Question

Give an account of the population growth curves.

Answer 1

Populations exhibit a specific pattern of increase. When the number of organisms in a population is plotted against the time, a population growth curve is obtained. Depending upon the environmental resistance, they are of two types:

(i) J-shaped: A population will double in size during a constant period of time. This is known as exponential growth. The rate of increase in numbers of a population undergoing exponential growth is proportional to the size of the population, and when plotted on a graph of numbers against time, such a population gives an exponential or J-shaped growth curve. Such optimum growth rarely occurs; it can be seen occasionally in bacterial populations with carefully managed environments. In such situations, environmental resistance factors do not exert any influence over time. Initially, the growth is slow but afterwards the population grows at a rapid rate that proceeds till enough food is available. However, in nature with limited resources, such a situation never arises and various factors of environmental resistance do not allow population growth to soar towards infinity.

J-shaped or exponential growth curve

(ii) S-shaped (sigmoid): An S-shaped (sigmoid) growth curve is obtained when the population first increases slowly, then more rapidly, and finally it slows down gradually due to environmental resistance until an equilibrium level is reached. It signifies the maximum size of population that an environment can carry or sustain

Logistic growth curve
(S-shaped or sigmoid)