- Email: [email protected]
Minimum animal populations
BOOK
REVIEWS
32 Mock, D.W., Drummond, H. and Stinson, C.H. (1990) Am. Sci. 78,438-449
33 Cash, K. and Evans, R.M. (1986) Be/mu. Ecol. Sociobiol. 18413-418 34 Williams, T.D. (1989) Oikos 55, 19-22 35 Anderson, D.J. (1990) Am. Nat. 135,334-350 36 Lamey, T.C. (1993) Oikos 66,293-297 37 Birney, E.C.and Baird, D.D. (1986) Am. Nat, 126,136-140 38 Bartlett,J. (1987)Behau.Ecol.Sbciobiol. 21,179-183
A quest for mechanism Plant Allometry: The Scaling of Form and Process by Karl .I. Niklas University of Chicago Press, 1994. s68.95ff47.95 hbk, $28.75/f19.95 pbk (xvi + 395 pages) ISBN 0 226 58080 6/O 226 580814
M
ost scientists desire to account for a large range of phenomena by the derivation of laws or rules from relatively simple underlying principles. Unfortunately, all too often this desire is not fulfilled in ecology and evolutionary biology. Yet, any plant (or for that matter any object) is subjected to the same physical and chemical rules. This makes scaling relations based on these rules very appealing for many because, by their nature, they should be generally applicable. Others may find scaling analysis a simple naive tool contingent of fragile assumptions in the light of the complexity of organisms. The author’s position is clear: ‘. .. the quest for mechanism can be sped on its way by means of scaling analysis’. Niklas deals with a great number of sub jects ranging from molecular traffic within living cells to the evolution of plant lifehistories. One of the objectives of this book is to show that, in contrast to the empirical approach to the relations between absolute and relative size, and between organic form and process, scaling relations can be analytically derived. For empirical scaling analysis, the methods and pitfalls of regression analysis are amply discussed (a 40-page appendix on methods is added). With regard to analytically derived scaling relations, great care is given to explain how arguments of similitude are constructed. By doing so, the book will prove useful both in teaching and in research. In most places, the assumptions made at different steps in the construction of analytically derived scaling relations are discussed and tested with empirical data whenever possible. This approach proves to be very instructive, for instance in the discussion on the ‘surface-area law’, the ‘314 power law for the scaling of growth to body mass’ or the l-3/2 self-thinning rule’. While the latter is still treated in a rather positive
134
39 Spalding, MC., Smith, J.P. and Forrester, D.J. (1994) Auk 111,328-336 40 Queller, DC. (1994)Am. Nar 144(SuppI.),S&l-S99 41 Buchholz, J.T. (1922) Bar. Gaz. 73,249-286 42 Cheplick, G.P. (1992) J. Ecol. 80,567-575 43 Kozlowski, T.T. (1973) inshedding ofPlant Parts (Kozlowski, T.T., ed.), pp. 3-44, Academic Press 44 Searcy, K.B. and Macnair, M.R. (1993) Evolution 47, 13-24
vein in most textbooks on plant population biology, it is argued here that the models from which this law is derived analytically should be rejected, because empirical scaling exponents for plant height are only superficially in agreement with them. Furthermore, it is argued that the empirical derivation of this law results from methodologically flawed regression analysis. Unfortunately, in the chapters that deal with reproduction and evolution, the scrutiny of the arguments becomes less when they can no longer be derived from physical laws. For instance, the way in which the pattern of female/male biomass allocation among anemophilous species is dealt with can be criticized on two rather obvious points. First, biomass allocation patterns are only discussed in relation with male fitness while it is clear that the relationship between investment and both male and female fitness determines the optimal allocation pattern. Second, it is not clear why tall plants have less local mating competition: Niklas states that they are better at dispersing pollen but seems to disregard the fact that they also produce more pollen. And, on a few occasions, models are presented without proper discussion of the alternatives. Having made these remarks it should immediately be added, however, that Niklas brings together most of the relevant literature, making the book a good starting point for further study. A creative reader may also be inspired to derive his/her own scaling relations. The relationship between plant mass and female fitness, mentioned above, may be derived for monocarpic plants from the scaling relations between reproductive and vegetative mass, plant height and mass, dispersal and plant height, and mass and density, which are extensively dealt with in the book. Any evolutionary biologist is at some point faced with the question, what is the relation between organic size and form and process.Then, Niklas’book will undoubtedly prove a reliable source of information. Although not all readers will go through the book from cover to cover, on the whole I think that Niklas has done a remarkable job. Peter G.L. Klinkhamer Institute for Evolutionary and Ecological Sciences, University of Leiden, PO Box 9516, 2300 RA Leiden, The Netherlands
45 Stephenson, A.G. and Winsor, J.A. (1986) Evolution
40,453-458
46 Lyon, B.E., Eadie, J.M. and Hamilton, J.D. (1994) Nature 371,240-243 47 Forbes, L.S. (1991) Oikos 62,325-332 48 Mock, D.W. and Forbes, L.S. (1992) Trends Ecol. Euol. 7,409-413
49 Bateson, P. (1994) Trends Ecol. Euol. 9,399-403 50 Snow, A.A. (1994) Am. Nat. 144 (Suppl.), S69-S83
How small is small? Minimum Animal Populations edited by Hermann Remmert Springer-Verlag, 1994. DM128.00 hbk (vii + 156 pages) ISBN 3 540 56684 8
W
ith increasing frequency, ecologists are being asked ‘How much habitat do we need to preserve to save this species?’ Sometimes the species is a large mammal or an exotic bird that evokes public support; Iother times it has less general appeal and is protected only because the mandates of law provide a tool for those concerned with the Iloss of biological diversity. But in either case ,ecologistsare being asked to provide answers about optimal size of reserves, number of 1reserves and if reserves should be isolated ,or linked. In response, the study of small Ipopulations was born in the early 1980sand Iits associated acronyms, such as minimum viable population size(MVP) and ‘singlelarge ,or several small’ reserves (SLOSS),began to 1receive serious attention. Now the 1990sare Iwell under way and we can begin to evaluate Ihow well the study of small populations has 1[ared over the past decade. Based upon this new book, I would have to report that pro gresswas patchy. While some of the chapters are well written and informative, the book is seriously lacking in a framework that would permit the reader to gain a clear understanding of either the intellectual and practical problems confronting conservation biologists or the advances that have been made. The cover of this book tells us that the data to be presented show that MVPdepends solely on the species in question, and that we should eschew the guidelines that geneticists have suggested. I somehow missed this message; instead I found that the book highlights a quite different problem: the paucity of good empirical data. The book pre sents data from birds, mammals, fish and beetles, with the emphasis on birds. This is a laudable attempt at presenting data from diverse sources, but the relevance of some of these data to the perseverance of small populations is far from obvious. Since this book is an edited collection, the question of relevance should have been TREE
vol.
10, no.
3 March
1995
BOOK resolved by the editor’s introduction. However, his short contribution provides little insight. In fact, he doesn’t refer to any of the work within the collection, beyond asserting that the problems of small populations vary depending upon the type of organism a truism but, since it is never developed further anywhere in the book, not a very help ful one. He also mentions a few examples of persistent, small vertebrate, populations, from which he concludes that deleterious effects due to inbreeding are the exception. This idea runs counter to the available data: inbreeding depression is the rule’, even in the presence of significant levels of selfing2, and models show that inbreeding depression can create a serious problem for the persistence of a small populations. It is probably just as well that the some what idiosyncratic introductory remarks are not developed elsewhere in the book. Instead we are provided with some of the basic ideas necessary for the discussion of MVP.Genetic, demographic and environmental stochasticity is introduced (Chapter 2) as is the basic theory of effective population size (Chapter 4). Both chapters also present well-balanced discussions of the influence of genetic and ecological factors on small populations (of birds and mammals, respectively). The theme of demographic and environmental stochasticity is expanded into a clear description of stochastic modeling (Chapter 6). I would recommend this chapter to anyone who is trying to understand how the simple equations of population growth are analyzed as stochastic models. I have one caveat-this chapter does not serve as a review, since the extensive literature of the subject is largely ignored. With the exception of the modeling chapter, the book is focused on presenting empirical data. In several chapters, this serves to highlight the problem that often the necessarydata don’t exist. For example, some of the best-studied taxa are birds, but the discussion of Amazonian birds (Chapter 7) illustrates our almost total lack of knowledge of some potentially threatened species. But even in well-studied cases, important data may be missing or overlooked. Thus, while I found the discussion of within-lake speciation of fishes quite fascinating (Chap ter 5), there is no discussion of issues that relate directly to the problems of small populations, such as the likely size of these fish populations when they differentiated or the size of lakes that permitted such differentiation. These questions are of great relevance because they directly address the issue of future evolutionary change within conserved populations. Long-term data from small populations are of great value in linking the predictions of stochastic models to the real world. Numerical data from 22 years of an island vole population are presented (Chapter 8) TREE
vol.
IO, no.
3 March
1995
REVIEWS
A re-appraisal of the skua’s behaviour was required but at a different locality. Many years on, this book is the account of the five summers’ work (1965-66 to 1969-70) undertaken by Young and colleagues on south polar skuasand Adelie penguins at Cape Bird (northern tip of Ross Island). This location was favoured because it had many groups of skuas and penguins, and the geography afforded excellent opportunities to record skua behaviour from a distance. Young writes with enthusiasm and some times passion. The well-illustrated text is reminiscent of Richdale’s Population Study of Penguins3in which a wealth of data is de scribed, mostly in a very rigorous and objective fashion, but mixed with delightful anecdotes and anthropomorphisms. Whether or not skuas can make decisions, be disconcerted, or appreciate penguins, may not seem the substance of good science, but only if read out of context. There is a detailed account of the range Leonard Nunney of foods available to skuas, the biomass of the food and those aspects of penguin breedDept of Biology, University of California, ing biology that may affect skuas feeding at Riverside, CA 92521, USA the penguin colonies. The methods used for observing and recording the skua foraging References 1 Thornhill, N.W., ed. (1993) The Natural History and feeding behaviour were carefully conof Inbreeding and Outbreeding, University of sidered and developed in the early stages of Chicago Press the study with an emphasis on observing 2 Montalvo, A.M. Ecology (in press) without disturbing. At times, considerable 3 Mills, L.S. and Smouse, P. (1994)Am. Nat. 144, tenacity on behalf of the observer was re 412-431 quired as is evident from the following quote: 4 Nunney, L. and Campbell, K.A. (1993) Trends ‘One’s recording was more at risk from goEcol. Euol. 8,234-239 ing to sleep through boredom than through being exhausted from frenzied activity’. We are rewarded with a very detailed set of results from those observations on skua feeding behaviour and Young uses and explores these results very fully. Although the opportunities for very detailed and extensive analysis (statistical or otherwise) of the skuas behaviour were limited by the amount Skua and Penguin and type of the data, Young does make full by Euan Young use of the information. The searching quesCambridge University Press, tions which preface the many sections pro Studies in Polar Research, 1994. vide the reader with much incentive to read f65.00/$99.95 hbk (xvi + 452 pages) on. There is some interesting modelling and ISBN 0 521 322510 analysis of the spatial interactions (but not processes). For those happier with quantin 1963,EuanYoung published two paper+* about his research on the south polar skua tative analysis rather than qualitative analy(Catharactu maccormicki) at Cape Royds sis, the latter chapters of the book are of (RossIsland, McMurdo Sound). The common considerable interest. While acknowledging occurrence of skuas raising only one chick limitations of the data, Young attempts some from a clutch of two eggs was confirmed, interesting and detailed analysis and modeland it was found that most skuas were feed- ling of the energy costs of alternative feeding not at the colony of Adelie penguins ing strategies. (Pygoscelis adeliae) but at sea. Were the In his final analysis, Young returns to the i skuaspredators of penguins or opportunistic criticisms made of his earlier work; are skuas scavengers? These early observations were predators of penguins, to what extent do later criticized. The population of Adelie skuas depend on penguins, and what are the penguins at Cape Royds was small, so there short-term and long-term implications of was little food available, and at larger colonies skuas and penguins breeding in close proxthere would be plenty of food for skuas. The imity? Any attempt to reveal his answers in methods of study may have affected the this brief review would not do justice to this skua’s behaviour. book. and they illustrate dramatic fluctuations and a carrying capacity (mediated through female territoriality). The author concludes that rare immigration events prevent the extinction of the population, a statement that links directly to an important observation made in the theoretical chapter: that a low immigration rate can be very important at preventing extinction. This idea has a clear analogy with the view that low levels of immigration can prevent the loss of genetic variability from an otherwise isolated population. The analogy supports my belief, which runs counter to that of this book’s editor (but not, apparently, to that of the contributors) that ecological and genetic arguments more often than not lead to very similar conclusions4. The current trend of some writers to create a false dichotomy between ecological and genetic contributions to the study of small populations will, I hope, be short-lived.
Ornithological studies in Antarctica
I
REVIEWS
32 Mock, D.W., Drummond, H. and Stinson, C.H. (1990) Am. Sci. 78,438-449
33 Cash, K. and Evans, R.M. (1986) Be/mu. Ecol. Sociobiol. 18413-418 34 Williams, T.D. (1989) Oikos 55, 19-22 35 Anderson, D.J. (1990) Am. Nat. 135,334-350 36 Lamey, T.C. (1993) Oikos 66,293-297 37 Birney, E.C.and Baird, D.D. (1986) Am. Nat, 126,136-140 38 Bartlett,J. (1987)Behau.Ecol.Sbciobiol. 21,179-183
A quest for mechanism Plant Allometry: The Scaling of Form and Process by Karl .I. Niklas University of Chicago Press, 1994. s68.95ff47.95 hbk, $28.75/f19.95 pbk (xvi + 395 pages) ISBN 0 226 58080 6/O 226 580814
M
ost scientists desire to account for a large range of phenomena by the derivation of laws or rules from relatively simple underlying principles. Unfortunately, all too often this desire is not fulfilled in ecology and evolutionary biology. Yet, any plant (or for that matter any object) is subjected to the same physical and chemical rules. This makes scaling relations based on these rules very appealing for many because, by their nature, they should be generally applicable. Others may find scaling analysis a simple naive tool contingent of fragile assumptions in the light of the complexity of organisms. The author’s position is clear: ‘. .. the quest for mechanism can be sped on its way by means of scaling analysis’. Niklas deals with a great number of sub jects ranging from molecular traffic within living cells to the evolution of plant lifehistories. One of the objectives of this book is to show that, in contrast to the empirical approach to the relations between absolute and relative size, and between organic form and process, scaling relations can be analytically derived. For empirical scaling analysis, the methods and pitfalls of regression analysis are amply discussed (a 40-page appendix on methods is added). With regard to analytically derived scaling relations, great care is given to explain how arguments of similitude are constructed. By doing so, the book will prove useful both in teaching and in research. In most places, the assumptions made at different steps in the construction of analytically derived scaling relations are discussed and tested with empirical data whenever possible. This approach proves to be very instructive, for instance in the discussion on the ‘surface-area law’, the ‘314 power law for the scaling of growth to body mass’ or the l-3/2 self-thinning rule’. While the latter is still treated in a rather positive
134
39 Spalding, MC., Smith, J.P. and Forrester, D.J. (1994) Auk 111,328-336 40 Queller, DC. (1994)Am. Nar 144(SuppI.),S&l-S99 41 Buchholz, J.T. (1922) Bar. Gaz. 73,249-286 42 Cheplick, G.P. (1992) J. Ecol. 80,567-575 43 Kozlowski, T.T. (1973) inshedding ofPlant Parts (Kozlowski, T.T., ed.), pp. 3-44, Academic Press 44 Searcy, K.B. and Macnair, M.R. (1993) Evolution 47, 13-24
vein in most textbooks on plant population biology, it is argued here that the models from which this law is derived analytically should be rejected, because empirical scaling exponents for plant height are only superficially in agreement with them. Furthermore, it is argued that the empirical derivation of this law results from methodologically flawed regression analysis. Unfortunately, in the chapters that deal with reproduction and evolution, the scrutiny of the arguments becomes less when they can no longer be derived from physical laws. For instance, the way in which the pattern of female/male biomass allocation among anemophilous species is dealt with can be criticized on two rather obvious points. First, biomass allocation patterns are only discussed in relation with male fitness while it is clear that the relationship between investment and both male and female fitness determines the optimal allocation pattern. Second, it is not clear why tall plants have less local mating competition: Niklas states that they are better at dispersing pollen but seems to disregard the fact that they also produce more pollen. And, on a few occasions, models are presented without proper discussion of the alternatives. Having made these remarks it should immediately be added, however, that Niklas brings together most of the relevant literature, making the book a good starting point for further study. A creative reader may also be inspired to derive his/her own scaling relations. The relationship between plant mass and female fitness, mentioned above, may be derived for monocarpic plants from the scaling relations between reproductive and vegetative mass, plant height and mass, dispersal and plant height, and mass and density, which are extensively dealt with in the book. Any evolutionary biologist is at some point faced with the question, what is the relation between organic size and form and process.Then, Niklas’book will undoubtedly prove a reliable source of information. Although not all readers will go through the book from cover to cover, on the whole I think that Niklas has done a remarkable job. Peter G.L. Klinkhamer Institute for Evolutionary and Ecological Sciences, University of Leiden, PO Box 9516, 2300 RA Leiden, The Netherlands
45 Stephenson, A.G. and Winsor, J.A. (1986) Evolution
40,453-458
46 Lyon, B.E., Eadie, J.M. and Hamilton, J.D. (1994) Nature 371,240-243 47 Forbes, L.S. (1991) Oikos 62,325-332 48 Mock, D.W. and Forbes, L.S. (1992) Trends Ecol. Euol. 7,409-413
49 Bateson, P. (1994) Trends Ecol. Euol. 9,399-403 50 Snow, A.A. (1994) Am. Nat. 144 (Suppl.), S69-S83
How small is small? Minimum Animal Populations edited by Hermann Remmert Springer-Verlag, 1994. DM128.00 hbk (vii + 156 pages) ISBN 3 540 56684 8
W
ith increasing frequency, ecologists are being asked ‘How much habitat do we need to preserve to save this species?’ Sometimes the species is a large mammal or an exotic bird that evokes public support; Iother times it has less general appeal and is protected only because the mandates of law provide a tool for those concerned with the Iloss of biological diversity. But in either case ,ecologistsare being asked to provide answers about optimal size of reserves, number of 1reserves and if reserves should be isolated ,or linked. In response, the study of small Ipopulations was born in the early 1980sand Iits associated acronyms, such as minimum viable population size(MVP) and ‘singlelarge ,or several small’ reserves (SLOSS),began to 1receive serious attention. Now the 1990sare Iwell under way and we can begin to evaluate Ihow well the study of small populations has 1[ared over the past decade. Based upon this new book, I would have to report that pro gresswas patchy. While some of the chapters are well written and informative, the book is seriously lacking in a framework that would permit the reader to gain a clear understanding of either the intellectual and practical problems confronting conservation biologists or the advances that have been made. The cover of this book tells us that the data to be presented show that MVPdepends solely on the species in question, and that we should eschew the guidelines that geneticists have suggested. I somehow missed this message; instead I found that the book highlights a quite different problem: the paucity of good empirical data. The book pre sents data from birds, mammals, fish and beetles, with the emphasis on birds. This is a laudable attempt at presenting data from diverse sources, but the relevance of some of these data to the perseverance of small populations is far from obvious. Since this book is an edited collection, the question of relevance should have been TREE
vol.
10, no.
3 March
1995
BOOK resolved by the editor’s introduction. However, his short contribution provides little insight. In fact, he doesn’t refer to any of the work within the collection, beyond asserting that the problems of small populations vary depending upon the type of organism a truism but, since it is never developed further anywhere in the book, not a very help ful one. He also mentions a few examples of persistent, small vertebrate, populations, from which he concludes that deleterious effects due to inbreeding are the exception. This idea runs counter to the available data: inbreeding depression is the rule’, even in the presence of significant levels of selfing2, and models show that inbreeding depression can create a serious problem for the persistence of a small populations. It is probably just as well that the some what idiosyncratic introductory remarks are not developed elsewhere in the book. Instead we are provided with some of the basic ideas necessary for the discussion of MVP.Genetic, demographic and environmental stochasticity is introduced (Chapter 2) as is the basic theory of effective population size (Chapter 4). Both chapters also present well-balanced discussions of the influence of genetic and ecological factors on small populations (of birds and mammals, respectively). The theme of demographic and environmental stochasticity is expanded into a clear description of stochastic modeling (Chapter 6). I would recommend this chapter to anyone who is trying to understand how the simple equations of population growth are analyzed as stochastic models. I have one caveat-this chapter does not serve as a review, since the extensive literature of the subject is largely ignored. With the exception of the modeling chapter, the book is focused on presenting empirical data. In several chapters, this serves to highlight the problem that often the necessarydata don’t exist. For example, some of the best-studied taxa are birds, but the discussion of Amazonian birds (Chapter 7) illustrates our almost total lack of knowledge of some potentially threatened species. But even in well-studied cases, important data may be missing or overlooked. Thus, while I found the discussion of within-lake speciation of fishes quite fascinating (Chap ter 5), there is no discussion of issues that relate directly to the problems of small populations, such as the likely size of these fish populations when they differentiated or the size of lakes that permitted such differentiation. These questions are of great relevance because they directly address the issue of future evolutionary change within conserved populations. Long-term data from small populations are of great value in linking the predictions of stochastic models to the real world. Numerical data from 22 years of an island vole population are presented (Chapter 8) TREE
vol.
IO, no.
3 March
1995
REVIEWS
A re-appraisal of the skua’s behaviour was required but at a different locality. Many years on, this book is the account of the five summers’ work (1965-66 to 1969-70) undertaken by Young and colleagues on south polar skuasand Adelie penguins at Cape Bird (northern tip of Ross Island). This location was favoured because it had many groups of skuas and penguins, and the geography afforded excellent opportunities to record skua behaviour from a distance. Young writes with enthusiasm and some times passion. The well-illustrated text is reminiscent of Richdale’s Population Study of Penguins3in which a wealth of data is de scribed, mostly in a very rigorous and objective fashion, but mixed with delightful anecdotes and anthropomorphisms. Whether or not skuas can make decisions, be disconcerted, or appreciate penguins, may not seem the substance of good science, but only if read out of context. There is a detailed account of the range Leonard Nunney of foods available to skuas, the biomass of the food and those aspects of penguin breedDept of Biology, University of California, ing biology that may affect skuas feeding at Riverside, CA 92521, USA the penguin colonies. The methods used for observing and recording the skua foraging References 1 Thornhill, N.W., ed. (1993) The Natural History and feeding behaviour were carefully conof Inbreeding and Outbreeding, University of sidered and developed in the early stages of Chicago Press the study with an emphasis on observing 2 Montalvo, A.M. Ecology (in press) without disturbing. At times, considerable 3 Mills, L.S. and Smouse, P. (1994)Am. Nat. 144, tenacity on behalf of the observer was re 412-431 quired as is evident from the following quote: 4 Nunney, L. and Campbell, K.A. (1993) Trends ‘One’s recording was more at risk from goEcol. Euol. 8,234-239 ing to sleep through boredom than through being exhausted from frenzied activity’. We are rewarded with a very detailed set of results from those observations on skua feeding behaviour and Young uses and explores these results very fully. Although the opportunities for very detailed and extensive analysis (statistical or otherwise) of the skuas behaviour were limited by the amount Skua and Penguin and type of the data, Young does make full by Euan Young use of the information. The searching quesCambridge University Press, tions which preface the many sections pro Studies in Polar Research, 1994. vide the reader with much incentive to read f65.00/$99.95 hbk (xvi + 452 pages) on. There is some interesting modelling and ISBN 0 521 322510 analysis of the spatial interactions (but not processes). For those happier with quantin 1963,EuanYoung published two paper+* about his research on the south polar skua tative analysis rather than qualitative analy(Catharactu maccormicki) at Cape Royds sis, the latter chapters of the book are of (RossIsland, McMurdo Sound). The common considerable interest. While acknowledging occurrence of skuas raising only one chick limitations of the data, Young attempts some from a clutch of two eggs was confirmed, interesting and detailed analysis and modeland it was found that most skuas were feed- ling of the energy costs of alternative feeding not at the colony of Adelie penguins ing strategies. (Pygoscelis adeliae) but at sea. Were the In his final analysis, Young returns to the i skuaspredators of penguins or opportunistic criticisms made of his earlier work; are skuas scavengers? These early observations were predators of penguins, to what extent do later criticized. The population of Adelie skuas depend on penguins, and what are the penguins at Cape Royds was small, so there short-term and long-term implications of was little food available, and at larger colonies skuas and penguins breeding in close proxthere would be plenty of food for skuas. The imity? Any attempt to reveal his answers in methods of study may have affected the this brief review would not do justice to this skua’s behaviour. book. and they illustrate dramatic fluctuations and a carrying capacity (mediated through female territoriality). The author concludes that rare immigration events prevent the extinction of the population, a statement that links directly to an important observation made in the theoretical chapter: that a low immigration rate can be very important at preventing extinction. This idea has a clear analogy with the view that low levels of immigration can prevent the loss of genetic variability from an otherwise isolated population. The analogy supports my belief, which runs counter to that of this book’s editor (but not, apparently, to that of the contributors) that ecological and genetic arguments more often than not lead to very similar conclusions4. The current trend of some writers to create a false dichotomy between ecological and genetic contributions to the study of small populations will, I hope, be short-lived.
Ornithological studies in Antarctica
I