Extinction & Biogeography of Tropical Pacific Birds [Englisch] [Taschenbuch]

Oceania is one of the most fascinating biogeographic regions in the world, with a unique avian biodiversity which has risen over evolutionary time on a myriad of islands, of various sizes, spread across the western part of the Pacific. Characterized by a high degree of endemism, specialization, and unusual community composition, these contemporary avifaunas have been and continue to be at great direct and indirect risk from human activities - which have already caused widespread extinctions (Steadman 1995). Frequently, the only traces allowing the reconstruction of avian communities are bones: a silent language palaeontologists understand and use to gain insights into long-gone outcomes of selection in one of the most intriguing playgrounds of evolution.

In Extinction and Biogeography of Tropical Pacific Birds, David Steadman, a curator in the Division of Ornithology at the Florida Museum of Natural History in Gainesville, presents the results of more than twenty years of digging, excavating, and measuring hundreds of thousands of bones from more than 25,000 specimens from Hawaii to New Zealand. It marks the final step of a research effort which has resulted in the discovery of dozens of extinct species, previously unknown to science, and many more awaiting description It has also yielded valuable new data on tropical Pacific island species' biogeography and diversity. We now know that many Pacific Island bird communities were much more species rich than previously thought, flightlessness was more common and widespread, and on many islands the arrival of humans was directly followed by a sharp decline in vertebrate diversity - a fact previously well-documented on only a few islands. Steadman has achieved his goal and provided a natural history account of tropical island bird communities, with more detail and depth than ever before and with a great passion and drive. At a time dominated by molecular techniques, he managed to find funds, field sites, establish cooperation networks to generate a wealth of unseen empirical data. The result is impressive and weighs heavily, not only in terms of the more than six hundred pages the volume mounts to.

Steadman has structured his work into four parts, preceded by an introductory preface that sets the stage for the presentation of his findings. Part I (chapters 1-4) describes in detail the geography and geology, terrestrial flora and fauna, human history and availability of specimens, both dead and alive, on islands and in museums. It is very rich in detail, with regional and topographical maps, geological sketches, reflections on aspects of human geography, including photographs of archaeological artefacts and excavation sites, even detailed lists of field trips can be found. Part II (chapters 5-8) is concerned with species diversity in the four focal regions covered by the book: Melanesia, West Polynesia, East Polynesia and Micronesia including remote central Pacific islands. Again, rich in maps, this part of the book provides lists, sometimes down to the species level, of the occurrence of birds in the different geographic regions, again occasionally resolved down to the archipelago or island level. In Part III (chapter 9-15), the information structuring changes to taxa, encompassing megapodes, rails, pigeons and doves, parrots, other non-passerine land birds, passerines and finally seabirds. The chapter is rich in tables down to the species level of occurrences of species, on archipelago to island levels, and generously illustrated with photographs. Finally, part IV (chapter 16-22) addresses topics revolving around the rich data assembled: extinction, dispersal, colonization, faunal attenuation, equilibrium and turnover, species-area relationships, community ecology, conservation biology. At the end, a concluding chapter is added. Analyses offered, and used to draw conclusions, include: species-area plots, over different time scales (pre-human to today); graphs describing the representation of different genera on islands and island groups; and also visual materials, addressing ecological key factors such as trophic niche occupancy. A very personal `final word' wraps up this last part.

Although sometimes lengthy to read, repetitive (e.g. most obviously, the same photograph, figure 1-14, appears three times throughout the book) and loaded with information from many other areas of science, to a questionable degree of necessity, the book's strengths clearly lie in the enormous level of detail and the amount of novel data presented that are now accessible to the scientific community. Its weaknesses, however, reveal themselves in the preface, and even more so in the last chapter. Instead of using his data to test current theories on island biogeography, proposed by previous authors - such as Edward O. Wilson, Robert MacArthur (MacArthur and Wilson 1967), Ernst Mayr and Jared Diamond (Mayr 1942; Mayr and Diamond 2001) - Steadman chooses to criticize the leaders in the field based on very shaky grounds. The level of analysis presented in this book is very superficial and crude, omitting thorough testing of assumptions of current theory for which previously data was largely missing. While it may be argued that it would be too far-reaching to address detailed predictions, one would at least expect basic conceptual points to be addressed. It is, for instance, known that the number of species (S) on islands is influenced by area (A), distance (D) and elevation (L), which are on a regular basis effects addressed by statistical analyses, and that incomplete sampling, as is the case in this work, necessitates possible correction by estimation before using data in any analytical context. None of this can be found for prehistoric data. This book is full of anecdotal evidence, specific examples, and detailed conclusions. However, proper links between them are largely missing.

`I see little value in reducing a complex biological situation to an equation ...' writes the author in the preface. Yet of what value are data gathered at an unprecedented level of detail if not used to derive general patterns and test current theories on how bird communities on islands evolve? To go beyond the descriptive accounts of natural historians was exactly what MacArthur and Wilson believed was necessary when they first published their `Theory of Island Biogeography' in 1967 (see back cover of MacArthur and Wilson 1967). A true large-scale understanding of ecosystem organization and evolution cannot be derived from a pile of bird bones - a historical perspective is certainly valuable, but without integration into a modern biological framework, the beliefs, expectations, speculations and predictions presented in this book are hardly useful. The transition from belief to conclusion in science requires the mandatory step of data gathering and statistical hypothesis testing - the latter of which Steadman has largely chosen to ignore. The most fantastic dataset is useless unless one knows how to analyze it in order to further knowledge. Steadman's approach to `... sit around the same campfire, pass the bottle and swap lies' may not be the appropriate answer to contemporary problems in particular of conservation biology, and I see little ground for the author to claim that the `trend in science away from natural history and toward specialization and theory is out of control', as Steadman seems to believe. Today's extinction crisis is highly unlikely to be effectively dammed solely by digging up bones of the ghosts of evolution past. Instead, we need to accurately interpret this valuable data, and use it to better understand the complex evolutionary processes structuring nature. In the long run, this will prove the only way to improve the survival of the fascinating bird diversity of the western Pacific.

In summary I would, despite shortcomings, consider the volume well worth reading and as presenting impressive data. Once completely analyzed, the findings of Steadman's work will noticeably improve our knowledge on the evolutionary history of island avifaunas and beyond and find integration into the history of island biogeography as a milestone of progress.

Stefan M. Klose, Ulm, Germany, and Brisbane, Australia

REFERENCES

MacArthur RH, Wilson EO (1967) The Theory of Island Biogeography. Princeton University Press, Princeton, NJ

Mayr E (1942) Systematics of the Origin of Species. Columbia University Press, New York

Mayr E, Diamond J (2001) The Birds of Northern Melanesia - Speciation, Ecology and Biogeography. Oxford University Press, New York

Steadman DW (1995) Prehistoric extinctions of pacific island birds - biodiversity meets zooarchaeology. Science 267:1123-1131

(submitted to Ecotropica as a book review in Jan 2007)