Integrative and Comparative Biology Advance Access originally published online on July 7, 2007
Integrative and Comparative Biology 2007 47(5):790-793; doi:10.1093/icb/icm013
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Book Review |
Extinction & Biogeography of Tropical Pacific Birds. David W. Steadman.
UMDNJ-Robert Wood Johnson Medical School and Rutgers University Graduate Program in Ecology and Evolution, Piscataway, NJ 08854
Correspondence: E-mail: gochfeld{at}eohsi.rutgers.edu
Extinction & Biogeography of Tropical Pacific Birds. David W Steadman.
Chicago: University of Chicago Press: $45 (paper) ISBN: 978-0-226-77142-7 $110 (cloth) ISBN: 978-0-226-77141-0.
Among almost 600 pages, two quotes characterize David Steadman's synthesis and analysis of avian biogeography in Oceania. "Pre-historic bird bones (the heart of this book)" and "extinction of birds, a topic that will dominate this book." What a steal, to have so much information, data and interpretation packed into a single moderately priced volume. Although Steadman is well known as an avian paleontologist, this book represents a tour de force presentation of historical biogeography covering about a quarter of the globe, as well as analysis leading to Steadman's conclusion that it's all about extinction. This book is provocative and particularly the last third will certainly be controversial, attacking central beliefs or dogmas of island biogeography. Whereas Ernst Mayr (1945
), whose main area of field research was also in the southwest Pacific, had the impression that the avifaunas of Oceania were intact, Steadman shows the opposite. Surviving avifaunas are merely the tip of the historic iceberg, and most extinctions have occurred relatively recently and at the hand of humans, both "natives" and Europeans. Having a long-standing interest in Micronesia and being an avid birdwatcher, the Pacific Islands have posed both an intellectual and "athletic" challenge for me. There are simply too many of them. I agree with the author: "No place on earth is so geographically perplexing." How can you get your hands around hundreds of species on thousands of islands, particularly when the names of islands and their geopolitical boundaries keep changing. Should you approach it geographically or taxonomically. Steadman solves this dilemma by doing both.
Extinction & Biogeography is divided into four parts: (1) four chapters on geography, ecology, demography, archaeology, and avian data sources, (2) four regional chapters: Melanesia, West and East Polynesia, and Micronesia, (3) seven chapters on taxonomic groups, and (4) seven chapters on biogeography and conservation—including the analyses and critique of island biogeography. This is a big, data-rich, thought-provoking, profoundly disturbing, and hugely enlightening book. Although not a page-turner, it is clearly written, yet detailed, with over 1800 references, many by Steadman himself.
Steadman pulls together geology, physical oceanography, and historical climatology, with archaeology, paleontology, palynology, taphonomy, and even linguistics to weave a tapestry of extant, recently extinct, and prehistoric avian occurrence on many islands of the Pacific. It is apparent, and he repeatedly cautions, that so much remains unknown about the temporal, spatial, and taxonomic aspects of the paleontology of Oceania. There is a warning that many terrestrial biogeographers have recognized, but which applies to archipelagos such as Oceania: what we see today may have little relevance to their recent history. The biogeographic signal has been scrambled by human introductions and extinctions. In the light of so much uncertainty he could have tempered his speculations and conclusions.
Oceania's flora and fauna are largely Old World in origin. Steadman identifies isolation as an important variable influencing the prehuman avian (and also plant) species diversity. The Pleistocene to Recent period has been one of drastically fluctuating climate and sea level that impacted Oceania, alternately joining islands and sundering them into groups of isolated peaks—today's islands. Sea level today is, perhaps, 125 m higher than at the last glacial maximum 20,000 years ago, leading to much greater isolation. New Guinea and Australia were connected relatively recently, leading Steadman to consider New Guinea as a "continent" in historical context. Inspection of tables indicates that for many of the remote islands lower sea level would have had negligible impact on isolation, but New Caledonia would have been only 110 km from Australian shores, compared with 1280 km today.
Into this primarily watery world humans arrived perhaps as much as 60,000 years ago. Carbon dating plays a major role in Steadman's interpretation of bones, and imposes a historic limit of 45,000 years Before Present (BP), beyond which time 14C levels have approached background levels, hence the impact of the earliest arrival of humans is difficult to unravel or date with confidence. Steadman provides extensive discussion of human settlement, with admirable archaeologic documentation. There are many pages mapping ancient human sites on several islands with description and illustration of the bones encountered therein. Some sites provide information as old as 35,000 years BP, but most are in the 10,000–3000 year BP range.
Humans spread eastward out of Asia, and wherever they arrived, they exploited wildlife on land and sea. As they moved eastward, they encountered islands with depauperate mammalian faunas (due to limited prior colonization). Therefore, birds of various species bore the brunt of human predation. This is evident from some of the archaeologic sites that have been well characterized, and it appears that most extant (or at least most discovered) bird bones and fragments are associated with prehistoric or historic human settlements.
The human impact permeates this volume. For example, "Gone is the undescribed lowland forest that once must have covered much of Tahiti." Residual forest survives on areas too steep to cultivate. Deforestation and replacement by non-native species characterizes the flora, and to a large extent the fauna as well. As mentioned initially, extinction is a major theme. Whereas island biogeography emphasized turnover with the implication that the disappearance of an island population might be due to competition or stochastic events, Steadman emphasizes over and over the role of humans through direct exploitation, habitat destruction, and introduced predators, processes which remain a major theme today (Burger and Gochfeld 1994). Steadman emphasizes that the term "extinction" should apply to the end of an entire species, and uses the widely accepted term "extirpation" for the loss of a population from a geographic area or island. He decries the terms "local extinction" or "temporary extinction," which actually serves to weaken the impact of the term "extinction." The power of extinction is most evident in the chapter on rails, once a very speciose taxon, "all but a few of the many endemic flightless species [are] now extinct."
There is a wealth of speculation that is thought provoking. Polynesian islands have lost 50–90% of their native landbirds compared with about 20% on New Ireland. Steadman suggests that the latter avifauna, evolving with predatory native rodents, was therefore preadapted to survive with introduced rodents (Rattus), which quickly wiped out naïve birds on the Polynesias.
Although birds are well studied, Steadman repeatedly identifies distributional and taxonomic data gaps in knowledge of other terrestrial vertebrates and invertebrates. New Guinea, for example, offers few examples of bird bones or extinctions, which Steadman infers indicates major data gaps rather than invulnerability. That this is a work in progress can be inferred from Steadman's own acknowledgment of his increasing ability even over the past decade to identify bones to taxon, as more comparative material has become available. Indeed, there is an incomparable breadth of information here; for example, I was taken by the identification matrix of bone needles from Polynesian sites, giving the number of each type of bone attributable to five different taxonomic groups (including fruit bats).
There are three disappointments. (1) As a champion of biodiversity, we have to consider each species as a unique entity, hence a proper noun deserving of capitalization—contra newspaper traditions. The nonornithologic reader would not know, for example, that "red jungle fowl" refers to one of four species of jungle fowl, rather than merely a jungle fowl that is red. Specialty bird journals, such as The Auk, do capitalize the names of bird species, and general journals should follow suit. (2) Many tables provide invaluable species x island or genus x island matrices, summarizing information found nowhere else, but while some of the tables indicate whether a taxon is endemic to a particular island, others omit this valuable information, and do not indicate whether a bird is widespread, or endemic to an island or island group. (3) But these are minor criticisms. The more serious criticism is the lack of quantitative analysis of area, distance, and species diversity which would have enriched this volume. With this missed opportunity, future students will have a field day using these data to test more quantitatively the prevailing ideas in biogeography which Steadman has cast aside.
Probably most readers of this review will find chapters 18 ("Equilibrium and Turnover") and 19 ("Species-Area Relationships") most intellectually engaging. These include the wealth of qualitative data supporting Steadman's critique of island biogeography. The islands of the Pacific offer a laboratory for testing ideas of Island Biogeography as articulated by MacArthur and Wilson (1967) and expanded by Mayr and Diamond (2001). Steadman argues that colonization and extinction are not linked, and that Oceania does not support evidence for faunal equilibria. Also the theoretical models do not take into account that there are very few documented unassisted colonizations and very few documented unassisted extirpations. Future researchers will have ample opportunity to search for such examples.
Steadman clearly believes that extinction rates and species richness are unreliable indicators of biogeography wherever humans have settled. Yet, far from being nihilistic, Steadman incorporates humans as central to the current (last 30,000 years) of history. I am particularly gratified by Steadman's argument that not all species are equivalent. The extinction of a keystone predator (a large raptor), for example, has different consequnces than the loss of a nectarivore. To begin with, any one island may have only one of the former and several of the latter. Yet, the models take equivalency as a simplifying assumption.
Likewise Steadman identifies himself as "suspicious of anything elegant" such as the species–area (S–A) curve with its two parameters "only one of which requires field work." Steadman recognizes area and isolation, but asserts that they cannot be predictive if one ignores anthropogenic extinctions as well as variations in data quality. This may be a strawman, since earlier theorists may have underestimated, but certainly didn't ignore anthropogenic extinction.
Steadman shows convincingly that in the Pacific, particularly in Remote Oceania that had no neogene connection with continents, isolation is more influential than area or elevation. He adds, however, that extinction during, and due to, human occupation is the most influential factor. He provides a detailed analysis and alternative explanations of several S–A curves from MacArthur and Wilson (1967) and Mayr and Diamond (2001). He cautions that even today's inferences must be re-evaluated as new historical and pre-historical material are brought to light. There is more work for avian paleontologists.
Some of the ecological generalizations will hardly surprise readers. In Tonga most ground-nesting birds have been eliminated. Frugivores have taken a bigger hit than insectivores, which I infer is because they tend to be bigger than insectivores, and perhaps sweeter, not to mention congregating at fruiting trees where they are vulnerable to hunters. Steadman concludes: "Human presence on tropical islands" has been an environmental catastrophe, recognizing that anthropologists may be shocked by this view.
It would have come as no surprise to MacArthur and Wilson that the main value of their 1967 monograph was heuristic rather than predictive. On the first page of their preface they write: "We do not seriously believe that the particular formulations advanced in the chapters to follow will fit for very long the exacting results of future empirical investigation. We hope instead that they will contribute to the stimulation of new forms of theoretical and empirical studies." Steadman's work has met this expectation and has fueled such studies.
Steadman has some appealing biases. "Molecules are OK, but so are whole organisms or macroscopic bits thereof." He worries about "Young biologists who scoff at description even though they cannot describe." A recent game of ornithological jeopardy at the North American Ornithological Congress (2006) revealed fantastically knowledgable young ornithologists, who nonetheless could not answer some basic taxonomic questions about the families to which some common birds (e.g., Loons) belong. Some of my molecular colleagues act as if a whole animal is a confounder and refer to a cell culture as "in vivo." Steadman concludes, "We’re all trying to understand nature. That is a privilege to treasure and preserve." Anyone interested in historical biogeography in general or nature on Pacific Islands should pay attention to this fascinating work.
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Burger J, Gochfeld M. Predation and effects of humans on island nesting seabirds. In: Seabirds on Islands: Threats, Case Studies and Action Plans.—Nettleship DN, Burger J, Gochfeld M, eds. (1994) Cambridge, U.K: BirdLife International Conservation Series No. 1. 39–67.
MacArthur RH, Wilson EO. The Theory of Island Biogeography. (1967) Princeton, NJ: Princeotn University Press.
Mayr E. Birds of the Southwest Pacific. (1945) New York: Macmillan.
Mayr E, Diamond JM. The Birds of Northern Melanesia: Speciation, Ecology, and Biogeography. (2001) New York: Oxford University Press.
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