Question

What are the three main types of trophic pyramids studied in ecology?

Answer 1

Ecological pyramids are graphic representation of relationship between number of organisms, biomass, and productivity at each trophic level in an ecosystem. The trophic levels are the basic structure of interactions in biological communities. Trophic level indicates how food energy passes from one energy level to another in a food chain.

Each organism can be categorized in any of the trophic levels. The three main types of trophic pyramids in ecology are:

a) Pyramid of Numbers b) Pyramid of Energy c) Pyramid of Biomass

All these three pyramids are comprising of lower trophic level of primary consumers, followed by the next trophic level of secondary consumers and last trophic level of tertiary consumers.

a) Pyramid of Numbers: Pyramid of numbers indicates the relationship between different organisms that differ in numbers at different trophic levels. There is a gradual decrease/increase in number from lower trophic levels to higher trophic levels, depending on whether it is upright or inverted.

In this pyramid of upright grassland ecosystem, the lowest trophic level has the grasses, which are present in large numbers. The second level is occupied by herbivorous deers feeding on the grasses, that are lesser in number than the grasses. The third and fourth levels have wolves and lions respectively, which are further lesser in numbers. They feed on deers and wolves respectively. This pyramid is upright.

The pyramid of tree ecosystem is an inverted pyramid. Lowest trophic level is the produces (plants) which has the least numbers. The second level is of the herbivorous birds, which have more numbers than plants. The Parasites and hyperparasites that feed on the birds and parasites respectively, will have the largest numbers of organism. The numbers increase as the trophic level increases.

b) Pyramid of Energy: The pyramid of energy is the best representation of the ecosystem. There is a decrease in availability of energy from autotrophs at successive trophic levels. The energy lost at successive trophic levels is released as heat, respiration etc. Most of energy is available at the primary autrotroph level, followed by secondary consumer and least is available at the tertiary consumer level. Secondary consumers consume primary consumers or autotrophs while tertiary consumers consume the secondary consumers to obtain energy.

c) Pyramid of Biomass: The pyramid of biomass indicates the total biomass at various trophic levels in a food chain. Biomass is the mass of living organism per unit area of the ecosystem at a given time period. In this pyramid, the biomass either decreases or increases from lower trophic level to higher trophic level.

This pyramid can be upright or inverted. In upright pyramid of shallow water ecosystem, the primary producers the phytoplanktons have largest biomass, followed by the secondary herbivores (Zooplankton). The least amount of biomass is present in carnivores (small fishes and mollusks) with the smallest being present in large carnivores.

In a pond ecosystem, the pyramid is inverted. The algae, green plants, and green flagellates are the autrotrophs. These autrotrophs have the lowest biomass. Secondary consumers are the fishes that consume the autrotrophs. The fishes have higher biomass than the algae. The largest amount of biomass is present at the last trophic level, water snakes, and water birds that are the tertiary consumers.