64 ANIMAL ECOLOGY 



chemical, physical, and biotic — and the " niche " of an animal 

 means its place in the biotic environment, its relations to food 

 and enemies. The ecologist should cultivate the habit of 

 looking at animals from this point of view as well as from the 

 ordinary standpoints of appearance, names, affinities, and past 

 history. When an ecologist says '' there goes a badger " he 

 should include in his thoughts some definite idea of the animal's 

 place in the community to which it belongs, just as if he had 

 said *' there goes the vicar." 



1 6. The niche of an animal can be defined to a large extent 

 by its size and food habits. We have already referred to the 

 various key-industry animals which exist, and we have used 

 the term to denote herbivorous animals which are sufficiently 

 numerous to support a series of carnivores. There is in every 

 typical community a series of herbivores ranging from small 

 ones (e.g. aphids) to large ones (e.g. deer). Within the herbi- 

 vores of any one size there may be further differentiation 

 according to food habits. Special niches are more easily 

 distinguished among carnivores, and some instances have 

 already been given. 



The importance of studying niches is partly that it enables 

 us to see how very different animal communities may resemble 

 each other in the essentials of organisation. For instance, 

 there is the niche which is filled by birds of prey which eat 

 small mammals such as shrews and mice. In an oak wood 

 this niche is filled by tawny owls, while in the open grassland 

 it is occupied by kestrels. The existence of this carnivore 

 niche is dependent on the further fact that mice form a definite 

 herbivore niche in many different associations, although the 

 actual species of mice may be quite different. Or w^e might 

 take as a niche all the carnivores which prey upon small 

 mammals, and distinguish them from those which prey upon 

 insects. When we do this it is immediately seen that the 

 niches about which we have been speaking are only smaller 

 subdivisions of the old conceptions of carnivore, herbivore, 

 insectivore, etc., and that we are only attempting to give more 

 accurate and detailed definitions of the food habits of animals. 



17. There is often an extraordinarily close parallelism 



