Rationale

This near-endemic grassland species is becoming increasingly threatened by grassland contraction and wetland loss, with niche modelling showing that it will undergo a 47–61% reduction in suitable habitat between 1975 and 2050 from climate change (6–8% per decade). Already one major subpopulation, located in Soutpansberg Mountains, Limpopo Province, has been completely replaced at a key contact zone by the savannah species O. angoniensis over the past 90 years due to thicket habitats replacing grasslands. Ongoing grassland and wetland loss, primarily from agricultural and settlement expansion, may synergise with climate change to accelerate area of occupancy (AOO) reduction. Since this species is localised to montane grassland patches, it is more sensitive to habitat loss as it probably cannot utilise modified habitats. Nationally, there has been 32.8% decline in natural wetlands from 1990–2013/14, which is a combination of both genuine wetland loss through anthropogenic activities and the generally drier conditions currently that in 1990. Specifically, most distribution records (36%) are located in the Mesic Highveld Grassland Bioregion where there has been a 19% loss of moist grasslands since 1990 (A. Skowno unpubl. data). In KwaZulu-Natal specifically, there was a loss of 7.6% of the natural habitat between 2005 and 2011 (1.3% per annum), which, when extrapolated, equates to a 13% loss of habitat over a ten year time period. Thus, multiple lines of evidence corroborate past, continuing and future habitat loss. Under a precautionary purview, we list as Near Threatened A4c as a 20–30% decline in area of occupancy (AOO)—with a similar decline in population size—over ten years is possible due to the synergising effects of climate change and land use change (Taylor et al. 2016). We encourage more long-term surveys, such as that in the Soutpansberg, to identify other subpopulations that have been lost to landscape and climate changes.

Regional population effects: Rescue effect is not possible due to the disjunct distribution of populations within the assessment region and Zimbabwe.

Distribution

The species is widely distributed throughout the Highveld grasslands and Drakensberg Escarpment of South Africa, Lesotho and Swaziland, with isolated populations in the Soutpansberg Mountains of northern Limpopo and the Eastern Highlands of Zimbabwe (Monadjem et al. 2015). While indiscernible from O. irroratus, Engelbrecht et al. (2011) used mitochondrial data to delineate between the two cryptic species with the only known contact zone between the two species being Alice in the Eastern Cape. As this species has been split from O. irroratus, museum records will need vetting through molecular research to delimit distribution more accurately.

Worryingly, there has been a documented range contraction in the Soutpansberg Mountains of Limpopo Province due to habitat shifts from grassland to thicket: Comparison of occurrence data at a zone of sympatry between 1923 and 2013 revealed that while O. auratus was previously dominant, only O. angoniensis is currently found at the site (Taylor et al. 2016). This could indicate a savannah species displacing a grassland species as grasslands contract and are replaced by thicket woodlands due to climate change. Data from the wider Soutpansberg area support this trend: recent surveys in suitable grasslands habitats at > 1,300 m asl (typically O. auratus habitats) have revealed only O. angoniensis while O. auratus was only sampled at one locality in the eastern Soutpansberg (Taylor et al. 2016).

Habitat View more ecological information

Population trend

Trend

Threats

There are three main threats that may cause significant population decline in the near future:

1. Grassland and wetland habitat loss from agricultural expansion, human settlement sprawl and mining. In Mpumalanga, for example, only 51% of the grasslands are still natural and not previously ploughed and 40% of the grassland vegetation types are listed as threatened (Lötter 2015). Water abstraction or filling in of wetlands from human settlement and industrial expansion also leads to habitat loss. Similarly, suppression of natural ecosystem processes, such as fire, can also lead to habitat degradation through bush encroachment or loss of plant diversity through alien invasive species, and is suspected to be increasing with human settlement expansion. Overall, 45% of our remaining wetland area exists in a heavily modified condition, due primarily to onsite modification from crop cultivation, coal mining, urban development, dam construction, and overgrazing (and thus erosion) and off-site modifications from disruptions to flow regime and deterioration of water quality (Driver et al. 2012).
2. Overgrazing the vegetation around wetlands reduces ground cover and thus leads to decreased small mammal diversity and abundance (Bowland and Perrin 1989, 1993).The expansion of wildlife ranching will have to be monitored in this regard, as game overstocking may also affect wetland condition.
3. Climate change is projected to reduce area of occupancy significantly by reducing temperate grasslands and wetland habitats. Climate modelling shows that a 47–61% loss in AOO is expected between 1975 and 2050 depending on the dispersal ability of the species (Taylor et al. 2016). While the model predicts a range shift along the Indian Ocean Coastal Belt, where it occurs narrowly at present, this area is highly developed (Driver et al. 2012) and thus may not provide suitable alternative habitat. Coastal habitat transformation in KwaZulu-Natal is due primarily to sugarcane monocultures, forestry plantations and residential developments. Thus, the future distribution of the species may be severely fragmented, resulting in local extinctions (Taylor et al. 2016).

Land-use change and climate change may synergise to cause non-linear and accelerating population decline. For example, trapping data suggest that O. angoniensis has already replaced O. auratus throughout most of the Soutpansberg Mountain range except in the Entabeni area (Taylor et al. 2016). More research is needed to validate these trends in other regions.

The habitat of this species is declining, wetlands are the most threatened ecosystem in South Africa (Driver et al. 2012). The South African National Land-Cover change report found a 32.8% decline in natural wetlands nationally from 1990 – 2013/14, which is a combination of both genuine wetland loss through anthropogenic activities and the generally drier conditions currently that in 1990 (GeoTerraImage 2015). Habitat loss due to land transformation in the surrounding matrix further isolates wetlands from one another and exacerbates the degradation of individual wetlands. For example, sugarcane and forestry plantations are often planted right up to wetlands edges, not respecting the appropriate buffer. In KwaZulu-Natal alone, there an average loss of natural habitat of 1.2% per annum between in 1994 and 2011 from agriculture, plantations, built environments and settlements, mines and dams (Jewitt et al. 2015). Although no specific rates of habitat loss are available, 61% of Mpumalanga’s land surface between 2000 and 2014 have come under pressure from prospecting applications (Lötter 2015). Compounding habitat loss from land-use change is climate change. Projected range shifts under the A2 emission scenario of the Intergovernmental Panel on Climate Change showed increases (O. angoniensis) and decreases (O. auratus) that closely mirrored those expected for the savannah and grassland biomes respectively (Taylor et al. 2016).

Uses and trade

Conservation

They occur in many protected areas, such as Kruger National Park in Limpop/Mpumlanga, Pilansberg National Park in the North West (Power 2014), Rietvlei Nature Reserve in Gauteng (Taylor et al. 2016), Tussen-die-Riviere and Seekoeivlei Nature Reserves in the Free State (Ferreira and Avenant 2003), and Asante Sana Nature Reserve and Mountain Zebra National Park in the Eastern Cape (Kok et al. 2012). Mitigating habitat loss outside of protected areas is urgently. The following interventions should be implemented:

1. Using previously cultivated areas for development instead of remaining natural areas: In Mpumalanga, for example, old lands or previously ploughed areas now left fallow make up 8.9% of the grassland biome (Lötter 2015), and these areas should be prioritised for further development. Similarly, in KwaZulu-Natal, abandoned agricultural fields on marginal lands offer an opportunity for further development instead of transforming virgin land and at least 4% of the landscape is available for this (Jewitt et al. 2015).
2. Wetland conservation and restoration: land managers should maintain a vegetation buffer to reduce impacts of land-use practices (Driver et al. 2012). For example, the frequency of O. auratus and O. angoniensis has not changed between 1972 and 2013 as the wetland vlei areas have not changed significantly in structure (Taylor et al. 2016). Restoration will also create corridors between suitable habitat patches to allow for dispersal in responses to climate change.
3. Holistic management of ranchlands: including de-stocking, rotational grazing and buffering wetland vegetation, are encouraged.

• Land managers should decrease stocking rates to conserve vegetation around wetlands.
• Long-term, systematic monitoring is needed to establish subpopulation trends and threat levels.
• Prioritise old fields for development in systematic conservation planning.

• Long-term, systematic monitoring is needed to establish subpopulation trends and threat levels.
• Fine-scale studies on habitat loss and inferred impact on the species across the range of the species.
• Effects of overgrazing on the density and viability of this species.
• Effects of habitat connectivity on dispersal rates.
• Further vetting of museum records to delimit distribution more accurately.

Report Vlei Rat sightings on MammalMAP: The feeding signs of this species are easy to detect by short chopped lengths of grass and green moist faecal pellets (Skinner and Chimimba 2005).