Predation is a biological interaction where 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 parasitoidism (which always does, eventually). It is distinct from scavenging on dead prey, though many predators also scavenge; it overlaps with herbivory, as seed predators and destructive frugivores are predators.
Predators may actively search for or pursue prey or wait for it, often concealed. When prey is detected, the predator assesses whether to attack it. This may involve ambush or pursuit predation, sometimes after stalking the prey. If the attack is successful, the predator kills the prey, removes any inedible parts like the shell or spines, and eats it.
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Predators are adapted and often highly specialized for hunting, with acute senses such as vision, hearing, or smell. Many predatory animals, both vertebrate and invertebrate, have sharp claws or jaws to grip, kill, and cut up their prey. Other adaptations include stealth and aggressive mimicry that improve hunting efficiency.
Predation has a powerful selective effect on prey, and the prey develop antipredator adaptations such as warning coloration, alarm calls 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.
At the most basic level, predators kill and eat other organisms. However, the concept of predation is broad, defined differently in different contexts, and includes a wide variety of feeding methods; and some relationships that result in the prey's death are not generally called predation. A parasitoid, such as an ichneumon wasp, lays its eggs in or on its host; the eggs hatch into larvae, which eat the host, and it inevitably dies. Zoologists generally call this a form of parasitism, though conventionally parasites are thought not to kill their hosts. A predator can be defined to differ from a parasitoid in that it has many prey, captured over its lifetime, where a parasitoid's larva has just one, or at least has its food supply provisioned for it on just one occasion.[1][2]
There are other difficult and borderline cases. Micropredators are small animals that, like predators, feed entirely on other organisms; they include fleas and mosquitoes that consume blood from living animals, and aphids that consume sap from living plants. However, since they typically do not kill their hosts, they are now often thought of as parasites.[3][4] Animals that graze on phytoplankton or mats of microbes are predators, as they consume and kill their food organisms; but herbivores that browse leaves are not, as their food plants usually survive the assault.[5] When animals eat seeds (seed predation or granivory) or eggs (egg predation), they are consuming entire living organisms, which by definition makes them predators.[6][7][8]
Scavengers, 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.[9][10][5] Among invertebrates, social wasps (yellowjackets) are both hunters and scavengers of other insects.[11]
While examples of predators among mammals and birds are well known,[12] predators can be found in a broad range of taxa including arthropods. They are common among insects, including mantids, dragonflies, lacewings and scorpionflies. In some species such as the alderfly, only the larvae are predatory (the adults do not eat). Spiders are predatory, as well as other terrestrial invertebrates such as scorpions; centipedes; some mites, snails and slugs; nematodes; and planarian worms.[13] In marine environments, most cnidarians (e.g., jellyfish, hydroids), ctenophora (comb jellies), echinoderms (e.g., sea stars, sea urchins, sand dollars, and sea cucumbers) and flatworms are predatory.[14] Among crustaceans, lobsters, crabs, shrimps and barnacles are predators,[15] and in turn crustaceans are preyed on by nearly all cephalopods (including octopuses, squid and cuttlefish).[16]
Seed predation is restricted to mammals, birds, and insects but is found in almost all terrestrial ecosystems.[8][6] Egg predation includes both specialist egg predators such as some colubrid snakes and generalists such as foxes and badgers that opportunistically take eggs when they find them.[17][18][19]
Some plants, like the pitcher plant, the Venus fly trap and the sundew, are carnivorous and consume insects.[12] 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.[20] Some carnivorous fungi catch nematodes using either active traps in the form of constricting rings, or passive traps with adhesive structures.[21]
Many species of protozoa (eukaryotes) and bacteria (prokaryotes) prey on other microorganisms; the feeding mode is evidently ancient, and evolved many times in both groups.[22][12][23] 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 nanoflagellates, dinoflagellates, ciliates, rotifers, a diverse range of meroplankton animal larvae, and two groups of crustaceans, namely copepods and cladocerans.[24]
To feed, a predator must search for, pursue and kill its prey. These actions form a foraging cycle.[26][27] The predator must decide where to look for prey based on its geographical distribution; and once it has located prey, it must assess whether to pursue it or to wait for a better choice. If it chooses pursuit, its physical capabilities determine the mode of pursuit (e.g., ambush or chase).[28][29] Having captured the prey, it may also need to expend energy handling it (e.g., killing it, removing any shell or spines, and ingesting it).[25][26]
Predators have a choice of search modes ranging from sit-and-wait to active or widely foraging.[30][25][31][32] The sit-and-wait method is most suitable if the prey are dense and mobile, and the predator has low energy requirements.[30] Wide foraging expends more energy, and is used when prey is sedentary or sparsely distributed.[28][30] There is a continuum of search modes with intervals between periods of movement ranging from seconds to months. Sharks, sunfish, Insectivorous birds and shrews are almost always moving while web-building spiders, aquatic invertebrates, praying mantises and kestrels rarely move. In between, plovers and other shorebirds, freshwater fish including crappies, and the larvae of coccinellid beetles (ladybirds), alternate between actively searching and scanning the environment.[30]
Prey distributions are often clumped, and predators respond by looking for patches where prey is dense and then searching within patches.[25] 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.[33] For example, the black-browed albatross regularly makes foraging flights to a range of around 700 kilometres (430 miles), up to a maximum foraging range of 3,000 kilometres (1,860 miles) for breeding birds gathering food for their young.[a][34] With static prey, some predators can learn suitable patch locations and return to them at intervals to feed.[33] The optimal foraging strategy for search has been modelled using the marginal value theorem.[35]
Having found prey, a predator must decide whether to pursue it or keep searching. The decision depends on the costs and benefits involved. A bird foraging for insects spends a lot of time searching but capturing and eating them is quick and easy, so the efficient strategy for the bird is to eat every palatable insect it finds. By contrast, a predator such as a lion or falcon finds its prey easily but capturing it requires a lot of effort. In that case, the predator is more selective.[28]
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.[28]
A predator may also assess a patch and decide whether to spend time searching for prey in it.[25] This may involve some knowledge of the preferences of the prey; for example, ladybirds can choose a patch of vegetation suitable for their aphid prey.[38]
To capture prey, predators have a spectrum of pursuit modes that range from overt chase (pursuit predation) to a sudden strike on nearby prey (ambush predation).[25][39][12] Another strategy in between ambush and pursuit is ballistic interception, where a predator observes and predicts a prey's motion and then launches its attack accordingly.[40]
Ambush or sit-and-wait predators are carnivorous animals that capture prey by stealth or surprise. In animals, ambush predation is characterized by the predator's scanning the environment from a concealed position until a prey is spotted, and then rapidly executing a fixed surprise attack.[41][40] Vertebrate ambush predators include frogs, fish such as the angel shark, the northern pike and the eastern frogfish.[40][42][43][44] Among the many invertebrate ambush predators are trapdoor spiders and Australian Crab spiders on land and mantis shrimps in the sea.[41][45][46] Ambush predators often construct a burrow in which to hide, improving concealment at the cost of reducing their field of vision. Some ambush predators also use lures to attract prey within striking range.[40] The capturing movement has to be rapid to trap the prey, given that the attack is not modifiable once launched.[40] 589ccfa754
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