A test, not just a description
The claim is that conservation resources, which are always limited, can be directed more effectively by identifying a specific, bounded set of regions where the payoff per hectare protected is highest. Norman Myers proposed the biodiversity hotspot concept in articles published in 1988 and 1990, then formalised it with colleagues in a widely cited paper in Nature in 2000. Rather than describing biodiversity richness impressionistically, Myers set out an explicit quantitative test that a region either passes or fails, turning what could have been a subjective judgement about where nature is most valuable into a reproducible calculation that other researchers could check and apply themselves.
The two numbers that decide it
The test has two parts, and a region must satisfy both to qualify. First, it must contain at least 1,500 vascular plant species found nowhere else on Earth, representing over 0.5 percent of the world’s total vascular plant diversity, a bar meant to single out places of exceptional endemism rather than merely high overall species counts. Second, the region must already have lost at least 70 percent of its original primary vegetation, meaning the criteria deliberately combine irreplaceable biological richness with demonstrated, ongoing threat. A place can be extraordinarily diverse and still fail to qualify if it has not yet lost enough of its habitat, because the framework is built to prioritise urgency alongside richness.
Thirty-six places, a small footprint
Applying these two criteria worldwide identifies 36 regions as biodiversity hotspots. Collectively they cover only about 2.4 percent of Earth’s land surface today, yet they are estimated to support close to 60 percent of the world’s plant, bird, mammal, reptile and amphibian species, an extraordinary concentration relative to their area. Some individual hotspots hold as many as 15,000 endemic plant species, and several have already lost as much as 95 percent of their original vegetation, underscoring how much of their remaining extent is fragmentary rather than intact. Taken together, the 36 hotspots once covered a much larger share of global land area before habitat loss reduced them to their current extent.
Money follows the map
The framework’s influence has been substantial. Conservation organisations adopted the hotspot approach as a guide for where to concentrate limited funds, and by some accounts it has directed hundreds of millions of dollars toward these specific regions, among the largest sums ever committed to a single conservation strategy. Myers’s 2000 paper had been cited around 19,000 times by 2017, reflecting how deeply the concept became embedded in conservation science and practice, and Myers himself was recognised by Time magazine as a Hero of the Environment in 2007 largely on the strength of this work.
What the threshold leaves out
The approach has also drawn academic criticism. A 2003 analysis by Kareiva and Marvier argued that focusing narrowly on hotspots, defined by endemic species counts and habitat loss, neglects the cost-effectiveness of conservation spending in different regions and overlooks phylogenetic diversity, meaning how evolutionarily distinct a set of species is, rather than simply how many species there are. A hotspot rich in closely related species might, on this view, be prioritised over a less species-dense region that actually preserves more unique evolutionary lineages, a trade-off the original criteria do not directly address. This does not overturn the concept but marks a real limit on what a threshold built around two numbers can capture.
Myers’s wider record
Understanding this matters beyond biology because it is a working example of how a scientific definition becomes a policy instrument, translating a research paper directly into where conservation money actually gets spent. Myers’s broader career included other high-profile, sometimes contested estimates, including an early warning about tropical deforestation that satellite imagery later corroborated and a much-debated 1997 projection of fifty million environmental refugees by 2010, which he himself described as involving heroic extrapolation and which migration scholars later criticised. That mixed record is worth keeping in mind: the hotspot framework has proven durable and useful, but treating any single numerical threshold as the final word on conservation priority would be a mistake the underlying science does not itself endorse.