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Acid rain: never pure and rarely' simple
TREE vol. 2, no. 3, March
the behavioural traits of felids (infanticidal males) and the ecology of lions (high population densities, open terrain and a preference for large prey items). At the same time, it explains a lot about lions’ social behaviour - matrilineal groups, intragroup sharing and of prey, staunch defense of home ranges. Of course, different components of social behaviour will not have evolved independently, but the above description highlights the selective factors likely to have been involved. Packer’s conclusion that much of female cooperative foraging behaviour is a consequence, rather than a cause, of group living is supported by the available data. This new, more comprehensive interpretation of lion sociality underscores the fact that models which are designed to interpret data can only
be as accurate plete.
as the data are corn
References 1 Wilson, E. 0. (1975) Sociobiology: The New Synthesis, Harvard 2 Bertram, B. C. R. (1978) in Behavioural Ecology(Krebs, J. R. and Davies, N. B., eds), pp. 64-96, Blackwells 3 Macdonald, D. W. (1983) Nature301, 379-384 4 Packer, C. (1986) in EcologicalAspects ofSocia/Evo/ution (Rubenstein, D. I. and Wrangham, R. W., eds), pp.429451, Princeton University Press 5 Bouliere, F. (1963)Afr. Wild/. 17,21-27 6 Kruuk, H. (1972) The SpottedHyena, University of Chicago Press 7 Kruuk, H. (1975) in Function and Evolution in BehaviourfBaerends, G., Beer, C. and Manning, A., eds), pp. 119-141, Oxford University Press 8 Caraco, T. and Wolf, L. L. (1975)Am. Nat. 109,343-352 9 Schaller, G. B. (1972) The Serengeti Lion, University of Chicago Press
AcidRain:NeverPureandRarely Simple Mike Ashmore and Andrew Tickle Until recently, public debate in Britain about acid rain has focussed on effects on water and fisheries in Scandinavia, and forests in West Germany and other countries of central Europe. However, the majority of the pollutants emitted in Britain are deposited within the country, and there is now increasing concern about the effects of acid rain sensu lato within Britain. A recent one-day meeting at Imperial College, London, on ‘Acid Rain and Britain’s Natural Ecosystems’ brought together scientists, conservationists, industrialists and policy makers to assess the current scientific evidence on the subject, to identify priorities for new research and to evaluate the possible implications for pollution control policy’. The meeting was held im-
mediately after the announcement that the British government will spend f600 million on fitting flue gas desulphurization units to three large coal-fired power stations. As the first country to enter the Industrial Revolution, the effects of pollution are not new in Britain. Indeed, air pollution from coal-burning Mike Ashmore and Andrew Tickle are at the Department of Pure and Applied Biology, Imperial College of Science and Technology, Silwood Park, Ascot, Berks SL5 7PY, UK. 58
affected London as far back as the 13th century’. Lichenologists from the British Museum (Natural History) presented the well-documented case on lichen sensitivity to air pollutants (predominantly sulphur dioxide) which gave rise to the impoverished lichen floras of Britain’s towns. This trend has to some extent now been reversed by clean air legislation3, but they also presented new evidence on the loss of epiphytic lichens (notably in the genus Lobaria) in pristine areas distant from major sources of pollution, suggesting that the cause is an increasing acidity of the stem flows on host trees. The effects of both past and present pollution were illustrated by work in the southern Pennines. Here, studies have palaeoecological shown that many Sphagnum species were lost in the last century due to pollution from nearby industrial towns, such as Manchester and Sheffield4. However, despite the falling sulphur deposition in recent decades, Sphagnum species transplanted into this area still grow very poorly. Recent studies of their nitrogen metabolism at Manchester University suggest that it is now the deposition of nitrogen, rather than sulphur, which is critical for the plants’ surviva15. Such detailed elaboration
7987
IO Clark, C. W. Aim. Behav. 35 !in press) 11 Bertram, B.C. R. (1979) in Serengeti: Dynamics of an Ecosystem (Sinclair, A. R. E. and Norton-Griffiths, M., eds), pp. 159-179, Chicago University Press 12 Packer, C. and Pusey, A. E. (1985) in Evolution (Greenwood, P., Slatkin, M. and Harvey, P. H., eds), pp. 173-186, Cambridge University Press 13 Seidersticker, J. C., Hornocker, M. G., Wiles, W. V. and Massick, J. P. (1973) Wild/. Monogr. 35, l-6 14 Pusey, A. E. and Packer, C. Behaviour (in press) 15 Packer, C. and Pusey, A. E. (1984) in Infanticide: Comparative and Evolutionary Perspectives (Hausfater, G. and Hardy, S. B., eds), pp. 31-42, Aldine Press 16 Packer, C., Herbst, L., Pusey, A. E., Bygott, J. D., Hanby, J. P., Cairns, S. J. and Beraerhoff-Mulder, M. in Reprodtkve Suc,cess fclutton-Brock, T. H., ed.), University of Chicago Press (in press)
of physiological responses, showing a mechanistic link between pollutant input and ecological response, is unfortunately an isolated example in a field of research more characterized by uncertainty over possible causes. In the case of trees, the field evidence of declines in health is itself a matter of intensive debate6s7. The difficulty here is that few trees, once they reach a certain age, ever look entirely healthy. We do not yet have a scientific basis on which to separate the effects of the range of biotic and abiotic stresses to which trees are normally subjected, from those of pollution. Indeed, recent work has demonstrated that exposure to pollutants can alter the sensitivity of plants to a range of other stresses. There is a lack of survey data designed to test associations between pollution levels and tree health, and almost no experimental work with British native species on which to judge the potential impact of current pollution levels in the UK*. Furthermore, there is still no scientific consensus about the causes of the extensive forest declines seen elsewhere in Europe. Description of changes in the distribution of pollutants in the UK can provide circumstantial evidence of possible causes, but this is hindered by the lack of comprehensive monitoring data in the past. This type of background information is extremely important as changes in pollution levels are just one of many factors affecting Britain’s ecosystems since World War II. In lowland Britain, for instance, the enormous intensifica,,I,),I! ,,,,.. if <_I,, c illl,llllic,til,Wi ’,337 :I; SO? 3 Ihi c ‘,l”U
TREE vol. 2, no. 3, March
1987
tion in agriculture has resulted in dramatic loss of habitats and increased pressure on many others; this makes subtle effects of pollution difficult to detect. Increases in stream and lake acidity in some areas of upland Britain have been attributed both to widespread planting of conifers and to acid deposition. Elegant work at University College, London, has used fossil diatom assemblages to establish historical pH changes in lochs in the remote area of Galloway, in southern Scotland. In some of these lochs, changes in pH cannot be satisfactorily explained by afforestation or other changes in land use’,“. Higher up the food chain, there is evidence that the number of dippers (Cinclus cinclus) in Mid-Wales is lower in acidic streams, which have a lower abundance of food sources such as caddis flies and mayfly nymphs. For one tributary of the River Wye, a decline in numbers since 1963 has been associated with increased stream acidity in an area of extensive afforestation”. However, the more detailed scientific work needed to go beyond statistical associations observed in the field to an understanding of the causal link between the associated variables has only recently begun. The value of remedial measures to reduce the effects of acid rain was the subject of considerable debate, especially in relation to the treatment of lakes and their catchment areas by adding calcium (liming). Physiological studies have shown that the toxic effects of Hi and A13’ on fish are reduced in the presence of higher levels of calcium’2. The effects of liming are currently being studied in a large field experiment at Loch Fleet in Galloway’3. Liming catchments, rather than lakes directly, increases the period for which treatment is effective; however the effects of adding large quantities of lime to the vegetation in these naturally acidic upland ecosystems is unknown.
In summary, the strength of the scientific evidence linking changes in Britain’s ecosystems to acid rain is variable. For some groups of species, the processes linking acid deposition to observed effects are understood, and affected areas have been identified. In other cases, such as with certain lichens, birds and amphibians, there are associations between observed changes and acidification in the field, but the processes involved are not worked out. At the opposite extreme are effects on trees, in which both good field data and mechanistic understanding are lacking. This difference inevitably
dictates very different research priorities within and between each area. The detection of subtle changes to ecosystems is in itself problematical; to establish a causal relationship with pollutants may be well-nigh impossible. However, it is precisely such causal relationships that policymakers require. Furthermore the increasing political importance of the ‘green vote’ means that there is ever more pressure to make decisions rapidly. Yet it is a salutary reminder that it has taken 25 years of research in Scandinavia and elsewhere before of the scientific understanding causes of freshwater acidification and decline of fish stocks was good enough to convince the British government to take measures to reduce sulphur emissions - although Scandinavian governments had themselves been convinced fifteen years earlier. Paradoxically, Britain is in one sense in a stronger position than the Scandinavian countries which ‘import’ most of their pollutants, since the smaller contribution of foreign sources means that any control measures taken by the British government will have a more immediate benefit on any ecosystems which it judges to be at risk. The problem of advancing understanding of the many factors influencing the impact of acid rain on ecosystems to a level at which objective decisions on whether to invest in expensive pollution control measures can be made is one of the most intellectual problems demanding faced by ecologists today. In the words on one of the contributors to the meeting, paraphrasing Oscar Wilde, ‘acid rain is never pure and rarely simple’. References 1 Ashmore, M.R., Bell, J.N.B. and Garretty, C., eds (1987) Acid Rain and Britain’s Natural Ecosystems, Centre for Environmental Technology (Imperial College of Science &Technology, University of London)
*
Management G. E. W&on
*
Evolution
*
Sperm competition
Peat
erosion
cumulative
in the effects
southern of two
PennInes
centuries
may
of acid
represent deposition
2 Brimblecombe, P. (1975) Weather30, 388-396 3 Rose, Cl. and Hawksworth, D.L. 11981) Nature 289,289-292 4 Press, M.C., Ferguson, P. and Lee, J.A. (1983) Naturalist 108, 125-l 29 5 Woodin, S.J.. Press, M.C. and Lee, J.A. (1986) New Phytol. 99,381-388 6 Binns, W.O., Redfern, D.B., Rennolls. K. and Betts, A.J.A. (1985) Forest Health and Air Pollution: 1984 Survey (Research and Development Paper no. 142). Forestry Commission (UK) 7 Rose, C. and Neville, M. (1985) Tree Dieback Survey: final Report, Friends of the Earth Ltd 8 Ling, K.A. and Ashmore, M.R. AcidRain and Trees, Nature Conservancy Council (UK) (in press) 9 Flower, R.J. and Batterbee, R.W. (1983) Nature 305,130-l 33 10 Batterbee, R.W., Flower, R.J., Stevenson, A.C. and Rippey, B. (1986) Nature 314,350-352 11 Ormerod. S.J., Bailstone, M.A. and Tyler, S.J. (1985) Ibis, 127,332-340 12 Brown, D.J.A. (1983) Bull. Environ. Contam. Toxicol., 30, 582-587 13 Anon. (1986) Loch Neet Project: A Report of the Pre-intervention Phase 1984-86, Central Electricity Generating Board (UK)
of tropical soils through intercropping,
of carabid beetles, G. Hafffter in birds, T. Birkhead
the
the behavioural traits of felids (infanticidal males) and the ecology of lions (high population densities, open terrain and a preference for large prey items). At the same time, it explains a lot about lions’ social behaviour - matrilineal groups, intragroup sharing and of prey, staunch defense of home ranges. Of course, different components of social behaviour will not have evolved independently, but the above description highlights the selective factors likely to have been involved. Packer’s conclusion that much of female cooperative foraging behaviour is a consequence, rather than a cause, of group living is supported by the available data. This new, more comprehensive interpretation of lion sociality underscores the fact that models which are designed to interpret data can only
be as accurate plete.
as the data are corn
References 1 Wilson, E. 0. (1975) Sociobiology: The New Synthesis, Harvard 2 Bertram, B. C. R. (1978) in Behavioural Ecology(Krebs, J. R. and Davies, N. B., eds), pp. 64-96, Blackwells 3 Macdonald, D. W. (1983) Nature301, 379-384 4 Packer, C. (1986) in EcologicalAspects ofSocia/Evo/ution (Rubenstein, D. I. and Wrangham, R. W., eds), pp.429451, Princeton University Press 5 Bouliere, F. (1963)Afr. Wild/. 17,21-27 6 Kruuk, H. (1972) The SpottedHyena, University of Chicago Press 7 Kruuk, H. (1975) in Function and Evolution in BehaviourfBaerends, G., Beer, C. and Manning, A., eds), pp. 119-141, Oxford University Press 8 Caraco, T. and Wolf, L. L. (1975)Am. Nat. 109,343-352 9 Schaller, G. B. (1972) The Serengeti Lion, University of Chicago Press
AcidRain:NeverPureandRarely Simple Mike Ashmore and Andrew Tickle Until recently, public debate in Britain about acid rain has focussed on effects on water and fisheries in Scandinavia, and forests in West Germany and other countries of central Europe. However, the majority of the pollutants emitted in Britain are deposited within the country, and there is now increasing concern about the effects of acid rain sensu lato within Britain. A recent one-day meeting at Imperial College, London, on ‘Acid Rain and Britain’s Natural Ecosystems’ brought together scientists, conservationists, industrialists and policy makers to assess the current scientific evidence on the subject, to identify priorities for new research and to evaluate the possible implications for pollution control policy’. The meeting was held im-
mediately after the announcement that the British government will spend f600 million on fitting flue gas desulphurization units to three large coal-fired power stations. As the first country to enter the Industrial Revolution, the effects of pollution are not new in Britain. Indeed, air pollution from coal-burning Mike Ashmore and Andrew Tickle are at the Department of Pure and Applied Biology, Imperial College of Science and Technology, Silwood Park, Ascot, Berks SL5 7PY, UK. 58
affected London as far back as the 13th century’. Lichenologists from the British Museum (Natural History) presented the well-documented case on lichen sensitivity to air pollutants (predominantly sulphur dioxide) which gave rise to the impoverished lichen floras of Britain’s towns. This trend has to some extent now been reversed by clean air legislation3, but they also presented new evidence on the loss of epiphytic lichens (notably in the genus Lobaria) in pristine areas distant from major sources of pollution, suggesting that the cause is an increasing acidity of the stem flows on host trees. The effects of both past and present pollution were illustrated by work in the southern Pennines. Here, studies have palaeoecological shown that many Sphagnum species were lost in the last century due to pollution from nearby industrial towns, such as Manchester and Sheffield4. However, despite the falling sulphur deposition in recent decades, Sphagnum species transplanted into this area still grow very poorly. Recent studies of their nitrogen metabolism at Manchester University suggest that it is now the deposition of nitrogen, rather than sulphur, which is critical for the plants’ surviva15. Such detailed elaboration
7987
IO Clark, C. W. Aim. Behav. 35 !in press) 11 Bertram, B.C. R. (1979) in Serengeti: Dynamics of an Ecosystem (Sinclair, A. R. E. and Norton-Griffiths, M., eds), pp. 159-179, Chicago University Press 12 Packer, C. and Pusey, A. E. (1985) in Evolution (Greenwood, P., Slatkin, M. and Harvey, P. H., eds), pp. 173-186, Cambridge University Press 13 Seidersticker, J. C., Hornocker, M. G., Wiles, W. V. and Massick, J. P. (1973) Wild/. Monogr. 35, l-6 14 Pusey, A. E. and Packer, C. Behaviour (in press) 15 Packer, C. and Pusey, A. E. (1984) in Infanticide: Comparative and Evolutionary Perspectives (Hausfater, G. and Hardy, S. B., eds), pp. 31-42, Aldine Press 16 Packer, C., Herbst, L., Pusey, A. E., Bygott, J. D., Hanby, J. P., Cairns, S. J. and Beraerhoff-Mulder, M. in Reprodtkve Suc,cess fclutton-Brock, T. H., ed.), University of Chicago Press (in press)
of physiological responses, showing a mechanistic link between pollutant input and ecological response, is unfortunately an isolated example in a field of research more characterized by uncertainty over possible causes. In the case of trees, the field evidence of declines in health is itself a matter of intensive debate6s7. The difficulty here is that few trees, once they reach a certain age, ever look entirely healthy. We do not yet have a scientific basis on which to separate the effects of the range of biotic and abiotic stresses to which trees are normally subjected, from those of pollution. Indeed, recent work has demonstrated that exposure to pollutants can alter the sensitivity of plants to a range of other stresses. There is a lack of survey data designed to test associations between pollution levels and tree health, and almost no experimental work with British native species on which to judge the potential impact of current pollution levels in the UK*. Furthermore, there is still no scientific consensus about the causes of the extensive forest declines seen elsewhere in Europe. Description of changes in the distribution of pollutants in the UK can provide circumstantial evidence of possible causes, but this is hindered by the lack of comprehensive monitoring data in the past. This type of background information is extremely important as changes in pollution levels are just one of many factors affecting Britain’s ecosystems since World War II. In lowland Britain, for instance, the enormous intensifica,,I,),I! ,,,,.. if <_I,, c illl,llllic,til,Wi ’,337 :I; SO? 3 Ihi c ‘,l”U
TREE vol. 2, no. 3, March
1987
tion in agriculture has resulted in dramatic loss of habitats and increased pressure on many others; this makes subtle effects of pollution difficult to detect. Increases in stream and lake acidity in some areas of upland Britain have been attributed both to widespread planting of conifers and to acid deposition. Elegant work at University College, London, has used fossil diatom assemblages to establish historical pH changes in lochs in the remote area of Galloway, in southern Scotland. In some of these lochs, changes in pH cannot be satisfactorily explained by afforestation or other changes in land use’,“. Higher up the food chain, there is evidence that the number of dippers (Cinclus cinclus) in Mid-Wales is lower in acidic streams, which have a lower abundance of food sources such as caddis flies and mayfly nymphs. For one tributary of the River Wye, a decline in numbers since 1963 has been associated with increased stream acidity in an area of extensive afforestation”. However, the more detailed scientific work needed to go beyond statistical associations observed in the field to an understanding of the causal link between the associated variables has only recently begun. The value of remedial measures to reduce the effects of acid rain was the subject of considerable debate, especially in relation to the treatment of lakes and their catchment areas by adding calcium (liming). Physiological studies have shown that the toxic effects of Hi and A13’ on fish are reduced in the presence of higher levels of calcium’2. The effects of liming are currently being studied in a large field experiment at Loch Fleet in Galloway’3. Liming catchments, rather than lakes directly, increases the period for which treatment is effective; however the effects of adding large quantities of lime to the vegetation in these naturally acidic upland ecosystems is unknown.
In summary, the strength of the scientific evidence linking changes in Britain’s ecosystems to acid rain is variable. For some groups of species, the processes linking acid deposition to observed effects are understood, and affected areas have been identified. In other cases, such as with certain lichens, birds and amphibians, there are associations between observed changes and acidification in the field, but the processes involved are not worked out. At the opposite extreme are effects on trees, in which both good field data and mechanistic understanding are lacking. This difference inevitably
dictates very different research priorities within and between each area. The detection of subtle changes to ecosystems is in itself problematical; to establish a causal relationship with pollutants may be well-nigh impossible. However, it is precisely such causal relationships that policymakers require. Furthermore the increasing political importance of the ‘green vote’ means that there is ever more pressure to make decisions rapidly. Yet it is a salutary reminder that it has taken 25 years of research in Scandinavia and elsewhere before of the scientific understanding causes of freshwater acidification and decline of fish stocks was good enough to convince the British government to take measures to reduce sulphur emissions - although Scandinavian governments had themselves been convinced fifteen years earlier. Paradoxically, Britain is in one sense in a stronger position than the Scandinavian countries which ‘import’ most of their pollutants, since the smaller contribution of foreign sources means that any control measures taken by the British government will have a more immediate benefit on any ecosystems which it judges to be at risk. The problem of advancing understanding of the many factors influencing the impact of acid rain on ecosystems to a level at which objective decisions on whether to invest in expensive pollution control measures can be made is one of the most intellectual problems demanding faced by ecologists today. In the words on one of the contributors to the meeting, paraphrasing Oscar Wilde, ‘acid rain is never pure and rarely simple’. References 1 Ashmore, M.R., Bell, J.N.B. and Garretty, C., eds (1987) Acid Rain and Britain’s Natural Ecosystems, Centre for Environmental Technology (Imperial College of Science &Technology, University of London)
*
Management G. E. W&on
*
Evolution
*
Sperm competition
Peat
erosion
cumulative
in the effects
southern of two
PennInes
centuries
may
of acid
represent deposition
2 Brimblecombe, P. (1975) Weather30, 388-396 3 Rose, Cl. and Hawksworth, D.L. 11981) Nature 289,289-292 4 Press, M.C., Ferguson, P. and Lee, J.A. (1983) Naturalist 108, 125-l 29 5 Woodin, S.J.. Press, M.C. and Lee, J.A. (1986) New Phytol. 99,381-388 6 Binns, W.O., Redfern, D.B., Rennolls. K. and Betts, A.J.A. (1985) Forest Health and Air Pollution: 1984 Survey (Research and Development Paper no. 142). Forestry Commission (UK) 7 Rose, C. and Neville, M. (1985) Tree Dieback Survey: final Report, Friends of the Earth Ltd 8 Ling, K.A. and Ashmore, M.R. AcidRain and Trees, Nature Conservancy Council (UK) (in press) 9 Flower, R.J. and Batterbee, R.W. (1983) Nature 305,130-l 33 10 Batterbee, R.W., Flower, R.J., Stevenson, A.C. and Rippey, B. (1986) Nature 314,350-352 11 Ormerod. S.J., Bailstone, M.A. and Tyler, S.J. (1985) Ibis, 127,332-340 12 Brown, D.J.A. (1983) Bull. Environ. Contam. Toxicol., 30, 582-587 13 Anon. (1986) Loch Neet Project: A Report of the Pre-intervention Phase 1984-86, Central Electricity Generating Board (UK)
of tropical soils through intercropping,
of carabid beetles, G. Hafffter in birds, T. Birkhead
the