RELATIONS AMONG SPECIES 



367 



related, overlapping 

 climax communities 



A 



Figure 19.10 (continued) 



there may be fewer species in the primary biosere 

 than in any of its parent communities. This would be 

 the consequence of selection pressure. 



Within the new primary biosere, selection pressure 

 is brought about by the competition of organisms and 

 by the environment's affecting ecological amplitude. 

 These biotic and environmental influences cause in- 

 dividual species either to become extinct in the area 



or to enter a state of coexistence with other species. 

 The coexistence of surviving species is the basic step 

 to further evolution in the primary biosere. Such 

 further evolution is most pronounced in biotic re- 

 lationships. 



Perhaps the first evolved biotic relationships under 

 coexistence are competition and something approach- 

 ing commensalism that might be almost neutralism. 

 Starting immediately, but continuing to evolve for a 

 long time, some competition may evolve to amensa- 

 lism and then some amensalism to exploitation. Also, 

 some neutralism-commensalism may evolve into true 

 commensalism and then some commensalism to co- 

 operation. Perhaps later still, some cooperation 

 may transform into mutualism. Along with the 

 development of the negative interactions, especially 

 exploitation, the exploited species may evolve pro- 

 tective devices. However, this evolution is not in- 

 dependent; all classes of interorganism relationships 

 are and become further integrated into the synergistic 

 dynamics of the evolving community in which they 

 occur. 



CONSOLIDATING BIOSERE 



The consolidating biosere like the primary biosere, 

 is a special case of biotic succession. Therefore, the 

 consolidating biosere contains a sequence of serai 

 stages in which organisms, especially plants, tend to 

 control further development. Hence, this part of an 

 over-all biosere is marked by further complexity of 

 interspecific relationships and the presence and in- 

 creasing complexity of a simple ecosystem energy 

 cycle. 



Of importance here and throughout further evolu- 

 tion is the presence of dominant and subordinate 

 species. Dominants are plants most characteristic of 

 a community, because only dominants are found 

 throughout a community and cover or cast shade 

 upon a relatively high percentage of a community's 

 surface area. The dominents reflect the ecology of 

 an area because they are best suited to cope with the 

 physical environment and biotic relationships. Also, 

 dominants regularly influence the rest of their com- 

 munity. Often, dominants function in critical parts 

 of food relationships of the community, hence their 

 ecological success can determine the success of most 

 to all subordinate species. This possibility is further 

 supported by the fact that dominants influence 

 ecological factors, thereby partly affect the presence 



