Two Views on the Ecology and Economics of Intervention against Invasive Species


Invasion Biology . Davis, M. A. 2009 . Oxford University Press , Oxford , U.K. 244 pp. $55 (paperback). ISBN 978-0-19-921876-9.
Bioinvasions and Globalization. Ecology, Economics, Management, and Policy. Perrings, C., H.Mooney, and M.Williamson, editors. 2010. Oxford University Press, Oxford, U.K. 267 pp. $70 (paperback). ISBN 978-0-19-956016-5.

Invasion Biology by Mark Davis covers the biology of invasive species and follows the traditional “ontogeny” of arrival, establishment, persistence, and spread—that is thought to provide spatial and temporal context for the process of invasion by invasive species. The author challenges this stage-based process, contending that it can distort the biological realities of the invasion process, but that it is useful in directing human interventions to halt the invasion or mitigate its effects.

The first part of the book focuses on the theoretical underpinning of invasion biology in order to update Elton (1958) and Williamson (1996) theories. Davis’ points and the abundance of references are stimulating and useful and further understanding of how introduced species became established—past tense. The author concludes, however, that the ability to predict whether non-native species will establish, persist, or spread is still limited. He concludes that to be able to make reliable predictions there needs to be greater reliance on more general theories of ecology that describe how species interact and persist. For example, do the interactions between native predators and native prey differ fundamentally from interactions between non-native predators and native prey, or do sympatric non-native herbivores (or plants) compete in the same ways as those species that have evolved together?

The second part of the book discusses how non-native species affect the new systems they inhabit, and what humans can do to modify these effects. Most of the options for management focus on the novel and interesting. For example, returning to his point about understanding the ecological context of invasive species, Davis discusses ways to manage invasive species by managing more tractable components of the trophic system (species or vegetation) in which they exist so as to reduce numbers of individuals of the invasive species or reduce its effects. The pessimistic review by Rejmánek and Pitcairn (2002) of the difficulties of eradicating exotic plant species is noted in the book. This view has biased some conservation professionals against attempting eradication. The difficulties in eradicating weeds documented by Rejmanek and Pitcairn do not apply to introduced animals, for which there are many successful eradication projects (see the database of eradications of mammals on and ambitious plans for further large-scale eradication projects (Genovesi et al. 2010).

Davis asks two key questions: how has theory supported practice and how has practice advanced theory? His answer to the first is, not much, whereas he touches lightly on the answer to the second in a short section on active adaptive management.

Finally, Davis reflects on future directions for the discipline and makes the point that the language related to invasive species is so loaded with value judgments that it is constraining understanding of the biology of invasions. The author does not ignore value judgments—one person's invasive species is another's valued resource. Rather, he makes values transparent and treats them in the context of economics and other social sciences.

The Perrings et al. volume takes up the questions of how human values affect practices and policies used to manage invasive species. It is an edited compilation of 16 chapters by 36 authors designed to direct national and international policy and regulatory instruments for managing invasive species. The first six chapters describe some of the major drivers of the probability and rates of invasion—climate change, globalization of trade, and changes in land use. The next five chapters focus on the economics of invasive species management—who pays and how should intervention policies be developed to limit the adverse effects of invasive species. The next three chapters present case studies on assessing these effects and developing national strategies. The final two chapters are on national and international policy issues.

The introductory chapter points out that “the problem of invasive species is as much an economic problem as an ecological problem.” Throughout the volume, authors make it clear that economists often do not understand ecologists and vice versa, and they reinforce the need for integrated biological and economic models and actions. It seems to me the questions of who should pay and how much someone should pay depend primarily on when intervention is most effective and efficient and whether eradication is feasible or control must be sustained in perpetuity once the invasive species has arrived. For example, it could be argued that surveillance of shipments that will cross borders is a public good and its cost should be borne largely by taxpayers. Once an invasive species becomes established, however, it is in the public good that some agency intervene. By the time an agency is identified and an equitable allocation of funding is established, the problem may have worsened. Whether the invasive species is having undesirable economic effects and whether it can be eradicated are key factors in how aggressively an invasion will be handled.

Perrings et al. lays out four issues as major drivers of species invasions. Managing the drivers themselves (as opposed to managing the invasive species per se) is clearly one way to limit invasions. Managing the globalization driver by developing national and international policies to reduce invasion risks is likely to be the most practical—managing the biological characters of the invasive species is largely impractical and whether climate change will be managed for other reasons is a moot issue.

The chapters on climate change support the point of the authors’ of Invasion Biology: invasive species should not be considered biologically different from native species. Understanding the mechanisms of invasion is important if we are to assist native species to track climatic conditions that support their survival and persistence. Bioinvasions and Globalization. Ecology, Economics, Management, and Policy is an interesting collection of papers, but it leaves more questions than it answers.

Both books are about invasive species, but they have a different objectives and thus different target audiences. Davis seeks primarily to elucidate how invasive species spread and interact and thus how people might manage them. These goals are reflected in his list of research priorities in the concluding chapter. Perrings et al.'s book focuses primarily on how people might intervene in the colonization of an area by a non-native species, given social and economic constraints, and this is reflected in their final chapter on public policy. Both books are useful and sometimes provocative, but perhaps the target audience for each book should read the other book.