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An accurate test of PVA predictions must incorporate a large
number of data sets to obtain representative assessments for detailed models
(Brook et al., 2000). However, many field studies regarding wildlife populations
are of too short a duration to detect rare events, quantify the importance of
density dependence, or distinguish long-term trends (Beissinger & Westphal
1998).

The reliability of the predictions made using VORTEX is questioned
in multiple studies.  The predictions
based on population viability analysis are generally considered overly optimistic
unless all potential threats to an endangered species are included in the model
(Lacy 1993)(Ralls and Taylor 1997). VORTEX software does not consider the possibility
that even without any direct threat to the wildlife, population numbers can be
as affected by habitat fragmentation just as much as they are by overall loss
of habitat. The reduction in partridge spatial density caused by habitat
fragmentation will be likely to be a cause of both the particular pattern of
fragmentation and the demography and behaviour of the partridges (Kendall, 1998)(Lacy
et al., 1995). In addition, how threats such as hunting or feeding competition
with other wildlife sharing the habitat, will affect population numbers and
will depend on the pattern of fragmentation and on the demography and behaviour
of the partridges. For instance, the reserve size will affect poaching
intensity because the edges of the reserves will determine how easily
accessible the interior is to poachers and how often animals would roam out of
the relative safety of the reserve (Akcakaya and Burgman, 1995).

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The threats facing endangered species influence population size
through their effects on demographic rates and the spatial structure of habitat
patches. Therefore, until population viability analysis model using VORTEX consider
either the demography or spatial structure of the animals, it is likely that
the results are going to be inaccurate.

In conclusion, the predictive accuracy of a PVA using VORTEX
will only be useful if the distributions of the population rates will not adjust
in the future. As ecological systems are dynamic, regulating processes can
change, but it is usually impossible to predict how or when. Research is
required to estimate how changes from one regulating factor to another
influence the distribution of vital rates and population growth rates. Data on
the growth rate of populations should be collected following the initiation of
a management or conservation strategy, and the results and predictions of PVAs
should be reassessed, and if necessary strategies altered, following the
addition of these data. A useful application of PVAs would be to compare the
consequences of different management or conservation strategies, and exploring
theoretically the implication of model assumptions on extinction probabilities
and population dynamics (Possingham, 1993).

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