786 



ANIMALS AND THEIR ENVIRONMENT 



• •* 





Figure 38.4. An experiment to sliow the remarkable ability of the floinider to 



change its color and pattern to conform with its backgromicl. Left, a tiomider on a 



uniform, light backgroimd; right, the same fish after being placed on a spotted, darker 

 backgromul. (\'illee: Biology.) 



there was a significantly higher percentage of survivors among those 

 grasshoppers which matched their background. 



When an animal is protected by poison iangs, stinging mechanisms, 

 or some chemical which gives it a noxious taste, it is to its advantage to 

 have this lact widely advertised. In fact, many animals with such pro- 

 tective adaptations do have warning colors. A European species of toad, 

 lor example, has skin glands which secrete an unpleasant, unpalatable 

 substance. Its belly is bright scarlet, and whenever a potential predator, 

 such as a stork, swoops over a congregation of these toads, they flop on 

 their backs, exposing their scarlet bellies as a warning. The storks and 

 other birds apparently become conditioned to the association of the red 

 color and the bad taste, and do not try to eat the toads. 



Other animals survive by mimicking one of these protectively col- 

 ored animals. Some harmless, defenseless and palatable animals have 

 evolved to be almost identical in shape and color with a poisonous or 

 noxious animal of quite a different family or order, and, being mis- 

 taken for it by predators, are left alone. Examples of mimicry are par- 

 ticularly common among tropical insects. This type of adaptation is 

 successful only where there are many more genuinely disagreeable or 

 dangerous organisms than forms which mimic them. Obviously if a 

 predator finds that any considerable percentage of the animals with a 

 particular shape and color are palatable, he will not be conditioned to 

 avoid them. 



The reality of the selective advantage of color adaptations has been 

 much debated. It has been argued that animal vision may be quite 

 different from human vision; that animals may be color-blind, or per- 

 haps able to see light in the ultraviolet or infra-red part of the spectrum, 

 and therefore that an animal which appears to be protectively colored 

 to human eyes may be readily evident to its natural predators. How- 

 ever, many experimental studies, such as the grasshopper experiment 

 cited previously, have shown that protective coloration does has survival 

 value. 



Color and patterns may serve to attract other organisms when such 

 attraction is necessary for survival. The red and blue ischial callosities of 

 monkeys, and the extravagantly colored plumage of many birds, appar- 

 ently have an attraction for the members of the opposite sex. The vivid 

 colors of flowers appear to attract the birds or insects whose activities 



