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10 million species live on planet Earth. Each one is remarkable. But, none can survive on its own. All life depends upon connections… Unexpected, invariably complex, beautiful relationships between millions of plants and animals.

This time, in our grasslands, I want to show you why these antelope need these rhino… Why this lone wolf needs an ant. And the incredible secret that lies buried beneath them all. Connections like these create the planets great ecosystems. They are vital for all life.

I want to show you our world as you've never seen it before.

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Central Kenya… And this is whistling acacia grassland. The whistling actually comes from the breeze blowing across the holes in these hollow galls… And they're home to one of the grasslands most intriguing creatures. This lizard is the aptly named dwarf gecko, and this one has laid a couple of eggs down here in this gall on the tree. The perfect place for a nest, you might think. But this tiny lizard can only safely lay its eggs here thanks to one of Africa's largest most iconic and bizarre animals, the giraffe.

The story of why the gecko needs the giraffe is wonderful, and it will take us on a journey across the world, to some of our most breathtaking grasslands. They are habitats which occupy a quarter of the land surface of our planet.

They support some of the most spectacular wildlife… And yet grasslands lack one of the basic ingredients for life… A truly precious element. It's this – nitrogen, a colourless, tasteless gas. Is only when we chill it down to 196° below zero that we can actually see it.

Giraffes

I can tell you that almost everything that happens out here in this grassland ecosystems is governed by a craving for this rare resource. In fact, I'd go so far as to say that grasslands can only function because they can cope so ingenuously with so little of it. So, for once, perhaps this will make ecologists job a little easier, because to understand how grasslands work, all we need to do is follow the nitrogen.