RELATIONS AMONG SPECIES 



355 



TABLE 19.1 TEMPORAL CHANGES IN LIFE. THE PRIMARY SOURCES OF NONCYCLIC 



IRREGULAR, NONCYCLIC DIRECTIONAL, AND CYCLIC TEMPORAL CHANGES ARE 

 INDICATED FOR SPECIES, FOR COMMUNITIES, AND FOR ADJACENT COMMUNITIES. 



Type of Temporal Change 



Species Sources 



Community Sources 



Intercommunity Sources 



Noncyclic irregular 



Noncyclic directional 



Cyclic 



Nomadism 

 Emigration 

 Immigration 

 Replacement (after 

 death) 



Competition 

 Chance 

 Natural selection 



Arhythmic (phasic 



cycles) 

 Seasonal cycle 



(periodicity) 

 Migration 



Speciation 

 Extinction 



Integrated evolution 



Cyclic environment 

 (diurnation, 

 aspectation, etc.) 



Barrier changes 



Barrier changes 

 Cliseral shifts 

 Evolution 

 Succession 

 Regression 



Environment (causing 

 community pro- 

 gression) 



tion, the original remains and decomposers being 

 eliminated; but prior to reinvasion by the original 

 species, a sequence of intermediate creatures of dif- 

 ferent species may occur. 



Phasic cycles often are more complex than implied 

 by the outline above. Individual cycles within a 

 community may display unique additions or deletions 

 of stages from the "typical" cycle. Therefore, the 

 phasic cycles of any community (there can be many, 

 completely unrelated cycles) regularly create many 

 patches of life throughout a community that are 

 foreign to most of the community. The foreign nature 



of these patches can cause them to be confused with 

 noncyclic directional intercommunity changes, such 

 as succession, regression, cliseral shifts, and evolu- 

 tion of new communities. 



Community Changes. These phenomena involve 

 single groupings of similar life in a particular unit of 

 space, the life constituting a stand. 



Noncyclic changes include irregular ones due to 

 speciation and extinction and directional ones due to 

 evolution of the community as a whole. Actually, 

 community evolution is on an individual species 

 basis, involving individual perfection of adaptations 



death 



saprophytes 

 use nutrients 



bare ground 



germination 



seed 



PHASIC CYCLE 



PERIODICITY 



Figure 19.2 A phasic cycle in contrast to periodicity. 



