Requiem /Etemam the Last Five Hundred Years of Mammalian Species Extinctions
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CHAPTER 13 Requiem /Etemam The Last Five Hundred Years of Mammalian Species Extinctions R. D. E. MACPHEE and CLARE FLEMMING 1. Introduction This contribution provides an analytical accounting of mammal species that have disap peared during the past 500 years-the "modem era" of this chapter. Our choice of date was dictated by several considerations, but two are paramount. AD 1500 marks more or less pre cisely the beginning of Europe's expansion across the rest of the world, a portentous event in human history by any definition. It is an equally momentous date for natural history be cause it marks the point at which empirical knowledge of the planet began to burgeon ex ponentially. These two factors, linked for both good and ill for the past half-millennium, have affected every aspect of life on earth, and are thus fitting subjects to commemorate in a record such as this. A number of modem-era extinction lists (hereafter, "compilations") for Mammalia have been published in recent years (e.g., Goodwin and Goodwin, 1973; Williams and Nowak, 1986, 1993; World Conservation Monitoring Centre [WCMC), 1992; International Union for the Conservation of Nature and Natural Resources [IUCN], 1993, 1996; Cole et al., 1994}. One may wonder why yet another recension is needed. Superficially, the empirical problem seems uncomplicated: A species either exists or it doesn't-what is there to dis agree about? Regrettably, things are not so simple. A target taxon that has not been collect ed or seen for an appreciable interval may indeed be extinct-or it may simply not have been collected or seen. Unless someone has taken the trouble to search carefully and seriously for the target, mere lack of information on status should not be accepted blindly as evidence of extinction. Similarly, poor or outdated systematic studies are no more adequate for evaluat ing the status of a species than is incomplete inventorying or surveying. As we shall attempt to show, the quality of the evidence for evaluating whether a particular extinction has oc curred varies widely from case to case, and even in the best circumstances a clear-cut deci- R. D. E. MACPHEE and CLARE FLEMMING • Department of Mammaiogy, American Museum of Natural History, New York, New York 10024. Extinctions in Near Time, edited by MacPhee. Kluwer Academic/Plenum Publishers, New York, 1999. 333 334 R. D. E. MacPhee and Clare Flemming sion is often not possible. Does any of this matter? We think so, because reliable databases are essential to any science. Extinction lists are likely to play an ever-increasing role in con servation policy debates, and it is important to ensure that such lists are not replete with er roneous data. As we shall proceed to show in the rest of this chapter, here we can offer only a preliminary database for studies of very recent mammalian extinctions. If it were necessary to be absolutely certain that a loss had occurred before it could be counted, the list of modern-era extinctions would be very short indeed. This is the major reason that extinction rates are usually estimated by proxy measures, such as the one that relates annual loss of rain forest to some calculation of species richness (for an extended discussion, see May et al., 1995). The trouble is that proxy estimates are difficult to verify and can lead to rate estimates of enormous magnitude (see Brooks et al., 1997). For exam ple, we regard as being beyond meaningful empirical verification the recent claim that "ap proximately 1800 populations per hour (16 million annually) are being destroyed in tropi cal forests alone" (Hughes et al., 1997). Epistemologically, a more reasonable approach is to establish whether there is ade quate justification for one's belief that any particular extinction has taken place. The effi cient way to do this is to arrange knowledge about specific extinctions according to levels of apparent reliability. We have tried to achieve this goal by constructing a series of tables (Tables 1-4), each defined by the degree to which available evidence relating to extinction appears to justify a specific conclusion. An extinction (or, better, the evidence for an extinction) can be said to be resolved when it is found that it meets the following criteria: The name of the species thought to be extinct is valid systematically (e.g., the name is available and not preoccupied by another valid name); the species has been well characterized and, optimally, has been subjected to revi sionary review; no individuals belonging to this species have been collected, inventoried, or observed reliably in the last 50 years; and there is evidence of a positive nature that places the loss date within the period spanning AD 1500-1950. Extinctions thus resolved are placed in Table 1. Unresolved extinctions are those for which a meaningful prima facie case can be made. Because they currently fail to meet one or more of the stipulated criteria, how ever, their status cannot be resolved fully and must be held in abeyance until appropriate information is forthcoming. These potential instances of extinction are apportioned among Tables 2-4 according to the nature of their deficiencies (see below for additional descrip tions of tables). We are aware that several taxa might have been placed, with about equal justification, in a table other than the one we selected. Our allocations reflect the merits of individual cases as we see them. Obviously, the current organization of this extinction database is not immutable. Un resolved extinctions are potentially resolvable if evidence can be gathered that clarifies whatever point is in doubt. Similarly. a case that was thought to be fully adjudicated may be reopened if new evidence warrants it. This last point is important to note because we have taken special pains to identify taxa that should not be regarded as modern-era species level extinctions according to our criteria, even though they have been so listed in other compilations (see Table 7). It is appropriate to end this introduction with a word about the cause(s) of modern-era extinctions. This is a compendium of modern-era extinctions, not an explanation thereof (but see Section 7, Coda: Modern-Era Extinctions in Quaternary Perspective). The choice of wording is exact: This work is an actuarial account, in which our concern is to establish what losses occurred, where, and when. How they occurred is a topic of undoubted impor- Requiem IEternam 335 tance, but in only a tiny fraction of cases is it reasonably clear why particular species dis appeared (Caughley and Gunn, 1996; Flemming and MacPhee, 1997; MacPhee and Flem ming, in press). Systematic research on species that happen to be extinct is no more likely to uncover evidence regarding causes of loss than is ordinary armchair speculation. On the other hand, any investigation of causation that intends to stay grounded in reality requires reliable databases that assess the systematic facts as rigorously as possible. The companion chapter by Harrison and Stiassny (this volume) should be consulted for a parallel treatment of extinctions among freshwater fishes, using criteria similar to the ones defined here. It is of interest to compare the nature of the two databases, which dif fer notably in some respects (e.g., absence of fossil material of fishes, very large number of apparently extinct taxa based on limited hypodigms, number of extinctions in last half century). 2. Abbreviations and Conventions 2.1. Abbreviations CITES Convention on International Trade in Endangered Species of Wild Fauna and Flora EED effective extinction date (last reliable record of collection or observation) I Island, Islands IUCN International Union for the Conservation of Nature and Natural Resources of the World Conservation Union rcyrbp radiocarbon years before present (Le., before radiocarbon datum AD 1950) WCMC World Conservation Monitoring Centre WI West Indies yrbp years before present 2.2. Conventions Used in Tables 1-4 2.2.1. Effective Extinction Date (EED) * Target taxon died out post-1500, but date of loss not otherwise constrained 2.2.2. Evidence Categories 1 Target taxon collected or seen in living state between AD 1500 and 1950 2 Target taxon associated with remains of exotics having a documented introduction date of AD 1500 (or later); 3 Target taxon dated radiometrically; calibrated 14C date ± two sigma (standard errors) lying close to or within the period AD 1500-1950 2.2.3. Hypodigm Descriptions H Hypodigm consists of holotype only H + Hypodigm consists of two or three assigned specimens (including holotype) 336 R. D. E. MacPhee and Clare Flemming * Hypodigm consists of four or more specimens F Hypodigm consists of fossil material only (no wild-caught specimens). Here, "fos sil" is applied to bony remains of any age, such as mammal bones retrieved in mod em-era deposits in caves. 2.2.4 Body Size Classes BW Body weight (in kg). Unless otherwise indicated, weight estimates are derived from data reported by Silva and Downing (1995) for the species stipulated in the tables or close relatives in the same body size range. I =::;0.1 kg II 0.1 to <1.0 kg m 1.0 to <10 kg IV 10 to <100 kg V 100 to <1000 kg VI ~1000kg 3. Methods One of the motivations for the present chapter comes from our own sense of frustra tion with previous lists of modem-era extinctions (Flemming and MacPhee, 1995). In gen eral, they have nO,t been accompanied by the kinds of discussions that enable the interested but nonspecialist reader to interpret authors' justifications for including (or excluding) par ticular species. We consider this to be important. Although for reasons of space we present justifications in summary form in this chapter.