By SIMON ROMERO

c.2009 New York Times News Service

PUERTO AYORA, Galapagos Islands - The mounds of reeking garbage on the edge of this settlement 600 miles off Ecuador's Pacific coast are proof that one species is thriving on the fragile archipelago whose unique wildlife inspired Darwin's theory of evolution: man.

Tiny gray finches, descendants of birds that were crucial to his thesis, flutter around the dump, which serves a growing town of Ecuadoreans who have moved here to work in the islands' thriving tourist industry.

The burgeoning human population of the Galapagos, which doubled to about 30,000 in the last decade, has unnerved environmentalists. They point to evidence that the growth is already harming the ecosystem that allowed the islands' more famous inhabitants - among them giant tortoises and boobies with brightly colored webbed feet - to evolve in isolation before mainlanders started colonizing the islands more than a century ago.

The growth has become enough of a threat to the environment that even the government, which still welcomes growth in the tourism industry, has begun taking the politically unpopular step of expelling hundreds of poor Ecuadoreans from a province that they feel is rightfully theirs.

By limiting the population, officials hope to preserve the natural wonders that bolster one of Ecuador's most profitable sectors: tourism. But the new measures are also feeding a backlash among unskilled migrants who say they feel they are being punished while the country continues to enjoy the tens of millions of dollars that tourists bring to Ecuador, one of South America's poorest nations.

"We are being told that a tortoise for a rich foreigner to photograph is worth more than an Ecuadorean citizen," said Maria Mariana de Reina Bustos, 54, a migrant from Ambato in Ecuador's central Andean valley, whose 22-year-old daughter, Olga, was recently rounded up by the police near the slum of La Cascada and put on a plane to the mainland.

The first settlers came to the islands to live off the land; working as fishermen and ranchers and farmers. Now, most of those who make the short flight from Quito, the capital, or sneak on the islands in boats, are lured by different sorts of riches: the relatively high wages they can earn as taxi drivers and maids or workers in the islands' growing bureaucracy.

For decades, the country's leaders did little to prevent people from coming here, partly to build the tourist industry and, then, to ensure the government had a presence among the pioneers. There seemed to be something of a natural limit on growth: The country had put aside 97 percent of the archipelago as a park.

But as tourism and migration grew over the last decade, pressure began building within the archipelago's scientific and environmental community and abroad for Ecuador to act on curbing the island's population. The United Nations put the Galapagos on its list of endangered heritage sites in 2007.

Scientists here said people have already done significant damage, pointing to fuel spills, the poaching of giant tortoises and sharks and the introduction of invasive species - including rats, cattle and fire ants - that threaten animals endemic to the Galapagos.

Even seemingly benign human activities - like owning a pet - can have outsized consequences here.

"With people come cats, and with cats come threats to other animals found nowhere else in the world," said Fernando Ortiz, coordinator of the Galapagos program for Conservation International.

Conflict is built into the rules that allowed Galapagos to be colonized in the first place, despite a lack of fresh water in the archipelago. Technically, residency is granted to a limited number of people, including those born here and their spouses, people who arrived before 1998, and those with temporary work permits. Police, known in local slang as the "migra" - for their role in tracking down illegal migrants, set up impromptu checkpoints throughout the islands. But the same government that pays the police's wages also offers subsidies that started when Ecuador was interested in building the population. One subsidy allows gasoline to cost about the same here as on the mainland. Another allows residents to fly between the islands or to Quito for a fraction of what foreigners pay. Loopholes also flourish. For instance, a black market in residency thrives in which migrants marry established residents to obtain coveted identity cards.

The result: Puerto Ayora's streets beckon with discotheques, food stands and souvenir shops. On the outskirts, a billboard with the image of Leopoldo Bucheli, the pro-development mayor, celebrates a project called El Mirador that is clearing an area on the edge of town to build 1,000 new homes.

"All we want, like people anywhere on this planet, is a dignified existence," said Yonny Mantuano, 36, who bought a lot to build a home at El Mirador.

The government's somewhat schizophrenic view of life here is echoed by the sentiments of the people. Margarita Masaquiza, 45, an Indian from Ecuador's highlands who arrived here at the age of 14, abhors the government's expulsions.

"We built this province with our own hands, so, yes, it pains us to see our countrymen deported like animals," said Masaquiza. "After all, we are indigenous Ecuadoreans, how can we be illegal in our own country?"

But when asked how she felt about the impact of new migrants on her four children and four grandchildren, Masaquiza adopted a different tone.

"We must preserve opportunities for our families," she said.

Most people in Galapagos live on San Cristobal, an island where a penal colony functioned decades ago, and Santa Cruz, where Puerto Ayora is located. Development is spreading to other parts of the archipelago, as well. Isabela, the largest of the islands, offers a glimpse into the Galapagos frontier.

Despite its streets of sand, Puerto Villamil, Isabela's main town, looks not unlike a Phoenix subdivision circa 2007. Laborers work feverishly on 200 new cinderblock homes on the town's edge. Only about 2,000 people live in the town, but it boasts one of the Galapagos' highest rates of population growth, about 9 percent a year.

"I earn $1,200 a month here, while I could only earn $500 a month on the continent," said Bolivar Buri, 26, a construction worker born in Puerto Villamil who made a small fortune this year when he sold an empty lot for $8,000 that he bought six years ago for $600.

But even in the island's less spoiled areas, there is little doubt that this is not the land that Darwin left.

On the road from Puerto Villamil to the drizzle-shrouded crater of Sierra Negra volcano, subsistence hunters on horseback scan the forest for wild pigs, a species introduced by mariners over a century ago. White cattle egrets, another introduced species, fly overhead.

One recent day, Manuel Lopez, a cowboy and migrant from the mainland who tends a herd under the volcano's mist, emerged from a forest thick with guava trees.

He paused under the equatorial sun; his gaze narrowed.

"If it is God's will, I'm on this island to stay," said Lopez, 36.

"We must be in Galapagos for a reason," he said, prodding a visitor to reply. "Yes or no?"