M. A. Davis: Invasion biology
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- Lockwood, J.L. Biol Invasions (2010) 12: 971. doi:10.1007/s10530-009-9482-8
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Anyone who reads this journal is aware of the growing prominence of invasion biology in the scientific and popular literature. The field has quite literally grown exponentially over the last two decades. It is time for some perspective, and Invasion Biology delivers a heavy and welcome dose. The volume is geared for early career scientists (e.g., graduate students, post-docs, and junior professors), although anyone interested in the field will find something to like or dislike in this book. The author, Mark A. Davis, is a well-respected and long-time contributor to the study of biological invasions. He studies plant invasions, mostly from the viewpoint of a community ecologist. His choice of what to cover within Invasion Biology can be clearly assigned to this academic heritage. However, this volume represents much more than the standard routine of ‘senior ecologists takes measure of his own scientific discipline’. It is a fascinating hybrid collection of literature review, introduction of new theory, and critique.
The first Part of the book (Chaps. 1–6) represents the literature review, including a very useful review of the history of the discipline in Chap. 1. To include a good review together with the other Parts (see below) was a difficult task. From my perspective, the review in Part I tended to be cursory. However, there were three highlights that I want to mention. First, Davis presents a nuanced view of the invasion pathway, which has been a bit overly formalized within several recent publications including my own (Lockwood et al. 2007). Davis’ conception of the pathway brings a needed dynamism to the framework, although after reading his description a couple of times, I mostly wanted to sit down with Mark and ask him to clarify chunks of it. Second, Davis et al. (2000) are the primary force behind the fluctuating resource hypothesis of invasion success. Invasion Biology clarifies and expands on this hypothesis and illustrates why it has continued to provide a useful framework for understanding plant invasions. Third, and to me the best element of this Part, was Davis’ introduction of the “invasion cliff”. A book review cannot do this construct due justice, but the cliff integrates species’ traits, community (or habitat) invasibility, and propagule pressure under one rubric. It is an elegant attempt to mix three dominant themes in invasion biology to generate predictions of establishment success. The volume is worth your money just for this information alone.
The second Part (Chaps. 7, 8) concerns impacts and management of invasive species. Possibly because I do not regularly read or review this type of invasion literature, I found this Part to be far more compelling in terms of its ability to comprehensively review the state of the science. I found myself marking citations all through this chapter because I had not seen them before yet they were pertinent to my own research. I suspect that most academic invasion biologists will also find this section useful, in large part because scientific knowledge related to impact and management seems to be where most of the truly new ideas are now emerging. I very much recommend it to anyone who ever wrote a sentence in one of their publications or grant proposals that included the term “management implications”.
The writing in this Part also really took off for me. Just to highlight one piece that made me laugh out loud, Davis reviewed the impacts of non-native species on food webs and communities and recalled the sea lamprey (Petromyzon marinus) invasion of the Great Lakes that took place in the 1950s and 1960s. The sea lamprey caused a trophic cascade that eventually led to massive die-offs of non-native alewife (Alosa pseudoharengus), whose carcasses washed up and rotted on local beaches. This invasion was one in which Davis had suffered real impacts himself as he writes, “The author can attest that, for some romantically challenged teenagers who needed all the help they could get from moonlit beach ambiance, the alewife invasion was a tragic development”.
The final Part (Chaps. 9–12) is the truly unique part of this book. This Part is the one that will serve to challenge young scientists the most, and either irritate senior scientists or have them jumping for joy. Davis dares to touch the third rail of invasion biology, and then the fourth, fifth and sixth rails. Chapter 9 addresses issues of “framing”, including dealing head-on with the problems of deciding what constitutes a non-native versus a native species, meshing advocacy with scientific objectivity, and evaluating whether invasion biology is simply an attempt at “restorative nostalgia”. Chapter 10 updates and expands a 2001 call by Davis et al. (2001) to re-integrate invasion biology with the mainstream of ecology. He presents compelling evidence that publishing only within narrowly focused journals (of which Biological Invasions likely qualifies), citing only other invasion-focused research, and developing a terminology that often re-invents existing ecological or biogeographical ideas is counter-productive. Chapter 11 goes after some sacred cows in invasion biology, such as the common assertion that biological invaders are one of the leading causes of threat for imperiled species and that high species diversity prevents species invasion. Davis does not dispute the large ecological and economic costs of some invasive species, but he does rightly draw attention to the problem of unchallenged axioms and paradigms in the field. As the field grows, we must do a better job of challenging long-held assumptions and be bold enough to finally throw out those that have not withstood empirical testing.
The final chapter (12) is the most personal of the lot in that Davis “offer[s] some personal reflections on the field of invasion biology and its future”. As he acknowledges in this chapter, he comes close to arguing that the discipline should cease to be a specialized field in ecology and instead should be “…practiced more as a part of mainstream ecology.” The discipline is indeed transforming itself into a more pluralistic endeavor that explicitly recognizes its interdigitation with both ecology and evolutionary biology. This transition is inevitable, and ultimately for the best. And this is the “invasion biology of the twenty-first century” that Davis would like to help usher into being via this volume. He eloquently phrased this goal within the last pages of Invasion Biology like this; “Actually it (invasion biology) is not really our science: it is ours to tend. Others have tended it before us, and now it is our responsibility to tend it well, so that it will be in good condition when we pass it off to those who will follow us.”