Ecological Pyramid

1.0Introduction

The ecological pyramid serves as a visual representation of the trophic structure and function within an ecosystem. Originally conceptualized by Charles Elton in 1928, these pyramids are often referred to as Eltonian Pyramids. Subsequent refinements, particularly in terms of biomass, were introduced by Bodenheimer in 1938. The notion of a pyramid of productivity or energy was further developed by G. Evelyn Hutchinson and Raymond Lindeman in 1942.

2.0Food Chains and Food Webs

• You have read about the food chains and webs that exist in nature 
• Starting from the plants (or producers) food chains or rather webs are formed such that an animal feeds on a plant or on another animal and in turn, is food for another
• The chain or web is formed because of this interdependency 

Food Chain: Arrangements of organisms according to their food habits

e.g.

 Food webs: 

• Network of interconnected food chains 
• Facility of taste and choice 
• Energy flow ⟶ unidirectional but different path 

3.0Shape of Pyramids

The ecological pyramid typically features a base representing the producer level, followed by successive tiers representing various trophic levels that culminate in the apex consumers. The pyramid can take different shapes, such as upright (tapering towards the top), inverted (widening towards the top), or spindle-shaped (broader in the middle and narrower above and below).

In ecological pyramids, each tier—basal, mid, and top—illustrates parameter values corresponding to producers, herbivores, and carnivores within the ecosystem. This visual tool provides valuable insights into the distribution of biomass, energy, or productivity across different trophic levels

e.g.

4.0Types Of Ecological Pyramid

(i) Pyramids of number

(ii) Pyramids of biomass 

(iii) Pyramids of energy

(i) Pyramids of Number

In this type of pyramid the number of individual organisms in various trophic levels is shown. These pyramids are mostly upright because the number of producers [T₁] is maximum and the number of herbivores and carnivores decreases towards the apex or at successive trophic levels, such as the Grassland ecosystem and aquatic ecosystem.

(a) Aquatic ecosystem:

(b) Grassland ecosystem

(c) Tree dominated forest

But in a tree ecosystem, the pyramid of numbers is inverted. This is called a parasitic ecosystem because birds (herbivores) depend on the tree (producer) and parasites (consumer) depend on birds, therefore with an increase in the number of trophic levels, the number of organisms increases sequentially.

Note: The pyramid of numbers represents- Biotic potential.

Question: Define the shape of the ecological pyramid for the given below food chain of numbers.

 Solution: Spindle shape

(ii) Pyramid of Biomass: 

Pyramids of biomass represent the total amount of biomass of each trophic level of the ecosystem, mostly these pyramids are also upright (erect) e.g. (tree ecosystem), forest ecosystem but in aquatic ecosystems pyramid of biomass is inverted because in it producers are micro-organisms such as phytoplankton and their biomass is veryless.

(a) Grassland ecosystem:

Note:- All pyramids in grassland ecosystem are upright

(b) Tree ecosystem:

(c) Aquatic ecosystem (Ocean): Generally inverted

Note: Pyramid Biomass represents a standing crop.

(iii) Pyramid of Energy

Ecological energy pyramids serve as graphical representations depicting the amount of energy present at different trophic levels within an ecosystem. These pyramids exhibit an upright or erect structure due to the gradual decrease in energy as one ascends through successive trophic levels. This alignment is consistent with the principles of the 10% law proposed by Raymond Lindeman, stating that only approximately 10% of the energy obtained by an organism is transferred to the next trophic level, with the remaining 90% being utilized in metabolic activities and released as heat.

In accordance with the 10% law, the majority of energy is lost at each trophic level, underscoring the ecological weakness of top consumers like lions, despite their physical strength. This phenomenon highlights that, while these top predators may be robust in terms of physical attributes, they are ecologically vulnerable due to the limited energy available to them within the ecosystem.

It's crucial to note that energy pyramids not only represent the overall productivity of an ecosystem but also illustrate the transfer of production through different trophic levels.

Note: Pyramids of energy represent productivity.

5.0Importance of Ecological Pyramid

• Trophic Structure: Illustrates the hierarchical arrangement of trophic levels in an ecosystem.
• Energy Flow: Visualizes the efficiency of energy transfer from producers to consumers.
• Biomass Distribution: Indicates the quantity of living matter at different trophic levels.
• Ecosystem Stability: The pyramid shape reflects the stability or disturbances within an ecosystem.

6.0Limitation of Ecological Pyramids

• Species Overlap Oversight: Fails to consider species that belong to multiple trophic levels simultaneously.
• Exclusion of Food Web Complexity: Unable to accommodate the intricacies of a food web, disregarding the interconnected relationships among species.
• Neglect of Saprophytes: Omits saprophytic organisms, which play a vital role in nutrient recycling but are not assigned a specific place in traditional ecological pyramids.