Emergy and Hierarchy

A hierarchy is a form of organization resembling a pyramid where each level is subordinate to the one above it. Depending on how one views a hierarchy, it can be an organization whose components are arranged in levels from a top level (small in number, but large in influence) down to a bottom level (many in number, but small in influence). Or one can view a hierarchy from the bottom where one observes a partially ordered structure of entities in which every entity but one is successor to at least one other entity; and every entity except the highest entity is a predecessor to at least one other. In general, in ecology we consider hierarchical organization to be a group of processes arranged in order of rank or class in which the nature of function at each higher level becomes more broadly embracing than at the lower level. Thus we often speak of food chains as hierarchical in organization.

Most if not all systems form hierarchical energy transformation series, where the scale of space and time increases along the series of energy transformations. Many small-scale processes contribute to fewer and fewer of larger-scale processes (Figure 3). Energy is converged from lower- to higher-order processes, and with each transformation step, much energy loses its availability (a consequence of the second law of thermodynamics), while only a small amount is passed along to the next step. In addition, some energy is fed back, reinforcing power that flows up the hierarchy. Note in Figure 3 the

I II III IV

(Producers) (1° consumers) (2° consumers) (3° consumers)

I II III IV

(Producers) (1° consumers) (2° consumers) (3° consumers)

Exogenous inputs Exports

Parallel processes

Figure 3 Systems can be represented as hierarchical organization of energy flows and components. Hierarchical levels are aggregations of like components sometimes called trophic levels in ecosystems. At each level, energy is converged into fewer components (less biomass) and much energy is degraded. Within each level, there are parallel processes that have similar function. Larger energy flows are associated with components on the left (lowest quality), while small flows of available energy support components on the right (highest quality). Feedbacks from higher-level components act as control actions on lower-quality components.

Exogenous inputs Exports

Parallel processes

Figure 3 Systems can be represented as hierarchical organization of energy flows and components. Hierarchical levels are aggregations of like components sometimes called trophic levels in ecosystems. At each level, energy is converged into fewer components (less biomass) and much energy is degraded. Within each level, there are parallel processes that have similar function. Larger energy flows are associated with components on the left (lowest quality), while small flows of available energy support components on the right (highest quality). Feedbacks from higher-level components act as control actions on lower-quality components.

reinforcing feedbacks by which each transformed power flow feeds backward so that its special properties can have amplifier actions.

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