http://www.livescience.com/animalworld/060719_top_predators.html
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Top Predators Key to Ecosystem Survival, Study Shows
By Bjorn Carey
LiveScience Staff Writer
posted: 19 July 2006
01:00 pm ET
Top-level predators strike fear in the hearts of the animals they stalk. But when a deer is being mauled by a wolf, at least it can know that it's giving its life for the greater good.
A new study reveals how ecosystems crumble without the presence of top predators be keeping populations of key species from growing too large. It also provides a cautionary lesson to humans, who often remove top predators from the food chain, setting off an eventual collapse.
The study is detailed in the July 20 issue of the journal
Nature.
Food chain Whac-a-MoleBoom or bust
Removing a top predator can often alter the gentle balance of an entire ecosystem.
Here's an example of what can happen: When an area floods permanently and creates a series of islands, not all the islands have enough resources to support top predators. Top consumers are left to gobble up nutrients and experience a reproductive boom. The boom is felt throughout the system, though, as the booming species out-competes others, potentially driving the lesser species to extinction and reducing biodiversity.
Rooney refers to this type of ecosystem change as a "boom and bust cycle," when one species' population boom ultimately means another will bust. Bigger booms increased chances of a bust.
"With each bust, the population gets very close to zero, and its difficult getting back," he said.
Your role in all this
Humans often play a role in initiating boom and bust cycles by wiping out the top predator. For example, after gray wolves were hunted to near extinction in the United States, deer, elk, and other wolf-fearing forest critters had free reign and reproduced willy-nilly, gobbling up the vegetation that other consumers also relied on for food.
Or, more recently, researchers found that when fish stocks in the Atlantic Ocean are over fished, jellyfish populations boom. While jellyfish have few predators, removing the fish frees up an abundance of nutrients for the jellyfish to feast on.
Ecosystems provide us with the food we eat and help produce breathable air and clean water. But they're generally fragile and operate best when at a stable equilibrium, scientists say.
"These are our life support systems," Rooney said. "We're relying on them. This study points to the importance of top predators and that we need to be careful with how we deal with them." "
