The term used to describe the rate 'r' in the exponential growth equation, where b-d is represented by r, is:

Intrinsic rate of natural increase

The correct answer is Option (1) -Intrinsic rate of natural increase

In the exponential growth equation, if b - d is represented by r, then 'r' may be called the intrinsic rate of natural increase.

Exponential growth: Resource (food and space) availability is obviously essential for the unimpeded growth of a population. Ideally, when resources in the habitat are unlimited, each species has the ability to realise fully its innate potential to grow in number. Then the population grows in an exponential or geometric fashion. Algal bloom shows this type of growth curve. 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 =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. Exponential or geometric growth pattern of a population and results in a J-shaped curve when we plot N in relation to time.