PS 24-117 - The distribution of Webster's salamander, Plethodon websteri, in Mississippi in relation to local geology

Tuesday, August 9, 2011
Exhibit Hall 3, Austin Convention Center
Debora L. Mann1, Tom M. Mann2, Marie L. Thomas1, Molly Beth Jourdan1 and Kristin L. Foss1, (1)Biology Department, Millsaps College, Jackson, MS, (2)Mississippi Natural Heritage Program, Mississippi Museum of Natural Science, Jackson, MS

Plethodon websteri is a small, terrestrial salamander with a highly disjunct distribution across five states (SC,GA, AL, MS, LA). Optimal habitat for this species is described in the literature as deciduous forests with rocky substrates. The reason for P. websteri’s frequent association with surface rock is not known. These salamanders are active on the forest floor under leaves and woody debris from autumn to spring, after which they retreat underground. Development is direct, with no aquatic larval stage. P. websteri is imperiled in Mississippi, and its distribution is poorly known. The purpose of this study was to gain a more complete picture of the geographic distribution of P. websteri in Mississippi and to better understand its habitat requirements, especially with regard to local geology. Since known sites for the species in Mississippi are associated with surface rock and/or steep topographic relief, potential survey sites were located by examination of topographic maps and county geology bulletins. We searched for salamanders under woody debris, counting the number of items turned as a measure of effort.  Ten P. websteri populations were discovered in the following counties: Madison (1), Yazoo (1), Hinds (1), Claiborne (3), Copiah (1), Jefferson ( 1), and Winston (2).


These 10 sites combined with the 7 locations discovered by other researchers form an arc that extends from east-central to extreme southwestern Mississippi. The 6 populations in Winston and Choctaw counties in east-central Mississippi are not associated with evident surface rock, although the presence of shallow, subsurface rock has not been excluded. The 11 populations in the southwestern counties (Madison, Yazoo, Hinds, Claiborne, Copiah, Jefferson, and Wilkinson) are all associated with surface rock including sandstone, limestone, siltstone, and coarse gravel. Whether the apparent difference in habitat requirements between the east-central and southwestern Mississippi has any larger significance is not known.  Nor is it known how P. websteri actually uses rocks with which it is found. One hypothesis is that subterranean crevices associated with rock outcrops provide access to refugia where the salamanders escape the heat and drought of summer. Another hypothesis is that subsurface crevices in rocks serve as oviposition sites or “nurseries.” In support of the latter hypothesis, we have observed at several sites with rock outcrops that the smallest size-class (snout-vent length <15 mm) are concentrated within only a few meters of outcrops while larger juveniles and adults are distributed at greater distances from these rocks.

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