations. translated from Wallner, A. (1998) Die Bedeutung der Raubtiere in der Mythologie: Ergebnisse einer Literaturstudie. – Inf.bl. Forsch.bereiches Landsch.ökol. 39: 4–5. The fox was a symbol of fertility in ancient Greece, but a weather demon in northern Europe, and a creature of the devil in early Christianity; the fox is presented as sly, greedy, and cunning in fables from Aesop onwards. The big bad wolf is known to children in tales such as Little Red Riding Hood, but is a demonic figure in the Icelandic Edda sagas, where the wolf Fenrir appears in the apocalyptic Ragnarok. In the Middle Ages, belief spread in werewolf, men transformed into wolves. In ancient Rome, and in ancient Egypt, the wolf was worshipped, the she-wolf appearing in the founding myth of Rome, suckling Romulus and Remus. More recently, in Rudyard Kipling's 1894 The Jungle Book, Mowgli is raised by the wolf pack. Attitudes to large predators in North America, such as wolf, grizzly bear and cougar, have shifted from hostility or ambivalence, accompanied by active persecution, towards positive and protective in the second half of the 20th century.
Taxonomic range
Foraging
Search
Assessment
Capture
Ambush
Ballistic interception
Pursuit
Handling
Solitary versus social predation
Specialization
Physical adaptations
Diet and behaviour
Camouflage and mimicry
Venom
Electric fields
Physiology
Antipredator adaptations
Coevolution
Role in ecosystems
Trophic level
Biodiversity maintained by apex predation
Population dynamics
Evolutionary history
In human society
Practical uses
Symbolic uses
See also
Notes
Sources
External links
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