28 UNDERWATER GUIDE TO MARINE LIFE 



including man and is a direct result of evolution (Chapter 5). Adaptation 

 is exceedingly complex and can never be measured by a single factor such as 

 adaptive coloration, food-getting mechanisms, or breeding habits for the simple 

 reason that adaptation is an adjustment of all the activities of an animal or 

 plant. Because adaptation is so complex, it is never perfect. It is inconceivable 

 that any living thing could perfecdy adapt in every way to meet the ever- 

 changing requirements of the environment. This is not to say that adaptation is 

 not very successful, however. The adaptations for speed of movement are not 

 absolutely perfect in the mackerels, tunas, and spearfishes, but these fishes are 

 certainly not inadequate in meeting the demands of their predatory ways. 



Adaptation cannot be studied without reference to the question. Adaptation 

 for what? It is not specific enough to say that an animal is adapted for its 

 general environment. We must define what part of its environment, what 

 specific way of life, that animal has evolved to meet. In other words, where in 

 the community does that animal fit in? We know, for instance, that barbers, 

 bakers, and candlestick makers all have their particular adaptive skills in a 

 human community. It is no less obvious that groupers, parrot fishes, and sponges 

 have their separate places in a coral community as well. The adaptive place 

 of every animal is called its niche, and in order to define it, the community 

 must be re-examined. 



The various zones of the sea have been defined under the section on zoo- 

 geography in the last chapter. These zones were shown to be different in their 

 general physical characteristics of temperature, substrate, salinity, etc. In other 

 words, zones are defined by a set of physical characteristics. All the animals 

 of a zone were lumped together in a community, each species of which is 

 subject to similar physical characteristics. Different communities may difi^er in 

 many ways, but all communities are alike in one respect: Elton (1935) says 

 that the basic ground plan of all communities is dictated by food chains and 

 that the niche any animal occupies is largely determined by its place in the food 

 chain, that is, what it eats and what eats it. 



For instance, the herring is a plankton-eater and is eaten by a large number 

 of predatory fishes, such as tunas, swordfishes, etc. Therefore, it is best to 

 define "niche," as Elton points out, by an animal's relation both to its food and 

 to its enemies. 



"Niche" is an important concept and the discovery of its niche is vital in 

 understanding any animal. But, of course, the description of a niche cannot tell 

 us all there is to know about an animal. The ways it breeds, moves, is colored, 

 and behaves are all vital aspects that do not derive from a study of food patterns 

 alone. 



One point that must be emphasized is that animals are not continually 

 engrossed in one long struggle for existence throughout the whole of their 

 lives. As Elton (1935) emphasizes, animals are not always doing something. 

 It is true that all animals are adapted to a particular mode of life which revolves 

 around feeding, but it is not true that everything animals do or that every 

 anatomical characteristic they possess are of adaptive significance. Some actions 

 or characteristics may have little or no significance. If the diver is to interpret 

 adaptation correctly, he must learn to distinguish between significant and insig- 

 nificant traits and actions. 



