Dipodomys ingens (Merriam, 1904)
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publication ID |
https://doi.org/ 10.5281/zenodo.6611160 |
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DOI |
https://doi.org/10.5281/zenodo.6608358 |
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persistent identifier |
https://treatment.plazi.org/id/3C3D87A6-876A-B130-1B91-5413F6FDF930 |
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treatment provided by |
Carolina |
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Dipodomys ingens |
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61. View Plate 11: Heteromyidae
Giant Kangaroo Rat
French: Rat-kangourou géant / German: Riesenkangururatte / Spanish: Rata canguro gigante
Taxonomy. Perodipus ingens Merriam, 1904 View in CoL ,
“Painted Rock, 20 miles southeast of Simmler, Carrizo Plain, San Luis Obispo Co., Caltfornia.”
Based on molecular sequence analyses, D. ingens is a member of the heermanni species group, along with D. heermanni , D. gravipes , D. panamintinus , D. microps , and D. stephensi . Monotypic.
Distribution. W. USA (restricted distribution along the SW edge of the San Joaquin Valley, SC California ). View Figure
Descriptive notes. Head—body 137-149 mm, tail 174-198 mm, ear 13 mm, hindfoot 48-55 mm; weight 93-180 g (males) and 101-195 g (females). Male Giant Kangaroo Rats are slightly larger than females. Tail is ¢.128% of head-body length. This is the largest kangaroo rat, with five toes on hindfeet (including small claw on side of hindfoot), and broad skull. Upper parts are warm buff; tail is bicolored, with dull brownishblack crest and tuft. Chromosomal complement has 2n = 64 and FN = 98. The Giant Kangaroo Rat is the only large kangaroo rat with five toes on hindfeet. It is larger than sympatric Heermann’s Kangaroo Rat ( D. heermanni ) and the San Joaquin Kangaroo Rat ( D. nitratoides ); even juvenile Giant Kangaroo Rats have larger hindfeet than either sympatric species.
Habitat. Sandy-loam soils in level or gently sloping areas, with annual grasses and forbs and widely scattered desert shrubs. The Giant Kangaroo Rat is restricted to the most arid south-western edge of central California’s San Joaquin Valley and adjacent valleys and plateaus of inner Coast Ranges, which generally receive less than 15 cm of precipitation annually, nearly all in November—April. Colonies previously occurred at elevations of 90-885 m, but most extant colonies occur at elevations of 200-760 m. Prior to arrival of Spanish missionaries in the mid-1700s and agricultural development of the San Joaquin Valley in the 1960s and 1970s, habitat was dominated by San Joaquin saltbush ( Atriplex polycarpa, Amaranthaceae ) and perennial grasses; the area is now dominated by weedy annual plants. Long-term occupancy of burrow systems results in low mounds that support lusher, greener vegetation than in surrounding areas, composed of plants with larger seeds that are favored by the Giant Kangaroo Rat. Any shrubs sprouting near a mound are gnawed away and cleared. Following harvest of seed heads and clearing of plant debris by the mound inhabitant, the immediate area is barren relative to surrounding areas. Burrow systems have 1-5 openings, some with visible plugs, and range in depth from an average of 26 cm to a maximum of 46 cm. Seeds are stored in as many as 24 large caches in burrows but not in small pits in walls of tunnels (as in some other kangaroo rats). Few small nocturnal mammals share habitats favored by the Giant Kangaroo Rat. The diurnal Nelson’s Antelope Squirrel (Ammospermophilus nelsoni ) apparently uses entrances of unplugged burrows of the Giant Kangaroo Rat for temporary shelter from heat or predators. During the day, the Giant Kangaroo Rat will emerge from its burrow to aggressively chase away ground squirrels and birds attempting to steal surface seed caches. In suboptimal habitat to which the Giant Kangaroo Rat has been forced by agriculture, it coexists with Nelson’s Antelope Squirrel, the San Joaquin Kangaroo Rat, Heermann’s Kangaroo Rat, the San Joaquin Pocket Mouse ( Perognathus inornatus ), the California Ground Squirrel (Otospermophilus beecheyi), and the Southern Grasshopper Mouse (Onychomys torridus). Predators include common barn owls (7yto alba), great horned owls (Bubo virgimianus), Coyotes (Canis latrans), Kit Fox (Vulpes macrotis), American Badgers (Taxidea taxus), and a variety of snakes.
Food and Feeding. Diet of the Giant Kangaroo Rate contains seeds of forbs, grasses, and shrubs, including saltbush ( Atriplex , Amaranthaceae ) and plantain ( Plantago , Plantaginaceae ), and introduced filaree ( Erodium , Geraniaceae ) and peppergrass ( Lepidium , Brassicaceae ). The Giant Kangaroo Rat also eats green vegetation and insects when available. In some populations, Giant Kangaroo Rats make large stacks of separated seed heads on the surface near their burrows; one stack measured 1-2 m x 1-8 m and was 10 cm deep. Stacked seed heads cure in the sun for 4-6 weeks before being moved to burrow larders, each of which contains up to 91 of seeds.
Breeding. The Giant Kangaroo Rat is promiscuous or polygynous; males and females are asocial and aggressively territorial, and males have greater home ranges and mobility, particularly during breeding season. Body weight is only slightly higher for males or about equal between sexes. Number and timing oflitters are tied to environmental conditions; there may be no reproduction in years of food stress. When food is readily available but density is high, adult females may have only a single litter of 1-4 young, and young-of-the-year do not breed. During years of prolonged wet seasons with high seed production, but when densities are low, adult females may have 2-3 litters, and young-of-the-year females may breed at 12-13 weeks old. Populations of Giant Kangaroo Rats often comprise mostly adults; although during peak density, many individuals arejuveniles. Timing of reproduction appears to be cued,at least in part, by substances ingested along with new plant growth, so that litters arrive during highest seed abundance. Breeding season begins in December or January (during cool, wet winter). Gestation is ¢.32 days, and young are altricial.
Activity patterns. Giant Kangaroo Rats are most active outside of the burrow at night, but some individuals emerge from burrows in twilight around sunset and, less frequently, during the day, usually to aggressively defend surface seed caches near burrows. The Giant Kangaroo Rat is active year-round. Except during harvest time at the end of the growing season, nocturnal foraging is limited to only c.15 minutes during a 1-8-h period after sunset. Most foraging is done close to the burrow system. High-speed travel is estimated to be greater than 3 m/s.
Movements, Home range and Social organization. The Giant Kangaroo Rat is solitary, and both sexes defend non-overlapping home ranges. It appears to be highly territorial and more aggressive than sympatric species of kangaroo rats and is aggressive toward other species of rodents and, in the laboratory, toward a human observer. A captive Giant Kangaroo Rat hopped toward an observer, extending its body high in the typical aggressive or dominance stance and moved its head from side to side; it quickly returned to this position when repeatedly pushed away. Female home ranges remain constant throughout the year, while male home ranges expand significantly during the breeding season to overlap with home ranges of neighboring females. Home ranges (0-04 ha) are smaller than those of smaller-sized kangaroo rats (1-6 ha in Merriam’s Kangaroo Rat, D. merriami ) and c.50% of that of the similarly sized Banner-tailed Kangaroo Rat ( D. spectabilis ; 0-07 ha). Estimates of densities prior to agricultural development were 18-69 ind/ha in larger and denser colonies when Giant Kangaroo Rats dominated the community to the exclusion of other rodents, and their burrows were spaced over thousands of hectares. In 1979, densities were 22-25 ind/ha in the largest colonies (c.125 ha). Population declines are related to drought, resulting in cessation of reproduction, but even more rapid declines are due to torrential rainfall sustained over several days, resulting in drowning and hypothermia. Largest remaining populations of Giant Kangaroo Rats are in heavily grazed areas, and one population increased in density after shrubs were destroyed byfire.
Status and Conservation. Classified as Endangered on The IUCN Red List. The Giant Kangaroo Rat currently occupiesless than 2% ofits historical distribution and is found in only six regional populations in 3460 ha, with most populations in 1-5 ha and with densities less than one-half of their historical estimates. Habitat loss and fragmentation have resulted from agricultural and petroleum development.
Bibliography. Alexander & Riddle (2005), Best (1993a), Cooper & Randall (2007), Eisenberg (1963, 1993), Hall (1981), Ingles (1954), Jones (1993), Linzey & NatureServe (Williams & Hammerson) (2008a), Patton & Rogers (1993), Williams (1992, 1999d), Williams & Kilburn (1991, 1992), Williams et al. (1993).
No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.
