Red List of South African Species

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Least Concern (LC)
Assessors: Peter Taylor Rod Baxter Matthew Child
Contributors: Nico Avenant Margaret Avery Duncan MacFadyen Ara Monadjem Guy Palmer Beryl Wilson
Reviewers: Peter Taylor Rod Baxter Matthew Child

Rationale

Listed as Least Concern in view of its wide distribution within the assessment region, observed range expansions in Limpopo and North West provinces, ability to survive in modified habits, and because there are no threats likely to cause range-wide population decline. The savannah habitat is well-protected and thus this species is not expected to be significantly impacted by habitat loss. Conversely, climate change is projected to expand its area of occupancy by 30–123% between 1975 and 2050, mirroring the expansion of savannah habitat in the region. For example, recent evidence suggests it is usurping the grassland-adapted species O. auratus in the Soutpansberg Mountains, due to shifts in vegetation structure.

Regional population effects: It is a widespread species existing in largely intact habitats. Thus, the regional population is presumably connected.

Distribution

This is the most widespread of all Otomys species, occurring in mesic savannahs in southern and central Africa, as well as the foothills of major mountain ranges in Malawi, the western slopes of the Albertine Rift, Uganda, Kenya and northern Tanzania (Monadjem et al. 2015). Similarly, in the Drakensberg Range, it occurs on the lower slopes in savannah habitats. It occurs in the northern and northeastern provinces of South Africa, including Swaziland. Records from the Eastern Cape (De Graaff 1981; Bronner & Meester 1988) are not corroborated by museum specimens (Taylor 2013).

It has mostly an allopatric distribution with O. auratus overlapping only at the interface of the Grassland and Savannah biomes, around 1,000 m asl in KwaZulu-Natal and Swaziland and 1,300 m asl in Limpopo (Monadjem 1998; Taylor 1998; Nengovhela 2014). However, a recent range expansion has been documented in the Soutpansberg Mountains, Limpopo where it has expanded from the foothills to the peaks and has displaced O. auratus (savannah species replacing grassland species) due to vegetation transition from grassland to thicket (Taylor et al. 2016). Similarly, range expansions have been documented in North West Province where Power (2014) confirmed new local records at both S. A. Lombard and Bloemhof Nature Reserves, where previous intensive surveys in the areas did not reveal this species (Newbery 1995). Range expansion is projected to continue due to expansion of savannah habitats in response to climate change. Taylor et al. (2016) used MaxEnt models to determine an increase in area of occupancy between 30% (with limited dispersal) to 123% (with unrestricted dispersal) between 1975 and 2050.

Population trend

Trend

It is common to abundant in suitable habitats (Taylor 2013) and, given its currently expanding range, we suspect there are over 10,000 mature individuals within the assessment region and the population is likely to be increasing. More field surveys and long-term monitoring should be undertaken to confirm this. In Kenya, a population was recorded at a density of 30 animals / ha (Taylor 2013).

Threats

There are no major threats to this species. However, it can be locally threatened by habitat degradation due to overgrazing by domestic livestock and/or wildlife ranching. Further studies are needed to determine the resilience of this species to land-cover change. Unlike other Otomys species, climate change is projected to increase its area of occupancy along with savannah expansion and extend widely into grassland areas currently occupied by O. auratus (Taylor et al. 2016). For example, habitat change from open grassy plains to dense thicket has seen O. angoniensis completely replace O. auratus at a key zone of sympatry in the Soutpansberg Mountains, Limpopo between 1923 and 2015 (Taylor et al. 2016).

Uses and trade

This species is not known to be traded or utilised in any form.

Conservation

This species is present in many protected areas, including Kruger National Park. Although no specific interventions are necessary at present, the following interventions are encouraged that will benefit all small mammals:
  1. Using previously cultivated areas for development instead of remaining natural areas.
  2. Land managers should maintain a vegetation buffer around wetlands to reduce impacts of land-use practices (Driver et al. 2012).
  3. Holistic management of ranchlands: including de-stocking, rotational grazing and buffering wetland vegetation, are encouraged.
Recommendations for land managers and practitioners:
  • Land managers should decrease stocking rates to maintain vegetation around wetlands.
  • Prioritise old fields for development in systematic conservation planning.
Research priorities:
  • Effects of savannah habitat loss and degradation.
  • Effects of range expansion on other Otomys species.
Encouraged citizen actions:
  • Report vlei rat sightings on virtual museum platforms (for example, iSpot and MammalMAP): The feeding signs of this species are easy to detect by short chopped lengths of grass and green moist faecal pellets (Skinner & Chimimba 2005; Taylor 2013).

References 

[@book{275,
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 author = {Skinner, J.D. and Chimimba, C.T.},
 publisher = {Cambridge University Press, United Kingdom},
 title = {The Mammals of the Southern African Subregion},
 year = {2005}
}
,@techreport{5228,
 author = {Power, R.J.},
 institution = {Department of Economic Development, Environment, Conservation & Tourism, North West Provincial Government, Mahikeng},
 title = {The distribution and status of mammals in the North West Province},
 year = {2014}
}
,@techreport{5228,
 address = {Pretoria, South Africa},
 author = {Driver, A., Sink, K.J., Nel, J.N., Holness, S., Van Niekerk, L., Daniels, F., Jonas, Z., Majiedt, P.A., Harris, L. and Maze, K.},
 institution = {South African National Biodiversity Institute and Department of Environmental Affairs},
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 year = {2012}
}
,@article{5228,
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,@book{14262,
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}
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,@phdthesis{15652,
 author = {Davis, R.M.},
 school = {University of Pretoria},
 title = {The ecology and life history of the vlei rat, <i>Otomys irroratus</i> (Brants, 1827), on the van Riebeeck Nature Reserve, Pretoria. Ph.D Thesis.},
 year = {1973}
}
,@article{15652,
 author = {Nengovhela, A., Baxter, R.M. and Taylor, P.J.},
 journal = {Zoology},
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 title = {Temporal changes in cranial size in South African vlei rats (<i>Otomys</i>): evidence for the “third universal response to warming.”},
 volume = {50},
 year = {2016}
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,@article{15652,
 author = {Bronner GN, Meester JAJ.},
 journal = {Mammalian Species},
 pages = {1–6},
 title = {<i>Otomys angoniensis</i>},
 volume = {306},
 year = {1988}
}
,@article{15652,
 author = {Malan G.},
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 title = {Otomyine rodent refuge habitat: does it represent habitat quality for pale chanting-goshawk families?},
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}
,@phdthesis{15652,
 author = {Nengovhela A.},
 school = {University of Venda},
 title = {Investigating past, present and future distributions of cryptic species of vlei rats (Otomys auratus, O. irroratus s.s. and O. angoniensis) in South Africa, with a focus on Limpopo Province. M.Sc. Thesis},
 year = {2014}
}
,@techreport{15652,
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 author = {Newbery CH.},
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}
,]
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