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The Importance of Species

The Importance of Species: Perspectives on Expendability and Triage

Peter Kareiva
Simon A. Levin
Copyright Date: 2003
Pages: 448
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  • Book Info
    The Importance of Species
    Book Description:

    A great many species are threatened by the expanding human population. Though the public generally favors environmental protection, conservation does not come without sacrifice and cost. Many decision makers wonder if every species is worth the trouble. Of what consequence would the extinction of, say, spotted owls or snail darters be? Are some species expendable?

    Given the reality of limited money for conservation efforts, there is a compelling need for scientists to help conservation practitioners set priorities and identify species most in need of urgent attention. Ecology should be capable of providing guidance that goes beyond the obvious impulse to protect economically valuable species (salmon) or aesthetically appealing ones (snow leopards). Although some recent books have considered the ecosystem services provided by biodiversity as an aggregate property, this is the first to focus on the value of particular species. It provides the scientific approaches and analyses available for asking what we can expect from losing (or gaining) species.

    The contributors are outstanding ecologists, theoreticians, and evolutionary biologists who gathered for a symposium honoring Robert T. Paine, the community ecologist who experimentally demonstrated that a single predator species can act as a keystone species whose removal dramatically alters entire ecosystem communities. They build on Paine's work here by exploring whether we can identify species that play key roles in ecosystems before they are lost forever. These are some of our finest ecologists asking some of our hardest questions.

    They are, in addition to the editors, S.E.B. Abella, G. C. Chang, D. Doak, A. L. Downing, W. T. Edmondson, A. S. Flecker, M. J. Ford, C.D.G. Harley, E. G. Leigh Jr., S. Lubetkin, S. M. Louda, M. Marvier, P. McElhany, B. A. Menge, W. F. Morris, S. Naeem, S. R. Palumbi, A. G. Power, T. A. Rand, R. B. Root, M. Ruckelshaus, J. Ruesink, D. E. Schindler, T. W. Schoener, D. Simberloff, D. A. Spiller, M. J. Wonham, and J. T. Wootton.

    eISBN: 978-1-4008-6677-9
    Subjects: Biological Sciences

Table of Contents

  1. Front Matter
    (pp. i-iv)
  2. Table of Contents
    (pp. v-viii)
  3. Contributors
    (pp. ix-xii)
  4. Preface
    (pp. xiii-xiv)
  5. Foreword
    (pp. xv-xviii)

    Not everyone is enthusiastic about protecting biodiversity. The practice of conserving species and biodiversity requires major societal sacrifices, and in many cases cannot be accomplished without substantial economic costs. Given these costs, it is not surprising that members of the public often ask conservationists whethereveryspecies must be protected. Of course, many of the hard decisions surrounding conservation have nothing to do with science—they represent a choice among values and are of a political, ethical, and philosophical nature. Still, there is a need for scientists to respond to questions about the consequences of losing particular species or segments...


    • [Part I Introduction]
      (pp. 1-4)
      P. Kareiva and S. A. Levin

      For decades, Bob Paine has exhorted ecologists to conduct field experiments in which species are removed and the community-wide responses to those removals noted. The lessons learned from these manipulations of natural communities have been impressive and have reshaped our understanding of ecological systems. Given the central role of experiments in community ecology, it is surprising that the large body of results from species-removal experiments has been so neglected in the debate surrounding the importance of biodiversity. After all, there is no more straightforward way of examining the importance of a species than to remove it. Thus, experimental investigations of...

    • Chapter 1 Native Thistles: Expendable or Integral to Ecosystem Resistance to Invasion?
      (pp. 5-15)
      Svata M. Louda and Tatyana A. Rand

      One way of addressing the question of whether some species are expendable is to ask what role, if any, a minor species, even one that seems obnoxious, plays in the functioning of its community. Thistles (Cirsiumspp.) are prickly plants native to North America that are numerically minor and are often considered unattractive or undesirable. So, thistles might be considered expendable. Yet, can we assume that such minor, seemingly undesirable species can be eliminated without disrupting important interdependencies or losing key ecological services? Our long-term studies of thistle-insect interactions are beginning to provide evidence that even such species may play...

    • Chapter 2 The Overriding Importance of Environmental Context in Determining the Outcome of Species-Deletion Experiments
      (pp. 16-43)
      Bruce A. Menge

      Classic ecological experiments such as those of Paine (1966, 1974) leave little doubt that species loss can have profound consequences on a community. At the same time, there can be striking variation in these consequences. Thus, to understand the consequences of a loss of species from a community, one must learn the factors that are responsible for the variation observed in studies of removals, losses, introductions, or invasions of species. An ultimate goal in such efforts is prediction: can we forecast what will happen when a species is deleted from a community or ecosystem? It is still far from clear...

    • Chapter 3 Species Importance and Context: Spatial and Temporal Variation in Species Interactions
      (pp. 44-68)
      Christopher D. G. Harley

      The science of ecology must deal with two emerging realities: (1) the human presence on Earth is having an effect on virtually all species, and (2) these effects do not always work in humanity’s best interest. Many academic disciplines—forestry, fisheries biology, and conservation biology, to name a few—focus on developing strategies for managing and sustaining nonhuman species, and for minimizing the harm that we indirectly inflict upon ourselves through resource extraction, food production, and economic development. The common thread uniting these fields is the idea that the benefits of human endeavor (redwood decks, grilled salmon, and sport utility...

    • Chapter 4 Effects of Removing a Vertebrate versus an Invertebrate Predator on a Food Web, and What Is Their Relative Importance?
      (pp. 69-84)
      Thomas W. Schoener and David A. Spiller

      Ecologists routinely simulate species loss. At first, these simulations were carried out mainly in theory, but over the last couple of decades, they have increasingly been carried out in practice via so-called “removal experiments.” It is tempting to think that such experiments bear on the question of species importance, since they involve comparisons among communities with and without the removed species. The spatial scale is of course contracted: species are typically eliminated from very small spatial units (Kareiva and Andersen 1988). For procedural reasons as well as the need to capture the underlying spatial structure, the bias toward a small...

    • Chapter 5 Understanding the Effects of Reduced Biodiversity: A Comparison of Two Approaches
      (pp. 85-104)
      J. Timothy Wootton and Amy L. Downing

      This volume poses the question of when, if ever, a species is expendable. Even if we believe that species are never expendable, many species are at risk of extinction, and we need to prioritize efforts to conserve them. Before we can even begin to address these issues, however, we must be capable of determining the consequences of species extinction, with the ultimate goal of predicting an extinction’s effects on the ecosystems on which we depend. Meeting this challenge also requires developing an understanding of the effects of extinction in natural ecosystems. Therefore, it is worth considering what goals we should...


    • [Part II Introduction]
      (pp. 105-108)
      P. Kareiva and S. A. Levin

      Most contemporary discussions of biodiversity and species expendability begin and end with humans—begin, because we humans are the dominant agents changing the number and identity of species in most communities; and end, because we humans expend considerable energy attempting to affix value to biodiversity in terms of the services it provides to us. The following six chapters follow in this tradition, dwelling on the services of species and biodiversity, and on the dramatic impacts of humans on species assemblages.

      Two theoretical papers take very different modeling approaches to examine the value of biodiversity. Naeem argues for focusing on ecosystem...

    • Chapter 6 Models of Ecosystem Reliability and Their Implications for the Question of Expendability
      (pp. 109-139)
      Shahid Naeem

      The realization that a single species in a community may be the equivalent of a keystone in an arch has profound implications for the other—non-keystone—species in a community. Paine’s seminal contribution (1966) produced a compelling picture of nature in which the loss of a single species could lead to the local extinction of other species while its presence could foster the local coexistence of many species. The unintended and somewhat dangerous corollary of this powerful idea, however, is that many species are of lesser importance. In the same way the keystone of an arch is often protruded and...

    • Chapter 7 Predicting the Effects of Species Loss on Community Stability
      (pp. 140-160)
      Dan Doak and Michelle Marvier

      The question of how species richness and community organization may influence ecological stability has fostered a long-standing debate, recently revived through a spate of new field and microcosm studies (e.g., Tilman 1996; Naeem and Li 1997; McGrady-Steed et al. 1997) and modeling efforts (e.g., Doak et al. 1998; Hughes and Roughgarden 1998; Yachi and Loreau 1999). This new research has led to renewed claims regarding the importance of species diversity for various community and ecosystem functions as well as increasing efforts to develop simple principles to guide conservation policy and practice (e.g., Pimm 1991; Naeem 1998; Schwartz et al. 2000;...

    • Chapter 8 One Fish, Two Fish, Old Fish, New Fish: Which Invasions Matter?
      (pp. 161-178)
      Jennifer L. Ruesink

      The impacts of introduced species, both economic and ecological, grow on an almost daily basis as new species invade and new calculations are made (Simberloff 1981; Moyle et al. 1986; Humphries et al. 1992; OTA 1993; Cox 1999; Pimentel et al. 2000). Although the impacts of invasions capture public attention, most ecological theory focuses on the establishment of invaders, not their effects (Crawley 1986; Rejmánek and Richardson 1996; Williamson and Fitter 1996a, b; Veltman et al. 1996; Crawley et al. 1997; Tilman 1997a; Goodwin et al. 1999; Shea and Chesson 2002; a notable exception is Parker et al. 1999). Understanding...

    • Chapter 9 Ecological Gambling: Expendable Extinctions Versus Acceptable Invasions
      (pp. 179-205)
      Marjorie J. Wonham

      Species extinctions and invasions are increasingly altering biological communities, generating growing concern about their ecological effects. The central question of this book is how we determine which species removals are most harmful. The complementary question—how we determine which species additions are most acceptable—presents an instructive contrast.

      Species removals and additions are natural processes, and under standing their dynamics and consequences has long kept ecologists busy (e.g., Darwin 1859; Clements 1936; Elton 1958; MacArthur and Wilson 1967; Paine 1966, 1969a; Connell and Slatyer 1977; Pimm 1991; Tilman et al. 1997). Today, however, this natural ebb and flow of species...

    • Chapter 10 Rarity and Functional Importance in a Phytoplankton Community
      (pp. 206-220)
      Daniel E. Schindler, Gary C. Chang, Susan Lubetkin, Sally E. B. Abella and W. T. Edmondson

      Heightened scientific and public interest in biodiversity has been driven by the accelerated rates of species extinctions at local and global scales. The question of which species are expendable derives from the humble realization that society is not able to prevent the extinctions of all species with which humans interact. The benefits of preventing extinctions are often in direct conflict with economic development in human societies. Asking scientists to estimate the expendability of specific species is a seductive solution to asking which species are worth “saving” versus which species will not be missed if they go extinct. The problem of...

    • Chapter 11 Community and Ecosystem Impacts of Single-Species Extinctions
      (pp. 221-234)
      Daniel Simberloff

      Many authors have pointed out that species differ greatly in their importance to their ecosystem and community. Sometimes species matter to other species because they dominate the community in biomass; trees and coral, for example, provide physical structure. Other times, whether a species is common or scarce, some aspect of its activity is crucial to the persistence of the ecosystem. A species may be functionally unique in its ecosystem role; sometimes other species perform the same functions, or could perform them if that species were to disappear. These concepts—importance, function, uniqueness, and redundancy—have given rise to a variety...


    • [Part III Introduction]
      (pp. 235-238)
      P. Kareiva and S. A. Levin

      Can we ever really conclude that a species is expendable? While it is straightforward to identify a research protocol that provides evidence for the value of a species or of biodiversity in general, using science to conclude that a species is expendable seems unbearable to many ecologists and evolutionary biologists. This final section reveals the difficulty that leading ecologists experience when asked to consider a judgment that some species might in fact be expendable.

      First, Leigh points out that our current understanding of the interdependencies among species is so limited, and falls so short of the deep understanding required, that...

    • Chapter 12 Social Conflict, Biological Ignorance, and Trying to Agree Which Species Are Expendable
      (pp. 239-259)
      Egbert Giles Leigh Jr.

      Deciding which species are expendable is a singularly contentious question, at three levels. First, posing it looks very like sitting in judgment on God’s Creation. One need not be religious to be wary of this sort of pride. Second, if we do choose to sit in a judgment seat that belongs to Another, how do we decide what aspects or functions of ecosystems should be preserved or enhanced? Finally, if we are not put off by the orgy of self-centeredness involved in deciding whatwewant from ecosystems, how do we discern whether a particular extinction will bring on consequences...

    • Chapter 13 Which Mutualists Are Most Essential? Buffering of Plant Reproduction against the Extinction of Pollinators
      (pp. 260-280)
      William F. Morris

      By ensuring that plant reproduction occurs, animal pollinators act as essential components of both agricultural and natural ecosystems; hence, human societies depend indirectly on pollinators for both food and “ecosystem services” (Nabhan and Buchmann 1997). To the extent that such services can even be quantified, one estimate puts the value of the benefits humans receive from biotic pollination at about $120 billion annually (Costanza et al. 1997). The magnitude of the dependence of humans and other species on pollinator activities raises an important question: what aspects of the pollinator community are key to its ability to maintain plant populations? One...

    • Chapter 14 The Expendability of Species: A Test Case Based on the Caterpillars on Goldenrods
      (pp. 281-291)
      Richard B. Root

      Any decision that would cause the extinction of a species must be judged on both ethical and scientific grounds. In this chapter I consider only the scientific issues that are raised by such a decision. Specifically, I examine the issue of the expendability of species by taking a well-studied natural community and asking, “Does it contain any species that are functionally so insignificant that there would be no appreciable effects if the species were exterminated?” In other words, are the effects of such a loss so small that they cannot be distinguished from the normal variance in the properties of...

    • Chapter 15 An Evolutionary Perspective on the Importance of Species: Why Ecologists Care about Evolution
      (pp. 292-304)
      Stephen R. Palumbi

      From one point of view, no species in a community can be considered absolutely essential because all species eventually go extinct, and communities tend to persist longer than the life spans of individual species. The average life span of species, measured by the fraction of species in fossil assemblages that can be identified in modern communities, is on the order of 2 million years for mammals and up to 6 million years for marine bivalves (Stanley 1979). Over this time span, communities experience many species extinctions and replacements, the balance of which has long been thought to determine some of...

    • Chapter 16 Recovering Species of Conservation Concern—Are Populations Expendable?
      (pp. 305-329)
      Mary Ruckelshaus, Paul McElhany and Michael J. Ford

      Simply mentioning the notion of species expendability may seem reprehensible, but it is a question raised often when conservation biology meets conservation practice, as in this volume. In particular, when arguing for the value of biodiversity, biologists are faced with the challenge of examining the roles that particular species might play in community function and whether there are redundancies in the functions of certain species. Does every species need to be conserved for our ecosystems to function? The question of expendability also is important in conservation planning that occurs at the species level: does every population need to be saved...

    • Chapter 17 Virus Specificity in Disease Systems: Are Species Redundant?
      (pp. 330-346)
      Alison G. Power and Alexander S. Flecker

      Despite our increasing recognition of the key role that microbes play in ecosystem processes (e.g., Giller et al. 1997; Mills and Bever 1998; van der Heijden et al. 1998), concern over the loss of biodiversity in ecological communities rarely focuses on microbes—particularly pathogenic microbes which are more often targeted for eradication than preservation (but see Windsor 1995). Yet it is becoming clear that disease-causing microbes may be important in shaping biotic communities (Real 1996a), and their diversity significantly influences populations, communities, and ecosystems.

      We are surrounded by examples of the influence of disease on the landscape. One of the...

  9. Conclusion Bob Paine’s Contributions to the Science of Assessing Species Importance: Past, Present, and Future?
    (pp. 347-352)
    P. Kareiva and S. A. Levin

    When community ecology has completed its job, we will be better informed about the likely consequences, both long-term and short-term, of any particular extinction. Of course, there will always be surprises, and prediction will never be perfect; some core of unknowability will linger in any effort at prediction. Currently, however, we have much work to do in developing both the theory and the empirical foundations necessary for accurately predicting the aftermath of species losses. At times, our uncertainty regarding the consequences of losing species can seem overwhelming, even paralyzing. As a cure for the gloom cast by our ignorance, it...

  10. References
    (pp. 353-414)
  11. Index
    (pp. 415-427)