Global Biodiversity Assessment
Summary for Policy-Makers
Summary: ISBN 0-521-56480-8 1995
Full: ISBN 0-521-56481-6
The Global Biodiversity Assessment (GBA) is an independent, critical, peer reviewed scientific analysis of the current issues, theories and views regarding the main aspects of biodiversity. It provides an analysis of a wide range of biological and social science issues related to biodiversity (Box 3).
Biodiversity represents the very foundation of human existence. Yet by our heedless actions we are eroding this biological capital at an alarming rate. Even today, despite the destruction that we have inflicted on the environment and its natural bounty, its resilience is taken for granted. But the more we learn of the workings of the natural world, the clearer it becomes that there is a limit to the disruption that environment can endure.
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Besides the profound ethical and aesthetic implications, it is clear that the loss of biodiversity has serious economic and social costs. The genes, species, ecosystems and human knowledge that are being lost represent a living library of options available for adapting to local and global change. Biodiversity is part of our daily lives and livelihoods and constitutes the resources upon which families, communities, nations and future generations depend. The basis of any discipline is not the answers it gets, but the questions it asks. As an exercise in biodiversity conservation, a number of questions can be asked: What are the values associated with biodiversity? How can benefits be generated from this resource? How can these benefits be shared in a fair and equitable manner? How do humans influence biodiversity? What are the underlying causes for this influence and what are their ecological consequences? How do the natural dynamics of biodiversity and the human-induced changes in biodiversity affect the values and goods and services provided by biodiversity to society? Taken together, these questions bring out the multi-dimensional challenge that the issue of biodiversity conservation poses to policy-makers and scientists alike. Fortunately, the international community has recognized this challenge. The entry into force of the Convention on Biological Diversity, in December 1993, is illustrative not only of this recognition but also of a change in the overall strategy in conserving biodiversity. It signals a move to a more proactive position that simultaneously seeks to meet people's needs from biological resources while ensuring the long-term sustainability of Earth's biological capital. The United Nations Environment Programme has played a key role in the development of the issues relating to biodiversity. Our efforts have included the forging of the Convention on Biological Diversity its follow-up, and have included efforts to strengthen the national and global base of knowledge on biodiversity. This endeavour lies at the very core of UNEP's three-fold mandate:
An essential element is the collection and dissemination of knowledge generated by scientific research. In this regard the scientific community has been and shall continue to be UNEP's key partner in carrying out our mandate. It was in this spirit that UNEP commissioned the Global Biodiversity Assessment (GBA) project. Underlying this endeavour was an attempt to mobilize the global scientific community to analyse the present state-of-the-art knowledge and understanding of biodiversity and the nature of our interactions with it: in other words, to provide the scientific information to answer some of the questions posed above. It must be noted here that unlike the global agreements on Climate Change and Ozone Depletion, no formal scientific assessment was carried out prior to the final negotiation of the Convention on Biological Diversity. The Parties to the Convention clearly recognize the lack of knowledge regarding biodiversity, and the urgent need to develop our knowledge base in this area. However, let me hasten to add, there have been no formal links between the Assessment and the Convention. Nevertheless, governments were regularly informed of the progress made in the development of this document. UNEP was gratified when we received written submissions from experts from more than 50 countries, who peer-reviewed various parts of the Assessment in their personal capacity. The document produced is the result of an ambitious scientific endeavour, the outcome of the invaluable contributions of more than a thousand experts worldwide. It reflects a broad spectrum of views. The GBA is an independent critical, peer-reviewed scientific analysis of the current issues, theories and views regarding the main aspects of biodiversity. The Assessment does not concern itself with the assessment of the state of country-level or regional biodiversity. This was the fear expressed by some constituencies when this project was initiated. Its perspective is global with a focus on general concepts and principles. lt does not present any policy recommendations, although it does draw attention to possible policy implications of its major findings and to existing gaps in knowledge and capacity. Although the GBA does provide an analysis of a wide range of biological and social science issues pertaining to biodiversity, its range is by no means exhaustive. Issues such as fair and equitable sharing of benefits, financial mechanisms and technology transfer have not been treated as extensively as the more scientific issues. The emergence of new issues scientific, economic and social relating to biodiversity in the near future is a distinct possibility. In this context GBA should be regarded as a timely assessment of the subject as perceived by the global scientific community. UNEP believes that the GBA will provide a compendium of knowledge for the benefit of those involved in the implementation of the Convention on Biological Diversity and it will also serve as a useful tool for the scientific body of the Convention to begin its work. I also hope that the Assessment will provide a significant conceptual input in the implementation of the relevant chapters of Agenda 21 and some initiatives put forth by the Commission on Sustainable Development (CSD). Clearly the aim of the Assessment was not to present a consensus document. lt is, however, an important step in building scientific consensus and creating the foundation for implementing political consensus. It is my fond hope that the GBA will succeed on both these counts. This Summary for Policy-Makers presents the main conclusions drawn by the Assessment, with an emphasis on those aspects that will be of interest to policy-makers.
Elizabeth Dowdeswell Executive Director, UNEP
Interaction between human society and biodiversity
Biodiversity is a vital resource for all humankind
The Earth is home to a rich and diverse array of living organisms, whose genetic diversity and relationships with each other and with their physical environment constitute our planet's biodiversity. This biodiversity is the natural biological capital of the Earth, and presents important opportunities for all nations. It provides goods and services essential to support human livelihoods and aspirations, and enables societies to adapt to changing needs and circumstances. The protection of these assets, and their continued exploration through science and technology, offer the only means by which the nations of the world can hope to develop sustainably. The ethical, aesthetic, spiritual, cultural and religious values of human societies are an integral part of this complex equation.
The limited knowledge base
The distribution and magnitude of the biodiversity that exists today is a product of over 3.5 billion years of evolution, involving speciation, migration, extinction, and, more recently, human influences. Recent estimates of the total number of species range from 7 to 20 million, but we believe a good working estimate is between 13 and 14 million of which only about 1. 75 million species have been scientifically described, just under a ftfth of them plants or vertebrates. Less well studied groups of organisms include bacteria, arthropods, fungi and nematodes, while species that live in marine environments and beneath the ground are especially poorly known. Even for the 1. 75 million species that have been described, there is no comprehensive listing and we have a highly incomplete and patchy understanding of their reproductive biology, their demography, the chemicals they contain, their ecological requirements and the roles they play in ecosystems. Genetic diversity within species is known well for only a very small number of species primarily those that have direct importance for human health, scientific research and economic exploitation.
The threat to nature's adaptability
Diversity of species and genes affects the ability of ecological communities to resist or recover from disturbances and environmental change, including long-term climatic change. Genetic variation within species is the ultimate basis for evolution, the adaptation of wild populations to local environmental conditions, and the development of animal breeds and cultivated crop varieties which have yielded significant direct benefits to humanity. Losing the diversity of genes within species, species within ecosystems, and ecosystems within a region makes it ever more likely that further environmental disturbance will result in serious reductions in the goods and services that the Earth's ecosystems can provide.
Biodiversity is being destroyed by human activities at unprecedented rates
The adverse effects of human impacts on biodiversity are increasing dramatically and threatening the very foundation of sustainable development. The rate at which humans are altering the environment, the extent of those alterations, and their consequences for the distribution and abundance of species, ecological systems, and genetic variability are unprecedented in human history, and pose substantial threats to sustainable economic development and the quality of life. Loss of biological resources and their diversity threatens our food supplies, sources of wood, medicines and energy, opportunities for recreation and tourism, and interferes with essential ecological functions such as the regulation of water runoff, the control of soil erosion, the assimilation of wastes and purification of water, and the cycling of carbon and nutrients.
The downward spiral
During the last few millennia species have been made extinct as a result of human activities. Prehistoric colonization of islands in the Pacific and Indian oceans some 1000 to 2000 years ago by humans and their commensals, rats, dogs and pigs, may have led to the extinction of as many as a quarter of the world's bird species. Since 1600, 484 animal and 654 plant species are recorded as having gone extinct although this is almost certainly an underestimate, especially as regards tropical regions. Based on an assumed average life span of 5 to I 0 million years for organisms with adequate fossil records, the extinction rate for these groups has been estimated to be flfty to a hundred times the average expected natural rate. In addition, there has been widespread loss of populations and genetic resources. Because of the world-wide loss or conversion of habitats that has already taken place, tens of thousands of species are already committed to extinction. It is not possible to take preventive action to save all of them. Projections of impending extinctions due to habitat loss can be made using the empirical relationship between the number of species and the area of a habitat, derived from island biogeography. When applied to tropical forests, published estimates of the number of species that will eventually become extinct or committed to extinction due to projected forest loss over the next 25 years or so range from 2% to 25% in the various groups examined (mainly plants and birds).this would be equivalent to 1,000 to 10,000 times the expected background rate. If recent rates of loss of closed tropical forest (about 1% globally per year) were to continue for the next 30 years, the equilibrium number of species in the forest, as calculated by species-area techniques, would be reduced by approximately 5 to 10%. These potential extinctions would not be immediate: it could take decades or even centuries to reach the new equilibrium number of species. Comparable estimates have not been made for the impact of habitat loss in other biomes. For some groups of vertebrates and plants, between 5 and 20% of the identifted species are already listed as being threatened with extinction in the foreseeable future. These estimates depend strongly on predictions of future rates of forest loss which may increase or decrease, and on the effects of fragmentation. They will also be modified by the effects of conservation action such as the protection of areas of high diversity. Even if species do not become extinct, many of them will lose distinct populations or suffer severe loss of genetic variability through habitat loss or fragmentation. Natural and agricultural systems are being degraded through soil erosion, introduction of exotic species, fragmentation and pollution; the effects of these most recent human-induced changes will not emerge for some time yet suggesting that a substantial increase in the level of future extinctions of species or populations as a result of human activity is already inevitable.
The underlying causes
The primary causes underlying the loss of biodiversity are demographic, economic, institutional, and technological factors, including:
These underlying causes manifest themselves in the loss, fragmentation, and degradation of habitats; the conversion of natural habitats to other uses; overexploitation of wild resources; the introduction of non-native species; the pollution of soil, water, and atmosphere; and, more recently, signs of long-term climate change.
Without immediate action future options will be restricted
Unless actions are taken now to protect biodiversity, we will lose forever the opportunity of reaping its full potential benefit to humankind. Priority actions need to focus on improving the knowledge base, correcting past failures in policy and ensuring that conservation and sustainable use of the planet's resources and the equitable sharing of benefits are made an integral part of all socioeconomic development.
The conservation and sustainable use of biodiversity needs to become an integral component of economic development by correcting policy and market failures. This will require much greater levels of co-operation and co-ordination than has previously been seen in traditional sectoral approaches to the management of natural resources. A balanced mix of incentives and disincentives, working alongside conservation laws, market adjustments, and traditional regulatory techniques, is needed in managing biodiversity at the national level. Institutional and legal frameworks are needed to ensure that conservation and sustainable use of natural resources are integrated successfully into the wide range of social, cultural and economic contexts in which actions must be taken. The adoption of more ecologically based management systems, which take into account the effects on biodiversity of extracting goods and using ecological services promises a way of balancing human socioeconomic and long-term ecological considerations.
A wide variety of measures can be used to conserve biodiversity, including both in situ and ex situ methods. Effective in situ approaches include legal protection of endangered species, the preparation and implementation of species management or recovery plans, and the establishment of protected areas to conserve individual species and habitats. Protected areas generally must be augmented by additional measures, such as the preservation or establishment of safe corridors through areas of intensive human use, and must also return some economic benefit to local human populations if access and other restrictions are to be respected. Currently, the percentage of different biomes covered by protected areas ranges from less than 1% for temperate grasslands and lake ecosystems to nearly 10% for subtropical and temperate rain forests and islands. Ex situ conservation centres such as arboreta, aquaria, botanic gardens, seed banks, clonal collections, microbial culture collections, field gene banks, forest nurseries, propagation units, tissue and cell cultures, zoological gardens, and museums, can help to conserve stocks of both wild and domesticated animals, plants, fungi and microorganisms, but are less able to maintain their populations. Serious gaps exist even in the ex situ coverage of those species that are known to be of direct economic importance, particularly in the tropics. Indeed the only species that have been sampled in any depth are some of the major crop plants, certain pathogens of humans and crops, and 'model organisms'used in scientific research. Restoration and rehabilitation of habitats, which depend on the availability of material and its multiplication ex situ, will come to play increasingly important roles in re-establishing degraded and damaged ecosystems.
Sustainable use of biodiversity
Sustainable use of biodiversity is a key component of sustainable social and economic development. Management systems must take this into account explicitly, recognizing that social and economic measures may be just as important as technical considerations. Flexibility of management is needed so as to be able to respond to changing social, biological and physical environments, while still maintaining essential ecosystem functions. Appropriate incentives and the enforcement of management decsions and policies must be ensured. Finding the appropriate balance depends on the particular cultural, legal, economic, ownership, tenure and biological circumstances in each individual country.
Equitable sharing of benefits
An equitable sharing of income and assets is an important component of a strategy for conservation of biodiversity. In particular, an equitable distribution of the benefits of biodiversity conservation is a prerequisite for creating the incentives needed to maintain the Earth's biological wealth. Local benefit sharing has the effect of lowering the opportunity cost of forgoing conversion to commercial or other uses such as arable agriculture, pasture or industry.
The role of research, monitoring and inventory
Enhanced research, inventory and monitoring are important to promote responsible policy-making and management. Research into the uses and applications of biodiversity and its components is important as is further research into the ways in which biodiversity contributes to the provision of ecological services, so that those services can be sustained indefinitely. Monitoring and inventories are needed so that newly discovered life-forms can be properly documented and so that the status of individual species and particularly ecosystems can be gauged over time.
Building national capacity and expertise
Committed and skilled people are the key to successful maintenance and sustainable use of biodiversity. Training must be provided for those involved in managing protected areas, conducting biodiversity inventories, and developing and safeguarding ex situ collections of all kinds. An essential element in the training of the next generation of professionals will be the new focus on the broader aspects of resource management and the critical role of maintaining adequate levels of biodiversity in conjunction with the management of forestry, fisheries and agriculture. National training programmes and international exchange programmes must concentrate on producing more skilled scientists, particularly in the developing countries, and on improving the information-handling capacity of those countries through improved access to, and management of, information now available world-wide on computerized databases. Educating the public and making people aware of the issues involved in biodiversity are essential elements in improving the decision-making process.
Summary for Policy-Makers
The Earth is home to a rich and diverse array of living organisms, whose species, the genetic diversity they comprise, and the ecosystems they constitute add up to what we call biodiversity (Box 1). Biodiversity is the natural biological capital of Earth. It provides the goods and services essential to human livelihoods and aspirations, and enables societies to adapt to changing needs and circumstances. For example, forested ecosystems provide fuels, medicines, construction materials and animal habitat; wetlands and riparian ecosystems protect water quality and aquatic life; oceans provide food and energy, and regulate climate, and agricultural systems produce food. Ecosystems also afford opportunities for recreation and tourism. More generally, ecosystems provide for the processing, storing and cycling of carbon and nutrients, thus influencing the Earth's climate and atmospheric composition. Today, the scale of human impacts on the global biosphere is increasing dramatically due to activities that arise from the rapid growth in human population and increasing rates of consumption. Ecosystems are being altered and destroyed, while species in some groups of plants and animals are going extinct at rates some fifty to a hundred times higher than they otherwise would, and others are having their populations depleted. The genetic resources essential for industries such as agriculture, forestry and fisheries continue to be lost. This tragic loss and degradation of biodiversity holds serious economic, ethical and cultural consequences for humanity and the evolution of life on Earth. Indeed, the very foundation of sustainable development is being threatened. Societies should consider carefully how they interact with biodiversity (Fig. 1). if responsible measures are taken now, losses or alterations can be slowed or in some instances halted by integrating biodiversity concerns into national decision-making processes using a combination of social and economic policies and incentives; by utilizing scientific and technical knowledge more effectively; by addressing the underlying causes of biodiversity loss; and by building human and institutional capacity world-wide. One indication of the growing international concern about biodiversity was the emphasis given to the issue at the 1992 United Nations Conference on Environment and Development held in Rio de janeiro and the ensuing Convention on Biological Diversity. The Convention recognizes that actions are needed to conserve biodiversity, ensure the sustainable use of its components, and ensure the fair and equitable distribution of the benefits derived from its use.
Biodiversity is essential to human well-being
Human societies rely on a vast array of biological resources and their diversity to provide for essential goods and services. Direct uses include the production of food, clothing, materials for shelter and fuel, and medicines. Indirect uses provide a wide variety of ecosystem services, such as the maintenance of the composition of the atmosphere, protection of watersheds and coastal zones, maintenance of soil fertility, and the dispersal, breakdown and recycling of wastes. In addition, non-use or passive values that are based on ethical, aesthetic, spiritual, cultural and religious considerations underlie many aspects of biodiversity's importance to humanity. In many cultures, these values are just as, if not more, important than those related to economic use. Indeed, most of the world's religions teach respect for the diversity of life and concern for its conservation. Examples of the various types of economic values that are assigned to biodiversity are listed in Box 4.
Indirect use values: maintaining the provision of goods and services
Ecosystems, such as agroecosystems, forests, rangelands and coral reefs, differ in their ability to provide goods and services, and improper management can reduce their ability to provide those goods and services. Where specific ecosystems provide essential services, such as wetlands for water purification and waste assimilation, it is important that the ecosystem be large enough in area for its ecological functions not to be significantly impaired. Consequently, poorly managed activities can lead to degradation. For example, the conversion of forests and other natural vegetation types has often led to soil erosion and stream sedimentation resulting in loss of soil productivity, aquatic life and flood protection. Similarly, large-scale habitat degradation in many arid and semi-arid regions has been shown to lead to increased desertification. Some species are known to be important for the proper functioning of an ecosystem but the roles served by most species are not understood. Indeed, some species have a significance out of proportion to their abundance, such as the regulation of plant uptake of soil phosphorus by species of mycorrhizal fungi. The loss of these 'keystone' species would greatly reduce the productive capacity of an ecosystem. The geographical position of an ecosystem and its spatial relationship with respect to other ecosystems of similar or different type is often an important consideration. For example, coral reefs, mangroves and kelp forests can buffer adjacent terrestrial systems from ocean waves, and thus mitigate the effects of storms that would otherwise produce substantial erosion (Fig. 4). Riparian areas and wetlands purify water before it reaches streams and rivers. Retaining appropriate vegetation in these areas is more efficient for maintaining this ecological service than retaining similar vegetation elsewhere. Likewise, many animals and birds need large habitat areas or corridors of habitat that link small habitat fragments. The degree of habitat fragmentation and connectivity can affect their ability to forage for food, locate cover, or reproduce successfully. For plants the spatial arrangement of ecosystems can affect seed and pollen dispersal and subsequent reproduction. The provision of goods and services sustainably over long periods of time requires the maintenance of biodiversity at characteristic levels to ensure their continued ability to adapt to environmental and management perturbations. This is true of genetic diversity within species, species within ecosystems, and of ecosystems within a region. For example, because species often differ in their response to climate fluctuations, a change in climate may cause the local elimination of some species, while others will persist or may even flourish.
Box I What is biodiversity?
Biodiversity is defined by the Convention on Biological Diversity as 'the variability among living organisms from all sources, including terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are part, this includes diversity within species, between species and of ecosystems. More simply, biodiversity is the variety of the world's organisms, including their genetic makeup and the com munities they form. Biodiversity is dynamic: the genetic composition of species changes over time in response to natural and human-induced selection pressures; the occurrence and relative abundance of species in ecological communities changes as a result of ecological and physical factors (Box 2).
Ecological diversity. Ecological systems do not exist as discrete units, but repre sent different parts of a natural continuum. Although terms such as forest, grassland, wet land and coral reef are commonly used to denote ecological systems, their delineation and spatial scale often depend on the intended purpose of the classification (Fig. 3).
Some commonly used terms are:
Biome: a continental-scale region characterized by its distinctive vegetation and climate
Ecosystem: the individuals, populations and species that occur in a defined area, including their interactions with each other and with their physical environment.
Ecological community: a group of species inhabiting a particular area. Habitat -the biological and physical environment of a particular species.
Organismal diversity: The total number of species on Earth is estimated at between 13 and 14 million, of which only 1.75 million have been described. The enor mous diversity between these species, ranging from common annual herbs to bacteria of deep ocea n trenches, their arrangement into classifications reflecting their phyletic relationships, and the complex patterns of variation and distribution that they show, provide the very substance of biodiversity. Groups of interbreeding individuals within a species form distinct populations. Groups such as plants, birds, mammals, fishes, reptiles and amphibians the species with which we are most familiar account for only 3% of the estimated total, while the majority of species belong to groups such as insects, arachnids, fungi, nematodes and microorganisms (Fig. 2).
Genetic Diversity: Genetic differences between the individuals of a species provide the basis for the diversity that is found between species. Molecular studies have revealed a wealth of genetic variability in most species: in fact, individuals of vir tually all species are genetically unique. Genetic diversity can be described at multiple levels from single genes to visible multi-locus traits. It is expressed as genetic variability both within and between populations. The amount and distribution of genetic diversity vary extensively among species in ways which are incompletely understood. lt is well established, however, that genetic diversity within species is necessary to allow them to adapt to changing environmental conditions.
Fig 2: Diversity of Major Groups.
Box 2 The composition and levels of biodiversity
Ecological diversity Organismal
populations populations populations
individuals individuals individuals
Cultural diversity: human interactions at all levels
Fig. 3(a) Distribution of the world's terrestrial biomes (from Cox, C.B. and Moore, P.D. 1993. Biogeography: An ecological and evolutionary approach. Blackwell Scientific, London).
Fig. 3(b)'I'he world's biogeographic realms and provinces (after Udvardy, M.D.F. 1975. A classification of the biogeographical provinces of the world. IUCN, Morges, Switzerland).
Fig. 3(c) The world's ecoregions (after Bailey, R.G. and Hogg, H.C. 1986. A world ecoregions map for resource partitioning. Environmental Conservation 13: 195-202).
Box 3 The Global Biodiversity Assessment
The GBA was endorsed by the Global Environmental Facility in 1992. A Preparatory Group was convened by the United Nations Environment Programme (UNEP) in March 1993 to develop objectives and a preliminary outline. In May 1993, UNEP approved the GBA project, and held the initial meeting of the GBA Steering Group to establish the policies for preparing the Assessment and to approve a draft list of contents. The major issues associated with biodiversity were addressed by establishing 1 3 Sections:
Each Section was headed by a team of expert scientists, with up to four Coordinators and many Lead Authors chosen per Section in order to achieve broad geographical coverage and balanced representation of developing and developed country views. A total of over 400 experts from over 50 countries were formally involved. Teams met in one or more workshops to plan and write each Section. The draft text was submitted to extensive peer review: governments and organizations were asked to he p nomi nate reviewers. More than I I 00 scientific experts from over 80 nations were solicited for comments, resulting in more than 500 written reviews. The revised GBA Sections and a draft Summary for Policy-Makers (SPM) were then subjected to a comprehensive review workshop held in Panama in June 1995.
This SPM features those aspects of the full GBA that hold significant implications for Policy-Makers, including: the importance of biodiversity in human society; the dis tribution and magnitude of biodiversity; the influence of human activities on biodiver sity; the consequences of changes in biodiversity; and the conservation of biodiversity, its sustainable use; and the fair and equitable sharing of benefits derived from its use. Although the SPM provides policy-relevant information, it does not make policy recom mendations.
Box 4 Economic perspectives of values assigned to biodiversity
Direct value: The value of those components of biodiversity that satisfy human society's needs. Consumptive use of genes, species or ecological communities, or biological processes to meet needs, such as food, fuel, medicine, energy and wood. Non-consumptive use of components of biodiversity, such as recreation, tourism, science and education.
Indirect value: The value of biodiversity in supporting economic and other activities in society. This value stems from the role of biodiversity in maintaining ecosystem services that support biological productivity, regulate climate, maintain soil fertility and cleanse water and air.
Option value: The insurance premium people are willing to pay to keep the option of using biodiversity directly and indirectly in the future. The information or scientific option value of biodiversity is called quasi-option value.
Non-use or passive values
Non-use or passive values stem from altruism towards friends, relatives or other people who may be users (vicarious use value); altruism towards future generations of users (bequest value); and altruism towards non-human species or to nature in general (existence value). This may be motivated by moral, ethical, spiritual or religious consid erations.
Vicarious use value: What people are willing to pay (or the benefits they are willing to forgo) to ensure that other members of the present generation enjoy access to specific components of biodiversity.
Bequest value: What people are willing to pay (or the benefits they are willing to forgo) to ensure that future generations enjoy access to specific components of bio diversity.
Existence value: What people are willing to pay (or the benefits they are willing to forgo) to ensure the continued existence of specific components of biodiversity. Existence value is sometimes referred to as intrinsic value.
Fig. 4 The tropical coastal seascape showing buffering of the land from the ocean by reefs and the buffering of reefs from the land by coastal forests and seagrass beds (from Ogden, J.C. 1987. Cooperative coastal ecology at Caribbean marine laboratories. Oceanus 30-. 9-1 5)
Fig. 5 The centres of genetic diversity for major crops (from Primack, R.B. 1993. Essentials of Conservation Biology. Sinauer Associates, Sunderland, Mass).
Box 5 An example of direct benefits from complex ecological interactions
The day-flying moth Urania fulgens, of northern South America and Mexico, provides an example of how complex interactions between species can provide ecological goods. The caterpillars of the moth feed exclusively on trees and vines of the genus Omphalea. When the caterpillar population reaches locally high levels the plants become heavily defoliated, and this heavy defoliation causes the trees and vines to produce protective chemical toxins. As the plants in a location become unpalatable the moths begin to migrate to new areas. In this case, the toxic plant compounds, which have been shown to be effective against the HIV virus in vitro, are produced only from the interaction between plant and moth and only when moth populations reach a threshold intensity.
The direct use values of biodiversity
Of the estimated 240 000 known vascular plants, about 25% have edible properties. While 90% of human food supplied by only about 100 species, all communities in fact depend on a much wider range of species as part of their daily lives. The centres of diversity for major crops are shown in Fig. S. The ability to increase production of these food crops or to adapt commercial varieties to new pests and environmental conditions depends on the conservation, in gene banks, of the genetic diversity that has been collected by farmers over millennia as'landraces'and that occurs in wild relatives. Recently, this has led to the breeding of greatly improved high-yielding rice and wheat varieties which have raised the value of annual crop yields in Asia by US$ 1.5 and $2.0 billion, respectively. Marine fisheries provided about 84 million tonnes food for humans and livestock supplements and earned US$l I billion dollars for developing countries in 1993. Artisanal fisheries currently provide approximately 25% of the global fish catch and about 40% of the fish used for human consumption and employ the vast majority of the world's fishers, especially in developing countries. Advances in science, such as gene technology, are revealing new opportunities to generate economic and health benefits from biodiversity at the cellular and molecular levels. Biological processes are being used for industrial production and environmental clean-up-, the health industry uses enzymes from a variety of organisms; new bioassay techniques render biochemical prospecting for new medicines and other products vastly more efficient and newly discovered interactions among species may themselves provide direct benefits (Box 5). In 1993, about 80% of the 1 50 top prescription drugs used in the United States were synthetic compounds modelled on natural products, semi-synthetic compounds derived from natural products, or in a few cases natural products. In contrast, in China, for example, traditional drugs derived from medicinal plants accounted for about 40% of consumption of medicaments in recent years. The World Bank estimates that activities related to tourism world-wide approach US$2 trillion annually. Ecotourism is emerging as one of the fastestgrowing components of this industry, with as many as 2 3 5 million individuals participating in 1988, resulting in economic activity estimated at US$233 billion. More than half of this ecotourism was related to animals. How much biodiversity is there and where is it found? The distribution and magnitude of the biodiversity that exists today is a product of over 3.5 billion years of evolution, involving speciation, migration, extinction and, more recently, human influence. The current distribution and magnitude of biological diversity can be viewed at three levels: the diversity of ecological communities, species diversity, and genetic diversity. Inadequate knowledge of the diversity of ecological communities An ecosystem is a community of organisms and their environment which functions as an integrated unit. Forests are ecosystems. So are rotting logs, ponds, rivers, rangelands, whole mountain ranges, and indeed the planet itself. Ecosystems occur at many different scales, ranging from micro-sites to the biosphere, and species composition, structure and function within them changes continually over time. Ecosystems may grade into one another or be nested within a matrix of larger ecosystem units. Ecosystems are frequently delineated along boundaries that correspond to variations in the physical environment such as soil types, climate and elevation, and variation in faunal and floristic composition. Various classification systems have been devised, each of which defines bioregions or ecosystems somewhat differently, but which also recognize many broad similarities (Fig. 3). Since ecosystems are often defined with a specific purpose in mind, there is no single measure of ecological community diversity which can be uniformly applied. In spite of the difficulty in classifying and delineating ecological communities, at large scales there is some sense of the distribution and extent of the various types of ecosystems, such as wetlands or tropical forests. The extent and distribution of species' diversity Recent estimates of the total number of species range from 7 to 20 million, out of which we believe a good working estimate is about 13 to 14 million. Only about 1.75 million species have been described scientifically, of which slightly under a fifth are plants or vertebrates (Table I-I Fig. 6). Even for the 1. 75 million species described there is no comprehensive listing. In many cases the area from which a species was officially described has been so dramatically altered that it is no longer possible to re-find the species there. Also, many of the earlier descriptions of species failed to record site characteristics and habitat conditions at the collection sites. Estimates of species diversity are relatively good for plants and vertebrates although many remain to be described: in Brazil alone, five new species of monkey were described during the last decade. Less well characterized groups of organisms include bacteria, arthropods, fungi and nematodes, while species that reside on the deep-sea floor and below the ground are especially poorly known. Scientists know very little about most of the properties of most of the 1.75 million species that have been described, such as their reproductive biology, demography, the chemicals they contain, their ecological requirements and the roles they play in ecosystems. Domesticated species represent a tiny fraction of Earth's biota. Of the estimated 320 000 vascular plant species, about 25% have edible properties, but only about 3000 species are regularly exploited for food. An additional 2S 000-50 000 plant species are used in traditional medicine. Only about 30 of the estimated 50 000 vertebrate species have been domesticated. An additional 200 species of fish, molluscs, crustaceans, frogs, turtles and aquatic plants are grown for food and other products, and an increasing number of fungi and other microorganisms are also eaten or used in fermentation processes, in industrial processes, or for drugs. Additional efforts in taxonomy can aid in the identification of more economic uses (Box 6). For many groups of terrestrial organisms the number of species tends to increase, and population size and range decrease, from the poles to the Equator.
Fig. 6 Numbers of described species (open columns) and possibly existing species (dark columns) for those major groups of organisms expected to contain in excess of 100 000, with vertebrates for comparison (from Hammond, P.M. 1992. Species inven tory. In: WCMC, Global Biodiversity, Status of the Earth's Living Resources, 17-39. Chapman and Hall, London).
|Group||Number of described species*||Estimated total number|
The groups of organisms estimated to contain more than 100,000 species, with vertebrates and others listed for comparison (all numbers in I 000s).
However, there are numerous exceptions, and there are many groups of organisms for which we lack information on which to base informed statements. in the oceans, the variation in numbers of species follows a less defined pattern. Marine organisms tend to be more widely distributed due to the absence of physical barriers" they travel large distances, often with the aid of ocean currents, and those organisms that are rooted or stationary have easily dispersed seeds or larvae. Endemic species or relict species are those that are naturally restricted by geographic features, such as mountains, islands, peninsulas, continents or other physical features, or where unique local conditions (such as serpentine soils) lead to the evolution of species suited only to that specific environment. Remote oceanic islands have the world's highest percentages of endemic species, with only a small proportion of their native species being found anywhere else. In some situations 'relict' species represent the last remaining populations of formerly much more widely distributed species.
Inadequate knowledge of the genetic variability within species
Each species contains an enormous quantity of genetic information, and there is often substantial diversity in the genetic make-up of populations within a species.
Box 6 Biological classification - an essential tool for recognizing and understanding biodiversity
Discovering, describing and classifying species and their genetic variation atio us to 'take stock'of biodiversity, handle it and communicate about it, and describe nd analyse the patterns that it forms. Classifications of organisms into species, genera, families, orders, classes, phyla, and u ltimately the five generally recognized kingdoms of animals, bacteria, fungi, plants and protoctists, are based on their systematic and evolutionary relationships. These classifications are highly predictive and provide a framework that serves both as a reference toot and a summary of evolution ry relationships. For example, these relationships can be used to identify specie ith potentially similar uses, The chemical taxol, a valuable anti-cancer drug, was ori lnally discovered in a small population of North American yew (Taxus brevifolia). Scientists were able to predict its probable c>ccurrence In other species of the genus and ere thus able to extract a precursor to taxol on a sustainable commercial scale the commonly occurring European yew (Taxus baccata). Frequently, taxonomic in tion is used to trace the geographical origins of agricultural pests and diseases, tre- by leading to the identification of potential biological control agents. Taxonomic insights can also be imponant for conservation management strategies. For example' it is Important to consider whether a species of concern is the sole survivor of an evolutionary line, or is closely related to many others.
Depending on the details of the species'breeding system, the variability within populations may be as great as, or greater than, the variability between populations. However, with few exceptions we have only rudimentary knowledge of the products or functioning of most genes. Domestication for agriculture has led to the development of many cultivated crop varieties and livestock breeds. The number of distinct samples of germplasm collected for major crops ranges from 50 000 to 125 000 for maize, rice, barley and wheat. Although some genetic diversity has been lost as traditional breeds or varieties have been replaced by modern high-yielding disease-resistant forms, enormous genetic diversity is still seen in the large numbers of varieties grown in local regions. For example, Andean farmers cultivate thousands of different clones of potatoes, more than 1000 of which have different names, while in Europe, more than 700 unique breeds of cattle, sheep, pigs and horses have been identified.
Human demands and failures in economic markets: the underlying drivers of change
The rate at which humans are altering the environment, the extent of that alteration, and the consequences of these changes for biological diversity are unprecedented in human history, and are now beginning to pose substantial threats to the economic and cultural life of many societies. Depending on the circumstances, human activities may increase, maintain, or diminish the diversity of species, genes or ecological communities in a given region and at a given time, but the general trend is an increasing loss of biodiversity at the global scale. Some of these changes, such as extinction of species, are truly irreversible; others are not, but the challenge of managing natural resources without losing biodiversity has increased markedly. The transformations people have already made in land use have created conditions for extinctions that will persist for centuries, even if further destruction or degradation of habitats were halted immediately. Moreover, pressures on biological diversity are likely to increase still further as a consequence of human-induced climate change.
The underlying causes of the loss and degradation of biodiversity are:
The specific mechanisms by which the underlying causal factors result in the reduction and loss of populations, the extinction of species and the transformation and degradation of ecological communities include:
In continental terrestrial ecosystems, the most important mechanism is the loss, fragmentation and degradation of habitat. On islands, species introductions and habitat loss have been equally important mechanisms. In oceans, overharvesting and pollution are the most important factors. All of these mechanisms have been major influences on species and populations in freshwater ecosystems.
Box 7 Economic markets and policies do not reflect the full value of biodiversity
The economic challenge in managing biodiversity is to balance the benefits derived from exploitation of individual biological resources against the true social costs caused by the loss of the diversity of organisms and ecological communities. The private profit to be gained from transforming a habitat or over-exploiting a species may be substantial to an individual, but it is often less than the true cost to society. This is because the markets which determine the private profitability of using biological resources often ignore the wider costs of that use. They generally fail to capture the indirect use value of biodiversity in supporting a range of ecosystem services including, for example, water purification, regulation of runoff, waste assimilation, habitat provision and carbon storage. Furthermore, economic markets generally fail to accurately reflect the ethical, cultural, aesthetic and religious value of biodiversity. Because many of the costs of biodiversity are external to the market, they are ignored by private decision-makers. This often leads to the overuse or misuse of biological resources through such actions as deforestation or excessive harvesting of species. The challenge for policy-makers is to design institutions and incentives that will:
Policies to achieve these goals must be formulated in a wide variety of sectors that have not traditionally examined their consequences for biodiversity: e.g. agriculture, forestry, fisheries, energy and transportation.
The speed and scale of changes in biodiversity
The impact of human activities on ecosystems
The net effect of human activities may possibly be a greater overall diversity in the types of ecosystems and landscapes around the world, some of which are extremely important to societal well-being. Human activities are directly responsible for creating agroecosystems and cultural landscapes, for example. However, these increases in the diversity of ecological systems have come at the expense of impoverishment of a great number of natural communities, and the reduction of at least some ecosystem services. Although total area may or may not have changed for major vegetation types, the plant species composition within them has often been dramatically altered by practices such as various forms of logging, grazing, introduction of exotics and frag mentation, to the extent that many ecosystems contain only one or a few plant species, and at times no longer include any of the original species. For example, many native grasslands no longer exist as such, their species composition having been altered by the introduction of cattle and sheep. Northern temperate forests have changed dramatically in North America and Europe as a consequence of intensive logging, exploitation, and replanting, often with introduced species, over the last several hundred years. in terms of total area, forest and woodland communities have decreased globally by about 1 5% since pre-agricultural times. Northern temperate forests are currently relatively stable in total area. In the early to mid1 980s, humid tropical forests were losing approximately IO million hectares, or just under 1% per year globally, although there is good evidence that rates of forest conversion in parts of Central and South America have declined since. Dry tropical forests may have lost even more area. Since 1 700 there has been a five-fold increase in cropland, and since 1800 about a 24-fold increase in irrigated crop land (Table 2). The total area of grassland has remained roughly constant over the past 300 years, with loss through conversion to cropland being balanced by gain through deforestation. Coastal and lowland areas, wetlands, native grasslands and many types of forests and woodlands have been particularly influenced or destroyed. For example, the dry tropical forest of the Pacific coast of central America once covered 550 000 square kilometres-, now, less than 2% is intact. The United States has lost 54% of its wetlands-I Thailand has lost more than 50% of its mangroves, and the Atlantic forest of Brazil has been reduced to approximately 10% of its original I million square kilometres. Of a total area of 600 000 square kilometres of coral reefs, about 10% have already been eroded beyond recovery.
Loss of populations and species
Human impacts tend to severely reduce the size of many biological populations (Fig. 7), greatly increasing the risk that populations will be lost locally, and ultimately leading to some species' extinction. The loss of genetically distinct populations within a species is almost as important as the loss of an entire species. Population Viability Analyses for vertebrates and plants show that in some cases when numbers of individuals in a population decline to as low as a few thousand, random variation in environmental factors can rapidly lead to total extinction. Even when the species does not go extinct, its loss from a local region or a major reduction in its population can have significant consequences for human livelihoods and ecological services. Mass extinctions of biodiversity have been recorded in the geological record (Fig. 8). lt has been suggested by some authors that we are on the verge of a further mass extinction spasm. During the past few thousand years human activities have
Fig. 7 Human impacts tend to severely reduce the size of many biological populations, greatly increasing the risk that populations will be lost locally, and ultimately leading to some species' extinction (source as Fig. 5).
Fig. 8 A summary of mass extinctions showing the principal groups of animals affected by each event (from Given, D. 1992. Principles and Practice of Plant Conservation. 'Fimber Press, Oregon).
led to the extinction of species. The prehistoric colonization of the Pacific and Indian oceans by humans and their commensals such as rats, dogs and pigs, may have led to the extinction of as many as a quarter of the world's bird species. Since the year 1600, 484 animal and 654 plant species (mostly vertebrates and flowering plants) are recorded as having gone extinct, although this is certainly an under-recording, especially as regards the tropics. The rate of recorded extinctions in well-known groups such as birds and mammals has increased dramatically during this period: 38 species between 1600 and 1810 compared to 112 species between 1810 and 1992 (Fig. 9). Extinctions during these 390 years have been most numerous on islands and island archipelagos, and in freshwater ecosystems. Evidence suggests that extinction rates are lower in floras and faunas that have already undergone some form of severe environmental stress. For example, recent extinction rates in Mediterranean floras are much lower (0. 1%) in the Mediterranean proper where human impacts are oldest, than in Western Australia (I%), where human impacts are more recent. Among organisms with adequate fossil records, including invertebrates, mammals and diatoms, the average 'life-span' of a species has been calculated to be of the order of 5-10 million years. If this were to be applied to our estimate of approximately 13.5 million species of all groups currently alive, this would suggest that the expected current rates of extinction would be roughly one to three species per year. There is, however, uncertainty about the average 'life-span' of species in the fossil record and there is variation in life span estimates for different groups of organisms. Mammals have a relatively short average species 'life span' of about 1 million years, suggesting that one extinction would be expected approximately every two centuries, on average. The uncertainty as to the total number of extinctions among vertebrates and plants over the past century makes it impossible to assign a single estimate to recent extinction rates, but at least among vertebrates and vascular plants the recent rates are fifty to a hundred times the expected background.
Fig. 9 Time series of animal extinctions on islands and continents: all taxa (from WCMC Global Biodiversity, Status of the Earth's Living Resources. Chapman and Hall, London).
Table2 Global human-induced conversions in selected forms of landcover.
|cover||date||area (10^6 km^2)||date||area (10^6 km^2)||% change|
Two quantitative methods have been used to estimate pending rates of extinction. The first uses careful demographic analyses in selected species, and one assessment has projected that 50% of species in selected subsets of mammals, birds and reptiles are likely to go extinct within 100 to 1000 years. Because of the stringent requirements for data, this approach has only been applied to a small number of very well known species. The second approach uses the observation that the total number of species found in an area is related to the size of that area in a fairly simple way, quantified by a species area curve. Several estimates have been made of the potential loss of species due to tropical deforestation by using this empirical relationship and making assumptions about the future rate of loss of habitat. Published estimates of species that will become extinct or committed to extinction in tropical forests over approximately the next quarter-century range from 2% to 25% in the groups exam ined (variously: plants, birds, birds and plants, and all species). This would be equi valent to 1000 to 10000 times the expected background rate. If recent rates of loss of closed tropical forest (about 1% globally per year) were to continue for the next 30 years, the equilibrium number of species in the forest, as calculated by species-area techniques, would be reduced by approximately 5 to 10%. These potential extinc tions would not be immediate: it could take decades or even centuries to reach the new equilibrium number of species. Estimates are likely to be most accurate for groups such as beetles, birds, plant's and mammals, for which empirical data are easily available, but they may apply equally well to less-studied groups. These esti mates do not take into account the potential effects of fragmentation, increases or reductions in the rate of deforestation, or the potential effects of mitigative measures that might be taken in the interim that could retard or even prevent extinctions, such as the setting aside of protected areas which include 'hotspots' or concentrations of species' diversity. Comparable estimates have not been made for the potential impact of habitat loss in other regions. More qualitative methods of assessing the probability of species' long-term survival use the categories of IUCN The World Conservation Union. Threatened species are those that are thought to be at significant risk of extinction in the foreseeable future because of random or deterministic environmental factors, or by virtue of their rarity. Estimates for regions are constructed by taking into account those species for which enough is known about their population size, trends, and potential threats, and extrapolating estimates of habitat loss. In 1994, the minimum estimate for numbers of globally threatened animal and plant species was about 5400 animals and 26 000 plants (Table 3). About I 1% of bird species, 18% of mammals, 5% of fish, and I 1% of plants were catalogued as threatened. An analysis of the change in species'cat egorizations over time implies that 50% of bird and mammal species will be extinct within 200-300 years although these changes in status reflect not only biological factors but the state of knowledge of the species involved and the rate of data entry. However, for the vast majority of the 1.75 million described species or the many millions of undescribed species, no assessment of status has been made.
On to Global Biodiversity Assessment Part 2