Accurate Species Diversity Models Critical to Conservation Progress

May 6, 2004
© AScribe

DURHAM, N.C., May 6 (AScribe Newswire) -- Two ecologists have cited an urgent need for scientists advocating differing ecological models of species diversity to cooperate, given that global warming and habitat loss are speeding the decline of species worldwide.

The ecologists decry the fact that in the face of such problems, many scientists remain preoccupied with a century-old academic debate that distracts them from the urgent need to find a new model or models that can more accurately predict diversity patterns.

In a commentary in the May 7, 2004, issue of Science, Duke University ecologist Stuart Pimm and University of New Mexico biologist James Brown review current hypotheses about diversity patterns that have divided ecologists, biologists and paleontologists since the 19th century. They suggest the differences between the three camps might not be as great as perceived. Pimm is the Doris Duke Professor of Conservation Ecology at Duke's Nicholas School of the Environment and Earth Sciences, and Brown is a professor of biology at the University of New Mexico.

"There are statistical and conceptual issues with all explanations of diversity," Pimm and Brown wrote. "Like beauty, what constitutes a more fundamental explanation often lies in the eye of the beholder."

At the heart of the debate, said the authors, are questions scientists have been asking since Darwin first observed one of the world's great concentrations of small-ranged species on the Galapagos Islands. Such questions, said Pimm and Brown, include why the tropics have more species than other latitudes and the role climate or history play in species' evolution, geographic range and extinction.

Most hypotheses reflect one of three different schools of thought, wrote Pimm and Brown.

The first perspective asserts that diversity is the result of ecological processes, such as a location's temperature and rainfall, which make the location a more productive incubator and nursery for species diversity.

The second approach emphasizes historical factors, arguing that species survive and multiply best in regions that have avoided the devastation of periodic ice ages.

The third approach, a relative newcomer, explains species richness as a simple, statistical consequence of the fact that some species have larger geographical ranges than others, wrote the authors. These ranges are more likely to overlap in the species' mid-domains, which are often, but not always, located on or near the equator. For instance, a species mid-domain could be halfway up a mountainside in the tropical forests of Madagascar, hundreds of miles from the equator.

Pimm and Brown argue that, rather than expending so much energy tearing down each other's models, scientists should be cooperating to create a new body of knowledge and find more accurate models for predicting diversity patterns.

"The most discouraging thing," Pimm said, "is that after several hundred years this question is still being debated, at a time when it really needs to be answered, given the accelerating disappearance of species in so many places."

"It's not an either-or proposition," he added. "The mid-domain hypothesis explains why South American bird diversity peaks equatorially, but then so do the other approaches. The validity of one hypothesis does not deny the validity of its alternatives. The patterns of biodiversity we observe today are likely to have multiple causes."

For more information, contact Stuart Pimm at 305-852-9749 or stuartpimm@aol.com or Tim Lucas at 919-613-8084 or tdlucas@duke.edu