As Species Decline and Disappear, Predicting Diversity Patterns Takes on a New Urgency. But Which Models Should We Use?

In a new paper in Science, the Nicholas School’s Stuart Pimm argues that scientists should set aside century-old academic differences and work together to solve a more pressing, practical problem: Finding accurate diversity models to help slow the loss of endangered species and their habitats.

May 6, 2004/DURHAM, N.C. – When Charles Darwin first visited the Galapagos Islands, one of the world’s greatest concentrations of small-ranged species, he wrote, “This is where species are born.”

Today, it also is where species are dying.

The Galapagos and many other habitats that formerly were home to great concentrations of small-ranged species are now imperiled by global warming and the loss of their natural habitat. Their once-rich ranks of species are thinning, adding a new urgency to the quest of finding what many consider the Holy Grail of conservation ecology: A model, or models, that can more accurately predict diversity patterns.

But the scientists charged with finding solutions to the problem are caught up in a century-old academic debate that pits ecologists, biologists and paleontologists against one another rather than encouraging them to cross old lines and work together on an answer.

So writes Stuart Pimm, Doris Duke Professor of Conservation Ecology at the Nicholas School of the Environment and Earth Sciences at Duke University, in a commentary published in the May 7 issue of Science.

In the article, “Domains of Diversity,” Pimm and his co-author, James H. Brown, professor of biology at the University of New Mexico, review the strengths and shortcomings of historical and contemporary hypotheses about why the tropics have more species than other latitudes, and what role climate plays in species’ birth, geographic range and extinction.

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

Most hypotheses reflect one of three different schools of thought. The first asserts that diversity is the result of ecological processes, such as a location’s temperature and rainfall, which make it a more productive incubator and nursery for species diversity. The second approach places greater emphasis on 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. 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 of their energies tearing each other’s models down, scientists should be reaching across party lines to create a new body of knowledge and find new, more accurate models for predicting diversity patterns. “The most discouraging thing,” Pimm says, “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. The mid-domain hypothesis explains why South American bird diversity peaks equatorially, but then so do the other approaches,” he adds. “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.”

Contacts: Stuart Pimm, 305/852-9749 or stuartpimm@aol.com
Tim Lucas, 919/613-8084 or tdlucas@duke.edu