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Plethodon shenandoah Highton and Worthington, 1967
Joseph C. Mitchell1
1. Historical versus Current Distribution. Shenandoah salamanders (Plethodon shenandoah) are small members of the genus Plethodon known from only three small, isolated areas in Shenandoah National Park, Virginia. They occur on three separate mountains: Hawksbill, Stony Man, and The Pinnacles (Highton and Worthington, 1967; Jaeger, 1970; Highton, 1972, 1988b) that lie along the border of Madison and Page counties, Virginia. Their historical distribution is unknown.
2. Historical versus Current Abundance. Historical abundance is unknown. Current abundance apparently varies depending on microhabitat location. In the area of sympatry with eastern red-backed salamanders (Plethodon cinereus) outside of the talus, Shenandoah salamander density is low (about 0.1 individuals/m2; Griffis and Jaeger, 1998). Within-talus habitat densities are unknown but are probably higher in allopatry.
3. Life History Features. As with all members of the genus Plethodon, Shenandoah salamanders are terrestrial breeders and exhibit direct development (Wynn, 1991; Petranka, 1998).
A. Breeding. Reproduction is terrestrial.
i. Breeding migrations. Shenandoah salamanders do not migrate.
ii. Breeding habitat. The breeding microhabitat of this species is unknown. Mating probably occurs in spring and autumn.
i. Egg deposition sites. Eggs probably are laid in moist crevices underground (Jaeger, 1971a).
ii. Clutch size. Clutch size is 4–19 (average = 13), and females may produce eggs on a 2-yr cycle (Jaeger, 1980a, 1981b).
C. Direct Development. All larval development occurs in the egg. Young of the year emerge in September. Parental care of eggs is unknown.
D. Juvenile Habitat. Similar to adult habitat.
E. Adult Habitat. Shenandoah salamanders occupy relatively dry, north-facing talus slopes in each of the three known areas above 900 m elevation. Moist soil pockets and rocks characterize these habitats, and talus slopes support varying densities of hardwood trees. Jaeger (1970) described three microhabitats in the talus of Hawksbill Mountain that correlated with the distribution of Shenandoah salamanders. Type I talus is comprised of areas with rock and no soil; Type II talus has soil and leaf litter among rocks but not beneath them; and Type III talus has islands of soil among and under rocks. Shenandoah salamanders are most abundant in Type III talus, less so in Type II, and do not occur in Type I talus. Shenandoah salamanders could occupy deeper, moister soils outside the talus areas were it not for direct behavioral competition with eastern red-backed salamanders. Shenandoah salamanders have a higher tolerance to desiccation and are able to survive within drier talus slopes that are inhospitable to eastern red-backed salamanders (Jaeger, 1971a). However, Shenandoah salamanders face a higher risk of mortality due to environmental perturbations that may cause drying in the talus (Jaeger, 1980a).
F. Home Range Size. Unknown.
G. Territories. Shenandoah salamanders are poor competitors compared to eastern red-backed salamanders (Griffis and Jaeger, 1998). Eastern red-backed salamanders competitively exclude Shenandoah salamanders from moist soil pockets and effectively restrict them to drier talus (Jaeger, 1970, 1971a,b, 1972). Competition is mediated through interspecific aggression and territoriality (Thurow, 1976; Jaeger and Gergits, 1979; Griffis and Jaeger, 1998). Shenandoah salamanders are less aggressive than red-backed salamanders in territorial defense (Wrobel et al., 1980). Individual Shenandoah salamanders seldom invade territories defended by eastern red-backed salamanders, and they tend to snap at, rather than bite, intruders in their territories (Gergits, 1982).
H. Aestivation/Avoiding Dessication. Shenandoah salamanders are inactive during the dry summer and during periods of drought at other times of the year. Patterns of rainfall strongly influence surface activity.
I. Seasonal Migrations. Shenandoah salamanders do not migrate.
J. Torpor (Hibernation). Overwintering occurs below the frost line presumably in moist areas in deep rock crevices. Surface activity terminates in October and usually resumes in April (W.L. Witt, personal communication).
K. Interspecific Associations/Exclusions. Shenandoah salamanders occur largely allopatrically from eastern red-backed salamanders on two of the three isolates. Both species occur throughout the isolate on The Pinnacle (Highton and Worthington, 1967). Eastern red-backed salamanders are the major competitor of Shenandoah salamanders on the periphery of the Hawksbill and Stony Man isolates and exclude this species to areas of talus that eastern red-backed salamanders cannot tolerate due to the drier microhabitat (Jaeger, 1972). White-spotted slimy salamanders (Plethodon cylindraceus) occur in the area but they are encountered rarely (Jaeger, 1971b).
L. Age/Size at Reproductive Maturity. Age and size at maturity are unknown.
M. Longevity. Unknown, but probably similar to that for other small Plethodon (3–5 yr; Snider and Bowler, 1992).
N. Feeding Behavior. Shenandoah salamanders probably forage on the surface of the leaf litter and on low vegetation during moist nights, similar to sympatric eastern red-backed salamanders (Jaeger, 1978). They resemble other plethodontid salamanders in that they do not specialize and instead prey on a wide variety of invertebrates small enough to be ingested. Size of prey is limited to mouth size in these gape-limited predators. A list of prey species is in Jaeger (1972) and includes a wide variety of insects, arachnids, centipedes, millipedes, and worms. Kaplan (1977) determined in laboratory experiments that Shenandoah salamanders ingested Drosophila prey at rates of 0.006–0.012 prey/s. Prey assimilation efficiency is inversely related to temperature, as efficiency declined from 91% at 10 ˚C to 79% at 20 ˚C (Bobka et al., 1981).
O. Predators. Direct observation of predation has not been reported. Potential predators known to occur within the range include ring-necked snakes (Diadophis punctatus), short-tailed shrews (Blarina brevicauda), brown thrashers (Toxostoma rufum), and towhees (Pipilo sp.; Jaeger, 1971b).
P. Anti-Predator Mechanisms. Anti-predator mechanisms for Shenandoah salamanders include noxious skin secretions, immobility, and defensive postures (Brodie, 1977). Dodd (1989) determined the length of time salamanders remained immobile when disturbed in the field by close approach, through disturbance of nearby microhabitat, or when touched. Immobility times for Shenandoah salamanders averaged 5.9 s (range 1–36 s) and were significantly lower from times for seven other species of eastern Plethodon. One of 21 salamanders had an immobility time > 180 s in duration.
Q. Diseases. None known.
R. Parasites. None reported.
4. Conservation. Shenandoah salamanders were listed as Endangered by the Virginia Department of Game and Inland Fisheries on 1 October 1987 (Wynn, 1991) and as Endangered by the U.S. Fish and Wildlife Service on 18 August 1989 (U.S.F.W.S., 1989a). The primary threat is interspecific competition by eastern red-backed salamanders that limits their use of optimal habitat. Additional threats include alteration of forest canopy cover from defoliation by the introduced gypsy moth (Lymantria dispar), acid precipitation, and succession of the talus habitat (U.S.F.W.S., 1994d). Jaeger (1980a) documented the extinction of one subpopulation due to summer drought. Griffis and Jaeger (1998) described how interspecific competition, through interspecific aggression and territoriality, can lead to extinctions of sink populations by preventing dispersal of Shenandoah salamanders from the primary source population. The federal recovery plan outlines objectives to minimize human impacts in the national park while still allowing natural processes to occur (U.S.F.W.S., 1994d).
1Joseph C. Mitchell
Literature references for Amphibian Declines: The Conservation Status of United States Species, edited by Michael Lannoo, are here.
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Citation: AmphibiaWeb. 2017. <http://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 21 Aug 2017.
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