Chapter One: Introduction

The one process ongoing in the 1990s that will take millions of years to correct is the loss of genetic and species diversity by the destruction of natural habitats. This is the folly that our descendants are least likely to forgive us.

E.G. Wilson (1992)

The earth's biological foundation is erod-ing at a rate unequaled in at least 65 million years. Rapidly escalating human demands for natural resources are causing genes, species, and natural ecosystems to disappear at an unprecedented rate. Conservation is becom-ing a crisis discipline. Deciding what to conserve and where is an essential first step in managing the crisis.

In an ideal world, all biodiversity conserva-tion needs would be addressed without jeopar-dizing human aspirations for social and econom-ic development. Despite evidence of modest growth in conservation funding support (Abramovitz, 1994), it is clear that biodiversity conservation needs around the world will con-tinue to vastly exceed the financial resources available. This publication examines the scientif-ic basis for setting biodiversity conservation pri-orities, reviews practical experience from around the world, and recommends principles for mak-ing priority-setting an effective conservation tool at local, national, and international levels.

What Are We Losing And Why Should We Care

Extinction is a fact of life. Sooner or later, every species meets its fate; it may be over-whelmed by environmental change or by the debut of a new species. The fossil record indi-cates that, during the more than 3.5 billion year history of life, the average longevity of a species has ranged from less than a million years for some groups of mammals to about 10 million years for certain groups of invertebrates and flowering plants (Wilson, 1992). Whatever the circumstances of the species' demise, other species, perhaps new ones, have always found ways to use the resources previously consumed by those that have departed. Through the broad sweep of geological time, for each species that has disappeared, more than one species has replaced it. Gradually the world has become more, not less, biologically diverse in spite of the extinction that each species inevitably faces.

Although estimates vary widely, there may now be 30 million or more species on earth. Living organisms are found everywhere on the surface of the planet, including such inhospitable places as the polar icecaps and deep within sulfur springs thousands of meters below the surface of the Pacific Ocean. The interaction of species with each other and their environments has multiplied with the growing diversity of life, giving rise to new evolutionary pathways that eventually contribute to the formation of new species and ecosystems. One of these pathways produced the species Homo sapiens roughly one million years ago. Other evolutionary pathways have produced a vast array of species and productive ecosystems that have helped humans to succeed as a species.

The increase in biological diversity (see Box 1.1) has not been without its setbacks. Occasionally, changes in climate brought on by continental drift, massive volcanic eruptions, or asteroid impacts have caused mass extinction events that actually reduced the planet's biodiversity. The fossil record indicates that life has been impoverished by five massive extinction events during the past 450 million years, each of them wiping out between 25 and 50 percent of all biological families (Raup, 1988). At the end of the Paleozoic period 245 million years ago, as many as 96 percent of all species may have been eliminated, and the most recent mass extinction episode abruptly ended the dinosaur era at the end of the Cretaceous period 66 million years ago. After each of these major biological catas-trophes, life has recovered its diversity - but only after tens of millions of years.

A sixth major extinction event is now underway as large-scale rapid environmental change affects much of the earth's surface. This time the agent of environmental change is not astronomical or geological, but biological. Humans are the most powerful agent of environmental change driving the latest wave of extinctions. Human activities have already caused the destruction of over a third of the world's forests, and a majority of the world's native grasslands have been lost to either the plow or to desertification caused by overgrazing. The human species now appropriates 40 percent of the solar energy captured in the photosynthetic process of plants (Vitousek et al., 1986). Through the transformation of natural habitats into domesticated land uses (cropland, plantations, permanent pasture, and human settlements) and the direct consumption of wild flora and fauna, human uses of natural resources are exacting a heavy toll on other species. In the few plant and animal groups that are well known, extinction is taking place at far faster rates than before humans inhabited the earth. Conservative estimates indicate human activity has increased extinction rates of plants and vertebrates to between 10 and 100 times the normal "background" rate - a figure that may be much higher for invertebrates. According to Wilson (1992), "we are in the midst of one of the great extinction spasms of geological history."

In the vast majority of extinctions, we will never know what we are missing. Only a fraction (about 1.6 million species) of the world's total number of species - estimated to be between 10 million and as many as 30 million - have been identified and described by science. But even if human society does not notice the passage of these anonymous species, it is clear that biological resources in their myriad forms are essential to human welfare.

From the earliest days of recorded history, the fundamental social, ethical, cultural, and economic values of biological resources have been reflected in religion, art, and literature. Diversity in genes, species, and ecosystems has contributed immensely to the productivity of agriculture, forestry, fisheries, and industry. In many parts of the world, especially in predominantly agrarian and preindustrial societies, the daily lives of people and the biodiversity that surrounds them are closely intertwined. Wild species provide people with food, dyes, fibers, building materials, and medicinal plants, while home gardens and agricultural plots are planted with distinct domesticated crop varieties produced through many generations of breeding to balance productivity with adaptation to environmental conditions and human tastes. The livelihood of forest dwellers, farmers, trappers, fishermen, and others depend on their ability to manage the diversity of life to meet their per-ceived needs without necessarily diminishing the environment's capacity to meet their needs on the next day.

Box 1.1 The Diversity Of Life Biodiversity refers to the variety and variability among living organisms, the ecological complexes in which they occur, and the ways in which they interact with each other and their environment. Biodiversity is usually divided into three hierarchical categories - genes, species, and ecosystems. A more comprehensive definition, based on Sanderson and Redford (1994), is used here to better represent the components of biodiversity and how they are measured. Genetic diversity refers to the variability within a species. This diversity can be measured by the variation in genes within an individual species, population, variety, subspecies, or breed. Until recently, measurements of genetic diversity were applied mainly to domesticated species and populations held in zoos or botanic gardens. These techniques are increasingly being applied to wild species. Species diversity refers to the variety of species within a local area, region, or at the global scale. Such diversity can be measured in many ways, and scientists have not settled on a single best method. The number of species in a region - its species "richness" - is the most often used measure, but population biologists sometimes use a more precise measurement that weighs the presence of species versus their frequency at a given locality. Since the species is the unit best understood by lay people, and because of the work of taxonomists, much of the attention to biodiversity, including priority-setting, has been focused at the species level. Taxonomic diversity refers to the variety of organisms within a region at a taxonomic level higher than the species level (e.g., genera, families, order, etc.). When the objective is to preserve the greatest genetic variation, species from different higher taxa should be selected. For example, an island with two species of birds and one species of lizard has greater taxonomic diversity than an island with three species of birds but no lizards. Similarly, more species live on land than in the sea, but terrestrial species are more closely related to each other than ocean species are, so diversity is higher in marine ecosystems than a strict count of species would suggest. Diversity of communities and biotic processes refers to groups of different species that co-occur in the same habitat or area and interact through trophic (e.g., foodwebs) and spatial relationships. Pollination, predation, and mutualism are examples of biotic processes. Diversity is harder to measure at this level because the "boundaries" of communities are elusive. While there is no consensus approach to measuring diversity at this level - mathematical relationships of species co-occurrence and vegetation cover are two of the approaches used - the number and distribution of communities can be measured as long as a consistent set of criteria is used. Diversity of ecosystems refers to a community of organisms and their physical environment interacting as an ecological unit. Ecosystem processes differentiate this level from the community level and include abiotic factors such as fire, climate, and nutrient cycling that influence the composition, structure, and interaction of biotic communities. The difficulties of measuring diversity at this level are similar to those at the community level. This is also the level at which many evolutionary processes operate. Biodiversity conservation at the ecosystem level seeks to preserve the basic trophic structure (i.e., the food web of plants, herbivores, predators, and decomposers that transforms energy into life) and patterns of energy flow and nutrient cycling. At this level, conservation should seek to preserve properties and processes, not just species or assemblages of species. Sources: Sanderson and Redford (1994); WRI/IUCN/UNEP (1992)

In modern society, biodiversity contributes enormously to human welfare as well. For example, a quarter of the prescription drugs dispensed in the United States, and a substantially higher figure for all drugs worldwide, owe their existence to compounds first derived from plants. Two of the more well known examples of such drugs include vinblastine, an effective treatment for childhood leukemia derived from the rosy periwinkle of Madagascar, and taxol, a promising new treatment for breast, ovarian, and other cancers derived from the Pacific yew tree of the Pacific Northwest in the United States and Canada. The thousands of other drugs derived from plants include a variety of widely prescribed sedatives, stimulants, analgesics, antitumor agents, cardiovascular drugs, antimalarial agents, and birth control pills. The over-the-counter value of plant-derived pharmaceuticals alone exceeds $40 billion per year worldwide (Miller and Tangley, 1991). Yet only 5,000 plant species (most of them from temperate zones) have been comprehensively screened for their medicinal properties, leaving the vast pharmaceutical potential of plants (especially tropical plants) unknown (Kapoor-Vijay, 1992). Our understanding of the link between biodiversity and human welfare will continue to expand as, for example, researchers learn more about the role of soil microfauna - one of the least known parts of the biological world - in maintaining crop and tree productivity.

In a world faced with the potential for rapid environmental change caused by climate change and pollution, biodiversity offers options for agriculture, forestry, and other human activities to adapt to changing conditions. Advances in breeding, biotechnology, and genetic engineering have enhanced the value of wild species because their genes can now be used to confer new properties such as disease resistance or tolerance for a wider variety of environmental conditions to domesticated species. The loss of biodiversity reduces the options for nature and people to respond to changing conditions. As Noss (1993) observes, it is sustainability that depends on biodiversity, not the other way around.

Yet thousands of species and even entire communities of species around the world face premature extinction each year.¹ National-level biodiversity assessments are depressingly similar in their long lists of endangered species, unprotected ecosystems, threats to biodiversity, and inadequate conservation resources.² Deciding which species, habitats, and ecosystems have precedence in the allocation of conservation resources is a difficult, but inevitable aspect of conservation planning in the 1990s. Scientists, conservation agencies, non-governmental organizations, and donors have begun to set explicit biodiversity conservation priorities in a variety of ways.

Priority-Setting

For many people, setting conservation priorities is an uncomfortable task, akin to playing god. To others, it may seem a redundant activity that merely confirms what knowledgeable folks already know. Moreover, setting priorities may seem a poor use of resources since conservation priorities are not always influential and are sometimes overlooked entirely. However, every decision to spend rime, money, and effort in a particular place and in a particular way means that those conservation resources cannot be used somewhere else. In short, priorities are continually being established for biodiversity conservation - even if there is no deliberate process for doing so. This volume assumes that it is better to set priorities in an informed, transparent, and deliberate way than to leave them to chance and opportunity.

Biodiversity in the Balance was written with several audiences in mind. Policymakers with responsibility for defining conservation policy and implementing conservation strategies at the national and provincial/state levels will find the discussion of the policy context for setting priorities, and the range of available approaches, useful for planning, especially as countries move to implement the Convention on Biological Diversity. Donor agencies faced with increasing demands to support conservation efforts with limited financial resources are already increas-ingly involved with priority-setting efforts, and this volume should assist agency professionals involved in this valuable and complex task. Both policymakers and managers should benefit from the use of straightforward, non-technical language to discuss what can be complicated and technical concepts. Finally, this publication is written for scientists and conservation management professionals who have already done much to advance the cause of identifying efficient means for conserving biodiversity. It is hoped that they will benefit from seeing the range of approaches that have been developed and stand resolved to push the evolution of priority setting further.

Chapter II stresses that any set of conservation priorities reflects human values. In order to distinguish between the almost infinite variety of genes, species, and ecosystems, priority-setters assign values to elements of biodiversity. Two major value systems are applied to biodiversity: 1) its use value, and 2) its existence value. Use values may represent economic, scientific, ecological, or social and cultural benefits from biodiversity that people and institutions consider most important. The value of biodiversity can also be considered entirely separate from its use to humans or the biosphere. Valuing biodiversity simply because it exists is important to many people in cultures around the world. Given the range of values that people associate with biodiversity, it is nor surprising that there is no generally accepted universal scheme for establishing biodiversity conservation priorities. Chapter II also explores biological and social factors used in setting priorities and examines the general types of approaches that have been developed to establish biodiversity conservation priorities. Literally hundreds of approaches have been developed during the past two decades. This chapter categorizes and analyzes priority-setting approaches by the types of conservation objectives they are designed to support. These categories include genetically-based, species-based, ecosystem-based, and "integrative" (combining social and economic criteria with biological factors) approaches to setting biodiversity conservation priorities.

Chapter III reviews conservation priority-setting in practice. Specific examples of priority-setting at international, regional, and national scales are presented. These range from well-known schemes for setting global priorities such as the "hotspots" (Myers, 1988) and "megadiversity" approaches (Mittermeier and Werner, 1990) to regional (e.g., Amazonia) and national level efforts (e.g., Papua New Guinea). While these approaches are strongly influenced by the issues discussed in Chapter II, they are each unique, reflecting the enormous variation in bio-physical conditions, institutional values and objectives, and available resources.

Chapter IV presents a set of ten principles to strengthen the effectiveness of any process to set biodiversity conservation priorities. These principles were developed to build on the strengths and limitations of the approaches reviewed in Chapter III. They are based on the premise that an effective priority-setting process should provide a critical link between conservation goals and objectives and on-the-ground actions that make conservation a reality. These principles stress the importance of process and participation in priority-setting efforts, especial-ly at local levels.

Finally, Chapter V concludes with a summary of issues most vital to using priority setting effectively to support conservation policies and objectives. These issues include the importance of using clear objectives to guide priority-setting, the role of biogeographic representation in first-cut priorities, recognizing that non-biological factors will ultimately determine the fate of priorities, making priorities an integral part of national biodiversity strategies and action plans, and defining a complementary role for setting priorities at international levels.

Endnotes

1. Assuming there are 10 million species, current annual losses could range from 8,000 based on the most conservative estimates of Reid (1992a) to 85,000 based on Ravens (1988) estimates on extinctions due to tropical deforestation. Most of these estimated extinctions are of invertebrates in the tropics.

2. National level biodiversity assessments have been carried out by the World Conservation Monitoring Centre, and by government agencies and national and international nongovernmental agencies. Support for these assessments has generally come from various multilateral development agencies (eg, World Bank, United Nations Environment Program, Global Environment Facility), and bilateral agencies, especially the U.S. Agency for International Development (see WRI, 1992a). More recently, countries have begun to develop national country studies, strategies and action plans as called for under the Convention on Biological Diversity (see Miller and Lanou, 1995).

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Chapter Two: Biodiversity Conservation Priorities: Values And Approaches

Establishing biodiversity conservation priorities should be a conscious effort to assign values to genes, species, and/or ecosystems, and then to evaluate other criteria (such as risks and opportunities for their conservation) in relation to those values in order to arrive at a set of geographic priorities. Priority-setting is a complex process around which achieving consensus would be difficult if only one scheme existed. However, hundreds of approaches have been developed to support a range of conservation objectives, each with its own strengths and weaknesses.

In many ways, the benefits of establishing credible conservation priorities are self-evident. Efficiency in the use of limited conservation resources is the most obvious. Efforts spent deciding where and what to do first may be repaid in savings of time, finances, and personnel. The data and analysis required to establish priorities help give a more complete understanding of the distribution and status of biological resources in the geographic area evaluated. Many potential funders of biodiversity conservation efforts are likely to be more supportive if their resources are directed to strategic and well-justified priorities. A deliberate and well-documented priority-setting process can also provide transparency in conservation planning and decision-making. Transparency provides interested institutions and the public with a sense of what information was important in the selection of priorities and enhances the scientific credibility of conservation decisions.¹ Given the complexity of biodiversity, and the range of values, perspectives, and goals that influence how biodiversity is viewed, it is not surprising that there is no generally accepted universal scheme for establishing conservation priorities. Different criteria and conservation objectives characterize various approaches. This chapter, therefore, seeks 1) to examine the role human values and perspectives play in determining biodiversity conservation priorities; 2) to review criteria most frequently used to assign value to elements of biodiversity, and; 3) to categorize various priority-setting approaches by the type of conservation objective they are designed to support.

Priorities Are Value Statements

Just weeks before the United Nations Conference on Environment and Development (UNCED) was convened in Rio de Janeiro in June 1992, 98 nations gathered in Nairobi to conclude negotiations on a biodiversity convention after three years of complex and sometimes divisive debate. Although an international agreement was reached in the final hours of the Nairobi negotiations, and the Convention on Biological Diversity was forwarded to Rio for signature at the UNCED meeting, a number of countries expressed reservations almost immediately. Although most countries signed the convention in Rio, with the United States a notable exception,² a number did so with serious reservations. To some, the disagreements that arose in the late rounds of negotiation weakened the treaty by not specifying formulas or payment mechanisms for the use of genetic materials and for conservation financing in general. Other countries indicated that the failure to include a list of the most important ecosystems, habitats, and species for international conservation rendered the treaty hollow.

The disagreements over whether to include a list of biodiversity conservation priorities raised serious issues of sovereignty, responsibility, compensation, and values that limited progress in other areas of the convention as well. In many respects, the debate reflected fundamental differences in how various interests see biodiversity. Industrialized countries, most of them relatively poor in species diversity and natural habitats, argue that the global importance of biodiversity makes it part of the common heritage of mankind, for which all nations share some responsibility, regardless of where the biodiversity is found. These arguments, reflecting both ethical and utilitarian values, are motivated by many factors, including a desire to protect rights that allow developed countries to explore and exploit the commercial value of biodiversity found in the tropics. In developing countries, many of them relatively well-endowed in biodiversity, governments often view the species, habitats, and ecosystems found within their borders as sovereign resources valued primarily for the direct economic development benefits they may provide. For local peoples throughout the world, biodiversity often represents cultural, spiritual, and basic subsistence values that were left out of the formal discussions on the Biodiversity Convention.

In short, the debate on the Convention on Biological Diversity was motivated by concerns about whose priorities were being singled out, who would bear most of the burden to protect species and ecosystems, and who would benefit from their conservation. The inability of treaty negotiators to agree on a single set of global conservation priorities was perhaps inevitable given the differing views, values, and definitions associated with biodiversity.

The etymology of priority begins, not surprisingly, with the Latin word "prior" meaning first. The Medieval Latin "priorities" and subsequent Middle English "priorite" established a noun with much the same meaning that priority has today, or "that which has the most importance." In its most common modern English usage, priority is defined as something which has precedence or is established by order of importance or urgency. Importance, of course, is crucial to the meaning of priority and implies that whatever is a priority is something having great value or significance. Moreover, calling something a priority implies that its value or significance is greater than other things with which it is being compared. There are no self-evident priorities: priorities cannot be chosen before the set of things being considered are assigned relative values. Valuation is, itself, relative and depends on the valuer and his or her objectives.

Conscious consideration of biodiversity values in the priority-setting process provides benefits beyond the more obvious benefits described above. For example, the deliberate choice of values to be emphasized can help to clarify what values are not protected under a given conservation objective - values that may have to be considered under additional conservation objectives and protected by separate sets of priorities. Discussions about why, where, and how to conserve biodiversity when framed in terms of value considerations are likely to be more specific and tangible to the public. In short, value considerations that assess the many roles biological diversity plays in nature and in human societies can help us to disaggregate the immense complexity embodied in the term "biodiversity." Considering biodiversity values will in most cases reveal how little we know about the life around us and where we should look to learn more.

Unfortunately, the values which inform the establishment of biodiversity conservation priorities are usually left unstated by those making the determination. This leaves others with the task of identifying what underlying values are implied by priority-setting exercises as they try to decide whether the values assigned coincide with their own views on what is most important for conservation action. The most obvious area where values are revealed is in the criteria used by various schemes to narrow the elements of biodiversity considered for priority status.

Criteria For Assigning Conservation Value

Criteria provide standards to judge whether a thing or a process has certain desired properties, characteristics, or values. Any deliberate effort to establish biodiversity conservation priorities uses criteria, although they are not explicitly defined in all cases. Given the complexity of biodiversity and the many ways in which it is valued, the number of criteria that could be used to identify genes, species, or ecosystems as conservation priorities is enormous. In practice, however, a handful of criteria are most commonly used.

Biologically defined criteria are used in virtually all priority-setting schemes; some approaches use additional social, economic, institutional, and other criteria. The most commonly used biological criteria and several examples of economic, social and institutional criteria are summarized below. These criteria, in principle, can be used at any level of biodiversity (e.g., genes, species, ecosystems).

Biological Criteria

Ethical, historical, cultural, and political values are key determinants in shaping peoples' conservation priorities. Yet conservation biologists and international organizations typically seek to establish conservation priorities based on the biological and physical characteristics of biota. Under these criteria, biodiversity measurements (e.g., species richness and endemism levels) are a key determinant of biodiversity priorities (see Box 1.1). Most conservation priority schemes use one or more of the following biological criteria: richness, distinctiveness, rarity, representativeness, threat, and function. Often several criteria are combined to evaluate trade-offs and make value judgments before a set of priorities is reached.

Richness. Species richness refers to the number of species in a given area; the more species, the greater the species richness. Use of this criterion alone (without additional criteria) implies that all species are of equivalent value, and that areas with more species are of greater value to conservation than areas with fewer species. Species richness is very important in most schemes to identify biodiversity conservation priorities and is the simplest and most quantitative criterion available to identify priorities. For example, a habitat containing 800 species would be of greater conservation importance than a nearby habitat with only 500 species.

Although richness is usually applied at the species level, it can also be considered at the genetic and ecosystem levels. For example, a species population with relatively high genetic variation would be more important for conservation than a population of the same species where inbreeding has led to relatively little genetic variability. Or, a region with numerous ecosystem types (e.g., eastern slopes of the Andes) would be of higher conservation priority than a region with fewer ecosystem types (e.g., the cerrado).

Rarity. This criterion is used to assign higher conservation value to the least common genotypes, species, or ecosystems. This criterion also relies on quantitative information - in other words, the number of occurrences of a genotype, species, or ecosystem is the relevant measure for rarity. Nearly every approach to establishing conservation priorities employs this criterion, sometimes combined with one or more other criteria. For example, a genotype of a wild relative of an agriculturally-important species found in only one reproductively isolated small population would have higher conservation value than a widely distributed genotype found in a number of interbreeding populations of the same species.

Using the rarity criterion, the peregrine falcon (Falco peregrinus) would be accorded greater conservation value than the closely related, but much more common American kestrel (Falco spaverius).³ Likewise, ecosystems that are widespread and found in a number of locations (e.g., boreal spruce-fir forests) are less important to biodiversity conservation than are rate ecosystems of limited area (e.g., wetlands in arid regions). In other words, rarity constrains conservation options by leaving only one small location or population for conservation efforts. Conservation of widespread ecosystems and common species is less urgent because there are many more options.

Distinctiveness. In contrast to rarity, which simply measures the relative quantity of something, distinctiveness is a criterion used to assess the degree of separation of a population, species, or ecosystem from its nearest comparable analog. A species, for example, may be numerically common (and thus not rare) but could be exceedingly distinct in the sense that it has few if any closely related species - the duck-billed platypus (Ornithorhyncus anatinus) in Australia is an example.

The following dichotomies show how this criterion influences priority assessments. For example, conserving a plant community with many endemic species (i.e., species found nowhere else in the world) makes a greater contribution to the conservation of biodiversity than conserving a community containing many widespread but few endemic species. A species that is monotypic (the only species in the genus), or a species that is the only representative of its family or order is more deserving of conservation than is a species that belongs to a genus with many species.

In many parts of the world, however, our knowledge about the distinctiveness of species is limited. Many tropical species are not described by science and little is known about their genetic relationships.⁴ For example, in the South Pacific, The Nature Conservancy's efforts to identify conservation priorities is starting out simply by trying to identify major ecosystems and assess their rarity.

Representativeness. This criterion is used to ensure that conservation efforts in a given area include examples of all species or ecosystems (or genotypes of a particular species), depending on the level of interest. For example, this criterion is often used to design reserve systems containing different ecosystems typical of a region's variety of ecosystems. Alternatively, this criterion might be used to decide which of two sites within the same ecosystem has the most representative sample of species and ecosystem processes that characterize the ecosystem. At the genetic level, representativeness is an important criterion in selecting samples for ex-situ preservation in seed banks and captive breeding programs.

Threat. Under this criterion, elements of biodiversity facing the greatest imminent danger or harm (usually from human activities) are considered most worthy of conservation. In the case of a species, danger or harm usually means a decline in numbers that puts a species at risk of nor being able to maintain a viable breeding population. Causal relationships between potential threats and their effect on elements of biodiversity are frequently difficult to establish, and therefore this criterion usually adds a more subjective element into priority considerations. This criterion is widely used, usually in conjunction with "rarity" and "distinctiveness." In fact, "threat" tends to merge with "rarity" since as a species or ecosystem becomes more threatened, it is, by definition, becoming more uncommon. However, "rarity" tends to be a physical factor while "threat" adds a greater sense of time or urgency (i.e., some species are naturally rare but not threatened with extinction). The practical issue, once again, is that fewer options and less time are available to protect endangered species than other species. This criterion is often motivated by a sense of moral responsibility on the part of humans to avoid causing the loss of a species or habitat.

The use of the threat criterion in setting priorities might lead to the following results. For example, among African antelopes, a species listed by the World Conservation Union as "endangered" (e.g., Addax) would receive higher priority than one that is listed as "vulnerable" (e.g., Giant Eland) which in turn would receive higher consideration than one that is listed as "rare" (e.g., Yellow-backed Duiker) (IUCN, 1988).⁵ An unprotected natural habitat surrounded by intensive agricultural development would receive more priority than a similar habitat with less intensive agricultural development on only one side. When species are evaluated, a major weakness with this criterion is that our information on what is threatened is often simply a reflection of the state of knowledge about the species. We simply do not know enough about most species to know for sure whether, and to what degree, they and their habitat may be threatened. Obviously, our knowledge of threatened genotypes is even more limited. And while the World Conservation Union (IUCN) and many national and even state and provincial governments have developed classification systems for threatened and endangered species, no classification has been developed to categorize ecosystems by degree of threat.

Function. This criterion emphasizes the role that certain species, communities or ecosystems have in determining the ability of other species, communities or ecosystems to persist. The "keystone" concept is nearly synonymous with function in this context. Within biological communities, a keystone species is one (or sometimes a group of closely related species) that makes a disproportionately large contribution to community structure, composition, or processes. For example, fig trees and vines (Ficus spp.) provide a reliable source of fruit to primates, birds, and other fruit-eating vertebrates during periods of drought when other preferred sources of food are unavailable (Terborgh, 1986). Fig trees in turn depend on highly specialized wasps, which mature inside the developing fig fruit, for pollination. Thus the health of the Ficus spp. depends on the health of the wasp populations, while many species in the vertebrate community depend for survival on the continued productivity of the figs. In the islands of the Indian Ocean and the South Pacific, the seed dispersal and pollination relationships between pteropid bats ("flying foxes") and many plant species are so close that the rapid decline or extinction of these bats could have disastrous consequences for hundreds of species of tropical plants⁶ (Cox et al., 1991).

The keystone concept also applies to certain habitats and physical resources, which Primack (1993) calls "keystone resources." For example, mangrove forests growing in the intertidal zone of many tropical and subtropical coastlines are vital to the survival of many coastal and marine species. First, they provide breeding grounds and nurseries for juveniles of many marine fish species which later move into other coastal and marine habitats. Second, through the build-up of detritus from leaf litter, the periodic release of larvae from a tremendous diversity of species, and the abundance of their invertebrate life, mangrove habitats contribute much of the organic matter that makes its way into marine waters that are otherwise nutrient-poor, including coral reef ecosystems. In addition, mangrove forests protect beaches and shorelines and their biological communities from erosion and can protect low-lying coastal lands from saltwater inundation by lessening the Impact of ocean surges associated with typhoons. At the same time, mangrove ecosystems trap sediments resulting from upland soil erosion and thereby protect fragile coral ecosystems and other sensitive marine environments from destructive siltation. Clearly, mangrove forests are keystone ecosystems.

Physical resources can also play keystone roles. Salt licks and other mineral deposits provide essential mineral nutrients for many vertebrate species, especially in inland areas with heavy rainfall and mineral leaching. Dead standing trees and woody debris on forest floors support many vertebrate and invertebrate species in the Pacific Northwest of North America; their removal through intensive forest management can have damaging impacts on local levels of biodiversity (Hansen et al., 1991).

Where keystone relationships can be established, the strategic value of using this criterion to set biodiversity conservation priorities is obvious. Once again, limited knowledge constrains use of this criterion. As a result, relatively few priority-setting schemes have used it explicitly. However, as food webs, biogeochemical cycles and other ecological processes become better known, the use of the function criterion will undoubtedly grow in importance.

Social And Institutional Criteria

Some priority-setting schemes address non-biological criteria such as economic, cultural, or existence value to humans. Most of these schemes combine one or more of the biological criteria above with non-biological criteria, usually some aspect of human utility. In general, social and institutional criteria have been used less often than biological criteria in priority-setting mechanisms. Social and institutional criteria, however, have become more important in priority-setting as the contribution of social and institutional factors to successful conservation efforts has become more widely appreciated.

Utility. The utility criterion emphasizes the importance of biodiversity elements that have known or potential utilitarian value to humans. Utility may be defined as economic value but it can also be used to identify elements of biodiversity that have scientific, social, cultural, or religious significance as well. Since the same species or communities can have different utility values to various groups of people, this criterion introduces perhaps the most subjective considerations into the priority-setting process. For example, "degraded" forest areas may retain substantial biodiversity with utility to local people who depend on the local biota for food and other products but may be viewed as having relatively little utility to a government that is more interested in wildlife habitats that attract tourists. This is especially true when potential or future utility values are being considered, since human premonitions of what might have future value are usually little more than speculation.

Decidedly anthropocentric, the utility criteria more likely to produce conservation priorities that can draw widespread political support than biologically-defined criteria. Although the utility criterion has been increasingly used by conservationists in the last few years, it has not often been employed in published priority-setting schemes despite the emphasis human societies place on utilitarian values. Local traditional systems of conservation and management, on the other hand, often do focus on species of utilitarian value (e.g., Adisewojo et al., 1984; Alcorn, 1984; Johannes, 1984; Weinstock, 1985).

Elements of biodiversity that will be more highly valued using a utility criterion include wild plant species related to domestic food crops, wild relatives of domesticated animals, medicinal plants, fodder plant species for domestic animals, plant and animal species harvested by people, and animal species useful as research models. Likewise, an ecosystem that plays a critical role as the watershed for irrigation or drinking water, or that provides habitat for fish species important to local diets, will be accorded more value than an ecosystem that provides limited indirect ecosystem services to humanity. The concept of utility can, of course, change with time and geographic scale. For example, indirect ecosystem services, such as carbon sequestration in tundra ecosystems, may be viewed as having tremendous utilitarian value on a global scale as knowledge of climate change factors increases.

Feasibility. When decisions are made to allocate conservation resources, feasibility (something that is practical or easy to do) is often the most important factor. Feasibility may be defined in political, economic, logistical, or institutional terms. For example, a conservation project may be located in a particular place where political support is strong rather than in a more biologically diverse area where influential politicians or economic interests are opposed to the project. Many conservationists fear that this is the principal or only factor considered by policy-makers and that it is usually done without explicit justification. Feasibility, unlike biological criteria, can change rapidly and dramatically as policies and institutions shift. Perhaps for these reasons, feasibility is not widely used in priority-setting schemes.

Feasibility has its strengths, however, and is the most important criterion for assessing the likelihood that actions to conserve a particular species or ecosystem will succeed. Moreover, if feasibility is not explicitly considered as a criterion for selecting priorities, priority setters virtually guarantee it will be considered behind closed doors when government decision makers or funding agencies divide up the conservation pie.

The feasibility criterion could be used in the following way. Land ownership and resource tenure are vital aspects of conservation and sustainable natural resource management in many parts of the world (Lynch and Alcorn, 1994). Particularly in developing-country communities where people have lost tenure to land and resources, they have often also lost their incentive or ability to use local environments (e.g., forests, coastal areas, coral reefs, grasslands) or species (e.g., valuable trees, medicinal plants, or wildlife) in a sustainable way. This loss of tenure by local communities may create open access situations where resource depletion and degradation are rapid, even if the area is now under the ownership or stewardship of the government. In such situations, the feasibility criterion could be used to select an area with a stable tenurial system over one where tenurial systems are poorly defined or routinely ignored. In developed countries, the feasibility criterion applied to land ownership would probably have a different result; it is usually easier to create a protected area on publicly-owned land than by purchasing many small, privately-owned properties.

Other Social and Institutional Criteria. It is important to recognize that many people have other criteria that influence their decisions about assigning conservation values. These criteria include ethical/religious, historical/heritage, and social/cultural points of view (and there are likely to be others as well). Such criteria are often found in the informal knowledge systems of local peoples, nor just in developing countries but in Western societies as well. While few published methodologies for evaluating conservation priorities include these criteria,⁷ such issues are extremely important in many areas. They should be identified and included in assessments of biodiversity conservation priorities whenever possible.

Nor all people or institutions value biodiversity in the same way. Priorities depend on objectives that are rooted in how individuals, institutions, and other collective groupings of people (even nations) value biodiversity. The criteria people use are shaped by their cultural and historical experiences - which may have developed over hundreds or even thousands of years - as well as by social, economic, geographic, and scientific factors that prevail today.

There are, of course, numerous variations under all criteria - biological and social/institutional. For example, under the utility criterion, biodiversity elements can be evaluated in terms of their current utility or their future utility, for their local utility or their global utility. Value considerations are evident in conservation strategies around the world.

Criteria As A Reflection Of Societal Values

Two brief examples are presented here to illustrate how societal values influence the choice of criteria for setting biodiversity conservation priorities. One is from a developed country, the other from a developing country. These examples oversimplify the complex roles values play in choosing criteria and setting priorities in any society, but they do suggest that economic circumstances, development needs, and history are important influences in setting priorities at national levels.

The simple fact that a species (or a gene or an ecosystem) exists is reason enough for many people, especially in developed countries, to support conservation efforts. Existence value is defined by McNeely (1988) as the importance people attach "to the existence of a species or habitat that they have no intention of ever visiting or using; they might hope their descendants may derive some benefit from the existence of these species, or may just find satisfaction knowing that the oceans hold whales, the Himalayas have snow leopards, and the Serengeti has antelope." Existence value is not a priority-setting criterion at all, but it does fuel many priority-setting efforts that use biological-defined criteria such as rare or "threat." In the United States, the Endangered Species Act (ESA) is implicitly based on the existence value of species.

The ESA was designed to protect all species that meet scientific criteria for being "threatened" or "endangered." When a species is judged by the U.S. Fish and Wildlife Service to be vulnerable to extinction (i.e., when population levels or geographic ranges are severely reduced), human activities are restricted in critical parts of its natural habitat. Only scientific evidence, not social or economic considerations, are considered in granting a species protection under the Act. In other words, the ESA is based on the assumption that species are of value in themselves, not just because individual human beings or societal institutions have preferences for them. In reality, of course, social, economic, and political considerations do affect the priority under which species are accorded protection under the ESA (see for example, Mann and Plummet, 1995).

In Costa Rica, on the other hand, the National Biodiversity Institute (INBio) was established in 1989 to promote the conservation of biodiversity based on the premise "that tropical biodiversity will survive only to the extent that societies use it for intellectual and economic development" (Gamez et al., 1993). Although INBio seeks to develop a complete inventory of the country's biodiversity, it is concentrating initially on insects and plants - a choice guided in no small part by the chance to find chemical substances of potential interest to biotechnology concerns. In October 1991, Merck Pharmaceutical signed a $1 million contract with INBio in exchange for the opportunity to screen the sam-ples that INBio is collecting. INBio essentially brokers Costa Rica's wild biotic wealth to organizations interested in using that wealth for profit. The "utility" criterion in the form of known or potential economic values is thus prominent in Costa Rica's strategies for conserv-ing biodiversity. Similar strategies are being con-sidered by other tropical countries.

Most approaches to setting priorities use more than one criterion. Taken together, the criteria used in a given scheme reveal a considerable amount about the values and concerns of the people or institutions proposing or using the approach. Countries having priorities (nor necessarily a single set of priorities) chosen by using criteria that reflect a wide range of biological and social values will stand a better chance of maintaining the widest diversity of life and its benefits.

Approaches To Priority-Setting

A biodiversity conservation goal is usually expressed in broad terms. The overall goal expressed in the Convention on Biological Diversity, which most of the world's countries have now signed, is "...to conserve and sustainably use biological diversity for the benefit of present and future generations."⁸ Conservation objectives to support that goal, however, are usually defined - often implicitly - in terms of protecting a subset of an area's (or a country's, region's, or the world's) biodiversity. For example, conserving a country's economically important plant species, and conserving a representative array of a country's natural ecosystems, might be two objectives under a broader national conservation goal. The criteria described in the previous section help to narrow the subset. However, approaches to identifying conservation priorities under an objective are usually oriented toward one of the hierarchical levels of biodiversity - generic, species, or ecosystem.

A simple typology of priority-setting approaches contains several broad categories: 1) methods based on genetic analysis; 2) methods based on species analysis (including the use of systematics⁹ to analyze evolutionary relationships at taxonomic levels higher than species); and 3) methods based on the analysis of ecosystems. The priority-setting approaches in these three categories rely principally on biological information, but may use any of the biological or social/institutional criteria previously discussed. A fourth category of priority-setting approaches consists of integrative methods that include significant consideration of economic, social, and cultural factors in addition to biological information. Some approaches in each category may have characteristics that define another category. Nevertheless, the typology is essential to understanding the basic elements of the hundreds of priority-setting approaches that have been developed.

Genetically-Based Approaches

Genetic variation underlies the more visible diversity of life that we see expressed in individuals and populations of a particular species, the different species themselves, and the higher taxonomic orders that species belong to. With the rise of biotechnology and the perception that genes are the grist for the next (or the current) technological revolution, genetic diversity has become the focus of increased research - and controversies over who "owns" genetic resources and who benefits from their conservation.

Biological depletion occurs not only at the more visible species and higher levels of biological organization, but also at the genetic level. As Meffe and Carroll (1994) point out, "Many species are far from threatened, but their gene pools have been sorely reduced through the elimination of most of their populations." This is particularly true for most important agricultural crops and breeds of livestock. For example, trillions of individuals of wheat (Triticum turgida) flourish with each growing season, yet the great bulk of genetic diversity has disappeared with the loss of wild relatives (through habitat conversion) and primitive cultivars (replaced by more modern and genetically uniform cultivars).

Traditionally, efforts to characterize and conserve genetic diversity have been dominated by an emphasis on domesticated plants, particularly a few dozen agriculturally important species. A growing number of agricultural research institutions have sought ways to limit generic vulnerability - a uniformity of genotypes that leaves crops vulnerable to new environmental stresses, pests, and disease - by preserving the range of genetic diversity found in crop species and their wild relatives. During the past twenty years, endangered species recovery programs have stimulated considerable research on the genetic variability of remaining individuals and populations to find ways to ensure that populations do not succumb to a combination of inbreeding and a narrowed genetic base. Others are interested in conserving genetic diversity within populations because of their potential future utility (see Ledig, 1988), or because a decline in diversity represents interference in the evolutionary process and the loss of evolutionary potential (see for example, Hamilton, 1993; Mlot, 1989).

Genetic resources can be conserved in-situ in reserves or special management areas or in ex-situ facilities such as seed banks, zoos, botanical gardens, aquaria, etc. As collectors take plant cuttings or shake seeds of a specimen into an envelope for ex-situ preservation, or as conservation biologists protect the habitat of an animal population for in-situ conservation, they are deciding which genes of a species are most likely to persist, especially if the species is rare or highly endangered. This is where genetically-based approaches to identifying conservation priorities are needed.

Genetically-based approaches to setting priorities are used to support three general objectives. The first objective is to ensure that individuals representative of genetic variability within a species are included in conservation programs. The second objective is to help determine which population(s) contain the greatest genetic variation. And the third objective is to conserve populations across their geographic range and the ecotypes in which they are found to ensure that co-adapted gene complexes, nor just a representative sample of alleles, are conserved.¹⁰

Tools used for identifying genetically-based conservation priorities range from simple surrogate measures of underlying genetic variation (e.g., variation in plant or animal morphology) to highly sophisticated molecular genetic techniques. In most cases, analysis of enzyme variants (allozymes) is used to gauge the overall generic variability within a species, population, or a number of populations. Sampling strategies can be complex and considerable debate about the advantages and disadvantages of different sampling techniques is seen in the literature. These issues are beyond the scope of this publication and are discussed in detail elsewhere (see Falk and Holsinger, 1991; Hartl and Clark, 1990; and Schonewald-Cox et al., 1983).

Advantages and disadvantages of genetically-based approaches are summarized in Box 2.1. In most areas of the world, where information is scarce, species are numerous, and threats to diversity at all levels are acute, genetically-based approaches should probably be viewed as a secondary strategy for identifying conservation priorities. Genetically based approaches should be used to "fine-tune" priorities once the "coarse filter provided by ecosystem-based approaches (complemented by species-based approaches) has been applied. Woodruff (1992) suggests that ecological management is the cheapest and most effective way of conserving genetic diversity:

"Genetic factors do nor figure among the four major causes of extinction: overkill, habitat destruction and fragmentation - impact of introduced species - and secondary or cascade effects (Diamond, 1989). Thus, although genetic factors are major determinants of a population's long-term viability, conservationists can do more for a threatened population in the short-term by managing its ecology."

Nevertheless, genetically-based approaches to identifying conservation priorities are pivotal in some circumstances. These include setting priorities for small isolated populations, genetically vulnerable species of high economic or other value, and to identify individuals or populations for which there is no conservation alternative to ex-situ preservation in the short-term.

Species-Based Approaches

A species is the unit or element of the biodiversity spectrum - from genes to large-scale ecosystems - most commonly used by scientists and the public to represent biological variation. On the one hand, species are the most recognizable expression of genetic diversity. At the same rime, species are the building blocks of ecosystems (McNeely et al., 1990). In other words, species are viewed as the "common currency of biodiversity. Nor surprisingly, more biodiversity conservation efforts focus on species than any other element of life systems, including genes, populations, ecosystems, or ecosystem processes. Likewise, most approaches to setting biodiversity conservation priorities have relied heavily on the species as the basic unit for analysis.

Although biologists have been arguing over the details of species definitions since before Darwin, modern biology (nor necessarily botanists) has settled on a general definition first formulated by Ernst Mayr in the 1940s (Mayr, 1942). Wilson's (1988) formulation of the concept is as follows: "...species are regarded as a population or series of populations within which free gene flow occurs under natural conditions. This means that all the normal, physiologically competent individuals at a given time are capable of breeding with all the other individuals of the opposite sex belonging to the same species... By definition they do nor breed freely with members of other species."¹¹

Box 2.1 Advantages And Limitations Of Genetically-Based Approaches Advantages Genetically-based approaches may provide information critical to the successful conserva-tion of extremely rare or highly endangered species or populations. Genetically-based approaches are especially useful in identifying conservation priorities for domesticated species and their wild relatives, especially agricultural crop and livestock species, and other economically important species where genetic vulnerability is an issue. Priorities identified using generically-based approaches are very specific and actions needed to conserve targeted individuals or populations are usually easy to define and limited in scope. Limitations Many techniques relevant to genetically-based approaches are expensive, require consider-able experience and sophisticated lab equipment, and deciding which sampling strategies to use is important to the results but can be confusing - mistakes will reduce confidence in the results. Plant or animal tissues collected for genetic analysis must be carefully collected, transport-ed, and stored under demanding requirements (e.g., kept fresh or frozen in a hot humid environment) and maintained in appropriate storage facilities - sampling is often difficult or expensive and sometimes simply impractical. Genetically-based approaches may do little or nothing to help conserve ecosystems and dynamic ecological and evolutionary processes without which the value of genetic diversity preserved in isolation will be increasingly diminished over time.

The biological species concept is nor perfect. As Wilson (1992) notes, the concept "has been corroded by exceptions and ambiguities." The major weakness is that a species (or at least populations of a species) at some point in its evolutionary history may not be reproductively isolated. Hybridization between species does occur, and in some cases (especially plants), populations may partially interbreed enough to produce a good many hybrids on a persistent basis. These semi-species, for example, are very common among the white oaks of eastern North America (Whirremore and Schaal, 1991). Nevertheless, the white oaks (Quercus alba, Q. stellata, Q. macrocarpa, Q. muehlenbergii, and other Quercus spp.) do remain distinct since breeding within the species continues to be much more common than hybridization and the gene pool remains at least partially closed. Whatever the limitations of the concept, Wilson (1992) stares that, "the biological species is likely to remain central to the explanation of global diversity."

Even without such rational explanations, the species concept provides an intuitive appeal to peoples around the world. As Wilson (1992) relates, the prominent biologist Ernst Mayr discovered the nearly universal recognition of the species concept during the late 1920s when he was a young researcher in the Arfak Mountains on the island of New Guinea:

"Once settled in camp, Mayr hired native hunters to help him collect all the birds of the region. As the hunters brought in each specimen, he recorded the name they used in their own classification. In the end he found that the Arfak people recognized 136 bird species - no more, no less, and that their species matched almost perfectly those distinguished by the European museum biologists. The only exception was a pair of closely similar species that Mayr, a trained biologist, was able to separate but that the Arfak mountain people, although practiced hunters, lumped together."

Wilson (1992) maintains that the species classifications are more than cultural artifacts borne of convention about anatomy and more than scientific names that arose from intuition and historical accident. They are, he believes, natural units that widely separated peoples with no previous contact have developed to facilitate their survival. Wild birds were the Arfak peoples' principal source of meat. Similarly, Amerindian peoples in the Amazon and Orinoco Basins have put names on a thousand or more plants used for food, medicinal purposes, and fibers. If Wilson is right, it should nor be surprising that the species concept plays such a prominent role in conservation efforts.

The key feature of species-based approaches is their emphasis on analyzing population sizes and geographic distributions of individual species to identify conservation priorities. The species-based approach to setting conservation priorities does nor generally include analysis of biodiversity at higher levels of organization such as genera, families, communities, ecosystems, ecosystem processes, or biogeographic features. However, the analysis of evolutionary relationships at taxonomic levels higher than species is rapidly emerging as a tool for assessing biodiversity conservation priorities (Box 2.2).

A species-based approach may express priorities in terms of specific sites or habitats, but the habitat is nor necessarily chosen because it is threatened or rare. For example, the Kirtlands warbler (Dendroica kirtlandii) is one of the world's most endangered songbirds, and its nesting sites are a conservation priority for the species. These nesting sites are found in jack pine (Pinus banksiana) forests in lower Michigan, which are common elsewhere (e.g., upper Michigan, Minnesota, and Canada) and would nor necessarily be considered conservation priorities were it nor for the presence of a highly endangered bird species. Species-based approaches emphasize biological individualism (i.e., stressing the value of individual species), whereas ecosystem-based approaches emphasize the importance of interactions between genes, species, and biophysical processes.

Species-based approaches to setting conservation priorities are usually expressed in terms of two general objectives. The first is to conserve rare or threatened individual species. Species conservation priorities, and programs to protect them, often generate considerable response from the general public and political authorities. Save the tiger, save the panda, save the redwoods, elephants, whooping cranes, or the California condor, are frequently heard examples of such individual species conservation priorities. Priorities in these cases may be identified simply as the species (wherever they are found), or specific habitats critical to the survival of the species of concern. For example, conserving the whooping crane (Grus americana) has been a conservation priority for the U.S. Fish and Wildlife Service for nearly 50 years. With a population reduced to only 15 individuals in 1942 (Johnsgard, 1991), efforts to save the species from extinction have included designating the cranes' winter habitat in Texas as a national wildlife refuge, artificially re-establishing a second flock, and closely monitoring the original flock.

Box 2.2 The Use Of Systematic To Assess Priorities Most species-based approaches to conservation assume that all species are taxonomically equivalent. For example, when species richness is used to identify priorities, each species is given equal weight in making decisions about where to focus conservation efforts. This assumption is troubling for many biologists and conservationists who believe that some species are more important to conserve than others. In particular, conserving species that are the only representatives of a genus, family, or higher taxonomic group will do more to conserve biodiversity than saving species with many close relatives at the genus or family level. Using cladistic analysis12 and quantitative weighting techniques, systematists are becoming actively involved in developing new approaches for identifying conservation priorities (see Daugherty et al., 1990; Faith, 1992; Forey et al., 1994; May, 1990; Vane-Wright et al., 1991). The use of systematics in priority-setting efforts is appealing because it provides a firm biological and evolutionary basis for conservation. Such approaches have the potential to maximize the conservation of evolutionary pathways that more traditional species-based approaches do not. Robert May (1990) believes the combination of quantitative measures of taxonomic distinctness with more familiar ecological considerations of abundance and geographic distribution are vital to future conservation efforts. While there is considerable appeal to using quantitative measures of species relationships to identify priorities, there are also serious limitations as well. First, such approaches are even more limited by a lack of information than species-based approaches - the cladistic relationships of the vast majority of organisms are simply unknown. For the time being, cladistic analysis is possible only for limited number of plant and animal groups. Second, cladistic approaches are mainly concerned with conserving a representative genetic legacy of evolutionary history. While this is an important conservation objective, biodiversity has many values that are independent of evolutionary history and taxonomic distinctiveness. Advances in systematics and the growing interest of systematists in conservation, however, suggest the use of systematic tools to determine conservation priorities - in combination with other types of species and ecosystem-based analysis - will expand in coming years.

Species-based conservation priorities are sometimes driven by factors other than endangerment, such as species importance. Species importance may be defined in economic terms (e.g., wild relatives of maize or coffee) or in ecological terms (e.g., "keystone" species). It could be argued, for example, that it is more important to conserve a keystone species whose loss could trigger the greatest number of secondary extinctions than to conserve a more endangered non-keystone species. Symbolism can also be important in identifying species conservation priorities, as in the case of efforts to protect "national" birds such as the bald eagle in the United States or the Saint Lucian parrot in Sr. Lucia.

The second type of species conservation objective is to conserve habitats characterized by a high degree of species richness or endemism. Usually such objectives are further narrowed to protect habitats critical to a taxonomic grouping of species, birds, or plants, for example. Priorities are usually expressed in the form of specific sires or habitats important to the taxonomic grouping. For example, Birdlife International¹³ has identified 221 localities around the world with unusual concentrations of endemic bird species and labeled them as high priority sires for conservation (Bibby et al., 1992).

A species-based approach to biodiversity protection usually begins with several assumptions. The first is that species are discrete genetic groupings that best represent taxonomic distinctiveness. The second assumption is that species are optimal indicators of biodiversity since they package genetic diversity on the one hand, and form the building blocks of ecosystems on the other. Species richness is thus assumed to be relatively indicative of other biodiversity values - e.g., areas of concentrated species richness are likely to also represent considerable ecological heterogeneity or diversity.¹⁴ Species-based approaches often - but nor always - implicitly assume that some species are more important than others.

Some of the advantages and disadvantages to using species-based approaches to setting biodiversity conservation priorities are summarized in Box 2.3.

Ecosystem-Based Approaches

Ecosystem-based approaches to setting conservation priorities have been increasingly favored both because knowledge of variation at the species and genetic levels is so poor, and because entire ecosystems, nor merely isolated species, are under threat. Conservation of communities or ecosystems can preserve large numbers of species in a self-sustaining unit, while rescuing individual species has proven to be difficult, often ineffective, and extraordinarily expensive (Reid, 1992a). In the long run, spending $1 million on habitat conservation might conserve more species than the same amount of money spent to conserve a handful of threatened species. For these and other reasons, some approaches to setting conservation priorities are based on ecosystem or biogeographic classifications. Scott et al. (1991) make the following case for ecosystem-based approaches to identifying biodiversity priorities:

"Clearly, it is inefficient to save selected species while allowing the natural communities and ecosystems that support them (along with myriad inconspicuous species) to deteriorate. It would be wiser, surely, to identify and manage functioning representatives of each ecosystem type for the maintenance of native biodiversity. While very localized species, likely to be missed by a network of biodiversity management areas, would still require individual protection programs, such an integrated conservation strategy would ensure that the vast majority of species never become endangered."

Ecosystem approaches to setting biodiversity conservation priorities seek to conserve biodiversity by protecting most species within conservation areas that are representative of the array of more or less well-defined ecosystems or natural communities. A major challenge facing ecologists in many areas is how to classify ecosystems and at what scales. In any case, ecosystem approaches for identifying conservation priorities use multiple criteria such as species richness, endemism, and abundance, as well as considerations of the physical environment, ecological processes, and disturbance regimes (e.g., fire, storms, floods, drought, etc.) that help to define ecosystems.

The basic objective of most ecosystem-based approaches is to conserve the range of habitats (including their constituent species) and ecological processes found within the geographic scale of interest. Ecosystem-based approaches are sometimes favored because they can be used as a surrogate for detailed species knowledge. But ecosystem-based approaches also have value in their own right since they can protect habitats that might never be considered by species-based approaches. For example, ecological approaches may identify sites such as migration habitats, or important areas for the exchange of energy and nutrients, such as mangrove forests, that species-based approaches overlook. In the view of many ecologists, ecosystems are the most complex biological systems and include interactions and processes that represent a viral aspect of biodiversity nor captured in priority analysis based on a species approach. In short, conserving the whole (i.e., a healthy ecosystem) is worth more than conserving the sum of its parts (the species that are found in an ecosystem).

Box 2.3 Advantages And Limitations Of Species-Based Approaches Advantages Species-based approaches give the ability to selectively focus on those species that are most threatened, or those that are most valued from a particular perspective. In some cases, species-based approaches can be used as an efficient proxy for protecting natural communities or habitats in place of more complicated ecosystem approaches (e.g., using the "function" criterion to identify priority "keystone species" whose conservation would safeguard many dependent species).16 Species-based priorities are more likely to be understood and supported by the public than ecosystem-based approaches - people are fascinated by large mammals, but many have a difficult rime recognizing or understanding ecosystems and ecological diversity.17 Species-based approaches may be preferable in many areas where "natural" ecosystems no longer exist or have been heavily modified. Limitations Species definitions can vary - one biologist's species is another biologist's subspecies, or a different species altogether.18 For many parts of the world, the breeding patterns and other basic life history traits are unknown for the vast majority of species, and most species have yet to be "discovered" or even named by science.19 Monitoring and evaluating the success of species-based approaches can be difficult - it is easier, for example, to measure the loss of a hectare of forest or other natural habitat than it is to monitor changes in species numbers. Hotspots" (concentrations of species richness and endemism) for one taxonomic group are nor necessarily "hotspots" for another taxonomic group.20 Relying on species-based approaches, especially those that emphasize "threat" criteria, to identify priorities may leave decision makers with limited and restrictive conservation options. Actions to protect the species may preclude any sustainable use of the species (or its habitat) - uses which may have been possible at an earlier time.21

Protected areas are the most commonly used measure to conserve ecosystems. Not surprisingly, most ecosystem-based approaches to setting biodiversity priorities are designed to identify new protected areas or to strengthen existing areas. The 1982 IUCN Bali Action Plan (IUCN, 1984), for example, called for the establishment of a worldwide network of national parks and protected areas covering all terrestrial ecological regions. As part of the Action Plan, IUCN sponsored several efforts to evaluate regions around the world to determine the proportion of major biogeographic regions and habitat types included in protected areas, as well as the threats that face them, the need for action, and their conservation importance. Reviews were published for the Indo-Malayan Realm (MacK-innon and MacKinnon, 1986a), the Afrotropical Realm (MacKinnon and MacKinnon, 1986b), and Oceania (Dahl, 1986). During the past decade, similar efforts have been carried our at the national level in countries around the world (see McNeely et al., 1994).

Other measures besides protected areas can be used to conserve ecosystems (see UNEP, 1995). These include land management practices that avoid threatening species and disrupting ecological processes, and a wide range of legal and economic incentives to encourage habitat protection outside of protected areas. Ecosystem-based approaches could be used to identify areas where land management practices may need to be changed through the use of various legal and economic policies, including incentives to landowners.

Grumbine (1992) suggests ecosystem management should be practiced over a broad area including, but nor confined to, protected areas. To conserve biodiversity, he suggests ecosystem management should pursue four goals:

1. protecting enough habitat for viable populations of all native species in a region;
2. managing at regional scales large enough to accommodate natural disturbances (fires, wind, climate change, etc.);
3. planning over a period of centuries so that species and ecosystems may continue to evolve; and
4. allowing for human use at levels that do nor result in significant ecological degradation. Some of the advantages and limitations of ecosystems approaches are summarized in Box 2.4.

Integrative Approaches

Since Aristotle, science has had a tendency to break complex phenomena down into component parts and treat them as if they had little relationship to each other. Biodiversity thus becomes genes, species, populations, communities, and ecosystems, each with its separate constituent biological disciplines. And to this day, the natural world is usually viewed as standing quite apart from the human world - uncorrupted in the view of some, unharnessed in the view of others. Conservation priorities have frequently reflected these views - endangered species are to be protected in pristine natural habitats, protected areas sanitized of human influence.

However, during the past decade, many ecologists have begun to challenge these ways of viewing nature and its biological composition. In other words, biodiversity cannot be understood without looking at all of the hierarchical levels and their interactions. At the same time, advances in ecology, paleobiology, and conservation biology are calling into question the very meaning of a "natural" ecosystem. This has prompted some to go so far as to state that the overarching goal of ecological management should be to maximize human capacity to adapt to changing ecological conditions (Reid, 1994), not some romantic notion of maintaining natural "biological integrity."

The more holistic views of biology, together with the realization that humans are almost everywhere a vital part of the ecological landscape, have begun to influence the way in which biodiversity conservation priorities are set. These views emphasize that non-biological factors have a role to play in setting conservation priorities and that diversified strategies are needed to adapt to the myriad cultures and value systems around the world.

They emphasize the use of multiple biological and non-biological criteria. To accommodate the dynamic nature of ecosystems, holistic approaches to identifying biodiversity conservation priorities emphasize looking across the entire landscape - protected and unprotected, natural and heavily modified. The objectives of such approaches are nor necessarily the preservation of biodiversity for its own sake, but maximizing life's capacity to adapt to changing conditions. In a sense, it is nor biology but social issues - the desire to have an environment that supports human welfare - that are the unifying force of integrative approaches to identify biodiversity conservation priorities.

Box 2.4 Advantages And Limitations Of Ecosystem-Based Approaches Advantages Once some meaningful classification of ecosystems or habitats is developed, their size and distribution, unlike species populations, is relatively easy to determine. If representative ecosystems are conserved in large enough areas, the vast majority of species and much of their genetic diversity will be protected as well. Ecological processes (e.g., nutrient cycling, hydrological regulation, micro- and meso-climatic regulation, the maintenance of disturbance regimes upon which many species depend, etc.) are essential to the survival of many species. Only ecosystem-based approaches are likely to ensure the protection of these vital links to biodiversity. Ecosystem-based approaches are the most cost-effective way to identify conservation priorities that include a wide spectrum of biodiversity. If little is known about species distributions and conservation status, and time and financial resources are limited, habitat or ecosystem-based approaches are the only realistic option for analysis. Limitations What constitutes a "natural" ecosystem? Many ecosystem-based approaches attach priority to natural habitats (e.g., MacKinnon and MacKinnon, 1986a). In reality, nearly all ecosystems have been influenced to varying degrees by human activities.22 Despite many attempts to classify ecosystems, there is still no internationally recognized standard and most countries, including the United Stares,23 are still without a consensus classification scheme.24 Ecosystem-based approaches to identifying conservation priorities fail to include all rare or potentially endangered species. Localized species will sometimes be left our of priorities determined by ecosystem analysis, especially in the tropics where species ranges are typically quite small.25

Simply stared, the objective of integrative approaches to setting biodiversity priorities is to conserve biodiversity in the presence, nor the absence, of humans. This means setting priori-ties in the human-dominated landscapes that are found over two-thirds of the earth's land surface. Integrative approaches have also evolved because people realized that: 1) more than biological criteria are needed to select successful conservation projects, and; 2) conservation is a social and political process where feasibility is often defined in social, economic, and political terms.

Few methods, however, have been developed to identify conservation priorities outside of strictly "natural" landscapes. What does exist are nor so much methodologies for setting conservation priorities as criteria for assessing the social value of biodiversity in the landscape. Several approaches have been proposed or developed (MeNeely et al., 1990) to give more prominence to social factors in the establishment of biodiversity conservation priorities. Other approaches driven principally by biological information are also making more use of social factors, such as the evolving experts workshop process pioneered by Conservation International (Olivieri, et al., 1995).

Some of the advantages and disadvantages to integrative approaches are summarized in Box 2.5.

Box 2.5 Advantages And Limitations Of Integrative Approaches Advantages Integrative approaches can recommend priority areas for conservation that have a greater feasibility of actually being conserved because policy and institutional factors have been considered. Integrative approaches can help link biodiversity to other natural resources valued by humans for other reasons. This means that selected priorities will often have non-biological values that could strengthen political support for conservation actions.26 Integrative approaches can make the evaluation of economic, social, or political factors more explicit and transparent. These factors are usually applied by policymakers in a much less transparent way when priorities defined strictly on biological criteria are presented to them. Limitations Integrative approaches may de-emphasize biodiversity values to balance other social, economic, and political values. The consideration of non-biological factors as co-variables with biological factors could make it difficult to say whether a chosen priority is important mainly because of its biological values or because of the contribution of other variables.27 In many situations, it may be unclear which social, economic, or other non-biological factors are most important to conservation.28 Integrative approaches are largely experimental, and frameworks for evaluating non-biological factors in setting priorities are nor as well developed or tested as many biologically-based frameworks. Social, economic, and other non-biological data are often nor available at the appropriate scale (i.e., these data are usually at the aggregate national level) and some factors (e.g., institutional) can change rapidly and limit the useful life of the priorities.

Endnotes

1. Since information about biodiversity, threats to its conservation, and how it is valued will continue to change, conservation priorities should be revisited on a periodic basis. Knowing what information was used to determine priorities and guide decisions in earlier efforts is therefore viral to an informed reassessment of conservation strategies.

2. On June 4, 1993, President Clinton signed the convention. However, as of October 1, 1995, the U.S. Senate had nor yet ratified the convention. As of June 21, 1995, 118 countries had ratified the convention.

3. This is in terms of a global perspective. It might be noted that the kestrel is less common than the peregrine falcon in some areas (e.g., possibly in Alaska).

4. One method to compensate for this limited knowledge is to rely on patterns in a few well-known species that can serve as indicators of where endemicity might be concentrated.

5. The World Conservation Union (IUCN) has revised the IUCN categories of threat so that they are listed as follows: Extinct, Extinct in the Wild, Critical, Endangered, Vulnerable, Rare, Nor at Risk, Nor Evaluated, and Insufficiently Known.

6. Many plant species are entirely dependent on "flying foxes" for pollination and seed dispersal. On Guam, where the two native species of Pteropus have become extinct and virtually extinct, researchers have documented plant species that are no longer fruiting and others that are declining in abundance, signaling the effects of absent pollinators and seed dispersers (Meffee and Carroll, 1994).

7. The World Heritage Program of the United Nations (UNESCO) does explicitly consider these perspectives in its designation of World Heritage sires. The Papua New Guinea Conservation Needs Assessment (Alcorn, 1994) also explicitly considered social, legal, and cultural factors in its assessment of priorities.

8. See last paragraph of preamble to the Convention on Biological Diversity (UNEP, 1992).

9. Systematics is the study of biological classification (species, genus, family, order, etc.).

10. Co-adapted gene complexes are groups of alleles on one or more genes that adapt to the same selective pressures experienced in a particular environment.

11. Some plants and invertebrates, however, are physiologically bisexual; they can breed with themselves and do not breed with other individuals.

12. Cladistics is a taxonomic system used to classify organisms on the basis of evolutionary relationships. It uses a dichotomous branching scheme to develop ancestral "trees" or cladograms that can be used to quantitatively assess how closely related species are. This is done by tracing the shared possession of derived characters (e.g., morphological features such as beak structure in birds) back to a common parent taxon.

13. Formerly known as the International Council for Bird Preservation (ICBP).

14. This is nor always a reliable indicator, however, since species richness in many areas is poorly known.

15. For example, those concerned with the conservation of agricultural diversity will find a species-based approach more suitable since ecosystem-based approaches use a broad net (or a coarse filter) that does nor pinpoint agriculturally important species.

16. Similarly, using the "feasibility" criterion to identify priority "charismatic megavertebrates" with large habitat requirements may lead to conservation efforts that protect many other species, various natural communities, and even large samples of several major ecosystems. For example, the habitat requirements of the grizzly bear in North America, or the elephant in Africa, are likely to encompass the habitat requirements of hundreds or thousands of other species in a wide range of taxonomic groups.

17. In some cases, such as "tropical rainforests" in general or old-growth forests in the U.S. Pacific Northwest, ecosystem conservation has the potential to generate considerable public support.

18. Among the criteria for making species determinations are morphological discontinuity (i.e., large difference in size and appearance), interbreeding ability (physiological factors that prevent breeding), reproductive isolation (i.e., organisms cannot interbreed because of physical geographic barriers such as mountain ranges that separate two similar populations), relationships of ancestry and descent, ecological adaptation, and generic cohesion (Rojas, 1992). The problem is that the various criteria can cause a non-congruence between species classifications. This is especially true in plants where breeding (e.g., natural hybridization), genetics (e.g., polyploidy or multiple sets of genes), and evolutionary histories (e.g., reticulate evolution or reversion to earlier forms) can further complicate taxonomic determinations. In other words, how does one determine biodiversity conservation priorities when it is nor entirely clear what a species is in the first place? Even with some of the better known vertebrate species, different taxonomies can be used to obtain different priority rankings.

19. Even in countries such as the United States, the inventory of invertebrates species, for example, is far from complete. Moreover, vital data on population sizes, geographic distribution, and basic life history traits and habitat requirements are poorly known for the overwhelming majority of the world's species.

20. See, for example, Prendergast et al. (1993).

21. These considerations have generated a debate in the United States over the need to supplement or revise the Endangered Species Act so that ecosystem/habitat protection is emphasized rather than last-minute efforts to conserve an individual species (Reid, 1992b).

22. In some parts of the world (e.g., Europe, the Mediterranean region, Japan), virtually all ecosystems are heavily modified after centuries or several millennia of human culture. See Reid (1994) for an interesting discussion on the limits of using "natural" as a modifier for the definition of conservation objectives.

23. The most widely used classification scheme in the United Stares is the Bailey's Ecoregions system (Bailey and Hogg, 1989). Although widely used, other systems are used as well and The Nature Conservancy is developing a new classification system for the United Stares that it hopes will become the standard. Bailey (1989) also has devel-oped a global ecoregion system.

24. Ecosystems, like species, vary greatly and are poorly understood. Ecosystems are difficult to define since their size, composition, complexity, and distribution change with scale in both rime and space. Nor surprisingly, ecologists differ in their descriptions and definitions of ecosystems.

25. There will always be some need for individual species protection programs, even if comprehensive ecosystem protection programs are implemented.

26. For example, a priority area that has significant watershed value or tourism potential (in addition no biodiversity value) may be more socially and politically viable than an area selected solely for its biodiversity values.

27. This limitation could be overcome by making in clear exactly what factors (biological and non-biological) were considered, and how much weight was given no each. Biological and non-biological factors should be kept separate until the final integration stage.

28. This, of course, is also a problem for biological criteria, bun the uncertainties with respect to non-biological factors will generally be greater.

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