Hotspots Not Necessarily So Hot

Not all biodiversity hotspots are equal. New research shows that for birds, most hotspots are rich in either overall diversity, threatened species, or endemics but that very few are rich in all three types of diversity.

“The different types of hotspots vary greatly in their utility as conservation tools,” say David Orme of Imperial College, London, and 14 coauthors in Nature.

To identify hotspots, the researchers created a global database of the breeding ranges of nearly 10,000 bird species, divided the earth’s land surface into 20,000 grid cells of 100 km2 each, and then mapped the distributions of three measures of diversity: total number of species, number of threatened species, and number of endemic species. Next, the researchers used these maps to locate hotspots, which were defined as the top 2.5 percent of grid cells for each of the three types of diversity.

By this analysis, hotspots account for about 6 percent  (1,275 grid cells) of the land worldwide. However, a mere 2.5 percent (32 grid cells) of these hotspots  are rich in all three types of diversity. In contrast, more than 80 percent (1,051 grid cells) of the hotspots are rich in only one type of diversity. For example, overall species diversity is concentrated in tropical mainland mountains, whereas endemic species diversity is concentrated in archipelagos.

“Endemism hotspots actually contained a greater proportion of overall species richness than did the species richness hotspots and a greater proportion of the threatened species than did the threat hotspots,” say the researchers (see table).

Does this mean that it’s enough to protect hot-spots rich in endemic species? Hardly. “Our results indicate the need to use multiple indices of diversity in identifying areas of high conservation priority,” say the researchers.

Type of Hotspot
Diversity Threatened Endemic
% of all species 49 40 60
% of threatened species 27 40 41
% of endemic species 20 23 60

Orme, C.D.L. et al. 2005. Global hotspots of species richness are not congruent with endemism or threat. Nature 436:1016-1019.

By Robin Meadows

Photo: Hyacinth macaw (Anodorhynchus hyacinthinus). ©David April

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