Dealing with global climate change - Ecological Applications: Toward a Sustainable World - page 315

allowing the passage of four generations of sweetgum. Only when a colonist of an
unoccupied cell reaches reproductive maturity (at 25 years old) can it start contrib-
uting to the colonization of other cells. You can see that only a very small percentage
of the newly habitable area of sweetgum is likely to be actually occupied by 2100
(Figure 11.8c). Given the serious lag involved in species movement to newly habit-
able areas, managers may need to compensate by physically moving seeds or seed-
lings, especially of rare species unable to travel effectively through fragmented
landscapes. However, it would be unreasonable to expect to be able to transplant
whole communities.

11.3 Climate change
predictions based
on the theory of
population dynamics

In Chapters 5-7 you saw how knowledge of the population dynamics of key species
can be used when planning conservation, pest control and harvest operations. If we
know how birth and death rates are likely to be modifi ed as a result of climate
change, this can be incorporated in plans with a timetable stretching through the
twenty fi rst century.

11.3.1 Species
conservation - the
bear essentials

A long-term study of polar bears ( Ursus maritimus ) at Svalbard in Norway has
revealed a link between birth rate and an oscillating climate pattern where atmos-
pheric pressure in the Arctic switches between high and low. This Arctic Oscillation
is linked to the North Atlantic Oscillation discussed in Section 11.2.3. In years when
the Arctic Oscillation is in negative mode (higher than normal pressure over the
polar region), a larger proportion of female bears have cubs and also, on average,
they have a greater number of cubs (Figure 11.7b). Improved breeding success might
be due to the state of sea ice, and the access this provides to prey (seals). Alterna-
tively, there may be a climate effect on the productivity of phytoplankton, which
fuels the base of the polar bear food web (Derocher, 2005). What concerns us here,
however, is the expectation from global climate models that the Arctic Oscillation
is likely to change, with consequences for population viability of the bears. Polar
bear populations have long been under pressure from hunting and high body pol-
lutant levels. It will be important to quickly understand the nature of any further
threat posed by climate change.

11.3.2 Pest control -
more or less of a
problem?

Just as polar bears may be affected by global climate change, so may animals that
normally keep pest insects under control, whether naturally occurring spiders or
deliberately introduced biological control agents such as parasitoid wasps (Chapter
5). But the picture is more complex than this, of course, because climate change
might infl uence the success of the crops, their pests, or the pest's control agents, or
indeed all three - and in different directions.
Take the case of the aphid Rhopalosiphum padi that attacks cereal crops in
southern Britain. Newman (2005) begins with global climate change predictions.
His analysis includes a range of scenarios differing in the extent to which atmos-
pheric CO 2 increases during the twenty fi rst century (baseline for 1961 to 1990 of
319 ppm; low scenario 525 ppm, medium low 562 ppm, medium high 715 ppm, and
high scenario 810 ppm). He next couples these predictions with an ecological model
that links local climatic conditions (particularly temperature and rainfall), the
growth of cereal grasses (which depends on climate but also on soil water and
nutrients) and the population dynamics of the aphi ds (which respond directly to
climatic conditions, but also to plant drought stress and nitrogen available from the