Rationale
This species has a wide distribution across the assessment region and occurs in many protected areas, but is restricted to wetlands and waterlogged areas, thus leading to a patchy area of occupancy (AOO). We use wetlands as a proxy for suitable habitat and calculate the amount of natural habitat remaining within buffer strips around wetlands as the inferred area of occupancy (AOO), which yields 2,395â2,794 km2 (using a 32 m buffer strip). We suspect that these habitat patches are severely fragmented, as shrews have a poor dispersal ability and continuing rates of urban and rural expansion may have increased overgrazing and water abstraction, which may reduce the suitability of patches and the corridors between them. Similarly, we infer a continuing population decline based on high rates of habitat loss in all provinces, especially KwaZulu-Natal and North West (1.2% per annum from 1994â2011 and 0.5% per annum from 2006â2010 respectively). Additionally, climate change may cause a range contraction in the future as arid areas expand towards the east, representing an emerging threat. Thus, we list this species, under a precautionary purview, as Near Threatened B2ab(ii,iii,iv) because, although the AOO estimate > 2,000 km2, not all suitable habitat will be occupied.
Further field studies and research should assess the speciesâ distribution more accurately and examine whether artificial wetlands can compensate for the loss of natural areas. Regardless, it is reliant on natural vegetation and wet, muddy substrates. Thus, managers and landowners should restore and maintain buffers of natural vegetation around wetlands and keep stocking densities at ecological carrying capacity to ensure the persistence of this species.
Regional population effects: No significant rescue effects are possible as habitats are presumably fragmented between regions and the species is too small to disperse over long distances.
Distribution
This widely but patchily distributed species occurs in south-eastern Democratic Republic of Congo, Zambia, Angola, northeast Namibia, northwest Botswana (the Okavango Delta), Zimbabwe, southern Mozambique, Swaziland and north-eastern South Africa. There is a disjunction between the subspecies occurring within the assessment region (C. m. mariquensis) and the more northern subspecies (C. m. shortridgei). If the latter is revealed to be a full species through molecular research, C. m. mariquensis will become endemic to the assessment region.
Within the assessment region, it occurs in wetlands and waterlogged grasslands predominantly (both post-1999 and pre-2000 records) in KwaZulu-Natal, Mpumalanga, Limpopo, Gauteng and eastern North West provinces, while marginally occurring in the northern reaches of Free State Province (Fuller & Perrin 2001; Wandrag et al. 2002) at Seekoeivlei and Tussen-die-Riviere nature reserves, with a single isolated record from the University of Free State, Bloemfontein (N. Avenant unpubl. data). Although no data for Kruger National Park are available, it presumably occurs there. In Swaziland, it occurs in the highveld and middleveld regions (Monadjem 1998). In the North West Province, new records were obtained from Mafikeng and Bloemhof (Power 2014), which extends the range westerly and confirms anecdotal suggestions of its presence in the area (Rautenbach 1982). Its distribution will track waterlogged environments and will thus most likely shift east, reflecting the east-west aridity gradient across the country, as climate change is predicted to make the western regions drier (Erasmus et al. 2002).
Based on the records available, we infer the extent of occurrence (EOO) to be 397,992 km2. However, we suspect the species to be patchily distributed and fragmented within this wide area due to its reliance on moist habitats. Within the EOO, we calculated the amount of natural habitat remaining within buffer strips around wetlands as the inferred area of occupancy (AOO), which yields a range of 50,377â63,440 km2 (using 500 m buffer strip) to 2,395â2,794 km2 (using 32 m buffer strip). Although this is still a huge area, we suspect the lower estimates are more plausible as not all suitable patches will be occupied due to the natural patchiness of suitable habitats, its poor dispersal capacity and ongoing habitat degradation of patches and corridors between them. Given that this AOO estimate is uncertain, and applying a precautionary approach, it falls within the thresholds for Near Threatened (IUCN Standards and Petitions Subcommittee 2014).
Population trend
Trend
This can be a common and locally abundant species in suitable habitat. For example, it occurs in higher numbers than Rhabdomys pumilio at Lajuma in the Soutpansberg Mountains, Limpopo Province (R. Baxter and P. Taylor unpubl. data) and, at Seekoeivlei Nature Reserve in Free State Province, it was the most abundant small mammal sampled, constituting 41% of samples collected while Rhabdomys pumilio and Myosorex varius accounted for 28% and 22% respectively (Wandrag et al. 2002). However, due its patchy distribution, the total population size of the species is unlikely to compare to that of more widespread and generalist species. For example, Power (2014) reports that it is only locally common in wetlands in the mesic parts of North West Province, and it appears to be localised or patchily distributed in KwaZulu-Natal (J.Harvey unpubl. data).
Threats
The main threat to shrews is the loss or degradation of moist, productive areas such as wetlands and rank grasslands within suitable habitat. The two main drivers behind this are abstraction of surface water and draining of wetlands through industrial, agricultural, afforestation and residential expansion, and overgrazing of moist grasslands, which leads to the loss of ground cover (reduces habitat structural complexity) and decreases small mammal diversity and abundance (Bowland & Perrin 1989, 1993). Overgrazing is particularly threatening for this species, as it relies on medium to tall grass cover. Suppression of natural ecosystem processes, such as fire, can also lead to habitat degradation through bush encroachment or loss of plant diversity through alien invasives, and is increasing with human settlement expansion. There are also clear overlaps and synergistic effects between these threats. We infer a continuing population decline based on loss of natural habitat.
Wetlands are the countryâs most threatened ecosystem, with 65% of wetland ecosystem types threatened (48% of all wetland types Critically Endangered, 12% Endangered and 5% Vulnerable) because they are highly productive and hence become transformed for agriculture (Driver et al. 2012). 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). Although this species may occur in artificial wetlands, it is reliant on natural vegetation and wet, muddy substrates.
Uses and trade
There is no known subsistence or commercial use of this species.
Conservation
This species occurs in several protected areas. Although the loss of wetlands may be in part compensated by its ability to exploit man-made waterbodies (for example, farm dams), natural vegetation is key to its survival. The main intervention for this species is thus the protection and restoration of rank vegetation around wetlands. Biodiversity stewardship schemes should be promoted if landowners possess wetlands close to core protected areas or remaining habitat patches, and the effects on small mammal subpopulations should be monitored. Protecting such habitats may create dispersal corridors between patches that will enable adaptation to climate change. At the local scale, landowners and managers should be educated, encouraged and incentivised to conserve the habitats on which shrews and small mammals depend. Retaining ground cover is the most important management tool to increase small mammal diversity and abundance. This can be achieved through lowering grazing pressure (Bowland & Perrin 1989), or by maintaining buffer strips of natural vegetation around wetlands (Driver et al. 2012). Small mammal diversity and abundance is also higher in more complex or heterogeneous landscapes, where periodic burning is an important tool to achieve this (Bowland & Perrin 1993). Removing alien vegetation from watersheds, watercourses and wetlands is also an important intervention to improve flow and water quality, and thus habitat quality, for shrews. Education and awareness campaigns should be employed to teach landowners and local communities about the importance of conserving wetlands and moist grasslands.
Recommendations for land managers and practitioners:
- Landowners and communities should be incentivised to stock livestock or wildlife at ecological carrying capacity and to maintain buffers of natural vegetation around wetlands and riverine habitats.
- Enforce regulations on developments that potentially impact on the habitat integrity of grasslands and wetlands.
Research priorities:
- Additional field surveys are needed to clarify and confirm the distribution of this species, particularly around artificial waterbodies, agricultural landscapes and urban / rural gardens.
- The effects of climate change on its distribution and abundance should be specifically modelled.
Encouraged citizen actions:
- Citizens are requested to submit any shrews killed by cats or drowned in pools to a museum or a provincial conservation authority for identification, thereby enhancing our knowledge of shrew distribution (carcasses can be placed in a ziplock bag and frozen with the locality recorded).
- Practise indigenous gardening to sustain small mammals.
