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Dipodomys micropschisel-toothed kangaroo rat

By Christopher Rall

Geographic Range

The range of Dipodomys microps encompasses most of the arid regions of Nevada. It extends west to the Sierra Nevada, east to the Wasatch Mountains of Utah and south to the Colorado River. In southern California distribution is discontinuous, but populations occur as far south as Joshua Tree National Monument. At its northwest corner, the range extends north into southeastern Oregon and east into the Raft River Valley in Idaho. (Hayssen, 1991)

Habitat

The chisel-toothed kangaroo rat is a desert dweller. It is found in mountains at elevations between 1,000 and 3,500 m. Its abundance is primarily associated with two plants: Atriplex confertifolia in desert valleys and Coleogyne ramosissima (deciduous blackbush) in desert uplands. In San Bernardino County, California, D. microps is found in the yucca plant belt. Other dominant plants found in its habitat include Eurotia lanata (winterfat), Kochia americana (kochia), Grayia sponosa (hop sage), Agropyron (wheatgrass), Cercocarpus ledifolius (mountain mahogany), Juniperus (juniper), Artemesia tridentata (sagebrush), Sarcobatus vermiculatus (greasewood) and Larrea tridentata (creosote). In sympatry with D. merriami or D. ordii, D. microps is found in areas of gravel soil more than in areas with fine sand or clay. (Hayssen, 1991)

  • Range elevation
    1000 to 3200 m
    3280.84 to 10498.69 ft
  • Average elevation
    1200 m
    3937.01 ft

Physical Description

D. microps is a medium sized, 5-toed kangaroo rat with a narrow face, small ears and ever-growing cheekteeth. Its incisors are flat on the anterior side and less incurved than other members of the genus. Chisel-toothed kangaroo rats are about 270 mm long and weigh about 55 g. The body without the tail is about 112 mm in length. Tail length adds about 158 mm. Males are slightly larger than females on average. The fur is brown and gray above with a "gunmetal hue." D. microps is white below. The pelage is slightly darker than other Dipodomys species. Not including the feet, the hind leg is twice as long as the foreleg. The hind foot is the same length as the femur. There are 13 subspecies distinguishable by a combination of cranial and bacular measurements or by range. (Hayssen, 1991)

  • Sexual Dimorphism
  • male larger
  • Average mass
    55 g
    1.94 oz
  • Average length
    270 mm
    10.63 in

Reproduction

Males compete for access to females, usually with some aggression. Foot drumming among males may play a part in determining or securing access to females. That males are larger than females in a mammalian species typically is an indication that there is competition between males for females, and that there is some level of polygyny.

Copulation lasts 3-6 minutes. A copulatory plug is employed, indicating that there is some level of sperm competition, and therefore of females mating with multiple males.

Females do not accept copulations outside of their fertile period. Non-receptive females can be aggressive and even kill males attempting to mate with them. (Hayssen, 1991)

Most information on the reproduction of these animals comes from studies of captive animals. Female D. microps have an estrous cycle of about 12 days. Sperm production in males occurs from late autumn to early spring. Gestation takes 30-34 days, and average litter size is 2.4 young. Newborns weigh about 4 g and grow to 21 g in 4 weeks. Young appear above ground at the peak of Atriplex growth, when this plant has its highest water content. No information on time of weaning is available.

Little information is available on the timing and length of the breeding season except in the Owens Valley in Inyo County, California, where mating occurs in February and early March, with births occurring in March or early April. Pregnant females have been found from April until June in Nevada, indicating that the breeding season may vary geographically.

In exceptionally good years, females can produce two broods during the year, and the young of the year may reproduce. This means that the young mice may reach sexual maturity by as early as two months of age. (Hayssen, 1991)

  • Breeding interval
    Female D. microps breed once annually, on average. In unusually good conditions, females produce two litters in a year.
  • Breeding season
    varies geographically; sometime between late winter and early summer.
  • Average number of offspring
    2.4
  • Range gestation period
    30 to 34 days
  • Range age at sexual or reproductive maturity (female)
    2 (low) months
  • Range age at sexual or reproductive maturity (male)
    2 (low) months

As in all mammals, the young receive parental care from the mother. The young are born poorly developed and weighing only a few grams. Females nurse their young in a burrow until the young are ready to disperse.

  • Parental Investment
  • altricial
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female

Lifespan/Longevity

The average lifespan is 4.9 month, but this, is of course, misleading. Many kangaroo rats die young, and those who make it to adulthood can live a very long time. Although maximum lifespan for D. microps has not been reported, one captive D. ordii lived to be nearly 10 years old! (Hayssen, 1991; Nowak, 1999)

  • Average lifespan
    Status: wild
    4.9 months
  • Average lifespan
    Status: wild
    4.9 months

Behavior

Semi-fossorial and nocturnal, D. microps is most active above ground in the first few hours after sunset. It can use saltatorial, or jumping, motion and is capable of swimming. While richocheting around, D. microps uses its long whiskers to maintain constant contact with the ground. Sandbathing is an important activity for maintenance and olfactory communication. Captive animals denied the ability to sandbathe develope sores on their bodies.

Individuals can travel 350 meters per night in their foraging areas. Travel is not random, and an individual may use the same pathways over and over again. Home ranges for other members of the genus Dipodomys tend to be about 0.5 hectares, although no reports for D. microps were found.

Kangaroo rats in general are not highly social, and tend to be very territorial. One adult occupies a single burrow, although immatures may be found with a female. (Hayssen, 1991; Nowak, 1999)

Home Range

Home ranges for this species have not been reported, but other members of the genus have home ranges around 0.5 ha. (Nowak, 1999)

Communication and Perception

Modes of communication include olfactory and acoustic. Chisel-toothed kangaroo rats sandbathe to spread their scent and use foot drumming, possibly as territorial behavior. Aggressive encounters are also used as a form of communication in this species. (Hayssen, 1991)

Food Habits

D. microps eats leaves of Coleogyne ramossisima and Atriplex confertifolia primarily and seeds secondarily. Its chisel-shaped incisors are adapted to remove the salty outer parts of the leaves of Atriplex confertifolia (Saltbush). In the spring Atriplex leaves are eaten whole, but as salinity builds up in the outer parts of the leaves in summer and fall, these kangaroo rats use their incisors to access the nutritious and less saline inner parts of the leaves. Avoiding the salty parts of the plants enables D. microps to take advantage of the water content and nutrition in the leaves while maintaining water balance. None of the kangaroo rats needs to drink much, because this genus is able to use the water in their foods.

Seeds become a dominant part of the diet when leaves are unavailable. Granivory is more common in the southern part of the range. D. microps forages above ground at night. During the day, these kangaroo rats engage in coprophagy below ground.

D. microps assimilates 91.3% of its diet. The folivorous diet results in a reduced competition with sympatric congenerics, who specialize more in eating seeds. The unique diet of D. microps is also related to the large cheekpouch capacity of the species. Unlike their smaller-pouched relatives, D. microps has a whopping 4 cubic centimeters per pouch. In spite of the large capacity of their cheek pouches, these kangaroo rats are slower at filling them than are other species of kangaroo rat.

All kangaroo rats apparetnly cache food in their burrows. Cheek pouches help the rats carry food to the burrow. (Hayssen, 1991; Nowak, 1999; Vander Wall, et al., 1998)

  • Plant Foods
  • leaves
  • seeds, grains, and nuts
  • Other Foods
  • dung

Predation

Feral cats prey on Dipodomys microps. Although reports are lacking, it is likely that this species also falls victim to generalist nocturnal carnivores, such as foxes, coyotes, and owls. Snakes may also enter their borrows and take some animals. (Hafner, 2000b)

Ecosystem Roles

Because of its food caching behavior, this species likely disperses seeds. It is also a small mammal, and probably forms an important part of the diet of local predators. Because it potentially has as many as 4 sympatric congenerics in some parts of its range, the chisel-toothed kangaroo rat plays a role in regulating congener populations. (Jenkins and Breck, 1998; Lemen and Freeeman, 1986; Lemen and Freeman, 1987)

  • Ecosystem Impact
  • disperses seeds
Commensal/Parasitic Species
  • Atriplex confertifolia

Economic Importance for Humans: Positive

These animals are used in research.

  • Positive Impacts
  • research and education

Economic Importance for Humans: Negative

There are no reported negative impacts of this species on humans. However, it is likely that those animals occurring near agricultural areas could present a danger to crops, as has been reported for other species in this genus. (Nowak, 1999)

Conservation Status

Two subspecies are listed by the IUCN. Subspecies Dipodomys m. alfredi, the Gunnison Island kangaroo rat is redlisted as data deficient (DD). Gunnison Island is only 1 square kilometer and is located in the Great Salt Lake in Utah. Further demographic information is needed to make a determination as to its status. Subspecies D. m. leucotis, Houserock Valley kangaroo rat, is redlisted as Vulnerable due to limited range and potential habitat degradation through grazing and presence of feral cats. This subspecies occurs in Marble Canyon in Cocino County, northern Arizona. (Hafner, 2000a; Hafner, 2000b)

Other Comments

Durrant suggested that D. microps speciated from others in the genus as a result of the formation and subsequent recession of Lake Bonneville which occupied much of the Great Basin in the Pleistocene. D. microps can quickly colonize areas that were recently underwater. (Durrant, 1952; Hayssen, 1991)

Contributors

Nancy Shefferly (editor), Animal Diversity Web.

Christopher Rall (author), Humboldt State University, Brian Arbogast (editor), Humboldt State University.

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

acoustic

uses sound to communicate

altricial

young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

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.

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.

fertilization

union of egg and spermatozoan

folivore

an animal that mainly eats leaves.

fossorial

Referring to a burrowing life-style or behavior, specialized for digging or burrowing.

granivore

an animal that mainly eats seeds

herbivore

An animal that eats mainly plants or parts of plants.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

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.

nocturnal

active during the night

pheromones

chemicals released into air or water that are detected by and responded to by other animals of the same species

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

saltatorial

specialized for leaping or bounding locomotion; jumps or hops.

scent marks

communicates by producing scents from special gland(s) and placing them on a surface whether others can smell or taste them

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

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

solitary

lives alone

stores or caches food

places a food item in a special place to be eaten later. Also called "hoarding"

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

vibrations

movements of a hard surface that are produced by animals as signals to others

visual

uses sight to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

References

Durrant, S. 1952. Mammals of Utah: taxonomy and distribution. University of Kansas Publications, Museum of Natural History, 6: 1-549.

Hafner, D. 2000a. "Dipodomys microps ssp. alfredi" (On-line). Accessed November 14, 2001 at http://www.redlist.org/search/details.php?species=6697.

Hafner, D. 2000b. "Dipodomys microps ssp. leucotis" (On-line). Accessed November 14, 2001 at http://www.redlist.org/search/details.php?species=6679.

Hayssen, V. 1991. *Dipodomys microps*. Mammalian Species, 389: 1-9.

Jenkins, S., S. Breck. 1998. Differences in food hoarding among six species of heteromyid rodents. Journal of Mammalogy, 79: 1221-1233.

Lemen, C., P. Freeeman. 1986. Interference competition in the heteromyid communityin the Great Basin of Nevada, USA. Oikos, 46: 390-396.

Lemen, C., P. Freeman. 1987. Competition for food and space in a heteromyid community in the Great Basin Desert. Great Basin Naturalist, 47: 1-6.

Nowak, R. 1999. Walker's Mammals of the World, Sixth Edition. Baltimore and London: Johns Hopkins University Press.

Vander Wall, S., W. Longland, S. Pyare, J. Veech. 1998. Cheek pouch capacities and loading rates of heteromyid rodents. Oecologica, 113: 21-28.

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