It will take at least eight million years to restore species recently lost to extinction, according to a new study.

In Caribbean alone, more than half of the mammal species went extinct after human colonisation, said researchers from the Stony Brook University in the US.

Researchers compiled data on the New World leaf-nosed bats and their close relatives. These bats form an ecologically diverse group that includes the fishing bat, many fig-eating bats and vampire bats.

The group is ideal for studying the effects of recent extinction, as one-third of its species have become extinct in the Greater Antilles over the past 20,000 years, researchers said.

While there is a debate as to what caused these extinctions, the largest wave of species loss came after human arrival.

According to Liliana Davalos, professor at the Stony Brook University, it is hard to know whether or not these extinctions would have happened even without humans, as the number of species on islands results from the balance between species gained through colonisation and the formation of new species and losses from natural extinction.

Therefore, the team implemented models – known as island biogeography – including these three processes and based on the evolutionary histories of species both alive and extinct.

They found the number of species in the Greater Antilles had strong equilibrium tendencies over millions of years and recent extinctions had pulled the system away from this natural balance.

The tendency to equilibrium also enabled the team to use computer simulations to find out how long it would take for natural processes to restore the number of species found only 20 thousand years ago.

"Remarkably, it would take at least eight million years to regain the species lost," said Davalos.

"This incredibly long time required to restore diversity reveals the staggering consequences of extinctions, many caused by humans, on the long-term ecology of islands," Davalos added.

"Human-caused changes to Earth's ecosystems are accelerating," said Leslie Rissler from the US National Science Foundation's (NSF) Division of Environmental Biology.

"This study offers important information on how those changes will affect the loss and recovery of species in the future," said Rissler.

The study was published in the journal Nature Ecology and Evolution.