CHAPTER IX 

 BIOTOPES AND BIOCOENOSES 



Animal and plant life occupies the whole surface of the earth, 

 including both land and sea. Life extends into the depths of the ocean, 

 but it penetrates only a few meters deep in the solid earth. It rises 

 higher into the air, but not for long periods. The whole space occupied 

 by living organisms is called the "biosphere." 1 



The biosphere presents extremely varied aspects in its various parts, 

 both according to the habitat conditions and the living population. 

 A study of the biosphere thus requires a subdivision into the compo- 

 nent parts which correspond to these differences. But little has been 

 done in this direction by zoologists, whereas plant geographers have 

 long given serious attention to biogeographic studies upon an ecologic 

 background. From the botanical viewpoint we already have a com- 

 pletely worked-out classification and nomenclature for the major parts 

 of the biosphere, though unfortunately no unanimity has been attained 

 in this respect. 2 



Zoology cannot take over the phytogeographic system without re- 

 vision. Other principles of subdivision must frequently be applied for 

 animals on account of their vagility, with their consequently com- 

 pletely different mode of distribution, and on account of the relatively 

 greater importance of the marine and fresh-water animal life. Further- 

 more, what are primary divisions for the botanist, such as forest and 

 grassland, are themselves in turn the habitats in which animal life is 

 found. It is true that the zoological subdivisions will frequently be 

 based upon the botanical, but they must not slavishly follow the 

 botanical scheme and must find new principles of their own as the 

 occasion demands. 



The primary topographic unit is the "niche" or "biotope." Such a 

 unit is an area of which the principal habitat conditions and the living 

 forms which are adapted to them are uniform. The biotope is as basic 

 for the ecologic subdivision of the biosphere as the species is in the 

 systematic classification of living beings, though neither can be de- 

 fined with exactness. The biotope is directly conditioned by the simi- 

 larity of regional factors, such as the medium, climate, soil, etc., and 

 these factors condition an analogous development of the fauna and 



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