LLNL study finds current lemurs retreated to riparian environs

May 31, 2012

LLNL study finds current lemurs retreated to riparian environs

The extinction of several species of lemurs has had a profound effect on the lemurs of today.

In a new study appearing in the Proceedings of the Royal Society B, researchers have found that the extinction of at least 17 species of lemurs during the last 2,000 years in Madagascar has helped determine where today's lemurs are living and breeding.

The study may provide insight into the prevention of extinction of modern day lemurs.

"Factors surrounding extinction may force surviving species into marginal or previously unfilled niches of vacant land," said Brooke Crowley, now at the University of Cincinnati who conducted most of her research at the University of California, Santa Cruz and also at Lawrence Livermore National Laboratory.

The researchers, including Livermore's Tom Guilderson and Paula Zermeno, used the Lab's Center for Accelerator Mass Spectrometry to radiocarbon date temporal shifts in the niches of current lemur species following the extinction of eight large-bodied species.

Focusing their research on southwestern Madagascar, the team found profound isotopic shifts, both from the time when now-extinct lemurs abounded and from the time immediately following their decline to the present. (Isotopes are variants of a particular chemical element.) In this case, the researchers used carbon 13 and nitrogen 15 isotopes to determine the diets of extinct and current lemurs.

Researchers said that past lemur environments were drier than the protected, yet often degraded, riparian habitats that are used by lemurs today.

The cause of lemur extinction in Madagascar is debated, but humans were probably a central factor, the study states. The research team discovered that if the ecosystem of now extinct lemurs collapsed, it may have forced survivors to exploit new habitats and resources followed by a community-wide shift into marginal or previously new living areas

Guilderson and Crowley were able to date the carbon and nitrogen content of both extinct lemur diets as well as current lemurs. They found the lemurs that live in cool, moist locations and consume carbon 3 rich plants have lower carbon 13 and nitrogen 15 values than those living in hot, dry locations and consuming different plants.

They used carbon and nitrogen isotope data from bone collagen from four living species (ring-tailed lemurs, sportive lemurs, mouse lemurs and sifakas) and eight extinct species from six locations in the Spiny Thicket Ecoregion of southern Madagascar. They also analyzed fur and bone from each of the modern species from a single inland riparian forest.

Lemur species from 900 years ago fed in drier, open habitats that cover the majority of southwestern Madagascar today.

"The majority of extinct lemurs lived in areas that weren't necessarily close to rivers, so they likely were able to exploit dry habitats," Crowley said.

"Contrary to the long-held belief that the current lemur population is highest in riparian forests because those habitats harbor the best lemur resources, modern lemurs may prefer these habitats simply because they offer the greatest protection."

Other institutions include the University of Massachusetts, UC Santa Cruz and Dartmouth College. The work was funded by the University of California Office of the President through the UC-lab-fee program, the David and Lucile Packard Foundation, and the National Science Foundation.