CHAPTER V 



THE ANIMAL COMMUNITY 



" The large fish eat the small fish ; the small fish eat the water insects ; 

 the water insects eat plants and mud." 

 " Large fowl cannot eat small grain." 

 " One hill cannot shelter two tigers." — Chinese Proverbs. 



Every animal is (i, 2) closely linked with a number of other animals living 

 round it, and these relations in an animal community are largely food 

 relations. (3) Man himself is in the centre of such an animal com- 

 munity, as is shown by his relations to plague-carrying rats and (4) to 

 malaria or the diseases of his domestic animals, e.g. liver-rot in sheep. 

 (5) The dependence of man upon other animals is best shown when he 

 invades and upsets the animal communities of a new country, e.g. the 

 white man in Hawaii. (6) These interrelations between animals appear 

 fearfully complex at first sight, but are less difficult to study if the follow- 

 ing four principles are realised : (7) The first is that of Food-chains 

 and the Food-cycle. Food is one of the most important factors in the 

 life of animals, and in most communities (8) the species are arranged 

 in food-chains which (9) combine to form a whole food-cycle. This 

 is closely bound up with the second principle, (10) the Size of Food. 

 Although animals vary much in size, any one species of animal only 

 eats food between certain limits of size, both lower and (11) upper, which 

 (12) are illustrated by examples of a toad, a fly, and a bird. (13) This 

 principle applied to primitive man, but no longer holds for civilised 

 man, and (14) although there are certain exceptions to it in nature, it 

 is a principle of great importance. (15) The third principle is that of 

 Niches. By a niche, is meant the animal's place in its community, its 

 relations to food and enemies, and to some extent to other factors also. 

 (16), (17), (18), (19), (20) A number of examples of niches can be given, 

 many of which show that the same niche may be filled by entirely different 

 animals in different parts of the world. (21) The fourth idea is that 

 of the Pyramid of Numbers in a community, by which is meant the 

 greater abundance of animals at the base of food-chains, and the com- 

 parative scarcity of animals at the end of such chains. (22) Examples 

 of this principle are given, but, as is the case with all work upon animal 

 communities, good data are very scarce at present. 



I. If you go out on to the Malvern Hills in July you will 

 find some of the hot limestone pastures on the lower slopes 

 covered with ant-hills made by a Httle yellow ant {Acanthomyops 

 flavus). These are low hummocks about a foot in diameter, 



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