Red List of South African Species

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Least Concern (LC)

Rationale

Both species are listed as Least Concern as they have a wide distribution within the assessment region, where they likely occur in most protected areas, are abundant in human-transformed areas, including agricultural areas and areas affected by human disturbances, and because there are no significant threats that could cause range-wide decline. Additionally, these species are known as prolific breeders with population numbers likely to recover quickly after a decline. Because of their reproductive characteristics, population eruptions often occur under favourable conditions. Landowners and managers should pursue ecologically-based rodent management strategies and biocontrol instead of rodenticides to regulate population explosions of this species.

Regional population effects: For M. coucha, significant dispersal is unlikely because the bulk of the population occurs within the assessment region. There are two disjunct populations in Angola–Namibia and Zimbabwe– Mozambique. For M. natalensis, dispersal is highly possible through contiguous habitat along north and northeastern borders and because they utilise transformed habitats.

Distribution

These species have a very wide distribution across the savannahs, grasslands and agricultural landscapes of sub- Saharan Africa (Monadjem et al. 2015). Mastomys natalensis has the widest distribution of all African rodents (Colangelo et al. 2013), and are almost ubiquitously distributed across the African continent (van Hooft et al. 2008). Mastomys coucha is restricted to the grasslands and semi-arid savannahs of South Africa, Zimbabwe and Namibia, occurring south of the Zambezi River (Monadjem et al. 2015). It probably occurs in eastern and southern Botswana where there are records of Mastomys (previously assigned to M. natalensis; for example, de Graaff 1981) but that have not been sequenced or karyotyped. Similarly, its status in Mozambique is currently unknown. There are disjunct subpopulations in Angola– Namibia and Zimbabwe–Mozambique (Leirs 2013a). The exact distribution of these latter two populations should still be verified (Skinner & Chimimba 2005).

Within the assessment region, M. coucha generally occurs in the high altitude/moderate rainfall regions in the central and northeastern part of South Africa (Venturi et al. 2004) (Figure 1). It occurs throughout the North West Province (Skinner & Chimimba 2005; Leirs 2013a), where it is the most widespread and common murid (Power 2014), and the Free State (Lynch 1983; Skinner & Chimimba 2005; Leirs 2013a), where it is likely the only Mastomys species (Avenant 1996). It also occurs throughout the Limpopo and Gauteng provinces, throughout most of the Mpumalanga Province, excluding the southern parts, in the northeastern and eastern parts of the Northern Cape Province, in the southeastern and eastern parts of the Western Cape Province and in the western and northwestern parts of the Eastern Cape Province (Skinner & Chimimba 2005; Leirs 2013a). Lynch (1994) found that it is relatively uncommon in Lesotho, although later suggestions by Ambrose (2006) are that it may be more common. It occurs from the low lying regions to altitudes exceeding 2,500 m asl within Lesotho (Avenant 1996; Lynch 1994). According to Leirs (2013a), M. coucha may occur in a very small part of northern Swaziland, the possibility of which is not precluded by Monadjem (1998). Mastomys coucha co-occurs only marginally with M. natalensis in South Africa (Venturi et al. 2004), with a possible zone of overlap along the eastern escarpment. It overlaps more extensively in southern Zimbabwe (Gordon 1978) and northern Namibia (Monadjem et al. 2015). Additional research is still needed to determine the precise zone of parapatry (Venturi et al. 2004).

Within the assessment region, M. natalensis is predominantly found in the wetter, eastern regions (east of the Drakensberg escarpment), or in the low altitude/high rainfall eastern coastal region, extending to northeastern South Africa (Venturi et al. 2004) (Figure 2). This habitat preference appears to apply at small spatial scales too. For example, in Roan Camp, Kruger National Park, M. natalensis dominated in wetter areas, whereas M. coucha was found in relatively more high-altitude, low-rainfall areas (Kneidinger et al. 2014). Mastomys natalensis has been documented in Gauteng Province (Venturi et al. 2004), but as yet, not in the North West Province (Power 2014). A recent landscape genetics study of M. natalensis from the Hluhluwe-iMfolozi Park, KwaZulu-Natal Province, showed that the most significant landscape features shaping gene flow are slope aspect, vegetation cover, topographic complexity and rivers (Russo et al. 2016). Eastern facing slopes and thicket vegetation promote gene flow/movement throughout the landscape, whereas, topographic complexity and rivers act as barriers to gene flow (Russo et al. 2016).

There are likely to be errors in the distribution maps due to the inability of being able to separate the two species on morphological evidence. Even sperm morphology is very similar between M. natalensis and M. coucha (Breed 1995). The use of molecular research to vet and reclassify museum records should be used to more accurately delineate the areas of sympatry of these two species.

Population trend

Trend

Mastomys is often the most abundant genus in an area. For instance, MacFadyen (2007) found that in the Roan Camp, Kruger National Park, Mastomys spp. were the most abundant genus in, around and outside the enclosure, comprising 81% of captures. Mastomys coucha is a common species throughout their distribution range (Leirs 2013a) with expected cyclic fluctuations in population numbers (Avenant 2011). Its numbers generally dominate in human disturbed habitats or in areas exposed to a natural disturbance (Avenant et al. 2008; MacFadyen et al. 2012). On transects set near Kgomo-Kgomo in the North West Province, Power (2014) recorded 1–4 individuals in every trap set. Due to an opportunistic breeding behaviour, population outbreaks are often associated with this species under favourable conditions (Skinner & Chimimba 2005; MacFadyen et al. 2012), which may cause it to become an agricultural pest (Skinner & Chimimba 2005; Monadjem et al. 2011). Similarly, M. natalensis often sharply increases in abundance after some form of disturbance, such as fire (Monadjem et al. 2015). When M. natalensis numbers decrease in a population it may be associated with an increase in general small mammal species diversity (Monadjem & Perrin 2003). Rautenbach et al. (2014) found that M. natalensis was the most frequently captured rodent species at Phinda Private Game Reserve, KwaZulu-Natal Province, where abundance differed significantly amongst vegetation types but not amongst seasons, and it was most common in Acacia karroo and Combretum apiculatum woodlands. Dispersal rates and dispersal distances per generation in M. natalensis have been shown to be relatively high (van Hooft et al. 2008). Given these dispersal dynamics, M. natalensis exhibits a pattern of kin clustering at smaller geographic scales (van Hooft et al. 2008). It has also been recorded that individuals can move over distances larger than 400 m.

Threats

These species are important from a human health purview because they are a reservoir host for a number of organisms that cause human diseases (Keogh & Price 1981; Venturi et al. 2004; Skinner & Chimimba 2005; Leirs 2013a), and because their distributions are closely related to the outbreak of plague in some areas (Isaäcson et al. 1981). They may also be considered an agricultural pest in some areas, especially during population outbreaks (Monadjem et al. 2011). Due to these threats, rodenticides are often used to control these species (Makundi & Massawe 2011). It is, however, envisaged that poisoning will only have a short-term impact on Mastomys population numbers (Makundi & Massawe 2011), with populations likely to recover due to their reproductive characteristics (Skinner & Chimimba 2005). In Limpopo Province, for example, subsistence farmers whom experienced damage to staple crops from Rattus rattus, R. norvegicus and Mastomys spp. reported low success from rodenticides and kill-traps to control the damages (von Maltitz et al. 2003). Perhaps more important are the knock-on effects such poisons may have within the broader ecosystem through bioaccumulation or unintentional poisoning of non-target species, thus incentivising the use of ecologically-based management methods. It also is uncertain how the diseases associated with Mastomys species affect the rodents themselves (Leirs 2013b).

Uses and trade

Both species are used for the pet industry. However, this is not expected to impact the populations.

Conservation

These species are associated with a wide range of habitats, varying from disturbed areas to areas with more pristine habitat (Avenant et al. 2008; MacFadyen et al. 2012), and thus likely occur in most protected areas throughout their distribution range. As such, no specific interventions are necessary at present. However, the use of ecologically-based rodent management (EBRM) should be encouraged over the use of pesticides to limit population explosions (Makundi & Massawe 2011). Overall, EBRM relies on a strong ecological understanding of the target species and the development of species-specific management strategies at the farming level. It may include the reduction of key resources, such as food and nesting sites, at critical times of the year through habitat modification and the selective use of techniques for culling rodents at specific times of the year and in specific habitats (Singleton et al. 2004, 2007). For example, the use of owl nest boxes has been suggested as an important bio-control method in both small mammal ecosystem services (pollinators and seed dispersers) and management (Russo et al. 2016). In a recent study, no difference in M. natalensis population dynamics was observed within monocultures or mosaic agricultural lands, meaning that management in both agricultural systems could focus on the same aspects of the species’ ecology (Sluydts et al. 2009).

Bio-control should also be encouraged as an alternative single control method, although Vibe-Peterson et al. (2006) demonstrated that the introduction of more predators into an area may not have a clear impact on Mastomys population densities due to the influence of compensatory breeding.

Recommendations for land managers and practitioners:

  • Development and implementation of EBRM strategies suitable to Mastomys and applicable to specific areas (Makundi & Massawe 2011). For example, as has been trialled in Limpopo Province (von Maltitz et al. 2003).
  • The use of bio-control, such as owl boxes, to mitigate the threat of Mastomys as an agricultural pest and as a threat to human health.

Research priorities:

  • Accurate distributions of M. natalensis and M. coucha, including areas of sympatry, need to be determined using molecular markers (for example, Kneidinger et al. 2014).
  • Applied ecological studies need to be conducted that can inform and form the basis of EBRM strategies (Makundi & Massawe 2011).
  • The contribution of Mastomys spp. to the distribution and transfer of human diseases is also an important research area.
Encouraged citizen actions:
  • Farmers could contribute to the development and implementation of EBRM strategies.
  • Promotion of bio-control to regulate population explosions by attracting predators to an area. One method is to erect perches and install owl nest boxes in urban and rural green spaces.

Lead agencies, Partners and Funders

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