Plant and Animal Populations: Methods in Demography - Review

Ecology, July, 1999 by Robert P. Freckleton

Ebert, Thomas A. 1999. Academic Press, San Diego, California, xiii 312 p. $69.95, ISBN: 0-12-228740-1.

One of the clearest trends in ecology is the move towards a more predictive and quantitative approach. The reasons for this trend are numerous, but include the need for quantitative evaluation of the threats to species and systems from anthropogenic disturbance and the impacts of climate change, as well as a general desire to test ecological theory in the field. To this end, the need for analytically competent ecologists is increasing. The skills required are varied, but include: analysis of life-tables, numerical analysis, size- and age-structured matrix modeling and model analysis (including sensitivity analysis and calculation of confidence intervals). Correspondingly, there is an increasing demand for courses and text books that present complete, user-friendly introductions to these areas, particularly at the post-graduate level. Ideally these introductions should combine the theoretical bases for models and analytical approaches with the actualities of getting the job done, i.e., the programs or whatever else is needed to perform the analysis. This is the aim of Plant and animal populations: methods in demography. This book presents a complete course in single-species demographic analysis, combined with a series of computer programs and algorithms that perform the numerically dependent routines.

Plant and animal populations: methods in demography is derived from a graduate course in population modeling and analysis taught at San Diego State University by Thomas A. Ebert since 1988. The masters and doctoral students that take this course are generally initially unfamiliar with demographic analysis, and hence little prior knowledge is assumed. Similarly little formal mathematics is assumed. This lack of background, presumably, is representative of most new graduate students. To this end the first chapter is a rather gentle introduction to life-tables and the basic calculations required to work with survival rates, transition rates, and fecundity data. By chapter 2, however, the complexity increases and we are presented with integral equations, Newton-Raphson root finding, and calculation of moments. I feel that, without at least some familiarity with advanced mathematics, many students would struggle with this material. Given some mathematical competence, however, I found the first five chapters to provide a good introduction to standard methods of life-table analysis and structured population modeling. As with the rest of the book, what I found particularly useful was the number of data sets that are included for practice--most textbooks just explore one example for each technique that is outlined--as well as the inclusion of BASIC programs for performing most of the important analyses. I guess that, to the casual observer, these initial chapters may appear somewhat equation-laden and mathematical. Unfortunately, there is no way that this can be avoided since demographic analysis is by nature a mathematical subject. The structure of these introductory chapters is good, but I suspect that a number of students would struggle on the area of z-transformation of life-cycle graphs and it may have been better to present this topic later on and concentrate initially on the more fundamental material.

Following these introductory chapters that present the basic concepts and tools of structured population modeling, the rest of the book goes on to consider a range of other topics in model analysis. I thought the chapters on stage- and size-structured analysis could have been placed earlier in the book as they essentially introduce model forms rather than new analytical techniques. Chapters on sensitivity analysis and on calculating confidence intervals for population growth rates will be particularly useful and are very relevant to current trends in applied ecology, whilst the chapters on continuous functions for survival and size distributions move from the discrete nature of earlier matrix based approaches to continuous models.

In concentrating on demographics, one of the limitations of this book is that interactions between organisms tend to get ignored. Populations are, therefore, treated simply as numbers and processes such as interference, competition, and predation are not considered. For some types of species it would not be possible to analyze population dynamics without accounting for such processes. Of course there is only so much that a single text can address, but it would have been useful to have just a single chapter on the incorporation of such processes and the implications for the techniques and approaches that are presented. Of course, much of the literature on demographics, particularly that concerning stage- and size-structured models, has tended to ignore regulatory processes and in this sense the scope is not unrepresentative.

My overall evaluation of this book is that it provides lots of useful information and techniques and provides a comprehensive introduction to the analytical side of demographic modeling. This book could form the basis for a good course ill demographic modeling, but I think that the level of math would be a problem for some students. The book will also be very useful as a general reference on the subject. In terms of practicalities, it would have been useful had the programs been annotated, for example, with more REM statements to allow those not familiar with programming or BASIC to get to grips with the structure of the programs. It is good that these programs are available as downloads from the Web as this saves laborious typing. I would certainly recommend this book to anyone looking for a reasonably readable bridge into the daunting world of demographic analysis.