It's a paradox that's puzzled scientists for a half-century.
Models clearly show that the coexistence of competing species depends on those species responding differently to the availability of resources. Then why do studies comparing competing tree species draw a blank?
Competitors like black gums and red maples have coexisted for millennia in the shaded understories of eastern U.S. forests, yet species-level data offer scant proof that they respond differently to environmental fluctuations that limit access to light, soil moisture and other essential resources.
These are the very differences required for their long-term coexistence. Are the models and theory flawed? Or is it the data?
A paper in this week's issue of the journal Science offers new insights that may resolve the puzzle.
"Species differences do exist, consistent with theory, but species-level data don't show them," says forest ecologist James Clark of Duke University, the paper's author. In order to see them, he says, you have to go to the individual level.
"Scientists working to address pressing ecological issues, such as the spread of invasive species, will benefit from this finding," says Todd Crowl, program director in the National Science Foundation (NSF)'s Division of Environmental Biology, which funded the research.
Species-level studies--the preferred approach in nearly all past research on forest tree diversity--rely on average responses from sample populations to infer information such as average growth, reproduction and survival rates for entire species over time.
They're useful for many purposes, Clark says, but because they assess species' responses in only the handful of environmental dimensions that can be measured, they miss most of the subtle ways in which species differ.
"The environment varies in thousands of ways," he says. "Species can differ in how they respond in all these dimensions, a
|Contact: Cheryl Dybas|
National Science Foundation