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About this PDF file: This new digital representation of the original work has been recomposed from XML files created from the original paper book, not from the original typesetting files. Page breaks are true to the original; line lengths, word breaks, heading styles, and other typesetting-specific formatting, however, cannot be retained, and some typographic errors may have been accidentally inserted. Please SPECIES EXTINCTIONS 25 responses to future changes in climate and other physical phenomena (Burney, 1993). The marine invertebrate fossil record reveals at least five mass-extinction events during the past 500 million years, in which from 14% to 84% of the genera or families disappeared from the fossil record (Jablonski, 1991; Raup and Jablonski, 1993; Benton, 1995). Perhaps the two best known of these mass-extinction events are the Permian-Triassic (P-T) 245 million years ago and the Cretaceous-Tertiary (K-T) 65 million years ago. In addition to marine invertebrates, the P-T event involved extinction of terrestrial plants and insects (Retallack, 1995); the K-T event included most reptiles. A much more recent mass extinction, that of the Pleistocene- Holocene (PH) only 11,000 years ago, featured extinction of more than 100 terrestrial species of birds and large mammals in North, Central, and South America. Although extinction is common to the P-T, K-T, and P-H events, they differ from the current extinction event in several ways. The current extinction event differs from the three paleontological events in that it actually or potentially involves all groups of organisms, in any sort of nonmarine habitat. A particularly conspicuous aspect of today's situation is that many species of plants, as well as animals, are rare, endangered, or already have become extinct. For example, the Endangered Species List contained 695 U.S. and 521 non-U.S. endangered species and 169 U.S. and 41 non-U.S. threatened species in March 1995. Of that total, 995 were animals and 529 were plants. In two of the other three extinction events, plants suffered few if any losses. The evolutionary radiation of mammals that followed the K-T demise of most reptiles was possible only because most terrestrial plants survived the K-T event. As far as can be determined from the extensive late Quaternary pollen and plant macrofossil record, the loss of so many birds and mammals in the Americas during the P-H event was not accompanied by the extinction of plants, although the geographic ranges of plants changed dramatically at that time (Betancourt et al., 1990; Webb et al., 1993). Today, even though obscure or little-known species are lost with little or no notice (Wilson, 1992), we can document the date of loss of relatively well-known species to the nearest decade (e.g., the sea mink, Mustela macrodon, became extinct about 1880 (Nowak and Paradiso, 1983)), sometimes to the year (e.g., the Guam flycatcher, Myiagrafreycineti, became extinct in 1985 (Engbring and Pratt, 1985; Steadman, 1992)), or even to the day, in the case of the last passenger pigeon, Ectopistes migratorius, which died on September 1, 1914 (Schorger, 1955). Such precise dating is not possible for the paleontological extinctions. Because they occurred within the time range of radiocarbon dating, the 95% confidence limits to the estimated dates of P-H extinctions are ± 50 to 200 years (Stafford et al., 1990). But for the K-T and P-T events, even the most precise radiometric dating methods have use the print version of this publication as the authoritative version for attribution.

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About this PDF file: This new digital representation of the original work has been recomposed from XML files created from the original paper book, not from the original typesetting files. Page breaks are true to the original; line lengths, word breaks, heading styles, and other typesetting-specific formatting, however, cannot be retained, and some typographic errors may have been accidentally inserted. Please SPECIES EXTINCTIONS 26 margins of error (a 95% confidence interval) of ± 104 to 105 years and 105 to 106 years, respectively. Pinpointing prehistoric extinctions also depends upon the completeness of the fossil record, because failure to find a species in a certain fossil assemblage does not mean that the species is extinct; the absence could be a sampling artifact (Steadman et al., 1991). The P-T and K-T events are not as well documented as the P-H event because they are represented by many fewer paleontological sites, and a much greater variety of organic materials have withstood the mere 11,000 years since the P-H event. Furthermore, most species that were lost in the P-T and K-T events are related only distantly to living species; in contrast, many birds and mammals lost in the P-H event are survived by closely related species or genera that can be studied to help determine the paleoecology of the extinct species. A series of glacial-interglacial cycles have occurred during the past 2 million years. The cool glacial intervals have lasted 80,000 to 120,000 years, and the warm interglacial intervals have lasted only 10,000 to 20,000 years each. The temperature and atmospheric chemistry of our current interglacial period (the Holocene) have been unusually stable (Rampino and Self, 1992; Dansgaard et al., 1993; Mayewski et al., 1993); however, even subtle shifts in Holocene temperature or precipitation regimes can have dramatic local consequences on plant communities (Swetnam, 1993). The last interglacial interval, which probably had much more variable temperatures than the current one, lasted from about 130,000 to 115,000 years ago (Martinson et al., 1987; Shackleton, 1987; Appenzeller, 1993; Dansgaard et al., 1993; GRIP, 1993; Grootes et al., 1993). Global sea- level fluctuations between glacial and interglacial intervals have been on the order of 100 m (Shackleton, 1987; Pirazzoli, 1993). Warm interglacial climates have characterized about 15% of the past 2 million years (Imbrie and Imbrie, 1979). During glacial intervals, which featured continental ice sheets, expanding alpine glaciers, and periodic "armadas" of icebergs across the North Atlantic (Kerr, 1993a), the average air, soil, and groundwater temperatures were much cooler than today, even in subtropical Florida (Plummer, 1993) and in truly tropical localities (Markgraf, 1989). In those times, species could survive the great continental climatic fluctuations because they could move gradually across intact habitats. The response of plants and animals to climatic changes of the next glacial interval will likely be impaired by habitat fragmentation. Species with poor dispersal capabilities might be unable to shift their ranges across tracts of disturbed habitat. use the print version of this publication as the authoritative version for attribution.

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About this PDF file: This new digital representation of the original work has been recomposed from XML files created from the original paper book, not from the original typesetting files. Page breaks are true to the original; line lengths, word breaks, heading styles, and other typesetting-specific formatting, however, cannot be retained, and some typographic errors may have been accidentally inserted. Please SPECIES EXTINCTIONS 27 PREHISTORIC HUMAN IMPACT ON CONTINENTAL ECOSYSTEMS Although the causes of the P-T and K-T extinction events are topics of much interest, research, and speculation (e.g., Jablonski, 1991; Kerr, 1993b; Morell, 1993; Sharpton et al., 1993), we can be certain that humans were not involved. That might not be the case, however, for the P-H event and certainly is not so for the current extinction event. As far as can be determined, human activity has significantly increased rates of extinction-perhaps by orders of magnitude—over the background rate (see below) and therefore is the primary cause of the current extinction event (Wilson, 1992). How far back in time can we trace human impact? Humans, including early forms of Homo and modern Homo sapiens, have occupied much of Africa and Eurasia for hundreds of millennia (Diamond, 1992; Klein, 1992). Archaeological evidence (especially bone assemblages and stone tools) suggests that people in Africa and Eurasia have hunted large mammals since at least 100,000 years ago (Nitecki and Nitecki, 1986). This early human predation probably focused on small or weak individuals rather than large, potentially dangerous animals. A major advance occurred in hunting proficiency 40,000 years ago, perhaps coinciding with the evolutionary emergence of modern people (Klein, 1984). For the first time, systematic and organized predation on large, powerful animals became an important part of human subsistence. It is likely that the first appreciable human effects on vertebrate faunas occurred at this time (Klein, 1992). Nevertheless, only seven species of large mammals (one elephant, one horse, one camel, one deer, and three bovid species) disappeared from Africa during the late Pleistocene (Martin, 1984). This might be because African large mammals were hunted by humans while humans were evolving anatomically and behaviorally. As a result, most African mammals, to varying extents, were able to survive prehistoric human predation, because they had the opportunity to evolve in response to human predation as the humans evolved. In the Americas, the first human occupation was by modern Homo sapiens, who was able to cross the Bering Strait land bridge because of lowered sea levels. The North American vertebrate fossil record of the past 2 million years reveals little extinction without replacement until the first humans arrived about 11,000 years ago (Martin, 1990). At that time, an overall warming trend was also causing major changes in the latitudinal, elevational, and edaphic ranges for most species of plants (Webb et al., 1993). The P-H extinction event primarily affected large-mammal species ( ); nearly all amphibian, reptile, and small-mammal species survived. A variety of North American megafauna was lost, including two glyptodont, use the print version of this publication as the authoritative version for attribution.

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About this PDF file: This new digital representation of the original work has been recomposed from XML files created from the original paper book, not from the original typesetting files. Page breaks are true to the original; line lengths, word breaks, heading styles, and other typesetting-specific formatting, however, cannot be retained, and some typographic errors may have been accidentally inserted. Please SPECIES EXTINCTIONS 28 four ground sloth, two bear, two sabertooth, one cheetah, one beaver, two capybara, two mastodon, one mammoth, one horse, one tapir, two peccary, three camel, two deer, one pronghorn, and four bovid genera (Martin, 1984; 1990). The collapse of the large North American mammal communities led to the demise of dependent species, such as carrion-feeding birds that fed on the abundant variety of carrion provided by herds of large animals, much as in modern African game parks. For example, 11,000 years ago, when ground sloths, mammoths, mastodons, horses, tapir, camels, and other species existed across North America, the currently endangered California condor lived as far away as Florida and New York (Steadman and Miller, 1987). People spread rapidly across the Bering Strait and North America, and within only hundreds of years, descendants of these big-game hunters dispersed throughout Central and South America as well. Their spears tipped with stylistically distinctive projectile points have been found with the bones of extinct megafauna (especially mammoths) at sites radiocarbon-dated to within a century or two of 11,000 years ago. According to the "Pleistocene overkill theory," early big-game hunters were the primary or only cause of the collapse of American large-mammal communities (Martin, 1984; 1990; Diamond, 1992). Scientists opposed to the overkill theory generally believe that changing climates and habitats were the sole or main cause of the P- H extinctions, but cannot explain why American large-mammal communities that survived many glacial- interglacial cycles quickly collapsed at the same time human populations in North America first became significant. Some scientists favor a combination of climate and habitat stress and human predation as the cause for the P-H extinctions (Owen-Smith, 1987). Regardless of the cause (Martin and Klein, 1984), the extinctions must have had a serious effect on North American ecosystems that once included a variety of grazers and browsers, not to mention their predators and commensals. When climates warmed at the end of the last glaciation, plant communities of southern regions or low elevations did not simply move as entire communities. Instead, species of plants responded individually and, therefore, plant communities assembled during the Holocene were not the same as those that had existed farther south or at lower elevations during the late Pleistocene (Betancourt et al., 1990; Pielou, 1991). The distributions of surviving species of mammals also changed, again somewhat independently rather than as intact communities (Semken, 1983). With most of the large mammals extinct, some peoples shifted to a more generalized diet, while others specialized in hunting bison, which survived into the Holocene. Bones from North American Holocene archaeological sites might represent as many as 50 species of vertebrates ranging from frogs and songbirds to eagles, bear, deer, and moose. Many use the print version of this publication as the authoritative version for attribution.

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About this PDF file: This new digital representation of the original work has been recomposed from XML files created from the original paper book, not from the original typesetting files. Page breaks are true to the original; line lengths, word breaks, heading styles, and other typesetting-specific formatting, however, cannot be retained, and some typographic errors may have been accidentally inserted. Please SPECIES EXTINCTIONS 29 of these sites bear evidence of species well outside their known post-Columbian range (Semken, 1983; Pielou, 1991). Intertribal trading of birds and mammals might account for some of these distributions, although many, if not most, reflect formerly indigenous populations, including species such as the trumpeter swan, Mississippi kite, swallow-tailed kite, whooping crane, sand-hill crane, long-billed curlew, Carolina parakeet, ivory-billed woodpecker, common raven, fish crow, rice rat, Allegheny woodrat, fisher, and puma. Prehistoric hunting, trapping, habitat modification, and climate-driven habitat changes might have been involved in some of the contractions of species' ranges. In parts of North America, the domesticated bottle gourd, chili pepper, beans, squash, and maize existed 5,000-6,000 years ago. The more sedentary lifestyle that came with agriculture was accompanied by a reduced dependence on wild plants and animals. But the gradual transition probably entailed shifting cultivation rather than long-term use of the same plots, and hunting, trapping, fishing, and gathering remained an important part of subsistence in most of North America long after plants and animals were domesticated. At the time of European contact, North American Indians still hunted turkey, black bear, deer, elk, moose, bison, and many smaller species. Some species, such as the California condor (Simons, 1983; Bates et al., 1993) and eagles, were hunted for feathers, bones, or ceremonial purposes rather than for food. Agriculture affects ecosystems through the reduction or loss of certain species of plants and animals, the propagation of others, and modifications of landscape, soils, and water supply through deforestation, erosion, deposition, channeling, flooding, and draining (Steadman, 1995a). Use of pesticides, energy supplements, and grazing are other factors. Because of the good water supply and fertile alluvial soils, much early agriculture developed along major river valleys; consequently, riparian biotas have been disturbed for centuries, if not millennia (Rea, 1983). Chaco Canyon, New Mexico, is a clear example of prehistoric overexploitation of natural resources, as revealed by studies of plant macrofossils from ancient packrat middens (Betancourt and Van Devender, 1981; Betancourt et al., 1986). The buildings constructed at Chaco Canyon from about AD 900 to 1150 by the Anasazi required 200,000 beams from large coniferous trees (ponderosa pine, subalpine fir, and blue/Englemann spruce). The trees were brought from as far away as 75 km, because these alpine conifers cannot live in the low elevation of Chaco Canyon. When the Anasazi arrived, the area around Chaco Canyon was a pinyon-juniper woodland. The pinyon and juniper trees provided firewood for the Anasazi, who farmed a narrow band of floodplain soil near their dwellings. As time progressed, the Anasazi had to go 15 km or more from Chaco Canyon just to gather firewood. They had transformed the area from a use the print version of this publication as the authoritative version for attribution.

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About this PDF file: This new digital representation of the original work has been recomposed from XML files created from the original paper book, not from the original typesetting files. Page breaks are true to the original; line lengths, word breaks, heading styles, and other typesetting-specific formatting, however, cannot be retained, and some typographic errors may have been accidentally inserted. Please SPECIES EXTINCTIONS 30 pinyon-juniper woodland to a nearly woodless desert scrub. The removal of pinyon, juniper, and riparian trees produced soil erosion, increased runoff, and probably a lowered water table in Chaco Canyon, all of which made it difficult to continue irrigated farming of the valley bottom. Drought-stressed agriculture and lack of firewood might have caused the Anasazi to abandon Chaco Canyon about 700 years ago (Betancourt and Van Devender, 1981). Scattered junipers grow at Chaco Canyon today, but no pinyons do. The incised streambed would be virtually impossible to modify today for agriculture. Because of human activities that began more than 1,000 years ago, Chaco Canyon still sustains impoverished plant and animal communities and remains a poor place for people to live. Another example of prehistoric humans having a significant effect on the carrying capacity of their ecosystems involves the Aleuts, whose overexploitation of sea otters appears to have changed the coastal ecosystems of the Aleutian Islands as long as 2,500 years ago (Simenstad et al., 1978). PREHISTORIC HUMAN IMPACT ON ISLAND ECOSYSTEMS The relatively small land areas of islands result in small populations of organisms that tend to be more vulnerable to extinction than those on continents (MacArthur and Wilson, 1967). Compared with continental species, a much greater proportion of island species have become extinct or endangered during the past several centuries of exploration and exploitation. In the past 2 decades, we have learned that, at least for vertebrates, human-caused extinctions had occurred on the world's islands during prehistoric times. Those extinctions seem to have been due to the same processes that lead to the extinction of island species today: direct human predation, predation from introduced mammals (such as rats, dogs, and pigs), habitat changes (such as those caused by deforestation, agriculture, and introduction of exotic plants), and introduced pathogens (such as avian malaria and avian pox). One way to assess the environmental impacts of prehistoric peoples on oceanic islands is to study the biotic history of islands that never were inhabited in pre-Columbian times. According to biogeographic theory, background extinctions are a regular part of an island's biological heritage. Knowing the rate of background extinction allows the severity of the human-caused extinction we see today to be evaluated. The human history of the Galápagos Islands, for example, began with brief Spanish and British visits in the 16th and 17th centuries. We can examine the pre-Columbian Galápagos biota to determine the level of background extinction. Thirty-four species of reptiles, birds, and mammals are known to have become extirpated in the Galápagos during the Holocene (Steadman et al., use the print version of this publication as the authoritative version for attribution.

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About this PDF file: This new digital representation of the original work has been recomposed from XML files created from the original paper book, not from the original typesetting files. Page breaks are true to the original; line lengths, word breaks, heading styles, and other typesetting-specific formatting, however, cannot be retained, and some typographic errors may have been accidentally inserted. Please SPECIES EXTINCTIONS 31 1991). The Holocene vertebrate fossil record from the Galápagos is based upon 15 sites from five different islands, with nearly 500,000 identified bones spanning the past 8,000 years. This record reveals only three extinct populations or species that might have become extinct before human contact. In other words, 31 of the 34 known extinctions occurred after the arrival of people 200 years ago. A similar pattern has been corroborated in Tonga, where the arrival of humans 3,000 years ago caused more extinctions of birds than had occurred during the previous 100,000 years (Steadman, 1993). Approximately 9,600 species of birds exist today (Sibley and Monroe, 1990). The prehistoric human colonization of Pacific islands (Melanesia, Micronesia, and Polynesia) resulted in the loss of as many as 2,000 species of birds, especially flightless rails, but also petrels, ibises, herons, ducks and geese, hawks and eagles, megapodes, sandpipers, gulls, pigeons and doves, parrots, owls, and passerines (Steadman, 1989; 1991; 1993; 1995b). The world avifauna would be about 20% richer today had islands of the Pacific remained unoccupied by humans. In the Hawaiian Islands, at least 77 endemic species of birds have become extinct since the arrival of Polynesians nearly 2,000 years ago (James and Olson, 1991; Olson and James, 1991) (see Table 2-1). Furthermore, several individual island populations of species have been reduced or extirpated. Most extinct species of Hawaiian birds, including the majority of TABLE 2-1 Loss of Birds in the Hawaiian Islands Since Human Arrivala Species Number of Extinct Species Number of Extirpated Populations Petrels 1 2 Ibises 2 3 Waterfowl 9 17 Rails 12 14 Hawks 2 6 Owls 4 4 Crows 2 5 Warblers 0 1 Thrushes 1 4 Honeyeaters 6 9 Drepanidine finches 38 56 Total 77 121 use the print version of this publication as the authoritative version for attribution. a Data condensed from James and Olson (1991) and Olson and James (1991).

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About this PDF file: This new digital representation of the original work has been recomposed from XML files created from the original paper book, not from the original typesetting files. Page breaks are true to the original; line lengths, word breaks, heading styles, and other typesetting-specific formatting, however, cannot be retained, and some typographic errors may have been accidentally inserted. Please SPECIES EXTINCTIONS 32 cardueline finches (the "Hawaiian honeycreepers"), died out before the arrival of Europeans (Olson and James, 1982; 1984; James et al., 1987). On hundreds of tropical islands, including those that are a part of or affiliated with the United States (Puerto Rico, U.S. Virgin Islands, Hawaii, American Samoa, and various Micronesian island groups), the prehistoric and ongoing extinction of numerous populations and species of birds has consequences beyond losing the birds themselves. Most of the extinct land birds were omnivores, frugivores, granivores, or nectarivores; indigenous plants might have depended on those birds for pollination or seed dispersal. Many species of Pacific island trees and shrubs seem to have no natural means of intra- or interisland dispersal today. Because island biotas are so degraded (i.e., so many populations and species already are extinct), endangered-species programs on islands face an extraordinary challenge to maintain conditions that might permit the long-term survival of the remaining species. RELATING THE PAST TO THE PRESENT Ecosystem Degradation and Restoration Environmental problems often are viewed as modern phenomena. It is true that most plant and animal communities have been affected by the past 2 centuries of commercial and residential development; nonetheless, most of the earth was far from pristine in preindustrial times. The use of tools and fire has set humans apart from other animals for many millennia, and all ancient human societies had various effects on the ecosystems within which they lived (e.g., Simenstad et al., 1978; Betancourt and Van Devender, 1981; Betancourt et al., 1986; Diamond, 1992). By studying the effects prehistoric peoples had on the environment, we can begin to estimate the composition of plant and animal communities during two critical times: before human contact (when communities were pristine) and at western contact (when all previous human effects had been due to native peoples). Such knowledge is important for long-term projections of community stability, as well as to help understand to what extent various communities might recover from human disturbances. This is not to suggest that the environmental conditions that prevailed in 1492, when major European exploration of the Americas began, be the benchmark for discussion of the condition of any given ecosystem or a goal for restoration. First, North America was not pristine then. The last time our continent was unaffected by human activity was late in the last glacial interval, when a dramatically different climate resulted in plant and animal associations that simply would not be possible in today's climate. In addition, exact reconstructions of 1492 biotic communities would be impossible use the print version of this publication as the authoritative version for attribution.

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About this PDF file: This new digital representation of the original work has been recomposed from XML files created from the original paper book, not from the original typesetting files. Page breaks are true to the original; line lengths, word breaks, heading styles, and other typesetting-specific formatting, however, cannot be retained, and some typographic errors may have been accidentally inserted. Please SPECIES EXTINCTIONS 33 because so many species, subspecies, and varieties of plants and animals already have been lost. The grizzly bear, gray wolf, and mountain lion, for example, no longer occupy more than a million km2 of their former North American ranges (Mech, 1974; Currier, 1983; Pasitschniak-Arts, 1993). Given current habitat conditions and land-use patterns, restoration of these species would be impractical in much of their former ranges. However, we still can use information about the prehistoric environment data to help plan for the future. Many tracts of land in North America are relatively undisturbed, and if biologically feasible, we might try to restore locally extirpated species as part of a recovery program for endangered species. Rather than using past distributions as strict guidelines for restoration efforts, the data could be part of planning conservation programs, with a goal of preserving plant and animal communities that approach those of a less disturbed state. In some cases, such as on Pacific islands, prehistoric information provides clear direction for translocating endangered species onto islands that once were part of their natural range (Franklin and Steadman, 1991). Rates of Extinction In a 1992 report to Congress, the U.S. Fish and Wildlife Service categorized 711 species of plants and animals as follows: improving—69 (10%), stable—201 (28%), declining—232 (33%), extinct—14 (2%), and unknown—195 (27%) (USFWS, 1992). The relative proportions of these categories among plants and animals are similar, except for extinctions, all of which are animals. The 232 declining species eventually will become extinct unless the decline is halted. Rates of extinction are difficult to quantify precisely, in part because various authors measure them in different ways (Benton, 1995). However, examinations of relative rates of extinctions and of well-known biota make it clear that extinctions are increasing in many groups of organisms (Nott et al., 1995). For example, Nott et al. provided estimates of regional and global extinction rates based on some well- known examples. They listed 36 species that had become extinct in the past 100 years of the 8,500 species in the South African floristic community known as fynbos; another 618 were deemed to be at some risk of extinction. Forty taxa—mostly species—of the approximately 950 species of freshwater fishes in the United States became extinct in the past 100 years, with more than 100 at risk of extinction. Of the 297 North American species and 13 subspecies of freshwater mussels in North America, 21 have become extinct since the beginning of this century and 120 are endangered. Sixty species of mammals have become extinct in the recent past; of those, 18 were found among the 300 species in the use the print version of this publication as the authoritative version for attribution.

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About this PDF file: This new digital representation of the original work has been recomposed from XML files created from the original paper book, not from the original typesetting files. Page breaks are true to the original; line lengths, word breaks, heading styles, and other typesetting-specific formatting, however, cannot be retained, and some typographic errors may have been accidentally inserted. Please SPECIES EXTINCTIONS 34 nonmarine Australian mammal fauna. An additional 43 species have been lost from more than 50% of their former ranges. (Other well-known cases, such as birds and plants on islands and the cichlid fishes of Lake Victoria, are discussed elsewhere in this chapter.) Nott et al. (1995) made a conservative estimate of global extinction rates for various taxonomic groups by assuming that no other species in those groups had become extinct worldwide and then dividing the number of regional extinctions by the global number of species in the groups. The resulting estimated global extinction rates —which would have been larger if other known extinctions were included in the estimate—ranged from 10 to 1,000 times the estimated background rates. They predicted that future extinction rates, based on knowledge of species currently at risk of extinction, would be even higher. Part of the difficulty in grasping the significance of extinction rates is that they should be evaluated in intervals of millennia or more, as well as the seasons, years, or decades that measure most ecological studies. Another well-studied taxonomic group is North American birds. At least 20 to 40 species of birds were lost at the end of the Pleistocene, mainly because of the extinction of large mammals on which they depended (Steadman and Martin, 1984; Steadman and Miller, 1987; Emslie 1987, 1990). In the next 10,000 years, before the arrival of Europeans, only two North American species definitely became extinct, the flightless marine duck Chendytes lawi (Morejohn, 1976; Guthrie, 1992) and the small turkey Meleagris crassipes (Rea, 1980). In the past 200 years, at least five species of birds have been lost (great auk, Labrador duck, passenger pigeon, Carolina parakeet, and ivory-billed woodpecker). Two others, the Eskimo curlew and Bachman's warbler, are near extinction. Several other species persist today in small, local populations (e.g., California condor, whooping crane, red-cockaded woodpecker, black-capped vireo, golden-cheeked warbler, and Kirtland's warbler). Some of those last eight species are likely to die out in the next 200 years, as are others that are known to be endangered, threatened, or in decline today (see North American Breeding Bird Survey data for examples of birds whose populations have declined substantially in recent years). Most climatologists believe that the world will experience another ice age ''unless there is some fundamental and unforeseen change in the climate system" (Imbrie and Imbrie, 1979). Indeed, the earth's climate has varied as far back as we can tell anything about it and almost surely will continue to vary. If the extinction rate of birds continues to be about five species per 200 years or about 25 species per millennium, there could be hundreds fewer species to face the changing habitats that will come with North America's next ice age or any major climatic change. Speciation (i.e., the evolution of new species) is unlikely to offset these losses. The extinction of birds could use the print version of this publication as the authoritative version for attribution.

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About this PDF file: This new digital representation of the original work has been recomposed from XML files created from the original paper book, not from the original typesetting files. Page breaks are true to the original; line lengths, word breaks, heading styles, and other typesetting-specific formatting, however, cannot be retained, and some typographic errors may have been accidentally inserted. Please SPECIES EXTINCTIONS 35 affect other organisms as well. For example, many species of North American plants may face a northward range shift if the climate warms (or a southward shift if it cools); they will have to accomplish this task without the passenger pigeon, which was by far the most abundant consumer and disperser of their seeds until a century ago. Habitat Loss Species endangerment and extinction have three major anthropogenic causes—overhunting or overharvesting; introduction of nonnative species, including the spread of disease; and habitat degradation or loss. All three causes probably were factors in prehistoric as well as modern times. In some locations and for certain species, the first two have been the most critical. For example, the decline of some species of marine vertebrates, such as certain whales, can be attributed largely to commercial overexploitation. And many birds in the Hawaiian Islands have suffered from predation and diseases caused by introduced species (Olson and James, 1982; Ehrlich et al., 1992). For most species in decline and for most of those on the edge of extinction in the U.S. today, however, the most serious threat appears to be habitat degradation or loss (hereafter denoted as habitat destruction). Habitat destruction is the primary threat to the majority of endangered and threatened plants (Cook and Dixon, 1989) and is an increasing threat to songbirds and freshwater fishes (Miller et al., 1989; Ehrlich et al., 1992; Allen and Flecker, 1993; Noss et al., 1995) and perhaps for hundreds or even thousands of the lesser-known invertebrates in the United States (Deyrup and Franz, 1994). Habitat destruction is described either as the current rate of destruction (expressed in hectares/year) or as a cumulative amount of destruction (expressed as a percentage of some historic baseline). No comprehensive summary has been compiled of the current rates of destruction of major habitat types, but several studies have reviewed cumulative losses in particular regions, such as California (Jensen et al., 1993), and for particular habitat types such as wetlands (NRC, 1992a; 1995). A recent review of cumulative loss by Noss et al. (1995) is noteworthy for its broad scope and fine level of distinction with which it treats habitat types and locations. Noss et al. acknowledged that the information needed to provide uniform geographic coverage is missing, and that habitat destruction is better catalogued in the eastern United States than elsewhere. The discussion of cumulative losses that follows should be read with three considerations. First, habitat that is degraded or lost is not necessarily biologically depauperate. For example, grazed western grasslands and shrub use the print version of this publication as the authoritative version for attribution.

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About this PDF file: This new digital representation of the original work has been recomposed from XML files created from the original paper book, not from the original typesetting files. Page breaks are true to the original; line lengths, word breaks, heading styles, and other typesetting-specific formatting, however, cannot be retained, and some typographic errors may have been accidentally inserted. Please SPECIES EXTINCTIONS 36 steppe still support wildlife,1 just not the diversity that inhabited those lands before grazing. Second, even habitat that is not considered degraded or lost might not be able to support the abundance and variety of species that it once did. Such habitat might be used for recreation or other activities, or simply little of it might be left. Moreover, some habitats are fragmented or of such small area that they might no longer include the habitats required by some specialized species or might be below the critical area needed to support species with large home ranges. Finally, air or water pollution and climate change might be affecting the viability of habitat too subtly for the consequences to be revealed in surveys. Cumulative losses of wetlands have attracted much concern and scrutiny (NRC, 1992a), perhaps because 50% of animals and 33% of plants listed as endangered or threatened under the Endangered Species Act depend on wetland habitats (Nelson, 1989). Although wetlands comprise only a small percentage of the U.S. land area, they have been prime sites for conversion to agriculture or urban sprawl. According to the National Research Council (NRC, 1992a), approximately 30% (117 million acres) of U.S. wetlands have been converted (53%, if Alaska is excluded). In some regions and for some types of wetlands, the losses have been more severe. For example, California has lost at least 80% of its interior and coastal wetlands (Jensen et al., 1993). More than 85% of the flow of inland waters is now artificially controlled, and 98% of stream reaches has been degraded enough to be unworthy of federal designation as wild or scenic rivers (Benke, 1990). The cumulative losses of terrestrial and aquatic habitat reviewed by Noss et al. (1995) included 27 specific habitats that they classified as "critically endangered" (greater than 98% cumulative destruction). Those habitats included longleaf pine forests in the southeastern coastal plain, tall-grass prairie east of the Missouri River, dry prairie in Florida, native grasslands in California, and old-growth pine forests in Michigan. Other habitats, classified as endangered (between 85% and 98% cumulative destruction) included old-growth forest in the Pacific Northwest and elsewhere, red spruce forests in the central Appalachians, coastal heathland in southern New England and Long Island, all other tall-grass prairie, vernal pools in the Central Valley and Southern California, coastal redwood forests in California, and native shrub and grassland steppe in Oregon and Washington. Habitat loss is a direct threat to many species, and therefore important to administration of the Endangered Species Act. Indeed, the ESA's purpose "to provide a means whereby the ecosystems upon which endangered use the print version of this publication as the authoritative version for attribution. 1 Western grasslands are considered by some to be "healthier" than they were 100 years ago, although information is not available to assess this objectively (NRC, 1994).

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About this PDF file: This new digital representation of the original work has been recomposed from XML files created from the original paper book, not from the original typesetting files. Page breaks are true to the original; line lengths, word breaks, heading styles, and other typesetting-specific formatting, however, cannot be retained, and some typographic errors may have been accidentally inserted. Please SPECIES EXTINCTIONS 37 species and threatened species depend may be conserved" recognizes the importance of habitat to species, and for this reason, we return to the subject of habitat protection under the ESA in Chapters 4 and 5, where we describe modern ecological concepts of habitat, clarify the role of habitat in the protection of endangered species, and suggest ways in which the act's stated purpose can be better achieved. Introduced Species Much of the world's biota has been modified by the introduction of exotic (nonnative) species. Introduced plant species range from an estimated 7% of the total in Java to 28% in Canada and 47% in New Zealand (Heywood, 1989); introduced mammal species constitute about 95% of the total in New Zealand and Hawaii but much less than 5% in North America (Brown, 1989). Introduced birds are nearly 70% of the total in Hawaii (Brown, 1989), with "virtually no native land birds below 1000 m" (Pimm, 1989). Fish are among the most widely introduced of vertebrates; in many cases, their introductions were deliberate, as vividly described for the western United States by Lampman (1946). Even in continental areas, exotic fishes can constitute large fractions of the total number of species and have deleterious effects (Courtenay and Stauffer, 1984). For example, in California, 47 species of a total of 112 freshwater and anadromous species are introduced (Moyle, 1976); introduced species constitute substantial portions of the biota in other western states as well (e.g., Sigler and Sigler, 1987; Sublette et al., 1990). Despite the difficulty of proving that introduced species have caused extinctions, the circumstantial evidence is often overwhelming. Many extinctions, especially of birds and plants but also mammals, reptiles, snails, and others have been attributed to introduced species, especially on islands (Loope and Mueller-Dombois, 1989; Macdonald et al., 1989; Pimm, 1989) and in their analogs, isolated freshwater bodies (Ono et al., 1983). Groombridge (1992) considered that introduced species were responsible for 39% of all animal extinctions whose causes were known, and Macdonald et al. concluded that 12.7% of threatened terrestrial vertebrate species on mainland areas and 31% on islands were affected by introductions. For example, the National Research Council attributed the near extinction of the endangered Hawaiian crow or 'Alala (Corvus hawaiiensis), to introduced predators, introduced diseases, and habitat alteration (NRC, 1992b). The European zebra mussel (Dreissena polymorpha) (Ricciardi et al., in press) and the Asiatic clam (Corbicula fluminea) (Clarke, 1988) have been implicated in the extinctions of species of native freshwater mussels in the United States, especially in drainages of the Gulf of Mexico and Atlantic Ocean; those authors consider that further extinctions are likely. Solz and Naiman (1978) use the print version of this publication as the authoritative version for attribution.

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About this PDF file: This new digital representation of the original work has been recomposed from XML files created from the original paper book, not from the original typesetting files. Page breaks are true to the original; line lengths, word breaks, heading styles, and other typesetting-specific formatting, however, cannot be retained, and some typographic errors may have been accidentally inserted. Please SPECIES EXTINCTIONS 38 and Ono et al. (1983) attributed the extinction of the Ash Meadows (Nevada) killifish (Empetrichthys merriami) to competition and predation from introduced species, and Skelton (1993), Etnier and Starnes (1993), and Jenkins and Burkhead (1994) described local extirpation or near extinction of rare fish taxa by exotics and habitat degradation in South Africa, Tennessee, and Virginia. In the western United States and elsewhere, introduced salmonid species have hybridized with endemic forms (Behnke, 1992). Perhaps the most notorious of all exotic fish introductions is that of the Nile perch (Lates nilotica) into Lake Victoria in East Africa, where it has devastated the diversity of the endemic cichlid fishes. Estimates of extinctions there have been complicated by habitat changes and incomplete sampling, but Witte et al. (1992) estimated that 200 species of endemic cichlid fishes (of an original total of about 300) had "already disappeared or [were] threatened with extinction" mainly as a result of predation by the Nile perch. In many cases, the effects of exotic species have been exacerbated by habitat degradation. For example, loss of habitat reduced the Hawaiian crow population and made it more vulnerable to the effects of introduced predators and diseases (NRC, 1992b). Impoundments on the Colorado River changed the habitat to favor introduced species of fishes that compete with and prey on some native endangered species in addition to reducing spawning habitat for the native species and adversely changing the water temperature (Ono et al., 1983). Accidental species introductions have increased with increased human mobility and are not likely to decline in the near future. Deliberate introductions have occurred for hundreds of years and continue despite a growing awareness of the problems they can cause and laws and regulations that prohibit them. In a few cases, introductions are extremely well documented and studied as, for example, the various predatory species introduced into California to control the California red scale (Aonidiella aurantii), which was itself accidentally introduced from Australia between 1868 and 1875 (Luck, 1986). In general, the effects of introduced species are difficult to predict (NRC, 1986), although some progress has been made (Levin, 1989; Pimm, 1989; Simberloff, 1989; Ricciardi et al., in press). Unless they occupy small isolated areas, such as small islands or lakes, exotics are difficult to eradicate, although control is sometimes possible if started early, especially for many vertebrates (Groves, 1989; Macdonald et al., 1989). CONCLUSIONS AND RECOMMENDATIONS Several concepts from this chapter apply to the understanding of biological diversity and attempts to protect it. From these concepts we draw the following conclusions. use the print version of this publication as the authoritative version for attribution.

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About this PDF file: This new digital representation of the original work has been recomposed from XML files created from the original paper book, not from the original typesetting files. Page breaks are true to the original; line lengths, word breaks, heading styles, and other typesetting-specific formatting, however, cannot be retained, and some typographic errors may have been accidentally inserted. Please SPECIES EXTINCTIONS 39 • The current extinction event differs from extinction events in the fossil record in being less selective, i.e., it actually or potentially involves all taxonomic groups of organisms, in any sort of nonmarine habitat. Although the number of documented extinctions in recent years might appear to be small as a fraction of all extant species, it is important to understand that even so-called catastrophic extinctions took many thousands of years to occur. Thus, the appropriate focus is the rate of extinctions, and the current extinction rate appears to be significantly greater than background rates. Available evidence suggests that the current accelerated extinction rate is largely human-caused and is likely to increase rather than decrease in the near future. • Both modern and prehistoric human activities, especially those associated with agriculture and urbanization, have altered natural ecosystems such as forests, lakes, prairies, and floodplains through the reduction or loss of certain species of plants and animals, the propagation of others, and modifications of landscape, soils, and water supply. • On islands, including those that are a part of or affiliated with the United States, a relatively high percentage of species has become extinct or endangered because of both modern and prehistoric human activities. Direct human predation, predation from introduced mammals (such as rats, dogs, and pigs), habitat changes (such as deforestation, urbanization, agriculture, and exotic plants), and introduced pathogens (such as avian pox and avian malaria) account for these extinctions. Because island biotas already have lost so many populations and species and land resources are so limited, conservation programs on islands face an extraordinary challenge to maintain conditions that will allow the long-term survival of existing species. • The prehistoric and ongoing extinction of so many populations and species of birds on islands has consequences beyond losing the birds themselves. The losses of land birds, for example, may influence pollination or seed dispersal of indigenous plants. Based on these conclusions and as substantiated within this chapter, we make these recommendations. • Because we can relate many biotic events to abiotic events in earth history with reasonable accuracy, our knowledge of the past is important for predicting biotic responses to future changes in climate and other physical phenomena. Therefore, when feasible, conservation decisions should consider long-term impacts as revealed by our improved understanding of the earth's physical and biotic history. • The natural and anthropogenic processes affecting extinctions and speciation operate at various time scales. To understand the potential long- use the print version of this publication as the authoritative version for attribution.

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About this PDF file: This new digital representation of the original work has been recomposed from XML files created from the original paper book, not from the original typesetting files. Page breaks are true to the original; line lengths, word breaks, heading styles, and other typesetting-specific formatting, however, cannot be retained, and some typographic errors may have been accidentally inserted. Please SPECIES EXTINCTIONS 40 term impacts of the current extinction event, the process of extinction should be examined across these time scales. Extinction rates that seem low on first inspection could in fact result in major losses of species if evaluated on longer time scales. • There are three primary anthropogenic processes that lead to species endangerment and extinction— overharvesting; the introduction of nonnative species, including the spread of disease; and habitat destruction. For most endangered species in the United States today, the most serious threat is habitat destruction. Because of this, habitat conservation is the best single means to counter extinction. Introduced species also present a significant threat. Policies that prevent deliberate introductions and reduce the adverse effects of accidental introductions should be encouraged. REFERENCES Allen, J.D., and A.S. Flecker. 1993. Biodiversity conservation in running waters. BioScience 43:32-43. Appenzeller, T. 1993. Ancient climate coolings are on thin ice. Science 262:1818-1819. Bates, C.D., J.A. Hamber, and M.J. Lee. 1993. The California condor and the California Indians. Am. Indian Art 19:40-47. Behnke, R.J. 1992. Native Trout of Western North America. American Fisheries Society , Bethesda, Md. Benke, A.C. 1990. A perspective on America's vanishing streams. J. Am. Benthol. Soc. 9(1):77-78. Benton, M.J. 1995. Diversification and extinction in the history of life. Science 268:52-58. Betancourt, J.L., and T.R. Van Devender. 1981. Holocene vegetation in Chaco Canyon, New Mexico. Science 214:656-658. Betancourt, J.L., J.S. Dean, and H.N. Hull. 1986. Prehistoric long-distance transport of construction beams, Chaco Canyon, New Mexico. Am. Antiquity 51:370-375. Betancourt, J.L., T.R. Van Devender, and P.S. Martin, eds. 1990. Packrat Middens: The Last 40,000 Years of Biotic Change. Tucson, Ariz.: University of Arizona Press. Brown, J.H. 1989. Patterns, modes, and extents of invasions by vertebrates. Pp. 85-109 in Biological Invasions: A Global Perspective. SCOPE 37, J.A. Drake, H.A. Mooney, F. di Castri, R.H. Groves, F.J. Kruger, M. Rejmanek, and M. Williamson, eds. Chichester, U.K.: John Wiley & Sons. Burney, D.A. 1993. Recent animal extinctions: Recipes for disaster. Am. Sci. 81:530-541. Clarke, A.H. 1988. Aspects of corbiculid-unionid sympatry in the United States. Malacol. Data Net 2(3/4):57-99. Cook, R.E., and P. Dixon. 1989. A review of recovery plans for threatened and endangered plant species. World Wildlife Fund Report, Washington, D.C. Courtenay, W.R., Jr., and J.R. Stauffer, Jr. 1984. Distribution, Biology, and Management of Exotic Fishes. Baltimore, Md.: The Johns Hopkins University Press. Currier, M.J.P. 1983. Felis concolor. Mamm. Species 20. Dansgaard, W., S.J. Johnsen, H.B. Clausen, D. Dahl-Jensen, N.S. Gundestrup, C.U. Hammer, C.S. Hvidberg, J.P. Steffensen, A.E. Sveinbjörnsdottir, J. Jouzel, and G. Bond. 1993. Evidence for general instability of past climate from a 250-kyr ice-core record. Nature 364:218-220. use the print version of this publication as the authoritative version for attribution.

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About this PDF file: This new digital representation of the original work has been recomposed from XML files created from the original paper book, not from the original typesetting files. Page breaks are true to the original; line lengths, word breaks, heading styles, and other typesetting-specific formatting, however, cannot be retained, and some typographic errors may have been accidentally inserted. Please SPECIES EXTINCTIONS 41 Deyrup, M., and R. Franz, eds. 1994. Rare and Endangered Biota of Florida. Invertebrates, Vol. 4. Gainesville, Fla.: University Presses of Florida. Diamond, J. 1992. The Third Chimpanzee. New York: Harper Collins. Ehrlich, P.R., D.S. Dobkin, and D. Wheye. 1992. Birds in Jeopardy. Stanford, Calif.: Stanford University Press. Emslie, S.D. 1987. Age and diet of fossil California condors in Grand Canyon, Arizona. Science 237:768-770. Emslie, S D. 1990. Additional 14C dates on fossil California condor. Natl. Geograph. Res. 6:134-135. Engbring, J. and H.D. Pratt. 1985. Endangered birds in Micronesia: Their history, status, and future prospects. Pp. 71-105 in Bird Conservation 2, S.A. Temple, ed. Madison, Wisc.: University of Wisconsin Press. Etnier, D.A., and W.C. Starnes. 1993. The Fishes of Tennessee. Knoxville, Tenn.: University of Tennessee Press. Franklin, J., and D.W. Steadman. 1991. The potential for conservation of Polynesian birds through habitat mapping and species translocation. Conserv. Biol. 5:506-521. FWS (U.S. Fish and Wildlife Service). 1992. Endangered and Threatened Species Recovery Program. Report to Congress. U.S. Department of Interior, U.S. Fish and Wildlife Service, Washington, D.C. GRIP (Greenland Ice-core Project). 1993. Climate instability during the last interglacial period recorded in the GRIP ice core. Nature 364:203-207. Groombridge, B., ed. 1992. Global Biodiversity: Status of the Earth's Living Resources. New York: Chapman and Hall. Grootes, P.M., M. Stuiver, J.W.C. White, S. Johnsen, and J. Jouzel. 1993. Comparison of oxygen isotope records from the GISP2 and GRIP Greenland ice cores. Nature 366:552-554. Groves, R.H. 1989. Ecological control of invasive terrestrial plants. Pp. 437-461 in Biological Invasions: A Global Perspective. SCOPE 37, J.A. Drake, H.A. Mooney, F. Di Castri, R.H. Groves, F.J. Kruger, M. Rejmanek, and M. Williamson, eds. Chichester, U.K.: John Wiley & Sons. Guthrie, D.A. 1992. A late Pleistocene avifauna from San Miguel Island, California. Sci. Ser. Publ. 36, pp. 319-327. Natural History Museum of Los Angeles County, Los Angeles, Calif. Heywood, V.H. 1989. Extents and modes of terrestrial invasions by plants. Pp. 31-60 in Biological Invasions: A Global Perspective. SCOPE 37, J.A. Drake, H.A. Mooney, F. Di Castri, R.H. Groves, F.J. Kruger, M. Rejmanek, and M. Williamson, eds. Chichester, U.K.: John Wiley & Sons. Imbrie, J., and K.P. Imbrie. 1979. The Ice Ages: Solving the Mystery. Hillside, N.J.: Enslow Publishers. Jablonski, D. 1991. Extinctions: A paleontological perspective. Science 253:754-757. James, H.F., and S.L. Olson. 1991. Descriptions of thirty-two species of birds from the Hawaiian Islands. Part II. Passeriformes. Ornithol. Monogr. 46:1-88. James, H.F., T.W. Stafford, Jr., D.W. Steadman, S.L. Olson, P.S. Martin, A.J.T. Jull, and P.C. McCoy. 1987. Radiocarbon dates on bones of extinct birds from Hawaii. Proc. Natl. Acad. Sci. USA 84:2350-2354. Jenkins, R.E., and N.M. Burkhead. 1994. Freshwater Fishes of Virginia. American Fisheries Society, Bethesda, Md. Kerr, R.A. 1993a. The whole world had a case of the Ice Age shivers. Science 262:1972-1973. Kerr, R.A. 1993b. A bigger death knell for the dinosaurs? Science 261:1518-1519. Klein, R.G. 1984. Mammalian extinctions and Stone Age people in Africa. Pp. 553-573 in use the print version of this publication as the authoritative version for attribution.

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About this PDF file: This new digital representation of the original work has been recomposed from XML files created from the original paper book, not from the original typesetting files. Page breaks are true to the original; line lengths, word breaks, heading styles, and other typesetting-specific formatting, however, cannot be retained, and some typographic errors may have been accidentally inserted. Please SPECIES EXTINCTIONS 42 Quaternary Extinctions, P.S. Martin and R.G. Klein, eds. Tucson, Ariz.: University of Arizona Press. Klein, R.G. 1992. The impact of early people on the environment: The case of large mammal extinctions. Pp. 13-34 in Human Impact on the Environment: Ancient Roots, Current Challenges, J.E. Jacobsen and J. Firor, eds. Boulder, Colo.: Wheatview. Klein, R.G. 1994. The problem of modern human origins. Pp. 3-17 in Origins of Anatomically Modern Humans, M.H. Nitecki and D.V. Nitecki, eds. New York: Plenum. Lampman, B.H. 1946. The Coming of the Pond Fishes. Portland, Oreg.: Binfords & Mort. Levin, S.A. 1989. Analysis of risk and invasions and control programs. Pp. 425-435 in Biological Invasions: A Global Perspective. SCOPE 37, J.A. Drake, H.A. Mooney, F. Di Castri, R.H. Groves, F.J. Kruger, M. Rejmanek, and M. Williamson, eds. Chichester, U.K.: John Wiley & Sons. Loope, L.L., and D. Mueller-Dombois. 1989. Characteristics of invaded islands, with special reference to Hawaii. Pp. 257-280 in Biological Invasions: A Global Perspective. SCOPE 37, J.A. Drake, H.A. Mooney, F. Di Castri, R.H. Groves, F.J. Kruger, M. Rejmanek, and M. Williamson, eds. Chichester, U.K.: John Wiley & Sons. Luck, R.F. 1986. Biological control of California red scale. Pp. 165-189 in Ecological Knowledge and Environmental Problem-Solving: Concepts and Case Studies. Washington, D.C.: National Academy Press. MacArthur, R.H., and E.O. Wilson. 1967. The Theory of Island Biogeography. Princeton, N.J.: Princeton University Press. Macdonald, I.A.W., L.L. Loope, M.B. Usher, and O. Hamman. 1989. Wildlife conservation and the invasion of nature reserves by introduced species: A global perspective. Pp. 215-255 in Biological Invasions: A Global Perspective. SCOPE 37, J.A. Drake, H.A. Mooney, F. Di Castri, R.H. Groves, F.J. Kruger, M. Rejmanek, and M. Williamson, eds. Chichester, U.K.: John Wiley & Sons. Markgraf, V. 1989. Palaeoclimate in central and South America since 18,000 BP based on pollen and lake-level records. Quat. Sci. Rev. 8:1-24. Martin, P.S. 1984. Prehistoric overkill: The global model. Pp. 354-403 in Quaternary Extinctions, P.S. Martin and R.G. Klein, eds. Tucson, Ariz.: University of Arizona Press. Martin, P.S. 1990. 40,000 years of extinctions of the "planet of doom." Palaeogeogr. Palaeoclimatol. Palaeoecol. 82:187-201. Martin, P.S., and R.G. Klein, eds. 1984. Quaternary Extinctions. Tucson, Ariz.: University of Arizona Press. Martinson, D.G., N.G. Pisias, J.D. Hays, J. Imbrie, T.C. Moore, Jr., and N.J. Shackleton. 1987. Age dating and the orbital theory of the Ice Ages: Development of a high-resolution 0 to 300,000-year chronostratigraphy. Quat. Res. 27:1-29. Mayewski, P.A., L.D. Meeker, S. Whitlow, M.S. Twickler, M.C. Morrison, R.B. Alley, P. Bloomfield, and K. Taylor. 1993. The atmosphere during the Younger Dryas. Science 261:195-197. Mech, L D. 1974. Canis lupus. Mamm. Species 37. Miller, R.R., J.D. Williams, and J.E. Williams. 1989. Extinctions of North American fishes during the past century. Fisheries 14:22-38. Morejohn, G.V. 1976. Evidence of the survival to recent times of the extinct flightless duck Chendytes lawi Miller. Smithsonian Contrib. Paleobiol. 27:207-211. Morell, V. 1993. How lethal was the K-T impact? Science 261:1518-1519. Moyle, P.B. 1976. Inland Fishes of California. Berkeley, Calif.: University of California Press. Nadachowski, A. 1993. The species concept and Quaternary mammals. Quat. Int. 19:9-11. use the print version of this publication as the authoritative version for attribution.

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About this PDF file: This new digital representation of the original work has been recomposed from XML files created from the original paper book, not from the original typesetting files. Page breaks are true to the original; line lengths, word breaks, heading styles, and other typesetting-specific formatting, however, cannot be retained, and some typographic errors may have been accidentally inserted. Please SPECIES EXTINCTIONS 43 Nelson, J. 1989. Agriculture, wetlands, and endangered species: The Food Security Act of 1985. Endangered Species Tech. Bull. 14:6-8. Nitecki, M.H., and D.V. Nitecki, eds. 1986. The Evolution of Human Hunting. New York: Plenum. Noss, R.F., E.T. LaRoe, III, and J.M. Scott. 1995. Endangered Ecosystems of the United States: A Preliminary Assessment of Loss and Degradation. Biol. Rep. 28. U.S. Department of the Interior, National Biological Service, Washington, D.C. Nott, M.P., E. Rogers, and S. Pimm. 1995. Modern extinctions in the kilo-death range. Curr. Biol. 5:14-17. Nowak, R.M., and J.L. Paradiso. 1983. Walker's Mammals of the World. Baltimore, Md.: The Johns Hopkins University Press. NRC (National Research Council). 1986. Ecological Knowledge and Environmental Problem-Solving: Concepts and Case Studies. Washington, D.C.: National Academy Press. NRC (National Research Council). 1992a. Restoration of Aquatic Ecosystems: Science, Technology, and Public Policy. Washington, D.C.: National Academy Press. NRC (National Research Council). 1992b. The Scientific Bases for the Preservation of the Hawaiian Crow. Washington, D.C.: National Academy Press. NRC (National Research Council). 1994. Rangeland Health: New Methods to Classify, Inventory, and Monitor Rangelands. Washington, D.C.: National Academy Press. NRC (National Research Council). 1995. Wetlands: Characteristics and Boundaries. Washington, D.C.: National Academy Press. Olson, S.L., and H.F. James. 1982. Fossil birds from the Hawaiian Islands: Evidence for wholesale extinction by man before western contact. Science 217:633-635. Olson, S.L., and H.F. James. 1984. The role of Polynesians in the extinction of the avifauna of the Hawaiian Islands. Pp. 768-780 in Quaternary Extinctions, P.S. Martin and R.G. Klein, eds. Tucson, Ariz.: University of Arizona Press. Olson, S.L., and H.F. James. 1991. Descriptions of thirty-two species of birds from the Hawaiian Islands. Part I. Non-passeriformes. Ornithol. Monogr. 45:1-88. Ono, R.D., J.D. Williams, and A. Wagner. 1983. Vanishing Fishes of North America. Washington, D.C.: Stone Wall. Owen-Smith, N. 1987. Pleistocene extinctions: The pivotal role of megaherbivores. Paleobiology 13:351-362. Pasitschniak-Arts, M. 1993. Ursus arctos. Mamm. Species 439. Pielou, E.C. 1991. After the Ice Age. Chicago: University of Chicago Press. Pimm, S.L. 1989. Theories of predicting success and impact of introduced species. Pp. 351-367 in Biological Invasions: A Global Perspective. SCOPE 37, J.A. Drake, H.A. Mooney, F. Di Castri, R.H. Groves, F.J. Kruger, M. Rejmanek, and M. Williamson, eds. Chichester, U.K.: John Wiley & Sons. Pirazzoli, P.A. 1993. Global sea-level changes and their measurement. Glob. Planet. Change 8:135-148. Plummer, L.N. 1993. Stablnrichment in paleowaters of the southeast Atlantic coastal plain, United States. Science 262:2016-2020. Rampino, M.R., and S. Self. 1992. Volcanic winter and accelerated glaciation following the Toba super-eruption. Nature 359:50-52. Raup, D.M., and D. Jablonski. 1993. Geography of end-Cretaceous marine bivalve extinctions. Science 260:971-973. Rea, A.M. 1980. Late Pleistocene and Holocene turkeys in the Southwest. Natural History Museum of Los Angeles County Contrib. Sci. 330:209-224. Rea, A.M. 1983. Once a River. Tucson, Ariz.: University of Arizona Press. Retallack, G.J. 1995. Permian-Triassic life crisis on land. Science 267:77-80. Ricciardi, A., F.G. Whoriskey, and J.B. Rasmussen. In press. Predicting the density and use the print version of this publication as the authoritative version for attribution.

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About this PDF file: This new digital representation of the original work has been recomposed from XML files created from the original paper book, not from the original typesetting files. Page breaks are true to the original; line lengths, word breaks, heading styles, and other typesetting-specific formatting, however, cannot be retained, and some typographic errors may have been accidentally inserted. Please SPECIES EXTINCTIONS 44 impact of Dreissena infestation on native unionid bivalves from Dreissena field density. Can. J. Fish. Aquat. Sci. Schorger, A.W. 1955. The Passenger Pigeon: Its Natural History and Extinction. Madison, Wisc.: University of Wisconsin Press. Semken, H. A., Jr. 1983. Holocene mammalian biogeography and climatic change in the eastern and central United States. Pp. 182-207 in Late-Quaternary Environments of the United States, Vol. 2, H.E. Wright, ed. Minneapolis, Minn.: University of Minnesota Press. Shackleton, N.J. 1987. Oxygen isotopes, ice volume and sea level. Quat. Sci. Rev. 6:183-190. Sharpton, V.L., K. Burke, A. Camargo-Zanoguera, S.A. Hall, D.S. Lee, L.E. Marín, G. Suárez-Reynoso, J.M. Quezada-Mufieton, P.D. Spudis, and J. Urritia-Fucugauchi. 1993. Chicxulub multiring impact basin: Size and other characteristics derived from gravity analysis. Science 261:1564-1567. Sibley, C.G., and B.L. Monroe, Jr. 1990. Distribution and Taxonomy of Birds of the World. New Haven, Conn.: Yale University Press. Sigler, W.F., and J.W. Sigler. 1987. Fishes of the Great Basin: A Natural History. Reno, Nev.: University of Nevada Press. Simberloff, D. 1989. Which insect introductions succeed and which introductions fail? Pp. 61-75 in Biological Invasions: A Global Perspective. SCOPE 37, J.A. Drake, H.A. Mooney, F. Di Castri, R.H. Groves, F.J. Kruger, M. Rejmanek, and M. Williamson, eds. Chichester, U.K.: John Wiley & Sons. Simenstad, C.A., J.A. Estes, and K.W. Kenyon. 1978. Aleuts, sea otters, and alternate stable-state communities. Science 200:403-411. Simons, D.D. 1983. Interactions between California condors and humans in prehistoric far-western North America. Pp. 470-494 in Vulture Biology and Management, S.R. Wilbur and J.A. Jackson, eds. Berkeley, Calif.: University of California Press. Skelton, P. 1993. A Complete Guide to the Freshwater Fishes of Southern Africa. Halfway House, South Africa: Southern Book Publishers. Solz, D.L., and R.J. Naiman. 1978. The Natural History of Native Fishes in the Death Valley System. Sci. Ser. Publ. 30. Natural History Museum of Los Angeles County, Los Angeles, Calif. Stafford, T.W., Jr., P.E. Hare, L.A. Currie, A.J.T. Jull, and D.J. Donahue. 1990. Accelerator radiocarbon dating at the moelcular level. J. Archaeol. Sci. 18:35-72. Steadman, D.W. 1989. Extinction of birds in eastern Polynesia: A review of the record, and comparisons with other Pacific island groups. J. Archaeol. Sci. 16:177-205. Steadman, D.W. 1991. Extinction of species; Past, present, and future. In Global Climate Change and Life on Earth. New York: Routledge, Chapman, and Hall. Steadman, D.W. 1992. Extinct and extirpated birds from Rota, Mariana Islands. Micronesia 25:71-84. Steadman, D.W. 1993. Biogeography of Tongan birds before and after human impact. Proc. Natl. Acad. Sci. USA 90:818-822. Steadman, D.W. 1995a. Ecosystem integrity: The impact of traditional peoples. Pp. 633-647 in Encyclopedia of Environmental Biology, volume 1. San Diego, Calif.: Academic Press. Steadman, D.W. 1995b. Prehistoric extinctions of South Pacific birds: Biodiversity meets zooarchaeology. Science 267:1123-1131. Steadman, D.W. and P.S. Martin. 1984. Extinction of birds in the late Pleistocene of North America. Pp. 466-477 in Quaternary Extinctions, P.S. Martin and R.G. Klein, eds. Tucson, Ariz.: University of Arizona Press. use the print version of this publication as the authoritative version for attribution.

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About this PDF file: This new digital representation of the original work has been recomposed from XML files created from the original paper book, not from the original typesetting files. Page breaks are true to the original; line lengths, word breaks, heading styles, and other typesetting-specific formatting, however, cannot be retained, and some typographic errors may have been accidentally inserted. Please SPECIES EXTINCTIONS 45 Steadman, D.W. and N.G. Miller. 1987. California condor associated with spruce-jack pine woodland in the late Pleistocene of New York. Quat. Res. 28:415-426. Steadman, D.W., T.W. Stafford, Jr., D.J. Donahue, and A.J.T. Jull. 1991. Chronology of Holocene vertebrate extinction in the Galápagos Islands. Quat. Res. 35:126-133. Sublette, J.E., M.D. Hatch, and M. Sublette. 1990. The Fishes of New Mexico. Albuquerque, N.M.: University of New Mexico Press. Swetnam, T.W. 1993. Fire history and climate change in giant sequoia groves. Science 262:885-889. Turner, A. 1993. Species and speciation. Evolution and the fossil record. Quat. Int. 19:5-8. Webb, T. III, P.J. Bartlein, S. Harrison, and K.H. Anderson. 1993. Vegetation, lake levels, and climate in eastern United States since 18,000 yr B.P. Chap. 17 in Global Climates Since the Last Glacial Maximum, H.E. Wright, T. Webb III, and J.E. Kutzbach, eds. Minneapol, Minn.: University of Minnesota Press. Wilson, E.O. 1992. The Diversity of Life. Cambridge, Mass.: Harvard University Press. Witte, F.T.J. Goldschmidt, J. Wanink, M. van Oijen, K. Goudswand, E. Witte-Maas, and N. Bouton. 1992. The destruction of an endemic species flock: Quantitative data on the decline of the haplochromine cichlids of Lake Victoria. Environ. Biol. Fishes 34:1-28. use the print version of this publication as the authoritative version for attribution.