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How Many Species are Extinct?

Posted on June 24, 2013

A species is considered extinct “when there is no reasonable doubt that the last individual has died” (IUCN 2001). The absence of information about a particular species is not always a reliable and compelling piece of evidence that it has become extinct; its “disappearance” may be due to fundamentally technical reasons such as inadequate or less than exhaustive studies done on the species. This problem is further aggravated in the case of rare and cryptic species, which are difficult to observe or detect in the field. To deal with this situation, species for which information is rare should be viewed as deserving of extremely high priority for research and for conservation of the most likely habitat. Thus, reports of species extinction should be treated with caution until more exhaustive and extensive field data are available to substantiate these reports.

Although the fossil record is a marvelous source of information about many groups of organisms (e.g., hard-shelled marine invertebrates, large mammals), fossil data are scarce for most groups, and full explanations about the extinction of life forms in ancient history are few. Since the majority of the species on earth are still unknown, current extinction data are by definition incomplete. Many extinctions are undoubtedly unrecorded, especially among the non-vascular plants and invertebrate groups.

The global extinction record, as we know it, represents a very small proportion of species that have become extinct. The reported data on species extinction show that about 784 species, including at least 338 vertebrates, 359 invertebrates, 86 plants, and 1 protist (red algae), have disappeared since 1500 AD (Baillie et al., 2004, IUCN 2004a).

Because of the deplorable rate of deforestation and habitat loss in the Philippines, it is highly possible that more than a few native and endemic species have already disappeared; indeed, some may have disappeared even before they were discovered. However, the Philippine bare-backed fruit bat (Dobsonia chapmani) and Cebu flowerpecker (Dicaeum quadricolor) were thought to be extinct, but they have been recently re-discovered. No Philippine mammals or birds are known to have become extinct in the last century. Some species have persisted despite the severe loss of forest habitats, as in the case of the recently discovered frog (Platymantis insulatus) found on Gigante Island in Panay (Ferner et al. 2000). This island forest frog is listed Critically Endangered (IUCN 2004a), and therefore, it must be saved from extinction.

(By Corazon Catibog-Sinha and Lawrence Heaney in their book, “Philippine Biodiversity: Principles and Practice”, pp 136-137, published in 2006 in Quezon City. The publication was made possible with funding support from FPE, CI-Washington DC, Haribon, NEF, and WWF)

 

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