Jared Diamond has popularized the use of Easter Island as a model of ecologically driven social collapse brought about by unsustainable consumption (Easter Island's End , Discover, August 1995). He argues that the original inhabitants overharvested the available resource base. The result was disaster:
All these strands of evidence can be wound into a coherent narrative of a society's decline and fall. The first Polynesian colonists found themselves on an island with fertile soil, abundant food, bountiful building materials, ample lebensraum, and all the prerequisites for comfortable living. They prospered and multiplied.
After a few centuries, they began erecting stone statues on platforms, like the ones their Polynesian forebears had carved. With passing years, the statues and platforms became larger and larger, and the statues began sporting ten-ton red crowns-probably in an escalating spiral of one-upmanship, as rival clans tried to surpass each other with shows of wealth and power. ...
Eventually Easter's growing population was cutting the forest more rapidly than the forest was regenerating. The people used the land for gardens and the wood for fuel, canoes, and houses-and, of course, for lugging statues. As forest disappeared, the islanders ran out of timber and rope to transport and erect their statues. Life became more uncomfortable-springs and streams dried up, and wood was no longer available for fires.
People also found it harder to fill their stomachs, as land birds, large sea snails, and many seabirds disappeared. Because timber for building seagoing canoes vanished, fish catches declined and porpoises disappeared from the table. Crop yields also declined, since deforestation allowed the soil to be eroded by rain and wind, dried by the sun, and its nutrients to be leeched from it. Intensified chicken production and cannibalism replaced only part of all those lost foods. Preserved statuettes with sunken cheeks and visible ribs suggest that people were starving.
With the disappearance of food surpluses, Easter Island could no longer feed the chiefs, bureaucrats, and priests who had kept a complex society running. Surviving islanders described to early European visitors how local chaos replaced centralized government and a warrior class took over from the hereditary chiefs. The stone points of spears and daggers, made by the warriors during their heyday in the 1600s and 1700s, still litter the ground of Easter today. By around 1700, the population began to crash toward between one-quarter and one-tenth of its former number. People took to living in caves for protection against their enemies. Around 1770 rival clans started to topple each other's statues, breaking the heads off. By 1864 the last statue had been thrown down and desecrated.
Terry Hunt, an archaeologist working on Easter Island, thinks that new evidence makes it necessary to revise the story, a lot. For example, Diamond puts people on the island by 400 AD, while Hunt's work doesn't put them there before 1200.
Hunt points to a likely cause or contributory cause for the deforestation, an invasive species. Rats, brought to the island by the original settlers, played a big role in destroying the trees: Rethinking the Fall of Easter Island (American Scientist, Sept-Oct 2006).
The first settlers arrived from other Polynesian islands around 1200 A.D. Their numbers grew quickly, perhaps at about three percent annually, which would be similar to the rapid growth shown to have taken place elsewhere in the Pacific... For Rapa Nui, three percent annual growth would mean that a colonizing population of 50 would have grown to more than a thousand in about a century. The rat population would have exploded even more quickly, and the combination of humans cutting down trees and rats eating the seeds would have led to rapid deforestation. Thus, in my view, there was no extended period during which the human population lived in some sort of idyllic balance with the fragile environment.
It also appears that the islanders began building moai and ahu soon after reaching the island. The human population probably reached a maximum of about 3,000, perhaps a bit higher, around 1350 A.D. and remained fairly stable until the arrival of Europeans. The environmental limitations of Rapa Nui would have kept the population from growing much larger. By the time Roggeveen arrived in 1722, most of the island's trees were gone, but deforestation did not trigger societal collapse, as Diamond and others have argued.
There is no reliable evidence that the island's population ever grew as large as 15,000 or more, and the actual downfall of the Rapanui resulted not from internal strife but from contact with Europeans....
Newly introduced diseases, conflict with European invaders and enslavement followed over the next century and a half, and these were the chief causes of the collapse. In the early 1860s, more than a thousand Rapanui were taken from the island as slaves, and by the late 1870s the number of native islanders numbered only around 100...
...It was genocide, not ecocide, that caused the demise of the Rapanui. An ecological catastrophe did occur on Rapa Nui, but it was the result of a number of factors, not just human short-sightedness.
Invasive species are a negative externality of international trade. Michael Margolis and Jason Shogren look at How Trade Politics Affect Invasive Species Control (Resources for the Future, Jan 2004), and with Eric Buhle, Margolis, and Jennifer Ruesink consider the Bang for the Buck: Cost-Effective Control of Invasive Species with Different Life Histories (Resources for the Future, April 2004).
We worry about invasive species in Alaska. Rats could cause a lot of damage if they were introduced into an Aleutian or Bering Sea island with borrowing or cliff dwelling bird colonies. For example, rats were introduced on Kiska Island during the last world war: Assessing the Effects of Introducted Norway Rats (Rattus Norvegicus) on Survivial and Productivity of Least Auklets (Aethia Pusilla) (although its interesting that the least auklets weren't driven to extinction in the ~55 years since rats were introduced).
Minor revisions Aug 16.