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- Rainforest preserves in the rainforest come immediately to mind,
but also Madagascar, coral reefs.
- I mentioned the ``hotspot'' approach to conservation advocated
by Norman Myers and Conservation
International [6]: ``as many as 44% of all
species of vascular plants and 35% of all species in four
vertebrate groups are confined to hotspots comprising only 1.4% of
the land surface of the Earth.''3
- A little good news for a change. A concentrated effort
in a few high priority areas can, with careful long-term management,
ensure that a large proportion of the world's biodiversity will
survive us.
- We see the same phenomenon at a smaller scale. Dobson et
al. [2] compiled a database recording county-level
occurrences of all plants and animals protected under the Endangered
Species Act as of August 1995. Using this database they used a
sorting algorithm to identify ``hot spots'' for endangered species
for amphibians, arachnids, birds, clams, crustacea, fish, insects,
mammals, plants, reptiles, and snails.
- Select the county with the greatest number of endangered
species. In the case of a tie select the county with the smallest
area.
- Exclude all species found in that county from further
consideration.
- Return to step 1.
More than 50% of endangered species in each group are represented
with between 0.14 and 2.04% of land area.
- Of course things never turn out to be quite as simple as they
first seem. Luck et al. [3] point out that there's
a positive correlation between human population density and
species richness (birds, mammals, reptiles, amphibians, and
butterflies) in both Australia and the United
States (Figure 2), with the exception of
reptiles in Australia.
Figure 2:
The relationship between human population density and species
richness in Australia (upper) and the United States
(lower) (from [3]).
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- Fortunately, there's still some good news in the end. Suppose we
set as a conservation goal representing each species at least once
and choosing the smallest set of grid cells (or the grid cells that
would cost the least to acquire) that allow us to do that. Then
compare what happens under two scenarios: (1) ignore human
population density (effectively assuming all grid cells are equally
costly) and (2) assign each grid cell a cost proportional to human
population density. What you see is that under the second strategy,
overlap can be largely avoided (0% to ca. 10% depending on the
taxonomic group) and that the total area required for conseration is
only slightly
greater (Figure 3).4
Figure 3:
Percent of overlap between conservation targets and human
population density under the two scenarios (a) and the number of
grid cells included in the conservation targets under the two
scenarios (from [3]).
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Next: Significant species and natural
Up: Goals of a conservation
Previous: Large, intact, functioning ecosystems
Kent Holsinger
2009-11-16