‘OUR BEST FRIENDS AND CLOSE ASSOCIATES’. ALIEN SPECIES ON THE NORTH AMERICAN BATTLEGROUND

Cox, G.W. (1999) Alien species in North America and Hawaii: impacts on natural ecosystems. Island Press, Washington. xii + 387 pp, tables, glossary, index. Hardback: Price US$60.00. ISBN 1 559 63679 3. Paperback: Price US$30.00. ISBN 1 559 63680 7. In the clear, concise style characterizing Cox’s previous texts from his Dynamic ecology (1973) to Conservation biology: concepts and applications (1997), his latest work, Alien species in North America and Hawaii: impacts on natural ecosystems, constitutes a comprehensive synthesis of the history, distribution, impacts, management initiatives and policy dilemmas of some the most noxious introduced species in the 10 most seriously affected regions of the United States. Canada is treated to a much lesser degree and Mexico is mentioned in passing on only six occasions. The stated objective of the book is ‘to evaluate exotic invasions of North America in the light of the emerging science of invasion ecology’, and to ‘examine the seriousness of the threat of these invaders to North America, and what can be done to reduce this threat.’ As the subtitle suggests, the book is not a dispassionate evaluation of exotics. Rather, it attempts to fill the ‘education gap’ between concerned environmentalists and ‘the public at large [that] remains largely unaware of the seriousness of the threat’ to the native flora and fauna of North America, ‘the largest battleground in the global war against invasive exotics.’ The approach is nonmathematical, better described as a descriptive catalogue than an analytical treatize. For the layperson, the book provides numerous examples of aggressive exotics from representative biomes of North America, the full range of invaders (plants, plant diseases, marine invertebrates, terrestrial invertebrates, insects, freshwater fish and terrestrial vertebrates) and across a broad range of habitat types (bays, estuaries, lakes, rivers and streams, forests, tropical and semitropical lowlands, plains and intermontane grasslands, floodplains, mediterranean ecosystems, and island ecosystems). In addition to the litany of geographically referenced species accounts, also presented are their myriad impacts in clear nontechnical language, as well as a cursory review of existing invasion theory. A short, but well-conceived, glossary clarifies technical terms and theoretical concepts. To its merit, the book considers impacts beyond simply those on charismatic or priority conservation species, also presenting community and ecosystem level impacts. The most significant contribution for the technical audience is the extensive cataloguing of exotics and their impacts based on a thorough and well-referenced review of both historical and current publications; many references come from the 1999 primary literature. Also useful is a three-page listing of internet sites dedicated to exotic species. The book is divided into five parts with each of the 21 chapters being introduced with effective and engaging case studies that present key conceptual issues to follow. Part I provides the historical and conceptual background upon which the regional treatments of Part II are based. Here the uninitiated receive a ‘crash course’ in invasion ecology ranging from the source, identity and attributes of some classic invaders such as the zebra mussel (Dreissena polymorpha), the history of exotic species introductions and their studies with the de rigeur references to Elton’s pioneering work The Ecology of Invasions by Animals & Plants (1958) and Carson’s Silent Spring (1962), and the magnitude of ecological and economic impacts of ‘biotic pollution.’ The comprehensive 10 regional treatment chapters of Part II constitute the bulk of the book. Spanning the whole of the United States and drawing on examples from the primary literature, Cox demonstrates convincingly that not all ecosystems are equally invasible and no single theory can account for invasions and their impacts. For example, reviewing case studies from his home state, California, it is argued that species rich areas commonly considered more ‘stable’ and less invasible are in some instances highly vulnerable to aggressive exotics from a range of taxa. While the impacts of exotics are most evident in Hawaii where they have occasioned both documented extinctions and quantifiable ecosystem function disruption, Cox emphasizes that ‘unpredictability is a key feature in invasions’ and that they often lead to unforeseen outcomes such as ‘food web chaos’. Part III introduces some of the dilemmas created by exotic species, associated impacts and their management. Deliberately introduced game species, such as the brown trout, ring-necked pheasant and sika deer are often seen as desirable. Likewise, control of native North American species with anthropogenically extended ranges is fraught with controversy. Finally, a chapter dedicated to problems associated with domesticated species gone feral, ‘our best friends and closest associates’, provides a vivid example of the many conflicting issues of ecology and ethics. In particular for the lay audience, this section constitutes an effective means of tempering the knee-jerk response of ‘why isn’t anyone doing anything?’ that many of the preceding examples may have provoked. Additionally it demands that the reader consider his own role in species introductions and their control. Whereas the regional treatment briefly introduces some theoretical aspects of invasion ecology, Part IV is specifically dedicated to this purpose. The format is standard (invader attributes and differential ecosystem vulnerability) and the theories presented are well known to professional ecologists (variable invasibility of successional stages, the relevance of assembly rules, niche breadth and openness, and disturbance). However, this short section provides some of the most interesting reading and insightful commentary. The varied nature of impacts is also considered including abiotic ecosystem impacts such as those on hydrology and fertility to biotic impacts, including those on trophic structure or occasioned by genetic swamping via hybridization between natives and exotics. Surely a matter of opinion, the book may have benefited from this section occurring before the regional treatment thereby providing a theoretical backdrop upon which the many specific case studies of Part II might be considered. Cox boldly closes in Part V with a presentation of the economic implications of exotic species and management options that exist to control them. The book concludes with an explicit review of the shortcomings of existing management institutions and their lack of integration and provides concrete recommendations for the strengthening of global and national organizations charged with exotic species management. He notes these will be increasingly called upon as invasions continue with cultural and economic globalization and as their impacts become even less predictable in the face of global environmental change. Although the examples provided are confined to North America, the wide range of climates and habitat types considered makes the book relevant to those interested in biological invasions from other areas. Being a discipline involving rates of change over time, correlations involving multiple factors and subjects considered within a geographical context, the use of illustrations, figures and diagrams would have enhanced the well-conceived text. While useful data is frequently presented in tabular form, other graphic representations are lacking. Given the importance of scale and spatial context, maps in particular would have been useful. Although the well-written text might have benefited from the inclusion of such graphical conceptual aids, on the whole the book represents a valuable contribution to the invasion literature for lay and technical audience alike. No original data, results or theories to explain the many invasions are presented, but the book clearly achieves the professed goal of reviewing the state of alien invasions in North America in attempting to fill the existing education gap between the informed environmentalist and uninformed public at large.

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