Question

Read the following statements (A - D) related to ‘r’ and select the correct option stating true (T) and false (F).

A. If r is positive, the population is increasing in size.
B. If r is negative, the population is decreasing in size.
C. If r is zero, then the population growth rate is zero.
D. ‘r’ is constant for all organisms.

• A. A - F, B - T, C - T and D - F
• B. A - T, B - T, C - T and D - F
• C. A - F, B - F, C - T and D - T
• D. A - F, B - T, C - F and D - T

Answer 1

The correct option is B A - T, B - T, C - T and D - F

Intrinsic rate of natural increase or ‘r’ is the difference between the birth rate and death rate of population. ‘r’ is an important parameter selected for assessing the effect of any biotic or abiotic factors on population growth. It can be expressed as,
r = (b - d)
where,
b is birth rate i.e the total number of live births in a population per year
d is death rate i.e the total number of deaths in a population per year.

If ‘r’ is positive, then the population is increasing in size i.e the birth rate is greater than the death rate. Hence, statement A is true.
If r is negative, then the population is decreasing in size i.e the birth rate is lesser than the death rate. So statement B is true.
If r is zero, then the population growth rate is zero and population size remains constant as birth rate is equal to death rate. Hence statement C is true.
'r' varies depending on the type of organism, their habitat and availibility of resources. For example, a population of bacteria would have a much higher 'r' than an elephant population. The resources for growth in a population of elephants can become limited faster than the resources for growth in a population of bacteria. Hence statement D is false.