12 THE ECOLOGY OF ANIMALS 



tioned, among them bare sand, Molinia grass associa- 

 tion, and certain aquatic communities. Artificial 

 habitats have also been surveyed ecologically ; 

 examples are the survey of the pests of stored cocoa, 

 dried fruits, and spices in London warehouses 

 (Richards and Herford, 1930), of sewage (Peters, 

 1930), and of waterworks (Kirkpatrick, 1917). 



It should be understood that we have up to now 

 been referring almost entirely to complete surveys of 

 all groups of animals in major habitats, or at any 

 rate surveys that have aimed at completeness. A 

 number of workers have confined their attention to 

 more limited habitats. Examples are the surveys 

 of apple bark (Light, 1926) and of potato plants 

 (Walton, 1925), or surveys which have concentrated 

 on the ecology of one special group of animals, such 

 as Scourfield's survey of the Entomostracan Crustacea 

 of Epping Forest (1898), Boycott's survey of the 

 distribution of some British moUuscs (1921), Bris- 

 towe's extensive studies of the spider fauna of small 

 islands round the British coasts (1931, etc.), and 

 many more. 



It would be impossible to mention all the similar 

 surveys that have been carried out in other countries. 

 Attention is drawn to a few examples which illustrate 

 modern trends in methods of survey, and preference 

 has been given to papers in the English language. 



In North America much attention has been given 

 to the surveying of vegetation and wild life on the 

 Rocky Mountains, where the zones of vegetation are 

 called ' life zones '. Each of these zones contains 

 within itself a multiplicity of smaller divisions of 

 habitats. Thus the ' Canadian ' zone contains both 

 conifer forest, grassland, marsh, and lakes. A good 

 many such studies have appeared in The Ameri- 

 can Fauna, the serial publication of the United 

 States Bureau of Biological Survey. A complete 

 survey of the vertebrates of the Sierra Nevada 

 mountain life zones has been done by Grinnell and 



