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Succession 

 and Fluctuation 



In the previous chapter the nature of the community was discussed 

 as a characteristic group of plants and animals inhabiting an area. 

 The typical community maintains itself more or less in equilibrium, 

 but the members of the community are never in complete balance 

 with each other or with the physical environment. Changes in the 

 environment over a period of time are produced by variations in 

 climatic and physiographic influences and also by the activities of the 

 plant and animal inhabitants themselves. These modifications of the 

 habitat may cause sufficient changes in the dominant species so that 

 the existing community is replaced by a new community, or they may 

 cause marked fluctuations in the abundance of certain species within 

 the same community. In this chapter we shall consider the progres- 

 sive changes in communities leading to a relatively stable type of 

 community, the classification of communities, and the oscillations 

 within the community. 



ECOLOGICAL SUCCESSION 



Progressive changes in communities take place from one geological 

 epoch to another and also within much shorter periods of time. De- 

 tailed consideration of large-scale changes in the fauna and flora, such 

 as those caused by the passage of an ice age or the uplifting of a 

 mountain range, or those resulting from the evolution of new species, 

 is beyond the scope of our present task; such alterations in the biota 

 have great long-term significance, and they are discussed in treat- 

 ments on paleontology, climatology, biogeography, and evolution 

 (Shapley, 1953). Here we shall concern ourselves primarily with 

 the replacement of one community by another in particular areas and 

 within the same general climatic conditions. 



Observation has revealed the fact that in given biotopes certain 



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