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typically much better known than that of animals, the most the greatest number of threatened species, or areas con-
practical way to identify hotspots has been to locate areas taining the greatest number of endemic species. All three
containing high numbers of endemic plant species. Con- approaches are reasonable.
servation International considers two criteria when deter- In addition to considering species diversity, some scientists
mining whether an area qualifies as a hotspot. First, the area have argued that we should also consider the size of the human
must contain at least 1,500 endemic plant species. By con- population in diverse areas. For example, we might expect that
serving plant diversity, the hope is that we will simultane- natural areas containing more people face a greater probability
ously conserve animal diversity, especially for those groups, of being affected by human activities. Whereas the world has
such as insects, that are poorly cataloged. Second, the area an average human population density of 42 people per square
must have lost more than 70 percent of the vegetation that kilometer, the average hotspot has a human population of
contains those endemic plant species. In this way, high- 73 people per square kilometer. Such places may be at a higher
diversity areas with a high level of habitat loss receive the risk of degradation from human activities. This risk should be
highest conservation priority. High-diversity areas that are considered when determining priority areas for conservation,
not being degraded receive lower conservation priority. and it should motivate us to promote development that does
not come at the cost of species diversity.
What else can make a hotspot hot?
What are the costs and benefits of
The number of endemic species in an area is undoubtedly conserving biodiversity hotspots?
important in identifying biodiversity hotspots, but other sci-
entists have argued that this criterion alone is not enough. Conservation efforts that focus on regions with large num-
They suggest that we also consider the total number of spe- bers of species place a clear priority on preserving the larg-
cies in an area or the number of species currently threat- est number of species possible. However, people making
ened with extinction in an area. Would all three approaches these efforts do not explicitly consider the likelihood of
identify similar regions of conservation priority? A recent succeeding in this goal, nor do they necessarily consider the
analysis of birds suggests they would not. When scientists costs associated with the effort. For example, there may be
identified bird diversity hotspots using each of the three many ways of helping a species persist in an area, including
criteria — endemic species, total species richness, and threat- buying habitat, entering into agreements with landowners
ened species — their results, shown in TABLE SA2.1, identi- not to develop their land, or removing threats such as inva-
fied very different hotspot areas. Scientists using the three sive species. In the case of the California tiger salamander,
criteria to identify hotspots of mammal diversity reached for example, while eliminating invasive predators may not
the same conclusion. be feasible, it is possible to protect salamander habitat. In
As we can see, some areas of the world that have high 2011, the U.S. Fish and Wildlife Service agreed to designate
species richness do not contain high numbers of endemic more than 20,000 ha (50,000 acres) of habitat as being crit-
species. The Amazon, for example, has a high number of ical for the salamander’s persistence and in 2016 the agency
bird species, but not a particularly high number of endemic announced their plan to help populations of the salamander
bird species compared with other more-isolated regions of to recover by working with public and private landowners
the world, such as the islands of the Caribbean. Similarly, to protect critical salamander habitat.
areas with high numbers of threatened or endangered spe-
cies do not always have high numbers of endemic species. What about biodiversity coldspots?
These findings highlight the critical problem of deciding
whether conservation efforts should be focused on areas The concept of biodiversity hotspots assumes that our pri-
containing the greatest number of species, areas containing mary goal is to protect the maximum number of species.

TABLE SA2.1 Biodiversity hotspots for birds, identified by three criteria

Rank Total number of species Number of endemic species Number of threatened species
1 Andes Andes Andes
2 Amazon Basin New Guinea and Bismarck Archipelago Amazon Basin
3 Western Great Rift Valley Panama and Costa Rica Highlands Guyana Highlands
4 Eastern Great Rift Valley Caribbean Himalayas
5 Himalayas Lesser Sunda Islands Atlantic Coastal Forest, Brazil

166 UNIT 2 ■ The Living World: Biodiversity
Uncorrected proofs have been used in this sample.
Copyright © Bedford, Freeman & Worth Publishers.
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