Future of the Environment

This is how long it would take for nature to restore species to pre-human levels

One of some 1.5 million bats emerges from below the Congress Street Bridge near downtown Austin, Texas July 27, 2011, as they do every night in the summer, looking for food. The largest urban bat colony in the world lives below a bridge in Austin. The drought has killed off crops in Texas, and that in turn has killed off those delicious pests the Mexican free-tailed bats consider dinner. Each night they stream from under a bridge by the hundreds of thousands in a black cloud so large that it shows up on local weather radar. Picture taken July 27, 2011. REUTERS/Charlie L. Harper III (UNITED STATES - Tags: ANIMALS ENVIRONMENT) - RTR2PDN1

More than half of mammal species became extinct after human colonization in the Caribbean alone. Image: REUTERS/Charlie L. Harper III

Gregory Filiano
Media Relations Manager, Stony Brook Medicine
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Future of the Environment

More than half of mammal species went extinct after human colonization in the Caribbean alone. Can nature restore the numbers of species on islands to levels that existed before human arrival—and, if so—how long would it take for nature to regain this lost mammal diversity?

To answer these questions, researchers compiled data on 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, researchers say, because one-third have gone extinct in the Greater Antilles over the past 20,000 years.

While there is a debate as to what caused these extinctions, the largest wave of species loss came after the arrival of humans. It’s hard to know whether or not these extinctions would have happened even without humans, since the number of species on islands results from the balance between species gained through colonization and the formation of new species, and losses from natural extinction, says Liliana Dávalos, professor of ecology and evolution at Stony Brook University. So, the team implemented models—known as island biogeography—including these three processes and based on the evolutionary histories of species both alive and extinct.

The findings, published in Nature Ecology and Evolution, show that 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 allowed researchers to use computer simulations to find out how long it would take for natural processes to restore the number of species found only 20,000 years ago.

“Remarkably, it would take at least 8 million years to regain the species lost,” Dávalos says. “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.”

“Human-caused changes to Earth’s ecosystems are accelerating,” says Leslie Rissler, program director in the National Science Foundation’s Division of Environmental Biology. “This study offers important information on how those changes will affect the loss and recovery of species in the future.”

The National Science Foundation, the Alexander von Humboldt Foundation, the Brandenburg Ministry of Science, Research and Culture, the German Research to Valente, and the Netherlands Organisation for Scientific Research funded the work.

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