Environmental Science

ENVIRONMENTAL SCIENCE : HUMAN POPULATION AND ENVIRONMENT 223

Time

Population Growth

K (Carrying Capacity)

Steady State

Exponential Growth

(Log Phase) M ax. G rowth

Log Phase

Slow Growth

Figure 7.2. S-shaped growth curve.

(b) J-Shaped growth curve

The population increases whenever there is an increase in birth rate over death rate.
The factors of environmental resistance do not check population growth or stabilize the
growth (zero growth not established) then a J-shaped curve is obtained Fig. 3. It is hard to
speculate in the future of human population growth curve whether it will be S-shaped or
J-shaped. Growth curve are thus the graphical representation of a population in given time
period. It may be of S-shaped or J-shaped as mentioned.

Time

Population Growth

Limit

Figure 7.3. J-shaped growth curve.
When population increase in exponential (E) or geometric fashion (e.g. 2, 4, 8, 16, 32
.........) until the population runs out of some resources or encounters, some other limitation
(N). Growth then comes to a more or less abrupt halt in such cases and density usually
declines rapidly until conditions for another rapid growth is restored. Population with this
kind of growth form instability unless regulated by factors outside the population.

(i) Growth rate decreases as density increases. (Self-limiting or inverse density-

dependent type.)

(ii) Growth rate is high until density become high and factors from outside of the

population become limiting. (Density independent type.)

(iii) Growth rate is highest at intermediate density.

Causes of Population Growth

There is an ultimate carrying capacity for the human population and limiting factors
will come into play to cause populations to stabilize. However, unlike populations of other