Describe the pyramids of numbers Biomass and Energy

The pyramid of numbers, which as its name implies represents the number of organisms in each trophic level. For the oceans, the bottom level would be quite large, due to the enormous number of small algae. For other ecosystems, the pyramid of numbers might be inverted: for instance, in a forest, a plant community is composed of only a handful of very large trees, and yet there are many millions of inject grazers which eat the plant material.
Second is the pyramid of biomass which is a representation of the amount of energy contained in biomass, at different trophic levels for a given point in time. The amount of energy available to one trophic level is limited by the amount stored by the level below. Because energy is lost in the transfer from one level to the next, there is successively less total energy as you move up trophic levels. In general, we would expect that higher trophic levels would have less total biomass than those below, because less energy is available to them. Just as with the inverted pyramid of numbers, in some rare, exceptions, there could be an inverted pyramid of biomass where the biomass of the lower trophic level is less than the biomass of the next higher trophic level.
The oceans are such an exception because at any point in time the total amount of biomass in microscopic aigae is small. Thus a pyramid of biomass for the oceans can appear inverted (see -Figure 5.6b). You should now ask "how can that be?" If the amount of energy in biomass at j one level sets the limit of energy in biomass at the next level, as was the case with the hares < and foxes, how can you have less energy at the lower trophic level? This is a good question, and can be answered by considering as we discussed in previous CHAPTER, the all important aspect of "time". Even though the biomass may be small, the rate at which new biomass is produced may be very large. Thus, over time it is the amount of new biomass that is produced, from whatever the standing stock of biomass might be, that is important for the next trophic level.
The pyramid of energy shows rates of production rather than standing crop. Once done, the j figure for the ocean would have the characteristic pyramid shape (see Figure 5.6c). Algal populations can double in a few days, whereas the zooplankton that feed on them reproduces more slowly and might double in numbers in a few months, and the fish feeding on zooplankton might only reproduce once a year. Thus, a pyramid of energy takes into account the turnover rate of the organisms, and can never be inverted.
We see that thinking about pyramids of energy and turnover time is similar to our discussions of residence time of elements. But here we are talking about the residence time of "energy". The residence time of energy is equal to the energy in biomass divided by the net productivity, Rt = (energy in biomass / net productivity). If we calculate the residence time of energy in the primary producers of various ecosystems, we find that the residence times range from about 20-25 years for forests (both tropical rainforests and boreal forests), down to~3-5 years for grasslands, and finally down to only 10-15 days for lakes and oceans. This difference in residence time between aquatic and terrestrial ecosystems is reflected in the pyramids of biomass, as discussed above, and is also very important to consider in analyzing how these different ecosystems would respond to a disturbance or what scheme might best be used to manage the resources of the ecosystem.

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francis1897 answered the question on February 27, 2023 at 12:34