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Rationale

This species is listed as Least Concern because of its relatively wide distribution in habitat unlikely to be rapidly transformed, and because its population is not believed to be declining at present. There are no major land-use threats to this species within the assessment region, as it does not occur in the diamond mining areas. Climate change is, however, a major emerging threat to the species. The construction of renewable energy projects earmarked in some of its distributional area may represent another emerging threat. However, more research needs to be undertaken to explicitly define the impacts of these threats. This species is considered fairly rare but could be locally common in some portions of its range, for example, large numbers have been collected on the Namibian escarpment.

Regional population effects: Occasional dispersal of this species across the Orange River between South Africa and Namibia is likely, thus rescue effect is possible.

Distribution

The Pygmy Rock Mouse has the most extensive range of all Petromyscus species, and is distributed from South Africaâs Succulent- and Nama-Karoo biomes, northwards through western Namibia, including parts of the Namib Desert, and into the southwestern regions of Angola (Skinner & Chimimba 2005; Monadjem et al. 2015). Their altitudinal range limits are from 100 m to 2,000 m asl. Within the assessment region, they occur in rocky outcrops across the western Northern and Western Cape provinces. However, informal surveys have not recently recorded this species in koppies south of Springbok (C.S. Bragg unpubl. data) and so further vetting of museum records and field surveys should be undertaken to determine its current extent of occurrence.

Habitat View more ecological information

Population trend

Trend

There are no population estimates available for the Pygmy Rock Mouse. It is generally considered rare but may be relatively abundant in certain locations in parts of its range (Coetzee 2013), such as in its preferred habitat of rocky outcrops. This species typically has a high survival rate, forming stable populations, and exhibiting population demographics based on a low reproductive potential (Withers et al. 1980).

Threats

No major threats have been identified for this species. However, in association with global climate change, the projected vegetation shift in the semi-arid Succulent Karoo may represent a future threat to this species (Rutherford et al. 1999). Increased temperatures, in conjunction with an enhanced frequency and duration of drought, are predicted to have negative effects on resource availability for small herbivorous mammals in the arid regions of southern Africa (Hoffman et al. 2009). The conservative metabolic rates and summer torpor shown by P. collinus suggest tolerance to limited, periodic supplies of food such as that experienced in the summer rainfall season of southern African arid regions. During summer, resources are unpredictable but might be of sufficient quantity and quality for the mouse to have adequate energy reserves to enter torpor. Bragg (2000) showed that it was extremely risky for P. collinus to enter torpor. Thus, any prolonged droughts and concomitant shortages of food resources during summer, such as climate change-exacerbated droughts, are likely to have severe energetic consequences on this species.

The rapidly expanding construction of major solar farms in the Northern Cape may signify an emerging threat to this species as its range partially overlaps areas in the west of South Africa earmarked for projects (van der Westhuizen 2013). However, it is unlikely that these solar farms will impact the speciesâ habitat as their habitat is mostly limited to rocky outcrops and koppies, which is not suitable for the construction of solar farms, but the presence of these developments on the flats and plains might cause disruption of dispersal.

Overgrazing, which could be exacerbated by climate change, impacts on natural grazing capacity of the vegetation, which could lead to habitat loss for the species and in addition, increase predation risk as the vegetation cover decreases. It was observed that the species is not as aggressive as its habitat counterpart, Micaelamys namaquensis, and resource constraints, such as that caused by overgrazing or climate change-exacerbated drought periods, might lead to increased interspecific competition.

Uses and trade

This species does not appear to be utilised or traded in any form.

Conservation

No specific conservation initiatives have been identified for the Pygmy Rock Mouse. The range of this species extends into a number of protected areas, including Anysberg Nature Reserve, the Groot Swartberg Nature Reserve, Richtersveld National Park, Augrabies Falls National Park, and the Karoo National Park. However, field surveys are needed to confirm its presence in these protected areas. This species is likely to benefit from continued research into the potential threat of enhanced aridity associated with climate change, and how this may affect food resources for this species, as well as potential habitat loss in areas earmarked for alternative energy developments.

Recommendations for land managers and practitioners:

Systematic surveys needed to gather information on population size and trends.

Research priorities:

Population size, distribution and trend estimates.
Analysis of potential impacts of alternative energy projects falling within the distributional area.
Analysis of potential impacts of increased resource constraints and increased temperature extremes on energetics of the species under climate change scenarios.

Encouraged citizen actions:

Report sightings on virtual museum platforms (for example, iSpot and MammalMAP), especially outside protected areas. However, due to their morphological similarities, misidentification of this species with other Petromyscus species is common. See taxonomic note for distinguishing characteristics.
Encourage the inclusion of mitigation measures specific to the species in the Environmental Management Plans for new renewable energy developments overlapping with this speciesâ distribution.

References

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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}
}
,@phdthesis{275,
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 school = {University of Pretoria},
 title = {Small mammal responses to environmental gradients in the Groot Swartberg of the Southern Cape},
 year = {1982}
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,@phdthesis{16778,
 author = {Bragg CJ.},
 school = {University of KwaZulu-Natal},
 title = {Thermoregulation and torpor in the pygmy rock mouse, Petromyscus collinus - energy-conservative traits in a desert subject to the unpredictability of El Nino Southern Oscillations. Honours Thesis.},
 year = {2000}
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,@article{16778,
 author = {Brown JS, Kotler BP, Knight MH.},
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,]

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