Gardner, R. H., W. M. Kemp, V. S. Kennedy, and J. E. Petersen, editors. 2001. Scaling Relations in Experimental Ecology. Columbia University Press, New York, NY, USA

Beatrix E. Beisner

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Published: March 18, 2002

Scaling Relations in Experimental Ecology is the product of a 1997 workshop that examined a broad spectrum of empirical, theoretical, and practical questions associated with scale. The book focuses on aquatic ecosystems (and mainly lentic ones), with only a few explicit references to terrestrial systems. However, its insights are not limited to aquatic ecology. Although this book appears in the usually more theoretical Complexity in Ecological Systems series, it is a practical book that should appeal to anyone who is planning ecological experiments.

The book is divided into four parts that survey past and current approaches and thoughts on scale in experimental ecology. The first section, "Background," consisting of a chapter by Kemp, Petersen, and Gardner, presents an overview of the question of scale. They define scale and various associated terms, like scope and extent, and develop an approach for applying scaling relationships through a series of case studies (all from aquatic environments). One theme they develop, common to several authors in the book, is the need to develop a "science of scale."

The second section, "Scaling Theory," is divided in its approach, dealing both with the philosophical side of ecological research and vague terms like "scale" (in chapters by Wiens and Allen), and with methods for scaling based on allometric relationships, hierarchy theory, and power laws (in a chapter by Schneider).

The third section, "Scaling Mesocosms to Nature," discusses mesocosms and their relationship to natural processes. Chapters by Pace, Nixon, and Naeem assess when smaller scale experiments might be useful for predicting patterns at larger scales. A more focused chapter by Heath and Houde gives an example of how an individual-based model can be used effectively to predict the appropriate experimental unit dimensions required to understand fish performance in mesocosms.

The final section, "Scale and Experiment in Different Ecosystems," gives the reader a more specific look at scaling issues and solutions in freshwater (Frost et al.), terrestrial (King et al.), land-margin (mainly estuarine) (Boynton et al.), and marine (Scheurer et al.) ecosystems.

A main impetus for the book, mentioned in every chapter, appears to be the recent debate among aquatic ecologists on the usefulness of experiments at ecosystem scales (e.g., whole lakes) vs. the "bottle" or mesocosm experiments that are often conducted in the laboratory (Carpenter 1996, 1999, Drenner and Mazumder 1999). Here, a group of primarily "mesocosmologists" attempts to resolve this debate. Chapter authors include mainly practicing experimental ecologists who have worked at some point with "cosms." The authors take a levelheaded approach, stepping back from the intricacies of the debate, asking rather how a multiplicity of approaches can work synergistically to address ecological questions. Several authors acknowledge that there has been too much focus on small-scale experimentation, especially in recent years, at the expense of observational data, cross-system comparisons, and large-scale experimentation. As the chapter by Naeem suggests, it may not be within the scope of any single research program to address questions at all scales necessary, but an overall body of research done by many researchers on some of the big questions in ecology may resolve the issues. In this clever chapter, Naeem points out that the experimental scales used so far to address the biodiversity–ecosystem function debate are far from adequate to address the relationships derived from global, cross-system comparisons. He suggests that we continue the debate later, when there has been more work at several different scales.

One of the most exciting aspects of this book is the development of a framework for a "science of scale," set out initially in the chapter by Kemp et al., who ask that ecologists explicitly examine what scale means and how to use it in the design and interpretation of experiments. Pace states this requirement clearly by calling for ecologists to stop "soft extrapolation," where true extrapolation of results is avoided and the application of results to other scales is unclear. This book both demands and gives ecologists the tools to start being more explicit about how our smaller scale ecological experiments might scale up to the larger scales of ecosystems.

Another fundamental question this book asks repeatedly is why we actually do ecology? Is it so we can understand the "true" nature of ecological systems or is it so we can make accurate predictions for them? The chapter by Nixon provides some interesting discussion on this issue, as it relates to scale and mesocosm work in estuaries. I think it is valuable to examine the debate that has occurred about the appropriate scales for experimental research in light of our goals as ecologists. Naeem clearly lays out the main types of experimental routes currently used in ecology along a continuum of high internal/low external validity to low internal/high external validity. I think Naeem's continuum is a more useful view of research than the dichotomy of "field" vs. "bottle" experiments that thus far has been the focus of debate. Along this continuum, he is able to identify the major types of experiments that currently dominate research. Several other authors (e.g., Pace, Allen, Wiens) in the book also examine this philosophical question and decide that we're mainly in this game for prediction ability in the long run. Wiens suggests, as do several authors, that we may need to get away from purely reductionist approaches and include larger scale surveys as well if our goal is prediction. Overall, the consensus appears to be to consider where along the continuum of external to internal validity our research lies and to use a multiplicity of approaches to fully address ecological systems.

The combination of philosophy and methodology for developing scaling relationships presented in this book provides ecological researchers with the tools to more explicitly explore ecological systems from an experimental perspective. Because, as Allen (Gardner et al. 2001) puts it: "the bottom line, experimentation is all about scale."

Gardner, R. H., W. M. Kemp, V. S. Kennedy, and J. E. Petersen, editors. 2001. Scaling relations in experimental ecology. Columbia University Press, New York, New York, USA. 352 pp., cloth, U.S. $32.50. ISBN 0231114990.

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Carpenter, S. R. 1996. Microcosm experiments have limited relevance for community and ecosystem ecology. Ecology 77:667-680.

Carpenter, S. R. 1999. Microcosm experiments have limited relevance for community and ecosystem ecology: Reply. Ecology 80:1085-1088.

Drenner, R. W., and A. Mazumder. 1999. Microcosm experiments have limited relevance for community and ecosystem ecology: Comment. Ecology 80:1081-1085.