Environmental Engineering Reference
In-Depth Information
(a)
(b)
(c)
1.2
1.1
1.0
1.2
1.1
1.0
0.9
1.0
0.8
0.9
0.8
0.7
0.8
0.7
0.6
0.4
0.6
0.5
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0.2
0.5
0
1970 1975 1980 1985 1990 1995 2000
Year
1970 1975 1980 1985 1990 1995 2000
1950
1960
1970
1980
1990
2000
Year
Year
Fig. 1.4
Combined indexes of change in population size for various animal groups for which long-term data are available. In
each case the index is standardized at 1.0 for the fi rst year of the dataset. (a) Mean population sizes of British bird species
from 1970 to 2000: open circles - all species (105 species), squares - woodland species (33 species), closed circles -
farmland species (19 species). (b) Index of change in amphibian populations worldwide from 1950 to 1997, based on
accumulated annual changes in 936 populations of 157 species. (c) Index of change in vertebrate populations worldwide:
open circles - forest vertebrates (282 populations), closed circles - freshwater vertebrates (195 populations), squares -
marine vertebrates (217 populations). (After Balmford et al., 2003, where original references can be found.)
has been done and, moreover, in one of the world's biodiversity hotspots in the East
Asian tropics.
The island of Singapore has experienced exponential population growth, from
150 villagers in the early 1800s to more than four million people as it developed
into a prosperous metropolis. During this period 95% of Singapore's forest was lost,
initially to make way for crops and more recently for urbanization and industrializa-
tion. Many extinctions have been documented since 1800 (Figure 1.5 - green his-
tograms). In addition, species lists from nearby Malaysia can be used to infer the
likely pristine biodiversity in Singapore and provide an estimate of the number of
extinctions that have gone unrecorded (Figure 1.5 - blue histograms). It seems that
the majority of the island's species from a wide range of animal and plant groups
are now extinct, an unfortunate consequence of the economic 'success story' of
modern Singapore. Of course, Singapore is not unique and a similar exercise would
produce an equally uncomfortable result for most of the world's cities and nations.
No matter how uncertain the data may be and however imprecise our knowledge
of the history of Singapore, or anywhere else in the world, there is no room for
complacency - population declines and increased extinction risks need to be
confronted.
1.2.2
Biodiversity,
ecosystem function
and ecosystem
services
Most people regret any extinction and value species in their own right. But a reduc-
tion in biodiversity can also have consequences at a higher level of ecological
organization - that of the ecosystem. The
ecosystem
consists of all the species that
coexist in an area, together with their physicochemical environment. Ecosystem
ecologists pay particular attention to the way solar energy and chemical elements
are harnessed by plants in photosynthesis and subsequently pass between living
ecosystem compartments (herbivores, carnivores, decomposer organisms) and non-
living compartments (dead organic matter in soil or water). Ecosystem processes
that might respond to changes in biodiversity include the rate at which plants
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