Intraspecies Diversity Helps Ecosystems, Study Says

National Geographic News
August 21, 2002

Though it has long been known by scientists that an ecosystem needs different kinds of plants and animals for optimal functioning, University of Georgia scientists have recently found that the genetic diversity of species within a habitat also affects ecosystem processes. "It is not just the quantity of species diversity that matters, it is also the quality of genetic diversity," said lead author Mike Madritch, an ecology doctoral student at UGA. Madritch studied carbon and nitrogen fluxes during decomposition of leaf litter and found a significant link between nutrient output and the genetic variation of the leaves.

The study was co-authored with Mark Hunter, associate professor of ecology at UGA, and published this week in the Ecological Society of America's journal, Ecology. The research was funded by the National Science Foundation and the Andrew W. Mellon Foundation.

The study was conducted on a turkey oak (Quercus laevis Walter) sandhills community at UGA's Savannah River Ecology Laboratory in Aiken, South Carolina, where Madritch and Hunter analyzed the decomposition of nine different single-tree litter treatments and one mixed treatment that contained litter from all nine trees of the same species. They found a marked difference in the amount of carbon and nitrogen released based upon the parentage of the leaf litter.

"Diversity matters," said Madritch. "Our study shows that bringing a species population back from the brink of extinction to its original levels would not have the same effect on the environment as if the species never faced being endangered in the first place. When you build back from an endangered population, you necessarily are building from a limited gene pool, and we found that the variety in the genetic make-up matters to the system."

The researchers found not only that a reduction in genetic biodiversity affects the way an ecosystem functions, but they also found that a loss in genetic diversity reduces the predictability of how an ecosystem will work.

Single-tree litter treatments did not always yield less carbon and nitrogen than the mixed treatment. Sometimes the single-tree treatments produced more nutrients and sometimes they produced less, but the researchers say the nutrients were always significantly different than the mixed-litter treatment.

"The alarming part of this discovery is that you cannot predict the effect that reduced genetic biodiversity will have on an ecosystem," said Hunter. "Therefore, deforestation is like playing Russian roulette with our future. We know that relying upon fewer trees to recycle nutrients will make a difference, but we don't know what kind of difference. It's a chance I don't think is worth taking."

Madritch and Hunter are convinced that conserving genetic diversity within a species is as important as conserving species diversity for maintaining ecosystem functions. "This research is especially important in the current mass extinction period," said Hunter. "Plants capture the energy that drives the planet. By continuing to destroy plant habitats, we reduce the available gene pool. In the end it could harm the biggest ecosystem of all: planet Earth."

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