Heuweltjies are large mounds above or near the surface of the landscape, a type of soil surface feature that occurs widely in the south-western Cape of South Africa. Their formation has been the subject of a wide range of speculation and of debate.
Heuweltjies are large mounds above or near the surface of the landscape, a type of soil surface feature that occurs widely in the south-western Cape of South Africa. Their formation has been the subject of a wide range of speculation and of debate.
The Afrikaans word heuweltjie comes from the Dutch word heuveltje 'hillock, small hill'. [1]
Heuweltjies are large mounds above or near the surface of the landscape. Like other phenomena, such as Mima mounds and fairy circles, from which they have been poorly distinguished, particularly in early literature, they have been the subject of a wide range of speculation and of debate that has not yet been settled conclusively. [2] [3]
It is quite certain that not all types of heuweltjies have the same cause and nature. For one thing, the various organisms and circumstances that have been proposed to cause them do not occur throughout their range. For another, they differ in nature; some for example have been seen as improving soil fertility, an opinion documented at least as long ago as the early 20th century. [3]
Possible theories and discussions on the topic include the following:
One theory is that heuweltjies are fossil termite mounds. Within this hypothesis, there are two conflicting opinions on the origins of heuweltjies, one maintaining that heuweltjies were built by the harvester termite Microhodotermes viator , the other that heuweltjies were built by a now possibly extinct termite species. [4] The earliest radiocarbon dates on heuweltjies suggest an age of about 30,000 or even 40,000 B.P. [5]
Another theory is that heuweltjies are created by burrowing (fossorial) animals. Variants of this hypothesis are that the animals are mole-rats in the families Bathyergidae and Rhizomyinae; termites; or a combination of mole-rats and termites. In a review paper, Walter Whitford and Fenton Kay state that while the mounds appear to have been created by termites, mammals (aardvarks) partially maintain the mounds by feeding on and living in them. They show a (log-log) correlation between the surface area of mounds including Mima mounds, badger digs, bison wallows, mole-rat, prairie-dog and banner-tail kangaroo rat mounds, with the longevity of the disturbance ('biopedturbation', i.e. disturbance of soil by living agents including animals, roots, etc.): a heuweltjie of 100–1000 square metres is 1000–10,000 years old. [6]
Yet another theory is that heuweltjies are caused by differential erosion in places where the availability of water limits the growth of vegetation, creating natural patterns such as tiger bush. In favour of this theory, Michael Cramer and his colleagues note that heuweltjies contain at least ten times more soil than any termite nests in South Africa, and that they can occur on bedrock, which termites could not be tunnelling through to move soil upwards. Further, the heuweltjies had the same spatial distribution as bush-clumps, patches of woody vegetation forming patterns. They suggest that heuweltjies formed from bush-clumps as these protected the soil from eroding away, producing calcrete hardpans. [7]
In 2017 Corina Tarnita and colleagues published a paper in Nature which explained these and other related self-organised vegetation patterns by means of a general theory which integrates scale-dependent feedbacks and the activities of subterranean ecosystem engineers such as termites, ants, and rodents. [8]
Heuweltjies modify their local environment, creating a patchwork of habitats in the Nama Karoo ecosystem. Soils in heuweltjies are finer-grained, contain more water, and are more alkaline than surrounding soils, and they support differing animal and plant communities. Both aardvark and steenbok use heuweltjies as dung middens; they are often colonised by Brant's whistling rats ( Parotomys brantsii ); and sheep graze and leave dung on them. [9]
The aardvark is a medium-sized, burrowing, nocturnal mammal native to Africa. It is the only living species of the order Tubulidentata, although other prehistoric species and genera of Tubulidentata are known. Unlike most other insectivores, it has a long snout, similar to that of a pig, which is used to sniff out food.
A nest is a structure built for certain animals to hold eggs or young. Although nests are most closely associated with birds, members of all classes of vertebrates and some invertebrates construct nests. They may be composed of organic material such as twigs, grass, and leaves, or may be a simple depression in the ground, or a hole in a rock, tree, or building. Human-made materials, such as string, plastic, cloth, or paper, may also be used. Nests can be found in all types of habitat.
Deserts and xeric shrublands are a biome defined by the World Wide Fund for Nature. Deserts and xeric shrublands form the largest terrestrial biome, covering 19% of Earth's land surface area. Ecoregions in this habitat type vary greatly in the amount of annual rainfall they receive, usually less than 250 millimetres (10 in) annually except in the margins. Generally evaporation exceeds rainfall in these ecoregions. Temperature variability is also diverse in these lands. Many deserts, such as the Sahara, are hot year-round, but others, such as East Asia's Gobi, become quite cold during the winter.
Fairy circles are circular patches of land barren of plants, varying between 2 and 12 metres in diameter, often encircled by a ring of stimulated growth of grass. They occur in the arid grasslands of the Namib desert in western parts of Southern Africa, and in a part of the Pilbara in Western Australia. Studies have posited various hypotheses about their origins, but none have conclusively proven how they are formed. Theories include the activities of various types of termites, or the consequence of vegetation patterns that arise naturally from competition between grasses.
Mound-building termites are a group of termite species that live in mounds which are made of a combination of soil, termite saliva and dung. These termites live in Africa, Australia and South America. The mounds sometimes have a diameter of 30 metres (98 ft). Most of the mounds are in well-drained areas. Termite mounds usually outlive the colonies themselves. If the inner tunnels of the nest are exposed it is usually dead. Sometimes other colonies, of the same or different species, occupy a mound after the original builders' deaths.
A fossorial animal is one adapted to digging which lives primarily, but not solely, underground. Some examples are badgers, naked mole-rats, clams, meerkats, and mole salamanders, as well as many beetles, wasps, bees and spiders.
The Cape mole-rat is a species of mole-rat endemic to South Africa. It is the only extant species currently described as belonging to the genus Georychus.
The wildlife of South Africa consists of the flora and fauna of this country in southern Africa. The country has a range of different habitat types and an ecologically rich and diverse wildlife, vascular plants being particularly abundant, many of them endemic to the country. There are few forested areas, much savanna grassland, semi-arid Karoo vegetation and the fynbos of the Cape Floristic Region. Famed for its national parks and big game, 297 species of mammal have been recorded in South Africa, as well as 849 species of bird and over 20,000 species of vascular plants.
A gilgai is a small, ephemeral lake formed from a depression in the soil surface in expanding clay soils. Additionally, the term "gilgai" is used to refer to the overall micro-relief in such areas, consisting of mounds and depressions, not just the lakes themselves. The name comes from an Australian Aboriginal word meaning small water hole. These pools are commonly a few metres across and less than 30 cm (12 in) deep, however in some instances they may be several metres deep and up to 100 m (330 ft) across. Gilgais are found worldwide wherever cracking clay soils and pronounced wet and dry seasons are present. Gilgais are also called "melonholes, crabholes, hogwallows or puff and shelf formations".
Tsolwana Nature Reserve is an 8,500 hectare nature reserve situated on the edge of the Winterberg Mountain range. It is located 60 km west of Queenstown, and 30 km south- east of Tarkastad in Eastern Cape Province, South Africa and is managed by Eastern Cape Parks Board. Its western boundary is formed by the upper Black Kei River. The reserve's name originates from the Xhosa word for "spike", due to the presence of the cone-shaped hill, Spitskop.
Anoplolepis custodiens, commonly known as the common pugnacious ant, is a species of ant in the genus Anoplolepis, native to central and southern Africa. Individual ants may come in a range of colors and sizes. Found in dry and cultivated areas, it is an important source of prey for some pangolins and aardvarks. Although generally aggressive, ants from other colonies of Anoplolepis custodiens are not attacked.
The soil biomantle can be described and defined in several ways. Most simply, the soil biomantle is the organic-rich bioturbated upper part of the soil, including the topsoil where most biota live, reproduce, die, and become assimilated. The biomantle is thus the upper zone of soil that is predominantly a product of organic activity and the area where bioturbation is a dominant process.
Swartland Shale Renosterveld is a critically endangered vegetation type of the Western Cape, South Africa.
The Hodotermitidae are a basal Old World family of termites known as the harvester termites. They are distinguished by the serrated inner edge of their mandibles, and their functional compound eyes which are present in all castes. They forage for grass at night and during daylight hours, and the pigmented workers are often observed outside the nest. Their range includes the deserts and savannas of Africa, the Middle East, and Southwest Asia. Their English name refers to their habit of collecting grass, which is not unique to the family however.
Microhodotermes is a genus of southern African harvester termites in the Hodotermitidae. As with harvester termites in general, they have serrated inner edges to their mandibles, and all castes have functional compound eyes. Species of this genus are desert specialists of the Namib, Kalahari and Karoo, where their ranges overlap with Hodotermes.
Robertson Karoo is a semi-arid vegetation type, restricted to sections of the Breede River Valley, Western Cape Province, South Africa. It is a subtype of Succulent Karoo and is characterised by the dominance of succulent plant species, and by several endemic plants and animals.
The Bundu Farm site is a kidney shape depression of land located in the Bushmanland region of Northern Cape, South Africa. The excavations at this site during 1998-2003 had unearthed a sequence of archaeological remains including Earlier, Middle and Later Stone Age assemblages and preserved fauna. These discoveries give an insight into the occupation of the Bushmanland prehistoric people and possible connection of cultures and traditions between the central interior and the West coast of South Africa.
Meerkat National Park is a large National Park in the Northern Cape, South Africa, that encompasses the Square Kilometre Array's MeerKAT, PAPER and HERA telescopes.
Robert Mitchell Pringle is an American biologist and conservationist.