Ecologists need to reassess their conservation strategies, say researchers in this week's issue of Nature.
Conservation efforts have so far assumed that it mattered little whether experts assessed a region for how many threatened species it housed or how biodiversity-rich the area was.
The belief was that both these methods would come to the same conclusion about whether or not the region was a 'hotspot' and what type of conservation attention it required.
Ian Owens, of the UK Centre for Population Biology, and colleagues say this is not so.
They say the finding means that ecologists will need to reconsider conservation strategies for areas rich in biodiversity, which mostly lie in the tropics.
Owens's team mapped the distribution of bird species across the planet.
They then looked at three aspects of bird diversity, each of which defines a different type of hotspot. These were: how 'rich' an area is in terms of the number of species that are found in it at any given time, how many species live only in the area (these are known as 'endemic' species), and how many of them are threatened with extinction.
Conservationists previously thought these characteristics overlapped. For instance, they believed an area that was home to many threatened species was likely to have more species to begin with.
As a result, efforts to preserve species have so far given equal importance to all types of hotspot.
Owens and colleagues found the hotspots overlap far less than expected.
"Aspects of biodiversity such as rarity and extinction risk show very different geographical distributions, so they are probably produced by different mechanisms and will probably need different sorts of conservation effort," says Owens.
For instance, areas with high numbers of threatened bird species are linked to large numbers of people living close together.
Although these findings in birds are not easy to translate into conclusions for mammals and amphibians, says lead author David Orme, at Imperial College, London, there is evidence to suggest that the situation will be the same in these groups.
In an accompanying Nature article, Hugh Possingham and Kerrie Wilson, of the University of Queensland, Australia, say that the outlook for hotspots is not "all doom and gloom".
Focusing conservation efforts on hotspots of endemic species tends also to protect the other two types of hotspot, they say, giving the biggest return for a single conservation effort.
Speaking to SciDev.Net, Orme was slightly more cautious. The apparent advantage of focusing on endemic species hotspots could be that they encompass a broader geographical area, and are thus more likely to include areas of species richness, he explains.
While this 'blanket' approach may indeed protect a great number of species, Orme believes it is important to think of the mechanisms that threaten species. This could lead to more appropriate conservation efforts.
Orme adds that biodiversity experts should also consider the conservation of regions outside hotspots that may contain irreplaceable species.
Reference: Nature 436, 1016 (2005)