|Scientific Name:||Dipodomys stephensi (Merriam, 1907)|
|Taxonomic Notes:||According to Hall (1981) this species is possibly only subspecifically distinct from D. panamintinus, but others have found D. stephensi to be related to other species or to be distinct and well differentiated (see Bleich (1977) and Burke et al. (1991) for comments on the relationship of D. stephensi to other species of Dipodomys). Baker et al. (2003) and Patton (in Wilson and Reeder 1993, 2005) regarded D. stephensi and D. panamintinus as distinct species.|
|Red List Category & Criteria:||Endangered B1ab(i,ii,iii) ver 3.1|
|Assessor(s):||Linzey, A.V. & NatureServe (Williams, D.F. & Hammerson, G.)|
|Reviewer(s):||Amori, G. (Small Nonvolant Mammal Red List Authority) & Chanson, J. (Global Mammal Assessment Team)|
Listed as Endangered because its extent of occurrence is less than 5,000 km2, its range is severely fragmented and there is ongoing decline in its extent of occurrence, area of occupancy, and extent and quality of its habitat.
|Previously published Red List assessments:|
|Range Description:||The range of this species encompasses approximately 2,870 square kilometres in the San Jacinto Valley and adjacent areas of western Riverside County, southwestern San Bernardino County (at least formerly), and northwestern and north-central San Diego County, California in the United States (Bleich 1977, Williams et al. 1993). It is found at elevations of 55 to 1,250 m asl (USFWS 1997). As of the late 1980s, most extant populations were in western Riverside County, but the largest known population was on the Warner Ranch near Lake Henshaw, San Diego County (see Burke et al. 1991).|
Native:United States (California)
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||As of the late 1980s, there were 79 known extant populations (O'Farrell and Uptain 1989; see also Burke et al. 1991). Some of these populations no longer exist whereas subsequent surveys have revealed previously undocumented populations (see USFWS 1997). USFWS (1997) mapped a dozen "significant populations," noting that additional small fragmented populations also exist. Most existing populations occupy relatively small areas and probably are of less than optimal size for maximum viability. O'Farrell and Uptain (1989) found that 68 occupied sites were less than 40 hectares.|
Total adult population size is unknown but exceeds 10,000. As of the late 1980s, the largest known population included about 14,000 individuals (Burke et al. 1991). Population density estimates vary with location and season, and range from about five to 58 per hectare; perhaps about 20-40 per hectare would be typical (USFWS 1987, Bleich 1977, McClenaghan and Taylor 1993). Population densities can vary more than ten-fold in response to rainfall patterns (Price and Endo 1989). In Riverside County, peak numbers occurred in late spring-early summer; populations declined from late summer through winter; minimum monthly survival rates for adults was 0.79-0.87 (McClenaghan and Taylor 1993).
As in most small mammals, abundance is a misleading index to degree of jeopardy. Habitat decline is expected to continue (Burke et al. 1991), but the rate of habitat loss decreased in the 1990s, in part as a result of a habitat conservation plan initiated in western Riverside County (USFWS 1997). Price and Endo (1988) estimated that the historical habitat had been reduced by about 60 percent by 1984. USFWS (1990) categorized the status as "declining."
|Current Population Trend:||Decreasing|
|Habitat and Ecology:||Habitats include annual grassland and coastal sage scrub with sparse shrub cover, the former more favourable than the latter, commonly in association with Eriogonum fasciculatum, Artemisia californica, and Erodium cicutarium (USFWS 1997). Typical habitat includes sparsely vegetated areas (perennial cover less than 30%) with loose, friable, well-drained soil (generally at least 0.5 m deep) and flat or gently rolling terrain. This species may recolonize abandoned agricultural land. It is most abundant where stands of native vegetation remain (Matthews and Moseley 1990) but deceases as bunchgrass density increases (see Burke et al. 1991). In western Riverside County, shrub removal resulted in increased kangaroo rat densities (Price et al. 1994). Periods of inactivity are spent in underground burrows. Individuals may construct their own burrows or may nest in old burrows of the California ground squirrel or in abandoned burrows of pocket gophers (see Burke et al. 1991, USFWS 1997). In captivity, females construct elaborate nests (Bleich 1977).|
This species probably produces one litter per year or two litters per year under high rainfall conditions and perhaps none under drought conditions. Average litter size is about 2.5. In Riverside County, a peak in recruitment occurred in spring (McClenaghan and Taylor 1993). In some areas, young are born in late spring or early summer, and at least sometimes as late as July. In some years, young-of-the-year may reproduce. Life span appear to be relatively short, generally less than a few years.
Mean home range size for two populations in Riverside County were 570 sq m and 970 sq m (Bleich 1977). Price et al. (1994) found that the median of the maximum distances moved between captures was about 29 m for 557 individuals and home ranges were stable over time. Diet is probably similar to D. heermanni and D. panamintimus which feed primarily on seeds but also eat insects and herbaceous vegetation in the spring. Sagebrush may provide much of the food. More likely to forage in open, lit spaces than is sympatric D. agilis (Burke et al. 1991). Predators include owls and various carnivores.
The habitat occupied by Stephens' kangaroo rat is also attractive for agricultural and urban developments. The known range of the species is centred around a rapidly developing part of southern California. A significant portion of its former range has been lost, however, several major populations of the species remain. Suitable habitat for Dipodomys stephensi happens to be mostly on private land and it is threatened by agricultural and urban development and fragmentation. Apparently some areas have been intentionally ploughed or poisoned in efforts to eliminate this species (1988 Federal Register 54(190):38465-38469).
Certain non-native grasses (e.g., Bromus diandrus) can exclude this species from otherwise suitable habitat (USFWS 1997). Land management practices that lead to the development of thick vegetation have resulted in kangaroo rat population declines in some areas (USFWS 1997). Populations isolated by fragmentation are vulnerable to extirpation or decline from some types of grazing (e.g., excessive vegetation removal and burrow trampling by horses in small enclosures), off-road vehicle activity, rodenticide use, genetic bottlenecks, or unnaturally high levels of predation (by domestic cats associated with urban development).
Dipodomys stephensi is listed as Endangered by the United States Fish and Wildlife Service (1988). A Habitat Conservation Plan targeting the species has been prepared by Riverside County designating six major areas for study as potential preserve sites. Some of the land within these sites has been purchased for preserve use. Most of the major populations occur within the boundaries of existing protected areas including Lake Perris State Park, San Jacinto Wildlife Area, Sycamore Canyon Park, Lake Mathews Ecological Reserve, and Roy E. Shipley Reserve.
Some habitat has been protected through the establishment of San Jacinto Wildlife Area and Lake Mathews Ecological Reserve in Riverside County. The Riverside County Habitat Conservation Agency has implemented a habitat conservation plan for the creation of a reserve network within a portion of the species' range (USFWS 1997).
It is necessary to determine if the species is present in the Rawhide Motorcross Park and to estimate abundance. Habitat should be protected from agricultural and urban development. As of the early 1990s, existing state regulations and county zoning restrictions did not provide adequate habitat protection (Burke et al. 1991). Habitat conservation efforts should be directed at establishing a few large, widely separated preserves, rather than many smaller ones (Price and Endo 1989). For long-term population persistence, Burke et al. (1991) recommended a minimum reserve size of 1,320 ha (3,300 acres) of suitable habitat. Most extant populations occupy areas of less than 400 ha; Burke et al. (1991) proposed nine potential reserves (see also O'Farrell and Ulark 1989). Some reserves should be at higher elevations as these may serve as refuges during drought (Burke et al. 1991). For delisting, USFWS (1997) recommended the establishment of at least five reserves (at least 6,675 ha) in Riverside County and two in San Diego County.
It is necessary to obtain data on demography, dispersal, reproduction, and food habits; investigate taxonomic relationship to D. heermanni and D. panamintinus; and investigate grazing impacts.
|Citation:||Linzey, A.V. & NatureServe (Williams, D.F. & Hammerson, G.). 2008. Dipodomys stephensi. The IUCN Red List of Threatened Species 2008: e.T6682A12795176.Downloaded on 19 October 2017.|
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