|Scientific Name:||Rana muscosa|
|Species Authority:||Camp, 1917|
|Taxonomic Notes:||Yellow-legged frog populations now recognized as Rana sierrae formerly were included in Rana muscosa. Vredenburg et al. (2007) examined phylogeography of Rana muscosa as defined by Stebbins (2003) and determined that R. muscosa occurs in the southern Sierra Nevada and in mountains to the south and that populations in the Sierra Nevada north of this range comprise a distinct species (Rana sierrae).|
|Red List Category & Criteria:||Endangered B2ab(ii,iv,v); C2a(i) ver 3.1|
|Reviewer/s:||Global Amphibian Assessment Coordinating Team (Simon Stuart, Janice Chanson, Neil Cox and Bruce Young)|
Listed as Endangered because of a drastic long-term and likely ongoing decline that has resulted in a very small current area of occupancy, severe population fragmentation, and small estimated population size.
|Range Description:||Rana muscosa occurs in the southern Sierra Nevada of California and in mountains to the south in southern California. In southern California south of the Sierra Nevada, the historical range extended from Palomar Mountain in San Diego County northward and westward through the San Jacinto, San Bernardino, and San Gabriel Mountains of Riverside, San Bernardino, and Los Angeles counties; these formed four isolated clusters of montane populations (Vredenburg et al. 2007). Additionally, the species occurred as an isolated cluster of populations on Breckenridge Mountain, south of the Kern River in Kern County, and in the Sierra Nevada (west of the crest) in Tulare, Inyo and Fresno counties, extending north to Mather Pass (Vredenburg et al. 2007). The mountain ridges that separate the headwaters of the South Fork Kings River from the Middle Fork Kings River, from Mather Pass to the Monarch Divide, form the northern border of the range. Rana muscosa is now extirpated on Palomar and Breckenridge mountains and in much of the former range elsewhere in southern California and the southern Sierra Nevada (USFWS 2006, Vredenburg et al. 2007). Elevational range in southern California is 1,220-7,560 feet (370-2,290 meters (Stebbins 1985, USFWS 2002).|
|Range Map:||Click here to open the map viewer and explore range.|
Vredenburg et al. (cited by Macey et al. 2001) stated that there are only 3-4 healthy populations in the southern Sierra Nevada.
Historically, Rana muscosa was documented in approximately 166 localities in creeks and drainages in the mountains of southern California (Jennings and Hayes 1994). Currently the species is known from only seven or eight locations (Backlin et al. 2002, cited by USFWS 2002; Vredenburg et al. 2007).
Total adult population size is unknown but may not exceed a couple thousand (generously assuming 20 subpopulations averaging 100 adults); available information indicates fewer subpopulations and smaller subpopulation sizes. In southern California south of the Sierra Nevada, estimated population size in 2003 was around 183 adults (see USFWS 2006).
A precipitous decline in Rana muscosa/Rana sierrae appears to have occurred over the past 3-4 decades (Bradford 1991; USFWS 1999; Vredenburg et al., in Lannoo 2005). For the Rana muscosa/Rana sierrae complex as a whole, Jennings and Hayes (1994) mapped many more extirpated populations than extant populations.
Of the 79 historical R. muscosa sites studied by Vredenburg et al. (2007), only 3 sites contained frogs when revisited between 1995 and 2005 (96 percent extirpation rate). Rana muscosa probably has been extirpated from more than 99% of the historical range in southern California south of the Sierra Nevada (USFWS 2002).
Declines likely are continuing, but the current rate of decline (past 10 years) is uncertain.
|Habitat and Ecology:||
The habitat includes sunny riverbanks, meadow streams, isolated pools, and lake borders in the Sierra Nevada, rocky stream courses in southern California. The species seems to prefer sloping banks with rocks or vegetation to the water's edge (Stebbins 1985). Zweifel (1955) observed that the frogs in southern California are typically found in steep gradient streams in the chaparral belt and may range into small meadow streams at higher elevations. In contrast, Sierran frogs are most abundant in high elevation lakes and slow-moving portions of streams. This frog seldom is found away from water, but it may cross upland areas in moving between summer and winter habitats (Matthews and Pope 1999). Wintering sites include areas nearshore under ledges and in deep underwater crevices (Matthews and Pope 1999).
In southern California, USFWS (2006) concluded that Rana muscosa requires the following habitat elements: (1) Water source(s) found between 1,214 to 7,546 feet (370 to 2,300 meter) in elevation that are permanent. Water sources include, but are not limited to, streams, rivers, perennial creeks (or permanent plunge pools within intermittent creeks), pools (i.e., a body of impounded water that is contained above a natural dam) and other forms of aquatic habitat. The water source should maintain a natural flow pattern including periodic natural flooding. Aquatic habitats that are used by mountain yellow-legged frog for breeding purposes must maintain water during the entire tadpole growth phase, which can last for up to 2 years. During periods of drought, or less than average rainfall, these breeding sites may not hold water long enough for individuals to complete metamorphosis, but they would still be considered essential breeding habitat in wetter years. Further, the aquatic includes: a. Bank and pool substrates consisting of varying percentages of soil or silt, sand, gravel cobble, rock, and boulders; b. Open gravel banks and rocks projecting above or just beneath the surface of the water for sunning posts; c. Aquatic refugia, including pools with bank overhangs, downfall logs or branches, and/or rocks to provide cover from predators; and d. Streams or stream reaches between known occupied sites that can function as corridors for movement between aquatic habitats used as breeding and/or foraging sites. (2) Riparian habitat and upland vegetation (e.g., ponderosa pine, montane hardwoodconifer, montane riparian woodlands, and chaparral) extending 262 feet (80 meters) from each side of the centerline of each identified stream and its tributaries, that provides areas for feeding and movement of mountain yellow-legged frog, with a canopy overstory not exceeding 85 percent that allows sunlight to reach the stream and thereby provide basking areas for the species.
A petition to list the Rana muscosa/Rana sierrae complex as endangered cited the following threats: non-native fish introductions, contaminant introductions, livestock grazing, acidification from atmospheric deposition, nitrate deposition, ultraviolet radiation, drought, disease, and other factors (see USFWS 2000).
Extensive surveys in the Sierra Nevada clearly demonstrate the strong detrimental impact of introduced trouts on R. muscosa/Rana sierrae populations (Bradford 1989, Knapp and Matthews 2000). Removal of non-native fishes (relatively easy in some Sierra Nevada lakes) might easily reverse the decline (Knapp and Matthews 2000).
See Bradford (1991) for information on mass mortality and extinction of a population due at least in part to red-leg disease and predation on metamorphics by Brewer's blackbird; reestablishment of the extirpated population probably will be prevented through predation by introduced fishes.
Frogs of the Rana muscosa/Rana sierrae complex are possibly but probably not threatened by sublethal effects of low pH and elevated levels of dissolved aluminum (Bradford et al. 1992).
Fellers et al. (2001) documented oral chytridiomycosis (often indicated by oral disc abnormalities) in larvae and recently metamorphosed individuals of the Rana muscosa/Rana sierrae complex in the Sierra Nevada, where recent declines have occurred. However, loss of pigmentation of larval mouthparts does not always indicate chytridiomycosis (Batrachochytrium infection) (Rachowicz 2002).
Davidson et al. (2002) found support for the hypothesis that airborne agrochemicals have played a significant role in the decline of frogs of the Rana muscosa/Rana sierrae complex.
Southern California south of the Sierra Nevada: Threatened by predation by introduced trout (remaining frog populations generally are in upstream areas with barriers to trout colonization), recreational suction dredging for gold, human activities at campgrounds and day-use areas, and usual problems associated with small population size and population isolation (e.g., fire, flood, or drought could extirpate small populations, with little chance of reestablishment due to poor connectivity of populations). Human use in and along streams can disrupt the development, survivorship, and recruitment of eggs, larvae, and adult frogs (Jennings 1995; Stewart, in litt. 1995) and can change the character of a stream and its bank and associated vegetation in ways that make whole sections of a stream less suitable for the species (see USFWS 2002). Dams and diversions on streams alter natural hydrologic flow and may negatively impact breeding and foraging habitat and further exacerbate the decline of populations in southern California. Predatory non-native bullfrogs are present in many areas formerly occupied by R. muscosa (USFWS 2002) and likely are incompatible with viable R. muscosa populations. Pathogenic chytrid fungus (attacks larval mouthparts) may be a threat (USFWS 2002). Release of toxic or hazardous materials into streams is a potential threat (Jennings 1995, Backlin et al. 2002, USFS 2002).
All known populations and majority of habitat in southern California occur on lands managed by the U.S. Forest Service (USFWS 1999, 2002). Elsewhere, most occurrences are on lands administered by the U.S. Forest Service or U.S. National Park Service. Occurrence in protected, pristine areas does not ensure population persistence, due to threats from non-native fishes and disease.
A total of 8,283 acres (33.5 square kilometers) of stream segments and riparian habitat in portions of Los Angeles, Riverside and San Bernardino counties have been designated as critical habitat for the southern California distinct population segment of mountain yellow-legged frog (USFWS 2006). Almost all of the areas proposed as critical habitat are managed by the U.S. Forest Service's Angeles National Forest (ANF) and San Bernardino National Forest (SBNF). A small amount of privately owned land (approximately 119 acres) are also included as critical habitat.
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|Citation:||Geoffrey Hammerson 2008. Rana muscosa. In: IUCN 2013. IUCN Red List of Threatened Species. Version 2013.2. <www.iucnredlist.org>. Downloaded on 11 December 2013.|
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