Life history after ten years

Life history after ten years

Forum TRENDS in Ecology & Evolution Vol.17 No.8 August 2002 has to be interventionist. Keith et al. provide a lucid critique of different options fo...

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TRENDS in Ecology & Evolution Vol.17 No.8 August 2002

has to be interventionist. Keith et al. provide a lucid critique of different options for fire management, including a return to aboriginal burning practises, and advocate a new approach based firmly on scientific understanding. This incorporates new insights into how spatial and temporal variability in fire properties influence biodiversity. An attractive feature of Flammable Australia is that animals have at last been integrated into fire ecology. New models and data are reported that explore the interplay between landscape patchiness produced by different fire regimes and the meta-population dynamics of threatened animals. There is little here on fire as an evolutionary force and a biogeographical agent shaping Australia’s unique biota. Flammable Australia, we learn in a chapter by Kershaw and others, only appeared in the Miocene, when fires began to carve up the ancestral forests, replacing them with the precursors of today’s highly flammable floras. In a book that I strongly recommend as a companion volume, Bowman [1] has explored the biogeography of the tiny islands of ‘rainforest’ remnants surviving in a sea of Eucalyptus- and Acacia-dominated communities. Rainforest is a euphemism – the forests persist in sites with as little as 600 mm of annual rainfall. Rainforest lineages are floristically distinct from adjacent formations of ‘flammable Australia’. Bowman argues that the key difference between rainforest and the rest is relative tolerance to recurrent fires. The implication is that fire has been a major agent shaping the distinctive biogeography of a continent. If fires could be switched off, and the climate remained the same, Australia would look completely different. Did ancient fires create an intracontinental vicariance event after which fire tolerant and fire intolerant biotas evolved side by side? Why did flammable vegetation begin to spread? What limits the domain of fire, in the past and today? What functional attributes allowed access of some lineages to fire-prone ecosystems but denied access to others? Some of the answers are implicit in this book, but are presented for specific vegetation types. We need a general model on synergies between climate and ‘fuel’ to help us understand the ‘big’ questions – why fires began to burn in the Miocene, why human settlement often caused http://tree.trends.com

major changes in fire regimes, or how global vegetation might respond to future climate change. This book is a rich resource on fire in Australian ecosystems, and should be available to all fire ecologists. It contains innovative work on landscape ecology and conservation biology that will be of general interest. However, I do not think that it will do much to increase the citations on fire in our textbooks. Fire ecologists need to ask the general questions to reach the general audience that the topic warrants. William Bond Botany Dept, University of Cape Town, Rondebosch, 7701, South Africa. e-mail:[email protected] Reference 1 Bowman, D.M.J.S. (2000) Australian Rainforests: Islands of Green in a Land of Fire, Cambridge University Press

Published online: 06 June 2002

Life history after ten years Life History Evolution by Derek A. Roff. Sinauer Associates, Inc, 2002. £39.99 (527 pages) ISBN 0 87893 756 0

The new book by Derek Roff, Life History Evolution, differs from his 1992 book The Evolution of Life Histories: Theory and Analysis in emphasis as well as in the inclusion of recent developments in life-history research. In the 1992 book, life-history evolution was detailed by life-history trait: clutch size, age at first reproduction, and so on. Environmental variation was dealt with within each topic, depending on its perceived relevance to that topic. Organizing the book by life-history trait implied that the role of the environment in shaping life histories was secondary. Environmental variation might modify life histories, but it was not seen as deciding the major principles of the evolution of life-history patterns. This has now changed. Life History Evolution is organized not by life-history trait but by the main determinants of life-history evolution. It starts with the principles of the process of the evolution of life-history traits: quantitative genetics,

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especially genetic correlations, and tradeoffs among traits. Three chapters follow that deal with the evolved patterns of life-history traits, and are devoted to life-history evolution in a constant environment, in a stochastic environment and in a predictable environment. The emphasis is therefore on the decisive role of the environment in shaping patterns of life-history traits. This is most evident in the chapter on the evolution of life histories in a predictable environment, which contains the most new material. Latitudinal patterns provide much direct evidence for environmental influences on life histories, such as the influence of season length on growth rate and size in univoltine insects, and many experimental examples of such an immediate influence of the environment on life-history patterns are provided. The change in emphasis from the traits themselves to the environment as the principal determinant of life-history patterns is illuminating and one of the strong points of the book. Life History Evolution excels in relating life-history models to experimental evidence. Much care has been taken to document experimental life-history studies, and to relate their data to appropriate theory. Where possible, data are used to evaluate the choice between alternative theories. For instance, both evolution and demography can lead to patterns among life-history traits. Demography, because long-term stable numbers in the population constrain life-history parameters to conform to R0 = 1; and evolution, because a genetic tradeoff might exist in an optimal life history. In some cases, these alternative models lead to different predictions of the sensitivity of, for instance, adult mortality on the age at maturity. The framework for the analysis of life-history theory is found in quantitative genetics. In Life History Evolution, evolutionarily stable strategy (ESS) models are virtually absent; optimization is occasionally referred to and more often implicitly applied. Fitness is based upon the intrinsic rate of increase r, or on R0, as might be convenient in any particular model. There is no sense of any recent debate on fitness measures [1]. Virtually all analyses in the book ignore densitydependent number regulation, although, in the last chapter, the influence of density

0169-5347/02/$ – see front matter © 2002 Elsevier Science Ltd. All rights reserved.

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TRENDS in Ecology & Evolution Vol.17 No.8 August 2002

dependence on life-history evolution is mentioned as one of the more important areas of future research. Life-history theory exists in evolutionary ecology, which both uses ESS methods and discusses how to deal with densitydependent number regulation in the evolution of life-history traits [2]. This book quotes some articles from this more ecological and often more mathematical school but, on the whole, one of the skeins in the tapestry of life-history theory seems missing. In this, Roff’s background in quantitative genetics might play him false, and although this exemplary book provides a major survey of life-history evolution, it is not yet complete. Gerdien de Jong Evolutionary Population Biology, Padualaan 8, NL-3584 CH Utrecht, The Netherlands. e-mail: [email protected] References 1 Brommer, J.E. (2000) The evolution of fitness in life-history theory. Biol. Rev. 75, 377–404 2 Mylius, S.D. and Diekmann, O. (1995) On evolutionary stable life histories, optimisation and the need to be specific about density dependence. Oikos 74, 218–224

Published online: 06 June 2002

Hamilton, parasites and sex Narrow Roads of Gene Land – Volume 2. The Evolution of Sex by W.D. Hamilton. Oxford University Press, 2001. £50.00 pbk (928 pages) ISBN 0 19 850336 9

William Hamilton will undoubtedly be remembered as one of the outstanding evolutionary theorists of the second half of the last century. His early work on inclusive fitness, the evolution of senescence, and unusual sex ratios was immensely influential, and has been incorporated into the basic conceptual frameworks of the respective fields. This book, the second volume of his collected papers (covering 1981–1991), is concerned http://tree.trends.com

mainly with his theories of the role of host–parasite interactions in promoting the evolution of mate choice and maintaining sexual reproduction itself. The lengthy commentaries accompanying each paper (sometimes much longer than the papers themselves) show that he considered these ideas to be his most significant contributions to evolutionary biology. They also betray intense disappointment that the ideas have not been universally accepted, in spite of their wide influence on both theoretical and experimental research. Most of us would be pleased to have our ideas discussed as widely as Hamilton’s are. It is therefore hard to understand the rather peevish tone of some of his commentaries. Scientists are probably unwise to try to judge too closely the significance of their own work, although it might be less of a risk for someone as gifted as Hamilton than for most of us. Ultimately, we have to put up with the community’s judgement, for better or for worse. In this case, my feeling is that the reception of Hamilton’s ideas was reasonably fair. Hamilton’s fervent advocacy of the evolutionary significance of parasites has been of enormous service in stimulating research and debate. But the importance of the mechanisms that he proposed, relative to other forces affecting both the evolution of mate choice and sexual reproduction, still remains to be definitively established. For example, his theory of the maintenance of sex in host species postulates cycles of allele frequencies at loci conferring resistance to pathogens, and implies a very high additive genetic variance in fitness if the twofold cost of sex is to be overcome. As yet, there is no direct evidence for these as a widespread phenomenon. Many different population genetic mechanisms that can produce an advantage to genetic recombination and sexual reproduction have been proposed, but it is far from obvious how to distinguish among them. The commentaries will unfortunately provide little enlightenment to readers who are not already familiar with Hamilton’s work. They are emotional in style, and the arguments are obscured by rambling digressions and personal reminiscences. They might well, however, arouse a great deal of interest, because they express Hamilton’s views on many topics that are not immediately relevant to his scientific work. Some of these views

seem oddly näive, such as his apparent belief that Jews have an innately higher mathematical ability than the English (Einstein versus Newton?). Others are highly provocative, such as the suggestion that medical care will lead to a noticeable decline in the overall fitness of the human population within 40 years, because of the accumulation of deleterious mutations that would have otherwise been eliminated by selection. Hamilton proposes infanticide as a solution to this problem (Preface and Chapter 12). Although there is good reason to be concerned at the long-term consequences of mutation accumulation if current civilization persists, the timescale for significant effects on population mean fitness is likely to be one of centuries, rather than of decades. There are surely more urgent problems to contend with, such as the rate at which we are degrading our environment. Brian Charlesworth Institute for Cell, Animal and Population Biology, University of Edinburgh, Edinburgh, UK EH9 3JT. e-mail: [email protected] Published online: 06 June 2002

Carnivores: renaissance enigma? Carnivore Conservation edited by J.L. Gittleman, S.M. Funk, D. Macdonald and R.K. Wayne. Cambridge University Press, 2001. £34.95 pbk (xiii + 675) ISBN 0 521 66537 X

In a provocative introduction to Carnivore Conservation, the editors argue that carnivores are special and deserve the disproportionate resources and attention that they receive because they are a ‘renaissance taxa – involving a synthesis of conservation problems, causal factors, and solutions’. However, in Part 1 (Problems), Purvis et al. expose the enigma that carnivores represent for conservation biology. They are not particularly diverse,

0169-5347/02/$ – see front matter © 2002 Elsevier Science Ltd. All rights reserved.