Year : 2003 | Volume
| Issue : 1 | Page : 171-172
Book review 4
Department of Plant Genetics and Breeding, University of Agricultural Sciences, GKVK Bangalore, India
K N Ganeshaiah
Department of Plant Genetics and Breeding, University of Agricultural Sciences, GKVK Bangalore
Source of Support: None, Conflict of Interest: None
|Date of Web Publication||20-Jul-2009|
|How to cite this article:|
Ganeshaiah K N. Book review 4. Conservat Soc 2003;1:171-2
S.P. Hubbell, The Unified Neutral Theory of Biodiversity and Biogeography. Princeton: Princeton University Press, 2001, $35. ISBN: 0-691-02128-7.
Plant communities differ with respect to the number, abundance and spatial distribution of species, at both local and regional scales. The factors shaping these patterns have been among the most important issues confronting ecologists and conservation biologists during the last two to three decades. Communities everywhere are characterised by a few simple features: the presence of a certain number of species, some species being more abundant than others and the spatial structuring based on the location of individuals. Past efforts to understand these patterns have been piecemeal, and few have dared to develop a theory that could parsimoniously explain the emergence of these patterns. Hubbell, in this book, proposes a unified theory of biodiversity and biogeography. The novelty of the approach and the unorthodoxy of Hubbell's conclusions render this monograph a landmark in the science of biodiversity.
Hubbell-s obsession is with the dynamics of the structure of forest communities. His observations of the structure and dynamics of plant communities in permanent plots scattered all over the world significantly contribute to the penetrating questions he raises in the book. While describing the simple but repetitive patterns of species abundance observed in diverse communities, he reviews various attempts, starting from Fisher. It turns out that earlier researchers were merely complacent with describing patterns and had in fact identified the wrong signals in the species abundance patterns. They did not seriously search for the processes underlying the patterns and those who did (e.g., McArthur-s broken stick model), did not offer meaningful mechanisms. Hubbell-s inquiry begins from these earlier attempts, and ends in raising serious doubts about the role of niche differentiation and interspecific competition in shaping species assemblages.
Hubbell-s triumph may be traced to two factors. The first is a consequence of his intense probing into species abundance patterns. Hubbell shows that species abundance patterns were entirely different from the assumed lognormal distributions, and that they are indeed lognormal like with a large left trail. The second is a consequence of a radically different analyses of the data sets, from which he shows that number of individuals in any defined community increases linearly with area-a simple fact with far-reaching implications to the understanding of the structure of communities.
Based on stochastic models describing the dynamics of communities, he builds a theory of death, migration and speciation, and shows that the observed patterns of species abundance of a given community could be explained purely as a function of these parameters. He demonstrates that depending upon the proximity among, and the sizes of, communities, their composition and species assemblages could change merely by the stochastic processes of death and dispersal (bringing about the spatial structuring of the diversity).
One of the most important spin-offs of Hubbell's modeling exercise is the emergence of a fundamental value of Biodiversity q (a product of the size of the meta-community [J] and the rate of speciation), the parameter that decides the level of biological diversity of a community at equilibrium state. Thus Hubbell's work attempts to tie together the three components of ecosystem: biodiversity, species abundance and spatial structuring.
Thus, the most striking argument emerging in the book is that the structure and organisation of communities can be explained purely as a stochastic combination of species available in the regional or at a meta-community level and that any given state of a community is a consequence of the levels of death and dispersal that are considered neutral (equal) among species. This argument obviously shocks evolutionary ecologists because it implies that niche differentiation and competition have little role, if any, in shaping communities. But the powerful predictions and their tests offered by Hubbell justify the argument.
Hubbell develops and organises the entire argument very lucidly. Even a novice in the area of ecological modeling can follow the arguments. The book is sure to stir up a lot of discussion amongst ecologists and conservation biologists. Several predictions in the book are likely to serve as key hypotheses demanding to be tested by field ecologists in the years to come. This book raises a number of challenges for researchers in the area of biodiversity and conservation ecology, and even for conservation policy-makers. Undoubtedly the book sows the seeds of a new science of biodiversity.