A revised textbook on conservation

Conservation Biology. 2nd edition. Cardinale, B. J. , and J. D. Murdoch. 2025. Oxford University Press, New York, NY. xviii+654 pp. US149. 99 (paperback). ISBN 978-0-1976 6701-9. The science underlying conservation has come a long way from the early 1970s, when one of its founders, Michael Gilpin, urged students not to take up conservation biology before tenure because the science was so weak. Now conservation biology is an eminent and flourishing field, full of discourse and debate based on sound research, exemplified both by papers in this journal and the book under review. Billed as a textbook to support courses for upper division undergraduates, the book weighs in at 1. 8 kg, contains 569 pages of text, and includes more than 1100 references. I estimate it would take me 24 continuous hours to read every word, despite the presence of many fine illustrations. It is presumably not designed to be used in this way, but rather for course instructors to point to sections that round out a lecture. For example, I assume that a two-page table of the minutiae of how a species gets classified on the International Union for Conservation of Nature Red List, coupled with a lengthy in-text discussion, is meant to illustrate the rigor being invested in such assessments. An alternative approach could be to simply summarize the main criteria required to be placed in a certain category (population size, declining population, small area of habitat, models indicting probability of extinction). That approach would reduce this section by 90%. Similar arguments could be applied to the entire book. Which one is more effective as a teaching tool? Probably they complement each other, but the mass of writing in this book does mean that some important concepts get buried in a few words (e. g. , phylogenetic diversity). Four sections cover the distribution of species, the value of biodiversity, the threats to biodiversity, and how to conserve biodiversity. The first section also contains an interesting chapter on the history of conservation biology (including much on the extent to which racism was involved in the early North American conservation movement; a particular addition to this edition). In the second section, the stated values of nature include moral, ethical, religious, and educational as well as our sheer wonder at where we lie on the tree of life. More tangible values are summarized. We learn that the top 20 pharmaceutical products used in the United States were first identified in natural products and how the loss of wetlands contributed to the devastation by hurricane Katrina in New Orleans in 2005. In this section, the authors commendably emphasize that values go beyond the financial. Nevertheless, many decisions and elections do depend on economics. Cost–benefit analyses are required, not just to assess whether the natural state is paying its way economically but also to ask how it can be made to do so. Accordingly, I feel the chapter on economic evaluations should be one of the most important in the book, but it mostly consists of verbal descriptions of valuation procedures. A useful contribution does explain the concepts of consumer and producer surpluses. For example, the economic value of a park could be estimated from the amount of money people spend to visit it, but it could also be estimated from the amount of money people would be prepared to spend to visit it (the difference being the consumer surplus). Unfortunately, the accompanying figure gives the—perhaps unintended—impression of the surplus being the money spent. Beyond this, two big issues in economics that particularly affect conservation are externalities and discounting. Externalities are touched on in several places, but it would be important to raise their prominence and describe how a management action can create multiple externalities, each falling on different segments of the population. Discounting issues are scarcely mentioned. A third unappreciated issue in conservation biology is the use of multipliers. The salary received by guides to a park affects local GDP not just directly but also indirectly because guides spend their salaries locally. It would be useful in future to expand on all three. Perhaps in the third edition. The third section covers threats. Following E. O. Wilson's (2002) HIPO (habitat loss, invasive species, pollution, and overharvesting), we are now in the era of COPHID (climate change and disease added). The organization here is HICO, with pollution placed in the habitat chapter and a surprisingly limited discussion of disease, despite the huge impacts of West Nile virus, avian flu, SARS COVID-19, HIV, white nose disease, wheat blast, potato blight, and so forth. The fourth and final section contains five interesting chapters that lie at the heart of how to conserve biodiversity. They are conservation of selected species in their own habitat; conservation of habitat through parks; various landscape-level issues that range from where to put parks to how to improve agricultural ecosystems; ex situ conservation (zoos, transplants, resurrection of extinct species) ; and possibilities for restoration and sustainable development. To give a flavor of the many examples covered, the three outtakes (boxes) in the chapter on parks describe the Half-Earth project, a marine park in Kiribati, and consider whether strict regulations on park entry (“fines and fences”) work. I was particularly impressed with this fourth section, which is perhaps what conservation biology is all about, whereas the earlier sections may be considered more the science behind conservation. The book is not only comprehensive in scope but impressive for its balance. A real problem for conservation biology is that the science does not always favor conservation. For example, when economic aspects are the deciding factor, habitat conversion to farmland may be favored. This can result in a reluctance to publish findings. Certainly, it is the more dire states of nature and gloomy predictions that get published in the prominent journals. Resulting biases have resulted in several debates, for example, on whether climate change will cause an enormous number of extinctions, whether setting aside habitat in an untouched state is essential to meet conservation goals, whether we are in the sixth mass extinction, whether valuations of nature are reasonable (What does an average of 33 trillion dollars for global ecosystem services mean? ), or even whether extinction itself is bad, given it has happened throughout Earth's history. To their credit, the authors summarize each side of these and other debates well. An additional laudable feature is the authors’ concern for social issues; albeit these sometimes create conflicts with conservation biology. At one point, the authors note that Indigenous people form less than 5% of the global population but control 50% of remaining wildlands, which they have been successfully managing. This gets rather lost later when the rise of harvesting of animals is attributed to technological advances (e. g. , guns and snares) and the increase in human population without mention of another important driver, access to markets. All three of these drivers surely apply to Indigenous people. Indeed, later the authors state, perhaps accidentally: “Local people and their living practices comprise the greatest threat to biodiversity conservation” (p. 475). For such a large book, it seems churlish to criticize it for what is missing and note the few errors I found, but some important concepts are not there, among them the North American model of conservation, which emphasizes the importance of hunting (Mahoney the concept of shifting baselines; mass mortality events attributed to unusual heat; climate velocity; and ocean acidification. The authors begin the book by stating they have “carefully chosen the most important quantitative concepts, methods, tools, techniques and models that students need for a career in conservation. ” They conclude by stating “you have learned how to use models that help manage biodiversity. ” In the 567 pages in between, I do not think they achieve this, nor is the book obviously designed in this way. Instead, it is as much a description of pattern as of process. For example, of the 51 boxes, about half are biological examples and only eight can be considered quantitative. It is not explained why models are needed, issues of probability are not considered (Their statement, “experts can be wrong, ” is perhaps better replaced with “experts attach a probability which implies alternative outcomes are to be expected. ”), and the equations themselves are often presented without explanation. For example, the multispecies Lotka–Volterra model with logistic growth is provided early in the book, while the logistic model of population growth itself is introduced (and later introduced again) chapters later. The section on exponential growth contains the odd statement that it happens faster than geometric growth. Similar statements apply to conceptual issues, for example, biomagnification is described as a pattern but there is no explanation for the process that leads to it. The book includes a list of the kinds of employment available for those trained in conservation biology that seems very much for the North American market, but the principles are general and there are many examples from the tropics. It may be compared with another well-illustrated and easily downloaded 590-page book, which draws exclusively on examples from sub-Saharan Africa (Wilson & Primack, 2019). Chapters in the two books have similar titles and run almost in parallel. The Wilson and Primack book is the easier narrative because all introduced concepts are well developed and examples are well focused (there is little presentation of quantitative models). The book under review mentions many features not discussed by Wilson and Primack, but they are sometimes buried in short paragraphs or sentences, and as I noted the models are also described very briefly. Both are useful references, and whether I were in Africa, North America, or elsewhere, I would recommend consulting both because they complement each other well. But again, a course instructor is likely to have their own set of notes to draw on, as do I. Despite my criticisms, I conclude by noting that I learned much from this book, which in sum is impressive for its clarity, accuracy, and—as might be expected from its size—thorough discourse on the topics covered.