Kern Plateau Salamander
© 2012 William Flaxington (1 of 6)
Batrachoseps robustus Wake, Yanev and Hansen, 2002
Robert W. Hansen1
1. Historical versus Current Distribution. Kern Plateau salamanders (Batrachoseps robustus) are endemic to the southeastern Sierra Nevada of California and have only recently been described (Wake et al., 2002). Their range consists of three principal units: the Kern Plateau (Tulare County), where they have been recorded from a number of sites; the eastern slopes of the Sierra Nevada draining into Owens and Indian Wells valleys (Inyo County), where they are restricted to steep, east-facing canyons; and the Scodie Mountains (Kern County), south of the main body of the species’ range. The elevational range is from 1,700–2,800 m on the Kern Plateau (Tulare County); 1,430–2,440 m on the Sierran east slope (Inyo County); and 1,980–2,025 m in the Scodie Mountains (Kern County).
2. Historical versus Current Abundance. Populations from the Kern Plateau and east slope Sierran canyons appear stable. An extensive wildfire burned through the Scodie Mountains within the last decade, and the status of populations there is uncertain as a recent survey (2002) failed to locate any salamanders (R.W.H., personal observation).
3. Life History Features.
A. Breeding. Reproduction is terrestrial. Timing of courtship and oviposition are unknown, but are likely to vary somewhat with elevation and perhaps with levels of seasonal precipitation. Adult females (gravid though physiologically not ready for egg laying) were found in early May at 2,070 m elevation on the Kern Plateau (Wake et al., 2002). This site is a seasonal seepage that may disappear by May–June and is located in an otherwise dry singleleaf pinyon pine forest.
Many of the females collected from various high elevation sites (≥ 2,200 m) on the Kern Plateau during July have contained small to large ova (this variation in development of ova is usually present even within a local population).
i. Breeding migrations. Unknown.
ii. Breeding habitat. Unknown.
i. Egg deposition sites. Eggs of this species have not been found in the wild. However, we have found aggregations of gravid females in association with wet substrates—under cover at margins of seeps, springs, or creeks. At one such site (near Osa Meadow, Tulare County, 2,680 m elevation, 22 July), we found 21 large adults, most of which were females. Nine of these were found within a rotted lodgepole pine log saturated from snowmelt. We suspect that such localized wet areas probably serve as oviposition sites. However, nests have not been discovered in the field and communal nesting is unknown for members of the robust clade of slender salamanders (subgenus Plethopsis; Jockusch and Mahoney, 1997).
ii. Clutch size. Uncertain, although five gravid females induced to oviposit in the lab laid three eggs each while retaining 1–3 eggs (Wake et al., 2002).
C. Direct Development. Eggs incubated in the lab at 13 ˚C hatched after 96 and 103 days (Wake et al., 2002). Hatchlings are black, usually with gold or silver flecking, and measure ca. 12–13 mm SVL.
D. Juvenile Habitat. Hatchlings often are found under smaller cover objects (small rocks and pieces of bark) not utilized by adults.
E. Adult Habitat. Kern Plateau salamanders occur in a broad range of ecological settings, from high elevation coniferous forests to semiarid pinyon pine/sagebrush associations. In general, salamanders occurring in mesic pine-fir forests are more broadly distributed on a local scale and are less closely associated with surface moisture. By contrast, populations occupying the southeastern Kern Plateau, eastern slope Sierra Nevada canyons, and Scodie Mountains are restricted to areas of permanent or seasonal surface moisture. During favorable periods of surface moisture and temperature, Kern Plateau salamanders may be found under rocks, under or within downed logs, or among bark rubble.
Detailed descriptions and photographs of representative localities throughout the range of this species are provided by Wake et al. (2002).
F. Home Range Size. Unknown.
G. Territories. Unknown.
H. Aestivation/Avoiding Dessication. Timing and duration of seasonal activity vary with elevation, availability of surface moisture, and annual variation in precipitation (Wake et al., 2002). Lower elevation populations (≤ 2,000 m) may be active in all but the coldest periods, retreating below ground by late summer or early spring; exceptions occur where a local population is associated with perennial surface moisture, in which case activity may continue during summer. At higher elevation sites, activity on the surface is confined to a few months, perhaps May–June to October (Wake et al., 2002). Substrate temperatures for salamanders found under surface cover ranged from 5.2–25.0 ˚C (mean = 13.5 ˚C, n = 217; Wake et al., 2002). As local surface conditions dry, adult salamanders are scarce, but juveniles may still be present; perhaps there is pressure to accumulate fat reserves prior to aestivation (Wake et al., 2002).
I. Seasonal Migrations. Unknown.
J. Torpor (Hibernation). The lower threshold for surface activity appears to be about 5 ˚C. Some high elevation populations of this species occur in areas subject to long periods of cold winter weather and although activity may be reduced, we suspect that some activity might occur where snow-covered soil and logs remain above freezing.
K. Interspecific Associations/Exclusions. At the western margin of the Kern Plateau, relictual slender salamanders (B. relictus) have been found at a single high-elevation site only 1.6 km from the nearest locality for B. robustus, and sympatry is expected (Hansen, 1997; Wake et al., 2002). On the Sierra Nevada eastern slope (Inyo County), the range of B. robustus extends as far north as Olancha Creek, where it meets the southern range limits of an undescribed species of web-toed salamander (Hydromantes sp.). Within Olancha Creek Canyon, Hydromantes sp. occupy higher elevations (≥ 1,800 m), and Kern Plateau salamanders have not been found here above 1,800 m elevation. Both species have been taken under adjacent rocks at 1,800 m elevation, but this is the only known instance of sympatry (Giuliani, 1989; Wake et al., 2002). The distributional pattern is one of geograhical replacement with virtually no overlap, suggesting that range expansion might be limited by competition.
L. Age/Size at Reproductive Maturity. This is a large, robust species of Batrachoseps, with females attaining larger average and maximum size. Average size of 10 adult males was 51.9 mm SVL (maximum 58.9 mm); 10 adult females averaged 58.2 mm (maximum 61.3 mm; Wake et al., 2002). There is little variation in adult size among Kern Plateau populations. Average adult size may be smaller in east slope Sierra Nevada canyons, although samples are small. The smallest gravid female was 44 mm SVL (Wake et al., 2002).
M. Longevity. Unknown.
N. Feeding Behavior. In the laboratory, Kern Plateau salamanders have been observed to use a projectile tongue to capture small invertebrates.
O. Predators. Unknown, although garter snakes are likely predators.
P. Anti-Predator Mechanisms. We recorded responses of 79 individuals in the field as they were discovered under surface cover: attempt to crawl away (73%), immobility (16.5%), thrashing (5%), and coiling (3.8%; Wake et al., 2002). García-París and Deban (1995) observed partial coiling (body coiled, but tail extended) in all three individuals tapped on the back in a lab setting. Rarely, sticky skin secretions are produced. Tail autotomy is rare in robust members of this genus (B. campi, robustus, and wrighti—the subgenus Plethopsis), in strong contrast to attenuate species (subgenus Batrachoseps) in which tail loss is a common defensive strategy.
Dorsal coloration varies in this species. In general, salamanders from low-rainfall areas are relatively lighter in coloration, while those from more mesic portions of the range, such as the red fir forests on the northern Kern Plateau, display dark dorsal patterns that appear cryptic against darker substrates (Wake et al., 2002).
Q. Diseases. Unknown.
R. Parasites. Unknown.
S. Comments. Although only recently described, specimens now allocated to B. robustus were first collected in 1972 on the Kern Plateau, but misidentified as Tehachapi slender salamanders (B. stebbinsi; Richman, 1973). Detailed field surveys initiated in 1979 revealed additional populations of this species on the Kern Plateau and in the Scodie Mountains; in the mid 1980s, populations were discovered on the eastern flank of the Sierra Nevada in Inyo County. References to this species (as Batrachoseps sp. or “Kern Plateau Salamander”) prior to its formal description appear in Hansen (1980, 1997; distribution; regional species diversity), Stebbins (1985; distribution, illustration), Macey (1986; regional biogeography), Giuliani (1988, 1990, 1996; field survey reports), Macey and Papenfuss (1991a,b; distribution and regional biogeography), Wake (1993; membership in Plethopsis), García-París and Deban (1995; defensive behavior), Jennings (1996b; distribution map), Jockusch (1996, 1997b, 2001; phylogeography; number of trunk vertebrae; similarity to B. campi), Jackman et al. (1997; confirmation of membership in Plethopsis), Jockusch and Mahoney (1997; reproduction), Jockusch et al. (1998; regional species diversity), and Jockusch and Wake (2002; phylogeography).
Studies of mtDNA gene sequences, allozymes, and morphological data (Yanev, 1980; Jockusch, 1996; Jackman et al., 1997) confirm that B. robustus, together with Oregon slender salamanders (B. wrighti) and Inyo Mountains salamanders (B. campi), are phylogenetically distant from other species of Batrachoseps. Despite the relative isolation of the Scodie Mountains populations, they are relatively little differentiated from populations in the main body of the species’ range on the Kern Plateau and western Owens Valley based on allozyme studies (Wake et al., 2002). Despite their proximity to populations of Inyo Mountains salamanders (B. campi; 43 km), Kern Plateau salamanders are as differentiated (or more so) from them as from Oregon slender salamanders (B. wrighti).
4. Conservation. Kern Plateau salamanders have been found to be surprisingly widespread on the Kern Plateau, especially on the more mesic portions, as well as being present in virtually every stream-bearing canyon on the eastern flank of the Sierra Nevada in Inyo County (from Olancha Creek south to Ninemile Canyon). The two isolated populations in the Scodie Mountains are quite small and are comparatively more vulnerable to habitat disturbance. Nearly all populations occur on public lands administered by the USDA Forest Service or U.S. Bureau of Land Management. Some sites have been affected by road construction, timber harvesting activities, or forest fire suppression efforts. A critical habitat feature for this species at most localities is surface moisture in the form of springs, seepages, or creek margins—we suspect these are oviposition sites based upon the discovery of small aggregations of gravid females. This is a Forest Service Sensitive Species.
1 Robert W. Hansen
2 David B. Wake
Literature references for Amphibian Declines: The Conservation Status of United States Species, edited by Michael Lannoo, are here.
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Citation: AmphibiaWeb. 2018. <http://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 21 Mar 2018.
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