untitled

As we saw earlier in this chapter, the geometric model can be readily translated

into the exponential model:

Nt=N 0 ert

Hence, it is straightforward to shift between representation of population dynamics

in continuous time and discrete time. Such simple models are most appropriate for

small populations introduced into a new environment or for a short period follow-

ing a perturbation. For example, the George River caribou herd in eastern Canada

grew exponentially at a rate of r=0.11 during a 30-year period following recovery

from overharvesting (Messier et al. 1988).

The dynamic behavior of a population – whether it increases, decreases, or remains

stable – is determined by its age- or stage-specific mortality and fecundity rates inter-

acting with the underlying distribution of ages or stages in the population. A wide

variety of techniques are available for estimating age-specific parameters, summarized

in the life table. When age-specific rates of fecundity and survivorship remain con-

stant, the population’s age distribution assumes a stable form, even though its size

may be changing. These demographic parameters determine the rate of population

change over time, forming the logical basis for many conservation and management

decisions.

POPULATION GROWTH 89

300

200

100

0

0246810

t

N

t

Fig. 6.4Population
changes according to
the geometric model
with λ=1.65.

6.9 Summary