Predation 57559 225563588 2008-07-14T09:36:37Z DocWatson42 38455 Moved the "External links" section. {{Redirect6|Prey| other uses|Prey (disambiguation)|other uses of the word predator|Predator (disambiguation)}} <!-- Note: This article uses American English --> [[Image:Hawk eating prey.jpg|thumb|300px|right|A juvenile [[Red-tailed Hawk]] eating a [[Microtus|California Vole]]]] In [[ecology]], '''predation''' describes a [[biological interaction]] where a '''predator''' organism feeds on another living organism or organisms known as '''prey'''.<ref name=Ecology>Begon, M., Townsend, C., Harper, J. (1996) ''[[Ecology: Individuals, populations and communities]]'' (Third edition) Blackwell Science, London</ref> Predators may or may not kill their prey prior to [[feeding]] on them, but the act of predation always results in the (ecologically significant) death of the prey<ref>[http://www.britannica.com/search?query=predation Britanica: pray]</ref>. The other main category of [[heterotroph|consumption]] is [[detritivore|detritivory]], the consumption of dead organic material ([[detritus]]). It can at times be difficult to separate the two feeding behaviors<ref name=Ecology />, for example where parasitic species prey on a host organism and then lay their eggs on it for their offspring to feed on its decaying corpse. The key characteristic of predation however is the predator's direct impact on the prey population. On the other hand, detritivores simply eat what is available and have no direct impact on the 'donor' organism(s). ==Classification of predators== [[Image:Sundew with prey.jpg|[[Sundew]],''Drosera'' with prey|thumb|150px]]The unifying theme in all classifications of predation is the predator lowering the [[fitness (biology)|fitness]] of its prey, or put another way, it reduces its prey's chances of survival, reproduction, or both. Ways of classifying predation surveyed here include grouping by [[trophic level]] or diet, by specialization, and by the nature of their interaction with prey. ===Functional classification=== Classification of predators by the extent to which they feed on and interact with their prey is one way ecologists may wish to categorize the different types of predation. Instead of focusing on what they eat, this system classifies predators by the way in which they eat, and the general nature of the interaction between predator and prey species. Two factors are considered here: How close the predator and prey are physically (in the latter two cases the term ''prey'' may be replaced with ''[[host (biology)|host]]''). Additionally, whether or not the prey are directly killed by the predator is considered, with the first and last cases involving certain death. ====True predation==== [[Image:Male Lion and Cub Chitwa South Africa Luca Galuzzi 2004.JPG|thumb|[[Lion]] and cub eating a [[Cape Buffalo]]]] A true predator is one which kills and eats another organism. Whereas other types of predator all harm their prey in some way, this form results in their instant death. Predators may hunt actively for prey, or sit and wait for prey to approach within striking distance, as in [[ambush predator]]s. Some predators kill large prey and dismember or chew it prior to eating it, such as a [[jaguar]], while others may eat their (usually much smaller) prey whole, as does a [[bottlenose dolphin]] or any [[snake]]. In some cases the prey organism may die in the mouth or [[digestive system]] of the predator. [[Baleen whale]]s, for example, eat millions of microscopic plankton at once, the prey being broken down well after entering the whale. [[Seed predation]] is another form of true predation, as [[seed]]s represent potential organisms. Predators of this classification need not eat prey entirely, for example some predators cannot digest [[bone]]s, while others can. Some may merely eat only part of an organism, as in grazing (see below), but still consistently cause its direct death. ====Grazing==== [[Grazing]] organisms may also kill their prey species, but this is seldom the case. While some herbivores like [[zooplankton]] live on unicellular phytoplankton and have no choice but to kill their prey, many only eat a small part of the plant. Grazing livestock may pull some grass out at the roots, but most is simply grazed upon, allowing the plant to regrow once again. [[Kelp]] is frequently grazed in subtidal kelp forests, but regrows at the base of the blade continuously to cope with browsing pressure. Animals may also be 'grazed' upon; female [[mosquito]]s land on hosts briefly to gain sufficient [[protein]]s for the development of their offspring. [[Starfish]] may be grazed on, being capable of regenerating lost arms. ====Parasitism==== [[Parasitism|Parasites]] can at times be difficult to distinguish from grazers. Their feeding behavior is similar in many ways, however they are noted for their close association with their host species. While a grazing species such as an [[elephant]] may travel many kilometers in a single day, grazing on many plants in the process, parasites form very close associations with their hosts, usually having only one or at most a few in their lifetime. This close living arrangement may be described by the term [[symbiosis]], 'living together,' but unlike [[mutualism]] the association significantly reduces the [[fitness (biology)|fitness]] of the host. Parasitic organisms range from the macroscopic [[mistletoe]], a [[parasitic plant]], to microscopic internal parasites such as [[cholera]]. Some species however have more loose associations with their hosts. [[Lepidoptera]] ([[butterfly]] and [[moth]]) larvae may feed parasitically on only a single plant, or they may graze on several nearby plants. It is therefore wise to treat this classification system as a continuum rather than four isolated forms. ====Parasitoidism==== [[Parasitoid]]s are organisms living in or on their host and feeding directly upon it, eventually leading to its death. They are much like parasites in their close symbiotic relationship with their host or hosts. Like the previous two classifications parasitoid predators do not kill their hosts instantly. However, unlike parasites, they are very similar to true predators in that the fate of their prey is quite inevitably death. A well known example of a parasitoids are the [[ichneumon wasp]]s, solitary insects living a free life as an adult, then laying eggs on or in another species such as a caterpillar. Its larva(e) feed on the growing host causing it little harm at first, but soon devouring the internal organs until finally destroying the [[nervous system]] resulting in prey death. By this stage the young wasp(s) are developed sufficiently to move to the next stage in their life cycle. Though limited mainly to the insect order [[Hymenoptera]], parasitoids make up as much as 10% of all insect species.<ref>[[Charles Godfray|Godfray, H.C.J.]] (1994) ''Parasitoids: Behavioral and Evolutionary Ecology''. Princeton University Press, Princeton.</ref> ===Degree of specialization=== {{Further|[[Generalist and specialist species]]}} Among predators there is a large degree of specialization. Many predators specialize in hunting only one species of prey. Others are more opportunistic and will kill and eat almost anything (examples: [[human]]s, [[leopard]]s, and [[dog]]s). The specialists are usually particularly well suited to capturing their preferred prey. The prey in turn, are often equally suited to escape that predator. This is called an [[evolutionary arms race]] and tends to keep the populations of both species in equilibrium. Some predators specialize in certain classes of prey, not just single species. Almost all will switch to other prey (with varying degrees of success) when the preferred target is extremely scarce, and they may also resort to [[scavenger|scavenging]] or a herbivorous diet if possible.<ref>citations needed</ref> ===Trophic level=== Predators are often another organism's prey, and likewise prey are often predators. Though [[blue jay]]s prey on [[insect]]s, they may in turn be prey for [[snake]]s, which may themselves be the prey of [[hawk]]s. One way of classifying predators is by [[trophic level]]. Organisms which feed on [[autotroph]]s, the producers of the [[trophic pyramid]], are known as [[herbivore]]s or ''primary consumers''; those that feed on [[heterotroph]]s such as animals are known as ''secondary consumers''. Secondary consumers are a type of [[carnivore]], but there are also tertiary consumers eating these carnivores, quartary consumers eating them, and so forth. Because only a fraction of energy is passed on to the next level, this hierarchy of predation must end somewhere, and very seldom goes higher than five or six levels. A predator at the top of any [[food chain]] (that is, one that is preyed upon by no organism) is called an [[apex predator]]; examples include the [[orca]], [[tiger]], and [[crocodile]] and even omnivorous humans. An apex predator in one environment may not retain this position if introduced to another habitat, such as dogs among crocodilians. The problem with this system of classification is that many organisms eat from multiple levels of the food chain. A carnivore may eat both secondary and tertiary consumers, and its prey may itself be difficult to classify for similar reasons. Organisms showing both carnivory and herbivory are known as [[omnivore]]s. Even supposedly strict herbivores may supplement their diet with meat. [[Carnivorous plant]]s would be very difficult to fit into this classification, producing their own food but also digesting anything that they may trap. Organisms which eat [[detritivore]]s would also be difficult to classify by such a scheme. ===Predation as competition=== An alternative view offered by [[Richard Dawkins]] is of predation as a form of [[Competition (biology)|competition]]: the [[gene]]s of both the predator and prey are competing for the body (or '[[survival machine]]') of the prey organism.<ref>Dawkins, R. 1976. ''[[The Selfish Gene]]'' Oxford University Press. ISBN 0-19-286092-5</ref> This is best understood in the context of the [[gene centered view of evolution]]. ==Ecological role== Predators may increase the [[biodiversity]] of communities by preventing a single species from becoming dominant. Such predators are known as [[keystone species]], may have a profound influence on the balance of organisms in a particular [[ecosystem]]. Introduction or removal of this predator, or changes in its population density, can have drastic cascading effects on the equilibrium of many other populations in the ecosystem. For example, grazers of a grassland may prevent a single dominant species from taking over.<ref>Botkin, D. and E. Keller (2003) ''Enrivonmental Science: Earth as a living planet'' (p.2) John Wiley & Sons. ISBN 0-471-38914-5</ref> ==Adaptations and behavior== The act of predation can be broken down into a maximum of four stages: Detection of prey, attack, capture and finally consumption.<ref name="Alcock">Alcock, J. (1998) ''Animal Behavior: An Evolutionary Approach'' (6th edition). Sinauer Associates, Inc. Sunderland, Massachusetts. ISBN 0-87893-009-4</ref> The relationship between predator and prey is one which is typically beneficial to the predator, and detrimental to the prey species. Sometimes, however, predation has indirect benefits to the prey species,<ref>Bondavalli, C., and Ulanowicz, R.E. (1999) Unexpected effects of predators upon their prey: The case of the American alligator. ''Ecosystems'', '''2''': 49 - 63</ref> though the individuals preyed upon themselves do not benefit.<ref>Dawkins, R. (2004) ''The Ancestor's Tale'' Boston: Houghton Mifflin ISBN 0618005838</ref> This means that, at each applicable stage, predator and prey species are in an [[evolutionary arms race]] to maximize their respective abilities to obtain food or avoid being eaten. This interaction has resulted in a vast array of [[adaptation]]s in both groups. ===General=== [[Image:Bristol.zoo.dead.leaf.mantis.arp.jpg|right|thumb|Camouflage of the dead leaf [[praying mantis|mantis]] makes it less visible to both its predators and prey.]] One adaptation helping both predators and prey avoid detection is [[camouflage]], a form of [[crypsis]] where species have an appearance which helps them blend into the background. Camouflage consists of not only color, but also shape and pattern. The background upon which the organism is seen can be both its environment (e.g. the [[praying mantis]] to the right resembling dead leaves) other organisms (e.g. [[zebra]]s' stripes blend in with each other in a herd, making it difficult for [[lion]]s to focus on a single target). The more convincing camouflage is, the more likely it is that the organism will go unseen. [[Image:Automeris ioPCCA20040704-2975AB1.jpg|left|thumb|Mimicry in ''Automeris io '']][[Mimic]]ry is a related phenomenon where an organism has a similar appearance to another species. One such example is the [[drone fly]], which looks a lot like a [[bee]], yet is completely harmless as it cannot sting at all. Another example of batesian mimicry is the [[io moth]], (''Automeris io''), which has markings on its wings which resemble an owl's eyes. When an insectivorous predator disturbs the moth, it reveals its hind wings, temporarily startling the predator and giving it time to escape. Predators may also use mimicry to lure their prey, however. Female [[firefly|fireflies]] of the genus ''[[Photuris (genus)|Photuris]]'', for example, copy the light signals of other species, thereby attracting male fireflies which are then captured and eaten.<ref>Lloyd, J.E. (1965) Aggressive Mimicry in Photuris: Firefly Femmes Fatales ''[[Science (journal)|Science]]'' 149:653-654.</ref> ===Predator=== [[Image:Stud 327 with Blesbuck.jpg|right|thumb|220px|A [[South China Tiger]] as the predator feeding on the [[blesbuck]], the prey]] While successful predation results in a gain of [[Biological thermodynamics|energy]], hunting invariably involves energetic costs as well. When [[hunger]] is not an issue, most predators will generally not seek to attack prey since the costs outweigh the benefits. For instance, a large predatory fish like a [[shark]] that is well fed in an [[aquarium]] will typically ignore the smaller fish swimming around it (while the prey fish take advantage of the fact that the apex predator is apparently uninterested). [[Surplus killing]] represents a deviation from this type of behaviour. The treatment of consumption in terms of [[cost-benefit analysis]] is known as [[optimal foraging theory]], and has been quite successful in the study of [[animal behavior]]. Costs and benefits are generally considered in energy gain per unit time, though other factors are also important, such as [[essential nutrient]]s that have no caloric value but are necessary for survival and health. ''Size-selective predation'' involves predators preferring 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.<ref name="Molles">{{cite book | last =Molles | first =Manuel C., Jr. | title =Ecology: Concepts and Applications | publisher =The McGraw-Hill Companies, Inc.| edition = International Edition | date =2002 | location =New York | pages =586 p | id = ISBN 0-07-112252-4 }}</ref> Size may also act as a [[refuge (ecology)|refuge]] for large prey, for example adult elephants are generally safe from predation by lions, but juveniles are vulnerable.<ref name="Molles" /> It has been observed that well-fed predator animals in a lax captivity (for instance, [[pet]] or [[farm]] animals) will usually differentiate between putative prey animals who are familiar co-inhabitants in the same human area from wild ones outside the area. This interaction can range from peaceful coexistence to close companionship; motivation to ignore the predatory instinct may result from mutual advantage or fear of reprisal from human masters who have made clear that harming co-inhabitants will not be tolerated. Pet [[cat]]s and pet [[mouse|mice]], for example, may live together in the same human residence without incident as companions. Pet cats and pet [[dog]]s under human mastership often depend on each other for warmth, companionship, and even protection, particularly in rural areas. <!-- Further material - prey drive, stalking, luring, playing with prey --> ===Anti-predator adaptations=== {{Main|Antipredator adaptations}} Antipredator adaptations have evolved in prey populations due to the selective pressures of predation over long periods of time. ====Mobbing behavior==== <!-- This section is a little large for something so specific --> [[Mobbing behavior]] occurs when a species turns the tables on their predator by [[co-operation (evolution)|cooperatively]] attacking or harassing it. This is most frequently seen in [[bird]]s, though it is also known to occur in other social animals. For example, nesting [[gull]] colonies are widely seen to attack intruders, including humans. Costs of mobbing behavior include the risk of engaging with predators, as well as energy expended in the process; [[mockingbird]]s can effectively force a cat or dog to seek something less troublesome. One mockingbird might fly in front of the cat or dog, enticing it to lunge, while another pecks at the cat or dog from behind. While mobbing has [[convergent evolution|evolved independently]] in many species, it only tends to be present in those whose young are frequently preyed on, especially birds. It may complement [[crypsis|cryptic]] behavior in the offspring themselves, such as camouflage and [[hiding]]. Mobbing calls may be made prior to or during engagement in harassment. Mobbing behavior has functions beyond driving the predator away. Mobbing draws attention to the predator, making stealth attacks impossible. Mobbing also plays a critical role in the identification of predators and inter-generational learning about predator identification. Reintroduction of species is often unsuccessful because the established population lacks this cultural knowledge of how to identify local predators. Scientists are exploring ways to train populations to identify and respond to predators before releasing them into the wild. <ref>[http://www.blackwell-synergy.com/doi/abs/10.1046/j.1523-1739.2000.99326.x Blackwell Synergy - Conservation Biology, Volume 14 Issue 5 Page 1317-1326, October 2000 (Article Abstract)<!-- Bot generated title -->]</ref> Mobbing can be an interspecies activity: it is common for birds to respond to mobbing calls of a different species. Many birds will show up at the sight of mobbing and watch and call, but not participate. It should also be noted that some species can be on both ends of a mobbing attack. Crows are frequently mobbed by smaller songbirds as they prey on eggs and young from these birds' nests, but these same crows will cooperate with smaller birds to drive away hawks or larger mammalian predators. On occasion, birds will mob animals that pose no threat. [[Black-headed Gull]]s are one species which aggressively engages intruding predators, such as [[Carrion Crow]]s. Experiments on this species by Hans Kruuk involved placing hen eggs at intervals from a nesting colony, and recording the percentage of successful predation events as well as the probability of the crow being subjected to mobbing.<ref>Kruuk, H. (1964) Predators and anti-predator behaviour of the black-headed gull ''Larus ridibundus''. ''Behaviour Supplements'' 11:1-129</ref> The results showed decreasing mobbing with increased distance from the nest, which was correlated with increased predation success. Mobbing may function by reducing the predator's ability to locate nests, as predators cannot focus on locating eggs while they are under direct attack. ====Advertising unprofitability==== [[Image:Thompson's Gazelle.jpeg|right|thumb|Thomson's Gazelles exhibit stotting behavior.]] Once a predator has detected its prey, one would expect it to pursue it. However, it is not always profitable for the predator to do so. Consider the example of a [[Thomson's Gazelle]] being spotted by a predator. Giving chase to prey requires a sacrifice in energy. If, however, there is some way the prey species can convey the information that it is unprofitable, energy will be saved by both organisms. Thomson's Gazelles are hunted by species such as [[lion]]s and [[cheetah]]s. When they see the predator approach, they may start to run away, but then slow down and ''stot''. [[Stotting]] describes a behavior involving jumping into the air with the legs kept straight and stiff, and the white rear fully visible. Obviously this behavior is maladaptive if they hope to outrun the predator, so it must serve some other purpose. Although other [[scientific hypothesis|hypotheses]] have been put forward, evidence supports the proposition that they stot to [[animal communication|signal]] an unprofitable chase. For example, cheetahs abandon more hunts when the gazelle stots, and in the event they do give chase, they are far less likely to make a kill.<ref>Caro, T. M. (1986) The functions of stotting in Thomson's gazelles: Some tests of the predictions. ''[[Animal Behaviour (journal)|Animal Behaviour]]'' 34:663-684.</ref> [[Aposematism]], where organisms are brightly colored as a warning to predators, is the antithesis of camouflage. Some organisms pose a threat to their predators - for example they may be [[poison]]ous, or able to harm them physically. Aposematic coloring involves bright, easily recognizable and unique colors and patterns. Upon being harmed (e.g. stung) by their prey, the appearance of such an organism will be [[memory|remembered]] as something to avoid. <!-- ====Alarm signals=== [[[[Signalling theory]]|Signalling]] the threat of predation to other members of a community can be a costly behavior for an organism, as it may involve informing the predator of not only its presence, but its exact location. -Specific alarms for different predators -Kin selection (ground squirrels example) --> ==Population dynamics== It is fairly clear that predators tend to lower the survival and [[fecundity]] of their prey, but on a higher level of organization, [[population]]s of predator and prey species also interact. It is obvious that predators depend on prey for survival, and this is reflected in predator populations being affected by changes in prey populations. It is not so obvious, however, that predators affect prey populations. Eating a prey organism may simply make room for another if the prey population is approaching its [[carrying capacity]]. The [[population dynamics]] of predator-prey interactions can be modelled using the [[Lotka–Volterra equation]]s. These provide a [[mathematical model]] for the cycling of predator and prey populations. ==Humans and predation== <!-- Humans as predators, predators of humans, predators in culture (e.g. as pets and symbols) --> ===In conservation=== Predators are an important consideration in matters relating to [[Wildlife conservation|conservation]]. [[Introduced species|Introduced]] predators may prove too much for populations which have not [[coevolved]] with them, leading to possible [[extinction]]. This will depend largely on how well the prey species can adapt to the new species, and whether or not the predator can turn to alternative food sources when prey populations fall to minimal levels. If a predator can use an alternative prey instead, it may shift its diet towards that species in a behavior known as [[functional response]], while still eating the last remaining prey organisms. On the other hand the prey species may be able to survive if the predator has no alternative prey - in this case its population will necessarily crash following the decline in prey, allowing some small proportion of prey to survive. Introduction of an alternative prey may well lead to the extinction of prey, as this constraint is removed. Predators are often the species endangered themselves, especially [[apex predators]] who are often in competition with humans. [[Interspecific competition|Competition]] for prey from other species could prove the end of a predator - if their [[ecological niche]] overlaps completely with that of another the [[competitive exclusion principle]] requires only one can survive. Loss of prey species may lead to [[coextinction]] of their predator. In addition, because predators are found in higher trophic levels, they are less abundant and much more vulnerable to extinction. ===Biological pest control=== {{Main|Biological pest control}} Predators may be put to use in conservation efforts to control introduced species. Although the aim in this situation is to remove the introduced species entirely, keeping its abundance down is often the only possibility. Predators from its natural range may be introduced to control populations, though in some cases this has little effect, and may even cause unforeseen problems. Besides their use in [[conservation biology]], predators are also important for controlling [[Pest (organism)|pest]]s in [[agriculture]]. Natural predators are an environmentally friendly and sustainable way of reducing damage to crops, and are one alternative to the use of chemical agents such as [[pesticide]]s. ==See also== *[[Prey drive]] ==References== {{Wiktionarypar|predation}} {{commonscat|Predation}} {{reflist}} ==Further reading== *Barbosa, P. and I. Castellanos (eds) 2004. ''Ecology of predator-prey interactions'' New York : Oxford University Press. 394 p. ISBN 0195171209 *Curio, E. 1976. ''The ethology of predation'' Berlin ; New York : Springer-Verlag. 250 p. ISBN 0387077200 == External links == * [http://demonstrations.wolfram.com/PredatorPreyEquations/ Predator-Prey Equations] by Eric W. Weisstein, [[The Wolfram Demonstrations Project]]. {{feeding}} {{Biological_interaction-footer}} {{evo ecol}} [[Category:Predation|*]] [[Category:Biological pest control]] [[bg:Хищник]] [[ca:Depredació]] [[cs:Predátor]] [[da:Prædation]] [[de:Prädator]] [[es:Depredación]] [[fr:Prédateur]] [[io:Predato]] [[id:Pemangsa]] [[it:Predazione]] [[lt:Plėšrūnas]] [[hu:Ragadozó életmód]] [[nl:Predator]] [[ja:捕食]] [[no:Predator]] [[nn:Predasjon]] [[pl:Drapieżnictwo]] [[pt:Predação]] [[simple:Predator]] [[fi:Saalistus]] [[sv:Predation]] [[vi:Săn mồi]] [[tr:Avcı]] [[zh:掠食]]