On the Wings of Checkerspots: A Model System for Population Biology. Paul R. Ehrlich and Ilkka Hanski, eds. Oxford University Press, New York, 2004. 371 pp., illus. $64.50 (ISBN 019515827X cloth).
Forty-five years ago, Paul Ehrlich was hired as an assistant professor at Stanford University. There he initiated research, which continues today, on the Bay checkerspot butterfly (Euphydryas editha bayensis, family Nymphalidae, subfamily Nymphalinae, tribe Melitaeini) on Jasper Ridge, adjacent to the Stanford campus, to uncover processes at the population level of biological organization. He is currently Bing Professor of Population Studies and president of the Center for Conservation Biology at Stanford. As many know, Ehrlich was also the founder of ZPG, Zero Population Growth, now known as Population Connection. Ehrlich's concerns about human population growth come through at times in the book under review, but human population pressure is an ongoing threat to the world's biodiversity and ecosystems, so that is totally appropriate.
Ilkka Hanski has been professor of ecology at the University of Helsinki since 1988, but he began working on the Glanville fritillary (Melitaea cinxia) only in 1991. Before that, he had worked on mechanisms of coexistence of ecologically similar species that exploit highly ephemeral resources, including dung beetles and blowflies (dung and carcasses both arrive as small, temporary patches). Hanski had not, however, previously studied metapopulations in the field. In 1991, he changed emphasis when he was working with Matts Gyllenberg, a mathematician specializing in cancer cell populations. He convinced Gyllenberg that “real” populations would be much more interesting, and being familiar with Ehrlich's work, he began searching for an Old World relative of E. editha to study. He had never seen a Glanville fritillary alive, but inquiries suggested that it might be the right species and that the Åland Islands might be the right place to study it (especially since it had gone extinct in the rest of Finland in the 1970s).
Readers who are not population biologists or geographers have probably never heard of the Åland Islands, and neither had I. They are inconspicuous or absent on most maps, but an Internet search proved enlightening. They are a group of nearly 7000 islands, fewer than 100 of them inhabited, at the entrance to the Sea of Bothnia, slightly north of a line drawn between Helsinki and Stockholm, and substantially closer to Sweden.
I am not a population biologist, having done most of my work in systematics and biological control, but both of those subjects are intimately related to population biology; hence, the title of the book was intriguing. The volume is a synthesis of the research and writing of 15 contributors, but Ehrlich has contributed to six chapters and Hanski to nine, and they alone wrote chapters 1 and 15, so their involvement is significant.
The preface is fascinating because it gives the history of both the Ehrlich and the Hanski research programs and their collaborations with others. Following are chapters on checkerspot taxonomy and ecology, and on the structure and dynamics of populations of the Bay checkerspot and metapopulations of the Glanville fritillary; four chapters on aspects of reproductive and larval biology and on the species' natural enemies; two chapters on dispersal behavior and genetics; a comparison of checkerspots with other species; a discussion of their use as a model system; and a chapter on their conservation biology. Summary chapters on “What have we learned?” and “A look to the future” draw the most compelling strands together.
This book is a thorough series of essays on population biology as viewed through checkerspot biology. The authors point out that long-term studies have many difficulties, not the least of which are the problems ensuring continuity of funding and the likelihood that the composition of research groups will change. Another major difficulty is that of locating research sites in places where the habitats are not going to be destroyed by development or the research terminated for other reasons, especially in politically unstable countries.
On the Wings of Checkerspots includes extensive coverage of the development of methods for carrying out the authors' research on the Glanville fritillary and the Bay checkerspot. Both species occur over vast areas in patchworks of open meadows. M. cinxia is found from Spain to Lake Baikal in Siberia and from the Arctic to the Atlas Mountains in North Africa. E. editha occurs in much of the mountainous West of the United States and southern Canada. Both species have highly fragmented populations and neither moves much, resulting in great diversity, even from one habitat patch to another nearby. This has resulted in the development of a lot of interesting biological data, some of which are presented in detail. Ehrlich and Hanski were surprised to find that local extinctions, colonizations, and recolonizations were common in both species, but that they occurred most often in the M. cinxia populations.
The authors recommend butterflies as research subjects because they have the advantage of being easily spotted and identified in the field, and are easily marked with felt-tipped markers. They can then be released without injury or serious disturbance. I totally agree. In my experience of catching butterflies in many habitats and countries, checkerspots are ideal. They inhabit open meadows (not shrubs, treetops, undergrowth, or the like), they are easy to approach and catch even when they are not feeding, and they do not take flight into the next county when they are disturbed. Ehrlich and Hanski suggest that their studies should be used as model systems for organisms other than butterflies, with E. editha as a model for modern population concepts and M. cinxia for classic metapopulation concepts.
The color plates add much to an appreciation of the variation and similarity of checkerspot larvae and adults. They also provide good views of where the research was carried out, giving the reader an impression of the small patches that constitute many of the habitats. The similarities of some of the species are amazing. The plate of adults of a Pyrenees checkerspot community shows upper and lower views of males, and upper views of females, for six species of Melitaea and one of Euphydryas. These would be indistinguishable on the wing and difficult to identify in the hand for anybody without prior extensive experience.
The authors present an overview of the conservation status of butterflies in Europe and North America, together with a series of conservation lessons and 25 suggestions for their application. One important conclusion is that informed conservation decisions can often be made without exhaustive research. The authors also assert that humans are the insects' biggest problem, and that there is one contribution we can all make to butterfly conservation—to greatly expand the public's knowledge and appreciation of butterflies, so that more people will press decisionmakers to maintain butterflies as a valued component of the human environment.
In the “What have we learned?” chapter, Ehrlich and Hanski suggest that taxonomists, ecologists, and evolutionists should have concentrated their efforts on carefully chosen model systems instead of on the phylogenetic revisions of taxonomists or the isolated bits of information on a vast array of organisms gathered by ecologists. They also point out, however, that with the decimation of tropical rainforests, checkerspots are becoming more plentiful, because they are adapted to second-growth brushy vegetation. The argument is made that because tropical checkerspots are poorly known, a good cladistic analysis would be useful.
The philosophy of conservation comes through strongly, and it is emphasized in the final chapter, “A Look to the Future,” by the following statement: “In the case of the checkerspots, our knowledge of many aspects of their taxonomy, life histories, and population and metapopulation biology is already comprehensive enough to allow us to make useful predictions for science and conservation. Many lessons have been learned that, combined with those from studies of other organisms, should help us and others forge answers to much broader issues, ultimately to questions about humanity's relationship with the rest of the world” (p. 301).
The book is well written, well produced, and error free. My only suggestion would be that it should have had some notation indicating the chapter at the upper right corner of each page, since there are many references to other chapters that are difficult to locate.
Overall, this is an excellent book, even for those who do not have a strong interest in population dynamics. The history of the projects, the biology of the butterflies, and the philosophies promoted are worthy of anybody's time.