The Ecology of Freshwater Molluscs

  • Robert T. Dillon
Cambridge University Press: 2000. 509 pp. £75,$120

Molluscs have traditionally taken a back seat to insects and crustaceans in freshwater ecology, and rarely feature prominently in courses or textbooks on the subject. Yet recent work shows that suspension-feeding bivalves and grazing snails can control the abundance and composition of primary producers such as phytoplankton, and thus have far-reaching impacts on freshwater ecosystems.

Freshwater snails are intermediate hosts for important pathogenic trematodes of humans and livestock, thereby occupying a central place in what might be called medical limnology. Moreover, as hundreds of species of freshwater molluscs are extinct, or imperilled by human activities, the group urgently needs the attention of conservation biologists. In other words, there are good reasons to bring molluscan ecology closer to the ecological mainstream.

Rob Dillon believes that freshwater molluscs have their own special ecology, distinguished by their immobility, indiscriminate diet and high requirement for calcium. He also thinks they have a largely untapped potential to contribute to the advancement of general ecology, and his book covers their life history, diet, biotic interactions and distribution. The chapter on parasitism shows the importance and complexity of parasitic interactions, and will be especially valuable to ecologists, who tend to overlook parasitism as an important ecological factor. The book also contains original analyses of published data, and proposes a new framework (based on J. Philip Grime's triangular model) in which to interpret molluscan life histories and distributions.

The chief strength of this book is its presentation and analysis of a large, scattered body of literature on freshwater molluscs. The literature coverage is impressively wide and international (but not very multilingual), although some key studies are inexplicably missing. Similarly, several research topics that have figured prominently in freshwater molluscan ecology (for example, the ecological roles of molluscs and their historical biogeography) are poorly represented.

Dillon's analyses are alternately stimulating and irritating. I jotted down many ideas for new research projects in the margins of the book. At the same time, I feel that many of Dillon's conclusions are premature or even incorrect. Further, the narrow focus on molluscs has caused him to miss opportunities for making connections to the broader ecological literature on topics such as the selection of food items by herbivores and sublethal effects of predators on prey. Thus, this book should be read critically. Despite these flaws, however, it is a valuable resource for students seeking fresh research questions, readers looking for information about freshwater molluscs, and ecologists who want to see what freshwater molluscs have to offer.