Universal Energy Flow Model

A universal energy flow model is applicable to any living component, whether it be plant, animal, microorganism, individual, population, or trophic group, as shown in Figure 1.

Clinic Flow Model

Figure 1 Components of a model of ecological energy flow. I, input(or ingestion); NA, not assimilated energy; P, production; R, respiration; G, growth and reproduction; B, standing crop biomass; S, stored energy; and E, excreted energy.

Linked together, such graphic models can depict food chains or the bioenergetics of an entire ecosystem as shown in Figure 2.

The shaded box in Figure 1 represents the living, standing crop biomass of the component. Although biomass is usually measured as some kind of weight (living or 'wet' weight, dry weight, or ash-free weight), biomass should be expressed in calories, so that the relationships between the rates of energy flow and the instantaneous or average standing crop biomass can be established. The total energy input or intake is indicated by I The input is light for strict autotrophs and organic food for strict heterotrophs.

The concept oftrophic level is not primarily intended for categorizing species. Energy flows stepwise through the community according to the second law of thermodynamics, but a given population ofa species may be (and very often is) involved in more than a single trophic level. Therefore, the universal model of energy flow can be used in two ways. It can represent a species population, in which case the appropriate energy inputs and links with other species would be shown as a conventional, species-oriented food web diagram as seen in Figure 2. The model can otherwise represent a discrete energy level, in which case the biomass and energy channels represent all or part of many populations supported by the same energy source.

Not all of the input into the biomass of an organism, population, or trophic level is transformed. Some of the energy input may simply pass through the biological structure, such as when food is egested from the digestive tract without being metabolized or when light passes through vegetation without being fixed. This energy component is indicated by NU (not used) or NA (not assimilated). The portion used or assimilated is indicated by A. The ratio between A and I (the efficiency of assimilation) varies widely. It may be very low, as in light fixation by plants or food assimilation by detritus-feeding animals, or very high, as when animals or bacteria consume high-energy food such as sugars or amino acids. In autotrophs, the assimilated energy, A, is, of course, the gross primary production or gross photosynthesis. The analogous component (the A component) in heterotrophs represents food ingested minus food egested (feces). Therefore, the term gross primary production should be restricted to autotrophic production.

A key feature of the model is the separation of assimilated energy, A, into the P and R components. That part of the fixed energy, A, that is burned and lost as heat is designated respiration, R; that portion transformed to new or different organic matter is designated production, P. Thus, P represents net primary production in plants and secondary production in animals. Secondary production (SP) in consumer individuals is composed of tissue growth and litters ofnew individuals. The P component is energy available to the next trophic level, whereas the

Producers

Primary Secondary consumers consumers

NU E

Solar input (4000)

Producers

Primary Secondary consumers consumers

NU E

Solar input (4000)

Universal Energy Flow Model

Heat

kcal m 2 d

Heat

kcal m 2 d

4000

Figure 2 Simplified energy flow diagram depicting three trophic levels in a linear food chain. Standard notations for successive energy flows are as follows: La, light absorbed by plant cover; GPP gross primary production; A, total assimilation; NPP, net primary production; SP, secondary (consumer) production; NU, energy not consumed by next trophic level; E, energy not assimiliated by consumers (egested); I, input (or ingestion); B, standing crop biomass; and R, respiration. Bottom line in the diagram shows the order of magnitude of energy losses expected at major transfer points, starting with a solar input of 4000 kcal m~2 d~\

NU or nonassimilated component enters the detritus food chain (material to be broken down by bacteria and fungi).

The ratio between P and R and between the standing crop biomass, B, and R varies widely and is ecologically significant. In general, the proportion of energy going into respiration (maintenance energy) is large in populations functioning at higher trophic levels and in communities with a large standing crop biomass. R increases when a system is stressed. Conversely, the P component is relatively large in active populations of small organisms, such as bacteria or algae, in youthful, rapidly growing communities, and in systems benefiting from energy subsidies. When all the available incoming energy is needed to sustain all the basic structures and functions, the carrying capacity is reached. That is when P equals R.

Was this article helpful?

0 -1
10 Ways To Fight Off Cancer

10 Ways To Fight Off Cancer

Learning About 10 Ways Fight Off Cancer Can Have Amazing Benefits For Your Life The Best Tips On How To Keep This Killer At Bay Discovering that you or a loved one has cancer can be utterly terrifying. All the same, once you comprehend the causes of cancer and learn how to reverse those causes, you or your loved one may have more than a fighting chance of beating out cancer.

Get My Free Ebook


Responses

  • mehret
    Who is the proposal universal energy flow model?
    1 month ago

Post a comment