This is the BBC.

Hello, my guest on the Life Scientific today has spent her life trying to measure the richness and diversity of the different species here on Earth.

And she's concerned.

When Anne McGarran began her career, counting moths in an ancient Irish woodland, the study of

biodiversity was a very young science.

We can all sense that a tropical rainforest is more diverse

than a field of wheat, but turning what we see in the natural world into a meaningful

statistic is a challenge. It's like an optical illusion, Anne says. The more you

think about biodiversity, the more difficult it is to define. That hasn't stopped

her from trying and in 2007 she set up biotime a global database of how

biodiversity has changed over time in many biological communities around the world.

The results of the study came as quite a surprise.

Professor Anne McGurran from St Andrews University, welcome to the life scientific.

Thank you very much.

Well, Anne, as I just mentioned, it's easy enough to see that some ecosystems are more diverse

than others but why are you so keen to measure biodiversity? Well biodiversity is really the essence of life. We evolved in this planet and we evolved with the

biodiversity around us so it's essential to sustain us. We depend on biodiversity for food, for medicines, for the environment, for well-being, for everything really,

so it's absolutely fundamental to life.

So basically why wouldn't you want to measure it?

Absolutely, yes.

And you've traveled the world

measuring biodiversity of a range of different ecosystems, flooded forests and the

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