The perhaps most catchy image about relations between biodiversity and ecosystem functioning has been drawn by Paul and Anne Ehrlich in the preface of their book, Extinction, which was published in 1981. They describe the different biological species as ‘rivets’ holding together the wings of an aeroplane (symbolising the earth's ecosystems) in which we ourselves fly. But at the same time, the airline is paying a person (the now infamous ‘rivet popper’) to pop out the rivets of the wing one by one and sell them for profit. The rivet popper does not seem to be worried very much about what he is doing:
‘Don't worry’, he assures you. ‘I am certain the manufacturer made this plane much stronger than it needs to be, so no harm's done. Besides, I've taken lots of rivets from this wing and it hasn't fallen off yet. […] As a matter of fact, I am going to fly on this flight also, so you can see there's absolutely nothing to be concerned about.’
The message the authors want to convey is clear: the ecosystems of our planet are dependent on species and their diversity. While some (or many) species extinctions may go unnoticed, or at least without significantly impairing the functioning of our ecosystems, there may be a threshold in terms of species numbers beyond which the whole system collapses and becomes dysfunctional – the wing will fall off and the plane will crash.