How much is nature worth? A recent study in Kenya estimated that each lion in Amboseli National Park was worth $27,000 and each elephant herd $610,000 in tourist revenues a year. In Rwanda, the establishment of Volcanoes National Park -- where Dian Fossey worked with the endangered mountain gorillas -- not only saved the gorilla but has also become Rwanda's third largest source of foreign exchange, each gorilla worth some $10,000 in tourist dollars. And though few countries can boast such wildlife stars, it seems every developing nation worldwide is finding and promoting its natural attractions in the hope that the preservation of nature can prove more profitable than its exploitation.

In Central and South America, for example:

Tourism is now the third largest source of foreign exchange for Costa Rica, which has set aside 12 percent of its land for parks and reserves.

Belize has developed a marine park in an attempt to keep its extensive coral reef attractive to divers.

The Galapagos Islands and the rare forms of wildlife there bring a steadily increasing flow of foreign tourists and currency to Ecuador.

Brazil, touting its endangered rain forest, has developed tourism along the Amazon.

The new Nicaraguan government has set aside natural preserves to attract tourists: coral reefs, rain forests and white-water rivers.

In fact, nature preserves throughout the world and the conservation organizations that develop or manage them -- among them the Sierra Club, Conservation International, the Nature Conservancy and the World Wildlife Fund -- have hopes that tourism can be both a moral and financial boon to conservation. All subscribe to Sierra Club founder John Muir's idea that people who experience a place first-hand are more likely to be concerned with preserving it.

In Miami Beach in November, the week-long International Symposium on Ecotourism focused on how tourism can support preservation efforts in imperiled natural areas -- and, once the tourists come, how to prevent them from ruining the integrity of those very same places. The 300-plus symposium participants represented 28 countries and included tour operators, developers, environmentalists and government officials.

All the conferees related stories of the destructive power of tourism: Tourists diving and snorkeling on Caribbean coral reefs, for example, have severely damaged many of them by stepping on them, taking pieces of them and anchoring boats in them. Trekkers in Nepal have deforested whole trailsides for firewood. With no facilities for garbage disposal, many wilderness areas quickly become littered with the trash of less-than-conscientious visitors. Fishing for both food and sport may harm the ecology of small forest streams.

Along the Amazon in Brazil, new lodges bring in new tourists, which in turn promotes development. Douglas Trent, who as the head of Focus Tours in Bela Horizonte, Brazil, has led natural history tours in the Brazilian Amazon for the last several years, spoke of how tourism has brought the litter of civilization to the rain forest: plastic water bottles, trash bags and plastic nets and fishing line. Tourists harass the animals, swerve across the roads to kill anacondas, run boats close to rookeries to raise birds for photographers. Development along beach fronts or on unstable soils has caused erosion into streams.

And while locals might be expected to show concern about killing the area's allure, Trent has so far not found that to be the case. "The people who run the hotels don't care because they're booked -- everybody is making money."

This is not solely a third-world phenomenon. Tourism to Muir-inspired Yellowstone Park, for instance, has created uncontrolled growth and spiraling prices in the surrounding Montana communities.

Managers of a dozen or so wildlife preserves worldwide expressed concerns about the pressure from tour operators to increase the number of visitors allowed and to improve the tourist facilities, such as widening trails for larger groups of hikers or even for vehicles. In the Galapagos, for instance, the government has gradually increased the number of tourists it will allow on the islands. And as Dian Fossey's work with the gorillas became more publicized, Rwandan park authorities increased from six to 10 the size of groups allowed to view the gorillas. Just as hardy Muir found he had to make compromises and provide trails and eventually roads to get less rugged souls up into the mountains, the new ecotourists also require more creature comforts.

"The first question is always whether there are private bathrooms, and then air-conditioning," said Derry Bennett of the American Littoral Society, a coastal conservation group in Sandy Hook, N.J., that sponsors ecological tours. And while many tours still offer wilderness travel, trekking, canoeing and camping, as destinations become more popular, developers begin to build roads and lodges at or near the preserves. The increased number of tourists and the need for services can begin to strain the quality of the experience.

"You can't endlessly compromise," said Jon Kusler, executive director of the Association of Wetland Managers, one of the conference sponsors. "Because if you compromise too far, the resource goes and the tourists go with it."

"The preserve is like a baby," said Silvana Campello of the Nature Conservancy's program for Brazil in Washington. "You create it and then you take care of it. You can't tell a baby to go out and make money. I'm scared of people talking about development of reserves. I can see providing something for the tourist that puts up with a five-hour drive and the food at hand to see the birds and plants -- but that is only a limited number of people. And so these people will only contribute little to the needs of the preserve.

"For other people you have to build roads and hotels. My feeling is to concentrate your efforts on conservation and not development. Build the resorts someplace else. Because the problem is that once the money comes in, how do you say no more?"

William Aspinall, director of the Monteverde Cloud Forest Preserve in Costa Rica, said tour operators harangue him constantly about his controls on visitations, and even complained to the government about his reluctance to expand. Monteverde, however, is a private preserve; and although its maintenance is almost exclusively paid for by tourist entry fees, Aspinall said he is more interested in maintaining the integrity of the preserve than in increasing its cash flow. He said natives of the area have also had mixed feelings about the increased tourism, yet new lodges are being built and the area's first paved road is being planned.

The effects of ecotourism on the native culture of such usually rural areas was a major concern expressed at the conference, with participants agreeing that these effects may be the most far-reaching and difficult to manage.

"Ideally," said Richard Ryel of International Expeditions Inc., "ecotourism will give local inhabitants an economic base to enable them to preserve the local resource as a source of income." But the reality can be quite different.

Studies by the World Bank have found that under the best of circumstances, little more than half the money from tourism actually reaches the local level. "That was one reason," said Peter Riddleberger of the World Bank, "why we stopped funding tourism projects nearly a decade ago. Little of the money went to the poor of the countries, who ended up holding menial jobs at large resorts." In less developed areas, where large percentages of food, supplies and transportation must be brought from other areas, the locals receive as little as 10 percent of tourist revenues generated.

Such inequities can antagonize the local inhabitants, and create an unexpected backlash. For example, one participant told of a particularly insensitive tour operator in Ecuador who refused to allow his tour participants to patronize local businesses. When he built a tower to enable bird-watchers to get a view over the rain forest canopy, the local people clear-cut the forest in a wide swath around the tower, making it virtually useless.

And local cultures can be adversely affected in other ways. The creation of wildlife parks and preserves can cause local farmers to lose rights to traditional grazing and hunting lands. In other cases, social structures can change as locals are employed by burgeoning tourist facilities. Joe Peters, coordinator of international forestry programs at North Carolina State University, said that in Madagascar, locals hired as guides and paid $2 a day quickly accrued more wealth than anyone else in the village. The village elders lost prestige and the social life of the village began to change.

Mauricio Salazar, who runs a small nature lodge on his farm in the Atlantic lowlands of Costa Rica and came to the conference as representative of the local tourist board, also has found that the forces of big development usually win out over the efforts of local people to control the pace of tourism development. And as foreign interests take over local facilities, according to Salazar, the result is often "exploitation hiding behind the green mask of tourism."

For this reason, conference participants expressed only a wary enthusiasm for the possible entry of international funding agencies into the business of ecotourism. The U.S. Agency for International Development, for instance, sometimes working with conservation groups, has begun to fund ecotourism as alternative sustainable development projects in Third World countries.

The fear expressed at the conference was that the involvement of such agencies may support development that the tourist industry simply can't sustain, since tourism is a notoriously fickle industry, subject to whims of fashion, weather and (especially in developing countries) politics.

By the end of the conference, many conservationists seemed uneasy about the alliance between their own groups and tourist development interests. "I saw a lot of consultants hustling," said Carolyn Carr, an economist who works with the Sierra Club, a sponsor of the conference. "I saw them dreaming up projects without consultation with local people, and corraling governments and banks to fund them. And I'm not certain anyone is being very frank about the unreliable nature of tourism."

There is a limit, she allowed, to how much tourism can do. As Victor Emanuel, who sponsors worldwide tours for birdwatchers, put it, "Only certain areas have nature in a marketable package." For instance, while most of the mammal-rich African savannah is protected, only about 5 percent of the continent's 800,000 square miles of rain forest is equally secure. One researcher said that while a few square miles will satisfy the needs of tourism, reserves of 1,000 square miles are necessary for the preservation of rain forest ecology.

"And there are some places so fragile," said Carr, "we believe nobody should visit." Is ecotourism then being embraced too quickly?

The reversals of roles that ecotourism has already engendered were apparent at the conference. There were commercial tour operators boasting of untouched, untrammeled nature and conservationists trying to make it not only touchable but also commercial. "I'm concerned that all sorts of dubious characters are leaping onto the ecotourism bandwagon -- suddenly everyone is an ecotour operator," said the Sierra Club's Vivian Newman.

This balance of profits against numbers of tourists, Karen Ziffer of the Conservation Foundation told the conference, can be a troublesome complication. "True ecotourism based on true economic development can take a long time," she said, while market forces are looking for immediate satisfaction. She added that the wise approach must be broader from the beginning, for if nature and local development are dependent solely upon tourism, they may well be once again endangered after the ecotourists have all packed up and gone.

Nature, said Silvana Campello of the Nature Conservancy, is on a different kind of time schedule. "You can't look at it in the short term. It's like the man who wanted to build a cliffside hotel. The geologist told him the soil is not firm, it will fall. 'How long,' the developer wanted to know, 'will it take?' 'Sixty years,' said the geologist. 'Time enough,' said the other. Their time scales were totally different."

Elizabeth Boo, the World Wildlife Fund's ecotourism program officer, offered several recommendations for maintaining a perspective on ecotourism development: "Countries must pursue ways to gain the margin of benefit while minimizing the negative impacts." She added that countries should evaluate the role of nature tourism in their natural conservation and economic growth plans and coordinate those plans with park managers and local residents. Not every area, Boo pointed out, will be a "money maker," and that should not be the criterion on which an area is preserved. She agreed with Carr of the Sierra Club that some places should not be developed and that others could bear development in only a limited way. When it comes to that development, conservationists and tour operators ought to be called in to control the pace and the scale, according to Boo, and after development, tourists should be thoroughly educated in the values of the preserve.

Yet the possibility of ecologically sound tourism still attracts both nations and conservation groups because they believe the alternatives -- the destruction of the forests by lumbering, the expansion of mining or oil development -- will be far more damaging. Oswaldo Munoz, head of Nuevo Mundo Expeditions in Quito, Ecuador, made a plea for support of conservation efforts on his country's mainland, where the Ecuadoran rain forest is threatened by oil development and agriculture. Over the past 10 years, said Munoz, chain-saw imports have grown 600 percent and runoff from mining has wiped out the fish life in four river systems.

"The hope," said Vivian Newman, "is that ecotourism can buy a little more time."

Bruce Stutz is a New York writer who specializes in travel and natural history.