The Element of 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.

Photo courtesy Carl Roessler A leafy sea dragon, photographed off the coast of Australia. Leafy sea dragons have developed flowing appendages and vivid coloration that lets them blend in with the undersea plant life in their environment.

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.

Photo courtesy Scott Camazine Walking sticks have adapted to resemble their surroundings. Most of the time, their predators pass them by as they would a real twig.

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.

Examples of Biomes

Operation Conservation: Saving the Earth's Terrestrial Biomes
A Science WebQuest for 5th Grade
Desert	Prairie	Savannah
Taiga	Temperate Deciduous Forest	Temperate Rainforest
Tropical Rainforest	Tundra	Wetlands

Precipitation to Rain

Most precipitation that reaches the ground actually begins as snow high in the atmosphere. These snow flakes develop somewhere above the freezing level where the air temperature is less than 32 F (the dashed blue line), and begin to fall toward the earth as snow. If ground temperature is above 32 F, the freezing level must be located somewhere above the ground. The falling snow passes through the freezing level into the warmer air, where it melts and changes to rain before reaching the ground.

When the air temperature at the ground is less than 32 F, the precipitation begins falling as snow from the clouds.

Since it is falling into cold air, the snow does not melt on the way down and reaches the ground as snow. This is why cold air is important for there to be snow.

 

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The Moons
of Mars

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Mars has two small moons that are illustrated in the following figures, Phobos and Deimos.

Phobos (Ref)	Deimos (Ref)

These are examples of what are called minor satellites: small chunks of rock in orbit around planets as compared with large satellites like the Earth's Moon. As the adjacent images show, they are very irregular in shape. Phobos is 27 km long in its longest dimension and Deimos is 15 km long in its longest dimension.

Both are cratered and orbit the planet in rather low orbits. Phobos is only about 3000 miles above the Martian surface and orbits in a little over 7 hours (thus it makes more than 3 orbits in a single Martian day). Deimos is a little further out and orbits in about 30 hours.

The figure to the right (Ref) shows a rather spectacular image taken by the Viking 2 orbiter from an altitude of about 8000 miles above the Martian surface. The image looks down on a Martian shield volcano (Ascraeus Mons) which is about 200 miles across and in the center. The object down and to the left of the volcano is Phobos, which is 5000 miles below the orbiter, and 3000 miles above the Martian surface! (The regular horizontal rows of dots seen in the image are an artifact associated with the imaging; they don't correspond to real features.)

These moons of Mars were not formed in the same way as the Earth's Moon. They are probably fragments of larger objects broken apart in a collision. Such moons may be formed from collisions of objects originally in orbit around the planet, or they might also have been captured gravitationally at some point in the past. The adjacent image (Ref) compares the appearance of several minor satellites of the Solar System (Phobos, Deimos, Gaspra, and Ida). We shall encounter many such small moons around the giant planets like Jupiter and Saturn.

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