Deep thinking re empty niche for herbivore in Kruger National Park

(writing in progress) 
 
A conventional view of Kruger National Park in its ‘natural’ state is as follows.

The populations of herbivores were limited by the availability of water in the dry season.

According to this model, the provision of artificial water during the 20th century changed the regime fundamentally, to the point where the main constraint became food instead of water.

As readers may know, the Park authorities have been gradually reversing the policy of artificial provision of water, by closing certain boreholes.
 
To state this model succinctly:
 
Most species of ungulates can only forage up to 6 km from drinking water.
 
The area between the Sand and the Olifants, and the Letaba and Limpopo, Rivers had no dependable water during the dry season.
 
Thus the ungulates ventured on to the ‘plains’ only during the wet season, a pattern which constituted a seasonal ‘migration’ on a limited scale (more or less within what is now Kruger National Park).
 
One of the results is catastrophic collapses in the populations, e.g. in 1966 and 1983.
 
Another of the results is permanent degradation of vegetation around artificial water-points.
 
Two points occur to me, of which the first is probably not original, but the second may be.
 
Firstly, it is possible that in pre-European times there was a far more extensive migration to and from the northern third of Kruger Park, i.e. between the basalt plains in summer and the part of east-central Limpopo Province between Polokwane and Thohoyandou.

If so, the error of having provided artificial water would be all the more serious in its effects on the composition of the ungulate community (particularly w.r.t. eland, roan, sable, and tsessebe) and on the vegetation (particularly w.r.t. mopane and bothriochloa).
 
Secondly, there is a paleo-biogeographical anomaly in the genus Gazella in southern Africa.

Gazella is an extremely widespread genus, ranging today from East Africa right across North Africa to the shores of the Mediterranean, and across Arabia deep into Asia as far as India in the south and the Gobi Desert in the north.

With such a wide distribution, it is hardly surprising that Gazella formerly occurred also in South Africa.

Gazella vanhoepeni https://www.sciencedirect.com/science/article/abs/pii/S0031018206002355 and https://pubmed.ncbi.nlm.nih.gov/10330334/ and https://www.researchgate.net/figure/Examples-of-Makapansgat-specimens-used-in-the-mesowear-analysis-A-Tragelaphus-pricei_fig20_239521194
Phenacotragus (Gazella ) vanhoepni file:///C:/Users/Antoni%20Milewski/Downloads/titusland,+Slogett.pdf
Gazella gracilior https://core.ac.uk/download/pdf/39673535.pdf

Also see https://www.cambridge.org/core/books/abs/african-paleoecology-and-human-evolution/geology-fauna-and-paleoenvironmental-reconstructions-of-the-makapansgat-limeworks-australopithecus-africanusbearing-paleocave/D09BD949CC64B1779A00250DC58688A0 and https://www.britannica.com/place/Makapansgat and https://books.google.com.au/books/about/Fossil_Bovidae_from_the_Limeworks_Quarry.html?id=t92dvAEACAAJ&redir_esc=y

The surprise is that this genus went extinct in South Africa in the prehistoric period.

This is particuarly surprising because this extinction (which wiped out several species found nowhere but in southern Africa) cannot be explained as part of any ‘megafaunal’ extinction. If anything, it is a kind of ‘microfaunal’ extinction among ungulates, because Gazella is relatively small as grazers go.
 
So what I am starting to envisage is that there was formerly a situation, in northern Kruger National Park, similar to what we see in the Serengeti today: at least one species of gazelle occurred, superficially similar to the springbok (which belongs to a different genus and one restricted to southern Africa), but allopatric with the springbok, owing to the unsuitability of what is now Kruger National Park for the springbok.
 
Based on mesic East Africa, gazelles could have played at least two roles in the Pleistocene/early Holocene ecology of Kruger Park, as follows.
 
Firstly, Nanger spp. (called Grant’s gazelles in English but consisting of several spp.) are typically sedentary, and similar to the impala in this way, but far more drought-tolerant.

The classic manifestation of this is on the Serengeti Plains (i.e. the driest part of the Serengeti Ecosystem, where the soil is volcanic ash but all growth stops in the dry season). Here, the only herbivores remaining for much of the year are Grant’s gazelle and ostrich. I can easily visualise a similar gazelle on what are now the shrub-mopane plains, on basalt, of the northern two-thirds of Kruger National Park during the dry season.
 
Secondly, Eudorcas spp. (called Thomson’s gazelles in English but consisting of several spp.) are typically migratory, joining wildebeest, zebra and eland in a long-range movement from ‘arid-eutrophic’ to ‘moist-dystrophic’ extremes within an extended landscape.

I can easily visualise such a gazelle helping to graze the basalt plains of the northern two-thirds of Kruger Park in former times, returning to east-central Limpopo Province in the dry season. This kind of gazelle would compete in only a limited way with the impala, because its body mass is half that of the impala, and the impala is sedentary.
 
Regardless of the merit of these thoughts, would readers agree that the original, pre-European ecology of the northern two-thirds of Kruger National Park deserves to be thought out from scratch, while putting aside the current assumptions and ‘factoids’?

And if the answer is ‘not really’, then how can we explain the fact that a large part of Kruger National Park today bears an unpalatable grass (Bothriochloa) on a nutrient-rich soil?
 
(writing in progress)

Posted on August 07, 2022 07:55 AM by milewski milewski

Comments

Question of why flat-topped acacias do not feature in Kruger National Park at the scale of scenic elements:
 
Although the following https://www.krugerpark.co.za/africa_umbrella_thorn.html was supposedly taken in Kruger National Park (which I doubt), it is not typical of the Park. Where in the Park could one see this sort of scene? I cannot think of anywhere, offhand.
 
This is thought-provoking, because the elements of the scene seem so ‘normal’.

The tree is Vachellia tortilis in its typical form, and this species is widespread and common enough in Kruger National Park. However, for some reason the vegetation does not achieve this configuration in more than a few spots in the Park, if at all, at present.
 
Neither V. tortilis nor any other flat-topped tree achieves the status of dominating any scene in Kruger National Park, as far as I recall. Of course, one does find flat-topped individuals of V. tortilis. However, the plants are scattered and relatively small, and are hardly noticeable in the mix of trees e.g. combretums and knobthorn.

Other potentially flat-topped acacias, e.g. V. nilotica and Senegalia burkei, do not form the flat-topped shape in Kruger National Park, even where they are common in the vegetation.
 
In the prehistoric period, there may have been full migrations between what is now the Park and what are now the east-central parts of Limpopo and Mpumalanga Provinces. Perhaps there were still spp. of Gazella in the system. If so, scenes like that shown above may have been widespread in the area, including in the northern two-thirds of the Park, now dominated by shrub-mopane.

Posted by milewski almost 2 years ago

Execellently written! Indeed it’s a distinct possibility, that in the near or far future of climatic changes, these Gazelles could recolonize the areas in which they vanished.

Posted by paradoxornithidae almost 2 years ago
Posted by milewski almost 2 years ago
Posted by milewski almost 2 years ago
Posted by milewski almost 2 years ago

@milewski regarding mammal migration in Kruger National Park: this is discussed to some extent in the excellent book Shaping Kruger by Mitch Reardon.

The author postulates that historic mammal migration in the region would have fallen mostly in a east-west direction, i.e. to and from Mozambique (before such human-made concepts existed). The erection of the western boundary reserve fence in the 1950s disrupted the natural migration pattens of the local herbivores.

Much of the historic vegetation would have also differed: much of the area would have been shaped by pastoralists periodically burning the veld to improve pastures for their livestock. When the pastoralists were evicted by James Stevenson-Hamilton (hence his nickname 'Skukuza'), and a policy of fire suppression was instituted, this led to large stretches of formerly open habitat being taken over by trees and shrubbery, which in turn would have affected the composition of herbivore assemblages as species such as impala and kudu increased, and open-country species declined.

Posted by dinofelis almost 2 years ago

@dinofelis Many thanks for your helpful comment.

Posted by milewski almost 2 years ago

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