Southern African vlei rat

The Southern African vlei rat (Otomys irroratus) is a species of rodent in the vlei rat genus, Otomys, of the family Muridae in the order Rodentia. This is the type species of the genus.[2] It is native to the grasslands and swamps of southern Africa where it is a common species.

Southern African vlei rat
A southern African vlei rat, grazing beside a reed-fringed dam

Least Concern  (IUCN 3.1)[1]
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Rodentia
Family: Muridae
Genus: Otomys
Species:
O. irroratus
Binomial name
Otomys irroratus
(Brants, 1827)

Description

The Southern African Vlei Rat is a large-sized rat with dense and continuously replaced shaggy fur.[3] The head is large, the ears small, and the tail short. The dorsal parts are generally gray, brown, or black. The ventral parts are some shade of paler or darker grey. All of its digits are clawed, and the hind claws are longer than the fore claws.[3] The head-and-body length is about 160 mm (6.3 in) and the tail about 100 mm (4 in).[4] Both males and females have a similar mean mass of 143.7g.[3]

Distribution and habitat

The range extends from the far South Western Cape of South Africa, around the southern and eastern coast and adjacent interior, to subtropical regions in southern Natal. This part of its range includes Lesotho. Further north, it no longer occurs around the actual coast. Inland however, its range extends north to tropical areas, nearly to the northern boundary of the Transvaal, including parts of Swaziland. An apparently isolated population occurs still further north in tropical eastern Zimbabwe and adjacent Mozambique.[4] Its habitats include temperate low-altitude swamps and grassland, and subtropical and tropical high-altitude grassland, swamps, and plantations.[1] It is a terrestrial species that lives above ground in an open, bowl-shaped nest made of shredded grass near marshy areas with a lot of vegetation.[3]

Ecology

The Southern African Vlei Rat is mainly active at dusk and dawn. Most are diurnal, although some Vlei Rats show nocturnal activity.[5] It shares and creates runways with other coexisting species through the vegetation as it forages on the green vegetation on which it feeds.[3][5]

Diet and Feeding strategies

The Southern African Vlei Rat is a cecal digester and strict herbivore.[5][6] Its diet consists of the stems and leaves of grasses, herbs, shrubs, and grass seeds. However, they are not selective feeders and will eat nearly all green plant species in their habitat.[6] They also gnaw on the bark of pine trees in plantations, damaging the trees. They have adapted some degree of high tolerance for toxic plants.[6] Much of the digestive process takes place in the cecum with the aid of microbes, and the fecal pellets are often re-ingested.[3]

Life History and Reproduction

The Southern African Vlei Rat is mainly promiscuous in mating, although some populations are polygynous.[7] Females in polygyny mating systems can terminate their pregnancy, which may be a counter-strategy to infanticide.[7] Males and females preferably mate within their own population and discriminate between individuals of another population through their odor.[7] Females may give birth up to four times a year, producing 1-4 offspring, with a gestation period of five to six weeks.[8][7] In the eastern cape, they breed year long, whereas in Transvaal they mostly breed in August when food is most abundant.[3]

Their young are precocial at birth and are relatively large compared to other similar sized rodents.[3][9] They are covered with fur and their incisors erupted, which allows them to cling to their mother's nipples as she travels for their first two weeks after birth.[9] By day 2, their eyes are open, they can hear acutely, and can eat solid food.[9] They will eat both their own and others feces to obtain enough nutrients.[3] By day 5, they have coordinated body movement.[9] Approximately by day 13, weaning is complete.[9] They grow rapidly, reaching 71% of adult mass by the time they are 10 weeks old.[3] Females are sexually mature at 9–10 weeks old, but males mature later.[3] They have a lifespan of up to 2 years.[3]

Behaviors

The Southern African Vlei Rat is a k-strategist, quadrupedal, and can rapidly run along runways.[3] They are able to swim if needed.[9] They often use their forepaws to eat and discard food in piles by runways, as well as grooming and washing their face.[3]

This rat is solitary and aggressive towards other members of the species. Adult males have a home range of about 1,730 m2 (18,600 sq ft) and maintain a small home territory around the nest site. It communicates through olfactory signals by anal-gland marking of their territory.[3] There is a hierarchy in aggression: males and females who have mated, then males and females who have not mated, respectively.[3] When same-ranking individuals encounter each other, they start fighting and chasing each other, ending in serious wounds until one animals flees or shows submissive behavior.[3] Submissive behaviors include the rats in an upright posture exposing their stomach and chattering.[3]

Since they are non-burrowing, they keep warm through nonshivering thermogenesis and have low thermal conductance.[5] They have low metabolic rates which may be why they can feed on low quality food.[5]

Their predators are mainly barn owls and grass owls, but also include pythons, mole snakes, wildcats, mongooses, and cape clawless otters.[3]

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References
  1. Taylor, P.J.; Maree, S.; Monadjem, A. (2008). "Otomys irroratus". IUCN Red List of Threatened Species. 2008: e.T15654A4961508. doi:10.2305/IUCN.UK.2008.RLTS.T15654A4961508.en.
  2. Genus Otomys, Mammal Species of the World, 3rd ed.
  3. Bronner, G. (1988). "Mammalian Species Otomys irroratus" (PDF). The American Society of Mammalogists. Retrieved 2016-11-16.
  4. Mills, Gus & Hes, Lex (1997). The Complete Book of Southern African Mammals. Cape Town: Struik Publishers. ISBN 978-0947430559.
  5. Haim, A.; Fairall, N. (1987). "Bioenergetics of an Herbivorous Rodent Otomys irroratus". Physiological Zoology. 60 (3): 305–309. doi:10.1086/physzool.60.3.30162283. JSTOR 30162283.
  6. Curtis, B. A.; Perrin, M. R. (1979-01-01). "Food preferences of the vlei rat (Otomys Irroratus) and the four-striped mouse (Rhabdomys pumilio)". South African Journal of Zoology. 14 (4): 224–229. doi:10.1080/02541858.1979.11447675. ISSN 0254-1858.
  7. Pillay, Neville (May 27, 2008). "Mating strategy predicts the occurrence of the Bruce effect in the vlei rat Otomys irroratus". Behaviour. 146 (1): 139–151. doi:10.1163/156853908X390968. JSTOR 40296090.
  8. Jonathan Kingdon; David Happold; Thomas Butynski; Michael Hoffmann; Meredith Happold; Jan Kalina (2013). Mammals of Africa. A&C Black. pp. 583–585. ISBN 978-1-4081-8996-2.
  9. Davis, R. M. (1972-01-01). "Behaviour of the Vlei Rat, Otomys Irroratus (Brants, 1827)". Zoologica Africana. 7 (1): 119–140. doi:10.1080/00445096.1972.11447434. ISSN 0044-5096.
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