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Pantherophis obsoletus

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Taxonomy [top]

Kingdom Phylum Class Order Family
ANIMALIA CHORDATA REPTILIA SQUAMATA COLUBRIDAE

Scientific Name: Pantherophis obsoletus
Species Authority: (Say, 1823)
Common Name(s):
English Western Ratsnake
Synonym(s):
Coluber obsoletus Say, 1823
Elaphe obsoleta (say, 1823)
Pantherophis alleghaniensis (Holbrook, 1836)
Pantherophis spiloides (Duméril, Bibron & Duméril, 1854)
Taxonomic Notes: Burbrink et al. (2000) and Burbrink (2001) examined genetic and morphological variation in Elaphe obsoleta and determined that the nominal subspecies do not represent evolutionary lineages and should no longer be recognized. Further, these authors identified three clades within E. obsoleta, corresponding to populations (1) west of the Mississippi River (western clade), (2) east of the Mississippi River and west of the Appalachian Mountains and Apalachicola River (central clade), and (3) east of the Appalachians and the Apalachicola River (eastern clade). Burbrink (2000) recognized the three clades as distinct species: E. obsoleta (western clade), E. spiloides (central clade), and E. alleghaniensis (eastern clade). In mapping the distribution of the species, Burbrink indicated a very large area of "taxonomic uncertainty" extending from New England to northern Georgia. In this region the distribution of E. alleghaniensis was deemed "somewhat questionable with regard to hybridization with members of Elaphe spiloides." Although Burbrink concluded that the molecular data show that E. alleghaniensis and E. spiloides represent independently evolving units with separate evolutionary histories and thus should be recognized as different species under the evolutionary species concept, contact zones were not critically examined, so the nature and dimensions of clade boundaries, and the precise distributions of alleghaniensis and spiloides along the length of the Appalachians, remain uncertain. In view of the uncertainties and the need for further study, Burbrink's taxonomic revision has not been adopted in this database.

Under Burbrink's arrangement, E. obsoleta would be known as the "Western Rat Snake" (also rendered "Western Ratsnake")

Utiger et al. (2002) examined mtDNA variation in New World and Old World "Elaphe" and determined that North American rat snakes included in the genus Elaphe formed a monophyletic limeage that is distinct from Old World snakes that also have been regarded as Elaphe. They resurrected the genus Pantherophis for the rat snakes north of Mexico, including the following species: Pantherophis obsoletus (and P. alleghaniensis and P. spiloides, if one recognizes those taxa as species), P. guttatus, P. emoryi, P. vulpinus, P. gloydi, and P. bairdi. Crother et al. (2003) did not follow this taxonomy pending further research, and retained the traditional concept of Elaphe. Burbrink and Lawson (2007) agreed with Utiger et al. (2002) that these species do not belong in Elaphe, but suggested that the genus Pantherophis might belong in Pituophis. We place this species in Pantherophis, following Utiger et al. (2002) pending further information of the relationships of these taxa.

Assessment Information [top]

Red List Category & Criteria: Least Concern ver 3.1
Year Published: 2007
Date Assessed: 2007-03-01
Assessor(s): Hammerson, G.A.
Reviewer(s): Cox, N., Chanson, J.S. & Stuart, S.N. (Global Reptile Assessment Coordinating Team)
Justification:
Listed as Least Concern in view of its wide distribution, tolerance of a degree of habitat modification, presumed large population, and because it is unlikely to be declining fast enough to qualify for listing in a more threatened category.

Geographic Range [top]

Range Description: This species ranges widely in the east of the United States, extending into southern Canada. Its range extends from southern New England and southern Ontario west to southeastern Minnesota, and south to southern Texas, the entire Gulf Coast, and southern Florida (Conant and Collins 1991). As defined by Burbrink (2001), the range of Pantherophis obsoletus is as follows: west of the Mississippi River from southern Louisiana along the Gulf Coast to southern Texas, west to central Texas on the Edwards Plateau, and through Oklahoma, central and eastern Kansas, southeastern Nebraska, and southeastern Iowa to extreme southeastern Minnesota. However, this taxonomy/distribution has not been adopted in this database.
Countries:
Native:
Canada; United States
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: This species is represented by a very large number of occurrences (subpopulations). The adult population size is unknown but presumably exceeds 100,000. This snake is fairly common in many areas. The extent of occurrence, area of occupancy, number of subpopulations, and population size are probably relatively stable or declining at a rate of less than 10% over 10 years or three generations.
Population Trend: Stable

Habitat and Ecology [top]

Habitat and Ecology: Habitats include hardwood forest and woodland, wooded canyons, swamps, rocky timbered upland, wooded areas of streams and rivers, farmland near woods, old fields, barnyards, and rural buildings in wooded areas. This snake often occurs where wooded and open habitats (such as fields or farmland) are intermixed. It often climbs trees, especially rough-barked species or those with vines (Mullin and Cooper 2002), and it may sometimes enter water. Hibernation sites are in deep crevices or underground. Individuals exhibit very high fidelity to hibernacula (Prior et al. 2001).
Systems: Terrestrial

Threats [top]

Major Threat(s): No major threats are known. This snake thrives on partial deforestation. Locally, some populations have declined as a result of extensive deforestation and various forms of intensive development.

Conservation Actions [top]

Conservation Actions: Many occurrences are in protected areas.

Bibliography [top]

Bartlett, R D. and Bartlett, P.P. 1999. A Field Guide to Texas Reptiles and Amphibians. Gulf Publishing Company, Houston, Texas. xviii + 331 pp.

Burbrink, F.T. 2001. Systematics of the eastern ratsnake complex (Elaphe obsoleta). Herpetological Monographs 15: 1-53.

Burbrink, F.T. and Lawson, R. 2007. How and when did Old World rat snakes disperse into the New World? Molecular Phylogenetics and Evolution 43: 173-189.

Burbrink, F.T., Lawson, R. and Slowinski, J.B. 2000. Mitochondrial DNA phylogeography of the North American rat snake (Elaphe obsoleta): a critique of the subspecies concept. Evolution 54: 2107-2114.

Conant, R. and Collins, J.T. 1991. A Field Guide to Reptiles and Amphibians: Eastern and Central North America. Third Edition. Houghton Mifflin Company, Boston, Massachusetts.

Crother, B.I., Boundy, J., Campbell, J.A., de Quieroz, K., Frost, D., Green, D.M., Highton, R., Iverson, J.B., McDiarmid, R.W., Meylan, P.A., Reeder, T.W., Seidel, M.E., Sites Jr, J.W., Tilley, S.G. and Wake, D.B. 2003. Scientific and standard English names of amphibians and reptiles of North America north of Mexico: update. Herpetological Review 34: 196-203.

Dixon, J.R. 2000. Amphibians and Reptiles of Texas. With Keys, Taxonomic Synopses, Bibliography, and Distribution Maps. Second edition. Texas A & M University Press, College Station, College Station, Texas.

Dundee, H.A. and Rossman, D.A. 1989. The Amphibians and Reptiles of Louisiana. Louisiana State University Press, Baton Rouge, Louisiana.

Ernst, C.H. and Barbour, R.W. 1989. Snakes of Eastern North America. George Mason University Press, Fairfax, Virginia. 282 pp.

Ernst, C.H. and Ernst, E.M. 2003. Snakes of the United States and Canada. Smithsonian Books, Washington, D.C.

Harding, J.H. 1997. Amphibians and Reptiles of the Great Lakes Region. University of Michigan Press, Ann Arbor, Michigan. xvi + 378 pp.

IUCN. 2007. 2007 IUCN Red List of Threatened Species. Available at: www.iucnredlist.org. (Accessed: 12th September 2007).

Mount, R.H. 1975. The Reptiles and Amphibians of Alabama. Auburn University Agricultural Experiment Station, Auburn, Alabama. vii + 347 pp.

Tennant, A. 1984. The Snakes of Texas. Texas Monthly Press, Austin, Texas. 561 pp.

Tennant, A. 1997. A Field Guide to Snakes of Florida. Gulf Publishing Company, Houston, Texas. xiii + 257 pp.

Tennant, A. 1998. A Field Guide to Texas Snakes. Second edition. Gulf Publishing Company, Houston, Texas.

Trauth, S.E., Robison, H.W. and Plummer, M.V. 2004. The Amphibians and Reptiles of Arkansas. University of Arkansas Press, Little Rock, Arkansas.

Utiger, U., Helfenberger, N., Schmidt, B., Ruf, M. and Ziswiler, V. 2002. Molecular systematics and phylogeny of Old and New World ratsnakes, Elaphe auct., and related genera (Reptilia, Squamata, Colubridae). Russian Journal of Herpetology 9(2): 105-124.

Werler, J.E. and Dixon, J.R. 2000. Texas Snakes: Identification, Distribution, and Natural History. University of Texas Press, Austin, Texas.


Citation: Hammerson, G.A. 2007. Pantherophis obsoletus. The IUCN Red List of Threatened Species. Version 2014.2. <www.iucnredlist.org>. Downloaded on 26 October 2014.
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