Question 4: What are the three types of ecological pyramids. What information is conveyed by each pyramid with regard to structure, function and energy in the ecosystem.
Answer:
Ecological pyramid is given by Charles Elton in 1927 it is defined as the graphical representation of the numbers or biomass and accumulated energy at each trophic level in the food chain. The relationship between numbers, biomass and energy flow in biotic community can be represented graphically by ecological pyramids. The base of the each pyramid represents the producers or first trophic level while the apex represents the next trophic levels like tertiary or high level consumers and other consumer trophic levels in between them. There are three kinds of ecological pyramid which are as follows:
1. Pyramid of numbers: Graphical representation of the total number of the individuals of different species that belongs to each trophic level in the ecosystem is known as pyramid of number. It consists of horizontal bars that shows the specific trophic levels which are arranged in the sequential manner from producer to consumers level and the length of each bar represents the total number of individuals at each trophic level. In case of grassland ecosystem or pond ecosystem, it always shows upright pyramid because the numbering of the organisms decreases at successively higher trophic level. But in the tree ecosystem it always shows inverted pyramid, in this tree is a primary producer, so it would represent the base of the pyramid and the dependent insect population will represent the second trophic level.
Diagram of Upright pyramid of numbers in grassland ecosystem:
Diagram of Inverted pyramid of numbers in tree ecosystem:
2. Pyramid of biomass: This pyramid represents the total dry weight of living beings of different species at each trophic level at the particular time. In this all kinds of organisms at a trophic level are weighted. The biomass of the producer is much greater than the herbivore’s biomass and this is greater than the carnivore’s and so on. In forest ecosystem, it is represented that the shape is upright pyramid but in some aquatic ecosystem, like large lakes and oceans this pyramid usually shows in inverted form. The reason behind the inverted pyramid is, microscopic phytoplanktonic algae are the primary producers and being single- celled they do not get accumulate much biomass; and at a given time the total weight of the standing crop of phytoplankton is less when compared to herbivores or other consumers, thus the base of the pyramid being smaller than the upper structure in the aquatic ecosystem.
Diagram of Upright pyramid of biomass in forest ecosystem:
Diagram of Inverted pyramid of biomass in pond ecosystem:
3. Pyramid of energy: It shows the rate at which energy flows from one trophic level to the next. This pyramid reflects the law of thermodynamics with the loss of energy that occurs at each transfer from one trophic level to another, hence the pyramid is always upright. In this, a given trophic level always has a smaller energy content than the trophic level which is immediately below it because some energy is lost as heat is going from one level to another. Each bar represents the amount of energy is utilized at each level in the given time annually per unit area.
Diagram of pyramid of energy:
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