Page "Maximum sustainable yield" Paragraph 25

can be understood as the change in population ( N ) with respect to a change in time ( t ).

Equation 1. 2 is the usual way in which logistic growth is represented mathematically and has several important features.

First, at very low population sizes, the value of is small, so the population growth rate is approximately equal to, meaning the population is growing exponentially at a rate r ( the intrinsic rate of population increase ).

Despite this, the population growth rate is very low ( low values on the y-axis of figure 2 ) because, even though each individual is reproducing at a high rate, there are few reproducing individuals present.

Conversely, when the population is large the value of approaches 1 effectively reducing the terms inside the brackets of equation 1. 2 to zero.

The effect is that the population growth rate is again very low, because either each individual is hardly reproducing or mortality rates are high.

As a result of these two extremes, the population growth rate is maximum at an intermediate population or half the carrying capacity ().