|Scientific Name:||Spermophilus mohavensis|
|Species Authority:||Merriam, 1889|
|Taxonomic Notes:||Spermophilus mohavensis and S. tereticaudus hybridize along a small, narrow, stable contact zone (Helendale, Coyote Dry Lake) that coincides with a Wisconsinan pluvial barrier; the two taxa exhibit a consistent difference in diploid number (Hafner and Yates 1983, Hafner 1992).|
|Red List Category & Criteria:||Vulnerable B1ab(iii)c(iv) ver 3.1|
|Assessor(s):||Hafner, D.J. & NatureServe (Hammerson, G. & Williams, D.F.)|
|Reviewer(s):||Amori, G. (Small Nonvolant Mammal Red List Authority) & Chanson, J. (Global Mammal Assessment Team)|
Listed as Vulnerable because its extent of occurrence is approximately 20,000 km², its range is severely fragmented, and there is ongoing decline in the extent and quality of its habitat. Populations also experience extreme fluctuations, partly due to the effects of drought which deters the species from breeding in some years.
|Range Description:||The Mohave ground squirrel has a patchy (discontinuous) distribution (Hafner 1992, Gustafson 1993) in the northwestern corner of the Mohave Desert, south-central California in the United States, at elevations of 610-1,800 m asl (Best 1995); the range coincides with a cool mesic Wisconsinan refugium in the Mohave Desert. It occurs in southwestern Inyo, eastern Kern, extreme northeastern Los Angeles, and northwestern San Bernardino counties (Wessman 1977, California Department of Fish and Game 1990, Best 1995); from Olancha, Inyo County, south to Victorville, San Bernardino County, and from the Tehachapi Mountains of Kern County to the Granite Mountains in San Bernardino County (Biosystems Analysis 1989). The Mojave River generally defines the extreme southeastern boundary of the range, but the species historically occurred east of the river in Lucerne Valley (Stewart 2005; see list of specimens examined by Hafner 1992). Its extent of occurrence is approximately 20,000 km² (Stewart 2005).|
Native:United States (California)
|Range Map:||Click here to open the map viewer and explore range.|
This species is rare throughout much of its range. Significant population declines have been recorded across most of the range between 1980 and 2000, and this decline is not correlated with winter rainfall, which generally increased between 1984 and 1998 (Leitner 2001, Brooks and Matchett 2002). Hafner (1992) hypothesized that low dispersal ability might be one of several possible explanations for the persistence of a stable contact zone between S. mohavensis and S. tereticaudus, the species is relatively mobile compared to other ground squirrel species. Harris and Leitner (2004) found that the size of female home ranges in years of no reproduction appears to vary in response to food availability, and that alternating size of the home range may be an adaptive response to an arid, variable environment.
Total adult population size is unknown but may exceed 100,000 (assuming an average density of about one adult per hectare (Leitner and Leitner 1998) and 430,000 hectares of occupied habitat). However, the spatial and temporal distribution of this species is highly dynamic, which makes it difficult to make a reliable estimate of overall population size.
Stewart (2005) mapped 22 locations in which this species was captured during trapping surveys in 2002-2004 (Leitner 2005). These represent four core areas plus two additional areas in which squirrels are present at low densities (Stewart 2005).
This ground squirrel exhibits large fluctuations in local population size. Further information on overall trend is needed.
Recent monitoring data reveal that over twenty percent of the historical range of this species is no longer occupied (Stewart 2005).
|Habitat and Ecology:||
This ground squirrel inhabits desert areas with deep sandy or gravelly friable soils and an abundance of annual herbaceous vegetation. Habitats include alluvial fans where desert pavement is absent. Habitats in order of decreasing favourability: (1) creosotebush association, (2) shadscale association, (3) alkali sink association, and (4) Joshua tree association. Nests are in underground burrows. Individuals may use several different burrows.
Mating occurs in February-March (Harris and Leitner 2004). Litter size is 4-6; young are born in late March or early April (Biosystems Analysis 1989). No reproduction occurs during the driest years; for example, Harris and Leitner (2004) found that no reproduction occurred at their study site when early winter precipitation (October-January) was less than 30 mm.
Populations fluctuate with environmental conditions (Leitner and Leitner 1998). Populations in marginal habitats may become extirpated during extended droughts. After the return of favourable conditions, those areas may be recolonized from adjacent areas following the resumption of reproduction and dispersal of offspring from core habitats (Gustafson 1993). Long-distance movement by juveniles might be critical for connecting local populations and recolonizing sites after local, drought-related extirpation (Harris and Leitner 2005).
Mohave ground squirrels feed on green vegetation and seeds. May also eat carrion. Remains underground August until late winter or early spring (reportedly emerges in February or March, or, according to Biosystems Analysis , March in the south and May in the north). Active during the spring and summer.
The primary cause of the decline is the conversion of habitat to urban, suburban, agricultural, military, and other human uses (Gustafson 1993), including livestock grazing, off-highway vehicle use, energy production, and transportation infrastructure (California Department of Fish and Game 1990, Stewart 2005). Over 78% of the habitat within the species' range is either naturally unavailable, severely degraded, or is in a land-use category that represents a threat to the ground squirrel; the remainder is under threat from continued development and habitat fragmentation (Stewart 2005). The planned Fort Irwin expansion would fragment one of four remaining populations that appear to be stable, posing a serious threat to the species' persistence (Stewart 2005). Current regulatory mechanisms are believed to be inadequate to protect this species (Stewart 2005). Spermophilus tereticaudus may be expanding its range at the expense of S. mohavensis (Wessman, in Hafner 1992).
S. mohavensis fails to reproduce during years of drought rather than risking a delay in accumulating fat reserves for aestivation. Periods of prolonged drought therefore is a potential threat to the population. The taxon exists as isolated populations with a scattered distribution. Recruitment from neighbouring colonies is thought to be rare (Hafner et al. 1998).
Only 9% of the suitable habitat within the historical range exists in a protected state. Stewart (2005) determined that this species occurs on a large number of protected areas (federal wilderness areas, state parks, state ecological reserves, etc.) on lands encompassing about 1,800 km². Nearly two-thirds of the range is in federal ownership (Stewart 2005).
Habitat needs to be protected from development and excessive grazing. Off-road vehicle traffic should be restricted or eliminated at inhabited sites. Consideration of this species in federal land use decisions should be promoted.
Obtain data on reproduction, dispersal, demography, food habits, habitat needs, and the effects of fire, grazing, and off-road vehicle use.
|Citation:||Hafner, D.J. & NatureServe (Hammerson, G. & Williams, D.F.) 2008. Spermophilus mohavensis. The IUCN Red List of Threatened Species. Version 2014.2. <www.iucnredlist.org>. Downloaded on 21 August 2014.|
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