A forest without predators may not last long. When predators vanish, herbivore (plant eating) animal populations explode, leading to the mass destruction of plant life and eventually to the destruction of the forest itself.
A research team led by John Terborgh of Duke University made a census of the herbivores and trees on several islands in Lago Guri, a lake in Venezuela that was created in 1986 when a river was dammed to produce hydroelectric power. When the water rose, the smallest of the islands lost nearly all of its predatory animals, such as jaguars, snakes and hawks. The situation was a unique natural experiment, testing two competing theories of how ecosystems are structured.
The first theory, the so-called bottom-up theory, says that plants are in control and the availability of edible plants determines how many herbivores an ecosystem can support, which in turn determines how many predators it can support.
The other theory is the top-down theory, which argues that the predators are in charge. They keep the herbivores in check, thereby determining the abundance of plants.
The bottom-up theory says nothing much should have changed in the Lago Guri after the predators disappeared. But the team?s findings show that the absence of predators has had a profound effect on the islands? ecosystems.
They found that herbivores such as howler monkeys, iguanas and leaf-cutter ants were 10 to 100 times more prevalent on the lake?s six smallest islands than they were on the mainland. The density of young trees on these islands was less than half that on six larger islands in the lakes, which had retained some of their predators.
However, the pendulum could swing back to bottom-up if the herbivores gobble up all the edible plants on the islands. If that happens, the small number of remaining plants could limit animal populations.
The researchers say that predators play a key role in maintaining biodiversity. An overabundance of herbivores ?threatens to reduce species-rich forests to an odd collection of herbivore-resistant plants. Along the way, much plant and animal diversity will probably be lost.? This process is already happening in North America, where deer populations have greatly increased. To read more about this,click here.
Some naturalists are trying to deal with this problem by reintroducing predators such as coyotes and wolves into the wild. But how are humans supposed to defend themselves against these predators?
Troy Hurtubise of Ontario, Canada has one solution: a bear-proof suit. Fifteen years of tinkering and $100,000 have gone into the design of the suit, which incorporates plastic, rubber, chainmail, galvanized steel, titanium and thousands of feet of duct tape.
While wearing the suit, Troy has survived 18 collisions with a truck, being hit by a tree trunk, and many hits by arrows, bullets, axes and baseball bats. ?I?ve never had a bruise,? says Hurtubise.
But he?s never tested it against a real Grizzly bear. He plans to test it in a ?controlled attack? with a Kodiak bear, which will instructed by its handler to attack for 10 seconds. ?Real teeth, real claws, real power,? Hurtubrise says.
He expects the outside of the suit to be ripped to shreds. ?The suit?s a toy to the bear,? he says. ?He?ll make his way to the titanium.? Hurtubise feels the titanium layers around his chest, head and lower body will protect him. If there?s a weakness in the suit, it will be in the chainmail joints.
Hurtubise says he?s a bit anxious. ?Little things like trucks and baseball bats and axes and things – you don?t feel that,? he says. ?This is a bear.?
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