Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Confirmed: How plant communities endure stress

31.01.2013
The Stress Gradient Hypothesis holds that as stress increases in an ecosystem, mutually supportive interactions become more significant and negative interactions, such as competition, become less so.

The idea has been hotly debated but is now backed by a review of hundreds of studies co-authored in Ecology Letters by Mark Bertness, professor of biology at Brown, who first formally proposed the hypothesis in 1994. The time has come, he said, to test its application and predictive value.

Ecology is rife with predation, competition, and other dramatic “negative interactions,” but those alone do not determine the course life on Earth. Organisms sometimes benefit each other, too, and according to the Stress Gradient Hypothesis, their “positive interactions” become measurably more influential when ecosystems become threatened by conditions such as drought. Ecologists have argued about the hypothesis ever since Brown University ecologist Mark Bertness co-proposed it in 1994; Bertness says a large new global meta-analysis he co-authored in Ecology Letters definitively shows that it is true.

The evidence, principally analyzed by former Brown visiting graduate student Qiang He of Shanghai Jiao Tong University in China, comes from 206 studies of 727 shifts of plant interactions amid varying degrees, or gradients, of stress on six continents. Examining the data from each paper and contacting original authors when necessary, He determined the overall trends across the many experiments.

In the vast majority of studies, as stress increased, the significance of interactions shifted toward mutual support in that positive interactions, such as those that promoted neighbors’ survival, strengthened in influence, and negative interactions, such as those that hindered neighbors’ growth, weakened. In some studies, stress did not change interactions, but negative interactions never increased as stress did, no matter what kinds of plants were involved, what kinds of conditions they were under, or where they were.

Stress in Sardinian sand dunes

Grasses, trees and shrubs have obvious differences, but in times of stress their communities exhibit less negative competitive pressure and more facilitative, positive interaction.“Our results show that plant interactions generally change with increased environmental stress and always in the direction of an outright shift to facilitation (typical for survival responses) or a reduction in competition (typical from growth responses),” the authors wrote in the paper published online. “We never observed an increase in competition at higher stress. These findings were consistent across fitness measures, stress types, growth forms, life histories, origins, climatic zones, ecosystems and methodologies.”

Analyses of studies of grasses, trees, and shrubs, for example, found that despite the obvious differences among these plant types, they all shifted toward less negative or more positive interactions.

“Typically, highly competitive species [e.g., grasses] have decreased competitive or neutral effects at high stress, whereas less competitive species [e.g., trees] have strong facilitative effects at high stress,” the authors wrote.

Overall, the researchers found, studies with observations of greater degrees of stress increase — “longer” stress gradients — also observed greater degrees of shift toward positive interactions.

The hypothesis and the importance of positive interactions in ecology began to occur to Bertness in the 1970s and 1980s. As a junior faculty member at Brown, along the shores of Rhode Island, he noticed that seaweeds and barnacles would never survive the heat stress above the tides in isolation. They could only persist in groups, suggesting that with stress, organisms were better off together — despite their competition — than apart.

It’s the same reason why sparsely planted gardens wilt in hot, dry conditions while more densely planted gardens survive. Mutually beneficial soil shading becomes more important than competition for that soil moisture when it becomes scarce.

Bertness published the Stress Gradient Hypothesis in Trends in Ecological Evolution with Ray Callaway, then a graduate student at the University of California–Santa Barbara. Callaway is now a professor at the University of Montana.

A shift in research?

Mussel beds in Patagonia

Hundreds of studies over two decades from sites around the world suggest that the Stress Gradient Hypothesis can be employed as a rule of thumb. “We’re no longer in the casual, earlier stages of ecology,” says biologist Mark Bertness.Nearly two decades later with so much evidence now assembled, Bertness said, ecologists should feel confident enough in the Stress Gradient Hypothesis to employ it as a “rule of thumb.” Rather than continuing to debate whether the hypothesis is valid, he said, researchers could now focus on crafting experiments to probe how much predictive value the hypothesis has and test its applications to conservation biology.

The hypothesis suggests, for example, that marine ecosystem managers who want to help tropical fish should focus on sustaining foundational species in the ecosystem, such as corals. With the ecosystem’s foundation shored up the natural tendency among species toward greater positive interactions under stress should allow the fish to weather stress better.

“We’re no longer in the casual, earlier stages of ecology,” Bertness said. “In our lifetimes we’re watching Caribbean coral reefs die, kelp forests die, and salt marshes and sea grass beds being decimated. We need to figure this stuff out quickly. These are no longer intellectual arguments without consequence.”

In other words, with nature under stress, Bertness hopes that He’s efforts to pull together the available data will lead ecologists to pull together so that they can apply the guidance the hypothesis provides.

In addition to He and Bertness, the paper’s other author is Brown postdoctoral scholar Andrew Altieri.

He’s visiting scholarship at Brown was funded by the Shanghai Jiao Tong University Visiting Scholar Fellowship.

Editors: Brown University has a fiber link television studio available for domestic and international live and taped interviews, and maintains an ISDN line for radio interviews. For more information, call (401) 863-2476.

David Orenstein | EurekAlert!
Further information:
http://www.brown.edu

More articles from Ecology, The Environment and Conservation:

nachricht Scientists team up on study to save endangered African penguins
16.11.2017 | Florida Atlantic University

nachricht Climate change: Urban trees are growing faster worldwide
13.11.2017 | Technische Universität München

All articles from Ecology, The Environment and Conservation >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: A “cosmic snake” reveals the structure of remote galaxies

The formation of stars in distant galaxies is still largely unexplored. For the first time, astron-omers at the University of Geneva have now been able to closely observe a star system six billion light-years away. In doing so, they are confirming earlier simulations made by the University of Zurich. One special effect is made possible by the multiple reflections of images that run through the cosmos like a snake.

Today, astronomers have a pretty accurate idea of how stars were formed in the recent cosmic past. But do these laws also apply to older galaxies? For around a...

Im Focus: Visual intelligence is not the same as IQ

Just because someone is smart and well-motivated doesn't mean he or she can learn the visual skills needed to excel at tasks like matching fingerprints, interpreting medical X-rays, keeping track of aircraft on radar displays or forensic face matching.

That is the implication of a new study which shows for the first time that there is a broad range of differences in people's visual ability and that these...

Im Focus: Novel Nano-CT device creates high-resolution 3D-X-rays of tiny velvet worm legs

Computer Tomography (CT) is a standard procedure in hospitals, but so far, the technology has not been suitable for imaging extremely small objects. In PNAS, a team from the Technical University of Munich (TUM) describes a Nano-CT device that creates three-dimensional x-ray images at resolutions up to 100 nanometers. The first test application: Together with colleagues from the University of Kassel and Helmholtz-Zentrum Geesthacht the researchers analyzed the locomotory system of a velvet worm.

During a CT analysis, the object under investigation is x-rayed and a detector measures the respective amount of radiation absorbed from various angles....

Im Focus: Researchers Develop Data Bus for Quantum Computer

The quantum world is fragile; error correction codes are needed to protect the information stored in a quantum object from the deteriorating effects of noise. Quantum physicists in Innsbruck have developed a protocol to pass quantum information between differently encoded building blocks of a future quantum computer, such as processors and memories. Scientists may use this protocol in the future to build a data bus for quantum computers. The researchers have published their work in the journal Nature Communications.

Future quantum computers will be able to solve problems where conventional computers fail today. We are still far away from any large-scale implementation,...

Im Focus: Wrinkles give heat a jolt in pillared graphene

Rice University researchers test 3-D carbon nanostructures' thermal transport abilities

Pillared graphene would transfer heat better if the theoretical material had a few asymmetric junctions that caused wrinkles, according to Rice University...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Ecology Across Borders: International conference brings together 1,500 ecologists

15.11.2017 | Event News

Road into laboratory: Users discuss biaxial fatigue-testing for car and truck wheel

15.11.2017 | Event News

#Berlin5GWeek: The right network for Industry 4.0

30.10.2017 | Event News

 
Latest News

NASA detects solar flare pulses at Sun and Earth

17.11.2017 | Physics and Astronomy

NIST scientists discover how to switch liver cancer cell growth from 2-D to 3-D structures

17.11.2017 | Health and Medicine

The importance of biodiversity in forests could increase due to climate change

17.11.2017 | Studies and Analyses

VideoLinks
B2B-VideoLinks
More VideoLinks >>>