Question 6 of 9intermediate💡 UnderstandLong Answer5 marks

Define ecological pyramids and describe with examples, pyramids of number and biomass.

Correct Answer

Definition of Ecological Pyramids: Ecological pyramids are graphical representations of the relationship between organisms at different trophic levels. This relationship is expressed in terms of number, biomass, or energy. The base of each pyramid represents the producers (first trophic level), while the apex represents the tertiary or top-level consumers.

Pyramid of Number: This pyramid represents the number of organisms at each trophic level. In most ecosystems, it is upright—producers are more in number than herbivores, and herbivores are more in number than carnivores. For example, in a grassland ecosystem, nearly 6 million plants support only three top carnivores. However, exceptions exist—if we count insects feeding on a big tree, small birds depending on insects, and larger birds eating smaller ones, the shape differs from a typical upright pyramid.

Pyramid of Biomass: This pyramid represents the total biomass at each trophic level. It generally shows a sharp decrease in biomass at higher trophic levels and is upright in most ecosystems. However, in the sea, the pyramid of biomass is generally inverted because the biomass of fishes far exceeds that of phytoplankton. A small standing crop of phytoplankton supports a large standing crop of zooplankton.

Limitations: Ecological pyramids do not accommodate a food web, assume a simple food chain, and do not consider the same species belonging to multiple trophic levels. Saprophytes are also not given any place despite their vital role.

Exercise: EXERCISES | Q: 8 | (Page 11)
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Explanation

This 5-mark answer defines ecological pyramids and describes both pyramid of number and pyramid of biomass with examples from the textbook. The answer includes the upright nature of pyramids in most ecosystems, specific examples like grassland (for numbers) and sea (for inverted biomass), and mentions key limitations. All content is derived strictly from the provided context.

Solution Steps

  1. Step 1: Define ecological pyramids with their basis (number, biomass, energy) and structure (base=producers, apex=top consumers)

  2. Step 2: Describe pyramid of number - upright in most ecosystems, grassland example with 6 million plants supporting 3 top carnivars, exception of tree-based ecosystem

  3. Step 3: Describe pyramid of biomass - generally upright with sharp decrease at higher levels, inverted in sea due to fish biomass exceeding phytoplankton

  4. Step 4: Briefly mention limitations - food webs not accommodated, saprophytes excluded, species at multiple trophic levels not considered

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