Environment-Community 

 Interrelations 



Each organism performs a particular function and 

 occupies a particular situation in its environment. 

 The term niche is used to indicate either phenome- 

 non. However, the more complex of the two niches is 

 the functional one. The place niche is the immediate 

 physical and biological environment, the home range 

 of an animal or the surroundings of a plant. The func- 

 tional niche is the ecological role played by each crea- 

 ture in its community; it also refers to a particular 

 community function that is performed by one or more 

 species in their environment. 



The fundamental workings of an ecosystem include 

 the operation of functional niches and the transfer of 

 energy that is a part of this operation. This basic en- 

 ergy comes from the sun as radiant energy, or light, 

 and is used by plants to form food to support their life 

 processes. In addition, these plants, including their 

 stored foods, are ingested and transformed by ani- 

 mals to the simpler chemical compounds, that sup- 

 port animal life processes. This entire energy cycle, 

 which encompasses organism nutrition and the trans- 

 fer of certain nutrients through the ecosystem, in- 

 cludes most to all biogeochemical cycles that collec- 

 tively may also be called a biogeochemical cycle. 



ENERGY CYCLE 



The transfer of energy in an ecosystem encompasses 

 both the cycle of transfer and the functional niches 



found within the cycle. The cycle can be reduced to 

 fundamental "steps" and nonessential "steps," and 

 the functional niches can be treated in many ways 

 (Figure 20.1). 



FUNDAMENTAL STEPS 



Essential components in the operation of an eco- 

 system energy cycle include the following: 



(1 ) Production of radiant energy by the sun. 



(2) Utilization of solar energy, carbon dioxide, 

 water, and various minerals by photosynthetic plants 

 to form organic materials, chemical compounds that 

 contain carbon and are synthesized by life. 



(3) Decomposition of dead photosynthetic plants 

 to inorganic compounds by saprophytic bacteria. 



(4) Transformation of inorganic compounds by 

 chemosynthetic bacteria, the transformers, to com- 

 pounds that can be used by photosynthetic plants. 



.\ole: The essential components of an ecosystem 

 usually are more than sunlight, carbon dioxide, wa- 

 ter, minerals, and photosynthetic plants (steps 1 and 

 2), because most plants must get their mineral 

 nutrients from steps three and four, from pre-existing 

 organic compounds that are first decomposed and 

 then transformed into minerals. (Note: many ecol- 

 ogists consider decomposition and transformation a 

 single step.) This condition exists because most 

 plants are unable to obtain minerals directly from 



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