Environmental Engineering Reference
In-Depth Information
example, it has been suggested that new species may move in faster from lower eleva-
tions, and latitudes, than resident species will recede to higher elevations or the
poles (Walther et al., 2002).
11.4.2 Food-web
interactions - Dengue
downunder
In Section 11.3.2 you saw how the effect of climate change on a target species (a
pest aphid in this case) came about by altering a food-web interaction. Aphid density
was modifi ed partly by direct impacts of temperature and moisture, but also via
changes to the performance of the cereal plant upon which the aphid feeds. Equally,
changing patterns in the distribution and productivity of marine plankton (Figure
11.1) may exert effects on the productivity of the fi sh at the top of the food web, and
thus change the sustainable yield of fi sheries. And the Australian butterfl y at most
risk from climate change ( Hypochrysops halyetus in Section 11.2.1) is unusually
vulnerable not only because of its specialized requirement for a unique food plant,
but also because it depends on the presence of a particular ant species in a mutual-
istic relationship. Climate change might therefore affect the butterfl y directly, or
indirectly via these food-web interactions.
I explained in Section 9.2 how the risk of certain diseases in humans depends on
the way key species interact in food webs. Climate change can play a role here too.
Take Dengue fever, for example. This is a potentially fatal viral disease currently
limited to tropical and subtropical countries where its mosquito vectors occur. No
mosquito species currently in New Zealand is capable of carrying the disease, but
both of the world's most important vectors ( Aedes aegypti and A. albopictus ) have
been intercepted at New Zealand's borders. If a vector mosquito population becomes
established, it needs only a single virus-carrying human traveler to trigger an out-
break of the disease. de Wet et al. (2001) coupled knowledge of the mosquitos' fun-
damental niches (in terms of temperature and precipitation) with climate change
scenarios, to predict areas of high risk of mosquito invasion and thus of establish-
ment of the disease. Under present climatic conditions, A. aegypti is unlikely to be
able to establish anywhere in New Zealand but A. albopictus could invade the north-
ern, subtropical part of the North Island (Figure 11.12a). Under a climate change
scenario, most of the North Island and some of the South Island would be at risk of
invasion by A. albopictus . Under the same scenario, the greater Auckland area in the
north of the North Island, where a large proportion of the human population lives,
would become susceptible to invasion by the more effi cient virus vector A. aegypti
(Figure 11.12b). Vigilant border surveillance is the key, with emphasis on northern
ports of entry and particularly Auckland, where most passengers and cargo arrive
(including the imported tyres that provide a prime transport route for mosquito
larvae) (Hearnden et al., 1999).
11.4.3 Ecosystem
services - you win
some, you lose some
People are part of ecosystems and obtain a variety of priceless ecosystem services
free - provision of suffi cient water, productive soils, fl ood control, recreational
opportunities such as skiing and so on (Section 9.8). Schroter et al. (2005) evaluated
for the whole of Europe the likely effect on selected ecosystem services of climate
change. Predictions were based on an expected population size of 419 million people
by 2080 (compared to 376 million in 1990), an atmospheric CO 2 concentration of
709 ppm and, according to four different model scenarios, average temperature rises
of between 2.7 and 3.4˚C and percentage changes in precipitation ranging from a
reduction of 0.6% to an increase of 2.3%.
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