How is variation necessary for existence of each species ? Explain with example.

Explanation

The population of organisms fill niches in the ecosystem, using their ability to reproduce. During reproduction the consistency of DNA copying is important for the maintenance of body design. This allow the organism to use that particular niche. Thus, the stability of populations of species in particular niches are maintained by the process of reproduction.
There are chances that niches can change due to reasons beyond the control of organisms. The changes may be in form of fluctuations in temperature of the earth, varying water level, meteorite hits or any other ecological imbalance.
Under such conditions any alteration in the particular kind of niche is surely going to hit the population of reproducing organisms. The affected population may be wiped out due to this. Few individuals of this population, with some variations in their DNA may survive.
Example: A population of bacteria living in water with moderate temperature. Because of global warming the temperature of water may be increased, many bacteria may die, but few temperature resistant bacteria may survive and grow further.
Thus, variation is useful for the survival of species.