The Shrinking World: Ecological Consequences of Habitat Loss. Ilkka Hanski. International Ecology Institute, Oldendorf/Luhe, Germany, 2005. 307 pp. EUR 47.00 (ISSN 09322205 cloth).
Ilkka Hanski, professor of ecology andsystematics at the University of Helsinki, has championed the importance of incorporating a spatial perspective into the study of populations for more than 25 years. Recognizing his leadership in this area—a field of study now known as metapopulation dynamics—the International Ecology Institute of Oldendorf/Luhe, Germany, awarded Hanski its Ecology Institute Prize in 1999. Awarded annually since 1987, this prize comes with the expectation that the recipient will write a book for the institute's Excellence in Ecology (EE) book series, which consists exclusively of books by award recipients. The Shrinking World: Ecological Consequences of Habitat Loss represents Hanski's contribution to this series.
The stated purpose of the EE book series is to describe the current understanding of ecological patterns and processes, to show how ecological knowledge can be used effectively to benefit nature and humankind, and to bring all this to the attention of a broad audience, including fellow scientists, teachers, students, and decisionmakers. In explaining his goals for this book, Hanksi makes it clear what he tried to do and what he did not try to do. He did not want to attempt a comprehensive review of the extent and nature of habitat loss worldwide. Nor did he want to document and describe in detail past and current species extinctions. Rather, Hanski's aim was to write a book on habitat loss and its ecological consequences that would focus largely on populations rather than on species, and would describe the ecological processes by which species persist, or fail to persist, in natural landscapes consisting of multiple and connected populations. To my mind, Hanski has accomplished his goal, although given the book's focus, I would have changed one word in the subtitle so that it read “Population Consequences [instead of “Ecological Consequences”] of Habitat Loss.”I suspect that individuals who pick up the text solely on the basis of its title may be expecting something different from what is presented.
Most ecologists should find The Shrinking World a highly readable introduction to and overview of the basics of metapopulation ecology. Since 1991, Hanski has edited three other books on the subject, most recently Ecology, Genetics and Evolution of Metapopulations, coedited with Oscar Gaggiotti and published in 2004, which the editors suggested could be used as a textbook. Personally, I found the current book much more amenable to class usage than the 2004 volume, at least for classes being introduced to metapopulation ecology.
The Shrinking World consists of only five chapters. The first two lay the groundwork by discussing the nature of habitats (including the important distinction between macrohabitats and microhabitats) and habitat loss, and distinguishing between the consequences of habitat loss at the macro and micro levels. Hanski describes four kinds of habitat loss: loss of quality, loss of area, loss of connectivity, and loss of continuity. Chapters 1 and 2 will probably be of more interest to readers who come to the book with only a modest ecological background. Chapters 3 and 4 are the heart of the book; this is where Hanski addresses population responses (e.g., increase, decline, extinction, and persistence) to the different types of habitat loss. The material included in these chapters ranges from descriptive overviews of particular systems to the presentation of mathematical models that Hanski and his colleagues have developed to simulate various aspects of metapopulation dynamics. The final chapter addresses a variety of issues, including the impacts of climate change on habitat loss, the possibilities and limitations of habitat restoration, the role of conservation in society, and the importance of engaging children with nature.
The most important contribution of this book is its consistent emphasis on understanding persistence and extinction as a metapopulation process. In making this case, Hanski calls for more protection of “ordinary” habitats, noting the limitations and drawbacks of focusing conservation efforts solely on individual biodiversity hotspots. In addition, Hanski provides information that may be new, and perhaps surprising, to some readers. For example, the species richness of birds in many cities throughout the world has noticeably increased during the past 50 years, because the growth of urban area is often accompanied by an increase in birds' habitat quality (more foraging and breeding sites) and a decrease in the number of predators. Another counterintuitive finding is that large-bodied animals may actually be less affected by habitat fragmentation and alteration than many small-bodied animals. The reason, Hanski explains, is that large-bodied animals are often more likely to be generalists and also more flexible in their habitat requirements—that is, better able to accommodate habitat change through alterations in their behavior—whereas many small animals are habitat specialists, frequently microhabitat specialists, and are unable to negotiate any abrupt change in their habitat. For this reason, although bird and mammal diversity may be surprisingly high in many urban settings, as urban parkland may provide adequate macrohabitat structure, the diversity of many invertebrate and fungal species may be considerably reduced in human-altered landscapes because necessary microhabitats, such as decaying wood, are absent.
I very much enjoyed this book. In some ways it is peculiar in its organization, format, and writing style, although it must be noted that some of this distinctiveness is imposed by the editors of the series. Chapters are written according to a strict basic format, each concluding with a section titled “Summary of Five Items to Remember,” and each beginning with a “prelude,” which is a personal narrative intended to help set the context for the material to follow. For example, the prelude to the first chapter begins,“Mosquitos kept biting us fiercely as we leaned over the fallen log of a large Norway spruce.”I suppose one could say there is more quaintness than substance in these preludes, but I enjoyed reading them nevertheless.
Partly because of the distinctive prescribed format, and partly because the author was trying to meet the institute's goal that the EE books speak to a diverse audience, I found that the accessibility and depth of presentation varied. There are sections that should be easily accessible to the general reader but that the expert may find unnecessary, interspersed among sections that will be of more interest to the expert but probably not very accessible to the general reader. Ultimately, if one is going to try to reach such a diverse audience, I think the approach Hanski took is the right one, as opposed to one that tries to present all the material at some mid level of difficulty, which both groups would perceive as unsuitable. Readers are likely to find themselves skipping over certain parts of the text because the material is either too basic or too difficult for them, and then settling down in other parts for more intense consideration of the material.
Although most readers may find some material unsuitable or unnecessary, I do recommend this book to all the members of its intended diverse audience. In particular, I think it would be an excellent book for classes and seminars exploring population ecology, because of its content and its reasonable price. In fact, I have decided to use it in my advanced undergraduate seminar in conservation biology next semester.