Biodiversity has become something of a buzzword these days. But, like all widely used terms, its meaning has become a little fuzzy, a bit like the definition on a well-worn bank note.

All of us are mindful of the need to preserve species and the different environments of which they form a part. Yet how many of us, if pressed, would be able to define what biodiversity is? And how are the criteria of what constitutes ecological richness determined?

University of Otago senior lecturer in Philosophy Dr James Maclaurin and Professor Kim Sterelny, of Victoria University and Australian National University, examine these and other related questions in What is Biodiversity? published by the University of Chicago Press.

Their book presents a timely exploration of a concept increasingly important in scientific, environmental and political arenas - and which potentially has wider application in fields such as social engineering, where concepts of diversity are similarly shaped by value judgments.

Maclaurin opens a discussion of his book with a simple hypothetical scenario he calls "swapsies". What if, he proposes, New Zealand and Australia each "swap" 10 species. We receive a cluster of diverse marsupials and reptiles, while our Australian colleagues are given a variety of grasses. Australians, Maclaurin suggests wryly, would feel somewhat "hard done by", even though it is a "fair" swap, species for species.

What this scenario highlights is the complex framework of biological, genetic, morphological, economic, psychological, social and political factors that shape our thoughts about ecological value. Current related concepts such as sustainability, Maclaurin suggests, demand similar scrutiny.

"We can't just regard something inherently as a good thing," says Maclaurin. "We have to look at the values and functions associated with it, and have practical arguments as to why it's important."

Understanding the processes which shape our thinking about biodiversity will, Maclaurin argues, help us formulate conservation initiatives. And, at a time when resources for these initiatives are heavily in demand, it is crucial that sound reasoning underpins decision-making about their allocation.