Dipodomys stephensiStephens's kangaroo rat

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Geographic Range

Dipodomys stephensi are commonly called Stephen's kangaroo rats. This species of kangaroo rat is confined to a relatively small geographical range, approximately 1,100 square miles. They can be found in North America, in Riverside County through northern San Diego County, in the state of California ( http://ecoregion.ucr.edu/mshcp/full.asp?sp_num=6308).

Habitat

Stephen's kangaroo rats are found in arid and semi-arid habitats with some grass or brush. They prefer open habitats with less than 50% protective cover. They require soft, well-drained substrates for building burrows and are typically found in areas with sandy soil. ( http://ecoregion.ucr.edu/mshcp/full.asp?sp_num=6308).

Physical Description

Total body length in Stephen's kangaroo rats, from the head to the tip of the tail, can be up to 330 mm. The tail can be twice as long as the body. The relatively bare tail ends with a tuft of dark and white fur. Stephen's kangaroo rats have large hind feet which are used for jumping. The body is covered with light brown fur which becomes lighter on the ventral surface and legs. Ears are small and lay back against the head. Eyes are large, which is an important adaptation for these nocturnal creatures (Storer, 1963 ; http://www.desertusa.com/aug96/du_krat.html).

Kangaroo rats have several remarkable adaptations to desert life. Their large ears and enlarged auditory bullae permit keen hearing and the perception of low frequency sounds. These adaptations allow Stephen's kangaroo rats to avoid nocturnal predators such as owls or rattlesnakes (Raven, 1999).

Kangaroo rats also use water very efficiently. Most mammals obtain water through drinking and food consumption. Stephen's kangaroo rats have specialized kidneys that produce highly concentrated urine. As a result, Stephen's kangaroo rats are never required to drink water because a sufficient amount is obtained through food and metabolic activity (Raven, 1999).

  • Average mass
    65 g
    2.29 oz

Reproduction

Breeding occurs twice a year, in summer and in winter. Each year Stephen's kangaroo rats produce, on average, 5 young. Numbers of young per litter is correlated with amount of rainfall, higher rainfall resulting in higher litter size. The gestation period is approximately 30 days with weaning occuring between 18 to 22 days after birth. Offspring are born in enlarged burrows, which often double as locations of food storage. Age of sexual maturity is estimated to be acheived at 3 months, and females must weigh 55 g before they can produce milk.

( http://ecoregion.ucr.edu/mshcp/full.asp?sp_num=6308 ; http://www.animalinfo.org/species/rodent/dipostep.htm ; Storer, 1963)

  • Key Reproductive Features
  • gonochoric/gonochoristic/dioecious (sexes separate)
  • sexual

Behavior

Stephen's kangaroo rats are nocturnal and are not sexually dimorphic. All members are solitary and maintain asymmetrical territories which often overlap with related species of rodents. The time of most activity occurs between 9 P.M and 3 A.M. Males and females do not form a pair bond and males do not contribute to raising young.

Kangaroo rats travel primarily by saltatory locomotion, they use their long hind feet to hop and can acheive high speeds in this manner. Each individual hop may be up to 2 meters long. Only when an animal is moving slowly will it use its forelimbs.

Dustbathing is vital to the health of kangaroo rats. When prevented from dustbathing their fur becomes matted and unhealthy and they develop sores on their body.

( http://ecoregion.ucr.edu/mshcp/full.asp?sp_num=6308 ; http://www.ocregister.com/science/features/edgeofnature/stephenskangaroorat.shtml)

Communication and Perception

Food Habits

Stephen's kangaroo rats are granivores. Seeds are collected in cheek pouches and stored in either shallow holes or nesting burrows (Storer, 1963).

Economic Importance for Humans: Positive

Stephen's kangaroo rats are important in maintaining the ecological integrity of arid and semi-arid habitats where they occur. They modify habitats by impacting the structure of vegetation and they serve as important prey sources for raptors, foxes, coyotes, and other predators.

Economic Importance for Humans: Negative

The feeding habits of Stephen's kangaroo rats causes a decrease in the grass and shrub density. Research indicates that "their removal from plots resulted in the habitat converting from desert shrub to grassland".

Stephen's kangaroo rats may take enough grain from neighboring agricultural fields to be important economically but generally they do not adversely affect human populations.

( http://ecoregion.ucr.edu/mshcp/full.asp?sp_num=6308).

Conservation Status

Currently, Stephen's kangaroo rats are listed as threatened under the Endangered Species Act of the United States. Farming is the number one threat to Stephen's kangaroo rats because it limits food availability and destroys burrows. Development for agriculture has resulted in a loss of 95% of appropriate habitat for Stephen's kangaroo rats. Overgrazing by domesticated animals, such as horses and cattle, also limits the food supply.

( http://ecoregion.ucr.edu/mshcp/full.asp?sp_num=6308).

Contributors

George Bruque (author), Fresno City College, Jerry Kirkhart (editor), Fresno City College.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

chaparral

Found in coastal areas between 30 and 40 degrees latitude, in areas with a Mediterranean climate. Vegetation is dominated by stands of dense, spiny shrubs with tough (hard or waxy) evergreen leaves. May be maintained by periodic fire. In South America it includes the scrub ecotone between forest and paramo.

chemical

uses smells or other chemicals to communicate

desert or dunes

in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

tactile

uses touch to communicate

threatened

The term is used in the 1994 IUCN Red List of Threatened Animals to refer collectively to species categorized as Endangered (E), Vulnerable (V), Rare (R), Indeterminate (I), or Insufficiently Known (K) and in the 1996 IUCN Red List of Threatened Animals to refer collectively to species categorized as Critically Endangered (CR), Endangered (EN), or Vulnerable (VU).

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

References

"Animal Info -Stephen's Kangaroo Rat" (On-line). Accessed October 6, 2000 at http://www.animalinfo.org/species/rodent/dipostep.htm.

"Dudek and Associates Species Account, Western Riverside County MSHCP" (On-line). Accessed October 6, 2000 at http://ecoregion.ucr.edu/mshcp/full.asp?sp_num=6308.

August 1996. "Kangaroo Rats Genus Dipodomys" (On-line). Accessed November 11, 2000 at http://www.desertusa.com/aug96/du_krat.html.

Brennan, P. May 3, 1998. "Strange appearance serves a useful purpose" (On-line). Accessed October 6, 2000 at http://www.ocregister.com/science/features/edgeofnature/stephenskangaroorat.shtml.

Nader, I. 1978. Kangaroo rats : intraspecific variation in Dipodomys spectabilis Merriam and Dipodomys deserti Stephens. Urbana: University of Illinois Press.

Raven, P., G. Johnson. 1999. Biology. Boston: McGraw-Hill Companies.

Storer, T., R. Usinger. 1963. Sierra Nevada Natual History. Los Angeles, California: University of California Press.