Conservation of endangered species - Ecological Applications: Toward a Sustainable World - page 122

modeled populations will have been subject to a run of deleterious values for repro-
duction or mortality, refl ecting the reality, for example, that a sequence of very dry
or very wet years will occur occasionally in nature. The probability of extinction is
most favorably affected by a 10% decrease in adult mortality in the Springsure popu-
lation (halving extinction probability from 0.084 to 0.042). On the other hand,
extinction probability of the Oakey population is most sensitive to a 10% increase
in fertility (reducing extinction probability from 0.464 to 0.321).
Managers concerned with critically endangered species do not usually have the
luxury of monitoring populations to check the accuracy of their predictions. But
Penn et al. (2000) were able to check their predictions because the koala populations
have been continuously monitored since the 1970s. The predicted population trends
are close to the actual recorded trends, particularly for the Oakey population, and
this gives added confi dence to the modeling approach (Figure 5.5).
How can such modeling be put to management use? Local authorities in New
South Wales are obliged both to prepare comprehensive koala management plans
and to ensure that developers survey for potential koala habitat when a building
application affects an area greater than 1 hectare. Penn et al. (2000) argue that
population viability modeling can be used to determine whether any effort made to
protect habitat is likely to be rewarded by a viable population.

5.4.2 The royal
catchfl y - a burning
issue

The life histories of plants present particular challenges for simulation modeling,
particularly where there is seed dormancy, highly periodic recruitment or clonal
growth (Menges, 2000). However, as with endangered animals, different manage-
ment scenarios can be simulated in population viability analyses. The royal catchfl y,
Silene regia , is a long-lived prairie perennial whose range has shrunk dramatically.
Menges and Dolan (1998) collected demographic data for up to 7 years from 16
populations in the Midwest of the USA. The populations, whose total adult numbers
ranged from 45 to 1302, were subject to different management regimes. This species,
whose seeds do not show dormancy, has high survivorship and frequent fl owering,
but successful germination is very episodic - most populations in most years fail to
produce seedlings. Population projection matrices, such as the one illustrated in
Table 5.3, were produced for each population in each year (using another simulation

Table 5.3 An example of a projection matrix for a particular Silene regia population from 1990 to 1991, assuming successful
germination of seedlings. Numbers represent the proportion changing from the stage in the column to the stage in the row
(bold values represent plants remaining in the same stage). 'Alive undefi ned' represents individuals with no size or
fl owering data, usually as a result of mowing or herbivory. Numbers in the top row are seedlings produced by fl owering
plants. The fi nite rate of increase λ for this population is 1.67. The site is managed by regular burning. (After Menges &

Dolan, 1998.)

Small Medium Large Alive

Seedling Vegetative fl owering fl owering fl owering undefi ned

Seedling - - 5.32 12.74 30.88 -

Vegetative 0.308 0.111 0 0 0 0

Small fl owering 0 0.566 0.506 0.137 0.167 0.367

Medium fl owering 0 0.111 0.210 0.608 0.167 0.300

Large fl owering 0 0 0.012 0.039 0.667 0.167

Alive undefi ned 0 0.222 0.198 0.196 0 0.133