Question

In theory, populations of organisms can increase exponentially. What does this mean and why is it rarely seen in nature?

Answer 1

Exponential growth is observed when the resources availability is unlimited in the habitat, the population of an organism living in the habitat grows in an exponential or geometric fashion. Resource (food and space) availability is obviously essential for the unimpeded growth of a population. Ideally, when resources are unlimited, each species has the ability to realize fully its innate potential to grow in number, as Darwin observed while developing his theory of natural selection. Then the population grows in an exponential or geometric fashion. If in a population of size N, the birth rates (per capita birth) are represented as b and death rates (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'.

This growth is rarely seen in nature because resources are always limited.