Integrative and Comparative Biology Advance Access originally published online on July 23, 2008
Integrative and Comparative Biology 2008 48(4):543-545; doi:10.1093/icb/icn075
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Book Review |
Foraging: Behavior and Ecology. David W. Stephens, Joel S. Brown, and Ronald C. Ydenberg, editors.
Odum School of Ecology, University of Georgia,
Athens, Georgia, USA 30605
E-mail: pulliam2{at}uga.eduThe
The Australian Museum, 6 College Street, Sydney,
Australia NSW 2010 E-mail:
Graham.Pyke{at}austmus.gov.au
Foraging: Behavior and Ecology. David W. Stephens, Joel S. Brown, and Ronald C. Ydenberg, editors.
Chicago, IL: The University of Chicago Press, 2007. 576 pp. ISBN 0-226-77263-2 (cloth), $99.00 and 0-226-77264-0 (paper), $45.00.
Naturalists and scientists have for centuries observed and recorded many details of what, when, and where species eat, but the first conceptual framework for a theory of foraging by wild animals did not begin to emerge until the late 1960s with the seminal paper of MacArthur and Pianka (1966
). These authors suggested that foraging behavior evolved to maximize individual fitness subject to constraints and, in this sense, animals may forage optimally. Interest in foraging theory exploded in the 1970s as experimental studies of foraging supported many of the predictions of the early models. A number of reviews and books (e.g. Pyke et al. 1977; Stephens and Krebs 1986) in the late 1970s and 1980s summarized the first two decades of foraging studies and gave generally upbeat assessments of the state of the growing theoretical and empirical foraging enterprise.
The recent book Foraging Behavior and Ecology edited by Stephens, Brown, and Ydenberg (2007) takes the book by Stephens and Krebs (1986) as a starting point and asks what has happened in foraging studies in the past 20 or so years. One stated aim of this book is to provide guidance to "a hypothetical graduate student at the beginning of her career." The authors contend that "the last two decades of foraging studies have seen a pleasing lockstep among empirical, modeling, mathematical, and computational advances." Furthermore, they contend that many "new concepts have emerged" including the realization that "foragers must balance food and safety," "state dependence" (i.e. the idea that tactical foraging decisions depend on state variables such as fat reserves), and the extension of foraging into the realm of "foraging games and the consequences of foraging as a group." We reviewed the book keeping the "hypothetical graduate student" in mind, and we asked if the book provides enough depth of coverage of the new concepts emerging in the field to be useful to her in choosing a research topic, while at the same time providing enough background to give her an overview of the scope and history of the field. Finally, we evaluated the claim that "empirical, modeling, mathematical, and computational advances" are advancing in "lockstep."
The book clearly demonstrates that foraging studies have grown and evolved in the past 20 years and much of this growth has occurred at the interface between behavioral ecology and other disciplines. For example, Whelan and Schmidt (Chapter 5) show how optimization models have helped physiologists understand digestion, and they argue convincingly that post-ingestive processes, ignored in early foraging models, can have a strong influence on foraging decisions such as diet selection and feeding rate. Similarly, physiological constraints and optimization techniques have been combined to provide new insights into herbivory (Chapter 6), energy storage (Chapter 7), and provisioning (Chapter 8). Brodin and Clark (Chapter 7) use state-variable models combined with dynamic optimization methods to show how animals might balance the "delicate trade-off between predation and starvation" when making foraging decisions and to yield insights into problems as varied as hoarding behavior, fat storage, and daily time budgets, all behaviors in which current actions influence future options.
Cognitive constraints as well as physiological ones clearly have an impact on foraging behavior. Chapter 2 by Stevens presents a useful review of signal detection and related theories and provides a good overview of how information processing influences foraging decisions. (Unfortunately, this chapter suffers from a lack of careful proof reading and an interesting discussion of memory rules and how animals weigh past and present experience is interrupted by numerous typographical errors and missing symbols). Chapters 3 (Sherry and Mitchell) and 4 (Adams-Hunt and Jacobs) show that memory and cognition play important roles in foraging. The detailed descriptions of biochemical and anatomical mechanisms are interesting in and of themselves, but, unfortunately, the authors do little to demonstrate how such mechanisms constrain foraging decisions. For example, interesting discussions of the role of the hippocampus in spatial memory and the prefrontal cortex in cognition would have been more relevant to the remainder of the book had they been accompanied by a discussion of the evolution and phylogeny of cognition, and what we might expect regarding the cognitive abilities of various animal taxa faced with real foraging decisions.
A hypothetical graduate student reading this book would see that foraging is an integrative research area relevant to, and drawing on, many other disciplines. Nonetheless, she would receive an incomplete picture of the foraging literature because the book gives little or no attention to a number of important topics of current research interest. Accordingly, the graduate student would surely want to supplement the book with recent papers covering topics like animal movement and search, co-evolution, resource defense and territoriality. The hypothetical graduate student might also be disappointed in the extent to which the book presents and evaluates possible future directions for foraging research. Each chapter points to relatively "safe" research extensions related to details of the topic at hand and the authors’ own idiosyncratic interests, but only the final chapter by Rosenzweig steps far back and speculates on emerging topics, and no chapter suggests totally new topics that might be fruitfully explored with cost-benefit analysis.
With a couple of notable exceptions (e.g. Sherry and Mitchell, Chapter 3 and Adams-Hunt and Jacobs, Chapter 4), the book does not fully deliver on the promise to portray "the stepwise and interlocked manner" in which observations, experimentation, and theory have developed. For example, the chapters on population dynamics and community ecology (Chapters 11 and 12), point out convincingly that foraging behavior needs to be and, in some cases, has been, successfully incorporated into models of population and community dynamics, but, with the exception of studies of "giving up density," the authors present little evidence that these concepts have had much influence on the conduct of empirical studies. Perhaps these promising ideas have not yet had time to fully permeate into the design of laboratory and field studies and, if so, explicitly pointing this out might be just what our hypothetical graduate student would need to know to stimulate her own thinking.
Stephens, Brown, and Ydenberg made a deliberate decision to omit the word "optimal" from the title of the book (Chapter 1). This, we believe, does not reflect the central role that optimization models continue to play in foraging studies and panders to the misguided and misdirected critics of the approach. The optimization approach has, it seems to us, been impressively successful at providing a framework for understanding empirical observations and designing field and laboratory experiments. Those who have seen foraging theory (a.k.a. optimal foraging theory) as a ‘complete waste of time’ have surely missed the boat. Indeed, the entire book is based on the very successful idea that fitness has been maximized by natural selection and all of the presented models assume that some fitness-related currency is maximized. That we increasingly discover that foraging is a complex process with a richness that we never knew and is affected by so many factors from cognitive and physiological constraints to predation and social interactions, and that we can embrace new concepts and hypotheses in response to these discoveries; clearly indicate the power of foraging theory rather than its failings.
Despite some deficiencies noted above, the book should serve the hypothetical graduate student described above reasonably well and, if amply supplemented by papers from both the historical and modern literature, would provide an excellent basis for a graduate-level course. The book contains an enormous amount of interesting and useful information and ideas, and is the kind of book that rewards repeated reading. As pointed out by the authors, the book clearly indicates that foraging theory, like Mark Twain at the time of his rumored death, is very much alive and well, and shows signs of remaining this way well into the future. We recommend this book to anyone who wishes to learn more about this very lively area of research.
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 References |
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MacArthur RH, Pianka ER. On the optimal use of a patchy environment. Am Nat (1966) 100::603–9.[CrossRef][Web of Science]
Pyke GH, Pulliam HR, Charnov EL. Optimal foraging: a selective review of theory and tests. Q Rev Biol (1977) 52::137–54.[CrossRef]
Stephens DW, JR Krebs. Foraging theory. (1986) Princeton, NJ: Princeton University Press.
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