Thursday, 12 June 2008
In an interesting June 2008 BioScience paper, authors McKelvey, Aubry and Schwartz, USDA Forest Service scientists, liken anecdotal evidence to an illusion of reality. Specifically, they suggest that anecdotal statements regarding the occurrence of rare or elusive animal species, sometimes reported by trained and experienced biologists and "often accompanied by inconclusive physical evidence, such as castings or pictures of tracks, fuzzy or distant photographs, or nondiagnostic acoustic recordings," are "inherently unreliable." This unreliability factor increases with the rarity of the species, leading the authors to propose adopting a "gradient of evidentiary standards for occurrence records that increases in rigor with species' rarity." They argue that, in the case of undocumented species, the only acceptable evidentiary standard is a specimen. Three case studies were presented in support of the authors' contentions: the fisher (Martes pennanti) in the northwestern states, the wolverine (Gulo gulo) in California, and the Ivory-billed Woodpecker (Campephilus principalis) in southeastern states.
There seems little in this paper that is objectionable, although some may find some of the authors' statements to be debatable. For example, concluding that "the ivory-billed woodpecker probably became extinct in the southeastern United States by the middle of the 20th century," based on the failure, to this point, of researchers and volunteers to secure definitive evidence, could be construed as a bit presumptuous given the expertise, background and reliability of those Cornell and Auburn researchers who are convinced that the Ivory-billed Woodpecker is indeed not extinct.
The paper provides no alternative explanation for the fact that many sighting reports of rare or elusive species "are located in areas where the sighting is plausible, according to historical information on the organism's distribution and ecological relations." Minimizing the significance of such correlations potentially obscures the reality that some rare species may, in fact, exist as indicated by occurrence data. Such appears to be illustrated by the case of the Pacific states fisher as presented in the paper. Follow-up surveys, based on anecdotal reports, documented population pockets scattered throughout the indicated range. While the probable extent of the species' distribution was evidently overestimated, the range and habitat and existence of fishers was corroborated.
Not all anecdotal accounts of rare or elusive species are valid. That cannot be argued. The same thing is true of undocumented species reports, at least with regard to the sasquatch. However, the TBRC takes great care to sort out information that is dubious. Posted reports from reliable witnesses, including biologists and comparable professionals, demonstrate ecological relationships that cannot be reasonably dismissed as coincidental. The TBRC maintains that compelling photographic/videographic images can serve to document the existence of an undocumented species. Prominent scientists have endorsed that position. Upon recognition of the validity of the photographic/videographic evidence, additional efforts would then be necessary to secure the kind of indisputable physical evidence to enable the formal classification of either a new species or the rediscovery of a species thought extinct.
Source: BioScience. Vol. 58 No. 6. The Use of Anecdotal Occurrence Data for Rare or Elusive Species: The Illusion of Reality and a Call for Evidentiary Standards.