Question

I am a high school student and I am very confused about ecological pyramids. My textbook states that the biomass of zooplankton in an aquatic ecosystem is more than that of phytoplankton (I don't know why?) But if I just memorize it then I think that their energy pyramid should also be inverted because more biomass would mean more organic matter {food} and hence more chemical energy available to the next trophic level. This should be true if we are considering all organisms present at a trophic level and not a single organism at each trophic level, right? So why is the energy pyramid always upright? Shouldn't it be the same as the biomass pyramid?

Please explain in simple language using examples;it would be very helpful. I think you're right and your textbook is wrong. It would be interesting to know (a) what textbook this is (maybe it's the same as the one I quote below?) and (b) what your teacher says if you ask them this question.

In general the energy content of a trophic level is roughly proportional to its biomass (although in going from terrestrial plants to animals we might expect the energy/gram to increase, since terrestrial plants contain a lot of energy-poor structural material). Both energy and biomass would also be proportional to numbers if individuals in each trophic level were approximately the same size (this can go in either direction; whales are much bigger than the plankton they eat, beavers are much smaller than the trees they eat ...)

For oceanic phytoplankton and zooplankton respectively, some reasonable mass/energy conversions are phytoplankton: 2-3 calories per milligram (cal/mg) dry weight (Platt and Irwin 1973); zooplankton: 3-9 cal/mg dry weight (Davis 1993). (ZP are about 3x more energy-rich than PP.)

Answer 1

Energy pyramids are always upright because energy is lost at each trophic level, typically about 90%, leading to less energy available at higher levels.

Biomass pyramids can be inverted, like with zooplankton having greater biomass than phytoplankton due to the high turnover rate of phytoplankton which reproduce quickly and sustain higher trophic levels.

Step-by-step explanation:

The concept of ecological pyramids is a visual representation of the relationship between different trophic levels within an ecosystem.

There are three types of ecological pyramids: pyramids of energy, number, and biomass. While biomass and number pyramids can sometimes be inverted or diamond-shaped, energy pyramids are always upright.

This is because energy, as it moves up each trophic level, is lost primarily through metabolic processes and as heat, leading to less energy available at higher trophic levels regardless of biomass.

An inverted biomass pyramid, such as in the English Channel where zooplankton have a greater biomass than phytoplankton, occurs not due to a lack of production but because of the rapid consumption and high turnover rate of the phytoplankton.

Phytoplankton reproduce quickly, so even with a lower biomass at any given time, they continuously support the levels above them. The upright nature of the energy pyramid is maintained because, despite the high biomass of zooplankton, the amount of energy transferred from one trophic level to the next higher level is only about 10%, in accordance with the ten percent law.

Therefore, the energy available to the primary consumers from the producers is significantly reduced at higher levels, enforcing the upright shape of the energy pyramid.

For example, if producers in a pyramid have 1,000,000 kilocalories of energy, primary consumers might only receive 100,000 kilocalories due to energy losses.