But a handful of protected areas will not be sufficient to save the countless species of plants and animals facing extinction worldwide, according to a new study by scientists from Stanford University and the National Autonomous University of Mexico (UNAM). Writing in the Dec. 15 online edition of the Proceedings of the National Academy of Sciences (PNAS), the researchers say that it's time for ecologists to reconsider the hotspot approach to conservation.

"Hotspots, which have played a central role in the selection of sites for reserves, require careful re-thinking," wrote Gerardo Ceballos, professor of ecology at UNAM, and Paul R. Ehrlich, the Bing Professor of Population Studies at Stanford, co-authors of the PNAS study. "Assigning global conservation priorities based on hotspots is at best a limited strategy."

The idea of funneling resources into biodiversity hotspots was proposed in 1988 and quickly adopted by Conservation International and other leading environmental groups. "Few topics in conservation biology have received as much attention as hotspots of species diversity," Ceballos and Ehrlich wrote. "Hotspots have been widely used to determine priority areas for conservation at different geographic scales and in recommending concentrating resources in those regions to maximize the number of protected species."

Hotspot criteria

Hotspot biodiversity is usually based on one of three factors-the number of total species (species richness), the number of unique or endemic species (endemism) or the number of species at risk.

According to Ceballos and Ehrlich, however, a critical assumption of hotspot ecology that has not been widely tested is the extent to which the three factors overlap on a global scale. "Wide overlap among these three types of hotspots implies the selection of fewer sites to represent all species and the possibility of using one of them as a surrogate for the others," they wrote.

For the PNAS study, the authors assessed the global distribution of 4,818 species of land mammals, with the goal of evaluating the "utility of hotspots for determining conservation priorities for the mammals of the world."

What they discovered is that there is actually very little overlap among the three types of hotspots-those defined by species richness, endemism or threat of extinction. In fact, only 16 percent of mammalian species were common to all three, according to the study.

"We found that if you use species richness as a criterion, you're not going to protect the endemic or endangered species," Ceballos explained. "So the 'hotspot' approach, which was extremely valuable in focusing attention on species diversity in the past, has limitations. What's needed is a more comprehensive analysis that also takes into account the species that live outside the hotspots."

Paper parks

According to the authors, most of the planet's biodiversity lies within developing countries, where habitat is often threatened by political instability. "And what reserves might have already been established in hotspots frequently are 'paper parks' or subject to local human population pressures," they wrote. "The likelihood of species migrations in response to global climate change adds further complexity to the development of conservation strategies, and further limits the present usefulness of the classic hotspot approach."

To date, ecologists have identified 34 biodiversity hotspots that cover about 15 percent of the surface Earth-areas such as the West African rainforest, Japan, California and the Mediterranean coastline. "But even if we can protect 10 percent of the Earth, which is the target set by the World Conservation Union [IUCN], we still won't prevent species extinctions," Ceballos said. "Most of the significant habitats that need protecting are outside of hotspots, and we should do a better job managing them properly."

The study was supported by UNAM, the John Simon Guggenheim Memorial Foundation, CONABIO (Mexico), the Stanford Center for Conservation Biology and the LuEsther T. Mertz-Gilmore Charitable Trust.

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