Predation
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Predator)
- For alternative meanings of predator and prey, see Predator (disambiguation) and Prey (disambiguation).
Meat ants feeding on a
cicada; some species can prey on individuals of far greater size, particularly when working cooperatively
In
ecology,
predation describes a
biological interaction where a
predator (an organism that is hunting) feeds on its
prey (the organism that is attacked).
[1] Predators may or may not kill their prey prior to
feeding on them, but the act of predation always results in the death of its prey and the eventual absorption of the prey's tissue through consumption.
[2] Other categories of
consumption are
herbivory (eating parts of plants) and
detritivory, the consumption of dead organic material (
detritus). All these consumption categories fall under the rubric of
Consumer-Resource Systems [3] It can often be difficult to separate our various types of
feeding behaviors[1]. For example, parasitic species prey on a host organism and then lay their eggs on it for their offspring to feed on it while it continues to live or on its decaying corpse after it has died. The key characteristic of predation however is the predator's direct impact on the prey population. On the other hand, detritivores simply eat dead organic material arising from the decay of dead individuals and have no direct impact on the "donor" organism(s).
Selective pressures imposed on one another has led to an
evolutionary arms race between prey and predator, resulting in various
antipredator adaptations.
The unifying theme in all classifications of predation is the predator lowering the
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 the predator's interaction with prey.
[edit] 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). Additionally, whether or not the prey are directly killed by the predator is considered, with true predation and parasitoidism involving certain death.
[edit] True predation
A true predator can commonly be known as one which kills and eats another organism. Whereas other types of predator all harm their prey in some way, this form certainly kills them. Predators may hunt actively for prey, or sit and wait for prey to approach within striking distance, as in
ambush predators. Some predators kill large prey and dismember or chew it prior to eating it, such as a
jaguar; others may eat their (usually much smaller) prey whole, as does a
bottlenose dolphin swallowing a fish, or a
snake or
duck or
stork swallowing a
frog. Some predation entails
venom which subdues a prey creature before the predator ingests the prey by killing, which the
box jellyfish does, or disabling it, found in the behavior of the
cone shell. In some cases the venom, as in
rattlesnakes and some
spiders, contributes to the digestion of the prey item even before the predator begins eating. In other cases, the prey organism may die in the mouth or
digestive system of the predator.
Baleen whales, for example, eat millions of microscopic plankton at once, the prey being broken down well after entering the whale.
Seed predation and egg predation are other forms of true predation, as
seeds and
eggs represent potential organisms. Predators of this classification need not eat prey entirely, for example some predators cannot digest
bones, while others can. Some may eat only part of an organism, as in grazing (see below), but still consistently cause its direct death.Some of the prominent examples of true predators are lion , tiger,etc.
[edit] 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
mosquitos land on hosts briefly to gain sufficient
proteins for the development of their offspring.
Starfish may be grazed on, being capable of regenerating lost arms.
[edit] 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 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.
[edit] Parasitoidism
Parasitoids 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 wasps, 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,
Diptera and
Coleoptera parasitoids make up as much as 10% of all insect species.
[4][5]
[edit] Degree of specialization
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:
humans,
leopards, and
dogs). 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
scavenging or a herbivorous diet if possible.
[citation needed]
[edit] Trophic level
Predators are often another organism's prey, and likewise prey are often predators. Though
blue jays prey on
insects, they may in turn be prey for
cats and
snakes, which, in the latter's case, may themselves be the prey of
hawks. One way of classifying predators is by
trophic level. Organisms which feed on
autotrophs, the producers of the
trophic pyramid, are known as
herbivores or
primary consumers; those that feed on
heterotrophs 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, and may go only as high as three trophic levels (for example, a
lion that preys upon large herbivores such as
wildebeest which in turn eat
grasses). 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,
sperm whale,
anaconda,
Komodo dragon,
tiger,
lion,
bald eagle, and
Nile crocodile -- and even omnivorous humans and
grizzly bears. An apex predator in one environment may not retain this position as a top predator if introduced to another habitat, such as a
dog among
alligators or a
snapping turtle among
jaguars; a predatory species introduced into an area where it faces no predators, such as a
domestic cat or a
dog in some insular environments, can become an apex predator by default.
Many organisms (of which humans are prime examples) eat from multiple levels of the food chain and thus make this classification problematic. 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
omnivores. Even herbivores such as the
giant panda may supplement their diet with meat.
Scavenging of carrion provides a significant part of the diet of some of the most fearsome predators.
Carnivorous plants would be very difficult to fit into this classification, producing their own food but also digesting anything that they may trap. Organisms which eat
detritivores or
parasites would also be difficult to classify by such a scheme.
[edit] Predation as competition
An alternative view offered by
Richard Dawkins is of predation as a form of
competition: the
genes of both the predator and prey are competing for the body (or '
survival machine') of the prey organism.
[6] This is best understood in the context of the
gene centered view of evolution. Another manner in which predation and competition are connected is throughout
intraguild predation. Intraguild predators are those that kill and eat other predators of different species at the same trophic level, and thus that are potential competitors.
[7]
[edit] Ecological role
Predators may increase the
biodiversity of communities by preventing a single species from becoming dominant. Such predators are known as
keystone species and 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.
[8]
The elimination of wolves from
Yellowstone National Park had profound impacts on the
trophic pyramid. Without predation, herbivores began to over-graze many woody brow species, affecting the area's plant populations. Additionally, wolves often kept animals from grazing in riparian areas, which protected beavers from having their food sources encroached upon. The removal of wolves had a direct effect on beaver populations, as their habitat became territory for grazing.
[9] Furthermore, predation keeps hydrological features such as creeks and streams in normal working order. Increased browsing on willows lenr and conifers along Blacktail Creek due to a lack of predation resulted in channel incision because those species helped slow the water down and hold the soil in place.
[9]
[edit] 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.
[10] 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,
[11] though the individuals preyed upon themselves do not benefit.
[12] 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
adaptations in both groups.
Camouflage of the dead leaf
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) or other organisms (e.g.
zebras' stripes blend in with each other in a herd, making it difficult for
lions to focus on a single target). The more convincing camouflage is, the more likely it is that the organism will go unseen.
Mimicry 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
fireflies of the genus
Photuris, for example, copy the light signals of other species, thereby attracting male fireflies which are then captured and eaten (see
aggressive mimicry).
[13]
[edit] Predator
While successful
predation results in a gain of
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 outweight 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 nutrients that have no caloric value but are necessary for survival and health.
Social Predation offers the possibility of predators to kill creatures larger than those that members of the species could overpower singly.
Lions,
hyenas,
wolves,
dholes,
African wild dogs, and
piranhas can kill large herbivores that single animals of the same species could never dispatch. Social predation allows some animals to organize
hunts of creatures that would easily escape a single predator; thus
chimpanzees can prey upon
colobus monkeys, and
harris hawks can cut off all possible escapes for a doomed rabbit. Extreme specialization of roles is evident in some hunting that requires co-operation between predators of very different species:
humans with the aid of
falcons or
dogs, or fishing with
cormorants or dogs. Social predation is often very complex behavior, and not all social creatures (for example,
domestic cats) perform it. Even without complex intelligence but instinct alone, some ant species can destroy much-larger creatures.
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.
[14] Size may also act as a
refuge for large prey, for example adult elephants are generally safe from predation by lions, but juveniles are vulnerable.
[14]
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
cats and pet
mice, for example, may live together in the same human residence without incident as companions. Pet cats and pet
dogs under human mastership often depend on each other for warmth, companionship, and even protection, particularly in rural areas.
[edit] Antipredator adaptations
Antipredator adaptations have evolved in prey populations due to the selective pressures of predation over long periods of time.
[edit] Aggression
Predatory animals often use their usual methods of attacking prey to inflict or to threaten grievous injury to their own predators. The
electric eel uses the same electrical current to kill prey and to defend itself against animals (
anacondas,
caimans,
jaguars,
egrets,
cougars,
giant otters, humans, and dogs) that ordinarily prey upon fish similar to an electric eel in size; the electric eel thus remains an apex predator in a predator-rich environment. Many non-predatory prey animals, such as a
zebra, can give a strong kick that can maim or kill, while others charge with tusks or horns.
[edit] Mobbing behavior
Mobbing behavior occurs when members of a species drive away their predator by
cooperatively attacking or harassing it. Most frequently seen in
birds, mobbing is also seen in other social animals. For example, nesting
gull colonies are widely seen to attack intruders, including humans.
[10] Costs of mobbing behavior include the risk of engaging with predators, as well as energy expended in the process, but it can aid the survival of members of a species.
While mobbing has
evolved independently in many species, it tends to be present only in those whose young are frequently preyed on, especially birds. It may complement
cryptic behavior in the offspring themselves, such as
camouflage and
hiding.
Mobbing calls may be made prior to or during engagement in harassment.
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.
[edit] Advertising unprofitability
Thomson's Gazelles exhibit
stotting behavior.
A
Thomson's Gazelle seeing a predator approach may start to run away, but then slow down and
stot.
Stotting is jumping into the air with the legs straight and stiff, and the white rear fully visible. Stotting is maladaptive for outrunning predators; evidence suggests that stotting
signals 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.
[15]
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
poisonous, 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 in such an organism will be
remembered as something to avoid.
[edit] Chemical defense
Some organisms have evolved chemical weapons which are effective deterrents against predation. It is most common in
insects, but the
skunk is a particularly dramatic
mammalian example. Other examples include the
Bombardier beetle which can accurately shoot a predator with a stream of boiling poison, the
Ornate moth which excretes a frothy alkaloid mixture, and the
Pacific beetle cockroach sprays a
quinone mixture from modified
spiracles.
[edit] Terrain Fear Factor
The "terrain fear factor" is an idea which assesses the risks associated with predator/prey encounters. This idea suggests that prey will change their usual habits to adjust to the terrain and its effect on the species' predation. For example, a species may forage in a terrain with a lower predation risk as opposed to one with high predation risk.
[16]
[edit] 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,
populations 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 equations. These provide a
mathematical model for the cycling of predator and prey populations.
Predators tend to select young, weak, and ill individuals.
[17]
[edit] Evolution of predation
Predation appears to have become a major selection pressure shortly before the
Cambrian period—around
550 million years ago—as evidenced by the almost simultaneous development of calcification in animals and algae,
[18] and predation-avoiding burrowing. However, predators had been grazing on micro-organisms since at least
1,000 million years ago.
[19][19][20][21][22]
[edit] Humans and predation
[edit] As predators
Humans are
omnivorous and use tools to exploit their environments; from
snares, clubs,
spears,
fishing gear,
firearms to boats and motor vehicles. Humans even use other predatory species, (such as dogs,
cormorants, and
falcons) in hunting and fishing; some people even enlist such non-predatory beasts, like horses, camels, and elephants in getting approaches to prey.
Humans have reshaped huge expanses of the world as ranges and farms for the raising of livestock, poultry, and
fish to be eaten as meat. However, it can be debated whether or not harvesting livestock fits strictly in the definition of predation.
Human raising and eating of livestock is part of
agriculture, and involves the feeding of and caring for animals, followed by their being slaughtered with an appropriate tool, cutting up, and cooking. In many cultures, animals are hunted or farmed by specialists (such as
ranchers or
fishermen), brought to a marketplace, and sold in pieces to the people who actually consume the meat.
[edit] As prey
A lone naked human is at a physical disadvantage to other comparable apex predators in areas such as speed, bone density, weight, and physical strength. Humans also lack innate weaponry such as claws. Without crafted weapons,
society, or cleverness, a lone human can easily be defeated by fit predatory animals, such as wild dogs, big cats and bears. There are even recorded instances of lone humans being preyed upon by large carnivores (see
Man-eater). However humans are not solitary creatures; they are social animals with highly developed social behaviors. Further humans and their ancestors (such as
Homo erectus) have been using stone tools and weapons for well over a million years.
Anatomically modern humans have been apex predators since they first evolved, and many species of carnivorous
megafauna actively avoid interacting with humans; the primary environmental competitor for a human is other humans.
Cannibalism has occurred in various places, among various cultures, and for various reasons. At least a few people, such as the
Donner party, are said to have resorted to it in desperation.
[edit] In conservation
Predators are an important consideration in matters relating to
conservation.
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 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, 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.
[clarification needed]
Predators are often the species endangered themselves, especially
apex predators who are often in competition with humans.
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.
[edit] 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
pests 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
pesticides.
Selain daya serap pasar dan pedagang, peternak lokal merupakan salah satu penentu terbentuknya harga pasar. Produksi dari ternak lokal biasanya sudah bisa mencukupi lebih dari 50 % kebutuhan pasar didaerahnya. Sedang kekurangannya biasanya baru dipenuhi oleh pedagang yang mengambil telur dari blitar atau daerah-daerah disekitarnya.
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