8
Mark Burgman et al.
various circumstances may be measured by their statistical power (Peterman
1990).
Western Australia harbors approximately 600 species of Acacia and approximately 10,000 species of vascular plants (these estimates include formally
described species and an estimate of the numbers of undescribed species). Many
of these species are endemic to the state, particularly the southwest region. Perhaps as many as 20% may be threatened by a number of processes including
agricultural land clearance, changed fire regimes, and soil-water–borne pathogens (particularly Phytophthora cinnamomi).
Western Australia has legislation that affords special protection to threatened
flora (and fauna). The state agency responsible for administering the Wildlife
Conservation Act, the Department of Conservation and Land Management, maintains a register of formally gazetted threatened flora, declared rare flora, together
with an informal list of priority flora taxa. Declared rare flora and priority flora
taxa are referred to here collectively as “conservation taxa.” The priority flora list
includes taxa for which there may be some reason for conservation concern; many
of these taxa are poorly known and require further study to assess accurately their
conservation status and, thus, consideration for being afforded the special protection of a declared rare flora taxon. The priority flora list therefore provides a
means of setting conservation and research priorities in Western Australia for taxa
being considered for declaration as rare flora. It comprises four categories:
• Category P1: taxa that are known from one or a few (generally fewer than five)
populations that are under threat
• Category P2: taxa that are known from one or a few populations, at least some
of which are not believed to be under immediate threat
• Category P3: taxa that are known from several populations, at least some of
which are not believed to be under immediate threat
• Category P4: taxa that are considered to have been adequately surveyed and
that, although being rare in Australia, are not currently threatened by any
identifiable factors (K. Atkins, personal communication)
The purposes of the present study are to undertake power tests of formulas used
to infer threat from data of the kind found in herbaria and museums and to identify
patterns that may indicate trends in population size or range by testing collections
of 192 Acacia conservation taxa from Western Australia. The results of these tests
will help to clarify the capabilities and limitations of these tools.
Methods
Description of the Equations
The equation by Solow (1993) was designed to estimate the probability of extinction from sighting data. Burgman et al. (1995) wrote the equation in an analogous,
discrete-time form (assuming a Poisson process with a fixed chance of observation) including the number (frequency) of sightings. In this form, Solow’s test is
Mark Burgman et al.
various circumstances may be measured by their statistical power (Peterman
1990).
Western Australia harbors approximately 600 species of Acacia and approximately 10,000 species of vascular plants (these estimates include formally
described species and an estimate of the numbers of undescribed species). Many
of these species are endemic to the state, particularly the southwest region. Perhaps as many as 20% may be threatened by a number of processes including
agricultural land clearance, changed fire regimes, and soil-water–borne pathogens (particularly Phytophthora cinnamomi).
Western Australia has legislation that affords special protection to threatened
flora (and fauna). The state agency responsible for administering the Wildlife
Conservation Act, the Department of Conservation and Land Management, maintains a register of formally gazetted threatened flora, declared rare flora, together
with an informal list of priority flora taxa. Declared rare flora and priority flora
taxa are referred to here collectively as “conservation taxa.” The priority flora list
includes taxa for which there may be some reason for conservation concern; many
of these taxa are poorly known and require further study to assess accurately their
conservation status and, thus, consideration for being afforded the special protection of a declared rare flora taxon. The priority flora list therefore provides a
means of setting conservation and research priorities in Western Australia for taxa
being considered for declaration as rare flora. It comprises four categories:
• Category P1: taxa that are known from one or a few (generally fewer than five)
populations that are under threat
• Category P2: taxa that are known from one or a few populations, at least some
of which are not believed to be under immediate threat
• Category P3: taxa that are known from several populations, at least some of
which are not believed to be under immediate threat
• Category P4: taxa that are considered to have been adequately surveyed and
that, although being rare in Australia, are not currently threatened by any
identifiable factors (K. Atkins, personal communication)
The purposes of the present study are to undertake power tests of formulas used
to infer threat from data of the kind found in herbaria and museums and to identify
patterns that may indicate trends in population size or range by testing collections
of 192 Acacia conservation taxa from Western Australia. The results of these tests
will help to clarify the capabilities and limitations of these tools.
Methods
Description of the Equations
The equation by Solow (1993) was designed to estimate the probability of extinction from sighting data. Burgman et al. (1995) wrote the equation in an analogous,
discrete-time form (assuming a Poisson process with a fixed chance of observation) including the number (frequency) of sightings. In this form, Solow’s test is