BIOTOPES AND BIOCOENOSES 137 



The faunal regions and their subdivisions are based on common origin, 

 on relationships among the inhabitants, and their populations are 

 homologous. 



The ecological divisions of the biosphere are accordingly (to sum- 

 marize) the three biocycles, ocean, fresh water, and land; in these 

 subdivisions regions with a general similarity of habitus are recognized 

 as biochores, which may be united as superbiochores or subdivided 

 into subbiochores ; areas within the biochores which have uniform ex- 

 ternal habitat conditions are biotopes, and their variations are called 

 facies. 



Biocoenoses.— The population of these provinces is arranged in a 

 similar way. The sum total of living things, plant and animal, corre- 

 sponds with the biosphere, while the biocycles have their respective 

 faunae and florae, called the biota when both plants and animals are 

 included in one category. The plants considered with regard to their 

 ecological relations rather than their taxonomic affinities may be 

 spoken of as vegetation, 2 or as the phytome, while the animal life 

 similarly considered is called the zoome. The clearest correspondence 

 between an area and its population is found in the biotopes, whose 

 inhabitants, an animal community or biocoenosis,* form a well- 

 characterized unit. 3 A biocoenosis is the association of living things 

 which inhabit a uniform division of the biosphere and correspond in 

 the selection and number of species with the average external habitat 

 conditions. The members of a biocoenosis are dependent upon each 

 other, and are thus forced into a biological balance, which is self- 

 regulating and fluctuates about a mean. Biocoenoses form character- 

 istic communities, with interlocking interrelationships, without neces- 

 sarily including a single species limited to an individual biocoenosis. 



Not every site of biocoenosis is to be considered a biotope in a 

 biogeographical sense. The life of an oak forest, including the forest 

 itself, forms a biocoenosis, but so does an anthill in the forest, or a 

 hazel thicket on the edge of the woods, with their respective in- 

 habitants. The oak woods is a biotope; the two others are not. Bio- 

 geography cannot carry subdivision to the extreme that is possible for 

 ecology in its consideration of animal communities. 



The biotope as a biogeographical unit presents a characteristic bit 

 of the face of the earth, includes an area of determinate physiognomic 

 value, useful in a description of the earth's surface, for example of a 



* The tendency to regard an animal community as an assemblage of species 

 primarily controlled by the biotope, in contrast to a biocoenosis where the con- 

 stituent animals are primary, introduces aspects of ecology not particularly perti- 

 nent to the present geographical approach. 



