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Want a green world? Save predators

Predators are the key to keeping the world green, as they keep the number of plant-eating herbivores under control, says a study.

india Updated: Feb 28, 2006 15:18 IST

Predators are the key to keeping the world green because they keep the number of plant-eating herbivores under control, says a study.

The study puts at rest a theory that plants protect themselves from herbivores through physical and chemical defences.

Researchers led by John Terborgh, a professor of environmental science at Duke University's Nicholas School of the Environment and Earth Sciences, monitored vegetation at 14 sites of different sizes at Caroni Valley in Venezuela.

Within Caroni Valley, an area of 4,300 sq km was flooded in 1986 to create a lake (Lago Guri) containing hundreds of islands that were formerly fragments of a continuous landscape.

 

While nine of the sites studied were on predator free islands, others were on the mainland or on islands with a number of predators, reported the science portal EurekAlert.

They found that by 1997, small sapling densities on small islands were only 37 percent of those on large land masses and by 2002 this had fallen to just 25 percent.

Most of the vertebrates present in regional dry forest ecosystem had disappeared from small islands, including fruit eaters and predators of vertebrates, leaving a hyper abundance of generalist herbivores such as iguanas, howler monkeys and leaf-cutter ants.

"Mere numbers do not do justice to the bizarre condition of herbivore-impacted islets," the authors wrote in the March 2006 issue of the British Ecological Society's Journal of Ecology.

Their findings confirm the answer to one of ecology's oldest and thorniest questions: why is the world green?