- Email: [email protected]
Mosaic landscapes ecological processes
BOOK
-
Europe. This idea, which stresses continuity of local populations over long time periods, has come to be called the multiregional hypothesis. The opposing view holds that most branches of archaic Homo became extinct. More modern people evolved just once, in a restricted area. Africa or western Asia are considered the most probable homelands. Following this origin, Homo sapiens spread out over most of the Old World, to replace archaic groups including the Neanderthals of Europe. The replacement view (especially one version of it that has been dubbed the Eve hypothesis) gathered strong support from molecular studies in the later 1980s. Some of these findings have been challenged, and it is clear from current skirmishing that not all the questions have been answered. Apart from the controversy surrounding DNA comparisons, the prehistoric record continues to provide useful clues. It is this evidence from later Pleistocene fossils, coupled with anatomical information from recent skulls, that Marta Lahr marshals in order to advocate a single origin for all modern human populations. In the first part of the book, Lahr lays out the basis for the multiregional hypothesis and then systematically challenges claims made in support of continuity in the Far East. She identifies 30 craniodental traits said to characterize populations of eastern Asia and Australia and explores the actual distribution of these features in skulls from various parts of the world. As it turns out, many of the ‘regional’ characters turn up in Africa or Europe, and only a few reach the expected high frequencies in Asian groups. When the same traits are tracked back into the Pleistocene, it is apparent that they occur in archaic crania from Africa and also in early modern assemblages from Africa and the Middle East. But in the Ngandong hominids from Java (surmized to be a link to living Australasians), a number of these key features are not expressed at all. Having savaged the opposition, Lahr describes further observations that are consistent with the derivation of diverse modern forms from a common ancestral source. Comparisons of Late Pleistocene and recent crania suggest that vaults and faces have been reduced in size in several geographic regions. This decrease in size has been accompanied by ‘gracilisation’ of cranial superstructures such as the brow and occipital torus. However, these trends do not occur at the same time or same rate in all the groups. Australian skulls, for example, seem to be distinctive, in that they have become smaller without much simultaneous loss of robusticity. This patterning must reflect the particular evolutionary forces operating on populations inhabiting different environments. Lahr offers a scenario in which earlier humans dispersed not once but several TREE vol.
II,
no.
12 December
1996
times, first within an African homeland and subsequently into other continental areas. People may have moved out of Africa following a northern route to the Middle East and also, less certainly, a southeastern route into Arabia. Throughout this period, modern humans need not have interbred with more archaic groups to any significant extent. Such a scheme is highly plausible, and Lahr deserves a lot of credit for her very thorough presentation of so much evidence. Supporters of multiregional evolution will be hard pressed to counter her main points.
1
,
G. Phlllp Rightmlre Dept of Anthropology, Binghamton Binghamton, NY 13902-6000,
University, USA
Landscape ecology diversifies Land Mosaics: The Ecology of Landscapes and Regions by Richard T. T. For-man Cambridge University Press, 1995. f65.00/$110.00 hbk, f24.95/$39.95 pbk (xx + 632 pages) ISBN 0 52147462 0
Mosaic Landscapes Ecological Processes edited by Lennart Hansson,
Lenore Fahrig and Gray Merriam Chapman & Hall, IALE Studies in Landscape Ecology 2,1995. 547.00 hbk (xix + 356 pages) ISBN 0 412 45460 2
0
ur world is spatially heterogeneous - it is an almost endless series of nested mosaics of patches. These patches vary in content and their borders may be clear or fuzzy, straight or wiggly. The trouble is, we are not the only species to inhabit and move around in this patchwork; human impressions of the mosaic are not universal. And we only have the faintest of notions as to how other organisms perceive and react to patterns of spatial heterogeneity over their own ranges of scales. Recently, study of the ecological cons+ quences of spatial heterogeneity has been formalized under the title of ‘landscape ecology’. The term is highly fashionable, second only perhaps to ‘biodiversity’. However, just as with biodiversity, landscape ecology, and what it encompasses, has acquired a different emphasis and meaning for workers in different fields. Indeed, two separate facets of the subject have now developed, reflecting the aims and methods of the different scientists. These two books are a clear illustration of the two directions of thought.
01996,
REVIEWS
Forman’s book, Land Mosaics, is firmly entrenched in what may be regarded as the ‘classical’ school of landscape ecology, which has its origins in geography and uses human scales to define landscape mosaics and to describe organism responses, Under this view, landscapes are composed of discrete patches of particular habitat types, sometimes linked by ‘corridors’ of the same habitat, enveloped in a ‘matrix’ of different, but otherwise rather undefined ground cover. Not surprisingly, the approach has proved particularly appealing to landscape planners and engineers, whose job it is to apportion the land according to human usage and needs. On the other hand, the book by Hansson et al., Mosaic Landscapes Ecological Processes, takes a wholly ecological approach. Landscape mosaics are defined and examined in relation to the organisms living within them, the aim being to understand how spatial heterogeneity affects ecological processes and ecosystem structure and function. In this case, spatial scale becomes a sliding variable and ideas are not restricted to human perception of the habitat mosaic. In both books, spatial scale is introduced and discussed at an early stage, underlining the overall importance of this issue. However, as Forman admits in his preface ‘the world seen from an airplane window or an aerial photograph is the subject of this volume’. He adheres to this by largely ignoring the ecological implications of his account of scaling phenomena throughout the rest of the book. By contrast, the multi-authored book edited by Hansson et al. opens with a lucid discussion by John Wiens about scale and its relation to ecological theory. The ideas are then taken up by the authors of many of the remaining chapters. Scale is undoubtedly a major issue in modern landscape ecology and the different treatments are indicative of the different slants of the two books. Overall, I found Mosaic Landscapes a pleasure to read. Taking landscape pattern as the common starting point, the five major sections of the book offer discussion of some of the origins of spatial pattern (here limited to fire, large herbivores and physical changes caused by animals), responses of individuals and populations, population dynamics and genetics, species interactions, and finally some examples of the relevance of landscape pattern for conservation biology. Despite the obvious holes (including an overall lack of balance between animal and plant examples - the plants being underrepresented), the entire enterprise comes together splendidly, offering for the first time an appreciation of the ‘organism eye-view’ of landscape ecology. The discussions of movement patterns (Rolf Ims), competitive interactions (Ilkka Hanski) and predation rates at habitat edges (Henrik Andren),
Elsevier Science Ltd
521
BOOK
REVIEWS
among others, begin to answer the recent call for an integration of landscape ecology with behavioural ecologyl. In Land Mosaics, although I was frequently excited by the titles, I was disap pointed many times by the text that followed. After a general introduction, a group of three chapters deals with the number, size, shape and boundaries of landscape mosaics. This section of the book certainly has all the right ingredients, but they often come together in combinations that are oversimplistic and misleading rather than constructive. For example, the discussion of minimum viable population (MVP) size gives the impression that the ultimate goal is to find a single, robust number valid for most organisms. The important point - that different species are likely to have very different MVPs and that this must be taken into account in landscape planningz - is all but lost. Further sections of the book suffer similar weaknesses, but there are also some useful discussions. Part III deals with ecological ‘corridors’ -roads, powerlines, windbreaks, hedgerows, woodland tracts, streams and rivers -which apparently create a network within the habitat matrix. This is all very well if these linear landscape elements really have a corridor function; if they facilitate directional movement of individuals along them. While such behaviour has been observed for some species, the efficiency of human-scale corridors remains questionable for the majority of organismss. On the other hand, consideration of the ecological significance of such linear habitat structures is important and should not be ignored. Part IV considers mosaic patterns together with movements and flows (wind, water and organisms). These chapters offer an easy-to-understand account of some of the physical geographical influences on ecological landscape mosaics. The account of animal movements and metapopulation dynamics is confined mainly to vertebrate species and I found it rather naive and poorly structured. Part V introduces the time axis in landscape mosaics, with particular emphasis on planning and management. This is the strongest section of the book. Forman voices the frustration that many of us have that ‘in some planning circles public administration and economics have been substituted for the biological component’ (p. 440). He is also clearly concerned that future landscape planning and management should be successful in creating a sustainable environment. His discussions of the sociopolitical problems associated with largescale landscape ecology are often useful, but so much accent is placed upon human needs that I was left wondering: sustainable, yes, but at what cost to the diversity of natural ecosystems? 522
0 1996,Elsevier Science Ltd
Reading these two books together is an eye-opener, and I strongly recommend that anyone with an interest in spatial heterogeneity in ecology and/or landscape planning should indeed look at both. Mosaic Landscapes offers ‘a ‘state of the art’ discussion of the ecological theory, while Land Mosaics provides an all-embracing account of the problems of human landscape ecology. It is essential that workers in each field are aware of what the others are doing. Perhaps the final word is best left to E.O. Wilson who, in his foreword to Forman’s book, ob serves: ‘The vast majority of the inhabitants we never see, because they are too small and obscure: creepy-crawlies, immense in diversity, from insects to fungi and bacteria. All together, they are as important as the towering trees and the birds on which our attention is ordinarily focused’. For me, that says it all! John R. Haslett Institute of Zoology, University of Salzburg, Hellbrunner Strasse 34, A-5020 Salzburg, Austria
References 1 Lima, S.L. and Zollner, P.A. (1996) Trends Ecol. Euol. 11,131-135 2 Nunney, L. and Campbell, K.A. (1993) Trends Ecol. Evol. 8,234-239 3 Hobbs, R.J. (1992) Trends Ecol. Evol. 7, 389-392
Medicine on board spaceship Earth Interconnnections Between Human and Ecosystem Health edited by Richard T. Di Giulio and Emily Monosson Chapman & Hall, 1996. 6t42.50 hbk (xv + 275 pages) ISBN 0 412 62400 1 he much-debated concept of ecosystem health has at least three general meanings. In the political sense, legislators have used ‘ecosystem health’ to refer generally to environmental well-being. In the environmental toxicology sense, those who monitor, measure and manage pollutant discharges - like Glenn Suter or John Cairns have used the term to refer to ecosystem well-being as affected by chemicals and other pollutantG. In the ecological sense, biologists like David Rapport and Bob Ulanowicz have used the term in a variety of ways, usually to refer to the complexity, autonomy and total diversity of the whole biological system under consideration94. The second and third meanings of the term are the focus of a controversy over the way
T
that scientists ought to conduct ecological risk assessments (ERA). The toxicologists who perform ERA tend to follow the traditional human health paradigm and to examine effects of pollutants on individual species. The ecologists who do ERA tend to follow a more holistic paradigm and to examine ecosystem-wide effects of environmental degradation, such as changes in energy flow or biodiversity. The toxicological paradigm is more pre dictive, reliable and precise, but it is narrow and best suited only to species- or population-level effects, especially of chemicals. The holistic paradigm is less narrow and more comprehensive in covering ecosystemlevel effects, but it is less reliable and precise; it has less predictive power, and its proponents use a variety of different, often conflicting methodologies5. Which paradigm provides better assessments of ecological risk? The collection edited by Di Giulio and Monosson goes a long way toward answering this important question, even though the editors admit in several places that they ‘could not define’ what they meant by ‘ecosystem health’ (p. 261). Nevertheless, it is clear that the volume discusses how the same environmental insults affect both humans and the rest of the planet. The first chapters of the book survey interconnections between human and ecosystem health at the subcellular and molecular levels, whereas later chapters investigate these interconnections at the ecosystem and landscape levels. By the end of Chapter 8, the authors provide a scientific basis for understanding the later psychological, economic and sociological chapters that show how human values and policies affect both human health and environmental welfare and management. The main asset of the volume is the strength of the contributors. They include members of the US National Academy of Sciences (like John Cairns) and those who have made important scientific breakthroughs (like Theodora Colborn, who has articulated the hypothesis of low-level chemicals’ acting as endocrine disruptors). The volume also includes eminent risk assessors, such as Steven Bartell, and experts on the psychometrics of human risk perception, such as Paul Slavic. The table of contents reads like a Who’s Who in ecological risk assessment and environmental evaluation. The main flaw in the book is that it aims at multidisciplinary approaches to ecosystem and human health, but it gives us an overdose of papers by English professors and has no work by ethicists or political scientists. Also the scientific papers focus quite specifically on how chemicals affect ecosystem and human health, whereas the literary papers deal generally with environmental TREE vol.
II,
no. 12 December
1996
-
Europe. This idea, which stresses continuity of local populations over long time periods, has come to be called the multiregional hypothesis. The opposing view holds that most branches of archaic Homo became extinct. More modern people evolved just once, in a restricted area. Africa or western Asia are considered the most probable homelands. Following this origin, Homo sapiens spread out over most of the Old World, to replace archaic groups including the Neanderthals of Europe. The replacement view (especially one version of it that has been dubbed the Eve hypothesis) gathered strong support from molecular studies in the later 1980s. Some of these findings have been challenged, and it is clear from current skirmishing that not all the questions have been answered. Apart from the controversy surrounding DNA comparisons, the prehistoric record continues to provide useful clues. It is this evidence from later Pleistocene fossils, coupled with anatomical information from recent skulls, that Marta Lahr marshals in order to advocate a single origin for all modern human populations. In the first part of the book, Lahr lays out the basis for the multiregional hypothesis and then systematically challenges claims made in support of continuity in the Far East. She identifies 30 craniodental traits said to characterize populations of eastern Asia and Australia and explores the actual distribution of these features in skulls from various parts of the world. As it turns out, many of the ‘regional’ characters turn up in Africa or Europe, and only a few reach the expected high frequencies in Asian groups. When the same traits are tracked back into the Pleistocene, it is apparent that they occur in archaic crania from Africa and also in early modern assemblages from Africa and the Middle East. But in the Ngandong hominids from Java (surmized to be a link to living Australasians), a number of these key features are not expressed at all. Having savaged the opposition, Lahr describes further observations that are consistent with the derivation of diverse modern forms from a common ancestral source. Comparisons of Late Pleistocene and recent crania suggest that vaults and faces have been reduced in size in several geographic regions. This decrease in size has been accompanied by ‘gracilisation’ of cranial superstructures such as the brow and occipital torus. However, these trends do not occur at the same time or same rate in all the groups. Australian skulls, for example, seem to be distinctive, in that they have become smaller without much simultaneous loss of robusticity. This patterning must reflect the particular evolutionary forces operating on populations inhabiting different environments. Lahr offers a scenario in which earlier humans dispersed not once but several TREE vol.
II,
no.
12 December
1996
times, first within an African homeland and subsequently into other continental areas. People may have moved out of Africa following a northern route to the Middle East and also, less certainly, a southeastern route into Arabia. Throughout this period, modern humans need not have interbred with more archaic groups to any significant extent. Such a scheme is highly plausible, and Lahr deserves a lot of credit for her very thorough presentation of so much evidence. Supporters of multiregional evolution will be hard pressed to counter her main points.
1
,
G. Phlllp Rightmlre Dept of Anthropology, Binghamton Binghamton, NY 13902-6000,
University, USA
Landscape ecology diversifies Land Mosaics: The Ecology of Landscapes and Regions by Richard T. T. For-man Cambridge University Press, 1995. f65.00/$110.00 hbk, f24.95/$39.95 pbk (xx + 632 pages) ISBN 0 52147462 0
Mosaic Landscapes Ecological Processes edited by Lennart Hansson,
Lenore Fahrig and Gray Merriam Chapman & Hall, IALE Studies in Landscape Ecology 2,1995. 547.00 hbk (xix + 356 pages) ISBN 0 412 45460 2
0
ur world is spatially heterogeneous - it is an almost endless series of nested mosaics of patches. These patches vary in content and their borders may be clear or fuzzy, straight or wiggly. The trouble is, we are not the only species to inhabit and move around in this patchwork; human impressions of the mosaic are not universal. And we only have the faintest of notions as to how other organisms perceive and react to patterns of spatial heterogeneity over their own ranges of scales. Recently, study of the ecological cons+ quences of spatial heterogeneity has been formalized under the title of ‘landscape ecology’. The term is highly fashionable, second only perhaps to ‘biodiversity’. However, just as with biodiversity, landscape ecology, and what it encompasses, has acquired a different emphasis and meaning for workers in different fields. Indeed, two separate facets of the subject have now developed, reflecting the aims and methods of the different scientists. These two books are a clear illustration of the two directions of thought.
01996,
REVIEWS
Forman’s book, Land Mosaics, is firmly entrenched in what may be regarded as the ‘classical’ school of landscape ecology, which has its origins in geography and uses human scales to define landscape mosaics and to describe organism responses, Under this view, landscapes are composed of discrete patches of particular habitat types, sometimes linked by ‘corridors’ of the same habitat, enveloped in a ‘matrix’ of different, but otherwise rather undefined ground cover. Not surprisingly, the approach has proved particularly appealing to landscape planners and engineers, whose job it is to apportion the land according to human usage and needs. On the other hand, the book by Hansson et al., Mosaic Landscapes Ecological Processes, takes a wholly ecological approach. Landscape mosaics are defined and examined in relation to the organisms living within them, the aim being to understand how spatial heterogeneity affects ecological processes and ecosystem structure and function. In this case, spatial scale becomes a sliding variable and ideas are not restricted to human perception of the habitat mosaic. In both books, spatial scale is introduced and discussed at an early stage, underlining the overall importance of this issue. However, as Forman admits in his preface ‘the world seen from an airplane window or an aerial photograph is the subject of this volume’. He adheres to this by largely ignoring the ecological implications of his account of scaling phenomena throughout the rest of the book. By contrast, the multi-authored book edited by Hansson et al. opens with a lucid discussion by John Wiens about scale and its relation to ecological theory. The ideas are then taken up by the authors of many of the remaining chapters. Scale is undoubtedly a major issue in modern landscape ecology and the different treatments are indicative of the different slants of the two books. Overall, I found Mosaic Landscapes a pleasure to read. Taking landscape pattern as the common starting point, the five major sections of the book offer discussion of some of the origins of spatial pattern (here limited to fire, large herbivores and physical changes caused by animals), responses of individuals and populations, population dynamics and genetics, species interactions, and finally some examples of the relevance of landscape pattern for conservation biology. Despite the obvious holes (including an overall lack of balance between animal and plant examples - the plants being underrepresented), the entire enterprise comes together splendidly, offering for the first time an appreciation of the ‘organism eye-view’ of landscape ecology. The discussions of movement patterns (Rolf Ims), competitive interactions (Ilkka Hanski) and predation rates at habitat edges (Henrik Andren),
Elsevier Science Ltd
521
BOOK
REVIEWS
among others, begin to answer the recent call for an integration of landscape ecology with behavioural ecologyl. In Land Mosaics, although I was frequently excited by the titles, I was disap pointed many times by the text that followed. After a general introduction, a group of three chapters deals with the number, size, shape and boundaries of landscape mosaics. This section of the book certainly has all the right ingredients, but they often come together in combinations that are oversimplistic and misleading rather than constructive. For example, the discussion of minimum viable population (MVP) size gives the impression that the ultimate goal is to find a single, robust number valid for most organisms. The important point - that different species are likely to have very different MVPs and that this must be taken into account in landscape planningz - is all but lost. Further sections of the book suffer similar weaknesses, but there are also some useful discussions. Part III deals with ecological ‘corridors’ -roads, powerlines, windbreaks, hedgerows, woodland tracts, streams and rivers -which apparently create a network within the habitat matrix. This is all very well if these linear landscape elements really have a corridor function; if they facilitate directional movement of individuals along them. While such behaviour has been observed for some species, the efficiency of human-scale corridors remains questionable for the majority of organismss. On the other hand, consideration of the ecological significance of such linear habitat structures is important and should not be ignored. Part IV considers mosaic patterns together with movements and flows (wind, water and organisms). These chapters offer an easy-to-understand account of some of the physical geographical influences on ecological landscape mosaics. The account of animal movements and metapopulation dynamics is confined mainly to vertebrate species and I found it rather naive and poorly structured. Part V introduces the time axis in landscape mosaics, with particular emphasis on planning and management. This is the strongest section of the book. Forman voices the frustration that many of us have that ‘in some planning circles public administration and economics have been substituted for the biological component’ (p. 440). He is also clearly concerned that future landscape planning and management should be successful in creating a sustainable environment. His discussions of the sociopolitical problems associated with largescale landscape ecology are often useful, but so much accent is placed upon human needs that I was left wondering: sustainable, yes, but at what cost to the diversity of natural ecosystems? 522
0 1996,Elsevier Science Ltd
Reading these two books together is an eye-opener, and I strongly recommend that anyone with an interest in spatial heterogeneity in ecology and/or landscape planning should indeed look at both. Mosaic Landscapes offers ‘a ‘state of the art’ discussion of the ecological theory, while Land Mosaics provides an all-embracing account of the problems of human landscape ecology. It is essential that workers in each field are aware of what the others are doing. Perhaps the final word is best left to E.O. Wilson who, in his foreword to Forman’s book, ob serves: ‘The vast majority of the inhabitants we never see, because they are too small and obscure: creepy-crawlies, immense in diversity, from insects to fungi and bacteria. All together, they are as important as the towering trees and the birds on which our attention is ordinarily focused’. For me, that says it all! John R. Haslett Institute of Zoology, University of Salzburg, Hellbrunner Strasse 34, A-5020 Salzburg, Austria
References 1 Lima, S.L. and Zollner, P.A. (1996) Trends Ecol. Euol. 11,131-135 2 Nunney, L. and Campbell, K.A. (1993) Trends Ecol. Evol. 8,234-239 3 Hobbs, R.J. (1992) Trends Ecol. Evol. 7, 389-392
Medicine on board spaceship Earth Interconnnections Between Human and Ecosystem Health edited by Richard T. Di Giulio and Emily Monosson Chapman & Hall, 1996. 6t42.50 hbk (xv + 275 pages) ISBN 0 412 62400 1 he much-debated concept of ecosystem health has at least three general meanings. In the political sense, legislators have used ‘ecosystem health’ to refer generally to environmental well-being. In the environmental toxicology sense, those who monitor, measure and manage pollutant discharges - like Glenn Suter or John Cairns have used the term to refer to ecosystem well-being as affected by chemicals and other pollutantG. In the ecological sense, biologists like David Rapport and Bob Ulanowicz have used the term in a variety of ways, usually to refer to the complexity, autonomy and total diversity of the whole biological system under consideration94. The second and third meanings of the term are the focus of a controversy over the way
T
that scientists ought to conduct ecological risk assessments (ERA). The toxicologists who perform ERA tend to follow the traditional human health paradigm and to examine effects of pollutants on individual species. The ecologists who do ERA tend to follow a more holistic paradigm and to examine ecosystem-wide effects of environmental degradation, such as changes in energy flow or biodiversity. The toxicological paradigm is more pre dictive, reliable and precise, but it is narrow and best suited only to species- or population-level effects, especially of chemicals. The holistic paradigm is less narrow and more comprehensive in covering ecosystemlevel effects, but it is less reliable and precise; it has less predictive power, and its proponents use a variety of different, often conflicting methodologies5. Which paradigm provides better assessments of ecological risk? The collection edited by Di Giulio and Monosson goes a long way toward answering this important question, even though the editors admit in several places that they ‘could not define’ what they meant by ‘ecosystem health’ (p. 261). Nevertheless, it is clear that the volume discusses how the same environmental insults affect both humans and the rest of the planet. The first chapters of the book survey interconnections between human and ecosystem health at the subcellular and molecular levels, whereas later chapters investigate these interconnections at the ecosystem and landscape levels. By the end of Chapter 8, the authors provide a scientific basis for understanding the later psychological, economic and sociological chapters that show how human values and policies affect both human health and environmental welfare and management. The main asset of the volume is the strength of the contributors. They include members of the US National Academy of Sciences (like John Cairns) and those who have made important scientific breakthroughs (like Theodora Colborn, who has articulated the hypothesis of low-level chemicals’ acting as endocrine disruptors). The volume also includes eminent risk assessors, such as Steven Bartell, and experts on the psychometrics of human risk perception, such as Paul Slavic. The table of contents reads like a Who’s Who in ecological risk assessment and environmental evaluation. The main flaw in the book is that it aims at multidisciplinary approaches to ecosystem and human health, but it gives us an overdose of papers by English professors and has no work by ethicists or political scientists. Also the scientific papers focus quite specifically on how chemicals affect ecosystem and human health, whereas the literary papers deal generally with environmental TREE vol.
II,
no. 12 December
1996