Exponential growth is any change in numbers with time that occurs at a constant per capita rate.
1 might be a natural example of how bacteria multiply over time. This formula simply means that the slope of the line for N as a function of t is given by r N . So, the rate of change in numbers is proportional to the numbers present. Constant r represents the per capita recruitment rate in each time increment. It is a net value, being the net surplus of births after subtracting deaths.