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Confirmed: Stress Gradient Hypothesis: How Plant Communities Endure Stress

By Guest PostFebruary 5, 2013Natureandrew altieri, barnacles, brown university ecologist, caribbean coral reefs, China, climatic zones, ecology letters, ecosystem, environmental stress, global meta analysis, growth responses, heat stress, high stress, highly competitive species, hypothesis in 1994, iology at brown, jiao tong university, less competitive species, mark bertness, mussel beds, negative interactions, organisms, patagonia, predictive value, qiang he, ray callaway, reduction in competition, rhode island, rule of thumb, salt marshes, santa barbara, sardinian sand dunes, sea grass beds, seaweeds, shanghai, shift to facilitation, shores, soil moisture, stress gradient hypothesis, stress increase, stress types, survival responses, university of california, university of montana

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.

PROVIDENCE, R.I. [Brown University] — 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. (more…)

Airborne Technology Helps Manage Elephants

Washington, D.C. – For years, scientists have debated how big a role elephants play in toppling trees in South African savannas. Tree loss is a natural process, but it is increasing in some regions, with cascading effects on the habitat for many other species. Using high resolution 3-D mapping, Carnegie scientists have for the first time quantitatively determined tree losses across savannas of Kruger National Park. They found that elephants are the primary agents—their browsing habits knock trees over at a rate averaging 6 times higher than in areas inaccessible to them. The research also found that elephants prefer toppling trees in the 16-to-30 foot (5-8 m) range, with annual losses of up to 20% in these height classes. The findings, published in Ecology Letters, bolster our understanding of elephant conservation needs and their impacts, and the results could help to improve savanna management practices.

“Previous field studies gave us important clues that elephants are a key driver of tree losses, but our airborne 3-D mapping approach was the only way to fully understand the impacts of elephants across a wide range of environmental conditions found in savannas,” commented lead author Greg Asner of Carnegie’s Department of Global Ecology. “Our maps show that elephants clearly toppled medium-sized trees, creating an “elephant trap” for the vegetation. These elephant-driven tree losses have a ripple effect across the ecosystem, including how much carbon is sequestered from the atmosphere.” (more…)

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Confirmed: Stress Gradient Hypothesis: How Plant Communities Endure Stress

Airborne Technology Helps Manage Elephants