Sigmoid curve showing the three distinct phases of growth follows the sequence of
Lag phase, log phase and steady phase
In S - shaped or sigmoid growth, the population show an initial gradual increase in population size, followed by an exponential increase and then a gradual decline to near constant level.
Sigmoid growth curve is formed of five phases.
a) Lag phase - Period where individuals adapt to the new environment, so growth is slow.
b) Logarithmic or exponential phase (log phase) - Period of rapid rise in population due to availability of food and requirements in plenty and no competition.
c) Stationary phase (steady phase) - Finally, growth rate becomes stable because mortality and natality rates become equal. With limited nutrient availability, growth slows down.