66 



ANIMAL ECOLOGY 



history which has accumulated up to date in this rather hap- 

 hazard manner. This applies with particular force to facts 

 about the food habits of animals. Until more organised 

 information about the subject is available, it is only possible 

 to give a few instances of some of the more clear-cut niches 

 which happen to have been worked out. 



1 8. One of the biggest niches is that occupied by small 

 sap-suckers, of which one of the biggest groups is that of the 

 plant-lice or aphids. The animals preying upon aphids form 

 a rather distinct niche also. Of these the most important are 

 the coccinellid beetles known as ladybirds, together with the 

 larvae of syrphid flies (cf. Fig. 5) and of lacewings. The niche 



Moths 



^Caterpillars] 



llchneumons | 



jfUJrph^s 



y- > | LadyblrdB| — - ^Spiders | 



JI ^ -^ 



I Secretion} 



Dlsser 

 Wasps 



iPsammochareaj 



Fig. 5. — Food-cycle on young pine-trees on Oxshott Common. 

 (From Richards. ^^) 



in the sea and in fresh water which is analogous to that of 

 aphids on land is filled by copepods, which are mainly diatom- 

 eaters. This niche occurs all over the world, and has a number 

 of well-defined carnivore niches associated with it. If we take 

 a group of animals like the herbivorous grass-eating mammals, 

 we find that they can be divided into smaller niches according 

 to the size of the animals. There is the mouse niche, filled 

 by various species in different parts of the world ; the rabbit 

 niche, of larger size, filled by rabbits and hares in the palae- 

 arctic region and in North America, by the agouti and viscacha 

 in South America, by wallabies in Australia, and by animals 

 like the hyrax, the springbuck, and the mouse deer ^^ in Africa. 

 In the same way it can be shown that there is a special niche of 

 carnivorous snakes which prey upon other snakes — a niche 

 which is filled by different species in different countries. In 



