Nature and Human Society The Quest for a Sustainable World (1997) / Chapter Skim
Currently Skimming:
1 Defining Biodiversity
1 Defining Biodiversity
Pages 9-114
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 11... ...
BARRIERS TO PERCEPTION: FROM A WORLD OF INTERCONNECTION TO FRAGMENTATION DAVID T SUZUKI The Suzuki Foundation, 2211 West 4th Ave., Suite 219, Vancouver, BC V6K 4S2, Canada MAKING SENSE OF THE COSMOS THE GREAT molecular biologist and Nobel laureate Francois Jacob has stated that the human brain has a built-in need for order.
|
From page 12... ...
In this century, humankind has undergone massive changes with explosive speed. Harnessing the enormous power of technology, increasing in number ex' ponentially, and accepting a global economy based on endless growth and product tivity, we have become a superspecies capable as no other species has ever been of modifying the biophysical features of the planet on a geological scale.
|
From page 13... ...
But in cities, we live in a human-created habitat that is severely diminished in biological diversity. Our surroundings are dominated by one species us and the few plants and animals that we decide to share space with or cannot quite eliminate.
|
From page 14... ...
When the insecticidal properties of some molecules were discovered, the benefits of killing insect pests were obvious. At that time, geneticists knew enough to predict that resistant mutants would quickly render an insecticide ineffective, and ecologists understood that the use of broad-spectrum insecticides made little ecological sense when fewer than one-thousandth of all insect species are pests to human beings.
|
From page 15... ...
Because television is not serious, it cannot tolerate dead air." Now in reflecting on that exchange, I have recognized that when we assemble a nature film, we create an artifact: we send a photographer to the Arctic or the Amazon for months to get all kinds of shots-to-end-all-shots. Then in an editing room, we string them all together to produce an illusion that a tropical rain forest or the Arctic is a blur of activity.
|
From page 16... ...
To begin with, political action is predicated on the need to obtain tangible results in time for the next election, a timeframe that is too short to deal seriously with many of our most important challenges, such as species extinction and climate change. Thus, for example, in a study initiated by Prime Minister Brian Mulroney in 1988, it was found that Canada could readily achieve a 20% reduction in CO2 emission in 15 years for a net savings of $150 billion!
|
From page 17... ...
Now we under' stand that genetic diversity is the key to a species's resilience and adaptability as the environment changes. It also appears that species diversity within ecosystems
|
From page 18... ...
Human cultures are profoundly local and have enabled groups of our species to survive and flourish in environments as different as the Arctic, grasslands, mountain ranges, steaming jungles and rain forests, and arid deserts. We even flourish in New York, Tokyo, and London, for Heaven's sake!
|
From page 19... ...
The great temperate rain forests of British Columbia add "fiber" at the rate of 2-3% per year. Obviously, by cutting only 2% or 3% of the trees each year, forest companies could remove the equivalent of the entire forest in 35 or 23 years, respectively, and still have the entire forest left.
|
From page 20... ...
We have another level of fundamental needs, for we are social animals. As the young field of ecopsychology emphasizes, we are deeply embedded in the natural world, and it is an illusion to suggest that we are truly independent beings.
|
From page 21... ...
London UK: Cambridge Univ Pr. Levi-Strauss C
|
From page 22... ...
More recently, with growing alarm, they have widened their focus to include the causes of the accelerating decline of biodiversity in the human~saturated environ' meet. The first process, creation, is the concern of evolutionary theory; the second is the subject of the new discipline of conservation biology.
|
From page 23... ...
Understandable dissatisfaction with the biological species concept has encouraged the devising of an alternative definition, that of the phylogenetic species. In this view, the most meaningful species is a distinctive population with a monophyletic lineage in other words, derived from a single ancestral species.
|
From page 24... ...
The current trend of systematic theory is toward a higher degree of objectivity and consensus than existed in the past. A synthetic, truly biological species concept, providing considerable information about each genetically distinguishable population, seems attainable.
|
From page 25... ...
A bird species might only rarely cross this permanent water barrier, but when the event does occur, individuals from one island are able to invade the other island, where the colonists form a population almost entirely isolated from the source population. As the two populations separated by geographic barriers of whatever nature diverge, they progress from being genetically identical or nearly so to slightly or moderately different, at which point they can be called subspecies or, meaning the same thing in this context, geographic races.
|
From page 26... ...
· To add to the many complications inherent in geographic differentiation, species can also multiply in the absence of geographic barriers. Almost half of living plant species and a smaller number of animal species have arisen by polyploidy, the multiplication of entire chromosome sets.
|
From page 27... ...
In general, the greater the amount of energy available to the ecosystems, the larger the number of species; thus, high levels exist in the energy-rich coral reefs worldwide and the great tropical moist forests of South America, Africa, and Asia. The more environmental stability, as in the tropical forests and bottoms of the oceans, the greater the number.
|
From page 28... ...
The fullest and best-known radiation among animals is in the Hawaiian honeycreepers of the family Drepanidinae, whose 23 species (living and recently extinct) were derived from a single ancestral fringillid bird species.
|
From page 29... ...
The tragedy is that we are thoughtlessly tearing it down before we fully understand its origin, how it is sustained, and the essential role that it plays in human welfare. REFERENCES Because this essay is a primer of a broad array of topics, it is appropriate to recommend three general texts, of the many available, for a more detailed in' troduction: Raven PH, Evert RF, Eichhorn SE.
|
From page 30... ...
As discussed elsewhere (Collar 1997; Groombridge 1992; Heywood 1995; May 1994a; Wilson 1992) , biological diversity exists on many levels, from the genetic diversity in local populations of a species or between geographically distinct populations of a species, all the way up to communities or ecosystems.
|
From page 31... ...
Given the variety of ways of measuring the dimensions of life on Earth, I nev' ertheless believe that species are usually the best place to begin. For one thing, there is the practical reason that effective conservation action needs public sup' port, and the public identifies more easily with tangible biological species than with abstractions such as gene pools or ecosystems.
|
From page 32... ...
That pattern of attention among groups reflects the distribution of the taxonomic workforce, as summarized in table 1 (condensed from Gaston and May 1992~. Taking a very conservative estimate of 3 million invertebrate species as the global total, table 1 shows that the ratio of taxonomists to species is an order of magnitude greater for vertebrates than for plants and two orders of magnitude greater for vertebrates than for invertebrates.
|
From page 33... ...
recognizes 95,694 distinct species but acknowledges 152,079 species names, for an overall rate of resolved synonymy of 37%; the rates in individual orders range from 49% for lepidoptera to around 20% for mecoptera, megaloptera, and trichoptera. Moreover, any such assessment of synonymy rates must be a lower limit; other synonyms are yet to be uncovered or to accumulate in new work.
|
From page 34... ...
or the number newly described (60~. These reappraisals derive more from changing emphases in taxonomic research (in particular, the relatively recent shift toward phylogenetic concepts to replace earlier biological species concepts)
|
From page 35... ...
. Here we see order~of~mag' nitude assessments of species numbers, which highlight how any overall estimate of recorded species diversity is dominated by a few groups.
|
From page 36... ...
1.74 million by virtue of my estimating 0.23 million fewer insect species, and 0.01 million fewer nematode species. Hammond's 950,000 insect species
|
From page 37... ...
Before briefly discussing table 4, I emphasize the great uncertainty in many of its numbers. The overall range of estimates runs from 3 million to more than 100 million species, with a conservative estimate of the likely range being 5-15 mill lion eukaryotic species.
|
From page 38... ...
Estimates based on detailed keying-out of the fraction of species new to science in previously unexplored regions tend to give lower numbers around 3 million (for example, Hodgkinson and Casson 1993~. Conversely, estimates reached by using a chain of theoretical arguments to scale from numbers of beetle species in the canopies of individual tropical tree species to tropical insect species totals about 30 million (Irwin 1984~; reappraisal of such theoretical arguments has, however, suggested totals more like 3 million (May 1988, 1990; Stork 1988~.
|
From page 39... ...
Fungi Observing that there are about six to seven fungal species for each indigenous plant species in the United Kingdom, Hawksworth (1991) suggested that the global total of around 270,000 plant species should be scaled up to yield around 1.5 million species of fungi.
|
From page 40... ...
For an assessment of f, the fraction of all species to have lived since the Cambrian dawn of hard-bodied fossils (some 600 million years ago) that are alive today, we first ask what is the average life span of a species in the fossil record, from origination to extinction.
|
From page 41... ...
Graptolites in the Lower Palaeozoic seem to evolve particularly quickly: a collection of more than 30 species from the Silurian of Kazakhstan has examples of three successive species within a single graptolite zone, the duration of which is probably 500,000 years; thus, individual species life spans could be as short as 150,000 years. Likewise, Cambrian trilobites in the Acado'Baltic realm show 25 species with an average life span of 500,000 years.
|
From page 42... ...
These estimates, and supporting references, are set out in the lower part of table 5. In short, there is very great variability over a range of a factor of 100 among species life spans in the documented fossil record.
|
From page 43... ...
Such a 500'year estimate is, of course, misleading on several grounds. For one thing, recent and likely future extinction rates point toward qualitative reductions in the catalog.
|
From page 44... ...
1982. Tropical forests: their richness in Coleoptera and other arthropod species.
|
From page 45... ...
1992. Phylogenetic and ecologic patterns in the Phanerozoic history of marine biodiversity.
|
From page 46... ...
PIMM THOMAS M BROOKS Department of Ecology and Evolutionary Biology University of Tennessee, Knoxville, TN 37996-1610 THE SCIENTIFIC consensus is that if current rates of species extinction continue, the fraction of species lost will be comparable to that of the five major extinction events in Earth's geological past (Leakey and Lewin 1996~.
|
From page 47... ...
Calculating extinction rates as 'extinctions per species per year' provides a convenient frame of reference for calculating human impact (Pimm and others 1995~. We know the names of only a small fraction of the planet's species (May 2000)
|
From page 48... ...
This high speciation rate might have been a fortuitous baby boom in species, with current high extinction rates a natural pruning of evolutionary exuberance. In fact, the suggestion itself is wrong.
|
From page 49... ...
Despite these differences in places and taxa, we find high extinction rates in almost every group of species and in almost every kind of place. This "ecologically surprising conclusion" suggests that general ecological principles that work across all groups lead to substantial fractions of their constituent species becom' ing vulnerable to extinction.
|
From page 50... ...
Where there are not aggregations of range-restricted species, extinction rates will be low. There have been few bird extinctions in eastern North America an example to which we will return.
|
From page 51... ...
The Hawaiian Islands, eastern North America, and Great Brit' ain have broadly similar numbers of forest~living bird species (about 150~; the percentages of species restricted to those areas are 100%, 17%, and less than 1% respectively. Nor are areas rich in range~restricted species in one group always rich in another: eastern North America is a hot spot for salamanders but not for birds.
|
From page 52... ...
As the area of these hot spots shrinks because of habitat loss and fragmentation, how many species do we lose? One way to approach the question is simply to count the numbers of threatened and endangered species.
|
From page 53... ...
PIMM and THOMAS M BROOKS / 53 We can use this relationship to derive mathematically the species loss after fray' mentation of a once-continuous habitat area, Atonal, initially holding S~o~a~ species that are found only in this habitat (figure 1A)
|
From page 54... ...
For two recently deforested hot spots, insular Southeast Asia (Brooks and others 1997) and the Atlantic forests of South America (Brooks and Balmford 1996)
|
From page 55... ...
, rather than from the entire original area, Atonal ("global extinctions". Graphically, the eventual species loss is represented by the drop from Sorigina~ (figure 1A)
|
From page 56... ...
Conclusion 5. Isolated habitat fragments (certainly fragments of tropical rain forest)
|
From page 57... ...
We therefore pre' diet that about 500 of these bird species will go extinct in the next 50 years, pro' ducing an extinction rate of 1,000 extinctions per million species per year.
|
From page 58... ...
Tropical deforestation, in particular, is continuing and accelerating. The worst-case scenario is that we retain only the 5% of the world's tropical forests in protected areas an event that will happen within 50 years at current rates (Myers 1992~.
|
From page 59... ...
Prospective extinction rates vary greatly from group to group: 11% of bird species are currently threatened with extinction on the basis of our actions to date (Baillie and Groombridge 1996~. Birds appear relatively resistant to extinction.
|
From page 60... ...
1993. Hotspots and species diversity.
|
From page 61... ...
1988. Threatened biotas: "hot spots" in tropical forests.
|
From page 62... ...
1988. Our diminishing tropical forests.
|
From page 63... ...
THE ROLE OF POPULATIONS Biodiversity is generally taken to comprise not only species but also units of species plus ecological processes. Those units, or populations, are more im' 63
|
From page 64... ...
That is important because it is populations rather than species that supply us with the myriad environmental services (known ecosystem services) that support our lifestyles, if not our very survival.
|
From page 65... ...
Conservationists can well proclaim that by saving the lives of wild species, we might be saving our own. Yet we en' joy the manifold benefits of biodiversity's genetic library after scientists have in' tensively investigated only one in 100 of Earth's 250,000 plant species and a far smaller proportion of the millions of animal species.
|
From page 66... ...
Two anticancer drugs from the rosy periwinkle gener' ate sales totaling more than $250 million per year in the United States alone, and all plant~derived anticancer drugs combined save around 30,000 lives in the United States each year (Principe 1997~. According to the National Cancer In' stitute, tropical forests alone could well contain 20 plants with materials for sev' eral additional superstar anticancer drugs (Douros and Suffness 1980~.
|
From page 67... ...
The value of carbon storage in tropical forests as a counter to global warming is around $1,000-3,500/ha per year, depending on the type of forest (Brown and Pearce 1994~. The value of the carbon-storage service supplied by Brazilian Amazonia is estimated to be some $46 billion (Guttierez and Pearce 1992~.
|
From page 68... ...
Florida's coral reefs are estimated to generate $1.6 billion per year in tourism revenues (Adams 1995~. OVERALL FINDINGS A team of ecologists and economists has recently attempted a comprehensive evaluation of all the goods and services stemming from biodiversity.
|
From page 69... ...
1997. Nature's services: societal dependence on natural ecosystems.
|
From page 70... ...
1995. The value of undiscovered pharmaceuticals in tropical forests.
|
From page 71... ...
Then, we present estimates of population diversity, that is, the number of populations on Earth. Finally, we make a preliminary attempt to evaluate the rate of populations extinction.
|
From page 72... ...
These teen' efits include aesthetic enjoyment, discovery and improvement of pharmaceuticals and agricultural crops, species conservation, replenishment of stocks of economi' catty valuable species, and, perhaps most important, delivery of ecosystem services. Aesthetic Value Natural ecosystems are composed of populations of organisms, their physical en' vironments, and the interactions between them.
|
From page 73... ...
If local extinction does occur, individuals from other populations can recolonize the area. The threat of rapid global climatic change makes the safety net of population diversity for species even more important; a species that has many populations is more likely to include individuals that are genetically suited to new conditions than is a species that has only one or a few populations (Kareiva and others 1993~.
|
From page 74... ...
For now, we simply address numbers of populations.) Greater global population diversity probably enhances the delivery of global eco' system services, such as regulation of biogeochemical cycles and stabilization of climate (Alexander and others 1997~.
|
From page 75... ...
(Nabhan and Buchmann 1997~. Population diversity at a particular location (that is, local species diversity)
|
From page 76... ...
Again, we define population diversity as the number of populations on the planet; another aspect of popular tion diversity is the degree of divergence among populations, but we do not consider that aspect here. Many of the difficulties that plague attempts to estimate species diversity also hinder an estimation of population diversity.
|
From page 77... ...
First, we reviewed the literature on population differentiation for a broad range of taxa and estimated the average number of populations per unit area for a series of species. Then we calculated the average size of the range of a species with a sample of available species range maps.
|
From page 78... ...
If we assume that 14 million species exist globally and that two~thirds of all species exist in tropical forests, species diversity in tropical forests is declining by roughly 9,000-26,000 species per year, or 1-3 species per hour (this last calculation was reported incor' rectly in Hughes and others 1997~.
|
From page 79... ...
Here, z = 0.30, so a 90% decrease in area corresponds to a 50% decrease in species diversity. In contrast, the population curve is linear, so a 90% decrease in area corresponds to a 90% decrease in population diversity.
|
From page 80... ...
CONCLUSIONS The crisis of biodiversity is more severe than species extinction rates alone would suggest: Population extinction is occurring at a rate that is 3 orders of magnitude higher than the rate of species extinction. The rapid loss of population diversity means the loss of the benefits described above and, in particular, the loss of the life-support systems on which humanity relies.
|
From page 81... ...
1988. Do we need a new species concept?
|
From page 82... ...
1982. Tropical forests: their richness in Coleoptera and other arthropod species.
|
From page 83... ...
1995. Species diversity in space and time.
|
From page 84... ...
It is composed of a rich mosaic of habitats large and small, from some of the seem' ingly most homogeneous and remote, such as the deep~sea floor, to some of the most heterogeneous and accessible, such as the vibrant coral reefs. The world ocean is the greatest repository of biodiversity at the second highest level of taxonomic organization, the phylum.
|
From page 85... ...
As a complement to that literature, this paper describes for the layperson a general picture of biodiversity in the world ocean, how humans are altering it, and the threats that loom on the horizon. We also suggest some elements critical to any integrated management plan for minimizing human threats to marine biodiversity.
|
From page 86... ...
(Photo credit: Rod Catanach.) Most marine research is done relatively blind from surface research vessels, with nets used to sample the water column and grabs and corers to sample the sea floor.
|
From page 87... ...
Because different species assemblages are associated with different water masses, regional biodiversity is enhanced by these water-mass intrusions. In the immense sedimentary plains of the deep-sea floor, there is an extraordinary diversity of animals, perhaps rivaling the biodiversity of tropical rain forests.
|
From page 88... ...
Moreover, within the world ocean, the largest number of phyla are represented in the benthos. In contrast with the seemingly featureless sedimentary sea floor, coral reefs scream and shout with habitat complexity.
|
From page 89... ...
The other contender for this distinction is the deep~sea floor. Diversity and Ecosystem Function Marine ecosystems are knitted together by relationships among organisms, par' ticularly by who eats whom.
|
From page 90... ...
If one of these is removed by overexploitation or by a natural or human~assisted disaster the ecosystem changes dramatically. Sea otters are a keystone species of eastern Pacific kelp communities.
|
From page 91... ...
We close with some observations about the general patterns of marine biodiversity around the world. Primary Producers There are many similarities between terrestrial and marine environments.
|
From page 92... ...
Al' though chemosynthesis produces a small fraction of the sea's total primary pro' ductivity, it contributes to marine biodiversity by extending the living space of and facilitating a rich variety of microhabitats. Primary Consumers Most plant food is much smaller in the sea than on land, and so too are most marine primary consumers.
|
From page 93... ...
Most fish and marine mammals can' not eat phytoplankton directly, but need the zooplankton to repackage them into larger and more nutritious food (like energy bars)
|
From page 94... ...
Secondary Consumers Although predatory fish the predominant secondary consumers swim the entire world ocean, they eat and concentrate in particular areas during important stages of their life cycles, such as reproduction and early development as larvae and juveniles. Thus, for example, salmon return to spawn in the rivers of their births, and eels congregate for mass spawnings in the Sargasso Sea.
|
From page 95... ...
and dive to more than 600 m. Some Patterns of Marine Biodiversity and Their Causes Ptolemy once observed that it is the role of the scientist "to tell the most plausible story that saves the facts." This charge is difficult when the facts are few and several stories could "save" them equally well.
|
From page 96... ...
Threats to marine life from global climate change are imminent. Marine biodiversity can be affected by a single threat or several threats, sometimes with devastating and unknown consequences (figure 6~.
|
From page 97... ...
Maintaining healthy marine ecosystems requires constant vigilance; keeping a finger on the pulse of marine biodiversity could save its life and the critically important ecosystem services that it provides. Overexploitation of Resources Overfishing has dramatically reduced the stocks of many, perhaps most, of the preferred edible fish and shellfish species in the world ocean and led, for example,
|
From page 98... ...
For example, chemical pollutants have caused tumors and diseases in fish and shellfish and have affected reproduction in seabirds (DDT made pelican eggshells so thin that they broke when the birds sat on them) ; oil spills have resulted in local mass deaths of organisms at virtually every link in the food chain; agricultural fertilizers have killed coral reefs by stimulating the growth of seaweeds that overgrow them; and nutrient enrichment in estuaries has stimulated large algal blooms that sometimes lead to the consumption of most of, or all, the oxygen in the water column and deaths of immobile organisms.
|
From page 99... ...
Thus, marine biodiversity could be seriously affected if organisms cannot adapt to human~accelerated global climate changes that take place over decades or perhaps a century. COASTAL VULNERABILITY The most vulnerable parts of the sea are the coastal areas, the focal point of most human activities that threaten marine biodiversity.
|
From page 100... ...
Such data are, however, meager, at best, for most organisms in most environments in the sea. CONSERVATION STRATEGIES Entire issues of journals and several books have been devoted to strategies and tactics for conserving marine biodiversity at all levels.
|
From page 101... ...
Marine protected areas should be established for regions that present essential ecological conditions and promote critical ecological processes. Sanctuaries and reserves are but one component of an overall strategy for conserving marine biodiversity.
|
From page 102... ...
CLOSING COMMENTS The world ocean is experiencing substantial and startling losses of biodiversity. Arguments about whether coral reefs or rain forests support the greatest diversity are silly and dangerous; they divert attention from the real issues.
|
From page 103... ...
1993. Global marine biodiversity: a strategy for building conservation into deci sion making.
|
From page 104... ...
rip ~ COUNTRYSIDE BIOGEOGRAPHY AND THE PROVISION OF ECOSYSTEM SERVICES GRETCHEN C DAILY Department of Biological Sciences, Stanford University, Stanford, CA 94305-5020 HUMANITY HAS become a dominant force on Earth, altering important charac' teristics of the atmosphere, oceans, and terrestrial systems.
|
From page 105... ...
LIFE ON THE MOON Society derives a wide array of life-support benefits from biodiversity and the natural ecosystems within which it exists. These benefits are captured in the term "ecosystem services", the conditions and processes through which natural ecosystems, and the species that are a part of them, sustain and fulfill human life (Daily 1997; Holdren and Ehrlich 1974~.
|
From page 106... ...
. Biosphere 2 featured agricultural land and elements of a variety of natural ecosystems, such as forest, savanna, desert, and even a miniature ocean.
|
From page 107... ...
. MANAGEMENT OF NATURAL CAPITAL Maintaining Earth as a suitable habitat for Homo sapiens will require society to begin to recognize natural ecosystems and their biodiversity as capital assets, which, if properly managed, will yield a flow of benefits over time.
|
From page 108... ...
. Thus, New York City had a choice of investing in $6-8 billion in physical capi' tat or $1.5 billion in natural capital.
|
From page 109... ...
First, it is unlikely that many large, relatively undisturbed tracts of natural habitat will remain in the face of projected growth in the size, food needs, and environmental effects of the human population. Second, the potential for conserving many species might rest on preserving or enhancing some aspects of rural landscapes that contain remnants of native habitat in lieu of protecting large tracts of undisturbed habitat, which is generally much less feasible socioeconomically.
|
From page 110... ...
Measures of agricultural intensification include the frequency distribution of clearing sizes, the ratio of clearing to hedge' row areas, the spatial configuration and relative coverage of native and human' dominated habitats within the countryside landscape, the diversity of crops un' der cultivation, modification of the hydrological cycle, and the levels and types of chemical fertilizers and pesticides applied. · Which species traits confer an advantage for survival in the face of tropical deforestation and other major alterations of habitat?
|
From page 111... ...
Alterations in habitat that change the functional diversity and composition of plant species appear especially likely to have major effects on various properties of ecosystems (Hooper and Vitousek 1997; Tilman and others 1997~. · In the vicinity of Las Cruces in southern Costa Rica, a significant fraction of the native avian species appear to be persisting, at least temporarily, in open countryside habitats in a mixed-agricultural landscape that retains 27% of its oncecontinuous forest cover.
|
From page 112... ...
ACKNOWLEDGMENTS l am grateful for insightful comments from Scott Daily, Michael Dalton, Paul Ehrlich, Geoffrey Heal, and Jennifer Hughes. This work was supported by the generosity of Peter and Helen Bing, the Pew Charitable Trusts, and the Winslow Foundation.
|
From page 113... ...
2000. The loss of population diversity and why it matters.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.