THE ADAPTATION OF ANIMALS TO THE ENVIRONMENT 785 



new organism. Any mutation that increases the Hmits of temperature 

 tolerance of a species— makes it more eurythermic— may enable it to in- 

 habit a new part of the earth, at a higher latitude or higher altitude. 



Marine fish are usually adapted to survive within a certain range 

 of pressures and thus are found at certain depths. Animals adapted to 

 live near the surface are crushed by the terrific pressures of the deep, 

 and deep sea animals usually burst when brought to the surface. The 

 whale has a remarkable ability to withstand changes in pressure, and 

 can dive to depths of 2500 feet without injury. Presumably its lung 

 alveoli collapse when the pressure on the body reaches a certain point 

 and then gases are no longer absorbed into the blood. A man can sur- 

 vive pressures as great as six atmospheres if the pressure is increased and 

 subsequently decreased slowly. The increase in pressure increases the 

 amoiuit of gas dissolved in the blood, in body fluids and within the 

 cells. If the pressure is decreased suddenly, the gases come out of solu- 

 tion and form bubbles throughout the body. Those in the blood impede 

 circidation and bring about the symptoms of diver's disease, or "the 

 bends." The pilot of a jet plane may gain altitude so quickly that the 

 atmospheric pressure is reduced rapidly enough to bring bubbles of gas 

 out of solution in his blood and produce a type of the bends. 



355. Color Adaptations 



Adaptations are evident in the color and pattern of animals and 

 plants as well as in their structure and physiologic processes. Ecologists 

 recognize three types of color adaptation: concealing or protective color- 

 ation, which enables the organism to blend with its background and 

 be less visible to predators; warning coloration, which consists of bright, 

 conspicuous colors and is assumed by poisonous or unpalatable animals 

 to warn ott potential predators; and mimicry, in which the organism 

 resembles some other living or nonliving object— a twig, leaf, stone, or 

 perhaps some other animal which, being poisonous, has warning colora- 

 tion. 



Concealing coloration may serve to hide an animal which wants to 

 escape the notice of a potential predator or it may hide a predator from 

 his intended prey. Examples of such coloration are legion-the white 

 coats of arctic animals, and the stripes and spots of tigers, leopards, 

 zebras and giraffes which, though conspicuous in a zoo, blend impercep- 

 tibly with the moving pattern of light and dark typical of their native 

 savanna. Some animals-frogs, flounders, chameleons, crabs and others- 

 can change color and pattern as they move from a dark to a light back- 

 ground or from one that is uniform to one that is mottled (Fig. 38.4). 



To demonstrate experimentally that concealing coloration does 

 have survival value-that what looks to a man like a good match be- 

 tween animal and background will also fool the animal's predators- 

 investigators fastened grasshoppers with different body colors to plots of 

 different colored soils-light, dark, grassy or sandy. After these plots had 

 been exposed to the predatory activities of chickens or wild birds for a 

 given length of time, the survivors were tabulated. It was found that 



