- Email: [email protected]
Haunted hypotheses
BOOK REVIEWS algal blooms and fish kills. For an ecologist, the interesting phenomenon is that shallow lakes with the same nutrient loading can show very different ecological characteristics, and the same lake may also shift between states over time. In some productive shallow lakes, primary production is dominated by macrophytes and the water is transparent, whereas in other lakes primary production is dominated by phytoplankton and the water is turbid. Shallow lakes might thus provide an example of the presence of alternative states in an ecological system, a possibility predicted by many models but rarely observed in empirical studies1. If present, alternative stable states are not only of purely scientific interest, as their presence would allow for man-induced manipulations of these lakes. In the Ecology of Shallow Lakes, Scheffer brings together an impressive amount of current empirical knowledge concerning the effects of abiotic (e.g. light, sedimentation and resuspension) and biotic (e.g. phytoplankton, macrophytes, zooplankton, macroinvertebrates and fish) variables on the dynamics of shallow-lake ecosystems. However, his ambitions go beyond mere documentation: in almost every chapter of the book, a graphical bifurcation analysis is provided, including a description of the mechanisms that can lead to the presence of alternative states and the conditions under which alternative states are expected. Evidence in support of alternative stable states comes from results of biomanipulation studies, although the possibility that the lakes included in these studies were still in a transient phase cannot be ruled out. Scheffer termed the models used ‘minimal’ models. These employ ordinary differential equations, in which a limited set of variables are dynamic (e.g. phytoplankton and zooplankton), whereas other factors affecting the trophic dynamics, such as fish, are included only as nondynamic components. This is a drawback, because the analysis of the trophic dynamics as a whole, such as those done in trophic models2,3, is not carried out. Scheffer openly advocates that the dynamics of shallow lakes are characterized by chaotic behaviour. In general ecology, much effort has already gone into investigating the extent to which chaotic dynamics is actually present in natural communities. This has involved both the derivations of mathematical and statistical tools to analyse time-series data from field data and extensive experiments4,5. Unfortunately, these tools are not used by Scheffer. Instead, he restricts himself to promoting some general arguments for why natural communities should be intrinsically chaotic and, consequently, the reader is left relatively unconvinced. An extensive discussion is given to the interactions between Daphnia and algae, particularly the lack of paradox of enrichment TREE vol. 13, no. 10 October 1998
cycles (increased instability with enrichment), as predicted by standard predator– prey theory. As a reader familiar to the extensive theoretical and experimental literature on Daphnia–algae interactions, I was struck that the discussion was largely restricted to Scheffer’s own analyses, despite the rich literature in this research area6. The simultaneous presence of low algae biomasses and absence of the paradox of enrichment cycles with enrichment is a puzzling phenomenon in Daphnia–algae dynamics, which has occupied the attention of a group of prominent scientists for more than a decade6. This group has also demonstrated the existence of cohort driven cycles within Daphnia as a result of size-structured dynamics, a dynamics only briefly covered by Scheffer. The ubiquitous presence of size-structured processes in aquatic systems means that the ecosystem dynamics of shallow lakes can hardly be analysed within the framework of the minimal models used in the book. Scheffer indirectly discusses this problem in the last chapter, in which he advances individual-based models as tools for linking quantitative modelling and transparent biology. Here, it would have been more appropriate to discuss the class of physiologically structured models referred to as distributions models. These are individual-based models, based on a two-state concept (individual and population states), but also have the advantages of being well defined mathematically and lending themselves to investigations of long-term population dynamics7. Despite the shortcomings, I strongly recommend Ecology of Shallow Lakes to both aquatic ecologists and ecologists in general. More research is needed, but undoubtedly there is a strong case that alternative states in shallow lakes do exist. Scheffer’s book is successful in summarizing the evidence and in providing a mechanistic understanding of when alternative states are likely to be present in lakes.
Lennart Persson Dept of Animal Ecology, Umeå University, S-901 87 Umeå, Sweden ([email protected])
References 1 Connell, J.H. and Sousa, W.P. (1983) Am. Nat. 121, 789–824 2 Oksanen, L. et al. (1981) Am. Nat. 118, 240–261 3 DeAngelis, D.L. (1992) Dynamics of Nutrient Cycling and Food Webs, Chapman & Hall 4 Ellner, S. and Turchin, P. (1995) Am. Nat. 145, 343–375 5 Constantino, R.F. et al. (1997) Science 275, 389–391 6 McCauley, E. et al. (1998) Ecology 79, 1339–1356 7 De Roos, A.M., Diekmann, O. and Metz, J.A.J. (1992) Am. Nat. 139, 123–147
Haunted hypotheses American Pronghorn: Social Adaptations and the Ghosts of Predators Past by J.A. Byers The University of Chicago Press, 1998. $70.00/£55.95 hbk, $23.95/£19.25 pbk (xviii + 300 pages) ISBN 0 226 08698 4 / 0 226 08699 2
P
ronghorn antelope (Antilocapra americana) are remarkably fast. They are reputed to run at speeds of up to 100 km (60 miles) per hour, faster than a Thomsons gazelle fleeing a pursuing cheetah. Byers refers to this as ‘ridiculously too fast for any modern predator’. The theme of the book, Ghosts of Predators Past, is developed around the fact that this speed might reflect selection to escape the guild of 13 species of predators that roamed the North American savannas until the great Pleistocene extinctions. The overall aim is ‘to raise historical interpretation in behavioural ecology from its lowly status as the hypothesis of last resort toward equality with explanations that are based upon current utility’. This is laudable. However, although few biologists would dispute that behaviour reflects adaptation to the past, I found the arguments rather like a ‘just-so-story’ with little attempt to falsify specific hypotheses. For example, in Chapter 3 (The Selfish Herd: Modal Social Organization), Byers finds no benefit to grouping but costs in terms of feeding competition. He concludes that grouping behaviour is interpretable not in the light of current selection pressures, but rather in light of past predation selection, despite the fact that pronghorn response to current predators, coyotes (Canis latrans), is not investigated. Clearly, there is antipredator behaviour by both adult females and young fawns (Chapter 4). For the first three weeks of life, fawns remain hidden in the undergrowth and, up to about five days old, freeze when aware of danger. Mothers are extremely vigilant and make random visits to fawns, clearly trying to avoid giving away the fawn’s presence. Recruitment of fawns is generally very low, at little more than 10% in the National Bison Range (MT, USA), probably because the perimeter fence not only contains the pronghorn, but also coyotes! The three years of highest recruitment were years when the greatest number of coyotes were removed in the preceding spring. The other major element of the book is Social Adaptations. Although birth is highly synchronized, differences of a few days quickly lead to dominance hierarchies developing in fawns of both sexes, which can then confer competitive advantages when feeding. As a result, Byers suggests that relative birth
Copyright © 1998, Elsevier Science Ltd. All rights reserved. 0169-5347/98/$19.00
425
BOOK REVIEWS date influences lifetime reproductive success in females, although, as the number of individuals from the same cohort were usually few, I could not find the supporting evidence. In contrast, when discussing the benefit of differential investment in males, Byers questions the evidence that small initial differences in juvenile male red deer1 should be perpetuated into adulthood. Again, I could not find the data for pronghorn to support or refute the contention. Whatever characteristics enable females to become dominant, it apparently has no effect on lifetime reproductive success, although it does have a small effect on parturition dates. Indeed, the costs of dominance seem to be more apparent. Dominant females experienced shorter nearest-neighbour distances and higher interaction rates, although the possible benefits of feeding in more central locations in the herd, in terms of diet quality, were not assessed. As a result, Byers returns to his well rehearsed theme and suggests that dominance related behaviour is another example of social behaviour adapted to the recent past, rather than to the present. As in several other studies of mammals, female dominance is associated with significant variation in offspring sex ratios. Like red deer1, dominant pronghorn mothers tend to have more sons than daughters, which leads Byers to suggest that perhaps he failed to detect actual rank related differences in diet. In practice, it is not clear that the appropriate data were ever collected. Male reproductive strategies and the mating system, including female choice, are the subjects of separate chapters. Of particular interest is the change from territorial defence to harem defence, following a winter in which all males over five years old died. Byers suggests that the surviving young, inexperienced males are ineffective at adopting territoriality and, even after the age and sex structure is re-established, the tradition of territoriality is lost. Thus, clearly Byers believes that some behaviour is subject more to current selection pressures, albeit stochastic ones, than those in the Pleistocene. Although it is difficult to answer all the questions posed in a behavioural ecology study, the research could have made a bigger impact if it had focused more on the ecology of the system. A more multidisciplinary approach might have reduced the inevitable conclusion that virtually everything results from the Ghosts of Predators Past. In my view, this recurring theme and, in particular, the concluding chapter, is simply wild speculation that undermines an excellent study of a fascinating species, undertaken by a passionate biologist.
Steve Albon Banchory Research Station, ITE, Hill of Brathens, Glassel, Banchory, Kincardineshire, UK AB31 4BY ([email protected])
426
References 1 Clutton-Brock, T.H., Guinness, F.E. and Albon, S.D. (1982) Red Deer: Behavior and Ecology of Two Sexes, The University of Chicago Press
From aapa to zymogeny A Dictionary of Ecology, Evolution and Systematics (2nd edn) by R. Lincoln, G. Boxshall and P. Clark Cambridge University Press, 1998. £50.00 hbk, £17.95 pbk (ix + 361 pages) ISBN 0 521 59139 2 / 0 521 43843 X
The Encyclopedia of Ecology & Environmental Management edited by P. Calow Blackwell Science, 1998. £125.00 hbk (xv + 805 pages) ISBN 0 86542 838 7
A
good, up-to-date reference work in ecology and evolution has been badly needed throughout the 1990s, and just when I was thinking of starting to assemble one myself, along come these two excellent new works to fill the void. A Dictionary of Ecology, Evolution and Systematics is the second edition of the work of the same title, published in 1983 and now badly out of date. It contains around 14 000 entries, mostly crisply defined in fewer than 25 words, and has been written by just three coauthors; it also has some useful appendices – geological timetable, taxonomic hierarchies, soil profile nomenclature, etc. The Encyclopedia of Ecology & Environmental Management (note the confident definite article) has about a quarter as many entries, ranging from one-line definitions to short essays of up to a couple of pages, some with handy short reference lists, many of them clearly illustrated, and written by an army of >200 authors, coordinated by an Editorial Board and an Editor-in-Chief. Both books are definitely worth having, wherever you think you sit on the evolutionary–ecological spectrum. But, in sifting through them for nuggets for this review (and reviewing reference works is a thoroughly churlish activity), I began to wonder if there had been a deal between the two publishers to ensure that the reader would have to buy both books to gain a full picture. For example, the non-phylogeneticist would find an explanation of maximum likelihood methods in the Blackwell book and a definition of parsimony in the Cambridge book, but not vice versa. And neither book is particularly faithful to its title, sometimes penetrating
Copyright © 1998, Elsevier Science Ltd. All rights reserved. 0169-5347/98/$19.00
deep into what one would think to be the territory of the other. Blackwell, for instance, has an extended entry on molecular drive – that essential conceptual tool of ecologists and environmental managers; Cambridge, despite its evolutionary remit, doesn’t define it at all. More bizarrely, Cambridge doesn’t list F-statistics or QTLs, whereas Blackwell affords each a generous essay. These books sometimes leap even farther beyond the scope of their titles: one wouldn’t reach for a dictionary of ecology, evolution and systematics to find the meaning of the Latin et (if, indeed, one had forgotten it), or for an encyclopaedia of ecology and environmental management to look up Julian day, ISBN or, indeed, act of God (entry: see ‘act of nature’) – but there they all are. Blackwell even contains a definition of hunger (‘An abstract motivational response to a physiological need that is commonly restricted to higher animals’), which, incidentally, shows that the formality of scientific language doesn’t necessarily nail down a definition more precisely; the Collins primary definition, in exactly half as many syllables, is ‘a feeling of emptiness or weakness induced by lack of food’ – and surely lower animals (whatever that means) have physiological needs too. There are other quirks and oddities. Blackwell has two and a half pages on conservation and ecology in Argentina, but none on (say) Colombia or Brazil. Cambridge defines no fewer than ten terms with the prefix ‘tycho-’ (meaning chance or occasional), when surely to define the prefix alone would have been enough – even though this would have meant losing the gloriously useless ‘tychotroglobionte’, meaning an organism only occasionally found in caves (probably including most TREE readers). To be fair, the authors of the Dictionary rightly lament the existence of much of the material they feel obliged to define: as they point out in their preface, ‘[s]uch terminological monstrosities as bathyplanktohyponeuston do little to facilitate communication.’ Both books are reasonably faithful to the non-overlapping elements of their titles. Thus, Cambridge’s coverage of the taxonomic terminology – junior homonyms, justified emendations, nomina nuda and such – is excellent, while Blackwell is very good on the jargon and acronyms of environmental management. And in their central overlapping area of coverage – ecology – they make a very good partnership. I shall use both works a lot – Cambridge for a quick source of reference and Blackwell for quick revision, brushing up on the more intractable topics, and for brand-new knowledge (had you ever heard of a ‘larva flow’ …?). Buy the first one yourself, and get the library to buy the other.
Andrew Sugden TREE vol. 13, no. 10 October 1998
cycles (increased instability with enrichment), as predicted by standard predator– prey theory. As a reader familiar to the extensive theoretical and experimental literature on Daphnia–algae interactions, I was struck that the discussion was largely restricted to Scheffer’s own analyses, despite the rich literature in this research area6. The simultaneous presence of low algae biomasses and absence of the paradox of enrichment cycles with enrichment is a puzzling phenomenon in Daphnia–algae dynamics, which has occupied the attention of a group of prominent scientists for more than a decade6. This group has also demonstrated the existence of cohort driven cycles within Daphnia as a result of size-structured dynamics, a dynamics only briefly covered by Scheffer. The ubiquitous presence of size-structured processes in aquatic systems means that the ecosystem dynamics of shallow lakes can hardly be analysed within the framework of the minimal models used in the book. Scheffer indirectly discusses this problem in the last chapter, in which he advances individual-based models as tools for linking quantitative modelling and transparent biology. Here, it would have been more appropriate to discuss the class of physiologically structured models referred to as distributions models. These are individual-based models, based on a two-state concept (individual and population states), but also have the advantages of being well defined mathematically and lending themselves to investigations of long-term population dynamics7. Despite the shortcomings, I strongly recommend Ecology of Shallow Lakes to both aquatic ecologists and ecologists in general. More research is needed, but undoubtedly there is a strong case that alternative states in shallow lakes do exist. Scheffer’s book is successful in summarizing the evidence and in providing a mechanistic understanding of when alternative states are likely to be present in lakes.
Lennart Persson Dept of Animal Ecology, Umeå University, S-901 87 Umeå, Sweden ([email protected])
References 1 Connell, J.H. and Sousa, W.P. (1983) Am. Nat. 121, 789–824 2 Oksanen, L. et al. (1981) Am. Nat. 118, 240–261 3 DeAngelis, D.L. (1992) Dynamics of Nutrient Cycling and Food Webs, Chapman & Hall 4 Ellner, S. and Turchin, P. (1995) Am. Nat. 145, 343–375 5 Constantino, R.F. et al. (1997) Science 275, 389–391 6 McCauley, E. et al. (1998) Ecology 79, 1339–1356 7 De Roos, A.M., Diekmann, O. and Metz, J.A.J. (1992) Am. Nat. 139, 123–147
Haunted hypotheses American Pronghorn: Social Adaptations and the Ghosts of Predators Past by J.A. Byers The University of Chicago Press, 1998. $70.00/£55.95 hbk, $23.95/£19.25 pbk (xviii + 300 pages) ISBN 0 226 08698 4 / 0 226 08699 2
P
ronghorn antelope (Antilocapra americana) are remarkably fast. They are reputed to run at speeds of up to 100 km (60 miles) per hour, faster than a Thomsons gazelle fleeing a pursuing cheetah. Byers refers to this as ‘ridiculously too fast for any modern predator’. The theme of the book, Ghosts of Predators Past, is developed around the fact that this speed might reflect selection to escape the guild of 13 species of predators that roamed the North American savannas until the great Pleistocene extinctions. The overall aim is ‘to raise historical interpretation in behavioural ecology from its lowly status as the hypothesis of last resort toward equality with explanations that are based upon current utility’. This is laudable. However, although few biologists would dispute that behaviour reflects adaptation to the past, I found the arguments rather like a ‘just-so-story’ with little attempt to falsify specific hypotheses. For example, in Chapter 3 (The Selfish Herd: Modal Social Organization), Byers finds no benefit to grouping but costs in terms of feeding competition. He concludes that grouping behaviour is interpretable not in the light of current selection pressures, but rather in light of past predation selection, despite the fact that pronghorn response to current predators, coyotes (Canis latrans), is not investigated. Clearly, there is antipredator behaviour by both adult females and young fawns (Chapter 4). For the first three weeks of life, fawns remain hidden in the undergrowth and, up to about five days old, freeze when aware of danger. Mothers are extremely vigilant and make random visits to fawns, clearly trying to avoid giving away the fawn’s presence. Recruitment of fawns is generally very low, at little more than 10% in the National Bison Range (MT, USA), probably because the perimeter fence not only contains the pronghorn, but also coyotes! The three years of highest recruitment were years when the greatest number of coyotes were removed in the preceding spring. The other major element of the book is Social Adaptations. Although birth is highly synchronized, differences of a few days quickly lead to dominance hierarchies developing in fawns of both sexes, which can then confer competitive advantages when feeding. As a result, Byers suggests that relative birth
Copyright © 1998, Elsevier Science Ltd. All rights reserved. 0169-5347/98/$19.00
425
BOOK REVIEWS date influences lifetime reproductive success in females, although, as the number of individuals from the same cohort were usually few, I could not find the supporting evidence. In contrast, when discussing the benefit of differential investment in males, Byers questions the evidence that small initial differences in juvenile male red deer1 should be perpetuated into adulthood. Again, I could not find the data for pronghorn to support or refute the contention. Whatever characteristics enable females to become dominant, it apparently has no effect on lifetime reproductive success, although it does have a small effect on parturition dates. Indeed, the costs of dominance seem to be more apparent. Dominant females experienced shorter nearest-neighbour distances and higher interaction rates, although the possible benefits of feeding in more central locations in the herd, in terms of diet quality, were not assessed. As a result, Byers returns to his well rehearsed theme and suggests that dominance related behaviour is another example of social behaviour adapted to the recent past, rather than to the present. As in several other studies of mammals, female dominance is associated with significant variation in offspring sex ratios. Like red deer1, dominant pronghorn mothers tend to have more sons than daughters, which leads Byers to suggest that perhaps he failed to detect actual rank related differences in diet. In practice, it is not clear that the appropriate data were ever collected. Male reproductive strategies and the mating system, including female choice, are the subjects of separate chapters. Of particular interest is the change from territorial defence to harem defence, following a winter in which all males over five years old died. Byers suggests that the surviving young, inexperienced males are ineffective at adopting territoriality and, even after the age and sex structure is re-established, the tradition of territoriality is lost. Thus, clearly Byers believes that some behaviour is subject more to current selection pressures, albeit stochastic ones, than those in the Pleistocene. Although it is difficult to answer all the questions posed in a behavioural ecology study, the research could have made a bigger impact if it had focused more on the ecology of the system. A more multidisciplinary approach might have reduced the inevitable conclusion that virtually everything results from the Ghosts of Predators Past. In my view, this recurring theme and, in particular, the concluding chapter, is simply wild speculation that undermines an excellent study of a fascinating species, undertaken by a passionate biologist.
Steve Albon Banchory Research Station, ITE, Hill of Brathens, Glassel, Banchory, Kincardineshire, UK AB31 4BY ([email protected])
426
References 1 Clutton-Brock, T.H., Guinness, F.E. and Albon, S.D. (1982) Red Deer: Behavior and Ecology of Two Sexes, The University of Chicago Press
From aapa to zymogeny A Dictionary of Ecology, Evolution and Systematics (2nd edn) by R. Lincoln, G. Boxshall and P. Clark Cambridge University Press, 1998. £50.00 hbk, £17.95 pbk (ix + 361 pages) ISBN 0 521 59139 2 / 0 521 43843 X
The Encyclopedia of Ecology & Environmental Management edited by P. Calow Blackwell Science, 1998. £125.00 hbk (xv + 805 pages) ISBN 0 86542 838 7
A
good, up-to-date reference work in ecology and evolution has been badly needed throughout the 1990s, and just when I was thinking of starting to assemble one myself, along come these two excellent new works to fill the void. A Dictionary of Ecology, Evolution and Systematics is the second edition of the work of the same title, published in 1983 and now badly out of date. It contains around 14 000 entries, mostly crisply defined in fewer than 25 words, and has been written by just three coauthors; it also has some useful appendices – geological timetable, taxonomic hierarchies, soil profile nomenclature, etc. The Encyclopedia of Ecology & Environmental Management (note the confident definite article) has about a quarter as many entries, ranging from one-line definitions to short essays of up to a couple of pages, some with handy short reference lists, many of them clearly illustrated, and written by an army of >200 authors, coordinated by an Editorial Board and an Editor-in-Chief. Both books are definitely worth having, wherever you think you sit on the evolutionary–ecological spectrum. But, in sifting through them for nuggets for this review (and reviewing reference works is a thoroughly churlish activity), I began to wonder if there had been a deal between the two publishers to ensure that the reader would have to buy both books to gain a full picture. For example, the non-phylogeneticist would find an explanation of maximum likelihood methods in the Blackwell book and a definition of parsimony in the Cambridge book, but not vice versa. And neither book is particularly faithful to its title, sometimes penetrating
Copyright © 1998, Elsevier Science Ltd. All rights reserved. 0169-5347/98/$19.00
deep into what one would think to be the territory of the other. Blackwell, for instance, has an extended entry on molecular drive – that essential conceptual tool of ecologists and environmental managers; Cambridge, despite its evolutionary remit, doesn’t define it at all. More bizarrely, Cambridge doesn’t list F-statistics or QTLs, whereas Blackwell affords each a generous essay. These books sometimes leap even farther beyond the scope of their titles: one wouldn’t reach for a dictionary of ecology, evolution and systematics to find the meaning of the Latin et (if, indeed, one had forgotten it), or for an encyclopaedia of ecology and environmental management to look up Julian day, ISBN or, indeed, act of God (entry: see ‘act of nature’) – but there they all are. Blackwell even contains a definition of hunger (‘An abstract motivational response to a physiological need that is commonly restricted to higher animals’), which, incidentally, shows that the formality of scientific language doesn’t necessarily nail down a definition more precisely; the Collins primary definition, in exactly half as many syllables, is ‘a feeling of emptiness or weakness induced by lack of food’ – and surely lower animals (whatever that means) have physiological needs too. There are other quirks and oddities. Blackwell has two and a half pages on conservation and ecology in Argentina, but none on (say) Colombia or Brazil. Cambridge defines no fewer than ten terms with the prefix ‘tycho-’ (meaning chance or occasional), when surely to define the prefix alone would have been enough – even though this would have meant losing the gloriously useless ‘tychotroglobionte’, meaning an organism only occasionally found in caves (probably including most TREE readers). To be fair, the authors of the Dictionary rightly lament the existence of much of the material they feel obliged to define: as they point out in their preface, ‘[s]uch terminological monstrosities as bathyplanktohyponeuston do little to facilitate communication.’ Both books are reasonably faithful to the non-overlapping elements of their titles. Thus, Cambridge’s coverage of the taxonomic terminology – junior homonyms, justified emendations, nomina nuda and such – is excellent, while Blackwell is very good on the jargon and acronyms of environmental management. And in their central overlapping area of coverage – ecology – they make a very good partnership. I shall use both works a lot – Cambridge for a quick source of reference and Blackwell for quick revision, brushing up on the more intractable topics, and for brand-new knowledge (had you ever heard of a ‘larva flow’ …?). Buy the first one yourself, and get the library to buy the other.
Andrew Sugden TREE vol. 13, no. 10 October 1998