Physiological Diversity and Its Ecological Implications.—John I. Spicer and Kevin J. Gaston. 1999. Blackwell Science Limited, Oxford, United Kingdom. x + 241 pp. 99 text figures. ISBN 0-632-05452-2. Paper, $59.95.—Ecological physiology occupies the interface of two major disciplines within biology and, therefore, can offer integrative views of organisms that combine the insights and context of ecology with the analytical rigor of the best traditions of mechanistic physiology. Within the last decade, however, the status and preferred directions for research within ecophysiology have been the subject of substantial debate. Some, for example, argue that this discipline has essentially answered all of its initial, large-scale questions of how animals function in their natural environments and how they are adapted to them evolutionarily (e.g. Bennett 1987). Others have questioned this disciplinary hubris and have been impressed that we may well know much less than is commonly perceived. A single example, with apologies to my ornithological colleagues, is the physiological ecology of small mammals occupying hot deserts. Here, it is clear that many of the most familiar generalizations accepted in textbooks and taught to generations of students are misleading (Walsberg 2000).
Although many have called for new perspectives on ecological physiology, few have provided them in the exemplary fashion of Spicer and Gaston's Physiological Diversity and its Ecological Implications. This book provides a broad overview of variation in a host of ecologically relevant aspects of physiology (e.g. energy relations, temperature tolerance and regulation, water relations, ionic relations). Spicer and Gaston's essential thesis is that such variation has been largely ignored for too long and that understanding the nature, origins, and consequences of diversity in physiological systems is critical to understanding ecological physiology. Our lack of attention to physiological diversity has had major consequences. A salient example is the difficulty that such ignorance imposes upon understanding the evolution of physiological traits. Between two populations occupying contrasting habitats, for example, differences in physiological performance may be derived from genetic differences, or from acclimation, or from ontogenetic effects induced by growth and development in differing environments. If acclimation and ontogenetic effects are of major importance, then differences in physiological performance may well be buffered from effects of natural selection. Understanding the relative contributions of these alternative sources of variation is clearly vital to understanding the role of natural selection as well as the innate physiological lability of individuals.
Spicer and Gaston explore physiological diversity from several points of view. The book is organized following hierarchical levels of biological organization. That is, they first consider variation with time in an individual (including acclimation and ontogeny), then progressively explore variation between individuals, between populations, and between species. Within each hierarchy, they examine the patterns and structure of physiological diversity, its mechanistic bases, and notable weaknesses in our understanding.
I was particularly struck by three overall features of this book. First, it is broad in its taxonomic coverage. The examples discussed, which are myriad, cover a wide set of invertebrate and vertebrate animals. Second, the authors have provided useful and nondogmatic discussions of a variety of sometimes contentious issues such as the “beneficial acclimation hypothesis” and the importance of accounting for phylogenetic relatedness in physiological studies (“phylogenetically correct physiology”). Finally, throughout this book, Spicer and Gaston have taken care to explicitly identify important and inadequately understood questions in some detail. The book ends with a two-page list of critical questions that need to be addressed related to ecophysiological diversity.
The mechanics of the book also meet high professional standards. It is very well written, well illustrated, and replete with references and examples from both the older as well as recent (up to 1998) literature.
In summary, Physiological Diversity and its Ecological Implications effectively develops a valuable new perspective within ecological physiology. This book deserves to be read by all in the discipline, including graduate students as well as established researchers.