Cacosternum karooicum Boycott, De Villiers and Scott, 2002
Karoo Caco, Karoo Dainty Frog, Stofpadda (A), Karoo Blikslanertjie (A) Photos 58–60
Currently accepted name: Cacosternum karooicum
Red listing status: Data Deficient
Photo by Hardaker T. & , 2012. URL: FrogMAP: 448
RED LIST SPECIES
Status: Data Deficient (DD)
The following description is based on Boycott et al. (2002). C. karooicum is dorsoventrally flattened. The maximum snout–vent length recorded for this species is 26.3 mm in males and 30.8 mm in females. The dorsum is usually covered in small glandular warts. The dorsal colouration is uniform olive-brown to khaki-brown, sometimes tinged with red or orange, and the tip of the adpressed fifth toe reaches or extends beyond the second subarticular tubercle of the fourth toe. In breeding males, the gular region is a mustard yellow, whereas in females it is white with small dark patches.
The advertisement call of C. karooicum is a prolonged, coarse rattle, 0.5–1.48 s in duration, containing 22–59 pulses per call. The pulse rate is 42–44 pulses/s, and the emphasized frequency is 2–2.5 kHz (Boycott et al. 2002; H. Braack and A. Channing unpubl. data). The territorial call is a short, loud croak, 0.56–0.76 s in duration, emitted at an emphasized frequency of 2.5–3.2 kHz. This call is produced in separate groups of 6–8 notes and is not interspersed between the advertisement calls as is the case in C. namaquense (Boycott et al. 2002). Both advertisement and territorial calls of C. karooicum are longer in duration than those of C. namaquense.
C. karooicum is endemic to the arid Karoo regions of the Western and Northern Cape provinces of South Africa, where it is known from only a few widely separated localities. The most northerly record is Grootdrif (3118BD) in the Vanrhynsdorp district, which is the only area where the ranges of C. karooicum and C. namaquense are known to overlap. To the east, its distribution extends as far as Beaufort West district (3222BA, BC), bordering on the more mesic summer-rainfall region. Most of the known localities of C. karooicum are near the type locality in the Robertson district of the Little Karoo (3319DD) at the southern limit of its range (Boycott et al. 2002).
Although the species is currently known from only 11 grid cells, it is likely to occur in suitable habitat in the intervening areas. However, this frog appears to have a localized occurrence and specialized habitat preferences, and its distribution is therefore probably also fragmented. The atlas records are reliable, but incomplete.
C. karooicum occurs in arid areas in which rainfall is unpredictable. The vegetation type present in the Robertson area is Little Succulent Karoo, while the Cederberg and Vanrhynsdorp areas are covered by Lowland Succulent Karoo. These areas are situated at altitudes below 600 m and receive an average annual (winter) rainfall of less than 300 mm (Schulze 1997). The Beaufort West and Fraserburg records occur in Eastern Mixed Nama Karoo, situated at slightly higher altitudes (700–1400 m), and receive more annual precipitation (300–500 mm). These areas lie on an ecotone and receive both winter and, to a lesser extent, summer rain (Low and Rebelo 1996).
The species occurs on shales of the Karoo sequence (Boycott et al. 2002). The frogs’ flattened appearance and habit suggests that this species is lithophilic, aestivating in rock cracks and crevices during long, unfavorable dry periods.
Breeding usually takes place in shallow pools in the rocky beds of small, temporary streams and has also been recorded in a small man-made dam along a stream. The species appears to avoid larger impoundments. Common frogs such as Tomopterna delalandii, Afrana fuscigula, Bufo gariepensis and C. boettgeri breed at a large dam near the type locality, but C. karooicum was not observed breeding there.
C. karooicum is an opportunistic breeder, taking advantage of rainfall of sufficient magnitude, regardless of the season in which it occurs. In dry years, little or no breeding may take place. For example, at Vrolijkheid Nature Reserve, no breeding was recorded between major rainfall events, the first in July 1977 and the next in January–February 1981, a period of 3.5 years (Boycott et al. 2002).
Calling usually takes place at night, although on wet, overcast days, males may also call from well-concealed sites. Call sites are sometimes exposed, but more often are located in clumps of vegetation or beneath stones at the water’s edge. Males call while partially submerged, with the head, vocal sac and forelimbs projecting above the water. Calling males maintain a distance of approximately one meter from one another and produce territorial calls when approached by other males (Boycott et al. 2002).
Amplexus occurs in deeper water on the downstream side of rocks or overhanging vegetation, and the eggs are attached to submerged vegetation. At Vrolijkheid Nature Reserve, four clutches of eggs laid in July 1977 numbered 258–323, while nine clutches laid in January and February 1981 numbered 36–156. The time taken to reach metamorphosis under natural conditions was recorded as 28 days (Boycott et al. 2002).
C. karooicum occurs in the Karoo National Park, the Vrolijkheid Nature Reserve (type locality), and the Boesmanskloof Private Nature Reserve. Together with other frogs in the Western Cape and Northern Cape provinces, it is protected by Cape Nature Conservation Ordinance 19 of 1974, as amended. The few known populations of C. karooicum do not appear to be facing any immediate or foreseeable threats to their survival. In view of the paucity of information on the distribution and ecology of this species, it is classified Data Deficient (this publication).
The area occupied by this species has low industrial, mining and urbanization potential. The main form of land use is small-stock farming that presents a low level of threat to this species, apart from general problems associated with land degradation under poor veld management. Some road construction has occurred near the Oukloof population (3221BB), which could potentially reduce the availability of breeding habitat.
Recommended conservation actions
Surveys are required to determine the full extent of the distribution of C. karooicum. Research into the ecology and population dynamics of the species is necessary for conservation assessment. Landowners at recorded localities should be made aware of the presence of this frog and the importance of protecting its breeding habitat.
Current distribution map
Undated records; pre-1996; 1996 to 2002; 2003 to present
FrogMAP. 2018. Cacosternum karooicum Boycott, De Villiers and Scott, 2002. Animal Demography Unit. Accessed from http://frogmap.adu.org.za/?sp=415; on 2018-05-23 08:05:47.
Minter L.R., Burger M., Harrison J.A., Braack H.H., Bishop P.J. & Kloepfer D. (eds). 2004. Atlas and Red Data book of the frogs of South Africa, Lesotho and Swaziland. SI/MAB Series no. 9. Smithsonian Institution, Washington, D.C. Published by the Smithsonian Institution and the Avian Demography Unit (now Animal Demography Unit).