| Predator |
Article Index for Predator |
Information AboutPredator |
| CATEGORIES ABOUT PREDATION | |
| predation | |
| biological pest controlpredation | |
| biological pest control | |
| biological interactions | |
| eating behaviors | |
| ethology | |
|
eating a California Vole ]] In Ecology , predation describes a Biological Interaction where a '''predator''' organism feeds on another living organism or organisms known as '''prey'''.Begon, M., Townsend, C., Harper, J. (1996) ''Ecology'' (Third edition) Blackwell Science, London Predators may or may not kill their prey prior to feeding on them. The other main category of Consumption is Detritivory , the consumption of dead organic material ( Detritus ). It can at times be difficult to separate the two feeding behaviors, 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 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 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 ''. 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 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. 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 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 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 parasties such as Cholera . Some species however have more loose associations with their hosts. Lepidoptera 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 inevitable 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.Godfray, H.C.J. (1994) ''Parasitoids: Behavioral and Evolutionary Ecology''. Princeton University Press, Princeton. 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: Human 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 Scavenging or a herbivorous diet if possible. Trophic level Predators are often another organism's prey, and likewise prey are often predators. Though Bird 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, quaternary consumers eating them, and so fourth. 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 Human s. A superpredator in one environment may not retain this position if introduced to another habitat, however. 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 or 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. 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.Botkin, D. and E. Keller (2003) ''Enrivonmental Science: Earth as a living planet'' (p.2) John Wiley & Sons. ISBN 0-471-38914-5 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.Alcock, J. (1998) ''Animal Behavior: An Evolutionary Approach'' (6th edition). Sinauer Associates, Inc. Sunderland, Massachusetts. ISBN 0-87893-009-4 The relationship between predator and prey is one which is beneficial to the predator, and detrimental to the prey species. This means that, at each applicable stage, predator and prey species are in an Evolutionary Arms Race 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 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. '' 149:653-654. 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 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. 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 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. Anti-predator See Also: Antipredator adaptations Mobbing behavior Mobbing Behavior occurs when a species turns the tables on their predator by 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 Evolved Independently in many species, it only tends to be present in those whose young are frequently preyed on, especially birds. It may compliment 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. http://www.blackwell-synergy.com/doi/abs/10.1046/j.1523-1739.2000.99326.x Mobbing can be a 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.Kruuk, H. (1964) Predators and anti-predator behaviour of the black-headed gull ''Larus ridibundus''. ''Behaviour Supplements'' 11:1-129 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 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 '' 34:663-684. 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 Remembered as something to avoid. |
|
|