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of future extinction rates are based on combining the projections of species
distribution models using either species-area relationships (e.g. Thomas et al.,
2004b), or endemic-area relationships (Malcolm et al., 2006). While there has
been much debate over the validity of different methods, virtually all published
estimates of future risk project far higher rates than those observed in the
second half of the 20th century, which are already approximately two orders
of magnitude higher than in the Cenozoic fossil record (Leadley et al., 2010a).
For example, 20-30 per cent of plant and animal species assessed by the Fourth
Assessment Report of the IPCC (Fischlin et al., 2007) were considered to be at
increased risk of extinction if global temperature increases exceed 2-3°C. There
remains a high level of uncertainty as to how these predictions could translate
into realized rates of species loss, and at what rate this could occur (Leadley et al.,
2010a). It is possible that the rates could be overestimates if species are able to
find climatic refuge in spatially heterogenous environments or be underestimates
because they do not take into account dispersal limitations, species interactions
and the potential for tipping points in ecosystems to be exceeded. It is also
important to note that the majority of most commonly reported estimates, such
as that of Thomas et al. (2004), who projected 18-34 per cent of species to be at
increased risk of extinction by 2050, used only mid-range climate scenarios that
project up to 3°C warming, but not beyond to 4°C degrees or more.
Few Australian species have been studied in enough detail for credible projec-
tions to be made as to their future fate. Indeed the only generalization that can
be made with a high degree of confidence is that every species will be affected
differently. However, some broad ecological principles can be applied to help
understand patterns of vulnerability. Species with low reproductive rates, poor
dispersal ability, narrow geographic and/or climatic ranges, restricted genetic
variation, specialized to a particular habitat or food source, reliant on a narrow
range of other species and those otherwise rare or threatened by other stressors
are likely to be the most vulnerable (Steffen et al., 2009).
Projections from species distribution models (see Table 4.2 ; end of this
chapter) offer a fairly gloomy outlook for most species, consistently projecting
future declines in species' ranges and increased risk of extinction, even when
optimistic rates of dispersal are assumed: for instance, for West Australian
banksias (Fitzpatrick et al., 2008), koalas (Adams-Hosking et al., 2011), northern
macropods (Ritchie and Bolitho, 2008), native rats (Green, Stein and Driessen,
2008), the greater glider (Kearney, Wintle and Porter, 2010b), quokkas (Gibson
et al., 2010) and platypus (Klamt, Thompson and Davis, 2011). For some species,
the models indicate that loss of range may be driven primarily by rainfall rather
than temperature.
Relatively few Australian studies of impacts on species specifically incor-
porate projections of 4°C warming or above. Williams, Bolitho and Fox (2003)
modelled the impacts of temperature increases up to 7°C for endemic vertebrates
in north Queensland, finding that at 3.5°C, 38-67 per cent of frogs, 48-80 per
cent of mammals, 43-64 per cent of reptiles and 49-72 per cent of birds would
be 'committed to extinction', with 85-90 per cent of their suitable habitat lost.
 
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