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The problem of stemming the extinction crisis can best be framed by a question: In which areas would a given dollar contribute the most towards slowing the current rate of extinction? To accomplish this we first need to understand species’ distributions. This requires that we measure endemism: the degree to which species are found only in a given place. This can be thought of as a measure of “irreplaceability”. Since endemic species cannot be found anywhere else, the area where an endemic species lives is wholly irreplaceable. We also need to decide which species we should consider. Practically, vascular plants and vertebrate animals are the best candidates, because these are the only species for which we currently have sufficient data. Whether the distributions of plants and vertebrates are mirrored by terrestrial invertebrate species remains an open question, although some evidence suggests that they may be. It is less likely that the distributions of aquatic species will parallel these patterns, and so these represent an urgent research priority.

Our ultimate goal is to keep nature intact, which means that we must stop anthropogenic species extinctions. To approach this goal, we must slow the rate of species extinction as much as possible with whatever conservation resources we have at our disposal, which requires incorporating threats (or “vulnerability”) and costs into priority setting. Generally, the more threatened an area is, the more it will cost to conserve. However, because economic opportunity costs vary dramatically, there do still exist areas of relatively low cost in all hotspots.

We face a paradox in determining how to incorporate threats, costs, and opportunities into conservation priorities. Intuitively, we want to conserve the most threatened areas first, but we also want to get the greatest return for our conservation dollar. This paradox can best be resolved by identifying areas that hold species found nowhere else and that are guaranteed to lose species if the areas are not conserved. Among these, we rank our actions with the most threatened biodiversity receiving the most urgent action. Wherever we have choices we select opportunities for attending to areas that are the least expensive to conserve. In effect, we need a dual conservation strategy that always prioritizes endemic-rich areas and ensures that we protect the most threatened places, while preemptively protecting equally unique places that are not yet under extreme threat. Based on this theory, Conservation International uses a two-pronged strategy for global conservation prioritization, simultaneously focusing on the irreplaceable and threatened biodiversity hotspots and on the five high-biodiversity wilderness areas, which are irreplaceable but still largely intact.

Hotspots are not the only system devised for assessing global conservation priorities. BirdLife International, for instance, has identified 218 “Endemic Bird Areas” (EBAs) each of which hold two or more bird species found nowhere else. The World Wildlife Fund-U.S has derived a system called the “Global 200 Ecoregions”, the aim of which is to select priority Ecoregions for conservation within each of 14 terrestrial, 3 freshwater, and 4 marine habitat types. They are chosen for their species richness, endemism, taxonomic uniqueness, unusual ecological or evolutionary phenomena, and global rarity. All hotspots contain at least one Global 200 Ecoregion and all but three contain at least one EBA; 60 percent of Global 200 terrestrial Ecoregions and 78 percent of EBAs overlap with hotspots.


© Piotr Naskrecki
The coconut crab (Birgus latro), which is the largest terrestrial invertebrate in the world, is thought to have migrated to distant islands by floating on coconuts.
© Conservation International, photo by Russell Mittermeier
All 71 species of chameleons in the Madagascar and the Indian Ocean Islands Hotspot are endemic, representing 44 percent of the world's total.

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