The pyramid of biomass is a type of ecological pyramid. You can define an ecological pyramid as the pyramid that shows the food and energy relationship between different organisms which are distributed across various levels widely known as the trophic levels. These relationships amongst the organisms are expressed in terms of numbers, biomass and energy. You can learn more about the relationship between the organisms and the flow of energy across the trophic levels using pyramid diagrams of each of these characteristics. Hence, the most widely studied ecological pyramids that you will come across are:
Pyramid of Number,
Pyramid of Biomass, and
Pyramid of Energy.
Pyramid of Biomass
Now, biomass is defined as the total amount or weight of living organisms in a given area. Hence, when asked what is a biomass pyramid, the definition to be given is - a pyramid of biomass is the representation of the energy flow amongst the amount or weight of living organisms i.e. living biomass in a unit area from one trophic level to another. One additional point that you can note is that since the pyramid of biomass is the amount or weight of the living organisms, it takes into consideration the number of organisms living or the number of population of organisms at a given trophic level. As a consequence of the fact that the pyramid of biomass is an ecological pyramid, the general idea tells you that the lower trophic level which is composed of primary producers such as grass will be broad and the topmost trophic level which is made up of tertiary consumers such as carnivorous or omnivorous animals will be narrower. But this is not always true for the pyramid of biomass. You will find cases of such exceptions in examples of biomass pyramids below.
Examples of Pyramid of Biomass
Pyramid of Biomass in Grassland Ecosystem
A pyramid of biomass example which fits the common criteria of being broader at base and narrower at the top is the pyramid of biomass in grassland ecosystem which shows a decrease at higher trophic levels. A grassland ecosystem consists of grasses as the primary producers (PP) (because of their capacity to generate their own food with the help of sunlight), herbivores as the primary consumers (PC) (because they are dependent on the producers) and carnivores as the secondary consumers (SC) (as they are dependent on secondary consumers) and the tertiary consumers (TC) which can either be a carnivore or an omnivore. As the amount of grasses or the weight of the total biomass of the grass is huge in terms of the standing crops i.e.mass of certain living matter at a particular time than the biomass of herbivores or carnivores in a specified area, it forms the base of the pyramid. Subsequently, the herbivores such as rabbits, rats, etc., occupy the trophic level which is narrower and above the trophic level of grasses. Following, the herbivores, the carnivores such as snakes, lizards, etc. occupy the secondary consumers and the apex of the pyramid is occupied by the tertiary consumers such as an eagle. This upright model of the pyramid of biomass example is shown in the figure below.
Pyramid of biomass shows a sharp decrease in biomass at higher trophic levels
Pyramid of Biomass in Pond Ecosystem
As it has been mentioned, that the pyramid of biomass does not necessarily follow the bottom-broad and top-narrow model or the upright model for all ecosystems, you can explore on your own as well regarding the different pyramid models for different ecosystems. Then someone may also ask you this question - Pyramid of biomass is inverted in which ecosystem? The answer to this question is the pond ecosystem. The pyramid of biomass in pond ecosystem is:
A pond ecosystem consists of phytoplanktons at the base because they are the primary producers (PP) and the zooplanktons occupy the trophic level of primary consumers (PC). Small fishes of the pond acquire the trophic level of the secondary consumers which is even broader than that of primary consumers. The reason for this is the shorter lifespans of the phytoplanktons which causes a decrease in their living biomass as the standing crop. The phytoplanktons produce food from sunlight and even though their life spans are short their rapid reproductive cycle makes them capable of producing enough food and energy for the zooplanktons to consume. This unique feature of the pyramid of biomass is a prime example of the importance of the information obtained with respect to the relationship between different organisms.
As mentioned above, the pyramid of biomass and the pyramid of numbers are interrelated. So, for a pond ecosystem, the pyramid of number in pond ecosystem is the same as the pyramid of biomass in pond ecosystem to the last detail i.e. inverted pyramid.
Pyramid of Biomass for a Tree Ecosystem
The pyramid of biomass for a Tree ecosystem stands to represent the pyramid of biomass for any kind of ecosystem that involves trees. Therefore, the pyramid of biomass in a grassland tree ecosystem is neither different from the biomass pyramid for a forest ecosystem nor from the pyramid for a simple Tree ecosystem.
Going by the characteristic of productivity, the trees will occupy the basal trophic level as they are the primary producers. Now, when you think about the biomass of the primary consumer which is the insect residing on the tree and are dependent on the tree, you will find a similarity to the pyramid of biomass in pond ecosystem i.e. an inverted pyramid. But moving ahead, when one more trophic level is added on the top of the primary consumers, which consists of secondary consumers - the birds that are dependent on the insects then the pyramid design will become interesting. The pyramid of biomass for a tree ecosystem or the pyramid of biomass in a grassland tree ecosystem is shown below.
Just as the pyramid of number in pond ecosystem is the same as the pyramid of biomass in a pond ecosystem, the pyramid of number in forest ecosystem or the pyramid of number in grassland tree ecosystem or the pyramid number of tree ecosystem is the same as the pyramid of biomass in tree ecosystem.
Such a kind of pyramid of biomass is more suitable to provide information regarding the flow of energy from one trophic level to another rather than providing information about the relationship between the populations of the organisms on each trophic level.