Dealing with global climate change - Ecological Applications: Toward a Sustainable World - page 310

addition, many proteas are at risk because of a strong decline in habitable area
related to their expected movement to higher elevations. This happens partly because
the ranges of many species are already close to absolute upper elevational limits,
but also to some extent because of the 'conical' shape of mountains. As climate
warms, habitable area (and thus species range) shifts into the smaller and smaller
areas available at higher and higher elevations. In the case of Protea lacticolor , for
example, there is a predicted range loss in lowland areas, species persistence in the
uplands, and some new potential range at higher elevations (Figure 11.4).
Beaumont and Hughes (2002) used a similar approach to predict the effect of
climate change on the distribution of 24 Australian butterfl y species, which, like
the proteas, are strongly infl uenced by temperature and moisture. Under even a
moderate set of future conditions (temperature increase of 0.8-1.4˚C by 2050), more
than half the butterfl ies lose at least 20% of their ranges. One species at particular
risk is Hypochrysops halyetus in the coastal heathland of Western Australia. It is
predicted to lose 58-99% of its current range. In addition, less than 27% of its future
distribution occurs in locations that are currently occupied.
These examples illustrate two important points. The fi rst is that many species can
be expected to suffer a reduction in habitable area and, because smaller areas
support smaller populations, extinction risk is increased. The second point is just
as signifi cant: nature reserves may turn out to be in the wrong place in the shifting
template of temperature and moisture. When selecting protected areas, managers
must take account of predicted range shifts of the species to be protected. Equally,
climate-related shifts in range should also be considered when selecting candidate
species for habitat restoration.

11.2.2 Niche
theory and invasion
risk - nuisance on
the move

Spiny acacia ( Acacia nilotica subspecies indica ) is a woody legume whose native
range includes parts of Africa and extends into India. It is now on the march across
Australia where it was originally introduced as an ornamental plant and to provide
food and shade for domestic animals. Its spread has been dramatic and the plant is
now labeled a noxious weed because it reduces pasture production, impedes access
of livestock to water and makes stock mustering a diffi cult business. Given knowl-
edge of conditions in its natural range, Kriticos et al. (2003) determined the species'
fundamental niche (Box 2.1). This was defi ned in terms of optimal conditions of
temperature and moisture (and lower and upper tolerance limits), as well as thresh-
olds for cold stress, heat stress, dry stress and wet stress (water-logging). They then
modeled the acacia's invasion potential under two climate change scenarios. Both
assumed a middle-of-the-range 2˚C temperature rise, but this was coupled with
either a 10% increase or 10% decrease in rainfall, refl ecting the uncertainty sur-
rounding future precipitation in Australia.
Currently, the plant is spread widely through the range indicated by the model
based on present climatic conditions (Figure 11.5a), but it is not yet in all predicted
areas. When climate change is taken into account, its eventual invadable range will
be much larger (Figure 11.5b,c). This is partly because of changed climatic condi-
tions, but also because spiny acacia is expected to become more effi cient in its use
of water (making dryer areas inhabitable) as a result of a 'fertilizing' effect on growth
caused by increased atmospheric CO 2 . Thus, elevated atmospheric CO 2 concentra-
tion can have both indirect effects, via climate change, and direct effects on the
performance and distribution of plants (Volk et al., 2000). Given that we now know