The food coactions of organisms are important 

 since animals can obtain energy only from consumed 

 food. All activities of organisms constitute work and 

 require energy. The amount of work performed de- 

 pends on the amount of energy the organism can 

 mobilize. Hence the flow of energy through the eco- 

 system and the manner and efficiency with which it 

 is used is an important ecological process. 



ENERGY FLOW THROUGH THE 

 ECOSYSTEM 



Unlike nutrients, energy does not circulate 

 indefinitely through the ecosystem. Energy is con- 

 tinuously and rapidly lost, although a certain amount 

 of energy may pass through the ecosystem more 

 than once before it is entirely dissipated. Hence en- 

 ergy must continuously enter into the ecosystem from 

 the outside. 



14 



Ecological Processes 



and Community 



Dynamics: 



Energy Exchanges, 



Productivity, 



and Yield 



Acquisition 



The basic source of energy for all trophic levels 

 is solar radiation. A surface exposed normal to the 

 sun's rays, and outside the earth's atmosphere, would 

 receive energy at the rate of 1.94 g-cal/cm^/min. 

 This is the solar constant. On the earth's surface, 

 solar energy is effective only during the daylight 

 hours and, because of absorption in passing through 

 the atmosphere, scattering by smoke, dust particles, 

 and cloudiness, only about 46 per cent of daylight 

 radiation reaches the earth's surface (Fritz 1957), 

 although this varies with latitude, season, and lo- 

 cality. At Columbus, Ohio, located at latitude 40° N, 

 the average amount of solar energy is estimated as 

 follows (Shaw 1953) : 



Kcal/m^/day 

 Summer 6263 



Spring and autumn 3628 



Winter 1604 



Average 



3781 



The basic means by which solar energy is trapped 

 is the formation of sugar by plants that contain 

 chlorophyll ( Rabinowitch 1945^6) . In terms of moles 

 (Brody 1945) : 

 Photosynthesis — 



6 CO2 + 6 HoO 4- 709 Kcal — > 6O0 + CsHiaOe 

 Respiration — 



CeHiaOe + 60, — » 6 CO,. + 6 HoO + 674 Kcal 

 Respiration is going on at all times to furnish 

 energy for the plant's activities, and this energy is 

 derived from oxidation of the sugars formed in photo- 



200 



