496 



THE COMMUNITY 



population pressure is known for every 

 participating species, and until all the in- 

 terspecies population characteristics are 

 evaluated for each link in the food chain 

 and the varied energy relations are assayed. 

 Furthermore, it must be remembered 

 that over-all metabolism of a community 

 is the result of an always varying biologi- 



There are no known exceptions concerning 

 bacterial activity, but the photosynthetic 

 input of certain cave communities is in- 

 direct. As aspects of the concept of com- 

 munity metabolism, both these key indus- 

 tries are anabolic processes. The bacterial 

 industry is essential if soils and waters 

 are to support hfe. The heterotrophic 



GEOGRAPHIC LOCATION 



SE;ASO^■IAL CYCLE 

 CIRCULAT STAGNATION 

 GROWING SEASON 



PRODUCTIVITY 



Fig. 165. Diagram of certain inanimate and animate influences involved in the metabolism 

 of a lake community. (After Rawson. ) 



cal system of great complexity. This system 

 is affected by, and affects, the inanimate 

 portion of the community environment. 

 Some of the influences involved are sug- 

 gested in Figures 165 and 177. 



Before discussing general aspects of com- 

 munity metabolism, the nature of food in- 

 terrelations of aquatic and terrestrial com- 

 munities must be examined. Nearly all com- 

 munities have two interlocking key indus- 

 tries, the reorganization of inorganic and 

 organic compounds by bacteria, and the 

 photosynthetic activity of green plants. 



bacteria live by the oxidation or fermen- 

 tation of substances of organic origin, 

 whereas the autotrophic bacteria derive 

 their energy from inorganic materials. 



The autotrophs are commonly divided 

 into two groups: the chemosynthetic spe- 

 cies, which live by oxidation of such inor- 

 ganic materials as ammonia, carbon mon- 

 oxide, hydrogen, iron, and sulphur; and the 

 photosynthetic species, which apparently 

 contain complex pigments capable of utiliz- 

 ing sunlight. The chemoautotrophs are 

 characteristic of soils and have been treated 



