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A natural Benchmark for Ecosystem Function

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A natural Benchmark for Ecosystem Function
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    Letters   300  Conservation Biology, Pages 300–307 Volume 11, No. 2, April 1997   A “Natural” Benchmark forEcosystem Function  In a recent editorial Malcolm Hunter  (   Conservation Biology   10:  695–697)recommended the use of the at-tribute “natural” as a criterion for the evaluation of management op-tions. He summarized the point asfollows (p. 696): “using the word  natural   to mean ‘without human in-fluence’ in the context of conserva-tion would help define clear bench-marks for managing ecosystemsboth inside and outside ecologicalreserves.” I think the suggestion is il-lusory for the following reasons:First of all, humans are products of nature and, therefore, all human ac-tivities are necessarily based on pro-cesses of nature. Whether conserva-tionists like this or not, we simply have no choice in this respect (Haila& Levins 1992). This is obviously true of the functioning of the humanorganism, that is, digestion, respira-tion, excretion, and other physiologi-cal processes, but also of proceduresused in technology: minerals aresmelted and radioactive isotopes splitnot only in facilities constructed by us humans but also—without humaninfluence—beneath our feet insidethe Earth.This means that the phrase “with-out human influence” simply lacksempirical meaning. There is no litmustest available for drawing a distinc-tion between a human-induced natu-ral process and a naturally-induced,or “spontaneous,” natural process. We can draw the distinction some-times, but often we cannot. Conse-quently, the term natural   cannot of-fer a clear benchmark either.To this the counterargument may be raised that human-created nov-elty provides criteria. For instance,surely human activities create chem-icals that are completely new andoccur nowhere else in the universeknown to us—this, surely, is not“natural.” The first part of the argu-ment is true. New chemical sub-stances, however, are created by other organisms as well, continu-ously, for instance as a part of their evolving chemical defense—a well-known concept to evolutionary biol-ogists. Furthermore, the spontane-ous emergence of novelty in natureis not restricted to chemicals. In bio-logical evolution the very concept of “evolutionary novelty” implies thesrcin of something that has never occurred before.The implication is that novelty simply does not offer diagnostic cri-teria for something occurring “with-out human influence” either. We needspecific evidence to conclude that aparticular phenomenon deemed novelis due to human influence. The caseof human-manufactured artifacts is,of course, clear, but in the case of subtle ecological change the evi-dence may be hard to come by. Allcases of novelty simply cannot beunambiguously divided between nat-ural and human-induced sources.These empirical problems mergetogether with a more fundamentalphilosophical difficulty: we simply cannot know what nature is ulti-mately like. We can only observe na-ture from one restricted vantagepoint at a time and these certainly do not cover nature “as a whole.” We cannot even say what “nature asa whole” might mean. This implies,as both historians of ideas (e.g., Gla-cken 1967; Lovejoy 1948; Williams1980) and philosophers (Colling- wood 1945) have pointed out thatspecific human ideas about the char-acter of nature are metaphoric. Ac-cording to Collingwood (1945), thedominating metaphor in ancient times was “organism;” in the Renaissancethis was replaced by “machine.” Fur-thermore, such metaphors are, as arule, srcinally derived from society; Williams (1980) makes this point very convincingly. This applies to ba-sic ideas that seem absolutely “natu-ral” to us, for instance, that nature isgoverned by laws—Glacken (1967:16) notes this idea was probably con-ceived by Sumerian theologians as ananalogue to the order perceived insociety.Thus, what we specifically regardas natural is culturally laden. Think only of the multiple metaphors thatare discernible behind recent history of ecological thought (e.g., Egerton1973; Kingsland 1985; Taylor 1988;Haila 1992). Metaphor is a crucial vehicle in all scientific thinking. In a way this is self-evident: the only pos-sible way to approach “new” is to as-sume it resembles in some wayssomething already known (Levins1995). This happens through the useof metaphor.The attribute “natural” does notgive criteria for distinguishing hu-man influence from other naturalprocesses. This, however, does notmean that everything humans do isacceptable. Here I emphatically agree with Hunter. The threatening deterio-ration of global ecology makes it ab-solutely urgent to draw a distinctionbetween what is permissible and what is not in human activity. Thisdistinction must only be drawn us-ing criteria other than “natural” and“unnatural.” Where to find such criteria? Someuseful distinctions can be based on the view that life is not a “state” but a“process.” In some situations we canuse as a benchmark the need to main-tain the conditions that are needed for the continuation of nature’s spontane-ous reproductive processes. In thiscontext, however, the term natural   alone is as useless as it was before.The problem is where to draw bound-aries between “truly” natural and“only apparently” natural processes(apparently natural being such pro-cesses that resemble natural ones butare in actual fact influenced by humanactivity). Ultimately, such a bound-ary cannot be drawn (Haila 1995).The emphasis on process bringsforth another point in the arguments     Letters   301  Conservation Biology  Volume 11, No. 2, April 1997  of Hunter which requires clarifica-tion. He suggested that the term nat- ural   can be used in a time-indepen-dent fashion: “ . . . this objectiveassumes no particular benchmark intime. . . . (I)n the face of climatechange we are always dealing with amoving target” (Hunter 1996:696). Ido not think this holds true. Allchange in ecosystems is bound totime and location. This is becauseecosystems are not in long-term equi-librium—if they were, then history  would be written off each time theequilibrium point is reached. Theissue has practical relevance, for in-stance, when natural disturbance re-gimes are used to derive managementguidelines. Any particular disturbanceregime varies greatly both in spaceand in time, often on a surprisingly small scale. The term “disturbanceregime” by its very definition refersto a temporal and spatial pattern of aparticular type of event. There is no way of specifying the features of adisturbance regime except whenboth location and time are fixed.Ultimately I do not think we needto feel disempowered even though the attribute “natural” does not work. We know what we need: we need toprevent the deterioration of the glo-bal ecosystem. We also know quite alot about those human activities thatlead to such deterioration. From such knowledge we can derive criteria thatcan be used to prohibit these activi-ties, and as a counterpart, criteria thatstimulate activities ameliorating theconsequences of previous harmfuldecisions. While doing this, we neednot worry about whether a particu-lar activity, say planting trees, is nat-ural.It is important to point out that ev-ery choice of criteria is an ethicalchoice. This is because of the uncer-tainty concerning the consequencesof human actions. It is in this con-text that the ways of native peoplesare usually discussed—not that they  would be somehow more “natural”than the way of life stemming fromEuropean cultural heritage, but be-cause some native cultures in someparts of the Earth have adopted ethi-cal rules in their affairs with naturethat can teach us a lot. Whether thisis true in any particular case requiresseparate assessment; the case of na-tive North American cultures is dis-cussed in a remarkably balanced way by J. Baird Callicott (1989) inhis essay “American Indian land wis-dom?: sorting out the issues.”  As I have emphasized, ethicalchoices are not without material cri-teria. Material criteria help to draw distinctions among alternatives, butthe choice of a particular alternativehas an ethical component. In any single case there are always mutually conflicting interests and values in- volved because choices are made insociety and because nature impliesconflicting goals and values for dif-ferent people (Haila & Levins 1992).Conservationists and managers needto participate in the discussion anddeliberation between differing goalsand values in specific situations. Indoing this they use the knowledgeand wisdom they have to promotecriteria derived from the basic goalof preventing the deterioration of theglobal ecosystem. However, there areno shortcuts in this process. Nobody can speak for nature; ecologists, likeother human beings, can only speak for our own views, backing our ar-guments with as much knowledgeas we can.   Yrjö Haila    Department of Regional Studies and Environ-mental Policy, University of Tampere, P.O. Box607, 33101 Tampere, Finland, email atyrha@uta.fi  Literature Cited   Callicott, J. B. 1989. In defense of the landethic. Essays in Environmental Philoso-phy. State University of New York Press,New York.Collingwood, R. G. 1945. The idea of nature.Clarendon Press, Oxford, United Kingdom.Egerton, F. N. 1973. Changing concepts of the balance of nature. Quarterly Review of Biology 48:  322–350.Glacken, C. 1967. Traces on the Rhodianshore. Nature and culture in Westernthought from ancient times to the end of the eighteenth century. University of Cali-fornia Press, Berkeley.Haila, Y. 1992. Measuring nature: quantitativedata in field biology. Pages 233–253 in A. E. Clarke and J. H. Fujimura, editors.The right tools for the job. At work intwentieth-century life sciences. PrincetonUniversity Press, Princeton, New Jersey.Haila, Y. 1995. Natural dynamics as a modelfor management: is the analogue practica-ble? Pages 9–26 in A.-L. Sippola, P. Alaraudanjoki, B. Forbes, and V. Halli-kainen, editors. Northern wilderness areas:ecology, sustainability, values. Arctic Cen-tre Publications 7, Rovaniemi, Finland.Haila, Y., and R. Levins. 1992. Humanity andnature. Ecology, science and society.Pluto Press, London.Kingsland, S. 1985. Modeling nature. Episodesin the history of population ecology. Uni- versity of Chicago Press, Chicago.Levins, R. 1995. Preparing for uncertainty.Ecosystem Health 1:  47–57.Lovejoy, A. O. 1948. Essays in the history of ideas. Johns Hopkins University Press, Bal-timore.Taylor, P. J. 1988. Technocratic optimism,H. T. Odum, and the partial transforma-tion of ecological metaphor after World War II. Journal of the History of Biology   21:  213–244. Williams, R. 1980. Ideas of nature. Pages 67–85in Problems in materialism and culture. Verso, London.  Malcolm Hunter (   Conservation Bi- ology   10:  695–697) suggests that by defining all human activity as some-how “unnatural,” benchmarks for ecosystem functions would be moreeasily defined. Not so fast. More thana few reasons, both philosophicaland practical, make this recommen-dation much less workable than theeditorial implied.First, let’s not forget that conserva-tion, as it is written about in this jour-nal, is a human endeavor grounded inhuman ethics. Therefore, it is not toosurprising that many people becomeuneasy with the thought of eliminat-ing humanity from the equation whenspeaking “in the context of conser- vation.” The long-held viewpoint plac-ing humanity separate from, and usu-ally above, nature remains at the rootof much environmental degradationand is a view I assume most conser-    302    Letters  Conservation Biology  Volume 11, No. 2, April 1997   vation biologists seek to change. It isonly when human societies view themselves unambiguously as a partof their ecosystem that a responsiblestewardship ethic seems to take hold.The editorial suggested that, by defining ecosystems without humanactivity, it is somehow easier to moveon to evaluating relative impact of  various human actions. In my view, we accomplish this more easily by  viewing all human action as “natu-ral.” If one acknowledges this morerealistic place of humanity in the world, the term natural is no longer as ambiguous. Land managers andconservationists provide a consistent,intelligible message to the public when they scrutinize the past landuse practices of all previous humaninhabitants and distinguish the de-structive from the benign, or eventhe positive. Given current humanpopulation trends, better apprecia-tion of the more benign or positiveeffects of humanity on ecosystemsshould be of interest to conserva-tionists.The most obvious practical obsta-cle to adopting Hunter’s recommen-dation is the near-impossibility of distinguishing some human effectsfrom non-human effects on ecosys-tems. The effect of fire throughoutNorth America is a classic example. Around 1800 there were approxi-mately 1.9 million acres (770,000ha) of savanna and grassland insouthern, lower Michigan (Comer etal. 1995). The known historical com-positions of many forest ecosystemsthroughout the state also exhibit aclear fire history. Some fire thatshaped these systems undoubtedly resulted from Native American activ-ity, but it is not currently possible todistinguish the relative significanceof their activity from lightning strikes.If we cannot distinguish the relativesignificance of past human actionson the composition, structure, andfunction of ecosystems, where is our “natural” benchmark? By eliminatinghumanity from the equation, I sus-pect one could view all Midwesternsavannas as somehow unnatural and,therefore, not deserving of conserva-tion. Clearly, this problem gets worseelsewhere in the world with longer histories of human activity.Hunter partly justifies his proposalby reasoning that the period of hu-man contact in North America hasbeen short enough to be insignificantto the evolution of other biota. How-ever, the aim of biological conserva-tion is not limited to protecting theend products of evolution. In my  view, protecting the process of evolu-tion is our central interest. Most cur-rent definitions of biodiversity recog-nize genetic, species, and ecologicalscales (Keystone Center 1994). By protecting ecological diversity we ac-knowledge the importance of thechanging roles that species play indifferent ecosystems across time andspace. The roles of species in ecosys-tems clearly change over shorter timeframes than 10 to 20,000 years. Themostly gradual changes in GreatLakes ecosystems since the last glaci-ation undoubtedly resulted in ever-changing assemblages of species—and ever-changing selective pressureson individuals. Humans have played various roles (destructive, benign,and positive) in these ecosystemsover this time period and have par-ticipated in the process of evolutionin the region’s biota. In most cases it was the abrupt character of changein ecosystems, brought on by hu-mans over the past 200 years, thathas caused losses in regional biodi- versity. In large measure, our task isto mitigate those abrupt changes by restoring the structure and functionof ecosystems to the condition they might be in if change had continuedat a more gradual pace.The study of conditions in North  America just before European colo-nization has many practical benefitsnot well appreciated in the editorial.Utilizing knowledge of presettle-ment conditions in no way impliesthat Native American land uses weresuperior to those of European colo-nists. However, it does offer the op-portunity to describe ecosystemsfrom that time period. We can thenmore rigorously assess the changesthat took place with the rapid transi-tion from relatively low-density, low-impact human populations to high-density, high-impact colonists. Of course one should not blindly view the presettlement condition as a“template” for restoration, but it isimportant to learn what we can fromthis time period to determine what we can apply to the modern con-text. We are very fortunate in theGreat Lakes region to have as de-tailed a record as exists in the Gen-eral Land Office surveys and other historical sources. They offer many insights into the relative rarity, land-scape context, structure, composi-tion, and function of Great Lakesecosystems that we can apply on theground.Hunter dismisses the use of preset-tlement conditions because, “in theface of climate change, we are al- ways dealing with a moving target.”It is precisely for this reason thatknowledge of the time period imme-diately before European colonizationis so useful in North America. In plan-ning a system of conservation reservesthroughout a region that will captureas much ecological diversity as feasi-ble, which time period(s) might youchoose as your benchmark? Would you use 100,000 years ago, 8,000 years ago, 200 years ago, or today?Hunter suggests choosing no timeperiod, but the practical effect of that suggestion is to choose the cur-rent condition. Certainly current con-ditions are very important to utilizethe detailed information we have onmany ecosystems. However, it is ex-tremely important to place the cur-rent condition within the context of the past few hundred years. Other- wise, reserves will tend to representecosystems with a composition andstructure reflecting the above-men-tioned “abrupt” changes of the re-cent past. Although Hunter’s proposal ad-dresses the legitimate problem of people blindly assuming that all ac-tivities of absrcinal peoples are or  were superior to all recent colonists,     Letters   303  Conservation Biology  Volume 11, No. 2, April 1997  it reinforces a similar misguided no-tion that all human action is destruc-tive. In a very real sense, it de-empha-sizes the importance of culture and wisdom that humanity has accumu-lated over millennia while living inits environment. To me, that wisdomis the essence of conservation.  Patrick J. Comer   Michigan Natural Features Inventory, Box 30444,Mason Building, Lansing, MI 48909-7944, U.S.A.,email comerp@wildlife.dnr.state.mi.us  Literature Cited   Comer, P. J., A. D. Albert, H. A. Wells, B. L.Hart, J. B. Raab, D. L. Price, D. M. Kashian,R. A. Corner, and D. W. Schuen. 1995.Michigan’s presettlement vegetation: asinterpreted from the General Land OfficeSurveys 1816–1856. Michigan Natural Fea-tures Inventory, Lansing (digital map).Keystone Center. 1991. Biological diversity on public lands, report of the Keystonepolicy dialogue. The Keystone Center,Keystone, Colorado.  I had hoped my essay would stimu-late some readers to reach for their  word processors and thus was pleasedto see Patrick Comer’s and Yrjö Haila’sthoughtful letters. I agree with severalof their points (e.g., Comer on theimportance of learning about North  American ecosystems before Euro-pean settlement and Haila on the im-possibility of objectively knowing what nature is like) and will focushere on the major disagreements.Both writers seem to have over-looked that my primary intention was a semantic one, to clarify thedefinition of natural   as it is com-monly used in ecological literature(e.g., “natural disturbance regimes,” aphrase Haila himself uses in its con- ventional sense). Current usage of   natural   requires clarification be-cause it is often unclear whether or not the activities of indigenous peo-ple with limited technology are con-sidered natural.This ambiguity gives us threechoices. First, we could make spe-cific decisions about which humanactivities are natural and which arenot. The core of my essay focusedon explaining why such distinctions would be arbitrary and difficult tosupport, and I will not repeat thismaterial here.Secondly, we could accept Comer’sand Haila’s suggestion that all humanactivities are natural. If all human ac-tivities from burning grasslands tobuilding factories are natural, how-ever, the word has no utility and canbe deleted from our vocabulary. Im-portantly, I have frequently heard in-dustrialists use this argument to de-fend activities that no conservationists would condone. Haila supports theidea of including humans in a defini-tion of natural   by emphasizing thetight linkage between humans andnature. I do not question this linkageat all, but would note that, as anecologist who often thinks about thetight connections between forestsand streams, I still find it very usefulto have words such as “terrestrial”and “aquatic.”Third, we can use natural   and an-tonyms like anthropogenic   to makean unambiguous distinction betweenthe activities of humans and other species. Personally I believe humansare profoundly different from other species and that it is useful to have aterm with which to make this distinc-tion. Even if you do not believe thathumans are unique, it is still useful tohave words to distinguish “us,” thespecies that thinks about conserva-tion issues and is directly responsi-ble for “our” behavior. Perhaps wecould use anthropogenic   and non- anthropogenic   if natural   is too emo-tive, but I will be surprised to find“non-anthropogenic disturbance re-gimes” come into regular use.Speaking of emotive, both Comer and Haila suggest that I advocate de-fining all human activities as “unnat-ural.” Unnatural   , however, has astrong negative connotation and im-plies that I believe human activitiesare illegitimate, wrong, unethical, etc. A careful reading of my editorial willfind considerable support for respon-sible human activities, especially out-side of reserves, and the suggestionthat neutral terms such as anthropo-  genic   , cultural   , and artificial   arepreferable antonyms for natural   .Comer and many others have sug-gested that recognizing the unique-ness of humans is a root cause of envi-ronmental degradation. I understandthis argument but am not entirely convinced by it. I would respond with an analogy: most people think of themselves as unique individuals butdo not take this as a license to actunethically toward other individuals.Similarly many religious leaders havecalled for ethical behavior towardother species without questioningthe special niche of humans.I agree with Haila that deciding“what is permissible and what is notin human activity” is a key conserva-tion issue, far more important thandeciding what is natural or not. For me, however, this latter distinctionoften shapes the former. I find almostall activities of non-human speciespermissible (the population growth of lethal human pathogens would beone notable exception). In contrast,I find many human activities permis-sible and many not permissible. Moreto the point, I think it is sometimesuseful to evaluate the acceptability of a human activity by how similar or dissimilar it is to a natural activity (e.g., how closely does human pre-dation on a fish population resemblenatural predation). I think analyzingand discussing the differences andsimilarities between our actions andnatural processes can help sensitizeus to the gap between us and other species and encourage us to narrow the gap wherever appropriate.Clearly I have strayed beyond therealms of semantics into some phi-losophy, so let me end with a quotefrom Henry Beston’s “The Outer-most House.”“We need another and a wiser,and perhaps a more mystical con-cept of animals. . . . We patronizethem for their incompleteness, for their tragic fate of having taken formso far below ourselves. And therein    304    Letters  Conservation Biology  Volume 11, No. 2, April 1997   we err, and greatly err. For the ani-mal shall not be measured by man.In a world older and more completethan ours they move finished andcomplete, gifted with extensions of senses we have lost or never at-tained, living by voices we shallnever hear. They are not underlings;they are not bretheren; they are other nations, caught with ourselves in thenet of life and time, fellow prisonersof the splendor and travail of theearth.”  Malcolm Hunter   Department of Wildlife, University of Maine atOrono, Orono, Maine 04469, U.S.A., emailhunter@umenfa.maine.edu  ESUs and Conservation of Pests  Often we think of pest control asbeing at one end of the spectrum(management of abundance) andconservation (management of thethreatened and scarce) at the other.Perhaps though, it is a circle, with afused meeting point. Hambler andSpeight (1996), in their fascinatingreview of extinctions of non-marineinvertebrates in Britain, point outthat the last British record of the woodland-inhabiting moth,  Lyman- tria dispar   , was in 1907. This is oneof 43 insect species listed as lostfrom Britain. Yet to the contrary, Net-tleton (1996) mentions that in June1995, there was an outbreak of thismoth species, with such potential todo damage in Britain that even asighting of it must be reported to thelocal Plant Health and Seeds Inspec-torate. It is also illegal to keep livespecimens in that country. Indeed,   L. dispar   , well known as the gypsy moth, is a “non indigenous plantpest” (Nettleton 1996) to Britain.Ironically, dispar   is Latin for unlike,different, unequal.Taken at face value, these reportsare highly conflicting and give mixedmessages to those not in touch with the importance of evolutionarily sig-nificant units (ESUs) (Moritz 1994; Vogler & DeSalle 1994), includingthose of moths (Legg et al. 1996). Sooften we argue that species are rela-tively tangible and useful units for biodiversity assessment (e.g., Kitch-ing 1996). And rightly so, with due re-spects to other scalar units (genes,populations, ecosystems, and land-scapes) and approaches (processesand interactions) (Noss 1990).The point is that conservation andpest management schools are notmeeting minds, except perhaps over the ever-looming problem of alieninvasives. In cases such as the gypsy moth, we need to be much morespecific and mention more than sim-ply British or Asian strain and to cat-egorically use the subspecific epi-thet, say, britannica  and asiatica  ,and for the popular name, use Brit-ish gypsy moth or Asian gypsy moth.It would also be helpful if wemake clearer use of the terms “extir-pation” and “extinction” (Hunter 1996).  L. dispar   has been extirpatedin Britain, but  L. dispar ‘britannica’   is extinct.  Michael J. Samways   Invertebrate Conservation Research Centre, De-partment of Zoology and Entomology, University of Natal, P/Bag X01, Scottsville 3209, South Af-rica, email samways@zoology.unp.ac.za  Literature Cited   Hambler, C., and M. R. Speight. 1996. Extinc-tion rates in British nonmarine inverte-brates. Conservation Biology 10:  892–896.Hunter, M. L., Jr. 1996. Fundamentals of con-servation biology. Blackwell Science,Cambridge, Massachusetts.Kitching, I. J. 1996. Identifying complemen-tary areas for conservation in Thailand: anexample using owls, hawkmoths and tiger beetles. Biodiversity & Conservation 5:  841–858.Legg, J. T., R. Rousch, R. DeSalle, A. P. Vogler,and B. May. 1996. Genetic criteria for es-tablishing evolutionarily significant unitsin Cryan’s buckmoth. Conservation Biol-ogy 10:  85–98.Moritz, C. 1994. Defining ‘evolutionarily’ sig-nificant units’ for conservation. Trends inEcology and Evolution. 9:  373–375.Nettleton, G. 1996. Gypsy moth. Antenna. 20:  98–99.Noss, R. F. 1990. Indicators for monitoringbiodiversity: a hierarchical approach. Con-servation Biology 4:  355–364. Vogler, A. P., and R. DeSalle. 1994. Diagnos-ing units of conservation management.Conservation Biology 8:  354–363.  It is a symptom of parochialism thatnational Red Data Books (RDB) may include some species, or even ESUs,that are pests elsewhere. The British RDB lists  Platypus cylindrus  (F.) (anambrosia beetle) as “rare,” yet it is aserious pest in parts of continentalEurope and has recently become apest of oak in Britain itself! In thecase of the gypsy moth, however,the British race was quite distinct inmorphology and diet and apparently not a potential pest. To reduce theconfusion Samways discusses, wesuggest future national RDBs shouldattempt to make explicit both the in-ternational status of each speciesand what is known of their ESUs.Given the large number of speciesinvolved, a paucity of recorders, andthe volatile population dynamics of many species, RDBs for invertebrates will need frequent revision—perhapsthrough supplements. For example,the moth Sedina buettneri   , presumedextirpated, was rediscovered in Brit-ain in 1996 in a colony that has prob-ably been long overlooked (P. H. Ster-ling, pers. comm.). Whether potentialpests or not, recent discoveries or col-onists present problems for the RDBsand must be monitored. For example,the spider  Harpactea rubicunda  ,newly added to the British faunal list,has only been found near a largeport—where it might be a naturalrelict population or an introduction. Were resources to permit it, geneticevidence would help distinguish the evolutionary and conservationsignificance of the British popula-tion and might avoid wasting conser- vation efforts on an introduction.  Clive Hambler and Martin R. Speight    Department of Zoology, University of Oxford,South Parks Road, Oxford, 0X1 3PS, United King-dom, email martin.speight@zoo.ox.ac.uk 
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