4 THE ECOLOGY OF ANIMALS 



in which animals Hve. In a perfectly true sense, 

 animals and plants in nature are bound together into 

 a complex series of biotic communities, whose inter- 

 dependence is well illustrated by the action of earth- 

 worms on the soil and of the acidity of the soil upon 

 earthworms, or by the interaction of nulliporous 

 algae and of corals on a tropical coral reef. This 

 concept is ably discussed by Phillips (1931). But in 

 most investigations it is found advantageous to 

 separate plant and animal ecology in practice. At 

 the same time, owing to the great extent of ecological 

 field problems, team work by plant and animal 

 ecologists is capable of producing excellent joint 

 studies of animal and plant communities. The 

 difference in methods is soon realized by any one 

 who alternately attempts to count the trees in a 

 wood and the wood-mice that live under the roots 

 of the trees. 



The wide range of subjects that is called in to 

 assist the completion of any investigation on animal 

 ecology has already been mentioned. Any compre- 

 hensive survey has to refer to maps of topography, 

 geology, soil, climate ; agricultural influences such as 

 grazing ; conservation and protection generally ; the 

 vegetation ; and the systematic background upon 

 which such surveys depend for naming species. The 

 wide range of economic problems that are dependent 

 upon ecological studies is illustrated by the following 

 examples taken at random : the question of over- 

 fishing in the Baltic and North Sea, the feedmg 

 grounds and reserve population of Antarctic whales, 

 the acclimatization of foreign fish in East Africa and 

 New Zealand, the breeding grounds of the migratory 

 locust in North Africa or elsewhere, the control of 

 tsetse flies that carry sleeping sickness in Africa, the 

 zootropic (host-selection) habits of malaria- carrying 

 mosquitoes in Europe, the climatic (temperature and 

 humidity) limits of the rat fleas that carry bubonic 

 plague or of the larvae of hookworms, the fluctuations 



