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The collapse of the Easter Island's civilisation is often used as a cautionary tale to show the folly of humans who overexploit their surroundings, but scientists have now discovered what allowed the ancient inhabitants to flourish in the first place.

Tiny plant fossils preserved in the dental plaque on teeth found among human remains on the remote Pacific island have revealed what the doomed civilisation ate - sweet potato.

Scientists found starch grains from the popular tuber embedded in the hardened plaque from a selection of teeth from inhabitants of the island between the 14th and end of the 19th century.

Microfossils embedded in the dental plaque of ancient human teeth show early inhabitants of Easter Island ate a diet dominated by starch from sweet potato

They claim that the starchy, sweet tasting vegetable formed the predominant part of the islander's diet and was also a major source of water for them.

They believe the original Polynesian settlers brought the vegetable with them when they first arrived on Easter Island, or Rapa Nui as it is also known, sometime before the 1200 AD.

However, the study may also help to explain what led to the ultimate downfall of the civilisation that once flourished on Easter Island.

It is thought that the flourishing Rapa Nui civilisation, which numbered more than 15,000 at its peak, destroyed the trees that covered the island, leading to wars over dwindling resources.

Grains of silica from the palm trees that were once common over the island were found in the dental plaque of the ancient inhabitants, leading to claims that they had used them for food.

However, the latest research shows no sign of starch from palm trees on the teeth and that the palm fossils can actually become incorporated into the skin of sweet potatoes grown on the same ground.

This suggests that as the population grew, the islanders cut down the palm forest to make create land where they could grow their crops of sweet potatoes.

Monica Tromp, an anatomist at the University of Otago in New Zealand who conducted the work, said: 'By about AD 1500 the palm forest that covered most of the island was eradicated.

'The historic and modern aspect of the landscape is one of low-lying grasses, sedges and invasive shrubs, leaving no visible evidence of the extinct palm thought to have been dominant.

'The consistency of microfossils recovered from the dental calculus suggest that the plant component of the Rapa Nui diet probably did not change much through time.

'This would be expected as cultivation strategies of the sweet potato crops in the marginal Rapa Nui environment were refined over time.

'Sweet potato does not require processing or cooking before eating, and indeed was probably eaten raw as a source of both carbohydrates and water.' 

Easter Island is one of the most remote inhabited island in the world, more than 2,180 miles away from the coast of Chile and 1,289 miles from the nearest inhabited island. 

Cultivation of sweet potato may have given the inhabitants on Easter Island time to carve the distinctive stone moai heads that are the only visible signs left on the landscape of the once flourishing civilisation

Human teeth found at archaeological sites around the coast of Easter Island were studied by the scientists

Yet it is thought that shortly before 1200 AD, Polynesians sailed to the island and began to settle there, although some experts put the arrival of the first settlers as early as 800 AD.

The population on the island grew quickly as settlements were formed, thriving for hundreds of years.

It is thought that the rich and fertile land allowed the population time to develop a rich culture and gave them time to carve the distinctive moai stone heads that the island is now famous for. 

However, the destruction of the palm forests that covered the island led to much of the fertile soil washing away while the introduction of pests like the Pacific rat also damaged the natural wildlife.

It was thought that the trees were cut down to provide fuel and building material for the inhabitants.

But the latest findings, which are published in the Journal of Archaeological Science, suggest that they may have been cut down to make room for agricultural land for growing sweet potato.

By the time the first European explorers discovered the island in 1722, the population had dropped from around 15,000 to between 2,000 and 3,000 and the land was almost barren.

Starvation and war over the remaining resources are thought to have devastated the once stable civilisation and led to some of the famous stone heads being toppled. 

Grains of starch from sweet potato were found in the ancient dental plaque of teeth found on Easter Island

Easter Island now boasts a population of around 5,000 but by the time the second expedition of European explorers arrived at the island in 1877, its population had almost completely died out

Disease and slave raiding during the 19th century further reduced the population of the island to just over 100 by 1877.

Miss Tromp and her colleague Dr John Dudgeon from Idaho State University, studied 30 human teeth found with remains at archaeological sites around the island.

Embedded within the hardened dental plaque, also called dental calculus, were microscopic fossils from plants.

Initial work looking at these found the vast majority were microfossils, or phytoliths, from a species of palm tree (Paschalococos disperta) that went extinct shortly after the Polynesian's arrival.

However, further analysis also found starch grains that matched those from modern sweet potatoes.

The researchers also tested modern sweet potatoes grown in sediment similar to that of Easter Island and found that as the tubers grow, their skins incorporate palm phyotliths from the soil.

Miss Tromp said that it seemed likely that the sweet potatoes were brought to Easter Island by the first Polynesian settlers.

She said: 'The sweet potato starch grains were found on almost all of the teeth we looked at and so we think this is evidence that they had the sweet potato with them when the Polynesian settlers colonised the Island. It was not indigenous.

'We found palm phytoliths in a much larger quantity than the starch grains, which does support that there was once a large quantity of palm trees on Easter Island in the past.

'Phytoliths are usually found in every part of palm trees and so when they die their phytoliths are left behind in the soil indefinitely. 

'This does not necessarily mean that our research supports the conclusion that they were destroyed by humans - although there is other research that does support that conclusion.'

The scientists found that microfossils from palm trees can become incorporated into the skins of sweet potato, suggesting that the vegetables were grown in soil that had been cleared of palm trees