Alien Species in North America and Hawaii: Impacts on Natural Ecosystems.—George W. Cox. 1999. Island Press, Washington, D.C. xii + 387 pp. ISBN 1-55963-679-3. Cloth, $60.00, ISBN 1-55963-680-7. Paper, $30.00.—This book focuses on one of the greatest threats to biodiversity in North America, the spread of alien (or exotic) species into ecosystems across the continent. The United States is the most “invaded” country in the world for a variety of reasons discussed herein (despite the title, this book focuses on the United States with minimal treatment of Canada and Mexico). Cox makes the point that, for the general public, this huge threat to North American (=United States) biodiversity is generally unknown. Based on my own experience, I certainly agree. Particularly obnoxious exotic species clearly do become known to the public in the geographic area invaded (in my part of the country one thinks of zebra mussels, Dreissena polymorpha, or the Asian honeysuckles, Lonicera spp.), but Cox's exhaustive treatment makes it quite clear that the problem goes far beyond the better-known villains. The general public (including most of our undergraduate students) has little or no idea how severe the invasion is or its ecological implications.
The book is laid out in five parts. The first part (Introduction) comprises three chapters that indicate the extent and historical perspective of the problem. Half of the book is included in the second part (Regional Perspectives) wherein 10 regions of the continent (=United States) are treated. In terms of descriptive data, this is the meat of the book, and I found myself continually surprised by the great number of exotic species that have invaded each region. The third part of Cox's book (Biotic Perspectives) includes three chapters that discuss exotic species and the role that humans played in their introduction. That includes the deliberate introduction of game species and the spread of North American native species into new parts of the country, as well as the planned and unplanned release of human associates (e.g. cats, rats, mice, pigs, and goats).
The three chapters in the fourth part (Theoretical Perspectives) investigate ecological and evolutionary patterns, including such questions as: “What makes an invading species successful?” “What makes a community vulnerable to invasion?” “Might invaded communities reach alternative stable states?” and “What might be the evolutionary changes in both exotic and native species in invaded communities?” My guess is that, for many readers, that section is potentially the most interesting—it proved to be so for me. However, at the same time, I was somewhat frustrated to learn how little we know about those patterns and the fact that, at least at present, there simply are no clear answers to many of the questions raised.
The last part (Policy Perspectives) includes two chapters that ask the question, “What is to be done?” Even the most conservative estimates conclude that dealing with the impact of exotic species costs the United States several billion dollars a year (perhaps over $100 billion per year!). Although the arsenal of proposed “weapons” is broad, appropriate use of these will require ecological wisdom not always shown in the past.
Are the interests of The Auk readers affected by exotic species? Those of us who are field ecologists are working with bird study species whose ecology is very likely influenced in some way by invading plants, animals, and microbes, including pathogens. The impact of exotic species on the systems we study may be subtle or dramatic but, in any case, it would be unwise simply to assume that we don't need to take into consideration the presence of alien species in our field research. For example, if one finds reduced nesting success, is it due to competition with an exotic species for a nest site? Or, is it due to parasitism by Brown-headed Cowbirds (Molothrus ater)? Similarly, are high nest-predation rates the result of an introduced predator? Is reproductive success low because the feeding rate to nestlings is low, perhaps as a result of competition for food with an exotic species? Maybe an introduced pathogen is reducing food availability or directly affecting nestling health. And on and on.
The intriguing result of reading Cox's book is that one begins to think about such questions. Cox provides so many interesting case histories about such a variety of habitats that it is inevitable that the reader interested in avian ecology will ponder such questions. Having said that, there is relatively little in the book that directly addresses birds, an exception being the treatment of avian introductions into Hawaii (with respect to bird introductions, the most invaded island archipelago in the world). The few bird examples given by Cox include the possible negative influence of introduced predatory crabs on native invertebrates and, thus, on Pacific coast shorebird populations (p. 55), the long-term impact of Dutch elm disease on Eastern U.S. forest-birds communities (p. 100), the disturbance of avian breeding habitats in southern Florida by the spread of the shrub known as Brazilian pepper (Schinus terebinthifolius) (p. 115), the consequences for native bird species as a result of exotic plants in grassland and riparian habitats (pp. 136, 148, 155), and the sad history of introduced game bird species throughout the U.S. (p. 200).
Should an avian ecologist buy this book? Let me answer by saying that an avian ecologist should read this book and request that your university library purchase a copy. Cox's treatments of species invasions in the habitats of North America are so informative that I think any field biologist working in one of these habitats would likely benefit from reading that habitat's treatment. Even if birds are discussed peripherally in some of those cases, the habitat summaries lead one to question in what ways one's study species might be influenced by exotic invaders. Certainly, for anyone who teaches a conservation biology course as I do, this book is essential reading. Even if one simply prepares a lecture or two on introduced species for another course, Cox's book clearly presents a wide variety of case histories to enliven a lecture. Without doubt, as I update my lectures on alien species, I will do so with Cox's book at my side.