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efugia, but not for the species that are currently there. Suitable refugia for upland
species are often thousands of kilometres away from the current locations of those
species. The sharp gradient in temperature between the upland areas and the
surrounding lowlands results in the closest areas with similar temperature being much
further south or, in some cases, simply not present anywhere in continental Australia
by 2085.
Tasmania features with moderate consistency across many climatic stability metrics.
Tasmania contains areas of least change for the past temperature and precipitation,
and least change in precipitation of the previous 60 years. Tasmania is also projected
to experience low absolute change in temperature and precipitation between current
and 2085, and have a moderate shift in terms of the number of SDs for both
temperature and precipitation. Tasmania will act as an important refugial area for
many species, provided they are already present there or can cross Bass Strait.
3.6 Climate change and biodiversity across the continent
When we modelled current and projected species distributions across the continent,
some very clear patterns emerged. First, there are projected to be very large shifts in
species richness across most of the continent. The models predict net species loss in
the north, west and centre of the continent; and net species gain in much of the south
and east of the continent. Large parts of central and western Australia are
predicted to lose approximately half of all vertebrate species currently in these
areas (Figure 22). By contrast, species richness may almost double in parts of
southern and eastern Australia. It is important to note that species gain to an area
(but not species loss) assumes that the species is capable of dispersing to that area.
Thus, although the inference regarding species loss is probably a robust estimate, the
inference regarding species gain is almost certainly an overestimate of the
realised species gain to these areas.
The areas predicted to gain and lose species are largely consistent in their proportional
increase in species richness across the four vertebrate classes we investigated. These
changes in species richness can be broken down into the species predicted to move
into an area by 2085 (‘immigrants’) and species predicted to move out of (i.e. be lost
from) areas (‘emigrants’). That the highest proportion of incoming and lowest proportion
of outgoing species are both found largely in the south and east reflects losses of the
north and western edges of species ranges, and contractions towards the south-east.
This observation is in agreement with observed shifts in bird species ranges over the
last 60 years (VanDerWal et al. 2013).
Our definition of refugia as places where species contract to, and persist in, during
unfavourable climates (sensu Keppel et al. 2012) suggests that refugia can be defined
as places with the highest number of immigrants and the lowest number of emigrants.
When we summed the accumulation of these areas (in a taxonomically representative
manner), we clearly identified numerous parts of southern and eastern Australia
as important refugia for terrestrial biodiversity.
The broad congruence between patterns found by modelling species, as well as
patterns found by inferring required rates of range-shift (based on climate) is
encouraging. However, caution must be exercised when evaluating this congruence, as
the same climate data were used in both the investigations of future climates and
projections of species distributions into the future.
Climate change refugia for terrestrial biodiversity 49