Biodiversity (1988) / Chapter Skim
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Part 1: Challenges to the Preservation of Biodiversity
Part 1: Challenges to the Preservation of Biodiversity
Pages 19-76
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'S ~:S C ,,,, I :' ~ lo'< ~ S , ~ .
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unpleasant truths, such as the following: ~ The primary cause of the decay of organic diversity is not direct human exploitation or malevolence, but the habitat destruction that inevitably results from the expansion of human populations and human activities. ~ Many of the less cuddly, less spectacular organisms that Homo sapiens is wiping out are more important to the human future than are most of the publicized endangered!
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is what makes ecologists so certain that today's trends of habitat destruction and modification especially in the high-diversity tropical forest (where at least onehalf of all species are believed to dwell) are an infallible recipe for biological impoverishment.
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Since Homo sapiens is one of (conservatively) 5 million species, this may seem an excessive share of the food resource.
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Aside from some limited environments, such as certain coral reefs, the effects of habitat destruction are relatively small away from shorelines and estuaries. This situation could, of course, change rapidly if marine pollution increases a distinct possibility.
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Along with fossil fuels, rich soils, ancient groundwater, and mineral deposits, genetic diversity is part of the inheritance of capital that Homo sapiens is rapidly squandering. What then will happen if the current decimation of organic diversity continues?
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People everywhere should understand the importance of the loss of diversity not only in tropical forests, coastal zones, and other climatically defined regions of the world but also in demographically delineated regions such as areas of urbanization. The geological record can tell us much about catastrophic mass extinctions of the past.
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Migrant Birds in the Neotropics: Ecology, Behavior, Distribution and Conservation. A symposium held at the Conservation and Research Center, National Zoological Park, Smithsonian Institution.
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TROPICAL FORESTS There is general agreement that remaining primary forests cover rather less than 9 million square kilometers, out of the 15 million or so that may once have existed 28
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Rapid population growth among communities of small-scale cultivators occurs mainly through immigration rather than natural increase, i.e., through the phenomenon of the shifted cultivator. As a measure of what ultrarapid growth rates can already impose on tropical forests, consider the situation in Rondonia, a state in the southern sector of Brazilian Amazonia.
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, who postulates an extinction rate in all tropical forests of perhaps 10,000 species per year. Of course many reservations attend these calculations.
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· , · ~ ~·-, · ~ square kilometers (~.5 times the size ot cat~torn~a', or slightly more than onetenth of the remaining undisturbed forests. As far as we can best judge from their documented numbers of plant species, and by making substantiated assumptions about the numbers of associated animal species, we can estimate that these areas surely harbor 1 million species (could be many more)
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Within the foreseeable future, by contrast, it seems all too possible that most tropical forests will be reducer! to much less than one-tenth of their former expanse, and their pockets of holdout species will be much less stocked with potential colonizers.
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1985. A comparison of recent estimates of disturbance in tropical forests.
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NORMAN MYERS / 35 Soule, M
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But it is my view that the coastal zone is being altered just as fast as tropical forests. The intent of this chapter is not to describe details of the biodiversity of coasts and oceans; rather, it is to examine the challenges we face in addressing this subject.
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Nevertheless, the major objective is to define coastal zone ecosystems and their ecological characteristics. 'The concept of Mother Earth, as named by the ancient Greeks.
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F Grassle of Woods Hole Oceanographic Institution and his associates, "quantitative samples fin the deep seal represent a fauna that rivals the tropical forests in diversity of species" (Grassle, personal communication, 1987~.
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It is Instructive to compare one aquatic a~a ce realms from this viewpoint. I cannot think of a terrestrial life form that does not have an aquatic equivalent, but counterparts of several marine life forms are so rare on land that cartoonists have to invent them; see, for example, the sit-andwait, cleception-bait gulper-predator in Figure 4-2.
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In sum, a major challenge in examining diversity lies in our perceptions and interpretations of it, taxonomically and functionally. ECOLOGICAL DIVERSITY A great diversity of life forms implies that there is an equally great diversity of food webs and trophic relationships, i.
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This is but one critical area where marine science lags. Retuming to the subject of biogeography, the realms, biomes, and provinces of the coastal zones and open oceans exhibit a remarkable array of environments.
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In concordance with this classification are distinct biotic assemblages. In tropical reefs, we find many species in a wide taxonomic array, similar to the variety of tropical forests (Figure 4~6~.
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Carleton Ray. are productive and diverse, but they are not nearly as useful for food production as are temperate seas, where schooling fishes predominate and can be easily caught over extensive banks and shelves.
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Extinction rates in the coastal zone ant! oceans are not known.
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The productivity of some marine systems may have been underestimated by half due to our ignorance of the role played by bacterioplankton and to the lack of appropriate methods of measurement. Also, it has recently been revealer} that wave energy creates the most productive ecosystems yet discovered, twice that of the most productive tropical forests (Leigh et al., 1987~.
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::::::~:~:~:::::::::~:~:::::::::~:~:~:::::::::::::::::::::::::::':2:':':::::::::::::::::::::::::::::::::::::::::::::::::::::: ' Shell Break FIGURE 4~9 The ecology of the coastal zone may be influenced by the distant and nearby environments identified in the figure. Courtesy B
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But the oceans remain foreign to most, and the concept of coastal zones as the broad systems they are continues to go largely unrecognized. Thus, the principal challenge, when addressing coastal and marine diversity, lies in recognizing its global role.
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is especially important for coastal zones and oceans, where we are so far behind. Perhaps this requires no less than a government office of biodiversity that would allocate two-thirds of its time, space, and effort to coastal and marine systems, reflecting their global proportions.
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:1227. World Resources Institute.
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With these data we can place our knowledge of present-day extinctions in the larger time context of the global evolution of life. Are the present and projected extinctions in the moist tropics unusual in the history of lifer What have been the evolutionary consequences of past extinction events, especially the mass extinctions' How resilient is the global biota when confronted with the elimination of large numbers of species within a short time' In our attempt to tackle these and related questions, there are serious problems of scale.
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Phanerozoic time included a number of profound perturbations: the mass extinctions. The most serious of these, near the end of the Permian period (250 million years ago)
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DAVID M RAUP / 53 ERA PERIOD EPOCH Pleistocene Age it (million years)
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Until more solid research is done on the detailed timing of extinctions in the fossil record, we will not know for sure whether the extinctions now projected for the contemporary moist tropics are typical of the history of life. EVOLUTIONARY CONSEQUENCES OF PAST EXTINCTIONS Little is known about the condition of the biosphere immediately following mass extinctions other than the tautological inference that biodiversity must have been less than immediately before the events.
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That is, they "rose again" after apparent extinction. The Lazarus taxa provide a special challenge for students of the fossil recorcl, because there are two equally plausible explanations for major gaps in the fossil record: species diversity may have been so low that the organisms were not preserved as fossils, or sedimentary environments conducive to fossilization may have been absent.
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On a global scale, the Pleistocene epoch was not a time of mass extinction, but it is certainly possible that there were extensive species kills in rain forest areas.
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This is true for shallow as well as deep time. In creep time, considering Phanerozoic time as a whole, the most pressing and relevant priorities are closer investigation of the timing of the great mass extinctions (Did the major events take place in a matter of days, years, or millions of years?
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Department of Agriculture, Forest Service, Southern Forest Experiment Station, Rio Piedras, Puerto Rico r ~ . ~ his chapter focuses on the empirical basis of estimates for species extinctions in tropical environments.
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If present land~use trends continue Unknown Different assumptions and an exponential function (see Table 6~2) Unknown National Research Council, 1980 Lovejoy, 1981 Ehrlich and Ehrlich, 1981 Myers, 1982 Unknown Unknown All tropical forests will disappear and half their species will become extinct Present rates of forest loss will continue Present trends will continue Forest regression will proceed as predicted until 2000 and then stop completely Myers, 1983 Oldfield, 1984 Raven, Missouri Botanical Gardens, personal communication to WRI and IIED, 1986 Simberloff, 1983 Norton, 1986 Simberloff, 1986 world was losing one species per day in the 1970s, and by the mid'1980s, the loss will increase to about one species per hour.
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RATE OF CHANGE IN TROPICAL FOREST AREAS The rate of change in tropical forests of all kinds has been discussed in depth only by Lanly (1982) , who made an effort to document the rate of increase in the area of secondary forests (by reforestation, afforestation, and natural regeneration; see Figure 6~1)
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subtropical life zones are capable of supporting forests. About 19 million square kilometers of mature forests exist in the tropics and are distributed as follows: 42% in the dry forest life zones, 25% in the wet and rain forest life zones, and 33% in the moist forest life zones (Brown and Lugo, 19821.
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The fact that the intensities and consequent impacts of human activity vary among life zones has important implications for the reliability of species extinction estimates. In summary, those who calculate species extinction rates must not assume that all tropical forests are subjected to equal rates of deforestation, respond uniformly to reductions in area, contain the same density of species, or turn into sterile pavement once converted.
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Correcting for differences in species richness of forests, forest recovery rates, and (differential human impact by forest type will certainly lower any of the estimates that now lack consideration of mitigating factors. Furthermore, the functions used to relate forest loss to species loss are still to be established experimentally.
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64 ~ V7 ._ en X ~ o ._ V Lti ~ at v: ·V o U)
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At a regional level, one also has to consider the importance of exotic species in the maintenance of species richness, particularly in ecosystems subjected to the impact of human activity. This approach seeks balance by consiclering factors that maintain species richness as well as those that decrease it.
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Secondary forests in high-impact regions obviously require time to fulfill their role as foster ecosystem for endangered species, but in due time, a wide variety of tree species appear to return to forest lands. An extreme example of the importance of species conservation and of humandominated habitats acting as foster ecosystems for endangered species is that of the Chinese maiden hair tree (Ginkgo biloba)
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From page 67... ...
expanded this idea to the effects of global perturbations on the history of life on the planet. Studies of regeneration strategies for mature forests have indicated that clisturbance is usually associated with the early phases of seedling germination and establishment in most forest types, including tropical forests (Pickett and White, 1985~.
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From page 68... ...
Experience in the Luquillo Experimental Forest Biosphere Reserve in Puerto Rico has demonstrated that species richness can be partially restored to lands previously used heavily for agriculture, that growing timber need not eliminate all natural species richness on site, and that tropical lands respond to sensible care through management. I know of no technical reason why sensible land management in tropical areas cannot leas!
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1982. The storage and production of organic matter in tropical forests and their role in the global carbon cycle.
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The Role of Tropical Forests on the World Carbon Cycle. A Symposium held at the Institute of Tropical Forestry in Rio Piedras, Puerto Rico, on March 19, 1980.
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While scientists argue about the relative enormity of tropical deforestation and its impact on biological diversity, the loss of populations, species, and entire ecological communities in human population 71
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An estimated 18% of all European butterfly species are considered to be vulnerable to or imminently faced with extinction (Heath, 1981~. Unfortunately, losses of animal and plant species are restricted neither to tem' perate zone urban areas nor to the developed world.
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Inner city park developers have traditionally introduced plantings of exotic species. Such settings fulfill many of the aesthetic and utilitarian roles that natural habitats offer, but their establishment and maintenance costs tent!
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The Endangered Species Act with its mandate outlawing the "take" of any enciangerec! species is the best tool for protecting biological diversity in urban areas of this country.
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Oak woodland preserves near San Francisco are likely to require more area to protect their complement of biological diversity than will native grassland preserves in the same geographic area. In the urban United States, three groups must interact to assist the Endangered Species Act in protecting biological diversity.
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Endangered Species Act of 1973. United States Code, 1984 Lawyers Edition.
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