13 



Dynamics of 

 the Ecosystem 



In the tvvo previous chapters we have discussed the composition of 

 communities, their progressive changes, and the fluctuations that occur 

 among their members. We shall now consider the dynamics of the 

 ecosystem as a whole, that is, the operation of the community and its 

 environment as a functional unit. We shall also discuss certain quan- 

 titative aspects of the interdependencies in the ecosystem, including 

 the concepts of productivity. 



FUNDAMENTAL OPERATION 



What natural situation shall we select for the study and illustration 

 of the fundamental operation of the ecosystem? We might take the 

 whole world as a unit. We could measure the energy received by 

 the earth and follow its transformations; we could measure the 

 amounts and kinds of organic matter that are elaborated. In other 

 words, we could evaluate the earth as a mechanism for biological 

 transformations. A study of this sort is of interest and involves sub- 

 ject matter treated in the field of biogeochemistry in which the distri- 

 bution and transformation of biologically important materials are 

 traced (Hutchinson, 1948). However, we are more often concerned 

 with the operation of particular types of ecosystems, and, in any event, 

 an investigation of the variations from place to place and from time to 

 time would be required before an adequate summation could be made 

 for the entire world. 



In selecting an area for study we might go to the opposite extreme 

 and investigate a single plant together with the space immediately 

 surrounding it. Although certain relations of the exchange between 

 the plant and its environment would be revealed, the unit studied 

 would probably not be large enough to include all related influences. 

 Ideally, it would be desirable to study an area that is large enough 

 to be representative and to contain all the fundamental factors, and at 

 the same time that is cut off from outside influences. A completely 



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