56 ANIMAL ECOLOGY 



spend an unexpectedly large proportion of their time doing 

 nothing at all, or at any rate, nothing in particular. For 

 instance, Percival ^~^ says of the African rhinoceros : *' After 

 drinking they play . . . the rhino appears at his best at night 

 and gambols in sheer lightness of heart. I have seen them 

 romping like a lot of overgrown pigs in the neighbourhood 

 of the drinking place." 



Animals are not always struggling for existence, but when 

 they do begin, they spend the greater part of their lives eating. 

 Feeding is such a universal and commonplace business that 

 we are incHned to forget its importance. The primary driving 

 force of all animals is the necessity of finding the right kind 

 of food and enough of it. Food is the burning question in 

 animal society, and the whole structure and activities of the 

 community are dependent upon questions of food-supply. 

 We are not concerned here with the various devices employed 

 by animals to enable them to obtain their food, or with the 

 physiological processes which enable them to utilise in their 

 tissues the energy derived from it. It is sufficient to bear in 

 mind that animals have to depend ultimately upon plants for 

 their supplies of energy, since plants alone are able to turn 

 raw sunlight and chemicals into a form edible to animals. 

 Consequently herbivores are the basic class in animal society. 

 Another difference between animals and plants is that while 

 plants are all competing for much the same class of food, 

 animals have the most varied diets, and there is a great diver- 

 gence in their food habits. The herbivores are usually preyed 

 upon by carnivores, which get the energy of the sunlight at 

 third-hand, and these again may be preyed upon by other 

 carnivores, and so on, until we reach an animal which has no 

 enemies, and which forms, as it were, a terminus on this food- 

 cycle. There are, in fact, chains of animals linked together 

 by food, and all dependent in the long run upon plants. We 

 refer to these as " food-chains," and to all the food-chains in 

 a community as the " food-cycle." 



8. Starting from herbivorous animals of various sizes, 

 there are as a rule a number of food-chains radiating outwards, 

 in which the carnivores become larger and larger, while the 



