Okay, let's move on. Let's try to analyze the amount of energy present in the environment at one time. Elton took the idea of the pyramid of numbers to the next level, creating the idea of a pyramid of biomass.
So, although the pyramid of numbers or any other representation is used to show the energy flow from one living organism to another, A clearer picture of the inefficient energy that is getting transferred around here, we spoke about it in detail in the earlier module, is provided by the pyramid of biomass. What is biomass though? It's the mass of living material.
at every trophic level like biomass of plants in a rainforest, the biomass of earthworms in the soil. So biomass does not just give you an idea of the mass but also of the sample size in every trophic level. Sample size.
What do I mean by this? Biomass is the mass of a living organism multiplied by the total number of organisms in that trophic level. That's what biomass gives you. So you actually know How many organisms are present?
It makes it easier to compare the food value of a small number of large organisms with a large number of small organisms. This the pyramid of numbers doesn't allow. The biomass in every organism is the same. trophic level is usually lesser than the trophic level below it. Most of the food eaten by animals either remains undigested or serves as a source of energy for the animal to survive.
So, only a proportion of the food contained converted into new tissue serves as food for the next trophic level right so for example for every hundred kilojoules of energy consumed by a cow only four kilojoules is converted into new tissue 43 kilojoules is not even absorbed into the cow so to make the cow a better energy converter what do you need to do You should give it food that is easier to digest, to reduce the energy lost in digestion. I think you are getting the point. So, how does the pyramid of biomass look?
Is it upright? Is it inverted? Is it both?
Let's move to the forest ecosystem first. The larger net biomass of the producers overweighs the smaller weight of the consumers, making the pyramid of biomass upright. But the same pyramid is going to be inverted in the aquatic ecosystem.
Why? I want you to think, pause this video for a minute, think about it. Think about why is it inverted? Why can't it be upright like the one in the forest?
Now, let me tell you. Hope some of you have the answer. In oceans, a food chain typically starts with the phytoplankton and ends at predatory fish. Now, phytoplankton, although at the lowest trophic level, and form the base, they have the least biomass. And the value increases gradually towards the predate of fishes like the sharks, the whales having huge maximum biomass.
Okay, how does this happen? Well, the turnover of photosynthetic phytoplankton is really really fast. By turnover I kind of mean life cycle. They graze so quickly and heavily by the herbivorous zooplankton that are larger than them and also have longer lifespans and because of this reason phytoplankton never actually develop a large population size.
But this concept again makes me think if the biomass of the phytoplankton is less than of the mass of fish feeding on them, how do these larger species actually survive? Let me just tell you that nature has its mysterious ways, caters to the needs of all its children. The plankton reproduce at such great rates that they constantly renew the supply of food to support these many insects, small, even big fishes.
However, if something happened to the pond's environment, you know, drastically, and subsequently the death of the pond, of the plankton happens, the fish and the insect populations would obviously decline. But let me tell you, while these two pyramids, numbers, biomass look lovely, they seem totally accurate, the sad truth is that they do have some weaknesses and one weakness of both of them is that they misrepresent or they misinterpret the energy flow within the system.