Playing to a Tough Crowd

Authors


Introduction to Population Ecology. Rockwood , L. L. 2006 . Blackwell Publishing , Malden , Massachusetts . 350 (xi + 339) pp . $44.95 (paperback) . ISBN 1-4051-3263-9 .

Population ecology is critical to conservation biology—as well as many other areas—yet teaching it presents some special difficulties. First, the topic necessarily involves a fair amount of mathematics, but students attracted to ecology and conservation are often poorly trained in, and sometimes rather frightened by, math. Second, the students we teach are a mixed bunch—some are interested in population ecology, some are interested if they can be shown immediate application of an idea, and there are always some who are interested only if the professor juggles while lecturing.

Given these problems, writing a textbook on population ecology presents a set of formidable challenges. One must choose which of these fractions of students to address. Related to this are hard choices about the level of intellectual rigor to demand. An overlapping set of issues has to do with how much mathematics to include and how to explain the math.

Rockwood aims his book at a particularly tough crowd to please. His students, he explains in the preface, typically work for government or private wildlife or conservation agencies or zoos, and are taking courses to move ahead in their careers. They have, he says, little sympathy for “theory for the sake of theory” and want quickly to see application. The book is written so that the only real mathematical background required is some algebra; although Rockwood uses calculus and matrix algebra, students do not actually need to be able to differentiate, integrate, or invert anything to follow the text. This said, there is somewhat more math in this volume than in the Begon, Townsend, and Harper (2005) and less mathematical sophistication than in Vandermeer and Goldberg (2004). In a rough sense, the topics covered by all 3 books are similar.

Introduction to Population Ecology has some welcome features. The chapter on density dependence introduces the possibility of complex dynamics in simple models. This material might be of greater interest to the intended audience if it included some reference to debates among modern ecologists as to how much chaos actually occurs in nature and how one might distinguish chaos from stochasticity. It might also be helpful to students to point out that complex dynamics occur in the discrete logistic because of delayed feedback. I was happy to find that the chapter on host–parasite interactions covers much of what I normally cover in an introductory ecology class. On the other hand, I was surprised that there was little discussion of host-disease systems of current ecological interest (such as sudden oak death in California or foot-and-mouth disease in British cattle). There is a fairly lengthy discussion of the biology and chemistry of plant–herbivore interactions.

Having spotted these features, and knowing the author's intended audience, I was sure I could write a laudatory review. I sat down to read a bit more closely. Unfortunately, the more closely I read, the more problems I found. That may be an argument against close reading, but I cannot recommend this book. Given the choice of target audience, it seems especially important to be precise in both math and in prose explanations, to critically examine the ideas, and to tie the theory strongly to empirical studies. The book seems to me to be uneven on all of these accounts.

Some topics are discussed with little critical evaluation. For example, in discussing survivorship curves, Rockwood distinguishes between those based on following one or more cohorts and “static” samples based on the ages at death of a number of individuals. Regrettably, readers are not told that the latter approach leads to a valid estimate only if the population growth rate is one and the population is at stable distribution.

This may seem to be a technical quibble, but there are many other examples. The chapter on plant–herbivore interactions describes Feeney's apparency theory but provides no discussion of current thinking on its utility. In the chapter on life histories, there is a section on bet hedging, but the term is not defined and an example is not provided. A long discussion of Cole's (1954) paradox includes the assertion (long since shown to be false; Bryant 1971) that it depends on his assumption of zero mortality. In the same chapter, there is a discussion of reproductive value that might well cause a reasonable student to conclude that this quantity is rather arbitrary because different methods of calculation (with different results) are mentioned with no guidance as to the differences between them.

What of new, growing areas of interest? Study of biological invasions is probably the fastest-growing research area in population ecology; both the number of empirical studies and of hypotheses proposed to explain invasions has grown dramatically over the last few years. Yet there is no discussion of these hypotheses, and I found mention of only a single case, used as an example of exponential growth. Study of dispersal biology has also grown of late, as a result of dramatic improvements in estimation methods as well as important theoretical strides. But dispersal is not discussed and neither are mark-recapture methods, which have revolutionized much estimation of animal survival and have even begun to have an important impact in plant ecology.

We do need a text that can help communicate the basic ideas and recent advances in population ecology to people entering careers in government agencies, nongovernmental organizations, environmental consulting firms, and others who will use these studies as a basis for management plans and policies. This book, unfortunately, does not oblige.

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