Comment on the growth curve given below. | Class 12 Biology Chapter Organisms and Population, Organisms and Population NCERT Solutions

Population is the changing entity and we can say this because of the change in number (increases or decreases) of individuals in the population with the time which is determined by the four factors: Birth, Death, Immigration and Emigration. It also represents the growth curves: Exponential and Sigmoid shape.

The Upper diagram that is showing in the question represents the Logistic growth or Sigmoid shaped curve. In this growth curve, resources are unlimited but they are slowed down by the limiting factors in the idealized situation (i.e. contains limited factors). When the population density increases each individual will contain their own few resources. And, their limit will be set by their environmental factor over the space. It is also be limited by the various factors like predation, competition, climatic conditions etc. The curve shows slow growth initially at the establishment state and then get more faster at exponential phase and then suddenly slows down due to various environmental resistance factors like completion, predation etc. and then finally stable or stationary phase comes where the population becomes stable (no increase occurs from this stage) and is represented by K (carrying capacity). The S- shaped curve is also known as Verhulst- Pearl Logistic curve, which is represented by the following equation:

Where, N is the population size

r is the intrinsic rate of increase;

• If r is positive then the population is increasing
• If r is positive then the population is decreasing
• If r is zero then the population does not change in size

dN/dt is the rate of change in population numbers over the time

K is the carrying capacity.

This equation can also be written as: