Efficiencies 



499 



represents a net production lor the herbivore equal to 2^2 pt'r cent of 

 the food consumed. Obviously in the case of a mammal a large part 

 of the food energy goes into heat production, and any active animal 

 burns up considerable fuel in its locomotory activities, including 

 foraging for food. Fish culturists have found that about 1 kg of fish 

 can be produced for every 5 kg of meat consumed— or an efficiency 

 of about 20 per cent for this highly digestible type of food. Measure- 

 ments of the efficiencies of various steps in production for pond com- 

 munities have been made by Lindeman (1942), for oceanic plankton 

 by Riley, Stommel, and Bumpus (1949), and for certain farm crops by 

 Transeau ( 1926 ) . A schematic representation of the chief compo- 

 nents in the ecosystem of Georges Bank, a fishing area off the coast of 

 Massachusetts, shown in Fig. 13.12, summarizes our present knowledge 

 of the quantitative relations involved. The blanks indicate the gaps 



Radiant energy: 3,000,000 gcal/day 



Currents 



Migration 



^9000_g:ca/^ 



Fish landed 



1.6-7.7g-cal/day 



Migration 

 Currents 



Fig. 13.12. Principal components and processes involved in production on 

 Georges Bank, off Massachusetts. Values are averages for the whole bank per 

 square meter of sea surface. Maximum and minimum values vi^ithin the cogwheels 

 are for the standing crop; those over the wheels are for net production rate. 

 Average yield during 1923 to 1945 is indicated at right. (Clarke, 1946.) 



