Monographs in Population Biology, no. 32
Stephen P. Hubbell
PrincetonUniversity Press, Princeton, NJ
2001, 375 pp.
Price: $37.50 (paperback), $82.50 (hardcover)
ISBN: 0-691-02128-7 (paperback), 0-691-02129-5 (hardcover)
 

This book is number 32 in Princeton’s “Monographs in Population Biology” series. It was written to promote the potential of neutral theories to explain many ecological and biogeographic phenomena. Neutral theories use stochastic factors instead of deterministic niche interactions (such as competition, predation, and parasitism) in their explanations. Hubbell starts with MacArthur and Wilson’s (1967)equilibrium theory of island biogeography and builds a model o fcommunity organization, which he uses to explain the world’s biodiversity patterns and several other phenomena of ecological and biogeographic interest.

The book is well organized and well written. The chapter summaries are especially helpful. To understand the mathematical workings of the models, one needs to understand matrix algebra, but excellent verbal explanations of the models’ biology make the arguments of the book accessible to anyone with a background in ecology and biogeography. There are several minor errors in the book(spaces missing between words, misspellings, etc.); I found 23, but undoubtedly missed some. None of the ones I caught obscures the meaning of the text. The index could be more complete; some terms I thought should be indexed were missing.

Early chapters outline the history of the study of relative abundance patterns, which describe the number of individuals in each of the community’s member species. Fisher et al’s (1943) logseries distribution of individuals over species, Preston’s (1962) lognormal distribution, and several others are explored. Hubbell concludes that none of these distributions fits the data actually collected in extensive surveys. That observation triggers his presentation of the unified neutral theory, which predicts the relative abundance pat-terns found in nature much better.

The next several chapters present the theory and use it to model some of the most fundamental biogeographic and ecological questions, thus theoretically unifying these questions and their explanations in a single model. Hubbell begins by building a model to predict the species identification of individuals that replace community members that die or emigrate. Some of the fundamental assumptions of this model include:

(1) All resources are generally being used by community members; hence, individuals can be added only by replacement.

(2) All local individuals are equivalent in the probability that one of their offspring will replace a lost individual. Thus, an individual from the most abundant species is the most likely re-placement. This is the basis for the word neutral in the title: success does not depend on competitive ability, but on probabilities based on current abundances.

(3) Immigrants from neighboring communities may also replace a lost member of the local community, but with a generally lower probability dependent on dispersal probabilities as well as relative abundances.

(4) Individuals of a species not present in the original community may be introduced into the local community, either by speciation events within the local community, or by immigration from neighboring communities.

The entire complex of local communities that interact as described in assumptions 3 and 4 is a meta community, in the same sense that a group of partially isolated populations is a meta population, and understanding the met a community is the goal of much of the book’s modeling effort. More assumptions are added to the model as more complex questions are encountered.

Problems modeled by Hubbell using the unified neutral theory include some of the most historically important in ecology and bio-geography. MacArthur and Wilson’s equilibrium theory of island biogeography is expanded by using the individual as the responding unit (MacArthur and Wilson’s unit was the species), and by incorporating speciation into the model. Patterns of relative abundance in communities, often explained in terms of the logseries or lognor-mal distribution, are explained by a new distribution called the “zero-sum multinomial,” which results from application of the unifiedneutral theory. Species-area relationships are explored and found to be “triphasic.” That is, the rate of the increase in the number of species encountered with increase in area sampled changes with geo-graphic scale. At small (local) and large (continental) scales, new species are added faster as more area is surveyed than at the intermediate (regional) scale. The unified neutral theory explains this phenomenon. Meta populations, punctuated equilibrium, speciation, and biodiversity patterns are all successfully modeled using the theory. This is an impressive array of questions all brought together under a single theory.  

In chapter 9, Hubbell deals with problems of sampling, parameter estimation, and theory testing. Some situations that the unified neutral theory does not model well are presented. These failures are explained by the absence of some of the assumptions of the theory in those situations, and that is seen as support for the validity of the model.

In the last chapter, Hubbell brings the neutral and classical niche-based arguments for the organization of communities together, as-signing roles to each but concluding that most communities are accurately modeled by the unified neutral theory because the effects of niche interactions often cancel one another, resulting in equivalent fitness among community members.

The book is worth reading for its review of the history of ideas of community organization alone, but it also makes a good case for considering neutral processes in attempts to explain that organization, and much more. Even if the grand unification Hubbell has at-tempted turns out to be contentious, as it surely will, it is a commend-able attempt at leading to new ways of looking at ecological and biogeographic problems and to new understanding of those problems. The book and theory are already stimulating discussion and research to that end (Davis 2003, Norris 2003, Tuomisto et al. 2003).

 

References Cited

Davis, M. A. 2003. Biotic globalization: Does competition from introduced species threaten biodiversity? BioScience 53: 481–489.

Fisher, R. A., A. S. Corbet, and C. B. Williams. 1943. The relation between the number of species and the number of individuals in a random sample of an animal population. J. Anim. Ecol. 12: 42–58.

MacArthur, R. H., and E. O. Wilson. 1967. The theory of island biogeography. Monographs in population biology, no. 1. Princeton University Press, Princeton, NJ.

Norris, S. 2003. Neutral theory: A new, unified model for ecology. BioScience 53: 124–129.

Preston, F. W. 1962.The canonical distribution of commonness and rarity. Ecology 43: 185–215 (part I), 410–432 (part II).

Tuomisto, H., K. Ruokalainen, and M. Yli-Halla. 2003. Dispersal, environment, and floristic variation of western Amazonian forests. Science299: 241–244.

Carl W. Hoagstrom
Department of Biological Sciences
Ohio Northern University
Ada, OH 45810
American Entomologist
Vol. 50, No. 2, Summer 2004