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BioDiversity PART 11 PRESENT PROBLEMS AND FUTURE PROSPECTS
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BioDiversity Nest and eggs of the endangered light-footed clapper rail in intertidal cord grass marsh in Tijuana Estuary, California, The nest floats but is anchored, to the grass so that it can rise and fall with the tide but not be flooded, or earned away. Photo courtesy of Christopher S. Nordly.
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BioDiversity CHAPTER 47 DIVERSE CONSIDERATIONS THOMAS E.LOVEJOY* Executive Vice President, World Wildlife Fund, Washington, D.C. Before dwelling on the economic, social, and political problems that are fundamental to present problems and future prospects, there are two aspects of natural science that require attention but have not yet been mentioned in this volume: the abundance of relatively few of the many species on Earth and the limitations deriving from our shallow knowledge of diversity. SPECIES ABUNDANCE One of the great questions of biological science arises when biological diversity is viewed through ecological glasses: Why are ecosystems generally made up of a large number of species of which only a few are abundant? While the roster of rarer species in an ecosystem is much longer in tropical regions than at higher latitudes, there is a general tendency to accumulate large numbers of species in all but the most simple ecosystems. This pattern can be generally portrayed by graphing the relative abundance (for example, the percentage of total individuals or of total biomass) of species against the order of species from most to least abundant (Figures 47–1 and 47–2). In early successional communities, there is a smaller number of species and the most abundant ones constitute a larger fraction of the community, i.e., are more dominant. * After the forum, Dr. Lovejoy joined the Smithsonian Institution as Assistant Secretary for External Affairs.
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BioDiversity FIGURE 47–1 Patterns of the relative abundance of species at five different stages of abandonment in old fields in southern Illinois. The patterns are expressed as the percentage that a given species contributes to the total area covered by all species in a community, plotted against the species’ rank and ordered from most to least abundant. The symbols are open for herbs, half open for shrubs, and closed for trees. From May, 1985, with permission. Figure 47–1 shows such an accumulation of species after an old field was abandoned in southern Illinois. Conversely, if a community is subjected to stress, e.g., from temperature, toxic substances, or the arrival of an alien species, this process is reversed: diversity declines and a small number of species become dominant and are often called nuisance growths. Figure 47–2 shows such a response to heavy fertilizer applications in experimental grass plots in England. There are excellent aquatic analogs to these patterns, many of which have emanated from the work of Ruth Patrick and colleagues at the Philadelphia Academy of Natural Sciences (Patrick, 1949, 1975; Patrick et al., 1969). The meaning of pattern in relative abundance and diversity in communities has only begun to be initially understood and remains largely tantalizing (Fisher et al., 1943; Hutchinson, 1958; MacArthur, 1957, 1965; May, 1975; Patrick 1961, 1984; Preston, 1948). Furthermore, it is very difficult to understand the function of any of the large number of rare species in an ecosystem precisely because they are so rare. Indeed, there has been a tendency when considering endangered vertebrate species to think of them as ecologically nonfunctional or even ecologically extinct. I believe this is a highly dangerous and inappropriate attitude not only because
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BioDiversity rarity in an ecosystem is in fact the common condition but also because the true meaning of rare species in the system cannot easily be assessed for a moment but only when viewed over periods of environmental change. The role of an obscure species of yeast in the genus Cryptococcus (Brunner and Bott, 1974) is very telling in this regard. This species is rare in the aquatic communities of eastern Pennsylvania, presumably because of competition from other species. Its role and value are not immediately apparent. When either natural or human-generated mercury contamination occur, this yeast suddenly is at great advantage, because it is able to short-circuit a particular metabolic pathway along which mercury has toxic effects for organisms generally. The yeast is actually able to reduce methyl mercury to the elemental state and store the quicksilver in a vacuole that it subsequently deposits on a convenient surface such as a rock. Under conditions of elevated mercury concentration, the yeast temporarily becomes very abundant, while many previously abundant species in the community are depressed and diversity declines. The yeast literally cleans up the mercury contamination, thereby making itself rare again. The number of species that respond in this fashion to environmental change in a way that keeps them rare is probably not great. Nonetheless, all rare species in ecosystems are likely to be able to respond with population increases, given the FIGURE 47–2 Changes in the patterns of relative abundance of species in an experimental plot of permanent pasture at Parkgrass, Rothamsted, England, following continuous application of nitrogen fertilizer since 1856. (Species with abundance less than 0.01% were recorded as 0.01%.) Note that here time runs from right to left, so that the patterns look like the successional patterns of Figure 47–1 running backward in time. From May, 1985, with permission.
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BioDiversity right changes in environmental conditions. Many of these rare species are likely to be part of local habitats at any given moment, because the ecological conditions under which they flourish have occurred sufficiently frequently or recently for them to be represented. This means that the rare species in a sense reflect a variety of past conditions and confer some measure of ability for the ecosystem to respond to changing conditions. Survival strategies of this kind have as yet only been superficially explored. Nevertheless, the role rare species may play under changing conditions suggests that the accumulation of species in an ecosystem, while perhaps only an accident of the history of any particular system, can turn out to be of value. We thus have the beginning of an argument in favor of rare species in general—species attuned to conditions that are not prevalent at the moment but that may well return. At the present time, we are faced with a situation in which not just local ecosystems respond to stress by losing their diversity and by simplification; rather, the entire biosphere is subject to impoverishment. This inevitably means that individual ecosystems in a number of instances will be less diverse, because some of the species that would otherwise form part of the long list of rare species are doomed to extinction. LIMITATIONS OF OUR KNOWLEDGE To approach the global problem from a scientific perspective, we are immediately confronted by the second problem commanding attention, namely, the limitations deriving from our relatively shallow knowledge of flora and fauna. Recent discoveries of insect diversity in the canopy of South American tropical forests (Erwin, 1982, 1983, and Chapter 13 of this volume; May, 1986) warn us that we do not even know the extent of biological diversity on our planet to the nearest order of magnitude (Wilson, 1985, and Chapter 1 of this volume). Given such a poor inventory of life on Earth, biologists can say relatively little about which species occur where, which are in danger of extinction, where protected areas should be established, and where heavy environmental modification for development is permissible. What is desperately required is a revitalization of the science of biological systematics, with all the ancillary strength modern technology and molecular biology can provide, combined with a crash program of biological exploration. A decade or two of intensive biological mapping is needed while development is halted, or at least severely curtailed, in areas that are evidently the richest but least explored. SOCIOLOGICAL ISSUES I would now like to switch very abruptly to matters of the social sciences, which drive our societies in a multiplicity of little-appreciated ways. Consider the price of shoes, which on the face of it, seems but a matter of domestic detail far removed from the threat of massive extinctions in the tropics. Yet the U.S. shoe industry, far from strong, has been seeking tariff protection from the Brazilian shoe industry. If the U.S. government were to respond in a protectionist manner, what might
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BioDiversity be the consequences? Brazil’s struggles with its international debt would be the more difficult. Furthermore, its drive to increase exports would be even stronger, and as already apparent, the emphasis on export crops would lead to the intrusion of small farmers into the vital remaining natural areas. Shoe prices and similar isolated indices may not be a large factor. They might even prove to have no measurable impact on conservation, or they could even be a positive increment, if decreased Brazilian shoe exports reduced incentives for cattle ranchers. The point, however, is that a myriad of such unrelated issues swirl about our everyday lives and together with decisions made on Wall Street and in Washington, have a great deal to do with fueling the biological diversity crisis. Each and every one of us is more tightly connected to the global conservation problem than generally realized. This Gordian Knot of economic and political linkages deserves far greater attention than it has received up to the present time. Of course, there remain the great overarching issues such as population growth. I feel this acutely as I write from the great Indian subcontinent. When Indira Gandhi came to power in 1966, there were 480 million Indians, and when she left in violence in 1984, there were 250 million more. Since this trend continues, my environmental colleagues in New Delhi worry deeply about the long-term security of parks and reserves. The problem of population growth sometimes seems so enormous as to be intractable. Even with stringent birth control, future population growth is inevitable because of the very youthful age structure of populations in developing countries. Short of coercion, the only permanently ameliorative approach is to improve living standards while providing birth control devices and aggressive public education programs. That is not an instant solution, because human conditions cannot be improved overnight and a response in the form of reduced fertility does not happen right away either. There is no question that the association between development, population control, and conservation needs our continuing preoccupation. ECONOMIC PRESSURES Looming large in the picture is the massive international debt, now expressed in trillions of dollars. This economic goliath binds the industrialized and developing nations as surely as their shared interest in the protection of biological diversity. In many instances, all earned foreign exchange must be devoted to interest payments. This leaves little capacity to use foreign exchange to invest in the economic growth so necessary for improved living standards and all that goes with them, including a greater awareness of, and willingness to do something about, conservation problems. For some time, I have advocated the notion that some portion of the debt be allocated to these pressing problems of biological diversity. The money is already in the developing nations where the greatest conservation problems are, and much of it is unlikely to be returned to the lenders. Why not then arrange for some form of conservation credits where tropical debtor nations can use their own local currencies for national conservation projects? Already there is interest in buying debt at market-dollar values considerably less than face value and redeeming the
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BioDiversity paper in local currencies. Legislation is developing to encourage donation of such debt by commercial banks for international purposes. Whatever form these activities take, it must of course be fully sensitive to national sovereignty, but this should not be difficult to achieve since conservationists in the developing nations are as ardent as conservationists anywhere. Perhaps the most important point about the possibility of exploiting the international debt is not so much the example itself but rather the need to constantly seek new ways to elevate and expand the conservation effort. The scale of the problem is so great compared to the conservation efforts now under way that we will not succeed in safeguarding the majority of biological diversity without major innovation and major infusion of resources. It is all too easy to feel content with some hard-won conservation victory when problems crop up all around us like warriors sown from dragon’s teeth. From time to time in a flight of apparent silliness, I advance the notion of buying a major piece of west African real estate with substantial populations of gorillas and chimpanzees and setting up a new political entity, the “Kingdom of the Apes.” I do so not because such a possibility really exists. Rather, I do so because however fanciful the idea of a great silverback male gorilla being present at the UN General Assembly, it does suggest how apart we have set ourselves from other living things, and how awry our system of governing the world really is. We and our fellow vertebrates are largely along for the ride on this planet. If we want to perpetuate the dream that we are in charge of our destiny and that of our planet, it can only be by maintaining biological diversity—not by destroying it. In the end, we impoverish ourselves if we impoverish the biota. REFERENCES Brunner, R.L., and T.L.Bott. 1974. Reduction of mercury to the elemental state by a yeast. Appl. Microbiol. 27(5):870–873. Erwin, T.L. 1982. Tropical forests: Their richness in Coleoptera and other arthropod species. Coleop. Bull. 36(1):74–75. Erwin, T.L. 1983. Beetles and other insects of tropical forest canopies at Manaus, Brazil, sampled by insecticidal fogging. Pp. 59–75 in S.L.Sutton, T.C.Whitmore, and H.C.Chadwick, eds. Tropical Rain Forest: Ecology and Management. Blackwell Science Publishers, Palo Alto, Calif. Fisher, R.A., A.S.Corbett, and C.B.Williams. 1943. The relation between the number of species and the number of individuals in a random sample of an animal population. J. Anim. Ecol. 12:42–58. Hutchinson, G.E. 1958. Concluding remarks. Cold Spring Harbor Symp. Quant. Biol. 22:415–427. MacArthur, R.H. 1957. On the relative abundance of bird species. Proc. Natl. Acad. Sci. USA 43:293–295. MacArthur, R.H. 1965. Patterns of species diversity. Cambridge Philos. Soc. Biol. Rev. 40:510–533. May, R.M. 1975. Patterns of species abundance and diversity. Pp. 81–120 in M.L.Cody and J. M.Diamond, eds. Ecology and Evolution of Communities. Belknap Press, Harvard University, Cambridge, Mass. May, R.M. 1985. Population dynamics: Communities. Pp. 31–44 in H.Messell, ed. The Study of Populations. Pergamon Press, Rushcutters Bay, Australia. May, R.M. 1986. How many species are there? Nature 324:514–515. Patrick, R. 1949. A proposed biological measure of stream conditions based on a survey of the Conestoga Basin, Lancaster County, Pennsylvania. Proc. Acad. Nat. Sci. Phila. 101:277–341.
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BioDiversity Patrick, R. 1961. A study of the number and kinds of species found in rivers in eastern United States. Proc. Acad. Nat. Sci. Phila. 113(10):215–258. Patrick, R. 1975. Structure of stream communities. Pp. 445–459 in M.L.Cody and J.M.Diamond, eds. Ecology and Evolution of Communities. Belknap Press, Harvard University, Cambridge, Mass. Patrick, R. 1984. Some thoughts concerning the importance of pattern in diverse systems. Proc. Am. Philos. Soc. 128:48–78. Patrick, R., B.Crum, and J.Coles. 1969. Temperature and manganese as determining factors in the presence of diatom or blue-green algal floras in streams. Proc. Natl. Acad. Sci. U.S.A. 64:472–478. Preston, F.W. 1948. The commonness, and rarity, of species. Ecology 29:254–283. Wilson, E.O. 1985. The biological diversity crisis: A challenge to science. Issues Sci. Technol. 2(1):20–29.
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BioDiversity CHAPTER 48 THE CONSERVATION OF BIODIVERSITY IN LATIN AMERICA A Perspective MARIO A.RAMOS Director, Wildlife Program, Institute Nacional de Investigaciones, Sobre Recursos Bioticos, San Cristobal Las Casas, Chiapas, Mexico The increasing awareness of the need to preserve biological diversity in the world is demonstrated by the meetings that have been convened in developed countries. In the United States, for example, there were the Smithsonian Institution meeting in December 1985, the World Wildlife Fund meeting in September 1986, the National Academy of Sciences and Smithsonian Institution joint meeting in September 1986, and the meeting of the New York Zoological Society in October 1986. All are clear examples of this general trend. Although this awareness has come slowly to countries in the Third World, some important steps have been taken. In Latin America, for example, there has been a dramatic increase in the number of established protected areas (Harrison et al., 1984). What has been slow to come, in my opinion, is recognition that the preservation of the biological diversity in the world is a shared commitment between rich and poor countries and that major responsibilities fall into the hands of the countries where this diversity is found. Since the greatest diversity exists in the tropical areas of the world, these responsibilities generally lie within the developing countries. In these countries, however, social, economic, and political problems often make conservation of their diversity very difficult. The riddle of balancing development; stability in economic, social, and political terms; and conservation of their natural resources is difficult for any of the countries to solve by themselves. Because Mexico provides an instructive example of these problems in the Latin American region, I will summarize the general conditions that determine the context in which this
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BioDiversity conservation is now and will be taking place in the near future. I will also consider means to achieve the sharing of responsibilities among countries in the world. Here I pull together the knowledge and experience of many other people working in the region who have expressed their views in the recent meeting during the World Wildlife Fund’s Twenty-fifth Anniversary. CONSERVATION AWARENESS In Mexico, there has been a growing awareness of conservation issues, and new leadership has emerged within the scientific community and nongovernment organizations (NGOs) such as Monarca A.C. and Pronatura A.C. The new leaders have been responsible for the inclusion of environmental considerations in part of the government planning process and in political agendas. NGOs have flourished in the last 5 to 10 years. At present, there are probably 200 of these organizations located primarily in major cities throughout the country. In 1985, 22 NGOs established a federation in Mexico City. These organizations, supported by the scientific community, have pushed for improving environmental legislation and the establishment and protection of the conservation units within different habitats. In addition, they have discussed wildlife trade and have helped to organize and spread the conservation message among citizens in the country. A striking example is the controversial establishment and management of the Montes Azules Biosphere Reserve in Chiapas. International organizations such as the World Wildlife Fund/ Conservation Foundation and the Nature Conservancy International Program are supporting this grass-roots movement through direct economic support, official recognition, training of personnel, and infrastructure to help NGOs carry out their functions. THE SOCIOECONOMIC ENVIRONMENT Mexico is a clear example of a country in the process of development. It has slowed down its population growth from 3.3 to 2.3% per year, and it has two basic faces: an industrial one and a rural one. In addition to the problems stemming from industrial development, it has large rural and urban populations living in very marginal conditions. A comparison between 1940 and 1980 figures is revealing. There were about 19 million Mexicans in 1940, and in 1980, there were 68 million. By 1985, the population exceeded 79 million. Four million people lived in urban areas in 1940 and 41 million by 1980—a 10-fold increase, whereas rural populations changed from 15 to 27 million during the same period. Now, 65% of the population is concentrated in the central and southern part of the Mexican plateau (altiplano), where 80% of the total industry is also located. In addition, Mexico probably has the largest city in the world, Mexico City, which is home to about 18 million people. The city faces many environmental problems related to its size. Among the more pressing ones are air pollution control, solid waste and sewage disposal, water supply, encroachment on green areas, and the movement of rural populations into urban areas, where they live under extremely marginal conditions in huge slum areas within and around the city.
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BioDiversity FIGURE 51–1 (a) Global patterns of surface temperature increase, as projected by the Goddard Institute for Space Studies (GISS) model (Hansen et al., in press). Numbers are in degrees Celsius, (b) Global changes in moisture patterns. After Kellogg and Schware (1981). 1981). Other factors associated with rising temperatures that have biological implications include the direct physiological effects of rising atmospheric carbon dioxide concentration itself on plants (in Lemon, 1983) and a moderate sea level rise, variously estimated to be between 144 and 217 centimeters by 2100, according to the U.S. Environmental Protection Agency (EPA) (Hoffman et al., 1983). Plants will vary according to the way carbon dioxide concentrations affect their photosynthetic efficiencies and water requirements, thus altering interspecific relationships. In addition, changes in both precipitation and elevated carbon dioxide levels would alter soil chemistry (Emanuel et al., 1985; Kellison and Weir, in press).
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BioDiversity SPECIES RANGES SHIFT IN RESPONSE TO CLIMATE CHANGE By using the fossil record to study past responses of communities to similar climate changes, we can get some idea of how species ranges might respond to the physiological and competitive stresses imposed by future change. The most important observation is that, not surprisingly, species tend to track their climatic optima, retracting their ranges where conditions become unsuitable while expanding them where conditions improve (Ford, 1982; Peters and Darling, 1985). A general observation is that during past warming trends, species have shifted both toward higher latitudes and higher elevations (Baker, 1983; Bernabo and Webb, 1977; Flohn, 1979; Van Devender and Spaulding, 1979). During several Pleistocene interglacial periods when the temperature in North America was only 2° to 3°C higher than at present, osage oranges (Maclura sp.) and pawpaws (Asimina sp.) grew near Toronto, several hundred miles north of their present distribution; manatees (Trichechus sp.) swam off the New Jersey shore; tapirs (Tapirus sp.) and peccaries (Tayassu sp.) foraged in Pennsylvania; and Cape Cod had a forest like that of present-day North Carolina (Dorf, 1976). As to altitudinal shifting, during the middle Holocene when temperatures in eastern North America were 2°C warmer than at present, hemlock (Tsuga canadensis) and white pine (Pinus strobus), for example, were found 350 meters higher on mountains than they are today (Davis, 1983). In general, a short climb in altitude corresponds to a major shift in latitude, so that 3°C of cooling may be found by traveling either 500 meters up a mountain or 250 kilometers toward a pole (MacArthur, 1972). Evidence of such range shifts during periods of warming in the past, together with projections of range shifts based on physiological tolerances and computer-modeled future climatic conditions, suggest that in the United States, the oncoming warming trend may shift the area within which a particular species may flourish by as much as several hundred kilometers to the north. A projection for loblolly pine (Pinus taeda), for example, suggests that the southern limit of this species in the United States may shift more than 300 kilometers to the north by the year 2080 because of moisture stress (Miller et al., in press). Another simulation indicates that the doubling of atmospheric carbon dioxide concentrations expected by the early part of the next century would result in elimination of Douglas fir (Pseudotsuga taxifolia) from the lowlands of California and Oregon, because rising temperatures would preclude the seasonal chilling this species requires for seed germination and shoot growth (Leverenz and Lev, in press). On a larger scale, other simulations indicate that projected temperature changes (exclusive of changes in precipitation and soil characteristics) caused by a doubling of carbon dioxide concentration would result in the shifting of entire ecosystem complexes, including the loss of as much as 37% of boreal forest (Emanuel et al., 1985). Because each species disperses at a different rate, major climatic changes typically result in a resorting of the species constituting natural communities and the creation of new plant and animal associations (e.g., Van Devender and Spaulding, 1979; see also Figure 51–2), thereby causing new, sometimes stressful interactions among species.
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BioDiversity FIGURE 51–2 (a) Initial distribution of two species, A and B, whose ranges largely overlap, (b) In response to climatic change, latitudinal shifting occurs at species-specific rates and the ranges disassociate. LOCALIZED SPECIES MAY NOT BE ABLE TO COLONIZE NEW HABITAT If the entire range occupied by a species becomes unsuitable because of climate change, the species must either colonize a new, more suitable habitat or become extinct. The smaller the present range, the more likely it will be that the species will find the entire habitat unsuitable and therefore that extinction will occur. As discussed below, the vulnerability of many species will be increased by human encroachment that restricts them to small areas. Species restricted to reserves, like the one illustrated in Figure 51–3, are good examples. Imagine a restricted population like that represented in Figure 51–3. What is the chance that colonists, such as seeds or migrating animals, from the original population will find new habitat before the parent population becomes extinct? It will, of course, depend upon a number of factors: how much suitable area there is (i.e., the size of the target the colonists must reach), how far away the suitable area is, how many potential colonists are sent out (which will be a function of how large the original population is and the reproductive strategy of the species), how efficient these colonists are at dispersing themselves, how many physical barriers to dispersal exist, and how long some individuals within the original population can survive to reproduce. Although the number of colonists produced per parent and their intrinsic dispersal ability are likely to be essentially the same as during past times when species had to respond to climate change, this is not so for the other variables. For many species, the target areas to be reached will be reduced by development, the number of potential colonists will be reduced through reduction of the parent population, the length of time the parent population is allowed to exist may be reduced both through the rapidity of the climate change and development pressures, and, im-
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BioDiversity portantly, many more barriers to dispersal in the form of agriculture, urbanization, and other types of habitat degradation will be added to the natural physical barriers of mountains, oceans, and deserts. The predicament faced by a species in this situation is illustrated in Figure 51–4 for the Engelmann spruce (Picea ccengelmanni). For a plant, the Engelmann spruce is probably a moderate disperser. It has small, wind-dispersed seeds, and its natural dispersal rate, in the absence of barriers, has been estimated to be between 1 and 20 kilometers per century (Seddon, 1971). If we assume that climate change will cause a several-hundred kilometer shift in the potential range of many species in the United States during the next century, say 30 kilometers per year, a plant with the 1- to 20-kilometer per century rate of the Engelmann spruce would be in trouble. Although some species, such as plants propagated by spores, may be able to match the 30 kilometers per year needed, many other species could not disperse fast enough to compensate for the expected climatic change without human assistance. Even some large animals that are physically capable of rapid dispersal do not travel far for behavioral reasons. Rates for several species of deer, for example, have been observed to be less than 2 kilometers per year (Rapoport, 1982). FIGURE 51–3 How climatic warming may turn biological reserves into former reserves. Hatching indicates: (a) species distribution before human habitation; (b) fragmented species distribution after human habitation; (c) species distribution after warming. SL indicates the southern limit of species range.
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BioDiversity FIGURE 51–4 Obstacle course to be run by species facing climatic change in a human-altered environment. To win, a population must track its shifting climatic optimum and reach suitable habitat north of the new southern limit of the species range. SL1 is the species southern range limit under initial conditions. SL2 is the southern limit after climate change. The model assumes a plant population consisting of a single species, whose distribution is determined solely by temperature. After a 3°C rise in temperature, the population must have shifted 250 kilometers to the north to survive, based on Hopkins bioclimatic law (MacArthur, 1972). Shifting will occur by simultaneous range contraction from the south and expansion by dispersion and colonization to the north. Progressive shifting depends upon propagules that can find suitable habitat in which to mature and in turn produce propagules that can colonize more habitat to the north. Propagules must pass around natural and artificial obstacles like mountains, lakes, cities, and farm fields. The Engelmann spruce has an estimated, unimpeded dispersal rate of 20 kilometers/100 years (Seddon, 1971). Therefore, for this species to win by colonizing habitat to the north of the shifted hypothetical limit would require a minimum of 1,250 years. We know these threats are more than speculation, because the fossil record provides evidence that not only have ranges shifted in response to climate change, but in some cases their total extent was drastically reduced. For example, a large and diverse group of plant genera, including watershield (Brasenia), sweetgum (Liquidambar), yellow poplar (Liriodendron), magnolia (Magnolia), moonseed (Menispermum), hemlock (Tsuga), cedar (Thuja), and cypress (Chamaecyparis), were
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BioDiversity found in both Europe and North America during the Tertiary period. But during the Pleistocene ice ages, these all became extinct in Europe, presumably because the east-west orientation of such barriers as the Pyrenees, the Alps, and the Mediterranean blocked southward migration, while they persisted in North America, which has longitudinally oriented mountain ranges (Tralau, 1973). MANAGEMENT IMPLICATIONS How might the threats posed by climatic change to natural communities be mitigated? One basic truth is that the less populations are reduced by development now, the more resilient they will be to climate change. Thus, an excellent way to start planning for climate change would be sound conservation now, in which we try to conserve more than just the minimum number of individuals of a species necessary for present survival. In terms of responses specifically directed at the effects of climate change, the most environmentally conservative action would be to halt or slow global warming. Granted, this would be difficult, not only because fossil fuel use will probably increase as the world’s population grows but also because effective action would demand a high degree of international cooperation. If efforts to prevent global warming fail, however, and if global temperatures continue to rise, then amelio-rating the negative effects of climatic change on biological resources will require substantially increased investment in the purchase and management of reserves. To make intelligent plans for siting and managing reserves, we need more knowledge. We must refine our ability to predict future conditions in reserves. We also need to know more about how temperature, precipitation, carbon dioxide concentrations, and interspecific interactions determine range limits (see, for example, Picton, 1984, and Randall, 1982) and, most important, how they can cause local extinctions. Reserves that suffer from the stresses of altered climate will require carefully planned and increasingly intensive management to minimize species loss. To preserve some species, for example, it may be necessary to modify conditions within reserves, such as irrigation or drainage in response to new moisture patterns. Because of changes in interspecific interactions, competitors and predators may need to be controlled and invading species weeded out. The goal would be to stabilize the composition of existing communities, much as the habitat of Kirtland’s warbler (Dendroica kirtlandii) is periodically burned to maintain pine woods (Leopold, 1978). In attempting to understand how climatically stressed communities may respond and how they might be managed to prevent the gradual depauperization of their constituents, restoration studies, or more properly, community creation experiments can help. Communities may be created outside their normal climatic ranges to mimic the effects of climate change. One such relocation community is the Leopold Pines experimental area at the University of Wisconsin Arboretum in Madison, where there is periodically less rainfall than in the normal pine range several hundred kilometers to the north (W.R.Jordan III, University of Wisconsin, Madison, personal communication, 1985). Researchers have found that although the pines themselves do fairly well once established at the Madison site, many of
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BioDiversity the other species that would normally occur in a pine forest, especially the various herbs and small shrubs, have not flourished, despite several attempts to introduce them. If management measures are unsuccessful, and old reserves do not retain necessary thermal or moisture characteristics, individuals of disappearing species might be transferred to new reserves. For example, warmth-intolerant ecotypes or subspecies might be transplanted to reserves nearer the poles. Other species may have to be periodically reintroduced in reserves that experience occasional climate extremes severe enough to cause extinction, but where the climate would ordinarily allow the species to survive with minimal management. Such transplantations and reintroductions, particularly involving complexes of species, will often be difficult, but some applicable technologies are being developed (Botkin, 1977; Lovejoy, 1985). To the extent that we can still establish reserves, pertinent information about changing climate and subsequent ecological response should be used in deciding how to design and locate them to minimize the effects of changing temperature and moisture. Considerations include: The existence of multiple reserves for a given species or community type increases the probability that if one reserve becomes unsuitable for climatic reasons, the organisms may still be represented in another reserve. Reserves should be heterogeneous with respect to topography and soil types, so that even given climatic change, remnant populations may be able to survive in suitable microclimatic areas. Species may survive better in reserves with wide variations in altitude, since from a climatic point of view, a small altitudinal shift corresponds to a large latitudinal one. Thus, to compensate for a 2°C rise in temperature, a Northern Hemisphere species can achieve almost the same result by increasing its altitude only some 500 meters as it would by moving 300 kilometers to the north (MacArthur, 1972). As models of climate become more refined, pertinent information should be considered in making decisions about where to site reserves in order to minimize the effects of temperature and moisture changes. In the Northern Hemisphere, for example, where a northward shift in climate zones is likely, it makes sense to locate reserves as near the northern limit of a species’ or community’s range as possible, rather than farther south, where conditions are likely to become unsuitable more rapidly. Maximizing the size of reserves will increase long-term persistence of species by increasing the probability that suitable microclimates exist, by increasing the probability of altitudinal variation, and by increasing the latitudinal distance available to shifting populations. In the future, flexible zoning around reserves could allow us to move reserve boundaries in response to changing climatic conditions. Also, as habitat inside a reserve becomes unsuitable for the species or communities within, reserve land might be traded for nonreserve land that either remains suitable or becomes so as the climate changes. The success of these strategies, however, would depend on a highly developed restoration technology that is capable of guaranteeing, in effect, the portability of species and whole communities.
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BioDiversity ACTIONS THAT CAN BE TAKEN The best solutions to the ecological upheaval resulting from climatic change are not yet clear. In fact, little attention has been paid to the problem. What is clear, however, is that these changes in climate would have tremendous impact on communities and populations isolated by development and that by the middle of the next century, they may dwarf any other consideration in planning for reserve management. The problem may seem overwhelming. One thing is worth keeping in mind, however: the more fragmented and smaller populations of species will be less resilient to the new stresses brought about by climate change. Thus, one of the best things that can be done in the short term is to minimize further encroachment of development upon existing natural ecosystems. Furthermore, we must refine our climatological predictions and increase our understanding of how climate affects species, both individually and in their interactions with each other. Such studies may allow us to identify those areas where communities will be most stressed as well as alternative areas where they might best be saved. Meanwhile, efforts to improve techniques for managing communities and ecosystems under stress and for restoring them when necessary must be carried forward energetically. ACKNOWLEDGMENTS Ideas presented in this paper are based in part on an article, “The Greenhouse Effect and Nature Reserves,” by R.L.Peters II and J.D.S.Darling, published in BioScience 35(11):707–717, 1985. Research was supported by the Conservation Foundation. I wish to thank Joan Darling for her thoughtful collaboration, and I am grateful to Kathy Freas, James Hansen, Bill Jordan, William Kellogg, Thomas Lovejoy, Norman Myers, Elliott Norse, Pamela Parker, Christine Schonewald-Cox, James Titus, and Bruce Wilcox for encouragement, helpful comments, and review of manuscript drafts during the development of these ideas. REFERENCES Baker, R.G. 1983. Holocene vegetational history of the western United States. Pp. 109–125 in H. E.Wright, Jr., ed. Late-Quaternary Environments of the United States. Volume 2. The Holocene. University of Minnesota Press, Minneapolis. Bernabo, J.C., and T.Webb III. 1977. Changing patterns in the Holocene pollen record of northeastern North America: A mapped summary. Quat. Res. 8:64–96. Botkin, D.B. 1977. Strategies for the reintroduction of species into damaged ecosystems. Pp. 241–260 in J.Cairns, Jr., K.L.Dickson, and E.E.Herricks, eds. Recovery and Restoration of Damaged Ecosystems. University Press of Virginia, Charlottesville, Va. Davis, M.B. 1983. Holocene vegetational history of the eastern United States. Pp. 166–181 in H.E.Wright, Jr., ed. Late-Quaternary Environments of the United States. Volume 2. The Holocene. University of Minnesota Press, Minneapolis. Dorf, E. 1976. Climatic changes of the past and present. Pp. 384–412 in C.A.Ross, ed. Paleo-biogeography: Benchmark Papers in Geology 31. Dowden, Hutchinson, and Ross, Stroudsburg, Pa. Emanuel, W.R., H.H.Shugart, and M.P.Stevenson. 1985. Response to comment: Climatic change and the broadscale distribution of terrestrial ecosystem complexes. Clim. Change 7:457–460. Flohn, H. 1979. Can climate history repeat itself? Possible climatic warming and the case of paleo-climatic warm phases. Pp. 15–28 in W.Bach, J.Pankrath, and W.W.Kellogg, eds. Man’s Impact on Climate. Elsevier Scientific Publishing, Amsterdam.
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