Metapopulation Biology: Ecology, Genetics, and Evolution. – book reviews
A growing emphasis on the conservation of species in fragmented habitats has propelled metapopulation studies to the forefront of ecological research. New spatial analysis tools allow ecologists to quantify patchiness in species distributions, and to ask ever more specific questions about how that patchiness affects population dynamics and genetics. The time is right for Ilkka Hanski and Michael Gilpin’s edited volume, intended “to sketch the general limits of metapopulation biology.”
Their first effort in this area (Gilpin, Michael, and Ilkka Hanski [eds.]. 1991. Metapopulation dynamics: empirical and theoretical investigations. Academic Press, San Diego, California) linked a scatter of interesting contributions from a workshop that focused primarily on metapopulation ecology. This new volume, drawn from solicited papers, offers a more synthetic vision of the metapopulation approach by including both ecological and evolutionary studies. The editors set their goals on disseminating ideas “across the customary academic confines” and promoting “an expansion of the metapopulation concept.” The varied perspectives of 30 authors help achieve these goals. Although the 18 chapters spring from diverse disciplines, efforts have been made to point out similarities and logical progressions among the different approaches.
The volume is divided into four parts, each preceded by an editorial overview that weaves together the wide-ranging topics. Part I outlines challenges for the metapopulation approach, with chapters addressing the perceived gulf between complex natural systems and simple models. The leadoff chapter raises the interesting question of whether the rising “metapopulation paradigm” will provide more testable hypotheses and useful predictions than its putative predecessor, island biogeography. Part II defines the metapopulation approach from a theoretical perspective, from patch-level models of genetics and dynamics (including multi-species dynamics) to structured models of single-species dynamics. Here, the editors promote a more ecologically and demographically realistic approach to modeling dynamics, but miss an opportunity to discuss whether genetic models might benefit from a similar attention to dynamic detail. Part III focuses on the components of metapopulation dynamics: local extinction, rescue effects, and the dynamic and evolutionary components of recolonization. There are places where the reductionist approach of this section may lose touch with processes that operate at the metapopulation level. For example, the discussion of local extinction times ignores the effect of metapopulation occupancy on local growth. Finally, Part IV presents case studies. The first chapter, on butterfly dynamics, presents the only compelling match between theory and data, and includes a useful essay on improving realism in future models. The final chapter, on genetic variation in a group of plant populations, offers a convenient review of metapopulation genetic models. This study also reveals difficulties that arise in testing the predictions of patch-level genetic models with data from natural systems that are demographically structured.
The book is particularly useful for students, with reviews covering the conceptual foundations and models underlying metapopulation theory, empirical evidence for metapopulation dynamics, and butterflies as models for metapopulation processes. Also useful is a glossary of jargon in the first chapter, although later chapters unfortunately define some terms differently (especially “mainland-island” and “source-sink” metapopulations). Editorial efforts are evident throughout the text, with extensive cross-referencing among chapters. Most authors review their subject areas with the non-initiated in mind, although some chapters are more accessible than others. In particular, a key chapter on evolution in metapopulations presumes some familiarity with model assumptions.
A recurrent theme is the need to expand our definition of metapopulations. The editors suggest that the “classic” definition – of local extinctions balanced by recolonization – should be “superseded by a broader view, where any assemblage of discrete local populations with migration among them is considered to be a metapopulation, regardless of the rate of population turnover.” Some of the theory and much of the empirical research reported here promote a need for this broader definition. In fact, empirical evidence reveals that classic metapopulation dynamics is usually not responsible for long-term persistence of spatially structured populations or communities. Despite this fact, several studies appear to use the metapopulation concept successfully to organize data and ideas. However, we are left wondering how often theory based on a classic definition of metapopulations can predict the dynamics of natural systems. Of the case studies, only butterflies show real evidence of conforming to theoretical predictions, apparently because butterfly dynamics tend toward classic metapopulation dynamics. Before we can test predictions in natural systems that require a broader definition of metapopulations, do we need a broader theory? Or do we need to rescale our empirical studies? A book that raises these questions leads to lively discussion.
The goals of the book are generally met. Real metapopulations are acknowledged to exhibit dynamics other than extinction and colonization, and models begin to incorporate these dynamics. The stage is also set for bridging gaps among disciplines, although there remains a need for direct comparison of models inspired by evolutionary and ecological mechanisms.
The primary value of this book lies in its self-conscious exploration of a paradigm under which ecological and evolutionary models have proliferated without substantial empirical tests. Perhaps the metapopulation concept thrives because the rate of colonization via theoretical advances is faster than the rate of extinction via empirical tests. We cannot evaluate such criticism without a survey of the utility of the concept across disciplines. This “attempt to sketch the general limits of metapopulation biology” is a good place to begin evaluating the efficacy of the metapopulation approach. If the approach proves useful, then this book is also a step toward synthesis of ecological and evolutionary metapopulation biology.
CHRIS RAY and MARTHA HOOPES University of California, Davis Division of Environmental Studies Davis, California 95616
COPYRIGHT 1997 Ecological Society of America
COPYRIGHT 2004 Gale Group