Question

Given below is a pyramid showing various trophic levels in an ecosystem:

(a) From the organisms listed below, identify which one is to be placed at which trophic level:
Deer, Grass, Lion, Snake, Rabbit
(b) Discuss the reason why primary consumers will have more energy as compared to secondary consumers?
(c) Why is the base of the pyramid broad?

Hint:

Ecological pyramid: Broad base (producers) \(\Rightarrow\) narrow top (tertiary consumers). Reason: 10% energy transfer law. Primary consumers \(>\) secondary consumers in energy because energy decreases at each trophic level.

Answer 1

(a) Identification of Organisms at Different Trophic Levels:

In the given pyramid:

(i) Producers
(ii) Primary consumers
(iii) Secondary consumers
(iv) Tertiary consumers

From the given organisms:

– Grass → (i) Producers
Grass is an autotroph and prepares its own food by photosynthesis.

– Deer and Rabbit → (ii) Primary consumers
They are herbivores and feed directly on producers.

– Snake → (iii) Secondary consumer
Snake feeds on primary consumers like rabbit.

– Lion → (iv) Tertiary consumer
Lion is a top carnivore and feeds on secondary consumers or large herbivores.

(b) Reason Why Primary Consumers Have More Energy Than Secondary Consumers:

Energy in an ecosystem flows from producers to higher trophic levels. According to the 10% law of energy transfer, only about 10% of the energy from one trophic level is passed to the next level, while the remaining 90% is lost as heat, respiration, and other metabolic activities.

Since primary consumers feed directly on producers, they receive more energy. Secondary consumers feed on primary consumers and receive only a small fraction (about 10%) of the energy available at the primary level. Therefore, primary consumers have more energy than secondary consumers.

(c) Reason Why the Base of the Pyramid is Broad:

The base of the pyramid represents producers. It is broad because:

– Producers capture solar energy and convert it into chemical energy through photosynthesis.
– They have the maximum biomass and maximum energy in the ecosystem.
– They support all higher trophic levels.

Since energy decreases at each successive trophic level, fewer organisms can be supported at higher levels. Hence, the pyramid is broad at the base and narrow at the top.

Conclusion:
Grass forms the base as producer, deer and rabbit are primary consumers, snake is secondary consumer, and lion is tertiary consumer. Energy decreases at each level due to the 10% law, which explains why primary consumers have more energy and why the base of the pyramid is broad.