482 Dynamics of the Ecosystem 



overexploited or underexploited, abundance and growth must be 

 measured in accurate terms, but before this can be done the various 

 aspects of productivity must be clarified. 



Concepts of Productivity 



The three fundamental concepts of productivity are: (1) standing 

 crop, (2) material removed, and (3) production rate (Fig. 13.7). 

 Failure to distinguish these concepts has resulted in much confusion 

 in attempts to measure and to discuss the production of animals and 

 plants in difl:erent areas. 



1. standing crop 



JXL 



Carnivores 



Herbivores 



Green plants 



Pyramid of numbers 



D Yield to man 

 □ Emigration 

 D Deposits 



la 



Yield 



2. Material removed 



3. Rate of production 



Fig. 13.7. Concepts of productivity. (Clarke, 1946.) 



When the early naturalist entered a new area, his interest was at 

 first centered upon the identification and description of the species 

 present. With the growth of the ecological point of view the observer 

 added to his task the enumeration of each species and soon built up a 

 picture of the differences in abundance of the various members of 

 the food chain, leading to the concept of the pyramid of numbers. 

 The standing crop is the abundance of the organisms existing in the 

 area at the time of observation; it may be expressed as number of 

 individuals, as biomass, as energy content, or in some other suitable 

 terms. 



When the hunter, fisherman, or forester enters an area, he sees the 

 situation from a different viewpoint. The attention of such practical 

 ecologists is directed not so much to the fauna and flora as a whole as 



