The dynamic behavior of a population – whether it increases, decreases, or remains
constant – is determined by its age- or stage-specific mortality and fecundity rates
interacting with the underlying distribution of ages or stages in the population. The
long-term rate of population change can be calculated through use of a transition
matrix composed of these vital rates. Determination of the elasticity of the rate of
population change due to slight modifications of the vital rates can be a useful means
of evaluating alternative conservation and management options, as illustrated by the
case study with loggerhead turtles.252 Chapter 14
Fig. 14.3Predicted short-term population dynamics of Soay sheep on the island of Hirta depend on the initial age structure,
weather, and population density (Coulson et al. 2001a). Each individual graph displays the results of four simulations with identical
weather conditions and identical starting population size. In each graph, each line represents the outcome of one simulation
with different initial age and sex structure chosen from the data (see table below). The y-axis shows different starting
population sizes and the x-axis different mean values for the simulated weather distributions. NAO stands for the North
Atlantic Oscillation, a standard aggregate measure of weather conditions in the northern hemisphere (Stenseth et al. 2002).
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0246 024 6 0 246NNNHighIntermediateLowInitial population sizeMean NAO – 0.2 1.79 2.79
Good weather Bad weather
Winter weatherAge / sex structure (%)
Female
lambs
19
17
23
22Female
yearlings
5
8
10
13Female
adults
48
41
24
17Older
females
7
8
11
13Male
lambs
13
18
19
16Male
adults
7
8
13
19Older
males
1
0
0
0