306 PRINCIPLES OF ANIMAL BIOLOGY 



on temperature, light, and humidity, described above, introduces much 

 diversity. As a consequence of this heterogeneity, it is impossible to 

 regard vegetated areas as single ecological units. They consist of a 

 number of types mingled with one another. Attempts have been made 

 to classify them on the basis of predominant types of plants, but in an 

 elementary discussion it is not practicable to follow any of these schemes 

 through. 



References 



Chapman, R. N. Animal Ecology. 2d Ed. McGraw-Hill Book Company, Inc. 

 (Especially Chaps. XV, XVI, XVII on aquatic habitats.) 



Elton, C. E. Animal Ecology. Sidgwick & Jackson, Ltd. 



Hesse, R., W. C. Allee, and K. P. Schmidt. Ecological Animal Geography. John 

 Wiley & Sons, Inc. 



Pearse, a. S. Animal Ecology. 2d Ed. McGraw-Hill Book Company, Inc. 

 (Chap. IV, biological factors in ecology.) 



Semper, Karl. Animal Life. D. Appleton-Century Company, Inc. (Old, and 

 lacks the modern organization of ecology but discusses, chapter by chapter, 

 influence of food, light, temperature, water and air currents, etc., upon organisms.) 



Shelford, V. E. Animal Commimities in Temperate America. University of 

 Chicago Press. (Chap. XV, general discussion.) 



Weaver, J. E., and F. E. Clements. Plant Ecology. McGraw-Hill Book Com- 

 pany, Inc. 



