Ecological Pyramids: Definition, Types, Limitations and More

A graphical representation of the link between different living species at different trophic levels are called an Ecological Pyramids. This was presented by G.Evylen Hutchinson and Raymond Lindeman. Each trophic level’s biomass is allocated based on the number of individual organisms. A trophic level is formed by each step or level of the food chain. The first trophic level is occupied by autotrophs or producers.

They convert solar energy into a form that may be used by heterotrophs or consumers. Herbivores, or primary consumers, are at the second trophic level, small carnivores, or secondary consumers, are at the third, and larger carnivores, or tertiary consumers, are at the fourth. The various forms of ecological pyramids are determined by the amount of energy or biomass available to each trophic level. Continue reading to know more.

What is an Ecological Pyramid?

Definition: An ecological pyramid is a graphical or diagrammatic representation showing the relationship between the organisms at different trophic levels in a food chain.
Some key terms related to the ecology and ecological pyramids are as follows:

1. Trophic Level: The position occupied by an organism (in a food chain) or a group of similar organisms (in an ecological pyramid) is called a trophic level. Trophic literally means “Feeding”; hence the trophic levels are the sequential positions of organisms based on their feeding habits. Different trophic levels are as follows:
a. Producers: These are the primary consumers that include plants and other autotrophs.
b. Consumers: These are heterotrophic organisms. These organisms further can be classified as primary consumers (herbivores), secondary consumers (carnivores), and tertiary consumers (top carnivores) depending on the size of a food chain in an ecosystem
In a detritus food chain, decomposers constitute the secondary or tertiary trophic levels.

Sometimes a given species may occupy more than one trophic level in the same ecosystem at the same time. For example, the sparrow is a primary consumer when it feeds on seeds and fruits and becomes a secondary consumer when it eats insects and worms.

2. Food chain: It represents the transfer of energy through the series of an organism in a community. It is a sequence of eating and being eaten up at successive trophic levels.

3. Food web: It refers to a group of interrelated food chains in a particular community.

4. Biome: The term refers to a biogeographical unit consisting of the biological community that is formed in response to the regional climate conditions. These mainly include major ecosystems, for example, grassland, forest, desert, and ocean.
Charles Elton proposed the idea of the ecological pyramid, therefore also named Eltonian Pyramids. Bodenheimer, Hutchinson also contributed to the concept of the ecological pyramid. The 10% law of Lindeman is the basis for the pyramid of productivity or energy.

Energy Flow in An Ecosystem

The First law of thermodynamics states that energy can neither be created nor destroyed but can be transformed from one form to another. For example, the energy of sunlight can be transformed into food (chemical) and heat energy.

The Second law of thermodynamics states that with each successive energy transfer in a system, the amount of available energy is gradually reduced. For example, in an ecosystem, the transfer of food energy from one organism to another leads to the loss of a major fraction of food energy as heat due to metabolic activities. Only a small portion being stored in living tissues or biomass. Lindemann proposed a 10% law of energy flow based on the second law of thermodynamics. The energy flow in a system can be summed as follows:

Types of Ecological Pyramids

The ecological pyramids can be categorized into three types based on ecological parameters. These are described as follows:

Fig: An overview of Different types of Pyramids in the Ecosystem

Study Concept of Biodiversity

1. Pyramid of Numbers: This graphical presentation of pyramids deals with the relationship between the producers and consumers at sequential trophic levels in terms of their numbers. The pyramid of numbers may be upright or inverted depending upon the comparative numbers of producers and consumers in an ecosystem.

a. Upright Pyramid of Number: In the upright pyramid of numbers, there is a gradual decrease in the number of individuals while moving from producers (lower trophic level) to consumers (higher trophic level). This pyramid is found in the grassland ecosystem or cropland ecosystem and pond ecosystem.
i. In the grassland ecosystem, the grasses (producers) are in abundance. These occupy the broad base of a pyramid.
ii. Next comes the primary consumers (herbivores), such as grasshoppers that are less than that of grasses.
iii. Further comes the secondary consumers (primary carnivores), such as rats showing comparatively less population than grasshoppers.
iv. Rats are consumed by tertiary carnivores (secondary consumers), such as snakes that are larger in size but smaller in the population than rats.
v. The hawks are the top carnivore that is least in number and occupy the tapering apex of the pyramid.

Fig: Upright Pyramid of Number in Grassland and Pond Ecosystem

b. Inverted Pyramid of Number: The tree ecosystem and parasitic food chain show an inverted pyramid of numbers. The producers in the tree ecosystem are the least in numbers, and the population of consumers gradually increases at each trophic level.
i. The producers (trees) are positioned at the narrow part of the pyramid since they are the least in numbers.
ii. Birds and other herbivores that feed on tree products are comparatively high in number.
iii. Lice and bugs are parasites of birds and have a greater population than birds.
iv. The number of hyperparasites (fleas, microbes) in the tree ecosystem drastically increases and occupies the broad end of the pyramid.

Learn About Ecological Factors

c. Spindle-shaped Pyramid of Number: It is also known as a partially upright pyramid because there is neither sequential increase (upright) or sequential decrease (inverted) in the number of individuals in an ecosystem.
It can be summed up that there is an increase in the number while moving forward from producers to herbivores (primary consumers). It is further followed by a decrease in the number of carnivores (secondary consumers) while moving to the tertiary trophic level and above. Hence this graphical representation exhibits a phenomenon of Decrease \(\to \) Increase \(\to \) Decrease, designing a partially-upright or spindle-shaped pyramid. This type of pyramid of numbers is found in the forest ecosystem without parasites.
i. The producers exhibit a moderate population size that is neither least nor maximum; hence are not positioned at the broad base or tapering apex of the pyramid.
ii. The herbivores are comparatively more in number that feeds upon forest products and are placed almost in the middle part of the pyramid.
iii. The herbivores are being eaten up by carnivores (eagles) that are least in numbers and occupy the top end of the pyramid.

Fig: Inverted and Spindle-shaped (partially inverted) Pyramid of Number in Tree and Forest Ecosystem

2. Pyramid of Biomass: Biomass refers to the dry weight of living organisms.  The total amount of living (organic) matter in an ecosystem at a specific time is called standing crop. A typical pyramid of biomass is more fundamental as it shows the quantitative relationship of the standing crop.
This pyramid deals with the relationship between the dry weight of primary producers and consumers at different trophic levels in an ecosystem. It is easier to estimate the dry weight in an ecosystem than the number of individuals and the rate of energy flow at each trophic level. The pyramid of biomass may be upright or inverted in different ecosystems.
a. Upright Pyramid of Biomass: The straight or upright pyramid of biomass is found in grassland and forest ecosystems, where the gradual decrease in the biomass of organisms has been observed at successive trophic levels.

b. Inverted Pyramid of Biomass: The pyramid of biomass is inverted in the pond or marine ecosystem.
i. The biomass of phytoplankton will be smaller than that of zooplankton.
ii. The biomass of zooplankton will be lesser than that of primary carnivores (small fishes).
iii. The secondary carnivores (large fishes) have the maximum biomass.
iv. The phytoplankton, therefore, occupies the narrow tapering end of the pyramid, and the large fishes occupy the broad base of the pyramid.

Fig: Upright Pyramid of Biomass & Inverted Pyramid of Biomass

3. Pyramid of Energy: It is the graphical representation of the amount of energy per unit area accumulated at different trophic levels in an ecosystem. It is also called the pyramid of productivity.
The pyramid of energy is based on the concept of the flow of energy in a food chain proposed by Lindemann. According to Lindemann’s energy flow model, “only 10% of the total energy is transferred to the successive trophic levels and creating the biomass”. Remaining is utilized in respiration, hunting, and other activities or is lost to the surroundings in the form of heat. Hence the energy available at each trophic level is 10% of the previous level. It is called the ten percent law of energy. This leads to the formation of an upright pyramid of energy that is invariably formed in each ecosystem. The energy is highest at the producer level and gradually decreases as it moves to the subsequent levels, including herbivores (primary consumer), carnivores (secondary, tertiary consumers). In other words, it can be said that the pyramid of energy depicts the energy as a minimum at the highest trophic level and as a maximum at the lowest trophic level. An example of the pyramid of energy can be explained by assuming a certain numerical value of energy.
i. Suppose 2000 joules of solar energy are incident on the green vegetation. The plants can trap only 1% of the total solar energy. It means only 20 joules of solar energy will be converted into chemical energy by photosynthesis.
ii. The herbivores feed upon producers get only 10% of the energy stored in plants, that is 2 joules. The remaining 18 joules were lost to the environment.
iii. Carnivores feeding on herbivores would be able to store only 0.2 joules of energy as flesh.

Fig: Pyramid of Energy

Importance of Ecological Pyramids

1. Ecological pyramids represent the feeding relationship between the organisms of an ecosystem.
2. The effects of environmental changes on the organisms can be studied by comparing the data collected over the years in a graphical representation of an ecosystem.
3. Ecological pyramids show how efficiently the energy is transferred from one trophic level to another trophic level and determines the productivity of organisms at different trophic levels.

Frequently Asked Questions

Q.1. What is an ecological pyramid?
Ans: Ecological pyramids are the diagrammatic representation showing the relationship between the living organisms at different trophic levels respective to the structure and function of an ecosystem.

Q.2. Who introduced ecological pyramids?
Ans: Charles Elton introduced the concept of ecological pyramids, hence also called Eltionian pyramids.

Q.3. What are the types of ecological pyramids?
Ans: Ecological pyramids are of three types. These are named as follows:
1. Pyramid of Number
2. Pyramid of Biomass
3. Pyramid of Energy

Q.4. What is the importance of the energy pyramid?
Ans: An energy pyramid is the graphical representation of energy flow at different trophic levels, and therefore helps determine the productivity of trophic levels.

Q.5. Is the pyramid of numbers upright or inverted?
Ans: The pyramid of numbers can be upright or inverted. It depends on the number of organisms at different trophic levels in an ecosystem or food chain.
1. It is upright in the grassland ecosystem.
2. Inverted in the tree or parasitic ecosystem and may be spindle-shaped in the forest ecosystem.

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