(a) Compare, giving reasons, the J-shaped and S-shaped models of population growth of a species.
(b) Explain ‘‘fitness of a species’’ as mentioned by Darwin.

OR

(a) What is an ecological pyramid ? Compare the pyramids of energy, biomass and numbers.
(b) Write any two limitations of ecological pyramids.

a)
 

• b) Fitness of a species is based on the capacity of the organism to produce viable offsprings and maintain a stable population.
  
                                                OR
  
  a) The study of different trophic levels and their relatedness can be displayed in the form of ecological pyramids. These pyramids are also called Eltonian pyramids.
•  Pyramid of Energy: A pyramid of energy shows the flow of energy from one trophic level to other trophic levels. A pyramid of energy reflects laws of thermodynamics with each trophic level loosing energy. Pyramid of energy is always upright.
• Pyramid of Biomass: It represents the total dry weight of living beings at different trophic levels. Most of the ecosystems have upright pyramids. However in some aquatic ecosystems the pyramid becomes inverted.
• Pyramid of numbers: It represents the total number of individuals in a trophic level. It consists of primary producers, herbivores, carnivores, etc. Most of ecosystems, like grassland ecosystems have upright pyramids. But there are few exceptions to this. A single tree when becomes the producer of various organisms is an example of inverted pyramid of number.
  
  b) The ecological pyramids are based on food chain but not on food web. The ecological pyramids do not take decomposers into consideration.