Dipodomys elator

Geographic Range

The geographic range of Texas kangaroo rats, Dipodomys elator , is very limited, and the species is often referred to as a remnant or relict population. Because of human modification of the landscape, its range is now restricted to the north-central portion of Texas, but historically it was likely much greater. Texas kangaroo rats have been recorded in recent history in Motley, Cottle, Hardeman, Foard, Wilbarger, Baylor, Wichita, Archer, Clay and Montague counties in Texas, and Comanche county in Oklahoma. However, it has not been recorded in Oklahoma since 1905 and the Texas range now appears to be restricted to Motley, Hardeman, Wilbarger, and Wichita counties, and potentially Foard and Archer counties. These counties are estimated to contain 6,520 square km of potential habitat, but reliable information indicates the actual area to be much less.

• Biogeographic Regions
• nearctic nearctic
  • native native

Habitat

One reason for the highly truncated geographic range of D. elator is its requisite habitat. Texas kangaroo rats are found in association with mesquite grasslands with bare-ground areas and clay soil; it does not live more than 0.8 km from mesquite ( Prosopis glandulosa ) or on sand. The mesquite grassland cover-type has been greatly reduced by agricultural modification. This practice has caused the wholesale removal of the ecosystem and promoted the invasion of exotic species on remaining patches. Mesquite grassland cover has also been limited by the extirpation of bison , black-tailed prairie dogs , and fire ; these would have historically rejuvenated old patches on the landscape. Disturbance seems to be a key component for D. elator with its recent extirpation from sites where cattle-grazing was discontinued. The species also appears to need mounds for its burrows; historically these were mesquite root-balls, but bulldozer scrapes, road-cuts, and other earthworks seem acceptable.

• Habitat Regions
• temperate temperate
• terrestrial terrestrial

• Terrestrial Biomes
• savanna or grassland savanna or grassland
• scrub forest scrub forest

Physical Description

General:

As with all kangaroo rats , D. elator is characterized by a tail longer than its body. Unlike most other kangaroo rats, D. elator has a white tuft on the end of its tail. Additionally, it has one of the thickest tails per body length and one of the larger bodies of the genus. Mass ranges between 50 and 102 g. The tail length ranges from 135 mm to 205 mm with total body length from 260 mm to 345 mm. The tail length is generally 160% of the head plus body length. In addition to the white tuft, the tail has a dorsal and ventral stripe; both are a paler color than the buff-colored tail. The hind feet are also very long (42 mm to 49 mm), have four toes, and stand out next to the white thigh patches.

Pelage is somewhat variable from juvenile to adult, but generally consistent among adults. Juveniles sometimes have darker flanks, mid-dorsal areas, and hair tips. Additionally, individual hairs are thinner and do not grow as densely, especially on the belly. Adults are generally a buff color with blackish guard-hairs and a white belly.

The coat is replaced annually, with adults molting in the summer and non-adults molting in the fall. Molt begins at the nose and between the shoulders and proceeds in all directions from there.

D. elator has large eyes and small ears that are nearly hairless. Males are generally heavier than females and have larger skulls, but the sexes are otherwise externally indistinguishable. Average individual size varies geographically, with greater sexual dimorphism on the periphery than in the heart of the range. Texas kangaroo rats are very similar in appearance to Ord’s kangaroo rats, D. ordii , and Merriam’s kangaroo rats, D. merriami , but neither occurs within the range of D. elator .

The baculum of D. elator is nondescript in comparison to other mammals. Its average measurements are: total length, 13.13 mm; dorsovetral diameter at midshaft, 0.69 mm; dorsoventral diameter of base, 1.51 mm; lateral diameter at base, 1.47 mm. The baculum is generally straight, but may have a slight curve. It is round in cross-section, and has a distal end that is square to laterally expanded.

The dental formula of Texas kangaroo rats is the same as all Heteromyidae ; it exhibits an I 1/1, C 0/0, P 1/1, M 3/3 pattern for a total of 20 teeth. However, the cusp pattern of the P4 is unique in this species and highly differentiated from any other described tooth within the genus Dipodomys . The P4 consists of a double-cusped protoloph with accessory styles (protostyles) , and a transverse valley that extends across the entire tooth.

D. elator has 36 chromosomes (35 autosomal chromosomes, plus sex chromosomes) with a diploid number of 72. Molecular systematics indicate that D. elator is most closely related to D. phillipsii and diverged from it approximately 3,050,000 years ago. Intraspecific genetic examination indicates that differentiation has been occurring between disjunct populations which is likely the result of recent habitat reduction. Such habitat reduction has impeded migration, and reproductively isolated these disjunct populations.

• Other Physical Features
• endothermic endothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• male larger

Reproduction

There is currently no information on the mating system of Texas kangaroo rats. It is generally asocial and females are known to be antagonistic towards males when housed together in captivity.

Little is known about reproduction in D. elator . There is evidence of year round reproduction with spikes in spring and early summer, but young have been noted in May and from July through November. The litters produced late in the year are thought to result from spring juveniles reaching sexual maturity. Juveniles marked in spring have been noted as sexually mature in fall in both sexes. Females produce an average number of three young per litter and likely produce multiple litters per year. The level of post-weaning care is unknown, but given the asocial nature of Texas kangaroo rats, it is likely to be little to none. There is no evidence of burrow sharing post-weaning.

Although data on reproduction in D. elator are scant, much is known about reproduction within the genus Dipodomys , and many parameters are remarkably consistent between species. In general, the estrus cycle is between 5 and 13 days. Gestation lasts 29 to 36 days, with longer gestations occuring after a postpartum estrus. At birth, neonates are naked and helpless, and weigh between 3 and 6 g. Weaning takes place between 18 and 29 days of age. Young may remain in their natal nest for 4 to 5 weeks. It is likely that given the consistency of these parameters within the genus, D. elator is similar.

• Key Reproductive Features
• iteroparous iteroparous
• year-round breeding year-round breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• fertilization fertilization
• viviparous viviparous
• post-partum estrous

Beyond the investment by the female in gestation and lactation there is no information on parental investment in offspring. It is likely that there is little parental investment beyond this. Given the solitary nature of these animals, it is likely that only the female provides parental care.

• Parental Investment
• no parental involvement
• altricial altricial
• female parental care female parental care
• pre-fertilization
  • protecting
    • female
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • female
• pre-weaning/fledging
  • provisioning
    • female
  • protecting
    • female

Lifespan/Longevity

There is currently no information on the lifespan of Texas kangaroo rats. However, one member of another species in the genus, D. ordii , lived almost 10 years in captivity.

Behavior

D. elator is generally solitary; the only time it has been found in groups is when young have been found in the burrow together. It is also very quiet; the only sounds noted have been squeaks from marking (toe-clipping) and a thumping noise made upon entering a burrow.

D. elator is nocturnal, and does not become active until complete darkness. Its greatest period of activity occurs approximately two to three hours after nightfall. Weather and moonlight do not seem to affect activity levels; it has been observed under the full moon and has been active during a snowfall of 10 cm.

Texas kangaroo rats are very active stockpilers of food. In one instance, a single individual transported several bushels of wheat from the shed where it was stored to its burrow under the floorboards.

D. elator normally does not place its burrows near human habitation. Burrow systems are complex warrens with numerous opening and interwoven tunnels. The openings are generally bounded by the roots of a mesquite bush (or other imbedded object), are 5 to 10 cm in diameter, and though generally left open may sometimes be plugged (temporarily) by the resident. Tunnel systems average 2.5 m in total length, 46 cm under the surface, and have several dead-end chambers. There is typically a single nest chamber located near the bottom of the warren, and several food storage chambers. Tunnel diameter is typcially 5 cm to 12.5 cm, but may be as small as 2.5 cm with interwoven tunnels walls as little as 1 cm apart. Burrows maintain a very constant temperature of 15.5 ºC to 18 ºC even when surface temperatures range from 8 ºC to 36 ºC.

Texas kangaroo rats seem to have a very good knowledge of the location of both their own and surrounding burrow entrances. Upon release after trapping, individuals of this species have been noted to hop directly to the nearest burrow opening. There is evidence of interspecific antagonistic behavior between D. elator and Sigmodon hispidus , but D. elator seems to otherwise avoid interspecific contact.

Texas kangaroo rats are bipedal and move by hopping (saltatorial). They are very agile and fast. Movement is facilitated by the paths individuals clear through their territory to help them move from point to point.

Texas kangaroo rats also maintain several small, cleared, and inconspicuous patches of dust near burrow openings that are used for dust-bathing. This habit helps to remove ectoparasites without the necessity of water.

• Key Behaviors
• terricolous
• saltatorial saltatorial
• nocturnal nocturnal
• motile motile
• sedentary sedentary
• solitary solitary

Home Range

Texas kangaroo rats have a large home range when compared to other kangaroo rats . Home ranges varied in size from 0.01 ha to 0.19 ha with an average size of 0.08 ha. Population densities are high for this habitat type, with between 8.6 and 24.7 individuals per hectare. D. elator also travels long distances; it has traveled up to 108 meters between traps and up to 300 m along roadsides and field terraces.

Communication and Perception

Since D. elator is uncommon, nocturnal, and asocial, little is known about how it communicates. It is known to make a thumping noise upon entering a burrow, but the purpose of this is unknown. Nothing is known about scent marking or other means of territory delineation. It is known to have excellent vision and hearing and these likely facilitate communication. Also, tactile commmunication is likely in territorial conflicts, between mates, and between mothers and their offspring.

• Communication Channels
• tactile tactile
• acoustic acoustic

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical

Food Habits

D. elator feeds mainly on grasses and annual forbs. It also supplements its diet with perennial plants and a few insects. The seeds of Avena sativa , Sorghum halepense , and Cenchrus sp. are the major component of the grass portion; the florets and foliage of Erodium circutarium are the major component of the forb portion; and the seeds of Opentia sp. are the major component of the perennial portion of the diet. Texas kangaroo rats store large amounts of food to help themselves overwinter and they is not known to hibernate. During the spring and early summer, the green parts of several forbs are cached; in the late summer and fall, seeds are cached. Diet changes seasonally to take advantage of the available resources. These kangaroo rats continue to forage during the winter.

• Primary Diet
• herbivore herbivore
  • granivore granivore

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

• Foraging Behavior
• stores or caches food stores or caches food

Predation

There is only one recorded instance of a Texas kangaroo rat killed by an animal other than a human; that was by a rattlesnake . This is likely indicative of the animals that feed on D. elator . Any nocturnal predator large enough to take a 100 g rodent by surprise would have to be considered potential predators. This would include owls , canines , cats , weasels , and snakes .

Ecosystem Roles

D. elator has two main ecosystem roles. The first is to aerate the soil, which its digging does. This is very important in clay soils that are prone to poor oxygen and water absorption properties. The second is as a prey item. The mesquite grasslands in which it lives do not support high animal densities given the lack of standing water and food. An auxiliary role may be as a seed disperser, but this would only occur when an individual dies and seeds are left uneaten in its burrow.

Texas kangaroo rats also host many ectoparasites. These include: Geomylichus dipodomius , Echinonyssus incomptis , Androlaelaps fahrenholzi , Euschoengastia decipiens , Ixodes sp. larvae, Fahrenholzia pinnata , and Meringis agilis . Texas kangaroo rats also have their own species of nematode . This is Trichuris elatoris and it has not been found within any other species.

Vegetative species found in association with Texas kangaroo rats include Prosopis glandulosa , Bothriochloa saccharoides , Aristida purpurea , Bromus unioloides , Chloris verticullata , Panicum halli , Sporobolus cryptandrus , Tridens albescens , Xanthisma texanum , Hoffmanseggia glauca , Convolvulus equitans , Melampodium leucanthum , Monarda citriodora , Teucrium laciniatum , Linum pratense , Physalis viscosa , Solanum dimidiatum , and Tribulus terrestris .

Mammals found in association with the Texas kangaroo rat: Didelphis virginiana , Cryptotis parva , Sylvilagus floridanus , Lepus californicus , Spermophilus tridecemlineatus , Geomys bursarius , Chaetodipus hispidus , Perognathus flavus , Perognathus merriami , Reithrodontomys montanus , Peromyscus leucopus , Peromyscus maniculatus , Sigmodon hispidus , Neotoma micropus , Mus musculus , Mephitis mephitis , Taxidea taxus , Canis latrans , Procyon lotor , and Dasypus novemcinctus .

• Ecosystem Impact
• soil aeration soil aeration

Economic Importance for Humans: Positive

D. elator has no described economic importance. Given its rarity it has potential value for ecotourism, though this has not yet occurred.

Economic Importance for Humans: Negative

D. elator has no direct negative economic effect. It will opportunistically collect waste grain after harvest and, if allowed, it will take grain from inside human structures. However, given the rarity of the species it is unlikely to have a strong effect on crops. Given the protected status of the speciesd, it may reduce the potential actions of individual landowners on whose property it lives. Additionally, if it is decided that the habitat of this species must be restored, then this (potentially great) cost must be considered.

Conservation Status

Because of its rarity, limited range, and disjunct populations D. elator is of significant conservation concern. Additionally, except for the Copper Breaks State Park, Texas, the entire population resides on private land.

The IUCN Red List lists D. elator as vulnerable due to severely fragmented habitat and because this area is continuing to be degraded and reduced. The major source of this degradation is continued agricultural expansion.

The US Fish and Wildlife does not list D. elator as either threatened or endangered. It does not appear to be under consideration for listing either.

CITES does not list Texas kangaroo rats. This is likely because it is not used in the pet or medicine trade and is otherwise of no economic value.

Additional Links

Encyclopedia of Life

Contributors

Nancy Shefferly (editor), Animal Diversity Web.

Andrew Strassman (author), University of Michigan-Ann Arbor, Phil Myers (editor, instructor), Museum of Zoology, University of Michigan-Ann Arbor.

References

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Best, T. 1987. Sexual dimorphism and morphometric variation in the Texas kangaroo rat ( Dipodomys elator Merriam 1894). The Southwestern Naturalist , 32(1): 53 - 59.

Carrasco, M. 2000. Species discrimination and morphological relationships of kangaroo rats ( Dipodomys ) based on their dentition. Journal of Mammalogy , 81(1): 107 - 122.

Carter, D., W. Webster, J. Jones, C. Jones, R. Suttkus. 1985. Dipodomys elator . Mammalian Species , 232: 1 - 3.

Chapman, B. 1972. Food habits of Loring's kangaroo rat, Dipodomys elator . Journal of Mammalogy , 53(4): 877 - 880.

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Davis, W., D. Schmidly. 1994. The Mammals of Texas . Austin, Texas: University of Texas Press.

Hamilton, M., R. Chesser, T. Best. 1987. Genetic variation in the Texas kangaroo rat, Dipodomys elator Merriam. Journal of Mammalogy , 68(4): 775 - 781.

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

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Pfaffenberger, G., T. Best. 1989. Trichuris elatoris sp. n. ( Nematoda: Trichuridae ) from the Texas kangaroo rat ( Dipodomys elator ). Proceedings of the Helminthological Society of Washington , 56(1): 76 - 81.

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