♪ BOB: I moved to Seattle.
I'd barely been in the state of Washington.
I basically hadn't seen any of the Pacific Coast ecosystems.
I was totally naive.
But I knew what I wanted to do.
(wave rippling) (underwater sounds) (splashing sound) ♪ I discovered that if you remove the starfish, the system breaks down.
I realized all species don't have the same impact on the system they're in.
Some were important, others aren't.
(underwater sounds) ♪ MARY: Keystones hold a whole ecosystem together.
Even though they are a very little part of that structure.
JOHN: Bob Paine was the first one to show it.
When you remove the keystone species then the ecosystem and the biodiversity collapses.
And that applies to virtually all systems.
TONY: Bob Paine introduced me to the whole idea of keystones.
He found out the rules of how ecosystems work, and it was a seismic event in ecology.
BOB: This is an interesting idea.
What species matter and what don't.
Some fish make a big difference in lakes.
It turns out, on the plains of Africa, lions and leopards do make a difference.
If you remove them, and the system changes dramatically.
The message is clear, and it's been enormously important in how ecologists tend to view the world.
♪ Single species do matter.
♪ (underwater sound)