t's not quite eight in the morning, and the only people out in Tucson's Reid Park on this Sunday in early May are a few joggers and cyclists hurrying to finish their workouts before the sun gets any higher. It's already 80 degrees under a shockingly clear blue sky, and the light is rapidly turning mean. The park itself is pleasant and uninspiring, a well-watered lawn ringed by trees and dotted with picnic tables. It seems an unlikely place to glimpse the future of conservation science, but that's what I've been promised.
When I pull into the mostly empty parking lot, Mike Rosenzweig is already there, looking eager despite the heat, a battered pair of Zeiss Jena binoculars dangling from his neck. I'm barely out of my car before he's hustling me toward the rear of the lot, away from the park, toward what appears to be an unremarkable tangle of desert scrub. We sneak down the side of a dusty gully and, with an effect that's almost Secret Garden-like, are soon immersed in rich desert habitat. Shaded by paloverde and tamarisk trees, we walk along the bottom of the gully, listening to the songs of dozens of bird species that fill the morning air. At our approach, a jackrabbit scurries behind a yellow-flowering prickly pear, but a gila woodpecker clinging to the side of a saguaro keeps up its rat-a-tatting.
There's so much wildlife here that it feels as if we could be wandering through nearby Saguaro National Park, but we're not. We're in a suburban subdivision only two miles from downtown Tucson. This, Rosenzweig tells me, is the Arroyo Chico wash. Tucson's washes are vital to protecting the city from flash floods. Thirty years ago, developers and city officials thought they'd spruce up the washes by getting rid of the messy desert vegetation and encasing them in concrete. But this created a sluicing effect: Water tore through one part of town only to compound flooding elsewhere. In the past decade, the city has been working to preserve its remaining natural washes and to restore the others.
Rosenzweig is a professor of ecology and evolutionary biology at the University of Arizona, and being outdoors with him is a humbling experience. He seems to know the name of every bird, plant, lizard, and small burrowing mammal we see, and he has a preternatural ability to spot living creatures, like the black-chinned hummingbird perched in a tree 50 feet away that I would have sworn was a leaf. The effect of all this naming is dazzling, like light through a prism. Everything is separated out from the collective mass of "nature" to form a beautifully complex picture of diversity.
"It's a Harris's hawk," Rosenzweig exclaims, and without taking his ancient binoculars from around his neck, he thrusts them into my hands. I get my focus just in time to see the bird land in a distant bank of eucalyptus trees. Harris's hawks were rare in town in the mid-1970s, when Rosenzweig and his wife, Carole, first moved to Tucson, but they have become more prevalent in recent years. They are just one example of a native species that has learned, Rosenzweig says, to like living around people. And it's this kind of adaptability, coupled with our efforts to encourage it, that he believes could save the majority of the world's species from extinction.
ike most conservation scientists, Rosenzweig thinks we're living in the midst of a "mass extinction event." It's the sixth such die-off of species, but the first attributable to humans. This might seem cause for despair, especially for someone who once traveled 14,000 miles just to see some rare Japanese Tancho cranes. But in the Arroyo Chico wash, Rosenzweig sees an example of what he calls reconciliation ecology: a landscape that serves essential human needs while at the same time providing habitat for a good number of native species. With a mix of almost religious zeal and American can-do-ism, Rosenzweig is working to become the Johnny Appleseed of reconciliation ecology, a role for which he seems particularly well suited. Underneath a white beard that suffers from absentminded neglect, he has the honest, unguarded face of an optimist. His eyes seem to twinkle, as if he's about to impart a piece of good news.
Rosenzweig says he first became aware of the potential of reconciliation ecology several years ago, when he became "very depressed" after writing a textbook on species diversity. In a rapidly developing world, conservation biologists are dogged by the question of how much land needs to be protected in order to save as many of the world's species as possible from extinction. The theory that about half the earth's species could do fine on a mere quarter of its surface, based on work published more than 40 years ago by Frank Preston, has given a perverse sense of hope to some conservationists ("Look, we don't have to save as much as we thought"). The discovery of "hot spots" in the 1990s -- relatively small but superproductive habitats that house a disproportionate number of species -- only fueled that hope. The U.S.-based nonprofit Conservation International now claims, for example, that by protecting only 2 percent of the planet, we could save more than a third of the world's plants and animals.
Rosenzweig, meanwhile, was analyzing lists of species and crunching the numbers himself. "I was looking at flowering plants, ferns, insects, mammals, birds, cave fauna," he says. "I looked at data from islands, from chunks of mainland, whatever I could get." He also studied fossil records going back 400 million years. What he found confirmed his expectations: Because the earth is so dynamic, what were hot spots ages ago aren't necessarily hot spots today, and we have no way of predicting whether the hot spots we protect today will continue to be hot spots in the future, especially in the face of something as drastic as global warming.
The relationship between biodiversity and area, he concluded, is far more linear than scientists had supposed. In other words, if we protect only 2 percent of the earth's surface, we can expect to save only 2 percent of the planet's species. At first Rosenzweig was alarmed by these results, until he began to see anecdotal evidence of species that had adapted surprisingly well to living alongside humans -- and not just Canada geese, pigeons, kudzu, and rats. He decided that conservationists were, in some ways, asking the wrong question. People may be destroying wild habitats, but that doesn't necessarily equate with destroying species.