Whenever a habitat loses enough of the richness and variation among its living species, the study found, the ecological systems that nurture life begin to falter. Ecologists do not yet know how many species - or which ones - must be saved to keep an ecosystem functioning. They do know this: When ecosystems falter, they stop providing essential natural services like pure water from mountain watersheds, abundant fisheries, soul-sustaining landscapes. Damaged ecosystems also have global effects: Plants, for example, play an important role in the atmosphere's carbon cycle and thus in climate fluctuations.
"The urgency to quantify the roles that biodiversity plays in keeping ecosystems working well has spawned a whole new effort in science," said Stanford ecologist Harold Mooney, Secretary General of the International Council of Scientific Unions and a leader in the biodiversity study. "There are already compelling reasons to protect the diversity of life, but policymakers need more solid data to help them make hard choices about the consequences of decisions about issues such as land use."
On Saturday, Feb. 15, Mooney will describe the basic principles of that new scientific effort at the annual meeting of the American Association for the Advancement of Science in Seattle. He will speak at a session titled "The Global Biodiversity Assessment: The Importance of Biodiversity and Ecosystem Functioning," organized by Anthony C. Janetos of NASA. Other speakers will be plant biologist Chris Field, of the Carnegie Institute of Washington; ecologist Osvaldo E. Sala of the University of Buenos Aires; conservationist Walter V. Reid of the World Resources Institute; and Robert T. Watson of the World Bank.
Field, Janetos, Mooney and Sala are all scientific leaders of the ICSU biodiversity study, officially called the SCOPE study because it was conducted by the international Scientific Committee on Problems of the Environment. Watson chaired the international panel that organized the 1995 United Nations Global Biodiversity Assessment, where parts of the SCOPE study were first published. Mooney said at the AAAS meeting that Reid and Watson will discuss conservation and public policy issues, while the others will concentrate on what research needs to be done to find essential information about biodiversity and ecosystem function that those policies must depend on.
It is significant, Mooney said, that AAAS has organized a second session the following day on this topic, at which top ecologists and economists will discuss the economic and social value of ecosystems services - a value that is usually ignored in public policy planning. That session, "The Nature and Value of Ecosystem Services," has been organized by Oregon State University ecology Professor Jane Lubchenco, who is president of AAAS, with Stanford ecologist Gretchen Daily.
Mooney also pointed to a new book by science writer Yvonne Baskin, The Work of Nature (Island Press, 1997). It describes what the SCOPE scientists learned about the value of biodiversity, in language accessible to a lay audience.
Principles of biodiversity and ecosystems functioning"You'd think this would be a simple question: Does loss of biodiversity affect the function of ecosystems?"Mooney said. "But for some reason, until recently few scientists had focused on this issue."
It is not a new idea that environmental degradation and biotic destruction can damage essential natural services. Mooney credits his Stanford colleagues Paul and Anne Ehrlich as among the first scientists to introduce the topic, more than two decades ago. Most ecologists have become increasingly alarmed at the galloping loss of species around the world, and at threats to food, water and other supplies, Mooney said. "But until the past couple of years, very few of us took a detailed look at which services are provided by a functioning ecosystem, and how the loss of biodiversity can affect those services."
He said, however, that the SCOPE committee was able to make a preliminary study by reviewing the research of two kinds of scientists: those who study ecosystems and those who study population. "The new science of biodiversity and ecosystem functioning draws on the integration of these two approaches," he said. "Young scholars are already taking up the challenge of this new integrated scientific effort."
Mooney said that SCOPE drew several conclusions that may guide that effort.
- An ecosystem often can continue to function even after the loss of many of its native species, but at a price. The lack of genetic variability means that backup species are not available to take up the slack if essential life forms succumb to droughts, heat waves, bad weather or pest invasions. Without a "bank" of genetic variability to draw upon, crop breeders may not be able to respond quickly to new diseases.
- Some species have greater impact than others. Biologists have found "keystone" species that seem to disproportionately control the function of an ecosystem. One well-known example is the sea otter; when hunters removed otters from a coastal region, their favorite prey, the sea urchin, spread and decimated the local kelp forest, an essential nursery for the young of many sea animals. Keystones may be as small as a virus or as large as an elk, but without direct experimental research, it is difficult to predict which species is key to any given ecosystem.
When ecosystems are perturbed by adverse weather, human incursions or other assaults, the ones with the most species will be most resistant to collapse, and most likely to recover. Still to be discovered, Mooney said, is whether recovery is enhanced by the presence of many species, or many different types of species. It is costly to simplify an ecosystem. As an example, Mooney pointed to German farmers who recently began to tear out the hedgerows that bordered their fields. They lost the birds and insects that used to live there, and had to pay for chemicals to control crop pests that once were managed by the hedgerow-dwellers.
Simple ecosystems are especially vulnerable to disruptions. On small islands - for example, in the Hawaii chain and in the Arctic - the numbers of native species are small. The loss of even a few may leave some niches unfilled. On islands especially, invading species may have few competitors to halt their spread.
When an ecosystem is fragmented and disturbed, the flow of materials between sections of the landscape can be both disturbed and enhanced.
So far, attempts to reconstruct ecosystems have not been totally successful. "People have tried hard to fully restore a marsh and they can't do it," Mooney said. "They can't get it back to the way it was originally."
"This tells us that we ought to be prudent about practices that reduce diversity," Mooney said. "Unless we learn how to reconstruct ecosystems, we ought to be very careful before tearing them apart."
EDITORS: Mooney also is organizer of an AAAS session from 9:30 a.m. to 12:30 p.m. on Monday, Feb. 17: "Managing Marine Fisheries in an Ecosystem Context." Based on a 1996 study conducted for the National Research Council, the session will look at new ways to manage fisheries so they continue to provide food for the future.