Figure 5.1 provides a first clue to the causal interactions between the M aa - and M a -levels. The M aa -level, designated by area A, shows the ratios between population P and the eco-variables land N, nonrenewable resources R, and carrying capacity of the environment C. The impact on the ecosystem S c by population P is expressed by the aggregate ratio P/S c . The link to the M a -level, embracing area B, is given by Ā and k. Ā stands for average consumption and production activities, and k is a coefficient which expresses the degree to which Ā and P affect S c (see section on Social Choice in a Finite World, pp. 99–107). Ā and k depend on the M a -systems S e , S s , and S t . The overall eco-ratio ĀkP/S c exerts feedbacks on the population system— for instance, the Malthusian food-population feedback. The overall eco-ratio exerts, furthermore, feedbacks on the M a -system—for instance, responses to counter the Malthusian threat or adapting production and consumption activities to changed environmental and natural-resource conditions. To some extent, the eco-variables N, R, and C may be altered by policies (as denoted by the broken lines from the systems S e , S s , and S t )—for instance, intensification of new resource recoveries, etc.
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