446 



Succession and Fluctuation 



no succession appears to take place. Where conditions are not 

 changed by the inhabitants of an area so as to favor other species, 

 succession does not occur. If the existing community is destroyed in 

 many regions of the tropics or subtropics, the area will be repopulated 

 directly by the original species. The communities of the open ocean 

 and of the deep sea may be regarded as being in a climax condition. 

 Since the physical conditions of the sea— and also of large lakes— are 

 essentially unmodifiable by the plant and animal inhabitants, no eco- 

 logical succession takes place that is comparable to that found on land. 

 In the open ocean seasonal and short-term sequences in the communi- 

 ties of temperate regions occur, as they do on land, but growth of 

 marine organisms in the plankton or on the floor of the deep sea does 

 not change the nature of the physical environment in such a way as 

 to cause a permanent or irreversible replacement of one community 

 by another that regularly extends beyond the seasonal cycle. For a 

 further discussion of ecological succession the reader is referred to 

 Costing (1948), Alice et al. (1949, Ch. 29), and for special situa- 

 tions to Hutchinson (1941), Dansereau (1951), and Niering (1953), 



Photo by C. Davidson 



Fig. 12.10. Open "glades" maintained by limpets {Patella) on rocks in the tidal 



zone of the Isle of Cumbrae, Scotland. The browsing of these gastropods (seen 



on the large rock in the foreground ) curtails the invasion of the red alga, Gigartina 



stellata. Barnacles also inhabit the "glades." 



