protective coloration

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protective coloration

protective coloration, coloration or color pattern of an animal that affords it protection from observation either by its predators or by its prey. The most widespread form of protective coloration is called cryptic resemblance, in which various effects that supplement the similarity of color between the animal and its surroundings enable the creature to blend into the background of its habitat. Disruptive coloration, or irregular patches of contrasting colors, serve to distract the observer's eye from the outline of the animal. Thus the stripes of the tiger and the zebra make detection among the jungle grasses more difficult, whereas the leopard's spots are more suited to the mottled light and shade of the low branches from which it drops onto its prey. Many other creatures (e.g., frogs, lizards, and snakes) are dappled, barred, speckled, mottled, or otherwise distinctively marked or colored so that they blend with sand, water, snow, or specific vegetation, depending on their natural habitat. The pigmentation of some animals (e.g., the chameleon and the flounder) changes to resemble different backgrounds. In countershading, the upper surface of the animal is darker than the undersurface and produces the illusion of flatness. Countershading also aids many fish and birds by blending them with the sky or with the upper water surface when viewed from below and with the land or the sea bottom when viewed from above. Some animals undergo a seasonal variation in color: The stoat and the caribou turn from brown in summer to white in winter (when the stoat is known as ermine). A second type of protective coloration, in animals whose coloration or markings distinctly contrast with their habitat, serves as a warning device either to its predators (e.g., the skunk's stripe and the brilliant colors of many venomous snakes and distasteful insects) or to other members of their species in the vicinity (as the white tail patches of the pronghorn and the jack rabbit that are flashed on approaching danger). The adaptation of an organism's appearance to resemble that of another organism that is repugnant or dangerous to a potential predator is called mimicry. Coloration may thus be categorized as concealing, revealing, or deceiving. Although these devices are not invariably successful, they do increase the statistical chance for survival of the species. The most widely accepted explanation of the phenomenon of protective coloration is Darwin's theory of natural selection.


See R. A. Carr, Protective Coloration and Mimicry (1972); M. Edmunds, Defence in Animals (1974).

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Protective coloration

A strategy that organisms use to avoid or deflect the attacks of predators by misleading the latter's visual senses.

Protective coloration can be classified according to whether the functioning or malfunctioning of the vertebrate visual system is exploited. Exploiting the malfunction of the system means simply “not being seen”: the prey fails to attract the attention of the predator, usually because it is the same color as the general background or because it fails to cast a shadow. The organism avoids producing shadow by flattening itself against the substrate, or by countershading, in which the lower parts of a cylindrical prey such as a caterpillar are more lightly colored than the upper parts. As shadows normally form on the underside of cylinders, the shading cancels the shadow and makes the caterpillar optically flat. Animals that match their background often have an ability to select the appropriate background to rest on, or much less frequently can change their own color to match (as in the case of the chameleon).

Exploiting the functioning of the vertebrate perceptual system takes many forms. The vertebrate visual cortex decodes the image on the retina in a hierarchical process starting with the detection of edges. A moth may counter this by possessing strikingly contrasted patches of color on its wings, arranged in a random way. The outline of the moth is thus broken up, and the predator cannot decode it as a significant shape. The prey may also exploit the learning capacity of the predator. For example, insectivorous birds see leaves but do not attack them because they have learned (or perhaps know innately) that these are not edible. Resemblances to leaves, twigs, thorns, flowers, parts of flowers, and more bizarre objects like fresh turds (usually bird droppings) are very widespread. This type of camouflage is termed mimetic camouflage. Camouflage in general is often termed cryptic coloration.

Coloration may be considered mimetic if protection is achieved by a resemblance to some other existing object, which is recognized by the predator but not associated in its mind with feeding. Usually this negative or neutral association is learned, but in a minority of instances it is almost certainly innate. Small birds have an innate flight response to large eyes in close-up (which normally indicate that a cat or a predatory bird is dangerously close). This reaction is exploited by many moths and other insects, which have eyelike markings, sometimes very convincing in their shading and highlighting, on concealed parts of the wings. Attack by a bird causes such a moth to change its posture rapidly to reveal the fake eyes, thus frightening away the attacker. Motmots (birds which habitually prey on snakes) have a similar innate fear of the red, black, and yellow striping patterns of the deadly coral snakes. These patterns are mimicked by various nonvenomous snakes, and even some caterpillars.

Flash coloration describes the phenomenon in which the prey is cryptic when at rest, but reveals brilliantly colored parts while escaping. This behavior seems to function simply by startling the predator. Very small eye marks at the tips of the wings, or a false head at the wrong end of the body (shown by some coral reef fish, for example) may cause the predator to misdirect its attack.

Protection through the possession of a chemical or physical defense that is dangerous to one's potential predator, accompanied by a strikingly conspicuous pattern known as warning coloration (often black, red, yellow, and white), is widespread---the ensemble of defense and color is termed aposematic. The actual defense ranges from toxic venoms through stings (in wasps, for example), to the oozing of noxious foams or hemolymph (as in ladybirds), to the possession of toxic chemicals (cyanides, cardiac glycosides, alkaloids) that will poison the predator or simply produce a revolting taste. The function of the warning color is to remind the predator of its previous unpleasant experience.

Sometimes the term mimicry is restricted to resemblances between edible species and actively defended and warningly colored models (as opposed to inedible objects such as thorns). Much is known about the evolution of this kind of mimicry in butterflies (and to a lesser extent, in bees and flies). If the mimic is entirely edible, the relationship is parasitic; the mimic benefits from the resemblance, but as every encounter with a mimic reduces the predator's aversion, the model suffers some increase in the rate of attack. Such mimicry has traditionally been termed Batesian mimicry. Alternatively, the mimic may be almost or fully as defended as the model, leading to a mutualistic relationship known as Müllerian mimicry, in which both the model and the mimic species suffer a decreased rate of predation.

McGraw-Hill Concise Encyclopedia of Bioscience. © 2002 by The McGraw-Hill Companies, Inc.

protective coloration

[prə′tek·tiv ‚kəl·ə′rā·shən]
A color pattern that blends with the environment and increases the animal's probability of survival.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
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