This species is endemic to the Cape lowlands (below 280 m Asl), north of the city of Cape Town and west of the Cape Fold Mountains, in the Western Cape Province of South Africa. It occurs from the Cape Flats, through the wheat-growing region known as the Swartland, northwards for approximately 200 km to Graafwater, with two relictual populations occurring in the Olifants and Breede River valleys. Its EOO (14,505 km2) appears to have contracted over the last few decades, in tandem with increased urbanization, and it is now extirpated from the urban areas and immediate surroundings of Cape Town. However, this process has slowed in recent years.
Habitat and Ecology
It lives in undulating low-lying areas with poorly drained loamy to clay soils, although it is known from some shallow sandy habitats. The dominant vegetation in which it historically occurred was Renosterveld heathland, which can leach and acidify the surface water. However, its contemporary presence in disturbed agricultural land indicates that acidic water is not a prerequisite for this species. It breeds in shallow natural pools of water (vleis) and depressions in flat low-lying areas. The eggs are laid in numerous small clusters (20–50) attached to submerged vegetation in temporary water, with up to 400 eggs from a single female. It can tolerate some disturbance, and survives in many regularly ploughed wheat fields, possibly due to its burrowing to depths below the reach of conventional ploughs (they aestivate underground during the dry season).
Subpopulations are widely scattered and fragmented; and it generally does not occur at high densities at breeding sites. Most of the populations that were close to regions of heavy urbanization have been lost. Two historical sites, Stellenbosch original old golf course and Rosebank corner of Rondebosch Common, are now extinct, and the subpopulation from inland of Macassar to Faure area is possibly extinct. More surveys need to be conducted in the Macassar area to determine whether the species is still extant.
This species occurs in a habitat that is in high demand for urbanisation and agriculture, and over 90% of its former habitat has been transformed by agriculture or urbanization. These same areas are under pressure from alien invasive plants which threaten to dry the breeding habitats. The long-term viability of populations living in disturbed agricultural fields, which contain high levels of agro-chemicals, is uncertain.
It is known to occur in three protected areas: J.N. Briers-Louw Provincial Nature Reserve (near Paarl), Elandsberg Private Nature Reserve (near Hermon) and the adjoining Voëlvlei Provincial Nature Reserve. No conservation priorities are assigned to this species.
Knowledge of the biology and ecology of the species, together with how these are affected by habitat changes and different land uses, and in particular agrochemicals, are needed to better evaluate its status. This species is due for another systematic distribution survey.
Red List Status
Near Threatened (NT)
Listed as Near Threatened because, although it occurs in about 15 different locations and it is not considered to be severely fragmented, its extent of occurrence (EOO) is 14,505 km2 and the quality of its habitat in the southwestern Cape is declining making the species close to qualifying for Vulnerable under the B criterion.
IUCN SSC Amphibian Specialist Group, South African Frog Re-assessment Group (SA-FRoG) 2017. Cacosternum capense. The IUCN Red List of Threatened Species 2017: e.T3441A77163164. http://dx.doi.org/10.2305/IUCN.UK.2017-2.RLTS.T3441A77163164.en .Downloaded on 22 November 2018