The Speciation and Biogeography of Birds.—Ian Newton. 2003. Academic Press, London, UK. xii + 668 pp., 125 text figures. ISBN 0-12-517375-X. $75.00 (cloth).
Automated DNA sequencing technologies, the development of other easily automated genetic marker systems (e.g., single nucleotide polymorphisms, AFLPs), and the concomitant development of maximum-likelihood and Bayesian statistical methods to analyze these data have extended the depth of avian speciation studies to include inferences of effective population size, effective migration rate between populations, historical demographic changes within populations, branching relationships of gene copies or species, as well as a statistical framework for testing alternative hypotheses in each of these cases. These analyses do not supplant, but rather complement more traditional specimen-based speciation studies that examine quantitative characterizations of morphological variation in the organisms that actually interact with the environment. In tandem, these morphological and genetic analyses can provide unprecedented characterization of patterns of speciation, and keen insights into the underlying processes that shape them.
These developments are not the focus of Ian Newton's The Speciation and Biogeography of Birds, and readers expecting to find an in-depth summary of the latest and greatest knowledge regarding avian speciation will be disappointed. In spite of its title, the central thesis of this book is not avian speciation, but bird distributions and the ecological processes that shape them. This focus is evident in the book's overall structure. Excluding the “Introduction” and “Conclusions” chapters, the meat of the book is divided into five primary parts. The first of these (82 pages), entitled “Evolution and Diversity of Birds,” is the “speciation” component of the book. The other four main sections, collectively totaling 438 pages, or 84% of the meat, represents the “biogeography” part of the book: Part 2 (Major Distribution Patterns), Part 3 (Effects of Past Climates), Part 4 (Limitation of Species Distributions), and Part 5 (Bird Movements). The text's targets are “advanced students of population and evolutionary biology,” but jargon is minimized in the hopes of reaching a wider audience (e.g., bird-watchers).
Because birds are relatively large, not especially fecund, and often difficult to maintain in captivity, they were not destined to become a workhorse for laboratory speciation studies, a la Drosophila fruitflies (Coyne and Orr 2004). In most other respects, however, birds are ideal study organisms for speciation and historical biogeography studies, and the advent of DNA sequencing technologies has been a major facilitator. Molecular systematics is arguably one of the fastest growing fields in ornithology, with the number of published studies increasing almost exponentially over the past few years. In addition to providing insights into speciation and the historical branching patterns of lineages (Swofford et al. 1996), phylogenetic trees provide the framework for nearly all comparative studies (Pagel 1997). For a text focused on the speciation and biogeography of birds, it was odd to find so few phylogenetic trees—only three trees appeared in the entire book. Although Newton clearly recognizes the importance of phylogenetic trees (Sibley and Ahlquist's DNA-DNA hybrization-based “tapestry” is highlighted), most of the discussions of phylogenetics that did appear in the text were superficial or erroneous, beginning with the definition of “phylogeny” as the “study of evolutionary relationships” on page 24. To largely neglect this relevant and recent body of literature was a monumental weakness (for more details see Zink and Jones 2004).
Another inadequacy was that insufficient details were given for the well-studied systems in which avian speciation was addressed directly. For example, hybrid zones provide a natural laboratory for investigating pre- and post-mating reproductive isolation mechanisms (Harrison 1990), yet the best-studied systems were either ignored (e.g., Manacus manakins, Parsons et al. 1993) or older literature was cited when newer studies were available (e.g., Poecile chickadees, Bronson et al. 2003), or the study system was mentioned only briefly (e.g., Ficedula flycatchers, Saetre et al. 2001).
Structurally, the coverage of biogeography (Part 2) starts with a synthesis of the major distribution patterns of birds (subdivided into continental birds, island birds, and seabirds). Many extremely useful summary tables are presented, such as “Families of landbirds endemic to each zoological region,” “Numbers of bird species per family in different biogeographical regions,” and “Number of breeding seabird species in different regions.” Having all of this information in a single tome makes the book worthwhile for any student of avian biogeography. The next major section (Part 3) examines the role of past climate changes (e.g., glacial cycles) on the distributions of birds. Structurally, this section is subdivided into two chapters on glacial cycles in northern regions, one chapter on tropical regions, and a final chapter on disjunct ranges. This is largely a review of “suture zones” (Remington 1968), but, again, having all of the information in a single resource is valuable. Part 4 focuses on the contemporary factors that shape species distributions, beginning with a chapter on “Bird distribution patterns.” This chapter rehashes some of the ideas introduced in Part 2, and is followed by chapters on the factors that limit bird distributions and those that change bird distributions. This part ends with a chapter on “Crossing barriers”; this chapter seems a bit misplaced given that the next major part of the book (Part 5) focuses on “Bird Movements,” with chapters on both dispersal and migration.
A general criticism is that lots of topics are presented in each chapter, but few are discussed in sufficient detail or with the most recent citations. The result is that the text often moves along clumsily from one subtopic to the next, without any real transition between the ideas. For example, in Chapter 10 (Glacial Cycles in Northern Regions: Differentiation and Speciation) contiguous subtopics under the topic “Genetic Evidence for Past Climates” were “Population divergence in passerines,” “Population divergence of non-passerines,” “Patterns of colonization,” “Joining of populations following range expansion,” “Genetic evidence of species responses to barriers,” and “Population divergence in seabirds.” Collectively, these topics are covered in only 10 pages of text and the transitions between many of the subtopics are abrupt.
A positive aspect of the book is that summary tables and easy-to-interpret figures are abundant in most chapters. In addition, ample citations are presented within the text (all appear in a References section at the end of the book), providing plenty of jumping-off points into the primary literature. An Index contained nearly all of the topics for which I searched. The only weakness of the Index was the use of common names as the primary species flags. For example, the entry for Ficedula hypoleuca is “See Flycatcher, European Pied.” Because scientific names are the idiom of most researchers, especially those for whom English is not their first language, I was surprised that the scientific name was not primary.
In summary, the book suffers from an inappropriate title, with the consequences that many from the book's target audience will be missed, and worse, that many from its nontarget audience will be hit. Unfortunately, the title also masks the real strength of the book as a thorough treatment of avian distribution patterns and the ecological processes that shape them. The literature review alone makes it a valuable resource for any researcher interested in avian biogeography. Students using it as a textbook may find the conglomeration of subtopics within each chapter a bit cumbersome, but by carefully parsing the readings a lecturer could easily use this text in a course on avian biogeography. Its only other detraction as a textbook is that its scholarship suffers in some sections because relevant literature outside of ornithology is not incorporated into the narrative.