The nine chapters cover a range of factors which may impact on the diversity of parasites. It is perhaps strange that the authors discuss the subject of quantification of diversity and diversity indices in the last chapter. The earlier chapters take species richness as the measure of diversity, but only in Chapter 9 do the authors point out the short comings of this measure and the theoretical importance of phylogeny in assessing diversity.

The first chapter discusses the state of knowledge, emphasizing the ubiquity of parasites and the fact that so many of the species are known from their original description alone. The second chapter explores the techniques and caveats in estimating parasite diversity. The authors make the point that diversity can be overestimated if host-induced phenotypic variability is not taken into account. One of the papers quoted as reporting host-induced variation, however, is one of my own (Bray and des Clers, 1992) where, in fact, we indicated that there are probably several ‘cryptic’ species present, a conclusion supported by subsequent molecular evidence (Lumb et al. 1993; Bray et al. 1999). To be fair to the authors, they also point out that ‘cryptic’ species will cause underestimates of diversity. I reckon that this is likely to be a greater confounding factor than host-induced variability, such that most estimates based on morphology will be underestimates.

The third chapter applies epidemiological theory to parasite diversity, that is, diversity determinants in ecological, rather than evolutionary, time. They reckon that the small amount of evidence available indicates that epidemiological theory, especially as relating to such factors as host density or sociality, can predict parasite species richness particularly in parasites with a direct life-cycle. Chapter 4 discusses the host as a determinant of parasite diversity, whether by co-evolution, host switching, within host speciation or extinction. They draw the parallel between hosts and islands and apply MacArthur and Wilson's ideas on island biogeography. After a discussion of various host traits, from body-size to host-genetics and all imaginable factors between, we discover that the drivers of diversity are multifactorial and may never be fully understood.

The fifth chapter suggests that parasitism per se may favour diversification and discusses the features of parasitism that may be involved (note an error on p. 98, line 18, conspecific should read congeneric). The number of hosts in the life-cycle and specificity at each stage may appear important, but not in nematodes where the diversity of those with complex and simple life-cycles does not differ. Chapter 6 tackles the subject of biogeography, in it widest context, presenting some surprising and enigmatic results, e.g. diversity is higher in parasites of temperate than in tropical freshwater fish. Chapter 7 reviews the factors lowering the parasite risk of extinction, which apparently include low host specificity and the ability to drop hosts from the life-cycle. Chapter 8, in contrast to the remainder of the book, considers parasite diversity as a driver of host evolution.

As the authors point out, many conclusions are based on rather inadequate supporting evidence, or the support is weak. Because of this it might be said that the book is premature but, on the other hand, this might be considered a stimulus to students to study these aspects of parasite biology. Many chapters or passages could, almost unchanged, suggest a programme of study, and be of particular value in the design of field-work and collecting strategies or experiments. In summary, this relatively short book is a useful counterweight to the more conventional reviews of parasite diversity, and should interest (but not necessarily convince) all workers who would like to understand why parasitism is such a successful way of life.