predator
1 : one that preys, destroys, or devours
2 : an animal that lives by predation
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Link Source: http://en.wikipedia.org/wiki/Predation
Predation
From Wikipedia, the free encyclopedia
 | Look up predate or pre-date in Wiktionary, the free dictionary. |
- Predate redirects here. The verb "predate" may mean "[have a] date earlier than": see wikt:predate.
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 the prey.[2] 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[1], 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).
Selective pressures imposed on one another has led to an evolutionary arms race between prey and predator, resulting in various antipredator adaptations.
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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.
[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 the first and last cases involving certain death.
[edit] True predation
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 certain death. 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, while others may eat their (usually much smaller) prey whole, as does a bottlenose dolphin or any snake, or a 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 is another form of true predation, as seeds represent potential organisms. Predators of this classification need not eat prey entirely, for example some predators cannot digest bones, while others can. Some may merely eat only part of an organism, as in grazing (see below), but still consistently cause its direct death.
[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.[3][4]
[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]
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, 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 pig 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 such 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.
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.[5] 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 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.[6]
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.[7] 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.[7]
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.[8] 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,[9] though the individuals preyed upon themselves do not benefit.[10] 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.
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. 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).[11]
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 colubus monkeys, and harrier 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.[12] 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.[12]
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.
Antipredator adaptations
Antipredator adaptations have evolved in prey populations due to the selective pressures of predation over long periods of time.
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.
Mobbing behavior
 | This section may be too long to comfortably read and navigate. Please consider moving more of the content into sub-articles and using this article for a summary of the key points of the subject. (September 2009) |
Mobbing behavior occurs when a species turns the tables on their predator by cooperatively attacking or harassing it. This is most frequently seen in birds, 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, but it can aid the survival of members of a species. Mockingbirds can effectively force a cat or dog to seek something less troublesome through mobbing behavior. One mockingbird might fly in front of the cat or dog, enticing a common predator upon birds to lunge, while another pecks at the cat or dog from behind to inflict a sharp pain that forces the predator to hesitate when it encounters mockingbirds.
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 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 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.[13]
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 Gulls are one species which aggressively engages intruding predators, such as Carrion Crows. 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.[14] 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.
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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.
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]
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.
Evolution of predation
Predation appears to have become a major selection pressure shortly before the Cambrian period—around —as evidenced by the almost simultaneous development of calcification in animals and algae,[17] and predation-avoiding burrowing. However, predators had been grazing on micro-organisms since at least .[18][18][19][20][21]
Humans and predation
As predators
In much of the world, humans are the largest, best-organized, most cunning, and most powerful predators. The closest rival to humans in those characteristics in most of the world, the dog, is far more likely a collaborator than a competitor or a menace.
Humans are clever exploiters of tools from snares, clubs, spears, fishing gear, firearms to boats and motor vehicles in hunting other animals. Humans even use other animals (dogs, cormorants, and falcons) in hunting or fishing and such non-predatory animals as 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.
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 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.[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.
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.
See also
| Look up predation in Wiktionary, the free dictionary. |
 | Wikimedia Commons has media related to: Predation |
References
- ^ a b Begon, M., Townsend, C., Harper, J. (1996). Ecology: Individuals, populations and communities (Third edition). Blackwell Science, London. ISBN 086542845X, ISBN 0632038012, ISBN 0632043938.
- ^ Encyclopedia Britannica: "predation"
- ^ Godfray, H.C.J. (1994). Parasitoids: Behavioral and Evolutionary Ecology. Princeton University Press, Princeton. ISBN 0691033250, ISBN 0691000476. P. 20.
- ^ Feener, Jr., Donald H.; Brian V. Brown (January 1997). "Diptera as Parasitoids". Annual Review of Entomology 42: 73–97. doi:. http://arjournals.annualreviews.org/doi/pdf/10.1146/annurev.ento.42.1.73. Retrieved 2009-03-04.
- ^ Dawkins, R. (1976). The Selfish Gene. Oxford University Press. ISBN 0-19-286092-5.
- ^ Botkin, D. and E. Keller (2003). Enrivonmental Science: Earth as a living planet. John Wiley & Sons. ISBN 0-471-38914-5. P.2.
- ^ a b William J. Ripple and Robert L. Beschta. "Wolves and the Ecology of Fear: Can Predation Risk Structure Ecosystems?" 2004.
- ^ Alcock, J. (1998). Animal Behavior: An Evolutionary Approach (6th edition). Sunderland, Mass.: Sinauer Associates, Inc. ISBN 0-87893-009-4.
- ^ Bondavalli, C., and Ulanowicz, R.E. (1999). Unexpected effects of predators upon their prey: The case of the American alligator. Ecosystems, 2: 49–63.
- ^ Dawkins, R. (2004). The Ancestor's Tale. Boston: Houghton Mifflin. ISBN 0618005838.
- ^ Lloyd, J.E. (1965). Aggressive Mimicry in Photuris: Firefly Femmes Fatales. Science 149:653–654.
- ^ a b Molles, Manuel C., Jr. (2002). Ecology: Concepts and Applications (International Edition ed.). New York: The McGraw-Hill Companies, Inc. ISBN 0-07-112252-4.
- ^ Griffin, Andrea S.; Daniel T. Blumstein, and Christopher S. Evans (October 2000). "Training Captive-Bred or Translocated Animals to Avoid Predators". Conservation Biology 14 (5): 1317–1326. doi:. http://www.blackwell-synergy.com/doi/abs/10.1046/j.1523-1739.2000.99326.x. Retrieved 2009-03-04.
- ^ Kruuk, H. (1964). Predators and anti-predator behaviour of the black-headed gull Larus ridibundus. Behaviour Supplements 11:1–129.
- ^ Caro, T. M. (1986). The functions of stotting in Thomson's gazelles: Some tests of the predictions. Animal Behaviour 34:663–684.
- ^ Ripple, William J., and Robert L. Beschta. "Wolves and the ecology of fear: Can predation risk structure ecosystems?" BioScience 54: 755–66.
- ^ Grant, S. W. F.; Knoll, A. H.; Germs, G. J. B. (1991). "Probable Calcified Metaphytes in the Latest Proterozoic Nama Group, Namibia: Origin, Diagenesis, and Implications". Journal of Paleontology (JSTOR) 65 (1): 1–18. http://links.jstor.org/sici?sici=0022-3360(199101)65%3A1%3C1%3APCMITL%3E2.0.CO%3B2-R.
- ^ a b Bengtson, S. (2002), "Origins and early evolution of predation", in Kowalewski, M., and Kelley, P.H. (Free full text), The fossil record of predation. The Paleontological Society Papers 8, The Paleontological Society, pp. 289–317, http://www.nrm.se/download/18.4e32c81078a8d9249800021552/Bengtson2002predation.pdf, retrieved 2007-12-01
- ^ McNamara, K.J. (20 December 1996). "Dating the Origin of Animals". Science 274 (5295): 1993–1997. doi:. http://www.sciencemag.org/cgi/content/full/274/5295/1993f. Retrieved 2008-06-28.
- ^ Awramik, S.M. (19 November 1971). "Precambrian columnar stromatolite diversity: Reflection of metazoan appearance" (abstract). Science 174 (4011): 825–827. doi:. PMID 17759393. http://www.sciencemag.org/cgi/content/abstract/174/4011/825. Retrieved 2007-12-01.
- ^ Stanley (2008). "Predation defeats competition on the seafloor" (extract). Paleobiology 34: 1. doi:. http://paleobiol.geoscienceworld.org/cgi/content/extract/34/1/1.
Further reading
- Barbosa, P. and I. Castellanos (eds.) (2004). Ecology of predator-prey interactions. New York: Oxford University Press. ISBN 0195171209.
- Curio, E. (1976). The ethology of predation. Berlin; New York: Springer-Verlag. ISBN 0387077200.
External links
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Trophic Links: Predation and Parasitism
We wish to learn:
- how predators affect prey populations, and vice-versa
- what stabilizes predator-prey interactions and prevents their collapse
- how predation can result in complex interactions in natural communities
| 11/02/2005 |  Format for printing |
Introduction
Predation is used here to include all "+/-" interactions in which one organism consumes all or part of another. This includes predator-prey, herbivore-plant, and parasite-host interactions. These linkages are the prime movers of energy through food chains. They are an important factor in the ecology of populations, determining mortality of prey and birth of new predators. Predation is an important evolutionary force: natural selection favors more effective predators and more evasive prey. "Arms races" have been recorded in some snails, which over time become more heavily armored prey, and their predators, crabs, which over time develop more massive claws with greater crushing power. Predation is widespread and easy to observe. Neither its existence nor its importance is in doubt.The Development of Predation Theory
Mathematical models of predation are amongst the oldest in ecology. The Italian mathematician Volterra is said to have developed his ideas about predation from watching the rise and fall of Adriatic fishing fleets. When fishing was good, the number of fishermen increased, drawn by the success of others. After a time, the fish declined, perhaps due to over-harvest, and then the number of fishermen also declined. After some time, the cycle repeated. | The idea that a coupled system of predator and prey would cycle gained further support from analyses of fur trapping records of the Hudson's Bay Company. The number of furs purchased at the Company's forts was meticulously recorded, for well over 100 years. An analysis of the numbers of snowshoe hares, and one of their main predators, the lynx, provides a remarkable record of a predator-prey cycle. Peaks and valleys can be easily observed at roughly 8-10 year intervals. |
Logic and mathematical theory suggest that when prey are numerous their predators increase in numbers, reducing the prey population, which in turn causes predator number to decline. The prey population eventually recovers, starting a new cycle.
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These results suggested that the predator-prey system was inherently self-annihilating without some outside immigration. The question then arose: why are predator-prey cycles in nature apparently stable, while laboratory cultures quickly collapse?
What Stabilizes Predator-Prey Systems in Nature?
Observing that frequent additions of paramecium produced predator-prey cycles in a test-tube led to the idea that in a physically heterogeneous world, there would always be some pockets of prey that predators happened not to find and eliminate. Perhaps when the predator population declined, having largely run out of prey, these remaining few could set off a prey rebound. Spatial heterogeneity in the environment might have a stabilizing effect.A laboratory experiment using a complex laboratory system supports this explanation. A predaceous mite feeds on an herbivorous mite, which feeds on oranges. A complex laboratory system completed four classic cycles, before collapsing.
Observations of prickly pear cactus and the cactus moth in Australia support this lab experiment. This South American cactus became a widespread nuisance in Australia, making large areas of farmland unusable. When the moth, which feeds on this cactus, was introduced, it rapidly brought the cactus under control. Some years later both moth and cactus were rare, and it is unlikely that the casual observer would ever think that the moth had accomplished this. Once the cactus became sufficiently rare, the moths were also rare, and unable to find and eliminate every last plant. Inadequate dispersal is perhaps the only factor that keeps the cactus moth from completely exterminating its principal food source, the prickly pear cactus.
Prey defenses can be a stabilizing factor in predator-prey interactions. Predation can be a strong agent of natural selection. Easily captured prey are eliminated, and prey with effective defenses (that are inherited) rapidly dominate the population. Examples include camouflage in the peppered moth, and prey that are nocturnal to escape detection. Bats capture moths in flight, using sonar to detect them; some moths are able to detect incoming sonar, and take evasive action. Perhaps seriously unbalanced system simply disappear, and those that persist are ones in which the predator is not "too effective", likely because the prey has adaptations to reduce its vulnerability.
The availability of a second prey type -- an alternate prey -- can be stabilizing or destabilizing. Often a predator eats more than one prey. If a predator switches between prey A and B on the basis of their frequency, it will eat A when B is rare and B when A is rare. The prey should exhibit mild oscillations, and the predator should fluctuate little. This would stabilize prey abundances. However, if one prey species is abundant and the predator is unable to reduce its numbers, the result might be the maintenance of a continuously high predator density. Such an abundant predator might then eliminate a second prey species. This is a destabilizing effect of an alternative prey. The hare-caribou-lynx relationship in Newfoundland is a complex example of such a destabilizing effect.
Complex Interactions in Ecological Communities
Predation can have far-reaching effects on biological communities. A starfish is the top predator upon a community of invertebrates inhabiting tidally inundated rock faces in the Pacific Northwest. The rest of the community included mollusks, barnacles and other invertebrates, for a total of 12 species (not counting microscopic taxa). The investigator removed the starfish by hand, which of course reduced the number of species to 11. Soon, an acorn barnacle and a mussel began to occupy virtually all available space, out competing other species. Species diversity dropped from more than 12 species to essentially 2. The starfish was a keystone predator, keeping the strongest competitors in check. Although it was a predator, it helped to maintain a greater number of species in the community. Its beneficial impact on species that were weak competitors is an example of an indirect effect.When non-native species (exotics) invade an area, they often create "domino" effects, causing many other species to increase or decrease. The rainbow trout, beautiful, tasty, and beloved by anglers, has been purposefully spread to virtually all parts of the world where it can survive. In New Zealand, it has out-competed the native fishes, which now are found only above waterfalls that act as barriers to trout dispersal. Because it is a more effective predator than the native fish species, the invertebrates that are prey to the trout are reduced in abundance wherever trout occur. Algae, which are grazed by the invertebrates, increase because of reduced grazing pressure. This is an example of a trophic cascade.
Introduction of the opossum shrimp to Flathead Lake, Montana, is yet another example of complex interactions in ecological communities.
Summary
Predation, a "+/-" interaction, includes predator-prey, herbivore-plant, and parasite-host interactions. These linkages are the prime movers of energy through food chains and are an important factor in the ecology of populations, determining mortality of prey and birth of new predators. Mathematical models and logic suggests that a coupled system of predator and prey should cycle: predators increase when prey are abundant, prey are driven to low numbers by predation, the predators decline, and the prey recover, ad infinitum. Some simple systems do cycle, particularly those of the boreal forest and tundra, although this no longer seems the rule. In complex systems, alternative prey and multi-way interactions probably dampen simple predator-prey cycles.Predator-prey systems are potentially unstable, as is seen in the lab where predators often extinguish their prey, and then starve. In nature, at least three factors are likely to promote stability and coexistence. Due to spatial heterogeneity in the environment, some prey are likely to persist in local "pockets" where they escape detection. Once predators decline, they prey can fuel a new round of population increase. Prey evolve behaviors, armor, and other defenses that reduce their vulnerability to predators. Alternative prey may provide a kind of refuge, because once a prey population becomes rare, predators may learn to search for a different prey species.
Predation, while not the only cause of complex community interactions, has often been shown to have strong indirect effects and cascading effects. Predation also can be a strong agent of natural selection, as we saw in the case of the peppered moth.
Suggested Readings
- Purves, W.K., G.H. Orians and H.C. Heller. Life: The Science of Biology. Sinauer, Sunderland MA.
http://www.globalchange.umich.edu/globalchange1/current/lectures/predation/predation.html
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http://hubpages.com/hub/10_deadliest_Animals
Predator - Prey relationships: 10 deadliest animals
76Of course I am dangerous....
Summary of new study in Journal for Royal Society
Chimps and large predatory cats are more likely to target dimwitted prey less capable of escaping attack, a new study reports....The study focused on predators from africa and south america.
The finding supports a hypothesis first proposed in the early 1990s that predator avoidance has been a major driving force in the evolution of brain size.
One strategy for helping to ensure that offspring are born and the species survives is for an animal to mature early and reproduce before they are killed by a predator. Another option is to invest in physical or behavioral defense strategies. For animals that opt for the latter strategy, altering behavior is easier than evolving armor or a faster gait, but this requires greater cognitive capacities. This in turn requires a bigger brain.
"When these findings are put into perspective, it makes sense that being clever should help individuals avoid or escape danger," said study team member Susanne Shultz from the University of Liverpool in England.
A separate study earlier this year found that one type of monkey even has warning calls that distinguish between the threat of a preying bird or a ground predator. The black-capped chickadee, certainly no birdbrain, can not only warn of a threat but tell other birds how big the predator is.
The finding is detailed online in Biology Letters, the journal for the Royal Society of England.
this was an excerpt from: a no brainer, predators prefer dimwitted prey.But How dangerous am I?
Can you guess the 10 deadliest animals on the planet?
I was shocked at who was on this list:
Here are the top ten and with their method of predation/subtrafuge. Ranked by who kills the most people annually.
10) Posion Dart Frog, clearly not for kissing and one wonders if its habitat has extended into the Marina district in San Francisco (but that is another story)
9.) Cape Buffalo, also commonly known as the water buffalo. When faced with a predator, cape buffalos charge head on. That's 1,500 pounds of beast topped off with two big, sharp horns. You're lucky if there's only one - the real danger comes when a herd of thousands stampedes in your direction.
8.) Polar Bear, not so cuddly anymore! But one might have guessed this since I bet they get pretty hungry and have few chances at prey--making each kill important and a ruthless competitor.
7.) Elephant, Elephants kill more than 500 people a year worldwide. African elephants generally weigh in around 16,000 pounds. Here is a story of a friend of man/domesticated animal--which when mistreated can turn nasty. I have to say, I am rooting for the elephant on this one. Ever hear the story of how Louis Leaky would go after the poachers in africa?
6.) Australian Saltwater Crocodile, I don't know how they determined this would be the worst preditator after the Louisana type...We used to joke in Savannah about how the crocs would come up from the river and eat unwary poodles.
5.) African Lion, (or lioness to be more exact)
4.) Great White Shark, isn't interesting we have at least four animals/insects/fish/amphibians who are from the Cretaeous on this list?
3.) Australian Box Jellyfish,Also known as the sea wasp, this salad-bowl sized jellyfish can have up to 60 tentacles each 15 feet long. Each tentacle has 5,000 stinging cells and enough toxin to kill 60 humans.
2.) Asian Cobra, While the Asian Cobra doesn't hold the title of most venomous snake, it does the most with what it has. Of the 50,000 deaths by snakebite a year, Asian Cobras are responsible for the largest chunk.
1.) Mosquito, Sort of an unassuming predator, no? But some mosquitoes carry and transfer malaria causing parasites. As a result, these little pests are responsible for the deaths of more than two million people a year.
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Defense Mechanisms
By Regina Bailey, About.com
Leopard camouflaged in the grass.
U.S. Fish and Wildlife Service/Gary StolzDefense Mechanisms
There are several ways animals avoid falling prey to a predator. One way is very direct and comes naturally. Imagine you are a rabbit and you have just noticed a fox preparing to attack. What would be your initial response? Right, you'd run. Animals can use speed as a very effective means of escaping predators. Remember, you can't eat what you can't catch!Another defense mechanism is camouflage or protective coloration. One form, cryptic coloration, allows the animal to blend in with its environment to avoid being detected. It is important to note that predators also use cryptic coloration to avoid detection by unsuspecting prey.
Trickery can also be used as a formidable defense. False features that appear to be enormous eyes or appendages can serve to dissuade potential predators. Mimicking an animal that is dangerous to a predator is another effective means of avoiding being eaten.
Physical or chemical combat are other types of defense mechanisms. Some animals' physical features make them a very undesirable meal. Porcupines, for example, make it very difficult for predators with their extremely sharp quills. Similarly, predators would have a tough time trying to get to a turtle through its protective shell.
Chemical features can be just as effective. We all know the hazards of scaring a skunk! The chemicals released result in a not so pleasant aroma that an attacker will never forget. The dart frog also uses chemicals (poisons secreted from its skin) to deter attackers. Any animals that eat these small frogs are likely to get very sick or die.
Predator-Prey Relationship
To sum it all up, the predator-prey relationship is important to maintaining balance among different animal species. Adaptations that are beneficial to prey, such as chemical and physical defenses, ensure that the species will survive. At the same time, predators must undergo certain adaptive changes to make finding and capturing prey less difficult.Without predators, certain species of prey would drive other species to extinction through competition. Without prey, there would be no predators. Thus, this relationship is vital to the existence of life as we know it.
Defense Mechanisms
Predator or Prey GameEndangered Species
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Taking ADvantage
The Biological Basis of Human Behavior
by
Richard F. Taflinger
This page has been accessed 
since 28 May 1996.
For further readings, I suggest going to the Media and Communications Studies website.
This chapter examines human biological evolution over the last several millions years, and how that evolution has influenced how human respond to stimuli today.
Basic Biological Influences on Human Behavior:
Chapter Three
Biological EvolutionHuman beings are animals.
This is not a reference to our behavior (although, of course, some people do act like animals). It is a reference to the fact that humans are biological creatures, as much as crocodiles, cougars, and capabara. We are the product of millions of years of evolution, our physical make-up changing to make us fitter to survive and reproduce.
However, although humans are animals, we also have something that no other animal has: the most complex social structure on Earth. We gather in families, tribes, clans, nations. We have an incredibly sophisticated method of interacting -- speech. We can communicate over time and distance through printing and broadcasting. Our memories are the longest, our interactions the most intricate, our perception of the world simultaneously the broadest and most detailed.
The combination of biology and society is what makes us what we are and do what we do. Biology guides our responses to stimuli, based on thousands of generations of ancestors surviving because of their responses. Our social structures dictate restrictions on and alterations in how we carry out our biological responses.
Neither biology nor society stands without the other. For some people, this is a contradiction -- either nature (biology) controls people, or nurture (society) does. But in fact we filter everything through both to determine how we react to stimuli. The following is a discussion of the two sides of human nature: first, the biological basis of our responses to the world around us, and second, the social factors that affect those responses and make us human.
THE BIOLOGICAL BASIS OF HUMAN BEHAVIOR
The three main elements biology contributes to human behavior are: 1) self-preservation; 2) the reason for self-preservation, reproduction; and 3) a method to enhance self-preservation and reproduction, greed. I will discuss each in turn.
Self-preservation is keeping yourself alive, either physically or psychologically. The latter includes mentally or economically healthy. (Since human beings are very social creatures, we may also apply self-preservation to other people, such as our families. However, I will discuss that in the next chapter.)
BIOLOGICAL BASIS OF SELF-PRESERVATION
A lioness slowly, stealthily, works through the tall grass toward the herd of wildebeest. A doe, unaware of the danger lurking in the grass, separates slightly from the herd. With a rush, the lioness bursts into a run to take down the doe. The startled doe bounds away, running and swerving, trying to escape. The lioness, unable to keep up the pace, gives up, and the doe escapes back into the herd.
A zebra is not so lucky, and the pride feasts.
The Donner Party was a group of settlers trekking to California in 1846. Trapped by snow in the Sierra Nevada mountains, they survived as best they could. This included resorting to cannibalism when they ran out of food, eating the bodies of those who had died.
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To be successful as a species, the members of that species must have a desire tosurvive long enough to pass on their genes to offspring. A species with a death-wish diesout rather quickly. Those species that don't die out have members that have devoted someattention to staying alive long enough to have young. It is from those individuals and therefore species that all living things are descended.
The desire to stay alive is an instinctive one, built into the psyche of the organism. The organism will seek those elements of its environment that will enhance its chances for survival. These include food, water, oxygen, and periods of rest to allow the body to repair any wear and tear on the tissues.
Alternately, it will avoid or evade those elements that might reduce its chances for survival. Such dangers include predators, starvation, dehydration, asphyxiation, and situations that can cause damage to the body.
These seek or avoid drives influence the behavior of organisms: iron seeking bacteria will move toward magnetism, gnus will migrate hundreds of miles to find new pastures, a human will resort to cannibalism; an amoeba will flow away from an electric current, an antelope will run from a lion, a human will obey a killer or withstand torture.
The desire to stay alive is also a selfish instinct, since it is personal survival that the organism is seeking. The reason for that is explained under REPRODUCTION.
A phrase that has often been misquoted, "Survival of the Fittest," actually means survival of the fit. By fit, I mean an organism has those attributes that allow it to get the most out of its environment: gather food, drink, oxygen, rest, sex. The better it is at doing this, the more fit it is.
At this point I should discuss the niche. A niche is a position within an environment that calls for certain attributes to exploit that environment. An environment can contain any of a variety of elements: amount of water, from ocean to desert; type of land, from marsh mud to solid rock; amount of vegetation, from none (the Arctic and Antarctic) to abundant (rainforests). It can also contain animal life, from the tiniest insects to blue whales and everything in between. It is the combination and degree of each of these elements that create niches.
As an example, let's look at just one of these elements. Say there are many small animals, like mice, in an area. A small carnivore like a wildcat could find a lot of food. Thus, it would fit into this niche and thrive. However, when the number of mice decreases, the wildcat can find less food, and has a lesser chance of survival.
If the wildcat has competition from other small carnivores, like foxes, the one that is particularly good as a predator, through cunning or speed or some other attribute, will catch more food. This lessens the amount of food available for the competition, and thus drives the competition out. If the fox is better at catching mice (that is, more fit) than the wildcat, the wildcat will either die or have to move to another niche in which it will be the better predator.
On the other hand, if there are no small animals but many big animals, like antelope, neither a fox nor a wildcat would have much success preying on them. Thus, they wouldn't fit in such a niche. However, large carnivores such as lions would.
Of course, nothing stays the same forever. Niches alter through geologic, climatic and, in the present day, man-made changes in land, water and air. A volcano can create a new island. An ice age can lock up hugh quantities of water in ice caps and glaciers, creating areas of land where oceans once rolled. Continental drift can push seabeds to the tops of mountains. Humans can chop down forests and build cities. All these changes alter the niches, the environmental conditions under which the life in those niches live.
Of course, this means the life has to change as well, to match the new conditions. If it doesn't, it dies. An example is a moth in England. It was originally a mottled white, which allowed it to blend into the light bark of the trees in its area. However, in the 19th century factories in this area began to belch out soot from their chimneys that settled on the trees, changing the tree bark from mottled white to mottled black. The moth could no longer blend in and thus was easy prey to birds. However, some of the moths were darker and thus less noticeable. After a few generations of these darker moths surviving and passing on their genes, the standard color changed to mottled black, and the moth, now blending into the dark bark, survives.
Note that such changes are not conscious decisions made by the organism: the moth did not say to itself, "The bark is getting dark--I'd better change color, too." It is simply that there are variations between individuals in any species (an advantage of sexual reproduction and its combining of genes). Some of those variations are detrimental: the dark moth variations were easy prey when the tree bark was light. However, as the conditions in a niche change, those same variations can become advantageous, enhancing rather than weakening chances for survival.
Such changes in an organism's physical characteristics are, of course, accidental. If no variations exist in a species that contribute to survival when conditions change, or if conditions change too quickly for advantageous variations to be passed on to enough descendants,(1) the species can die out.
Other changes in an organism can develop over time. These are survival strategies, rather than physical changes, that improve the organism's chances for survival. For example, some animals have perfected the technique of hibernating during periods when the food supply is low. Marmots have developed a social structure that provides lookouts who watch for predators and sound a warning when one appears. Prairie dogs dig their burrows with multiple entrances and exits so if a predator comes in one door, the dogs can leave through another.
These survival strategies are adaptations to niche conditions, but unlike physical changes are not necessarily genetic changes. Such strategies as hibernation, of course, require genes that alter the animal's physiology to slow heartbeat, lower body temperature, and otherwise decrease its metabolism. Others are instinctive, hardwired genetically into the animal's brain, such as a fawn's curling up and freezing when predators are about.
However, some survival strategies are learned behaviors. That is, the young learn them from older animals that learned them from their ancestors. For example, most predators teach their young the techniques of successful hunting. In general, it appears the higher the complexity of the nervous system of the animal, the more likely strategies are learned rather than instinctive. Sharks, with a relatively simple nervous system, hunt by instinct and need no instruction on how to go about it. Lions, with a complex system, must learn the techniques of stealth, stalk, and attack.
Again, in most animals, the strategies are not conscious decisions, but responses to stimuli such as hunger, thirst, asphyxiation, fear, or exhaustion. If conditions change so the instinctive strategy is dangerous rather than beneficial, the animal can die. For example, the fawn's freeze response to fear would be deadly if there was no cover to hide in while frozen. The musk ox strategy is to form a stationary circle with the young in the center and the older members facing outward, rather than running away. This is excellent against wolves, but deadly when faced with spears and guns (perfect, however, for the human survival strategy of group hunting with weapons). The musk ox cannot consciously decide that this strategy isn't working and that they must try another.
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The combination of genetic and learned responses to stimuli create an animal's reaction to stimuli. For example, the genetically dictated instinctive reaction to a threat to self-preservation is the "fight or flight" syndrome. When threatened, an animal undergoes several physiological changes that have become genetically hardwired into the animal's body. The changes include an increased rate of respiration to provide more oxygen to the muscles, an accelerated heart beat to speed up the blood flow, a lessening in sensitivity to pain, and changes in the blood stream, including an injection of adrenalin and diversion away from the organs to the muscles. These physiological changes prepare the animal to either fight for survival or run away from danger.
However, learned responses can mitigate the instinctive, depending on the complexity of the animal's nervous system. That complexity increases an animal's options in reacting to stimuli. For example, an amoeba will avoid an electric field automatically -- an instinctive reaction unmitigated by a survival strategy. A starving rat, however, will run across an electrified grid that gives it painful shocks if there is food on the other side. It can learn a survival strategy -- the shocks, though causing the instinctive fight-or-flight physiological changes, aren't going to kill it. Starvation will.
All the above applies to humans as much as any other animal: humans desire personal survival; seek food, drink, rest, sex; fit into niches; must adapt to changing conditions.
Humans are subject to the same stimuli and reactions as any other animal. Hunger, thirst, asphyxiation, fear, and exhaustion are physical sensations that cause instinctive physical reactions. Most of these reactions are unpleasant, and people avoid the stimuli that cause them, or, if they're unavoidable, take actions to reduce them. Thus you eat when hungry, drink when thirsty, fight for air, run from dangerous situations, sleep. In any case, the reactions are good in that they tell you you're in a situation that could result in injury or death. These responses are instinctive, and we have no more control over them than we do over our eye color.
Actually, we do have control over our eye color. The reason we do is why our approach to self-preservation is different from all other creatures. We have a brain that is capable of perceiving and solving problems. We change our eye color with contact lenses. We react to a threatening situation through applying our brains to the problem and finding a solution to it.
The difference between humans and other animals is that, unlike any other animal (as far as we know), we can and do consciously respond or alter our response to a stimulus. The greatest example lies in the existence of amusement parks, where people deliberately subject themselves to stimuli that any other creature on earth would go to great lengths to avoid. Imagine, if you can, the reaction of a dog to a roller coaster. If it didn't leap out at the first movement, it would cringe in bottom of the car until it probably had a heart attack. Yet, humans go on such rides for fun, our minds accepting that the ride is safe, and thus control the terror such a thing would cause in any other creature.
Indeed, the physical manifestations of the stress of the workplace, such as ulcers, headaches, nervous breakdowns, is often considered a result of the fight or flight syndrome at work on the body, while the mind is required to remain under stimuli that no other creature would willing accept. For example, being bawled out by your boss would, in another animal, cause a fight or the chastized to run. Humans, though, stand, listen, nod their heads, say "yes, I understand" and go back to work (probably muttering uncomplimentary comments about the boss under their breath).
Even more, humans can alter rather than merely adapt to the environments in which we find ourselves to enhance our chances for survival. The invention of agriculture and the domestication of animals improved the food supply; the building of dwellings enhanced shelter from the elements; science and medicine have greatly increased human lifespan and the quality of that life. Human ingenuity has altered every aspect of the world to enhance the human life.(2)
However, humans live in an extremely complex society. Thus, self-preservation is a much more complicated proposition than among other animals. Eating to satisfy hunger is more than just finding proper vegetation or hunting; shelter for rest and recuperation is more than finding a convenient cave or nest; avoiding predators is difficult because it is often hard if not impossible to tell what is a predator (the only real predators on humans are other humans). Even avoiding dangerous situations (such as car crashes) is difficult because ofhuman technology. Things can happen so quickly danger isn't apparent until it's too late to do anything about it.
To deal with the complexity, human society has become, to a large extent, an economic one. That is, the connections between unrelated people is often based on distribution of resources (related people connect more through personal attachment). I will discuss these social factors in human self-preservation in the next chapter.
"Greed is good."
Wall Street
The above quote is from the popular movie, WALL STREET, starring Michael Douglas. When it was spoken in the movie, it was used as an ironic counterpoint: the character who said it was very successful following the credo, but ultimately it was his downfall. The audience may have though it was poetic justice. The credo, however, is merely a statement of biological necessity.
Greed has an extremely negative connotation for most people. It conjures up images of Ebenezer Scrooge and Shylock, chortling over their gold and ignoring the plights and miseries of others. However, it is actually the gathering of resources, the more the better. Biologically, for any organism that is successful greed is good.
Any form of life must gather resources that allow it to survive and reproduce. The resources may be food, water, sunlight, minerals, vitamins, shelter. Without these things, the organism dies. Since the two most basic purposes of life are to live and to reproduce, it should do everything it can to avoid dying through a lack of resources.
Greed is one organism getting a larger piece of the pie, more of the necessary resources, than other organisms. For example, in the Amazonian rain forest, an occasional
tree dies and falls. This leaves an opening to the sun in the continuous canopy of foliage. Plants and trees race each other to grow into that opening. The winners in the race fill the hole; the losers die through lack of sunlight. (Attenborough, 1990) The greed for sunlight means life.
Again, as for self-preservation and sex, greed is an instinctive reaction. When presented with resources, the instinct is to grab them, use them, take advantage of them. This isn't a conscious decision. An animal, when starving, wants more food; when thirsty, more water. If it means taking it from another animal, that's what it does if it can.
You may ask, what about those animals who feed their offspring, though they're starving themselves? Remember that the second purpose of life is to reproduce. This requires not only producing the young. Once it's born it must be kept alive until it's self-sufficient. If it dies, then all the time, effort and energy to produce it must be repeated to produce another one. However, once it reaches self-sufficiency the parent's genes will, most likely, be passed on to another generation. Keeping the offspring alive, even at the expense of the parent dying, is of paramount importance. Thus, a parent caring for its young at its own expense is not an act of selflessness; it's an act of genetic selfishness.
You may also point out that humans avoid being greedy. In fact, being greedy is something that is scorned, something to be ashamed of. Once again, as for self-preservation and reproduction, it's because humans are unique -- we have a conscious mind that influences their biological instincts. How that works is the topic of the next chapter.
NOTES
1There is a theory of critical mass, that the gene pool for a species must be large enough (that is, the breeding population must be large enough) to provide enough variations to counter adverse conditions or events. For example, the African cheetah population appears to be descended from only a few individuals; apparently most of the species fell prey to a disease that only a few survived because of a genetic immunity. Those few represented a gene pool too small to provide much in the way of variation, and there is a fear that something, perhaps another disease to which the current population has no genetic immunity, will kill off the remaining cheetahs.
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2 Of course, we can also argue that this same ingenuity has enhanced human life to the point that human life, and all other life on earth, is threatened. The human ability to alter the environment to help people survive has allowed so many people to survive that the Earth itself, which is need to support them, many not survive.
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Copyright © 1996 Richard F. Taflinger.
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In addition,
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