Are two rhinos worth a panda?

How much of our embattled biosphere is worth saving, at what cost to which people and with what benefit to which people? How do we reckon costs and benefits when we are dealing with entities such as species that are viewed by some people as of unique, and therefore of limitless value? How, too, should we deal with species insofar as they can be subject to irreversible injury through extinction?

The economist would say that everything has its price, whether we want to acknowledge that or not. Which conservationist would spend £1,000 a year to save the panda? And another £1,000 to save the chimpanzee, and then the rhino and the gorilla and so on? The economist would also say that our best guide to people's preferences lies with market prices. But how far can market prices illuminate our situation when the market is not concerned with the future beyond a decade or so, certainly not with several decades, let alone centuries or millennia? Yet the length of time it will take for evolution to come up with new species to replace the ones being lost will be several million years.

How, then, shall we set about the task of conserving biological resources? Answer: read books such as this, especially for its broad documentation of the whys and wherefores that abound in this complex field.

The book is avowedly interdisciplinary, and it succeeds fairly well in covering both the ecology and economics of biodiversity, plus several related disciplines such as genetics, sociology, law and governance. The authors pin their colours to the mast in the preface, when they state that "use [of biological resources] is inevitable (extensive, exploitative and sometimes devastating use)". Their book tries to "address how such use might be constrained within sustainable limits." This immediately sets an outsize cat among the pigeons, if that is a suitable phrase for a book on species. When I once documented the contributions of wild plants to medicine, agriculture and industry, my views were described in print by a fellow professional as "evil". Let us salute, then, the courage of the present authors for being forthright about their approach.

Their themes are well illustrated by the African elephant and the ivory trade. As elephant numbers decline and tusks come into shorter supply, ivory prices rise and thus increase the pressure for poachers to hunt down remaining herds before the "resource" gives out altogether. There are two potential responses: to ban the trade or to "manage" it. The first runs the risk of further stimulating the black market in ivory, the second seeks to impart economic value to elephants by putting a regulated price on their tusks.

Regrettably, a managed harvest of ivory is hardly practicable in those many parts of Africa where corruption is endemic at the highest government levels. Fortunately a few countries, notably Namibia, Botswana, Zimbabwe and South Africa, have kept corruption in check and their elephant herds are flourishing because local people (who receive most of the income from traded ivory) view elephants as sustainable funds on the hoof. Why then, these four countries protest, should they be deprived of a substantial source of conservation revenues from selling ivory through strictly controlled channels? Why should they be penalised just because other countries cannot get their policing act together?

The book comprises two main parts. Following a brief introduction, there is an extended overview of theoretical aspects, covering calculation of harvests, supply and demand patterns, self-regenerating yields, and other esoteric factors of wildlife exploitation. Then comes a second part with the "real life" stuff, presented in ten case studies ranging from mahogany and squid fisheries to gorillas and musk oxes. These are the meat of the book, and they illustrate the complexities of helping wildlife to pay its way in an overcrowded world. The whole is supported by almost 700 references.

The book is aimed at final-year undergraduate and master's students, as well as conservation professionals such as wildlife managers and policy makers. For some it will go into too much detail; there are few distilled conclusions and prescriptions, whether for policy or planning or management. For others, it will prove an abundant source of theoretical analysis and pragmatic application.

Norman Myers is a visiting fellow, Green College, Oxford.