Pyramid of Productivity
An ecological pyramid of productivity is often more useful, showing the production or turnover of biomass at each trophic level. Instead of showing a single snapshot in time, productivity pyramids show the flow of energy through the bigfood chain. Typical units would be grams per meter2 per year or calories per meter2 per year. As with the others, this graph begins with producers at the bottom and places higher trophic levels on top.
When an ecosystem is healthy, this graph produces a standard ecological pyramid. This is because in order for the ecosystem to sustain itself, there must be more energy at lower trophic levels than there is at higher trophic levels. This allows for organisms on the lower levels to not only maintain a stable population, but to also transfer energy up the pyramid. The exception to this generalization is when portions of a food web are supported by inputs of resources from outside of the local community. In small, forested streams, for example gone up greater than could be supported by the local primary production.
When energy is transferred to the next trophic level, typically only 10% of it is used to build new biomass, becoming stored energy (the rest going to metabolic processes). As such, in a pyramid of productivity each step will be 10% the size of the previous step (100, 10, 1, 0.1, 0.01).
The advantages of the pyramid of productivity:
- It takes account of the rate of production over a period of time.
- Two species of comparable biomass may have very different life spans. Therefore their relative biomasses is misleading, but their productivity is directly comparable.
- The relative energy chain within an ecosystem can be compared using pyramids of energy; also different ecosystems can be compared.
- There are no inverted pyramids.
- The input of solar energy can be added.
The disadvantages of the pyramid of productivity:
- The rate of biomass production of an organism is required, which involves measuring growth and reproduction through time.
- There is still the difficulty of assigning the organisms to a specific trophic level. As well as the organism in the food chains there is the problem of assigning the decomposers and detritivores to a particular trophic level.
Nonetheless, productivity pyramids usually provide more insight into an ecological community when the necessary information is available.
Read more about this topic: Ecological Pyramid
Famous quotes containing the words pyramid and/or productivity:
“So universal and widely related is any transcendent moral greatness, and so nearly identical with greatness everywhere and in every age,—as a pyramid contracts the nearer you approach its apex,—that, when I look over my commonplace-book of poetry, I find that the best of it is oftenest applicable, in part or wholly, to the case of Captain Brown.”
—Henry David Thoreau (1817–1862)
“It is ultimately in employers’ best interests to have their employees’ families functioning smoothly. In the long run, children who misbehave because they are inadequately supervised or marital partners who disapprove of their spouse’s work situation are productivity problems. Just as work affects parents and children, parents and children affect the workplace by influencing the employed parents’ morale, absenteeism, and productivity.”
—Ann C. Crouter (20th century)