The Element of Animal Disguise
In addition to background-matching coloration, many animals have distinctive designs on their bodies that serve to conceal them . These designs, which might be spots, stripes or a group of patches, can help the animal in a couple of ways. First, they may match the pattern of "the model," the background of the animal's surroundings. For example, animals that inhabit areas with tall, vertical grass often have long, vertical stripes. Second, they may serve as visual disruptions. Usually, the patterns are positioned "out-of-line" with the body's contours. That is, the pattern seems to be a separate design superimposed on top of the animal. This makes it hard for the predator to get a clear sense of where the animal begins and ends -- the pattern on the body seems to run off in every direction.
This disruptive coloration is particularly effective when animals in a species are grouped together. To a lion, a herd of zebras doesn't look like a whole bunch of individual animals, but more like a big, striped mass. The vertical stripes all seem to run together, making it hard for a lion to stalk and attack one specific zebra. The stripes may also help a single zebra hide in areas of tall grass. Since lions are colorblind, it doesn't matter that the zebra and surrounding environment are completely different colors.
Many fish species are similarly camouflaged. Their vertical stripes may be brightly colored, which makes them stand out to predators, but when they swim in large schools, their stripes all meld together. This confusing spectacle gives predators the impression of one big, swimming blob.
Generally, this sort of camouflage doesn't hide an animal's presence, it merely misrepresents it. A related camouflage tactic is for an animal to take on the appearance of some other object. One of the most famous examples of this sort of impressionist is the walking stick, an insect that looks like an ordinary twig. A predator can easily distinguish a walking stick from its surroundings, but the predator thinks its only a stick, and so ignores it. You can also see this sort of camouflage in some katydid species, which have evolved so that they look just like tree leaves.
Other animals use a more aggressive sort of mimicry. Several moth species have developed striking designs on their wings that resemble the eyes of a larger animal. The back of the hawk moth caterpillar actually looks like a snake head, a frightening visage for most predators the moth would come across. A simpler variation on this adaptation is simple color mimicry. In many ecosystems, smaller poisonous animals develop a bright coloration -- predators learn to steer clear of these colors, lest they get a mouthful of venom. Over time, other, non-poisonous species may develop the same coloration, cashing in on the nasty reputation of the poisonous species.
Mimicry is a different approach than ordinary camouflage, but it works toward the same end. By developing a certain appearance, an animal species makes itself a harder target for predators and a sneakier hunter for prey. In different areas around the world, you'll see all sorts of variations and combinations on the basic elements of camouflage. As animal species evolve, they become more and more in tune with their environment. Often, these sorts of adaptations are more effective survival tools than an animal's more aggressive weapons of defense (teeth, claws, beaks). After all, being entirely overlooked by a predator is preferable to having to put up a fight.
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