THE ANIMAL COMMUNITY 59 



are peculiar, the food-supply is of course ultimately derived 

 from plants, but owing to the isolation of the animals it is 

 convenient to treat them as a separate community. 



Certain animals have succeeded in telescoping the par- 

 ticular food-chain to which they belong. The whale-bone 

 whale manages to collect by means of its sieve-like apparatus 

 enough copepods and pteropods to supply its vast wants, and 

 is not dependent on a series of intermediate species to produce 

 food large enough for it to deal with effectively. This leads 

 us on to a more detailed consideration of the problem of 



Size of Food 



10. Size has a remarkably great influence on the organisa- 

 tion of animal communities. We have already seen how 

 animals form food-chains in which the species become pro- 

 gressively larger in size or, in the case of parasites, smaller in 

 size. A little consideration will show that size is the main 

 reason underlying the existence of these food-chains, and that 

 it explains many of the phenomena connected with the food- 

 cycle. 



There are very definite limits, both upper and lower, to the 

 size of food which a carnivorous animal can eat. It cannot 

 catch and destroy animals above a certain size, because it is 

 not strong or skilful enough. In the animal world, fighting 

 weight counts for as much as it does among ourselves, and a 

 small animal can no more tackle a large one successfully than 

 a light-weight boxer can knock out a trained man four stone 

 heavier than himself. This is obvious enough in a broad 

 way ; spiders do not catch elephants in their webs, nor do 

 water scorpions prey on geese. Also the structure of an 

 animal often puts limits to the size of food which it can get 

 into its mouth. At the same time a carnivore cannot subsist 

 on animals below a certain size, because it becomes impossible 

 at a certain point to catch enough in a given time to supply 

 its needs. If you have ever got lost on the moors and tried 

 to make a square meal off bilberries, you will at once see the 

 force of this reasoning. It depends, however, to a large 

 extent on the numbers of the prey : foxes find it worth while 



