Ecology Species Extinctions
by
Thomas Brooks
  • LAST REVIEWED: 17 May 2019
  • LAST MODIFIED: 26 August 2013
  • DOI: 10.1093/obo/9780199830060-0108

Introduction

The ecology of species extinctions is a topic that cuts through time to the earliest emergence of life on Earth, across space to the planet’s most remote corners, and over taxonomy from the world’s largest animals to teeming invertebrate diversity. Although extinction as a phenomenon has been recognized for centuries (above all, with awareness of dinosaur fossils), most characteristics of extinctions have been realized only since the early 1970s. Above all, these characteristics include selectivity, in at least three forms. Selectivity over time implies that most extinctions occur during discrete periods, referred to as mass extinctions. Five mass extinctions (Late Ordovician, Late Devonian, Late Permian, Late Triassic, and, most recently, end-Cretaceous) occurred through Earth’s geological history, of which the latter, sixty-five million years ago, killed the dinosaurs. Today, human impacts are driving a sixth mass extinction. Selectivity over space implies that most extinctions occur in a few places. This phenomenon results from the small and congruent distributions of many species, as well as those of many threatening processes. Finally, selectivity over phylogeny implies that some groups of species that are closely related (and therefore share many traits) face disproportionately high extinction risk. The greatest uncertainties about species extinctions concern causes, at all time scales. Were the “Big Five” mass extinctions caused by meteorite impacts or volcanism? Were the Pleistocene megafaunal extinctions caused by overkill or climate change? Is the current amphibian crisis caused by a spreading epidemic or a pathogen flourishing under global change? Resolving these controversies is key to extinction ecology as an applied science, because successful conservation policy and practice depend crucially on their answers. In this light, better documentation and analysis of the impacts of actions to prevent extinctions is probably the field’s single most urgent research front.

General Overviews

The field of extinction ecology lends itself well to overview and synthesis, across review papers, edited volumes, technical monographs, and popular science writing. Among review papers, Pimm, et al. 1995 is particularly influential in introducing a standard metric for reporting extinction rates across taxa and time scales. Purvis, et al. 2000 is important in setting the field on the track to become a predictive as well as a descriptive science, and Dirzo and Raven 2003 provides a strong botanical focus (within a literature that is generally animal dominated). Among edited volumes, Lawton and May 1995 is particularly pertinent in bringing together a number of important contributions to the field, while Rosenzweig 1995 is a key contribution among technical monographs. Three powerfully written books stand out among the more popular contributions to extinction ecology: Leakey and Lewin 1995, Quammen 1996, and Wilson 1992.

Extinction Through Earth History

Chronologies of the appearance and disappearance of life (most frequently at the level of genera) in the fossil record form the backbone of attempts to understand extinctions over the Phanerozoic (the last 542 million years). Early work is summarized in a concise synthesis in Raup 1991. Since the early 1990s, three major databases documenting extinctions in the fossil record have been developed: the Fossil Record 2, published by Benton in 1993, the Compendium of Fossil Marine Animal Genera, published by Sepkowski in 2002, and, initiated in 2000, the online, sampling-standardized Paleobiology Database (2012). Each has served as the basis for major analytical publications, with broadly concordant conclusions despite the different coverages and structures of the data: Benton 1995, Bambach 2006, and Alroy 2008, respectively. The incompleteness of the fossil record is a key challenge to interpretation of extinction data, in which light the analysis of the impacts of incompleteness on the relationship between extinction and diversification in Lu, et al. 2006 is an important one. Finally, two important papers draw lessons from extinction in the fossil record for current anthropogenic extinctions: Jablonski 1991 sets the stage for such comparison for early work in extinctions over earth history, with Barnosky, et al. 2011 providing a valuable, up-to-date review.

Mass Extinction Events

The discovery reported in Alvarez, et al. 1980 of excessive iridium in sixty-five-million-year-old strata led to the inference that a meteor impact caused the end-Cretaceous extinction of most dinosaurs and triggered extensive investigation into the “Big Five” mass extinctions of the geological past. Most proximately, it led to the discovery of the “smoking gun,” the Chicxulub Crater, likely to have been caused by the meteor impact, as documented in Alvarez 1997. Jablonski 2008 examines the spatial dynamics of the end-Cretaceous mass extinction. The evidence supporting the hypothesis of meteor impact sixty-five million years ago continues to mount, as reviewed in Schulte, et al. 2010, although Archibald, et al. 2010 makes clear that many paleontologists do not see it as the only cause, or as one that can be generalized to mass extinctions overall. Much recent attention has focused on the end-Permian mass extinction, which killed > 90 percent of marine species, with Basu, et al. 2003, for example, reporting the discovery of 251-million-year-old meteorite fragments that supported the idea that an impact was the cause. Benton 2005 is more cautious, suggesting the massive volcanism concurrent in Siberia as maybe a more likely cause, but admitting that the verdict on the issue is far from closed. Examination of the other mass extinctions has been less extensive, but work on these is also gaining momentum: for example, Ward, et al. 2001 provides important evidence for catastrophic collapse of marine productivity two hundred million years ago, concordant with the end-Triassic mass extinction.

  • Alvarez, L. W., W. Alvarez, F. Asaro, and H. V. Michel. 1980. Extraterrestrial cause for the Cretaceous-Tertiary extinction. Science 208.4448: 1095–1108.

    DOI: 10.1126/science.208.4448.1095Save Citation »Export Citation »

    A brilliant combination of geology, chemistry, astronomy, and ecology, documenting the anomalous presence of iridium (rare on Earth, abundant in meteors) in geological strata 65 million years old, consistent with a hypothesis that the end-Cretaceous mass extinction was caused by extraterrestrial impact.

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  • Alvarez, W. 1997. T. rex and the crater of doom. Princeton, NJ: Princeton Univ. Press.

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    A highly readable account of the discovery and science of the iridium discontinuity, and then of the Chicxulub Crater, off Mexico’s Yucatan Peninsula, the “smoking gun” proving that the end-Cretaceous mass extinction was caused by extraterrestrial meteor impact. Republished as recently as 2008.

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  • Archibald, J. D., W. A. Clemens, K. Padian, et al. 2010. Cretaceous extinctions: Multiple causes. Science 328.5981: 973.

    DOI: 10.1126/science.328.5981.973-aSave Citation »Export Citation »

    A brief letter, arguing that marine regression, volcanic activity, and changes in climatic patterns, as well as meteorite impact, caused the end-Cretaceous mass extinction, and raising doubts about the generality of impacts as drivers of mass extinction through the Phanerozoic, because other craters are not associated with impacts, while other possible drivers, including volcanic activity and marine regression, are. Available online for purchase or by subscription.

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  • Basu, A. R., M. I. Petaev, R. J. Poreda, S. B. Jacobsen, and L. Becker. 2003. Chondritic meteorite fragments associated with the Permian-Triassic boundary in Antarctica. Science 302.5649: 1388–1392.

    DOI: 10.1126/science.1090852Save Citation »Export Citation »

    The authors report meteorite fragments 251 million years old and so hypothesize that impact caused the end-Permian mass extinction. Within two years of this paper, the findings of extraterrestrial noble gas trapped in unusual carbon molecules at the P-T boundary and of a possible impact crater off Australia were both also published by the same team and journal.

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  • Benton, M. J. 2005. When life nearly died: The greatest mass extinction of all time. New York: Thames & Hudson.

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    Overview of the Late Permian mass extinction, 251 million years ago, charting its geology and victims and examining the hypotheses as to its cause, among which Benton views massive volcanism (from the Siberian Traps, in Russia), triggering runaway global warming, as a marginally more likely scenario than that of extraterrestrial impact.

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  • Jablonski, D. 2008. Extinction and the spatial dynamics of biodiversity. Proceedings of the National Academy of Sciences of the United States of America 105.S1: 11528–11535.

    DOI: 10.1073/pnas.0801919105Save Citation »Export Citation »

    Scrutinizes marine bivalve extinctions at the K-Pg boundary to discern that selectivity is reduced in mass extinction, extinctions and subsequent recovery are geographically heterogeneous, and reinvasion from the tropics is a major mechanism for recovery.

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  • Schulte, P., L. Alegret, I. Arenillas, et al. 2010. The Chicxulub asteroid impact and mass extinction at the Cretaceous-Paleogene boundary. Science 327.5970: 1214–1218.

    DOI: 10.1126/science.1177265Save Citation »Export Citation »

    Comprehensive review of evidence supporting the Chicxulub impact as the cause of extinction at the K-Pg boundary. Available online for purchase or by subscription.

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  • Ward, P. D., J. W. Haggart, E. S. Carter, D. Wilbur, H. W. Tipper, and T. Evans. 2001. Sudden productivity collapse associated with the Triassic-Jurassic boundary mass extinction. Science 292.5519: 1148–1151.

    DOI: 10.1126/science.1058574Save Citation »Export Citation »

    Sudden marine productivity collapse, coincident with the sudden extinction of marine plankton (Radiolaria), at the T-J boundary two hundred million years ago. Available online for purchase or by subscription.

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Prehistoric Extinction

Our understanding of species extinction over human prehistory has undergone dramatic revision over recent decades. While traditional interpretations have attributed documented Late Pleistocene extinctions to climate change (“ice age extinctions”), new evidence emerging from continents and, especially, from islands has shifted the balance of evidence toward human overkill as the primary driver. Burney and Flannery 2005 provides an integrated review of continental and island extinctions, while MacPhee 1999 is an important edited volume with contributions tackling a wide range of taxa, geographies, and causes. Flannery 2005, by focusing regionally on Australasia, gives insight into the fate both of continental (Australia, New Guinea) and island (New Caledonia, New Zealand) faunas after human colonization. Balmford 1996 presents the novel concept of extinction filters as using extinction history to explain vulnerability. While placing particular focus on prehistory, all four references draw lessons for current anthropogenic extinctions.

  • Balmford, A. 1996. Extinction filters and current resilience: The significance of past selection pressures for conservation biology. Trends in Ecology & Evolution 11.5: 193–196.

    DOI: 10.1016/0169-5347(96)10026-4Save Citation »Export Citation »

    Clever synthesis proposing “extinction filters”—past extinction events, known or unknown—as explanations for observed variation in vulnerability among the survivors. Available online for purchase or by subscription.

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  • Burney, D. A., and T. F. Flannery. 2005. Fifty millennia of catastrophic extinctions after human contact. Trends in Ecology & Evolution 20.7: 395–401.

    DOI: 10.1016/j.tree.2005.04.022Save Citation »Export Citation »

    Comprehensive review integrating continental megafaunal with island extinctions, judging the lack of synchronicity of extinctions between regions, and general concordance with time of first human contact, as overwhelming evidence for overkill. Highlights climate change interactions as a research priority.

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  • Flannery, T. 2005. The future eaters: An ecological history of the Australasian lands and people. New ed. Sydney, Australia: Reed New Holland.

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    A breathtaking tour of the ecological history of Australia, New Caledonia, New Zealand, and Papua New Guinea, presenting compelling evidence for mass extinction on human arrival in Australia > 35,000 years ago (as well as more-recent extinctions on European colonization of Australia, and in New Zealand). Originally published in 1994.

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  • MacPhee, R. D. E., ed. 1999. Extinctions in near time: Causes, contexts, and consequences. Advances in Vertebrate Paleobiology. New York: Kluwer Academic/Plenum.

    DOI: 10.1007/978-1-4757-5202-1Save Citation »Export Citation »

    An edited volume emerging from the 1997 American Museum of Natural History symposium on “Humans and Other Catastrophes,” encompassing thirteen important papers on Holocene extinctions, including a key paper on freshwater fish by Harrison and Staissny.

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Pleistocene Megafaunal Extinctions

The loss of large mammal species from Europe and America at the end of the Pleistocene c. ten thousand years ago, roughly concordant with the most-recent glaciations, has long been recognized and attributed to climate change. Since the mid-1980s or so, increasing evidence has suggested that human overkill was the primary driver, with the publication of Martin and Klein 1984 representing the key shift in interpretation. Subsequent advances in computer simulation, such as those in Alroy 2001, and in archaeological evidence and dating techniques, such as those used in Faith and Surovell 2009, have added substantial weight to the overkill hypothesis. By contrast, new data from the southern continents show dramatic lack of the global synchronicity that would be expected if climate change was the primary cause. In Australia, for example, Roberts, et al. 2001 documents the great wave of prehistoric megafaunal extinctions that occurred more than 40,000 years ago, rather than the timing c. twenty thousand years ago expected if the extinctions were driven by extreme aridity at the last glacial maximum. Moreover, the integrated global analysis in Surovell, et al. 2005, for elephants and their relatives, shows that extinctions were not just out of synchrony with climate change but were also in synchrony with the onset of human contact. Although some prominent scientists such as Grayson and Meltzer 2003 still favor major roles for climate change, current reviews such as Barnosky, et al. 2004 lean toward anthropogenic overkill as a primary driver, leaving open a subsidiary role for climate change, especially in Europe. Barnosky 2008 gives an innovative perspective by considering the biomass of wild megafaunal loss over time, and its progressive replacement by the biomass of humans and their domesticates.

First-Contact Island Extinctions

While the extinctions of megafauna at the end of the Pleistocene spanned roughly forty thousand years on the continents, recent work documented another extinction wave, generally of smaller-bodied species, that coincides with the arrival of humans to islands during the last two thousand years. Human overkill is widely accepted as the primary cause of these prehistoric island extinctions. The scientific frontier is focused on magnitude and geography, as fossil evidence has been unearthed from more and more islands and taxonomic groups. For Hawai‘i, Olson and James 1982, a pioneering work, first unveiled fossil evidence for pre-European extinction in an island avifauna. Pimm, et al. 1994 analyzes the growing body of documentation of Pacific bird extinctions to estimate that the number of extinct species not yet known would roughly double the known avifauna. Subsequent key analyses shed light on the extraordinary rapidity of island extinctions on first contact (as, for example, the documentation of the extinction of New Zealand’s moas, in Holdaway and Jacomb 2000) and on comparative timing of extinctions on islands relative to adjacent continents (exemplified by the finding, in Steadman, et al. 2005, of much-later survival of sloths in the Caribbean than in North and South America). In terms of synthetic work, Steadman 2006 provides an overview of bird extinctions from across the South Pacific, Goodman and Patterson 1997 is the key edited volume on anthropogenic extinction in Madagascar, and Tennyson and Martinson 2006 gloriously illustrates insight into New Zealand’s extinct birds. By the time of European expansion from 1500, only the Galapagos, St. Helena, and the Indian Ocean and subantarctic islands remained uncolonized and unaffected by anthropogenic extinction.

  • Goodman, S. M., and B. D. Patterson, eds. 1997. Natural change and human impact in Madagascar. Washington, DC: Smithsonian Institution Press.

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    Comprehensive edited volume, with prehistoric extinctions over the last two thousand years as a major focus.

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  • Holdaway, R. N., and C. Jacomb. 2000. Rapid extinction of the moas (Aves: Dinornithiformes): Model, test, and implications. Science 287.5461: 2250–2254.

    DOI: 10.1126/science.287.5461.2250Save Citation »Export Citation »

    The authors apply a Leslie matrix population model to show simulated times to extinction of < 160 years for eleven moa species, subsequent to Maori arrival in New Zealand in the late 1200s. Validation with archaeological carbon-14 dating supports extinction within a century—the fastest documented megafaunal extinction. Available online for purchase or by subscription.

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  • Olson, S. L., and H. F. James. 1982. Fossil birds from the Hawaiian Islands: Evidence for wholesale extinction by man before Western contact. Science 217.4560: 633–635.

    DOI: 10.1126/science.217.4560.633Save Citation »Export Citation »

    First synthesis of zooarchaeological exploration of Hawai‘i, documenting thirty-nine bird species to have become extinct contemporaneous with Polynesian colonization.

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  • Pimm, S. L., M. P. Moulton, and L. J. Justice. 1994. Bird extinctions in the central Pacific. Philosophical Transactions of the Royal Society of London B 344.1307: 27–33.

    DOI: 10.1098/rstb.1994.0047Save Citation »Export Citation »

    A clever application of mark-recapture analysis to Pacific birds known only from bones, only from skins, and both, to estimate the number of species known from neither. From this, Pimm and colleagues infer that at least double the currently known number of species existed before human arrival. Available online for purchase or by subscription.

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  • Steadman, D. W. 2006. Extinction and biogeography of tropical Pacific birds. Chicago: Univ. of Chicago Press.

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    Encyclopedic review of Pacific island ornithology, drawing on fossil evidence to provide insight into the collapse of the region’s avifauna over the last few thousand years. Steadman is an unapologetic empiricist: after devoting most of the book to precise documentation of Pacific birds according to geography (chapters 5–8) and taxonomy (chapters 9–15), he then uses these data to take potshots at theory and synthesis in extinction ecology and biogeography (chapters 16–22).

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  • Steadman, D. W., P. S. Martin, R. D. E. MacPhee, et al. 2005. Asynchronous extinction of late Quaternary sloths on continents and islands. Proceedings of the National Academy of Sciences of the United States of America 102.33: 11763–11768.

    DOI: 10.1073/pnas.0502777102Save Citation »Export Citation »

    Radiocarbon dating places the extinction of 90 percent of the Phyllophaga (sloths) lost in the Late Quaternary at 11,000 years ago (North America), 10,500 years ago (South America), and 4,400 years ago (Caribbean), a chronology consistent with human arrival (and hence suggesting overkill) but not with climate change.

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  • Tennyson, A., and P. Martinson. 2006. Extinct birds of New Zealand. Wellington, New Zealand: Te Papa.

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    Comprehensive species accounts for the fifty-eight species of birds (> 25 percent of the region’s avifauna) documented to have become extinct in New Zealand (plus Australia’s Norfolk and Macquarie Islands) since human colonization in the late 1200s; spectacular paintings by Martinson.

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Iconic Modern Extinctions

Species extinction attracts fatal fascination and passionate debate. In the case of extinctions in the geological record and in the Late Pleistocene, the lack of “smoking gun” evidence has led to deep controversies over drivers of extinction. By contrast, scientists have had the opportunity to observe modern extinctions as they unfold, or, at least, while the corpses are still fresh. These modern extinctions, driven by the impacts of European expansion during the last five centuries, have received encyclopedic scrutiny, with extensive primary research and numerous overviews and syntheses. Much of this is focused on iconic species. For example, Fuller 2002 documents in painstaking detail the loss of the world’s most famous extinct species, the dodo (Raphus cucullatus). Among other taxa, Owen 2004 describes the loss of the thylacine (Thylacinus cynocephalus); Crump, et al. 1992, the golden toad (Incilius periglenes). Some authors have documented modern extinctions in breadth rather than depth, with the beautifully illustrated Flannery and Schouten 2001, on 103 recently extinct vertebrate species, standing out. Similar attention has been focused on species that are “Extinct in the Wild” and survive only in zoos, aquaria, or cultivation. Examples include Juniper 2002, which is an account of the extinction of Spix’s macaw (Cyanopsitta spixii), and Thomson 1990, a review of the Franklin tree, Franklinia alatamaha. However, documentation of extinction is often hard to come by, and so a number of species that are “Possibly Extinct” are not yet considered to have been proven extinct. A tragic current example documented in Turvey 2009 is the Chinese river dolphin, Lipotes vexillifer, very likely to have been lost over the first decade of the 21st century, along with many of the rest of the Yangtze’s freshwater species. Finally, some researchers have provided geographic or ecological monographs about modern extinctions, exemplified by the review in Wilcove 1999 of species extinction (and conservation) in the United States.

  • Crump, M. L., F. R. Hensley, and K. L. Clark. 1992. Apparent decline of the golden toad: Underground or extinct? Copeia 1992.2: 413–420.

    DOI: 10.2307/1446201Save Citation »Export Citation »

    The first alarm sounding at the disappearance of the spectacular Incilius periglenes, from Monteverde cloudforest in Costa Rica. Hundreds of toads emerged to breed each year up until 1987, but only twenty-nine tadpoles metamorphosed that year. Just ten adults were found in 1988, one in 1989, and the species has not been recorded since. Available online for purchase or by subscription.

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  • Flannery, T., and P. Schouten. 2001. A gap in nature: Discovering the world’s extinct animals. New York: Atlantic Monthly Press.

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    A powerful survey of the thirty-five mammals, sixty-four birds, and four reptiles that human impacts have driven extinct since 1500, and for which sufficient material remains to have allowed Schouten to paint spectacular illustrations of each species.

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  • Fuller, E. 2002. Dodo: From extinction to icon. London: Collins.

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    Exhaustive and richly illustrated survey of the history, biology, and late-17th-century extinction of Raphus cucullatus, from Mauritius, and the related species on Réunion and Rodrigues, along with documentation of the role of the species in popular culture. Fuller wrote a similarly comprehensive monograph on the great auk, Pinguinus impennis, in 1999.

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  • Juniper, T. 2002. Spix’s macaw: The race to save the world’s rarest bird. London: Fourth Estate.

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    The tragic history of the decline of the spectacular Cyanopsitta spixii, from the caatinga of northwestern Brazil, up until the loss of the last wild individual in 2000. There is still an official captive population of seventy-one birds in Brazil, Germany, Qatar, and Spain, managed by the Brazilian Working Group for the Recovery of Spix’s Macaw; these birds are successfully reproducing, and there are maybe fifty more unregistered captive birds elsewhere.

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  • Owen, D. 2004. Tasmanian tiger: The tragic tale of how the world lost its most mysterious predator. Baltimore: Johns Hopkins Univ. Press.

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    An idiosyncratic but comprehensive account of the decline of the thylacine (Thylacinus cynocephalus), up to its extinction in the wild in 1933 (and in Hobart Zoo in 1936), including coverage of controversial subjects such as cloning and putative recent sightings. The video of the last individual is also well worth watching.

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  • Thomson, K. S. 1990. Benjamin Franklin’s lost tree. American Scientist 78.3: 203–206.

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    Review of the history, taxonomy, and disappearance of Franklinia alatamaha from the one site where it was ever known in the wild. Thomson considers the species to have been a Pleistocene relic, hanging on near the Altamaha River in Georgia until it was finally driven to extinction in the early 1800s. Fortunately, a number survive in gardens elsewhere in the United States. Available online for purchase or by subscription.

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  • Turvey, S. 2009. Witness to extinction: How we failed to save the Yangtze River dolphin. Oxford: Oxford Univ. Press.

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    Tragic indictment of collective failure to save the Baiji Lipotes vexillifer, as incidental mortality from fisheries, river transportation development, and pollution drove a collapse in the species’ population. The Baiji and numerous other Yangtze species (e.g., Yangtze paddlefish [Psephurus gladius] and Yangtze sturgeon [Acipenser dabryanus]) are now listed as “Critically Endangered (Possibly Extinct).”

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  • Wilcove, D. S. 1999. The condor’s shadow: The loss and recovery of wildlife in America. New York: W. H. Freeman.

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    Wonderful survey of the history and geography of species extinction, decline, and conservation in the United States. Eight chapters, with those on the eastern forests, freshwater, Hawai‘i, and the final, titular chapter, which draws lessons from the status of the California condor, Gymnogyps californianus (“Extinct in the Wild” in 1987, now “Critically Endangered,” with 213 reintroduced individuals), being particularly pertinent here.

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Rediscoveries

On the flip side of the coin from the iconic modern extinctions are a much-smaller number of equally famous rediscoveries of species that were previously declared extinct. The most astonishing of these cases concern species known only from the fossil record, such as the rediscovery of the coelacanth (Latimeria chalumnae) reported in Smith 1939. Similarly, at the genus level, the dawn redwood, Metasequoia, widespread in the Northern Hemisphere until the Miocene, was discovered extant in China in 1944. Less infrequent are rediscoveries of species supposedly extinct in recent times, as with the Chacoan peccary (Catagonus wagneri), documented in Wetzel, et al. 1975 as previously known only from pre-Hispanic archaeological specimens, and the golden-fronted bowerbird (Amblyornis flavifrons), found after an eighty-four-year absence (Diamond 1982). Maybe the case of the ivory-billed woodpecker (Campephilus principalis), reported in Fitzpatrick, et al. 2005, is the most famous rediscovery—or infamous, given that the evidence for the species’ survival is fiercely contested. Fisher and Blomberg 2011 assesses the issue comprehensively for mammals to examine correlates of rediscovery probability, while Scheffers, et al. 2011 shows that rediscovered mammals, birds, and amphibians nevertheless face elevated extinction risk. Viewed more broadly, it is clear that premature claims of extinction carry substantial risks: Collar 1998 describes the “Romeo error” as writing a species off the conservation agenda while it is still extant. In response, Butchart, et al. 2006 develops a method for tagging species assessments as “Possibly Extinct” to minimize such errors.

Measuring Extinction Risk

The science of extinction risk has roots in population biology, with major attention given to the development of models and associated software for population viability analysis (PVA) in the 1980s. Soulé 1987 is a classic edited volume on the subject, with Brook, et al. 2000 providing a comprehensive validation of the approach. The documentation of species considered threatened with extinction, organized by the Species Survival Commission of the International Union for the Conservation of Nature as the IUCN Red List of Threatened Species, dates back to the early 1960s, but for its first three decades it was based on expert opinion. Beginning in the late 1980s, the system was overhauled to provide a structure of quantitative categories and criteria (International Union for Conservation of Nature 2012), with Mace, et al. 2008 documenting the underpinnings of the system in PVA. Given that the IUCN Red List Categories and Criteria have now been applied to document extinction risk multiple times across all species in several entire higher taxa, Butchart, et al. 2007 shows that it is now possible to derive the aggregate rates at which whole groups of species are sliding toward extinction, as a “Red List Index.” Moreover, Brooke, et al. 2008 shows that documented Red List Indices (for birds) broadly mirror those projected had PVA or other quantitative analysis been applied. Stuart, et al. 2010 calls for massive expansion of the taxonomic and ecological coverage of the IUCN Red List. In addition to the measurement of extinction risk per se, measurement of the selectivity of extinction is an important associated field; McKinney 1997 provides a key overview of this subject.

  • Brook, B. W., J. J. O’Grady, A. P. Chapman, M. A. Burgman, H. R. Akçakaya, and R. Frankham. 2000. Predictive accuracy of population viability analysis in conservation biology. Nature 404.6776: 385–387.

    DOI: 10.1038/35006050Save Citation »Export Citation »

    Tests revealing high accuracy of PVA in predicting extinction risk for twenty-one population time series; also found high concordance among five different PVA software packages. Available online for purchase or by subscription.

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  • Brooke, M. de L., S. H. M. Butchart, S. T. Garnett, G. M. Crowley, N. B. Mantilla-Beniers, and A. J. Stattersfield. 2008. Rates of movement of threatened bird species between IUCN Red List categories and toward extinction. Conservation Biology 22.2: 417–427.

    DOI: 10.1111/j.1523-1739.2008.00905.xSave Citation »Export Citation »

    Analysis of changes in documented categories of bird extinction risk since the late 1980s; using the A–D criteria of the IUCN Red List was congruent with those predicted on the basis of equivalence with the E criterion (i.e., PVA or other quantitative analysis), except for “Critically Endangered” species for which the documented rate was lower, maybe because of effective conservation actions. Available online for purchase or by subscription.

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  • Butchart, S. H. M., H. R. Akçakaya, J. Chanson, et al. 2007. Improvements to the Red List Index. PLoS ONE 2.1: e140.

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    Important paper laying out the theory underpinning the global indicator of the rate at which entire groups of species are sliding toward extinction, building from initial formulation by Butchart, and many of the same authors in 2004 (S. H. M. Butchart, A. J. Stattersfield, L. A. Bennun, et al., “Measuring Global Trends in the Status of Biodiversity: Red List Indices for Birds,” PLoS Biology 2.12: e383).

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  • IUCN. 2012. 2001 IUCN Red List categories and criteria, version 3.1. 2d ed. Gland, Switzerland: IUCN.

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    The authoritative global system for measuring species extinction risk, structured across quantitative thresholds against five criteria (rapid population decline, small and declining range, small and declining population, very small population, quantitative analysis) and two extinct (“Extinct,” “Extinct in the Wild”), three threatened (“Critically Endangered,” “Endangered,” “Vulnerable”), and four other (“Near Threatened,” “Least Concern,” “Data Deficient,” “Not Evaluated”) categories.

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  • Mace, G. M., N. J. Collar, K. J. Gaston, et al. 2008. Quantification of extinction risk: IUCN’s system for classifying threatened species. Conservation Biology 22.6: 1424–1442.

    DOI: 10.1111/j.1523-1739.2008.01044.xSave Citation »Export Citation »

    The scientific rationale underpinning the IUCN Red List Categories and Criteria, as the culmination of work started by Georgina Mace with Russ Lande nearly twenty years before (G. M. Mace and R. Lande, 1991, “Assessing Extinction Threats: Toward a Reevaluation of IUCN Threatened Species Categories,” Conservation Biology 5.2: 148–157).

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  • McKinney, M. L. 1997. Extinction vulnerability and selectivity: Combining ecological and paleontological views. Annual Review of Ecology and Systematics 28:495–516.

    DOI: 10.1146/annurev.ecolsys.28.1.495Save Citation »Export Citation »

    A classic review paper, highlighting the similarities in extinction selectivity across traits (e.g., body size, abundance) and therefore phylogeny between the fossil record and in anthropogenic extinctions. Available online for purchase or by subscription.

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  • Soulé, M. E., ed. 1987. Viable populations for conservation. Cambridge, UK: Cambridge Univ. Press.

    DOI: 10.1017/CBO9780511623400Save Citation »Export Citation »

    The famous “blue book,” a slender, ten-chapter edited volume laying out theory and application of PVA.

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  • Stuart, S. N., E. O. Wilson, J. A. McNeely, R. A. Mittermeier, and J. P. Rodríguez. 2010. The barometer of life. Science 328.5975: 177.

    DOI: 10.1126/science.1188606Save Citation »Export Citation »

    A crucially important proposal for expansion of the coverage of the IUCN Red List across squamate, fish, invertebrate, fungi, and plant taxa, to assess extinction risk for 160,000 species in all. Stuart and colleagues estimate that this could be achieved with an investment of sixty million dollars.

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Modern Patterns of Extinction Risk

The data compiled for application of the International Union for the Conservation of Nature (IUCN) Red List Categories and Criteria now span > 60,000 species (, including comprehensive coverage of a number of entire taxonomic groups, allowing rigorous documentation of patterns of current extinction risk. With the extinction risk facing the world’s avifauna comprehensively assessed multiple times since 1988, patterns for birds are best known, as reported in BirdLife International 2000. Subsequent assessments for other taxonomic groups include those for amphibians, in Stuart, et al. 2004; mammals, in Schipper, et al. 2008; corals, in Carpenter, et al. 2008; and tunas and billfishes, in Collette, et al. 2011. Meanwhile, key syntheses include Baillie, et al. 2004, with subsequent additional themes covered in Vié, et al. 2009, both published online. The primary driver of modern anthropogenic extinction that emerges from these data is the destruction of natural habitats, with the introduction of non-native species that become invasive, the unsustainable harvest of wild species as overkill, and the pollution of the atmosphere with carbon dioxide (leading to climate change and ocean acidification) also important.

  • Baillie, J. E. M., L. A. Bennun, T. M. Brooks, et al., eds. 2004. A global species assessment. Gland, Switzerland: International Union for Conservation of Nature.

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    A comprehensive analysis of the IUCN Red List data set, incorporating chapters on threatened species across taxonomic groups, recent extinctions, trends, geography, causes of threat, the socioeconomic context, and conservation responses, with extensive appendices documenting methods and summary data.

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  • Carpenter, K. E., M. Abrar, G. Aeby, et al. 2008. One-third of reef-building corals face elevated extinction risk from climate change and local impacts. Science 321.5888: 560–563.

    DOI: 10.1126/science.1159196Save Citation »Export Citation »

    First assessment of the extinction risk facing 845 zooxanthellate reef-building coral species, finding 32.8 percent threat prevalence among the 704 species for which sufficient data exist to apply the criteria. Causes combine bleaching and disease, driven by elevated sea surface temperatures subsequent to 1998, with local direct anthropogenic impacts. Available online for purchase or by subscription.

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  • Collette, B. B., K. E. Carpenter, B. A. Polidoro, et al. 2011. High value and long life—double jeopardy for tunas and billfishes. Science 333.6040: 291–292.

    DOI: 10.1126/science.1208730Save Citation »Export Citation »

    Global application of the IUCN Red List Categories and Criteria to the sixty-one species of scombrids and billfishes, finding seven (11 percent) to meet the criteria to be considered threatened with high extinction risk, including the “Critically Endangered” southern bluefin tuna (Thunnus maccoyii). These seven are disproportionately long lived and disproportionately highly valued commercially.

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  • IUCN Red List of Threatened Species.

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    The key online resource for study of the risk of modern species extinction, comprising > 60,000 species assessed against the IUCN Red List Categories and Criteria.

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  • Schipper, J., J. S. Chanson, F. Chiozza, et al. 2008. The status of the world’s land and marine mammals: Diversity, threat, and knowledge. Science 322.5899: 225–230.

    DOI: 10.1126/science.1165115Save Citation »Export Citation »

    Global application of the IUCN Red List Categories and Criteria to the world’s 5,487 mammal species, revealing 25 percent threat prevalence for 4,651 non-“Data Deficient” species. Threats differ widely between terrestrial and marine species, driven by habitat loss and peaking in Southeast Asia for the former, and by accidental mortality and pollution and peaking in the northern oceans for the latter. Available online for purchase or by subscription.

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  • BirdLife International, eds. 2000. Threatened birds of the world: The official source for birds on the IUCN Red List. Barcelona: Lynx Edicions.

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    Landmark documentation of 1,186 bird species (11 percent) assessed as threatened on the IUCN Red List, with highly accessible introductory materials; brief documentation for “Near Threatened,” “Data Deficient,” and “Extinct” species; comprehensive summaries of species by country; and bibliography. The data have moved online since 2000.

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  • Stuart, S. N., J. S. Chanson, N. A. Cox, et al. 2004. Status and trends of amphibian declines and extinctions worldwide. Science 306.5702: 1783–1786.

    DOI: 10.1126/science.1103538Save Citation »Export Citation »

    First global application of the IUCN Red List to all 5,743 amphibian species globally, finding a threat prevalence of 42 percent of non-“Data Deficient” species. Threats varied geographically and taxonomically among habitat destruction, overharvesting, and enigmatic declines now known to have been caused by chytrid fungal disease. The same author team subsequently wrote this up as a book (Threatened Amphibians of the World, Barcelona: Lynx Edicions, 2008).

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  • Vié, J.-C., C. Hilton-Taylor, and S. N. Stuart, eds. 2009. Wildlife in a changing world: An analysis of the 2008 IUCN Red List of Threatened Species. Gland, Switzerland: IUCN.

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    An edited volume adding five new themes into analysis of the IUCN Red List: freshwater species, marine species, species from megadiverse taxa selected for assessment through sampling, species vulnerability to climate change, and a regional focus on the Mediterranean.

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Habitat Destruction

Documentation across multiple taxonomic groups and places shows that the destruction of natural habitats is the most severe anthropogenic driver of species extinction, at least on land. Approaches to understanding such habitat destruction have focused both on “natural experiments” at regional scales, and on modeling at global scales.

Regional Analysis

Ecologists have focused extensively on documenting, analyzing, and projecting species extinctions resulting from habitat destruction at regional scales. Given the logistical and ethical challenges of large-scale habitat manipulation, most of this has involved so-called natural experiments, targeting isolated remnants after the loss of the surrounding fragments. Some of these have modeled extinctions, for example on the basis of the species-area relationship, and then have validated model predictions with known data. Examples are Diamond, et al. 1987 for a single site (in Indonesia); Brook, et al. 2003 for a small country (Singapore); and Pimm and Askins 1995 for the entire eastern half of a continent (North America). Other approaches have focused on the mechanisms of extinction, with, for instance, Lens, et al. 2002 measuring the relative impacts of stress within habitat fragments and dispersal between them. Terborgh, et al. 2001 examines trophic cascades as a mechanism for driving extinction following habitat destruction. More recently, some studies, for example Bird, et al. 2011, have used such empirical evidence to calibrate models of economic scenarios and hence to develop regional projections of extinctions. The major exception to “natural” experiment approaches is the Biological Dynamics of Forest Fragments project, initiated by Tom Lovejoy near Manaus in the Brazilian Amazon in 1979. This experimental fragmentation has yielded dozens of publications, of which Laurance, et al. 2011 is an excellent current example, providing insight into the impacts of deforestation on extinctions.

  • Bird, J. P., G. M. Buchanan, A. C. Lees, et al. 2011. Integrating spatially explicit habitat projections into extinction risk assessments: A reassessment of Amazonian avifauna incorporating projected deforestation. Diversity & Distributions 18.3: 273–281.

    DOI: 10.1111/j.1472-4642.2011.00843.xSave Citation »Export Citation »

    Application of SimAmazonia 1 projections of spatially explicit deforestation by 2050 to the extent of suitable habitat for 814 forest-dependent Amazon bird species predicts a tripling in threat prevalence from 3 percent to 8–11 percent (24 to 64–92 species); an important paper in projecting application of the IUCN Red List Categories and Criteria.

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  • Brook, B. W., N. S. Sodhi, and P. K. L. Ng. 2003. Catastrophic extinctions follow deforestation in Singapore. Nature 424.6947: 420–426.

    DOI: 10.1038/nature01795Save Citation »Export Citation »

    Clearance of > 95 percent of Singapore’s 540 km² of forests over the last 183 years has caused documented local extinction of >28 percent of the island’s amphibians, birds, butterflies, decapods, fish, mammals, phasmids, reptiles, and vascular plants, with inferred extinction (given historical undersampling) < 73 percent. A particularly important paper in documenting extinctions following deforestation, broadly across taxonomic groups.

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  • Diamond, J. M., K. D. Bishop, and S. van Balen. 1987. Bird survival in an isolated Javan woodland: Island or mirror? Conservation Biology 1.2: 132–142.

    DOI: 10.1111/j.1523-1739.1987.tb00022.xSave Citation »Export Citation »

    Classic analysis of long time-series data on the birds of Bogor Botanic Garden in Indonesia, examining the degree to which the site is functioning as an “island” (with respect to the “mainland” of Java’s surviving montane forest) or as a “mirror” in taking on the characteristics of the successional avifauna of the surrounding urban and agricultural matrix. Available online for purchase or by subscription.

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  • Laurance, W. F., J. L. C. Camargo, R. C. C. Luizão, et al. 2011. The fate of Amazonian forest fragments: A 32-year investigation. Biological Conservation 144.1: 56–67.

    DOI: 10.1016/j.biocon.2010.09.021Save Citation »Export Citation »

    One of the most powerful syntheses from among many publications emerging from the world’s largest experimental study of habitat fragmentation, the Biological Dynamics of Forest Fragments Project, initiated in central Amazonia in 1979. Available online for purchase or by subscription.

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  • Lens, L., S. van Dongen, K. Norris, M. Githiru, and E. Matthysen. 2002. Avian persistence in fragmented rainforest. Science 298.5596: 1236–1238.

    DOI: 10.1126/science.1075664Save Citation »Export Citation »

    Variation in bird population persistence across twelve rainforest fragments (1–179 ha) in the Taita Hills, Kenya, is explained equally by dispersal (documented by six years of capture-recapture data) and by tolerance of habitat deterioration (estimated by fluctuating asymmetry measures). A key paper casting light on the mechanisms driving extinctions following deforestation. Available online for purchase or by subscription.

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  • Pimm, S. L., and R. A. Askins. 1995. Forest losses predict bird extinctions in eastern North America. Proceedings of the National Academy of Sciences of the United States of America 92.20: 9343–9347.

    DOI: 10.1073/pnas.92.20.9343Save Citation »Export Citation »

    Of the two hundred bird species found in the eastern North American forests, twenty-eight occur only in the region. At peak deforestation in 1872, 48 percent of the region retained forest. These data yield a prediction, from the species-area relationship, of about 16 percent extinction, which is directly validated by the fact that four bird species have become extinct.

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  • Terborgh, J., L. Lopez, P. Nuñez V., et al. 2001. Ecological meltdown in predator-free forest fragments. Science 294.5548: 1923–1926.

    DOI: 10.1126/science.1064397Save Citation »Export Citation »

    On twelve islands (0.25–150 ha) isolated by the flooding of the Lago Guri hydroelectric dam in Venezuela in 1986, vertebrate predators are extinct; densities of rodents, howler monkeys, iguanas, and leaf-cutter ants are 10–100 times greater than in adjacent forest; and densities of tree seedlings and saplings are drastically reduced. Evidence for a food web mechanism for extinctions following deforestation, triggered by the loss of predators. Available online for purchase or by subscription.

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Global Synthesis

Early work in global synthesis of species extinctions following habitat loss, such as that in Myers 1979, was visionary in calling attention to the issue but focused on case studies rather than modeling and validation. Subsequent assessments, such as Whitmore and Sayer 1992 (an edited volume) and the theoretical study in Tilman, et al. 1994, advanced the application of modeling techniques to the issue but emphasized the lack of validation data and uncertainties. More-recent work has focused on documentation (e.g., Myers, et al. 2000, a global identification of hotspots of species endemism and habitat loss) and on validation (e.g., Brooks, et al. 2002, a study of species extinctions from the biodiversity hotspots, and tests of these using the IUCN Red List)—deriving similar estimates of extinction rates to Myers’s initial estimates. Finally, some studies have now built from such mechanistic models to project future extinctions under a range of scenarios of habitat loss. For example, Wright and Muller-Landau 2006 is on the relationship between deforestation and human population to project future extinctions; the authors’ approach has been widely criticized, but their predictions are actually in fairly close agreement with the estimates of Myers and others. One possible driver that could massively reduce future habitat destruction is the development of a global agreement to reduce carbon dioxide emissions from deforestation and degradation, which, as Strassburg, et al. 2012 shows, could dramatically reduce projected future extinctions.

  • Brooks, T. M., R. A. Mittermeier, C. G. Mittermeier, et al. 2002. Habitat loss and extinction in the hotspots of biodiversity. Conservation Biology 16.4: 909–923.

    DOI: 10.1046/j.1523-1739.2002.00530.xSave Citation »Export Citation »

    Application of the species-area relationship to project extinction of endemic species across twenty-five hotspots (all > 1,500 endemic plants; none with > 30 percent habitat remaining), followed by validation using data from the IUCN Red List. For birds and mammals, species-area predictions are robust. For amphibians, reptiles, and plants, deforestation predicts that many currently unassessed species face high extinction risk.

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  • Myers, N. 1979. The sinking ark: A new look at the problem of disappearing species. Oxford: Pergamon.

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    One of the first overviews to raise the alarm on anthropogenic mass extinction, with particular attention to tropical deforestation in Brazil, Costa Rica, Indonesia, and Kenya; still highly relevant today.

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  • Myers, N., R. A. Mittermeier, C. G. Mittermeier, G. A. B. da Fonseca, and J. Kent. 2000. Biodiversity hotspots for conservation priorities. Nature 403.6772: 853–858.

    DOI: 10.1038/35002501Save Citation »Export Citation »

    Massively cited analysis documenting the highly uneven and coincident distribution of endemism and of threats from habitat destruction around the planet, with 35 percent of vertebrates and 44 percent of plants found only in twenty-five “biodiversity hotspots,” all retaining < 30 percent of their original vegetation and so with combined surviving habitat covering only 1.6 percent of the planet’s land area.

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  • Strassburg, B. B. N., A. S. L. Rodrigues, M. Gusti, et al. 2012. Impacts of incentives to reduce emissions from deforestation on global species extinctions. Nature Climate Change 2.5: 350–355.

    DOI: 10.1038/nclimate1375Save Citation »Export Citation »

    Models projected tropical-forest mammal and amphibian extinctions under business-as-usual deforestation up to 2100, by using four methods to relate habitat loss to species loss; shows that carbon prices > $10/metric ton CO2 in a system for climate change mitigation by “Reducing Emissions from Deforestation and Degradation” would reduce these projections by > 70 percent. Available online for purchase or by subscription.

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  • Tilman, D., R. M. May, C. L. Lehman, and M. A. Nowak. 1994. Habitat destruction and the extinction debt. Nature 371.6492: 65–66.

    DOI: 10.1038/371065a0Save Citation »Export Citation »

    Modeling indicates that extinctions will follow habitat destruction and fragmentation in a predictable fashion, over a time lag or “extinction debt.” Available online for purchase or by subscription.

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  • Whitmore, T. C., and J. A. Sayer, eds. 1992. Tropical deforestation and species extinction. London: Chapman & Hall.

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    A short edited volume, which provided important impetus toward better synthesis between modeling and empirical approaches to estimating species extinctions, especially those resulting from tropical deforestation. The chapters by W. V. Reid (“How Many Species Will There Be?”), D. Simberloff (“Do Species-Area Curves Predict Extinction in Fragmented Forest?”), and V. H. Heywood and S. N. Stuart (“Species Extinctions in Tropical Forests”) were particularly influential.

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  • Wright, S. J., and H. C. Muller-Landau. 2006. The uncertain future of tropical forest species. Biotropica 38.4: 443–445.

    DOI: 10.1111/j.1744-7429.2006.00177.xSave Citation »Export Citation »

    A relatively conservative projection of 21–24 percent (Asia) and 16–35 percent (Africa) extinction debts driven by tropical deforestation by 2030, on the basis of projected human population growth, the relationship between this and forest cover, and the species-area relationship. Sparked much criticism as too optimistic, including three responses in Biotropica, but actually not far divergent from many other estimates. Available online for purchase or by subscription.

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Invasive Species

While habitat destruction is undoubtedly driving most impending extinctions, invasive species have accounted for the largest number of modern extinctions to date. The impacts of invasive mammals on islands, either through direct predation and indirect effects such as competition and habitat modification, are best known; Blackburn, et al. 2004 tackles these examples in an analytical framework. However, introductions of species from numerous other taxonomic groups have driven elevated extinction risk. Examples are snakes (with direct predation driving bird extinctions on Guam; Savidge 1987), mollusks (with direct predation driving endemic snail extinctions in Polynesia; Cowie 1992), and fish (with indirect impacts of eutrophication as well as direct predation driving cichlid fish extinctions in Lake Victoria; Seehausen, et al. 1997). Perhaps the most challenging and controversial of current extinctions driven by invasive species has been the global decline of amphibians since the early 1980s. The impact of the fungal disease chytridiomycosis has now been shown to be a major contributor to this mass extinction. However, whether the disease is triggered as a spreading wave (as proposed in Lips, et al. 2006) or whether its emergence is triggered by climate change (as proposed in Pounds, et al. 2006) is hotly contested. A comprehensive overview in Skerratt, et al. 2007 suggests that the balance of evidence is leaning toward the former. Finally, Lockwood and McKinney 2001, an excellent edited volume, provides a rather different slant on invasive species, in considering them alongside extinctions from other causes as drivers of overall biotic homogenization.

  • Blackburn, T. M., P. Cassey, R. P. Duncan, K. L. Evans, and K. J. Gaston. 2004. Avian extinction and mammalian introductions on oceanic islands. Science 305.5692: 1955–1958.

    DOI: 10.1126/science.1101617Save Citation »Export Citation »

    Across 220 oceanic islands, the likelihood of any bird species having become locally extinct correlates with the number of invasive predatory mammal species established on the island. However, the number of currently threatened species is independent of invasive mammals, suggesting that island avifaunas have passed through a mammalian extinction filter. Available online for purchase or by subscription.

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  • Cowie, R. H. 1992. Evolution and extinction of Partulidae, endemic Pacific island land snails. Philosophical Transactions of the Royal Society of London B 335.1274: 167–191.

    DOI: 10.1098/rstb.1992.0017Save Citation »Export Citation »

    A grim account of the biology and extinction of the Partulidae snails following introduction since the 1950s of the predatory snail Euglandina rosea onto many Pacific islands, in an attempt to control the introduced giant African snail (Achatina fulica). In total, 127 species are known; 95 have been assessed on the Red List, with 65 percent “Extinct,” 31 percent “Threatened,” and the remainder “Data Deficient.” Available online for purchase or by subscription.

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  • Lips, K. R., F. Brem, R. Brenes, et al. 2006. Emerging infectious disease and the loss of biodiversity in a Neotropical amphibian community. Proceedings of the National Academy of Sciences of the United States of America 103.9: 3165–3170.

    DOI: 10.1073/pnas.0506889103Save Citation »Export Citation »

    Test of the “spreading pathogen” hypothesis for the impact of the chytrid fungus Batrachochytrium dendrobatidis on amphibians, on the basis of recognition of the apparent eastward movement of chytridiomycosis through Central America. The authors established sampling at El Copé, eastern Panama, in 2000, and detected no chytridiomycosis until 2004; after 2004, the site suffered mass mortality and loss of amphibian biodiversity across eight families of frogs and salamanders.

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  • Lockwood, J. L., and M. L. McKinney, eds. 2001. Biotic homogenization. New York: Kluwer Academic/Plenum.

    DOI: 10.1007/978-1-4615-1261-5Save Citation »Export Citation »

    A thirteen-chapter edited volume, significant for considering species introductions not only as important drivers of extinctions in their own right, but also for operating alongside extinctions in reshaping community ecology through homogenization.

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  • Pounds, J. A., M. R. Bustamante, L. A. Coloma, et al. 2006. Widespread amphibian extinctions from epidemic disease driven by global warming. Nature 439.7073: 161–167.

    DOI: 10.1038/nature04246Save Citation »Export Citation »

    The authors identify a relationship between the timing of Atelopus harlequin toad extinctions in the Neotropics and climate change, hypothesizing that the latter increases cloudiness and so decreases daytime maximum temperatures, but that climate change also increases nighttime minima—conditions that could allow Batrachochytrium dendrobatidis to flourish.

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  • Savidge, J. A. 1987. Extinction of an island forest avifauna by an introduced snake. Ecology 68.3: 660–668.

    DOI: 10.2307/1938471Save Citation »Export Citation »

    The brown tree snake, Boiga irregularis, reached Guam c. 1950, and since the early 1960s, the island’s birds have plummeted to effective extinction. Savidge documented northward correspondence in snake expansion with avian retraction and then backed up this evidence with experimental tests proving massive snake predation on birds in the South, none in the North. Available online for purchase or by subscription.

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  • Seehausen, O., J. J. M. van Alphen, and F. Witte. 1997. Cichlid fish diversity threatened by eutrophication that curbs sexual selection. Science 277.5333: 1808–1811.

    DOI: 10.1126/science.277.5333.1808Save Citation »Export Citation »

    Many of Lake Victoria’s five hundred haplochromine cichlid fishes have become extinct since c. 1980, driven by predation by the Nile perch (Lates niloticus), introduced in the 1950s, and by eutrophication caused by agricultural practices and Nile perch predation on primary consumers and detritus feeders. These homogenization impacts were depicted grippingly in Hubert Sauper’s 2007 film Darwin’s Nightmare. Available online for purchase or by subscription.

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  • Skerratt, L. F., L. Berger, R. Speare, et al. 2007. Spread of chytridiomycosis has caused the rapid global decline and extinction of frogs. EcoHealth 4.2: 125–134.

    DOI: 10.1007/s10393-007-0093-5Save Citation »Export Citation »

    Rigorous examination of how an infectious pathogen can drive amphibian species to global extinction. Proposes that the evidence supports (a) distributional spread of a highly pathogenic, virulent, transmissible pathogen (Lips’s hypothesis), rather than (b) abnormal environmental change resulting in an already widespread pathogen becoming highly pathogenic, virulent, and transmissible (Pounds’s hypothesis).

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Overkill

With the consolidation of evidence for mass megafaunal extinction through prehistoric overkill, it is no surprise to find direct harvest of species populations by people as a major cause of current extinction. Mammals and large birds bear the brunt of modern anthropogenic overkill, with “bushmeat” harvest a primary driver of current extinction in Asia and Africa, as reviewed in Milner-Gulland, et al. 2003. As in the Late Pleistocene, overkill is highly selective toward large-bodied species: Davidson, et al. 2009 shows that hunting of large-bodied (and relatively widely distributed) species sits alongside the destruction of habitat of relatively narrowly distributed (and generally small-bodied) species as a current pathway to extinction. The overkill pathway is by no means unique to mammals, though. Casey and Myers 1998 overturns historical perceptions of high resilience of marine species to harvest by documenting the near extinction of the barndoor skate (Dipturus laevis), and Dulvy, et al. 2003 shows that extinction in the sea through overkill (and, to a slightly lesser extent, habitat destruction) is widespread. Similarly, Peres, et al. 2003 proves extinction risk driven by overharvest for a plant, the brazil nut (Bertholletia excelsa). A solid set of theoretical studies underlie these taxonomically and biome-focused examinations of overkill. The early classic Clark 1973 projects extinction as a consequence of overexploitation, on the basis of a surprising mechanism: if a resource is valuable but slow growing, economic return will be maximized by eliminating the resource and investing the profits. Over and above these economic effects, Courchamp, et al. 2006 identifies a cultural driver, the “anthropogenic Allee effect,” which is based on what appears to be a common preference for rare species throughout human society, with powerful empirical tests of this effect added in Angulo, et al. 2009.

  • Angulo, E., A.-L. Deves, M. Saint Jalmes, and F. Courchamp. 2009. Fatal attraction: Rare species in the spotlight. Proceedings of the Royal Society of London B 276.1660: 1331–1337.

    DOI: 10.1098/rspb.2008.1475Save Citation »Export Citation »

    Clever experiments in La Ménagerie du Jardin des Plantes, Paris, to test the generality of the anthropogenic Allee effect, proving that zoo visitors are willing to spend more time looking for rare species, to expend more physical effort, to tolerate less pleasant conditions, and to pay more to see rare species, and to risk higher penalties to steal rare species.

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  • Casey, J. M., and R. A. Myers. 1998. Near extinction of a large, widely distributed fish. Science 281.5377: 690–692.

    DOI: 10.1126/science.281.5377.690Save Citation »Export Citation »

    An important contribution in changing popular assumption of resilience in marine species, documenting decline in records of barndoor skate (Dipturus laevis) from 10 percent in Newfoundland research survey tows in 1953 to none since the late 1970s, primarily as a result of trawl by-catch. The species is evaluated as “Endangered” on the IUCN Red List. Available online for purchase or by subscription.

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  • Clark, C. W. 1973. The economics of overexploitation. Science 181.4100: 630–634.

    DOI: 10.1126/science.181.4100.630Save Citation »Export Citation »

    Seminal economic analysis, exemplified by the “Endangered” blue whale (Balaenoptera musculus), showing that for populations that are economically valuable but reproduce slowly, high future discount rates can lead to extinction. Given the likelihood of private-sector adoption of high discount rates, public surveillance and control will therefore be necessary to avoid extinction. Available online for purchase or by subscription.

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  • Courchamp, F., E. Angulo, P. Rivalan, et al. 2006. Rarity value and species extinction: The anthropogenic Allee effect. PLoS Biology 4.12: e415.

    DOI: 10.1371/journal.pbio.0040415Save Citation »Export Citation »

    Human preference for rarity drives an anthropogenic Allee effect, whereby the rarer species become, the higher their value for harvest. Courchamp and colleagues document this with data for butterfly collections, wild-goat trophy hunting, exotic pet species regulated under the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), ecotourism, and traditional medicine products.

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  • Davidson, A. D., M. J. Hamilton, A. G. Boyer, J. H. Brown, and G. Ceballos. 2009. Multiple ecological pathways to extinction in mammals. Proceedings of the National Academy of Sciences of the United States of America 106.26: 10702–10705.

    DOI: 10.1073/pnas.0901956106Save Citation »Export Citation »

    Analysis of relationships between mammalian traits and extinction risk (on the IUCN Red List), by using decision trees, across roughly forty-five hundred species, reveals disproportionate threat to species with large body size and relatively small range size—likely due to hunting—as well as to those with absolutely small range sizes.

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  • Dulvy, N. K., Y. Sadovy, and J. D. Reynolds. 2003. Extinction vulnerability in marine populations. Fish and Fisheries 4.1: 25–64.

    DOI: 10.1046/j.1467-2979.2003.00105.xSave Citation »Export Citation »

    Meta-analysis of 133 marine species extinctions, demonstrating that (a) exploitation was the major cause (55 percent of extinctions), followed by habitat loss (37 percent); (b) commercial extinction can be simultaneous with biological extinction; and (c) fish populations do not appear to fluctuate more than do mammals, birds, or butterflies.

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  • Milner-Gulland, E. J., E. L. Bennett, and the SCB 2002 Annual Meeting Wild Meat Group. 2003. Wild meat: The bigger picture. Trends in Ecology & Evolution 18.7: 351–357.

    DOI: 10.1016/S0169-5347(03)00123-XSave Citation »Export Citation »

    A broad review of the massive overhunting of wildlife for meat, underway throughout the tropics, which is driving many local extinctions. Conservation responses should balance hunted with no-take areas across the landscape. Available online for purchase or by subscription.

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  • Peres, C. A., C. Baider, P. A. Zuidema, et al. 2003. Demographic threats to the sustainability of brazil nut exploitation. Science 302.5653: 2112–2114.

    DOI: 10.1126/science.1091698Save Citation »Export Citation »

    History and intensity of exploitation drive population size structure across twenty-three populations of the brazil nut, Bertholletia excelsa (assessed as “Vulnerable” on the IUCN Red List), in Brazil, Bolivia, and Peru, with persistently harvested populations lacking saplings < 60 cm diameter at breast height, indicating unsustainably low recruitment and hence likely senescence and collapse. Available online for purchase or by subscription.

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Climate Change

As with habitat destruction, analysis of extinctions driven by anthropogenic climate change can be subdivided into “natural experiments” at regional scales and modeling studies at the global scale. These raise a number of key issues. For example, the range of predicted extinction rates is still quite wide between studies, driven by differences in underlying data and methodology and maybe also by taxa and places considered. Meanwhile, these studies also raise the ominous question of whether climate change will overtake habitat destruction and other threats as the main driver of extinction in the future.

Regional Analyses

As with extinction risk from habitat destruction, the primary regional analytical approach to the impacts of climate change has been the identification of time-series data sets of species populations to allow modeling and validation. In some situations, modeling has yielded remarkably high predictive power, for instance in an analysis of birds in California over the last century (Tingley, et al. 2009) and in Raxworthy, et al. 2008, a work on Malagasy reptiles and amphibians. Other situations add complexity, however. For example, Foden, et al. 2007 shows range contraction toward the equator, without poleward expansion, for an African desert plant species—a dispersal time lag. Colwell, et al. 2008 successfully validates models of elevational range shift for tropical plants and ants but finds that this leaves depauperate lowland communities with no elevational or latitudinal source pools. Moreover, Crimmins, et al. 2011 finds changing water balance rather than temperature to be the primary driver of climate change responses by California plants, driving downslope movements. These complexities notwithstanding, current regional analyses of climate change impacts on species extinction are now beginning to build from these modeling and validation approaches toward projection. For example, Sinervo, et al. 2010 models extinctions with changing thermal niches for Mexican lizards and then extrapolates from these results to project lizard extinctions worldwide. Meanwhile, Hole, et al. 2009 opens another important research front by considering projected impacts across an entire network of sites identified as currently important for species persistence (for birds in Africa), finding the site network to be remarkably robust.

  • Colwell, R. K., G. Brehm, C. L. Cardelús, A. C. Gilman, and J. T. Longino. 2008. Global warming, elevational range shifts, and lowland biotic attrition in the wet tropics. Science 322.5899: 258–261.

    DOI: 10.1126/science.1162547Save Citation »Export Citation »

    Documentation of upslope range shifts of plant and invertebrate species in Costa Rica in response to climate change, leaving depauperate lowland communities. Available online for purchase or by subscription.

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  • Crimmins, S. M., S. Z. Dobrowski, J. A. Greenberg, J. T. Abatzoglou, and A. R. Mynsberge. 2011. Changes in climatic water balance drive downhill shifts in plant species’ optimum elevations. Science 331.6015: 324–327.

    DOI: 10.1126/science.1199040Save Citation »Export Citation »

    Analysis of altitudinal ranges of sixty-four plant species in California from the 1930s to the early 21st century shows significant downslope shift in optimal elevations, which the authors attribute to niche tracking of regional changes in water balance (rather than temperature). Important cautionary analysis for niche-modeling approaches to projecting extinctions from climate change. Available online for purchase or by subscription.

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  • Foden, W., G. F. Midgley, G. Hughes, et al. 2007. A changing climate is eroding the geographical range of the Namib Desert tree Aloe through population declines and dispersal lags. Diversity & Distributions 13.5: 645–653.

    DOI: 10.1111/j.1472-4642.2007.00391.xSave Citation »Export Citation »

    Impressive analysis of kokerboom (Aloe dichotoma), by using historical photographs and modern field survey, population modeling based on regional warming and water balance, and range-wide bioclimatic modeling, showing equatorward decline and range contraction but no commensurate range expansion, despite strong population trends poleward. The species’ extinction risk has not yet been assessed. Available online for purchase or by subscription.

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  • Hole, D. G., S. G. Willis, D. J. Pain, et al. 2009. Projected impacts of climate change on a continent-wide protected area network. Ecology Letters 12.5: 420–431.

    DOI: 10.1111/j.1461-0248.2009.01297.xSave Citation »Export Citation »

    Projected impacts of climate change (by using two modeling methods, three general circulation models, and time horizons of 2025, 2055, and 2085) on species extinction or survival in 863 sites identified as significant for the persistence of 815 African bird species. Importantly, about 90 percent of species are projected to retain climate space in at least one of these important bird areas over the coming century. Available online for purchase or by subscription.

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  • Raxworthy, C. J., R. G. Pearson, N. Rabibisoa, et al. 2008. Extinction vulnerability of tropical montane endemism from warming and upslope displacement: A preliminary appraisal for the highest massif in Madagascar. Global Change Biology 14.8: 1703–1720.

    DOI: 10.1111/j.1365-2486.2008.01596.xSave Citation »Export Citation »

    Survey of thirty species of reptiles and amphibians in the Tsaratanana Massif in northern Madagascar documents mean upslope shifts of 19–51 m, validating climatological predictions of 17–74 m upslope shifts. Three of the thirty species are predicted to lose all habitat even if < 2°C warming occurs; two of these were not detected in 2003. Available online for purchase or by subscription.

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  • Sinervo, B., F. Méndez de la Cruz, D. B. Miles, et al. 2010. Erosion of lizard diversity by climate change and altered thermal niches. Science 328.5980: 894–899.

    DOI: 10.1126/science.1184695Save Citation »Export Citation »

    Application of climate change scenarios to model and validate extinction driven by physiological impacts of warming for forty-eight Sceloporus species at two hundred sites in Mexico since 1975, and then to model impacts on species worldwide, projecting 20 percent lizard extinctions by 2080. Available online for purchase or by subscription.

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  • Tingley, M. W., W. B. Monahan, S. R. Beissinger, and C. Moritz. 2009. Birds track their Grinnellian niche through a century of climate change. Proceedings of the National Academy of Sciences of the United States of America 106.S2: 19637–19643.

    DOI: 10.1073/pnas.0901562106Save Citation »Export Citation »

    Results of the Grinnell Resurvey Project, with 2003–2008 surveys of fifty-three bird species at eighty-two sites in the Californian Sierra Nevada, initially inventoried by Joseph Grinnell in 1911–1929. Bioclimatic modeling accurately predicts changing distributions over space and up elevational transects.

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Global Synthesis

Global syntheses of extinction risk from climate change have emerged only since the turn of the 21st century, as the breadth of regional studies has expanded to provide confidence in broad-scale modeling, validation, and projection. In a very heavily cited paper, Thomas, et al. 2004 models projections of 18–35 percent extinction by 2050 across eighteen species groups in eight regions. Sekercioglu, et al. 2008 extends these approaches into three dimensions, in projecting implications of elevational range shifts for birds globally. An important meta-analysis in Maclean and Wilson 2011 provides global validation of such modeling studies. Similar work has been undertaken in the ocean environment, for example for 1,066 marine fish and invertebrates reported in Cheung, et al. 2009. Building from the predictions in Hoegh-Guldberg, et al. 2007 of massive ecosystem-level effects of ocean acidification, in conjunction with climate change, study of the impacts of these drivers on coral reef species extinction is an important research front. The incorporation of climate change drivers into documentation of extinction risk on the IUCN Red List is also in its infancy; Akçakaya, et al. 2006 provides important cautions to avoid misuse of the criteria, as well as suggesting some ways forward. In the early 21st century, some edited volumes and books tackling climate change and species extinction have also begun to appear, with maybe the most-important contributions being Lovejoy and Hannah 2005 and Pearson 2011.

  • Akçakaya, H. R., S. H. M. Butchart, G. M. Mace, S. N. Stuart, and C. Hilton-Taylor. 2006. Use and misuse of the IUCN Red List Criteria in projecting climate change impacts on biodiversity. Global Change Biology 12.11: 2037–2043.

    DOI: 10.1111/j.1365-2486.2006.01253.xSave Citation »Export Citation »

    Important clarification of misuses of the IUCN Red List Categories and Criteria to assess extinction risk from climate change—for example, in changing the temporal and spatial scales, confusing the spatial variables, and assuming linear relationship between abundance and population. Concludes with useful recommendations on appropriate applications for future work. Available online for purchase or by subscription.

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  • Cheung, W. W. L., V. W. Y. Lam, J. L. Sarmiento, K. Kearney, R. Watson, and D. Pauly. 2009. Projecting global marine biodiversity impacts under climate change scenarios. Fish and Fisheries 10.3: 235–251.

    DOI: 10.1111/j.1467-2979.2008.00315.xSave Citation »Export Citation »

    First broad-scale niche-modeling application of likely impacts of climate change on marine biodiversity, applying scenarios for the year 2050 to 1,066 exploited marine fish and invertebrate species to project likely extinctions and range changes.

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  • Hoegh-Guldberg, O., P. J. Mumby, A. J. Hooten, et al. 2007. Coral reefs under rapid climate change and ocean acidification. Science 318.5857: 1737–1742.

    DOI: 10.1126/science.1152509Save Citation »Export Citation »

    Sobering projections of compromised carbonate accretion in coral reefs—the most biodiverse marine ecosystem—resulting from likely late-21st-century atmospheric CO2 concentrations of > 500 parts per million and temperature increases of > 2°C, driving global warming and ocean acidification exceeding levels of the last 420,000 years.

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  • Lovejoy, T. E., and L. Hannah, eds. 2005. Climate change and biodiversity. New Haven, CT: Yale Univ. Press.

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    Twenty-four-chapter edited volume synthesizing key issues in climate change and species extinction, and illustrated with an additional nine case studies. The two editors have been central figures in synthesis of the subject, producing two further edited volumes on climate change and extinction: R. L. Peters and T. E. Lovejoy, eds., 1992, Global Warming and Biological Diversity (New Haven, CT: Yale Univ. Press); and L. Hannah, ed., 2012, Saving a Million Species: Extinction Risk from Climate Change (Washington, DC: Island).

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  • Maclean, I. M. D., and R. J. Wilson. 2011. Recent ecological responses to climate change support predictions of high extinction risk. Proceedings of the National Academy of Sciences of the United States of America 108.30: 12337–12342.

    DOI: 10.1073/pnas.1017352108Save Citation »Export Citation »

    Powerful meta-analysis comparing effect sizes of 130 observed impacts with 188 projections of climate change on biodiversity, and finding substantial concordance.

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  • Pearson, R. 2011. Driven to extinction: The impact of climate change on biodiversity. New York: Sterling.

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    A clearly written review and synthesis of climate change impacts on biodiversity, spanning physiological and phonological as well as population impacts.

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  • Sekercioglu, C. H., S. H. Schneider, J. P. Fay, and S. R. Loarie. 2008. Climate change, elevational range shifts, and bird extinctions. Conservation Biology 22.1: 140–150.

    DOI: 10.1111/j.1523-1739.2007.00852.xSave Citation »Export Citation »

    Neat combination of scenarios of climate change and habitat destruction to project bird extinctions by 2100, given bird distributions over space and across elevational ranges. Available online for purchase or by subscription.

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  • Thomas, C. D., A. Cameron, R. E. Green, et al. 2004. Extinction risk from climate change. Nature 427.6970: 145–148.

    DOI: 10.1038/nature02121Save Citation »Export Citation »

    Influential projections of 18–35 percent extinction resulting from climate change by 2050, derived by application of three species-area relationships and two dispersal assumptions to the results of bioclimatic modeling, by using midrange climate scenarios and point data for eighteen species groups (birds, mammals, reptiles, frogs, scattered invertebrate, and plant data) from eight regions.

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Consequences of Extinction

In contrast to the research directed toward the causes of species loss, the consequences of extinction have received surprisingly little attention. Maybe the earliest overview was Ehrlich and Ehrlich 1981, drawing primarily from case studies and extrapolation, given the paucity of data and analysis at the time. More-recent research provided evidence supporting the Ehrlichs’ conclusions in a number of dimensions. Some analyses have considered the implications of extinction across taxonomy, with Koh, et al. 2004 coining the phrase “co-extinction” to describe species loss in coevolved interspecific systems. Hooper, et al. 2012 reviews ecological consequences in terms of ecosystem processes, and Díaz, et al. 2006 examines the knock-on impacts of these for human well-being, with a particular focus on poverty and equity. Chivian and Bernstein 2008 is a major edited volume examining consequences from the perspective of human health. The ethical consequences of species loss have been subjected to less attention: Collar 2003 provides maybe the most important insight to date. Some more recent work has moved to place the consequences of extinction into other spatial and thematic frameworks. For example, Larsen, et al. 2012 documents the human well-being costs of losing important sites for biodiversity (and conversely, the benefits of safeguarding these). The broadest review, Rockström, et al. 2009, identifies nine planetary boundaries, the transgression of which incurs grave dangers; the authors consider anthropogenic species extinction to be one of three boundaries that have already been crossed.

  • Chivian, E., and A. Bernstein, eds. 2008. Sustaining life: How human health depends on biodiversity. Oxford: Oxford Univ. Press.

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    Weighty edited volume surveying the consequences of extinction for humanity. The authors are from Harvard Medical School, and so they place particular emphasis on medical issues: drug discovery, biomedical research, model organisms, emerging infectious disease, food production, and genetic modification of organisms.

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  • Collar, N. J. 2003. Beyond value: Biodiversity and the freedom of the mind. Global Ecology & Biogeography 12.4: 265–269.

    DOI: 10.1046/j.1466-822X.2003.00034.xSave Citation »Export Citation »

    An eloquent and powerful rationale for preventing extinctions. Collar categorizes most conservation rationale as either “oppositional” (assuming a proven case) or “institutional” (adopting the economic and utilitarian perspective opposed in the first place). He concludes by calling for “the courage and honesty to assert that the reason biodiversity matters is because it confers on us an imprecise, unmeasurable and immeasurable well-being that is located in the spirit rather than in the wallet.” Available online for purchase or by subscription.

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  • Díaz, S., J. Fargione, F. S. Chapin III, and D. Tilman. 2006. Biodiversity loss threatens human well-being. PLoS Biology 4.8: 1300–1305.

    DOI: 10.1371/journal.pbio.0040277Save Citation »Export Citation »

    Useful review of the consequences of biodiversity loss in undermining ecosystem services and hence human well-being, with particular attention to the unevenness of these impacts: the people who suffer most from biodiversity are those rural poor and traditional societies who can least afford such loss.

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  • Ehrlich, P., and A. Ehrlich. 1981. Extinction: The causes and consequences of the disappearance of species. New York: Ballantine.

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    Some of the earliest discussion of the consequences of anthropogenic extinctions, including both ethical and economic rationales for preventing extinction; the first use of the “rivet popper” analogy to communicate the risks to which humanity exposes itself by driving mass extinction.

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  • Hooper, D. U., E. C. Adair, B. J. Cardinale, et al. 2012. A global synthesis reveals biodiversity loss as a major driver of ecosystem change. Nature 486.7401: 105–108.

    DOI: 10.1038/nature11118Save Citation »Export Citation »

    Meta-analyses of the impact of species extinctions on productivity and decomposition show effects comparable to those of ultraviolet radiation and climate warming at intermediate levels of extinction (21–40 percent) and further comparable to those of ozone, acidification, elevated CO2, and nutrient pollution at high levels (41–60 percent).

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  • Koh, L. P., R. R. Dunn, N. S. Sodhi, R. K. Colwell, H. C. Proctor, and V. S. Smith. 2004. Species coextinctions and the biodiversity crisis. Science 305.5690: 1632–1634.

    DOI: 10.1126/science.1101101Save Citation »Export Citation »

    A clever paper, developing a model for extinction of species in coevolved, interspecific systems. Model is based on extinction risk of the host and level of host specificity, scaling it with empirical data and applying the model to roughly ten thousand species currently assessed as “Extinct” or “Threatened” on the International Union for the Conservation of Nature (IUCN) Red List, to predict that their loss will drive “co-extinction” of about sixty-three hundred species. Available online for purchase or by subscription.

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  • Larsen, F. W., W. R. Turner, and T. M. Brooks. 2012. Conserving critical sites for biodiversity provides disproportionate benefits to people. PLoS ONE 7.5: e36971.

    DOI: 10.1371/journal.pone.0036971Save Citation »Export Citation »

    The benefits of preventing extinctions through safeguarding the > 500 sites identified globally by the Alliance for Zero Extinction—in terms of climate change mitigation, freshwater provision to people downstream, biocultural diversity, and future option value—are predicted to be significantly greater than null model of the benefits of safeguarding random sites within the same countries or ecoregions.

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  • Rockström, J., W. Steffen, K. Noone, et al. 2009. A safe operating space for humanity. Nature 461.7263: 472–475.

    DOI: 10.1038/461472aSave Citation »Export Citation »

    The authors define nine earth system processes, compile empirical evidence to establish critical thresholds for each (beyond which humanity risks dangerous impacts), and test the planet’s current position relative to each. The nine are biodiversity loss (species extinction rates), climate change, nitrogen/phosphorus cycling, stratospheric ozone depletion, ocean acidification, freshwater use, land use, aerosol loading, and chemical pollution—of which the limits for the first three have already been transgressed. Available online for purchase or by subscription.

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Preventing Extinctions

By documenting the state of biodiversity, as measured through extinction risk, and assessing the causes and consequences of species extinction, one can develop a predictive science of conservation responses needed to prevent extinctions. Rodrigues, et al. 2006 explains how recent changes to the International Union for the Conservation of Nature (IUCN) Red List support conservation applications. The first step is to document those responses already in place. Donald, et al. 2010, for example, provides an overview and case studies of conservation actions underway to save the world’s “Critically Endangered” bird species. Next, comparison between the extent of current action and that predicted sufficient to prevent extinctions over the foreseeable future is necessary. Given the prevalence of habitat destruction as a driver of extinction, much such work has concentrated on “gap analysis” of current protected-area shortfall relative to that necessary to prevent extinctions from habitat loss. At broad spatial scales, for instance, Rodrigues, et al. 2004 shows that >20 percent of the world’s threatened vertebrates are unrepresented in protected areas. Considering fine spatial scales, Ricketts, et al. 2005 identifies the > 900 sites holding the entire global population of at least one highly threatened vertebrate species, finding that only a third of these “Alliance for Zero Extinction” sites are protected. Moreover, Butchart, et al. 2012 shows that safeguarding such sites halves the rate at which the species for which these sites are important are sliding toward extinction. Given the diversity of anthropogenic pressures driving current extinctions, it is important to plan, resource, and implement conservation actions to respond to all threats, not just habitat destruction (although, of course, safeguarding important sites protects species from threats such as hunting, as well). To support management agencies faced with the practical challenge of preventing extinctions, Joseph, et al. 2009 develops a project prioritization protocol to minimize species loss for a given annual budget. Following implementation, extinction ecology should guide monitoring of the success of conservation actions in preventing extinction. As a global example, Hoffmann, et al. 2010 uses actual Red List Indices and those that would likely have unfolded in the absence of conservation, finding that conservation actions have reduced the slide toward extinction by a fifth since the early 1980s. Finally, Geisel 1971 is worth inclusion, given Dr Seuss’s remarkable insight into the causes and consequences of, and responses to, extinction, in the early years of the wildlife conservation movement, with a target audience of primary-school children but with important lessons for all.

  • Butchart, S. H. M., J. P. W. Scharlemann, M. I. Evans, et al. 2012. Protecting important sites for biodiversity contributes to meeting global conservation targets. PLoS ONE 7.3: e32529.

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    Analysis of the World Database on Protected Areas, the Red List Index, and Alliance for Zero Extinction sites and Important Bird Areas. Finds that species with > 50 percent of their sites protected have slid toward extinction at only half the rate of those with < 50 percent of their sites under protection.

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  • Donald, P. F., N. J. Collar, S. J. Marsden, and D. J. Pain. 2010. Facing extinction: The world’s rarest birds and the race to save them. London: T & A. D. Poyser.

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    Six chapters (on the nature of rarity, causes of rarity, islands, conservation, rediscoveries, and future prospects), interspersed with twenty case studies of individual species designed to illustrate the points discussed in the general chapters.

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  • Geisel, T. S. 1971. The lorax. New York: Random House.

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    Extinction ecology and response for all ages, tackling deforestation, pollution, and climate change with remarkable foresight, with a powerful and upbeat ending. Republished as recently as 2012 (London: HarperCollins Children’s).

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  • Hoffmann, M., C. Hilton-Taylor, A. Angulo, et al. 2010. The impact of conservation on the status of the world’s vertebrates. Science 330.6010: 1503–1509.

    DOI: 10.1126/science.1194442Save Citation »Export Citation »

    Conservation success eventually leads to movement away from extinction, down through the IUCN Red List Categories. By removing these reductions in extinction risk for mammals, birds, and amphibians, since the early 1980s, from the overall calculation of the Red List Index, the authors show that the slide toward extinction would have been 20 percent faster without conservation efforts. Available online for purchase or by subscription.

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  • Joseph, L. N., R. F. Maloney, and H. P. Possingham. 2009. Optimal allocation of resources among threatened species: A project prioritization protocol. Conservation Biology 23.2: 328–338.

    DOI: 10.1111/j.1523-1739.2008.01124.xSave Citation »Export Citation »

    Method development for allocating a known budget among projects for reducing extinction risk—incorporating measures of economic cost, benefits in terms of aggregate reduced extinction risk, and probability of success of the action—with application to New Zealand. Available online for purchase or by subscription.

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  • Ricketts, T. H., E. Dinerstein, T. Boucher, et al. 2005. Pinpointing and preventing imminent extinctions. Proceedings of the National Academy of Sciences of the United States of America 102.51: 18497–18501.

    DOI: 10.1073/pnas.0509060102Save Citation »Export Citation »

    Identification of 794 species that are “Critically Endangered” or “Endangered,” and also effectively endemic to a single site, and documentation of these 595 sites, only one-third of which are protected. These “Alliance for Zero Extinction” sites comprise the “tip of the iceberg” of key biodiversity areas, contributing significantly to the global persistence of biodiversity.

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  • Rodrigues, A. S. L., S. J. Andelman, M. I. Bakarr, et al. 2004. Effectiveness of the global protected area network in representing species diversity. Nature 428.6983: 640–643.

    DOI: 10.1038/nature02422Save Citation »Export Citation »

    Overlaying data from the World Database on Protected Areas (> 100,000 sites) with the range maps from the IUCN Red List for all mammal, bird, amphibian, and turtle species finds that a minimum of 12 percent of threatened species, and 20 percent of all species, are unrepresented in protected areas. Available online for purchase or by subscription.

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  • Rodrigues, A. S. L., J. D. Pilgrim, J. F. Lamoreux, M. Hoffmann, and T. M. Brooks. 2006. The value of the IUCN Red List for conservation. Trends in Ecology & Evolution 21.2: 71–76.

    DOI: 10.1016/j.tree.2005.10.010Save Citation »Export Citation »

    Three major changes have recently been implemented through the IUCN Red List: (a) application of the 2001 quantitative categories and criteria, (b) move from assessments of “hand-picked” species to taxon-wide assessments, and (c) incorporation of extensive ancillary data. These changes make the Red List invaluable for informing species’ status, identifying sites for action, informing broader policy, evaluating state, and monitoring change.

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