COMPONENT RELATIONSHIPS 



tiplying the number of distinct com- 

 partments recognized; but this proc- 

 ess cannot be carried very far. Until 

 some more adequate technique is 

 devised to deal with the various types 

 of heterogeneity, the models devel- 

 oped will be but a pale reflection of 

 reality. 



Computers — Installations at the 

 disposal of ecosystem modelers are 

 often rather inadequate for the task. 

 Modeling teams may be obliged to use 

 rather slower machines, with limited 

 storage, whereas ecosystem simula- 

 tions are bound to be demanding 

 both of space and time. Programming 

 and model testing could be greatly 

 facilitated by a shift from batch 

 processing to interactive terminals, 



which are now available at few cen- 

 ters. 



Digital computers are, in principle, 

 far from ideal for the simulation of 

 continuous processes. One would 

 consequently expect a large hybrid 

 computer to be appropriate for eco- 

 system modeling; this may often call 

 for an alternation of continuous and 

 discontinuous operations, which could 

 be performed, respectively, on the 

 analogue and digital sections of a 

 hybrid computer. Unfortunately, the 

 programming of hybrid computers is 

 at present far more difficult than that 

 for digital computers, and facilities 

 for remote-terminal programming do 

 not exist. Hardware developments to 

 meet this need are to be hoped for; 



in any case, it is important that the 

 potentialities for ecosystem modeling 

 of hybrid as well as digital computers 

 should be fully explored. 



Interdisciplinarity — Continued em- 

 phasis should be placed on the need 

 for interdisciplinary training. Indi- 

 viduals brought up within one of 

 the traditional disciplines, with only 

 limited and casual contact across the 

 disciplinary frontiers, can contribute 

 to a program in systems ecology only 

 after extensive retraining, formal or 

 informal. We need personnel with 

 a broad training in the biological and 

 earth sciences, who have developed 

 expertise in certain aspects of mathe- 

 matics and computer science. This 

 is made more difficult by the rather 

 narrow curricula of many universities. 



Energy Relationships in Ecological Systems 



Energy is essential for life, but 

 since life itself is dynamic rather than 

 static, energy flow must occur at all 

 times. The earth ecosystem functions 

 because of the flow of energy from 

 a source, the sun, to a sink, outer 

 space, after passing through the bio- 

 sphere. The biosphere, which is that 

 zone of soil, rock, water, and air 

 containing organisms, is at an energy 

 state, or thermodynamic level, that is 

 compatible with life. This energy 

 state is neither too warm nor too 

 cold for life to exist and replicate. 



The thermodynamic level of the 

 biosphere fluctuates greatly, with 

 both random fluctuations and periodic 

 cycles. Some portions of the bio- 

 sphere (polar regions and upper 

 troposphere or lower stratosphere) 

 are relatively cold while other por- 

 tions (tropical regions and thermal 

 hot springs) are relatively hot. Nev- 

 ertheless, life has evolved to occupy 

 all of the earth's surface, some of 

 the subsurface, and a good deal of 

 the atmosphere. A part of our under- 

 standing of the earth ecosystem and 

 its many subsystems, including spe- 



cific biomes (see Figure IX-5), is to 

 understand the passage of energy 

 through the various components and 

 the thermodynamic levels of each and 

 every part. 



However, in order to understand 

 and interpret the significance of en- 

 ergy, of energy flow, and of a par- 

 ticular thermodynamic state in the 

 context of ecosystem analysis, one 

 must understand simultaneously the 

 life processes themselves. Ecology is 

 that body of knowledge concerning 

 the relationships between organisms 

 and environment, organisms interact- 

 ing with one another, and including 

 the effect of man on the ecosystem. 

 Ecosystems are those finite entities of 

 the landscape which include the or- 

 ganisms and the physical environ- 

 ment. One must understand the 

 physiological and biochemical re- 

 quirements of each species in the 

 ecosystem with respect to tempera- 

 ture, energy, and such effects as 

 photoperiodism, phototropism, and 

 the like. The thermodynamic status 

 of a plant or animal can be appre- 

 ciated only in the context of its 



particular and specific physiological 

 requirements. 



Life-Support Systems 



Primary productivity in the earth 

 ecosystem is the result of photosyn- 

 thesis. Each and every species of 

 plant responds uniquely to environ- 

 mental conditions — to the energy 

 status, to gas concentrations of the 

 atmosphere and water, to pollution, 

 to disease, and so on. The entire food 

 chain, web, or pyramid begins with 

 primary production. A "natural" eco- 

 system has many species of plants, 

 each collaborating with the others 

 to produce the total primary produc- 

 tion of the system but each respond- 

 ing in a special way to the variable 

 conditions. Herbivores consume the 

 plants and each herbivore responds 

 to the variable energy status of the 

 ecosystem in a unique way. Each 

 species of herbivore will have its 

 own physiological requirements and 

 biochemical responses to temperature, 

 light, moisture, gas exchange, pol- 

 lution, and so forth. Energy is trans- 



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