Areas with high biological diversity

• Rainforest preserves in the rainforest come immediately to mind, but also Madagascar, coral reefs.

• We've already talked about the ``hotspot'' approach 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.''

• 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.
  1. Select the county with the greatest number of endangered species. In the case of a tie select the county with the smallest area.

  2. Exclude all species found in that county from further consideration.

  3. 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]).

  

• 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).³

  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]).