A new hypothesis for the steenbok (Raphicerus campestris) in the Highveld of South Africa: it was naturally absent
It is easy to assume that the steenbok (Raphicerus campestris) was indigenous to the Highveld (https://en.wikipedia.org/wiki/Highveld) when European explorers arrived.
However, I suggest that it was actually absent.
This would help to explain why its current taxonomic status in the Highveld is so nebulous (https://www.inaturalist.org/journal/milewski/70638-the-steenbok-raphicerus-campestris-in-the-highveld-a-simple-question-gone-impossibly-complex#).
My argument is based on an ecological rationale, but seems consistent with the historical record.
The steenbok tends to be taken for granted as widespread and ecologically tolerant. However, it is more ecologically specialised than first it seems, in diet and habitats.
This species is part of a guild of relatively small herbivores including
- Antidorcas marsupialis (https://www.inaturalist.org/observations/66931375),
- Redunca fulvorufula (https://www.inaturalist.org/observations/74576197),
- Ourebia ourebi (https://www.inaturalist.org/observations/100711449), and
- Lepus capensis (https://www.inaturalist.org/observations/68999642).
All eat both grasses and dicotyledonous plants, in various combinations according to the seasons (https://www.researchgate.net/publication/230164079_The_feeding_ecology_of_a_very_small_ruminant_the_steenbok_Raphicerus_campestris).
Because it has so many competitors, R. campestris may have been somewhat limited in occurrence in prehistoric South Africa, when the full fauna of the Holocene remained.
The Highveld contained by far the most complex fauna of ungulates of any region of treeless grassland on Earth (https://www.sciencedirect.com/science/article/pii/S0254629915003051 and https://www.researchgate.net/publication/282619832_Why_was_the_Highveld_treeless_Looking_laterally_to_the_Pampas_for_global_edaphic_principles_beyond_biogeographical_accidents). This may have precluded a niche for R. campestris under natural conditions.
I suspect that it was only when the fauna was disrupted by human settlement that R. campestris spontaneously entered the Highveld, from the west and north.
The idea is that it filled in for the species virtually exterminated by settlers, particularly the formerly abundant and migratory A. marsupialis.
This is not to claim that R. campestris became abundant in the Highveld, but merely that it became viable there because of, rather than despite, anthropogenic disturbance.
Three subspecies were thus hypothetically recruited to the Highveld, then mixing there through hybridisation. These are R. c. campestris (southwesterly origin), R. c. steinhardti (northwesterly origin), and R. c. capricornis (northeasterly origin).
Another basis for my hypothesis is habitat, particularly the natural availability of cover.
In its original state, the Highveld was treeless over extensive areas, partly owing to the intense natural herbivory. This hypothetically made the grassland too open for R. campestris.
There are two situations, in the Highveld today, with some shrubby indigenous cover, viz.
- perennial drainage lines, and
- scattered rocky outcrops.
However,
- the former are typical habitat of the somewhat competitive Sylvicapra grimmia (https://www.inaturalist.org/observations/57811991) and Lepus saxatilis/victoriae (https://www.inaturalist.org/observations/11873978), whereas
- the latter were, I suspect, negligibly woody under the original regime of intense herbivory by Taurotragus oryx (https://www.inaturalist.org/observations/13007563 and https://www.inaturalist.org/observations?place_id=50327&taxon_id=75192&view=species) in particular.
The settlement of the Highveld has boosted the incidence of woody plants, for various reasons.
I consulted du Plessis S F (1969, The Past and Present Geographical Distribution of the Perissodactyla and Artiodactyla in Southern Africa), for information on the occurrence of the steenbok.
On page 100, du Plessis states for 'Orange Free State':
"Though no doubt occurring everywhere in this province in the past, practically no written records could be traced...Only Smith (Kirby, 1939) in 1835 mentions it as being common near the confluence of the Riet and Modder rivers".
This location (https://en.wikipedia.org/wiki/Riet_River) is actually west of Free State province and the Highveld, being located in the current Mokala National Park (https://en.wikipedia.org/wiki/Mokala_National_Park).
Much of the Highveld occurs in the former Transvaal (https://en.wikipedia.org/wiki/Transvaal_(province)). However, once again du Plessis (1969) largely draws a blank in the historical record.
The exceptions are as follows:
- "Mauch (Petermann, 1870): north of Lydenburg"
- "Holub (1881): near the Vaal River in western Transvaal"
- "Holub (1890): between Bloemhof and Christiana"
- "Baldwin (1894): the vicinity of Potchefstroom"
- "Randall (1895): the open flats in the Barberton District."
The relevant locations mentioned are:
- https://en.wikipedia.org/wiki/Lydenburg
- https://en.wikipedia.org/wiki/Bloemhof
- https://en.wikipedia.org/wiki/Christiana,_North_West
- https://en.wikipedia.org/wiki/Potchefstroom
- https://en.wikipedia.org/wiki/Barberton,_Mpumalanga.
All of these are rather marginal to the Highveld, except for Potchefstroom. However, the latter is located in the valley of a major drainage line (https://en.wikipedia.org/wiki/Mooi_River_(Vaal)).
On page 103, du Plessis states the incidence, as of 1969, as follows:
"Orange Free State: Van Ee (1962): fairly generally distributed throughout the province with the greatest numbers along the rivers and in the mountainous districts of the east, especially in the Fouriesburg, Tweeling, Petrus Steyn, Boshoff, Theunissen, Brandfort, Hoopstad and Koffiefontein districts. Roberts (1963): 45 in the Willem Pretorius Game Reserve".
The status in Transvaal (page 104) was similarly widespread, as of 1969.
So, dear readers, please prove me wrong in my suggestion that the steenbok was naturally absent from the Highveld, including virtually the whole of what is now Free State.
One way to do so might be to consult a work to which I currently lack access. This is by Skead (https://en.wikipedia.org/wiki/CJ_Skead), covering that part of the Highveld falling within the Eastern Cape (https://ace.mandela.ac.za/Historical-Incidence-of-the-Larger-Mammals/Authors/The-works-of-Cuthbert-John-(Jack)-Skead),
In the meantime, the following is a compendium of all the current photos of R. campestris, located in the Highveld, in iNaturalist:
https://www.inaturalist.org/observations/129166689
https://www.inaturalist.org/observations/105216875
https://www.inaturalist.org/observations/108317173
https://www.inaturalist.org/observations/69266940
https://www.inaturalist.org/observations/127743228
https://www.inaturalist.org/observations/127670769
https://www.inaturalist.org/observations/98953074
https://www.inaturalist.org/observations/130857789
Only four of the above observations show the animals clearly.
