This is Scientific American 60 Second Science.

I'm Cynthia Graber.

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Plants thrive all over the planet, despite the fact that many animals love to snack on

them. Various hypotheses account for all those

plants. One is that predators kill enough plant-eating animals to give vegetation a

chance. Another is that plants develop physical and chemical means to defend

themselves.

Now researchers have teased out some of these factors in an East African savanna.

The Impala, an African antelope, eats grasses and trees and is itself eaten by wild dogs and leopards.

Impala often munch on a tree called the Acacia.

Some Acacia have thorns and some don't.

The researchers found that the Impala, perhaps not surprisingly,

prefer thorn-free acacia.

Also, the animals avoid woody areas where predators are more likely to hide.

And as a result, the thorn-free vulnerable acacia are more plentiful in woody areas with plenty of predators.

But the thorny Acacia are more numerous on the open savanna

where they need to defend themselves.

The study is in the journal Science.

The researchers say their findings show that both plant defenses

and carnivorous predators help plants thrive.

They also say that when humans influence, in part by eliminating large predators, we disrupt

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