What is the value of 'r' (The Intinsic rate of natural increase ) for the following cases?
Note :- Use the reference of the exponential growth equation.
i- Norway Rat
ii- Flour beetle
iii- 1981 human population
Answer & explanation
Correct answer: option 2
If in a population of size N, the birth rates (not total number but per capita births) are represented as b and death rates (again, per capita death rates) as d, then the increase or decrease in N during a unit time period t (dN/dt) will be
dN/dt = (b – d) × N
Let (b–d) = r,
then dN/dt = rN
The r in this equation is called the ‘intrinsic rate of natural increase’ and is a very important parameter chosen for assessing impacts of any biotic or abiotic factor on population growth. To give you some idea about the magnitude of r values, for the Norway rat the r is 0.015, and for the flour beetle it is 0.12. In 1981, the r value for human population in India was 0.0205.