Rationale
(Changed due to Same category and criteria)
This species is listed as Least Concern because it is widespread within the fynbos biomes of the Western Cape and Eastern Cape, is present is several protected areas, and has a degree of tolerance for modified habitats. However, the population is expected to show slow declines in the future from climate change, with niche modelling showing that is will undergo a 12-24% reduction in area of occupancy by 2050 from climate change. Similarly, continued habitat loss of wetlands and associated vegetation will lead to a decline in the future. In the Western Cape, already 31% of all wetlands (plus a 32 m buffer) and riparian habitats have been lost to agricultural expansion. Thus, while we infer that the population is not threatened currently, it should be monitored as it may qualify for a threatened category in the future. Key interventions for this species include the conservation and restoration of wetlands and holistic management strategies to curb habitat degradation from overgrazing.
Distribution
Otomys species are generally associated with mesic grasslands and moorlands within alpine, montane and sub-montane regions of Southern, Central, East and West Africa (Monadjem et al. 2015). This species is endemic to South Africa and associated with Fynbos and Albany Thicket biomes in the Western Cape and Eastern Cape provinces of South Africa respectively (Monadjem et al. 2015), particularly wetlands. It marginally occurs in the Savannah and Nama Karoo biomes; for example, in the Fish River Valley (Engelbrecht et al. 2011). The contact zone with O. auratus occurs around Alice in the Eastern Cape (Engelbrecht et al. 2011). Its estimated area of occupancy (AOO) is 10,288 km² based on remaining natural fynbos and thicket habitats in 2013 (GeoTerraImage 2015). However, its AOO could be as low as 305 km² if considering only the area around wetlands (32 m buffer strip). Further vetting of museum specimens is needed to more accurately delimit distribution.
Population trend
Trend
It is a common species, especially in wetlands. For example, it is more common that O. laminatus in similar habitats. However, it tends to be trap-shy (Haim and Fairall 1987, Avenant 2011). For example, from 1,170 trap nights inside and outside the Great Fish River Nature Reserve, Eastern Cape, only four individuals were sampled (Lagesse and Thondhlana 2016). The population is projected to be declining due to decreasing habitat suitability under climate change (Taylor et al. 2016).
Threats
Although this species is not under significant threat at present, there are three main threats that may cause population decline in the future:
1) Wetland habitat loss and degradation from agricultural expansion, human settlement sprawl and agroforestry. 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). In the Western Cape, specifically, 31% of all wetlands (plus a 32m buffer) and riparian areas have been transformed/lost to agricultural land use (Pence 2012). 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 on-site 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) Climate change is projected to reduce AOO by 12-24% by 2050 through decreasing habitat suitability (Taylor et al. 2016). Most of these habitat declines will occur in the Western Cape because, while the fynbos component of the Eastern Cape will be heavily reduced, the species is able to persist in thicket habitats and thus its future distribution in this region will be relatively unaltered (Taylor et al. 2016).
3) 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. Overgrazing and climate change may synergise to cause non-linear and accelerating population decline. More research is needed to validate these hypotheses.
Conservation
This species occurs within several protected areas within the Western and Eastern Cape, although these are yet to be comprehensively documented. Although no specific interventions are necessary at present, the conservation and restoration of wetlands would greatly benefit this species. The following interventions are thus encouraged:
- Using previously cultivated areas for development instead of remaining natural areas.
- Land managers should maintain a vegetation buffer around wetlands to reduce impacts of land-use practices (Driver et al. 2012).
- 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.
