William F. Morris, Daniel F. Doak
Sinauer Associates, Sunderland, MA.
2002, 480 pp.
ISBN: 0-87893-546-0

More than 140 years ago, Charles Darwin observed and wrote that there are many threats to the biodiversity and viability of ecological communities. Fortunately, there have been many attempts by special interest groups (e.g., The Nature Conservancy) and through laws(such as the National Forest Management Act and the Endangered Species Act) to raise our awareness of the risk of extinction of many species. Answers to questions about which species are being threatened, how they are being threatened, and their likely future are essential if we are to improve our understanding of species viability and prevent extinction. We can answer these questions using quantitative approaches such as population viability analysis (PVA), which provides a wide range of population modeling and data-fitting methods for assessing the risk of extinction and management options for rare or endangered species. Quantitative Conservation Biology offers a conceptual frame-work for PVA that makes this process equally accessible to population modelers and conservation practitioners. The authors begin their treatise by pointing out that PVA has remained “largely the purview of academic conservation biologists,” who have tended to focus more on the process of modeling and have been “removed from the concerns of managing threatened species in the real world. ”They propose that this book will lessen the gap between modelers and conservation practitioners by presenting in a systematic manner the purpose, methodology, and limitations of PVA.

In Chapter 1, PVA is described as a process that covers a wide range of methods that provide an explicit and quantifiable approach for determining whether a population is extinction-prone, extinc-tion-vulnerable, or extinction-resistant. This chapter sets the tone for the remainder of the book by describing ways in which PVA has been used to link assessment (how well a population is doing) and management (what kinds of interventions are required to reduce the likelihood of extinction of a population).

Species-specific examples are given to show how PVA can be used to assess extinction risk of a single population (Yellowstone grizzly bears) and multiple populations of the same taxon (northern spotted owl). PVAs are also used to monitor population health (eastern northern Pacific gray whale), identify vulnerable life stages of a population (loggerhead sea turtles), and determine the initial seed population for the establishment of a new population (European beaver). Finally, Chapter 1 summarizes the range of data analysis and modeling approaches that are commonly used in PVA, from simple (count-based) procedures to more complex data-hungry (multisite) methods.

Chapter 2 then describes, in some detail, factors that influence population viability.

Each of the next nine chapters (3–11) contains a logical and more complete description, with practical examples, of the quantitative methods of PVA. In chapters 3, 4, and 5, the authors discuss the use of count-based population-level data in PVA. These data often are relatively easy to collect and, therefore, are more likely to be available to conservation planners and managers. The authors show how simple count data can be used to estimate average population growth and the degree of variability in that growth, both of which are useful metrics for assessing population viability.

Chapter 3 ends with a description of the key assumptions in simple count-based PVA, such as constant mean and variance parameters due to density-independence and lack of demographic stochasticity and negligible environmental variability and observation error. Count-based PVA methods that do not rely on these assumptions are covered exclusively in chapters 4 and 5.

Demographic PVAs are discussed in chapters 6–9. Unlike count-based PVAs, demographic PVAs account for different types of individuals in a population and are used to determine the viability of structured populations. Demographic PVAs are based primarily on projection population matrix models, are more data intensive, and require information on stage-specific rates such as development, survival, and reproduction. These requirements represent a weakness (as data collection is more expensive and labor intensive) and a strength (as these models are more accurate and management decisions are more targeted). Indeed, greater details of matrix-based demographic models can be found in books such as Caswell’s Matrix Population Models: Construction, Analysis, and Interpretation. However, it would be difficult to find another source that de-scribes the demographic PVA approach in as logical and compact a manner as presented in Quantitative Conservation Biology.

A species comprises populations that do not exist in isolation of each other. Therefore, development of species conservation options often requires the treatment of multiple populations. This is the focus of chapters 10 and 11, which describe the use of multisite PVAs that explicitly consider multiple populations and the spatial complexity of their environment. Multisite approaches to PVA are complex and require knowledge of methods that may depend on the simpler count-based and demographic approaches.

In the first 11 chapters of the book, PVA is presented as a conservation tool. In chapter 12, “Criticism and Caveats: When to Perform (and When Not to Perform) a Population Viability Analysis,” the limitations of PVA are discussed. Criticisms of PVA are usually based on the quality and quantity of the data used to develop the models and on our inability, in many cases, to validate these models before they are used to make predictions about population viability. The chapter ends with several general recommendations for improving the way PVA is used for population viability assessment.

It is easy, from this discussion, to get the impression that PVA is merely an exercise in species population modeling, for which there already exists a myriad of literature. However, this book is unique because it is written much like a tutorial that describes the process of PVA in a well-organized and easy-to-follow manner and does so insufficient detail (with specific real-world examples) to serve as a starting point for more detailed treatments. For those who are less mathematically inclined, notation is kept to a minimum and MATLAB and SAS code are provided (in print and downloadable form) as starting points in developing one’s own models. The book is sure to appeal to a wide audience and should serve as a useful resource for those who wish to better understand PVAs, as well as for more experienced theoreticians and conservation practitioners.

Carlyle Brewster
Department of Entomology
202 Price Hall, Virginia Tech
Blacksburg, VA 24061-0319
American Entomology
Vol. 50, No. 2, Summer 2004