2.4 Changes in Structural Characteristics 



The accumulation of information as the system matures leads, first 

 of all, to an increase in the variety* in the community. However, it should 

 be kept in mind that in mature communities, organisms which are taxonomically 

 or trophically similar tend to form local accumulations, which decreases the 

 variety encountered in small volumes of water. Nevertheless, the signifi- 

 cance of variety for any individual is rather constant in various systems 

 and increases as their maturity increases. Thus, for marine phytoplankton 

 it varies from 1.4-2.0 bits (per individual) for young systems to 3.5- 

 5.5 bits in later stages of succession (Zernova, 1974; Blasco, 1971). 

 The upper limit of variety is not over 4.5-5.5 bits, which, possibly, is 

 the limit of effectiveness in the construction of natural self-regulating 

 systems. 



The increase in variety which results from any ecologic succession 

 or any process of self-organization of ecosystems touches the most varied 

 characteristics of the community. For example, Margalef (1968, etc.) con- 

 siders an increase in the variety of pigments to be a characteristic sign of 

 the development of a phytoplankton community. However, the increase in 

 variety is manifested most clearly as a change in the species composition of 

 the community as it matures. 



An increase in variety has been clearly demonstrated in the community 

 of the tropical regions of the Indian Ocean (Timonin, 1971). In the 

 regions of upwelling water--in the early stages of development of communities-- 

 the index of species variety of zooplankton was found to be 1.5-2 bits, 

 while as the communities developed it increased to 2-2.5, and in comparatively 

 mature communities in stable, stratified water, it reached 3.5-4 bits. 



Simultaneously with species variety, trophic variety also increases 

 (Fig. 2). In the early stages of succession, we find primarily nonspecial ized 

 herbivores or omnivores, while in the later stages, species with more 

 selective feeding, consuming larger food items, predominate. The increase 

 in the share of macrophages (predators) and the lengthening of the food 

 chains are characteristic for mature oceanic systems (see Chapter II, 

 paragraph 1 ) . 



The changes in the store of energy in a community are primarily 

 manifested as changes in its biomass. In the initial stages of development, 

 be it in spring in cold-water zones or in a region of quasistationary 

 upwelling of water in the tropics, the biomass increases rapidly and is 

 initially concentrated in the most labile link of the chain--the phyto- 

 plankton. At this time in the euphotic layer there is a store of nutrient 

 substances, usually intensively replenished by the upwelling of the deeper 

 water. In later stages, most of the nutrients of the system are concentrated 



*When speaking of variety, we should keep its spectrum in mind, since 

 in individual small samples the variety of various systems may be identical, 

 in spite of great differences in variety of the general sets involved. 



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