because the vegetation stabilized that as well.
So the wolves, small in number,
transformed not just the ecosystem
of the Yellowstone National Park, this huge area of land,
but also its physical geography.
Whales in the southern oceans
have similarly wide-ranging effects.
One of the many post-rational excuses
made by the Japanese government for killing whales
is that they said, "Well, the number of fish and krill will rise
and then there'll be more for people to eat."
Well, it's a stupid excuse, but it sort of
kind of makes sense, doesn't it,
because you'd think that whales eat huge amounts
of fish and krill, so obviously take the whales away,
there'll be more fish and krill.
But the opposite happened.
You take the whales away,
and the number of krill collapses.
Why would that possibly have happened?
Well, it now turns out that the whales are crucial