Environmental Engineering Reference
In-Depth Information
Figure 4.1.
(a) Example of unbounded exponential population growth according to
the equation
N
(
t
) =
N
(0)
e
rt
where
N
(
t
) is population size (numbers) at some future time
t
,
N
(0) is initial population size and
r
is the net rate of increase. Solid circle represents the
baseline where
N
(0) = 10 and
r
= 0.10, solid square demonstrates the effects of increas-
ing
N
(0) to 11 and solid triangle demonstrates the effect of decreasing
r
to 0.09. (b)
Populations rarely continue to increase unbounded.The example of population growth
of domestic sheep introduced to Tasmania reveals that populations can level off at some
upper maximum size. The squares represent original census data points and the circles
are calculated from a statistical fit through the census data. Original data are presented in
Davidson (1938).
