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COMMUNITY ECOLOGY: 



of other species. In some cases, loss of all dominant 

 species would lead to extinction of the particular 

 community. However, particular dominant species 

 need not have such pronounced influence upon the 

 subordinate species of their community. 



Subordinate species respond only to a particular 

 influence of dominants, an influence that can be 

 maintained by a sequence of taxa. Therefore, if a 

 sequence of dominants have the same growth form 

 (trees, shrubs, etc.), all dominants might have the 

 same general influence and not lead to changes, or 

 even to much modification, of subdominants. Such a 

 sequence of dominants usually occurs through time, 

 and for this reason, subordinate species regularly are 

 taxonomically independent of the dominants. 



Returning specifically to the consolidating biosere, 

 each successive stage within the consolidating part of 

 the over-all biosere typically has more species, greater 

 refinement in its evolved interorganism relationships, 

 and therefore greater complexity than the previous 

 stage. These trends are common in spite of the fact 

 that species are lost to the community by extinction 

 or emigration. Other species are added by immigra- 

 tion (either of preadapted species that finally find a 

 highway through barriers, or of adjacent species that 

 finally evolve the ecological amplitude required for 

 entrance and a place in the ecosystem) and by specia- 

 tion. 



BIOTIC CLIMAX 



The stage of biotic climax can be any of the pri- 

 mary or secondary climaxes of biotic succession, but 

 must be the first climax originating in the abiotic 

 area. Once equilibrium is reached, further com- 

 plexity is possible if geomorphic changes occur. 

 (Perhaps certain changes in ecology can occur with- 

 out geomorphic change.) Again, this is especially 

 true if the geomorphic changes bring about climatic 

 changes. The consequence of change is isolation; 

 the space of the old biotic area (now containing many 

 individual stands of various serai stages and of the 

 climax) is fragmented. When this fragmentation is 

 caused by such things as arms of the ocean, glaciers, 

 and mountain ranges, the geomorphic causes prob- 

 ably lead to independent environmental changes in 

 the isolated segments of the old abiotic area. With 

 the development of progressively unique environ- 

 ments in each segment, there is increased extinction 

 and speciation, and growing complexity of ecological 



relationships. Finally, each isolated segment develops 

 into a unique climax community. Therefore, isolation 

 can lead to a situation somewhat similar to opening 

 of an abiotic area — at least, a situation in which a 

 unique biotic climax results. 



At any time during the period of isolation geo- 

 morphic changes can cause the once-isolated com- 

 munities to recombine. If the communities were not 

 separated long enough to become very dififerent from 

 one another, recombination can lead to a melting pot 

 in which a single climax community is the end prod- 

 uct. However, when isolated segments were sep- 

 arated long enough for the development of a certain 

 amount of diversification, the consequence of re- 

 combination is not a single melting pot. Rather, the 

 result is an interlocking and overlapping of com- 

 munities, both serai and climax, causing competition 

 of dominants and leading to different, but related, 

 new climaxes adjacent to one another. Such a com- 

 plex of communities is a biome, and the process by 

 which it was formed is called an isnlatwn-recombina- 

 tion cycle. 



So far in our discussion relationships have been 

 oversimplified, and they will continue to be so. The 

 reader must realize that the true complexity of bio- 

 geographical succession is being greatly minimized. 

 Perhaps recalling the great differences in life of the 

 past and the sequence of dominant taxa through time, 

 and remembering that all this reflects isolation- 

 recombination cycles is sufficient for understanding 

 the significance and great complexity of these cycles. 



BIOME 



Biomes must be visualized as chance aggregations 

 of similar, overlapping communities. The component 

 communities and their biome in lolo are imperceptibly 

 but constantly changing — are typically in some phase 

 of an isolation-recombination cycle, are subject to 

 competition and the influence of the resulting domi- 

 nant plants, are gaining and losing species, and are 

 evolving and changing taxonomic composition 

 through time. However, a biome also is composed of 

 a single growth formation (e.g., forest) in which 

 changes in dominants, no matter how different 

 taxonomically, need not cause any real change in the 

 influence of dominants on subordinate species or in- 

 dividual communities. Therefore, biomes are not 

 taxonomic units. Rather, they are ecological units 

 brought about by the influence of the physical en- 



