Parasites and Passerines Tell Different Tales

Nonequilibrium Ecology . Rohde, K. 2006 . Cambridge University Press , New York , NY . 234 ( xi + 223 ) pp . $120.00 (hardcover) . ISBN 0-521-85434-2 . $60.00 (paperback) . ISBN 0-521-67455-7 . Passerine birds have had a surprisingly substantial impact on the development of ecological theory. Studies of birds, most often passerines, have been central to such topics as niche theory, resource partitioning, energy allocation, and optimality, and to the broad range of behavioral ecology topics such as parental investment, parent-offspring conflicts, and sexy sons. They have been important despite being a relatively species-poor and ecologically atypical taxon. Passerines have strongly determinate growth; thus, juveniles are essentially full size at fledging, and individuals of a species are remarkably uniform in size. Consequently, each bird in a population has a very uniform set of ecological requirements and set of impacts on its environment, and these features remain largely constant throughout life. Passerines are among the less fecund organisms and provide much larger parental investments per offspring than is the case for any animals other than mammals. Passerines are homeotherms with high metabolic rates, and, perhaps because the requirements of flight limit their ability to store energy, they require a continuous supply of food and can quickly die in its absence. Finally, with the forelimbs specialized for flying and the hind limbs for perching, they are forced to use a quite inflexible jaw structure as the sole tool for food acquisition, manipulation, and consumption. In each of these aspects they are bizarre compared with the majority of organisms. In fact, as someone who does not work with birds, I marvel that they have been able to persist and diversify to the extent that they have. Intelligent design would never have produced such creatures—they are so tightly constrained by their morphology, ontogeny, and physiology that they must live continuously at the very edge of survival. It has always seemed strange to me that ecological ideas have been so heavily influenced by such atypical organisms. But then, some of the ideas central to ecological thinking have also seemed very strange to me, and maybe these two things are linked. Perhaps what is termed conventional ecology, or equilibrium ecology to use Rohde's terminology, got that way because of the strange organisms that fueled its development. In his book Nonequilibrium Ecology, Klaus Rohde sets out to redress both issues. The author provides abundant examples from the ecology of parasites and other organisms to demonstrate that what may possibly be true for some birds is not necessarily the norm for other kinds of creatures. As its title states, the book is also an attempt to draw attention to the very considerable evidence for the idea that ecological systems—populations, communities, ecosystems—are normally (usually) not at or moving toward equilibrial conditions. In my opinion, a book like this has been needed for some time, and I am pleased that Rohde has written it. How successful has he been? In drawing attention to the wealth of examples in which ecological patterns, processes, or principles have been investigated using what many might term novel systems, Rohde shows how profitable it can be to investigate ecological ideas using a broad sweep of taxa and systems. That his favored parasites get an enormous share of attention is fitting, given his expertise with these organisms and their considerable neglect in the mainstream literature. I had not appreciated, for example, the strength of data available from studies of parasites to address the question of empty niches. That the parasite data argue so strongly for an abundance of unused niche space, and therefore for the probability that species are not tightly packed into a fully exploited Hutchinsonian universe, is vindication both for the idea of nonequilibrium as the norm and for the use of diverse taxa in developing ideas. In building his argument in favor of a nonequilibrium world, Rohde is somewhat less successful. To be fully persuasive, this argument needs to be set out carefully and developed logically over a series of chapters. Instead, the reader has sometimes to work hard to follow Rohde's argument. This is partly because his concise writing style demands a lot of background knowledge. After many years of teaching ecology to advanced university students, I know how deeply ingrained are equilibrial ideas in our society and how very difficult it is to get students to open their eyes and see the evidence for lack of determinism even when it lies all about them. I fear that Rohde's book will not work well with the mass of students content with an easy approach to ecology, although it has ample information for those who truly want to investigate less conventional ways of seeing the world. I say less conventional in contrast to the conventional thinking of those who think they know about ecology after one introductory course and then move on to conservation biology, invasion biology, macroecology, or other trendy branches of ecology, especially branches that seem to require less science and more compassion for the natural world. In contrast, for those students and scientists who value hypotheses and the rigorous testing of them, it is clear that the equilibrium ecology that Rohde argues against is now but a tattered remnant of its earlier sparkling comprehensiveness. Nevertheless, Rohde's book provides them with substantial ammunition to use in building a new, more realistic ecological paradigm. Although the book is generally well put together, with a 26-page bibliography and taxonomic and subject indices, I wish Rohde and his publisher had paid more attention to the presentation of figures. Most of the illustrations are reprinted from other sources and, presumably to save space, are printed far too small. As a result, many figures are squished to the left-hand side of the page, whereas their captions spread extravagantly across its full width. Even with a magnifying glass, it is often difficult to see the details that are the sole reason for presenting the figure. Given that these figures usually illustrate aspects of the ecology of generally poorly known taxa (not birds), it is particularly unfortunate that they were not printed at larger scale. Despite this criticism, this is a useful book that should be read by any ecologist and particularly by any graduate student interested in a refreshingly different perspective on our science than the one dished up too frequently in survey courses and the conservation press.

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