Why no gazelle at the southwestern tip of Africa?

@capracornelius @paradoxornithidae @botswanabugs @koenbetjes @grinnin @matthewinabinett

Mediterranean-type climates, with dry summers and rainy winters, occur both in South Africa (shown in blue in https://www.researchgate.net/figure/Climatic-regions-of-South-Africa-48-note-the-climatic-variations-along-the-coastlines_fig1_334771843) and along the Mediterranean coasts of North Africa and the Levant.

And gazelles have been evolving and shifting their ranges across Africa and Asia for millions of years.

However, there is a puzzling faunistic difference:
No species of gazelle is indigenous to the southern area, whereas four species of gazelles are indigenous to the northern area, viz.

In South Africa there is one species of gazelle, namely the springbok (Antidorcas marsupialis, https://www.inaturalist.org/observations/35692467).

However, this species did not historically occur under the mediterranean-type climate of Western Cape Province (https://en.wikipedia.org/wiki/Western_Cape). The many observations in iNaturalist are of introduced populations.

Furthermore, even within its natural distribution in South Africa, the springbok avoids stony slopes, in contrast to

Why/how have these disparities in habitat arisen?

One partial explanation involves competing members of the ruminant fauna.

A crucial difference is that the following species of South Africa have no counterparts in North Africa or the Levant:

These species were, until recently, common in relevant environments at or near (https://www.researchgate.net/figure/Distribution-records-for-Southern-Mountain-Reedbuck-Redunca-fulvorufula-fulvorufula_fig1_325473215) the southwestern tip of Africa.

I hypothesise that, among them (i.e. collectively), these species arguably usurped the niche of gazelles.

The grey rhebok and mountain reedbuck prefer stony slopes, and the distribution of the former included most of the South African area of mediterranean-type climate. Both are similar in body size and partly similar in diet to the springbok.

The common eland is extremely large (adult female about 500 kg); the two species of Raphicerus are smaller than gazelles. However, all have diets that overlap those of gazelles enough for them to be potential competitors.

To 'rewild' the climatically similar stony slopes near Punta Almina (https://en.wikipedia.org/wiki/Peninsula_of_Almina) in the north and Cape Agulhas (https://en.wikipedia.org/wiki/Cape_Agulhas) in the south of the same continent, we would reintroduce

  • to the northern area only Cuvier's gazelle, but
  • to the southern area at least three species: grey rhebok, common eland, and steenbok/Cape grysbok.

It would be naive to expect that the same ecological function could be restored by simply 'reintroducing' the springbok in Agulhas National Park (see https://www.inaturalist.org/observations/3975537), even though it is by far the most similar antelope to Cuvier's gazelle that is available in the southern African fauna.

Posted on Μάιος 04, 2021 0445 ΠΜ by milewski milewski

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Are there no fossil gazelles in the Agulhas megafauna? Wiped out by modern humans in the last 50,000 years?

Venter, J.A et al., Large mammals of the Palaeo-Agulhas Plain showed resilience to extreme climate change but vulnerability to modern human impacts, Quaternary Science Reviews, https://doi.org/10.1016/j.quascirev.2019.106050

For instance, were was Antidorcas australis found?

Αναρτήθηκε από tonyrebelo σχεδόν 2 χρόνια πριν (Αναφορά)

Hi tonyrebelo, thanks for your comment. Not only is it possible that Gazella once occurred on the Agulhas Plain, but Antidorcas is well-known formerly to have occurred in East Africa. Both genera, namely Gazella and Antidorcas, have at various times lived in both South and East Africa. This means that the Recent pattern of distribution, in which Antidorcas has completely replaced Gazella in southern Africa, is presumably owing to the adaptive superiority of Antidorcas to Recent environmental conditions in southern Africa. The particular puzzle is why Antidorcas, so abundant in semi-arid southern Africa, failed to occur (or once occurred but failed to survive in the last few centuries) on the mesic coastal forelands (the Swartland and probably also the Ruensveld) of the southwestern Cape. It is hard to explain any of this according to human predation because this has been a constant throughout subSaharan Africa throughout the waxings and wanings of both genera of gazelles (Gazella and Antidorcas) in southern Africa including the southwestern Cape, including the area of mediterranean-type climate in Western Cape province, and including the Agulhas Plain.

Αναρτήθηκε από milewski σχεδόν 2 χρόνια πριν (Αναφορά)

Could it not be a areal issue. WIth the demise of the huge Agulhas plains, the Med mammals were squeezed to critical population sizes that could not cope with hunting and sheep and cattle. The problem with mountain gazelles is the extremely low carrying capacity of the Cape Med mountains so mountain specialists probably did not occur, but plains specialists would have.
We have large buffalo, large hartebeest and large springbok, that succumbed to human predation and rising sea levels - problems that were not an issue in tropical Africa because of its huge areas and relatively extensive populations (the s Cape Med region is less than 1% of the area)..

Αναρτήθηκε από tonyrebelo σχεδόν 2 χρόνια πριν (Αναφορά)

I agree that there is nothing puzzling about the lack of gazelles in the sandstone/quartzite mountains of the southwestern Cape. I know of no similarly nutrient-poor substrate, anywhere in Africa or Eurasia, inhabited by any of the eight genera of gazelles. However, what remains puzzling is that Antidorcas did not include in its habitat the nutrient-rich stony slopes, freshly weathering from dolerite, in the Karoo. From a South African perspective it might seem that Antidorcas is morphologically unsuited to negotiating obstacles in the form of rocks; but it is hard to sustain this view once one sees the competence of Gazella cuvieri and Gazella gazella on rocky slopes. Turning to the main question you just posed: if I understand it correctly, what you are suggesting is that the relatively nutrient-rich coastal forelands in the southwestern Cape occupied such a small area, after sea levels rose, that Antidorcas could not survive human predation within this area. My answer is as follows. In ruminants, reproductive rates are generally correlated with body size, the smaller species reproducing more rapidly than the larger species. This helps to explain why, by about 1900, the only species of wild ruminants surviving in either the Karoo or the coastal forelands of the southwestern Cape were those of body mass less than 30 kg (a size-range which includes the local form of Antidorcas). Applying this principle to the coastal forelands before European arrival: we would predict that, if anthropogenic extermination were to occur owing to the restricted area available to ruminants, it would be the larger species which disappeared first. More particularly, we would predict that the eland (Taurotragus) and the buffalo (Syncerus) would have disappeared before Antidorcas disappeared. This prediction fails, because in reality the eland (500kg), the buffalo (500 kg), the hartebeest (150 kg), and the bontebok (70 kg) - but not the springbok (Antidorcas, 30 kg) - remained at the time when Europeans arrived at what is now Cape Town. Broadening the scope of ungulates, three species of megaherbivores remained common at this time near what is today Cape Town, despite their reproductive rates being far more limited again than those of eland and buffalo. How, then, would anthropogenic factors explain why the local vegetation type in question, namely the renosterveld, was named after the hook-lipped rhino, and not named 'bokkeveld' after the springbok? Surely a habitat too restricted for the springbok would also be too restricted for the hook-lipped rhino/elephant/hippo/eland/buffalo/hartebeest?

Αναρτήθηκε από milewski σχεδόν 2 χρόνια πριν (Αναφορά)

I was thinking of the bigger megaherbivores (above Buffalo=Rhino size). No large gazelles? Not even on Agulhas?

Αναρτήθηκε από tonyrebelo σχεδόν 2 χρόνια πριν (Αναφορά)

Bergmann's rule (https://en.wikipedia.org/wiki/Bergmann%27s_rule) would predict that gazelles at high latitudes would be relatively large-bodied. The largest species of gazelle, including extinct forms, has/had average body mass for adult females of about 50 kg, and was/were not associated with high latitudes. Gazelles survive today as far north as the Gobi Desert, but the body mass of Gazella subgutturosa there remains less than 35 kg in adult females. There is another reason to doubt that gazelles have ever been particularly large in southern Africa. The pattern with bontebok/blesbok (Damaliscus pygargus), black wildebeest (Connochaetes gnou) and bloubok (Hippotragus leucophaeus) is to the contrary, because these are all - despite Bergmann's rule - remarkably small compared to their congeners in the tropics/subtropics.

Αναρτήθηκε από milewski σχεδόν 2 χρόνια πριν (Αναφορά)

Please see http://www.scielo.org.za/pdf/sajs/v103n1-2/12.PDF, which indicates that Antidorcas recki, the extinct southern African ancestor of modern Antidorcas marsupialis, was the smaller-bodied of the two.

Αναρτήθηκε από milewski σχεδόν 2 χρόνια πριν (Αναφορά)

If you find the link http://www.scielo.org.za/pdf/sajs/v103n1-2/12.PDF defective, please Google Temporal variation in Plio-Pleistocene Antidorcas...South African Journal of Science 103, January/February 2007.

Αναρτήθηκε από milewski σχεδόν 2 χρόνια πριν (Αναφορά)

Please see https://www.researchgate.net/publication/283993201_The_feeding_niche_of_an_extinct_springbok_Antidorcas_bondi_Antelopini_Bovidae_and_its_paleoenvironmental_meaning and https://www.sciencedirect.com/science/article/abs/pii/S1040618217315896. These refer to Antidorcas bondi. The ancestral Antidorcas recki was replaced in the Pleistocene by both marsupialis and bondi, the latter being a relatively specialised grazer comparable to Eudorcas thomsoni. It is possible that bondi was the main species on the Agulhas Plain (although the fossil distribution shows no evidence of it so far south). And if it occurred here it is possible that it shared the Agulhas Plain with Syncerus antiquus, Megalotragus priscus (which were larger than any modern relatives), Damaliscus niro, Equus capensis (similar to modern grevyi) and Ceratotherium simum (the still-extant square-lipped rhino, which did formerly range to the southern tip of Africa). It is even possible that all besides Antidorcas bondi were exterminated by human predation on the coastal forelands of the southwestern Cape. However, I doubt that human predation could have exterminated Antidorcas bondi here without ecological changes adverse to bondi, because bondi seems to have been a similarly small, rapidly reproducing species to marsupialis.

Αναρτήθηκε από milewski σχεδόν 2 χρόνια πριν (Αναφορά)
Αναρτήθηκε από milewski σχεδόν 2 χρόνια πριν (Αναφορά)

@milewski
I don't know much about the taxonomy of Antidorcas, but is it possible that Antidorcas bondi and Antidorcas marsupialis are conspecific?

Αναρτήθηκε από paradoxornithidae 3 μήνες πριν (Αναφορά)

Or is that not probable?

Αναρτήθηκε από paradoxornithidae 3 μήνες πριν (Αναφορά)

Conspecific? the one is a grazer and the other a browser - not likely!

Αναρτήθηκε από tonyrebelo 3 μήνες πριν (Αναφορά)

@paradoxornithidae @tonyrebelo

Please see:

https://www.tandfonline.com/doi/abs/10.1080/00359198609520116

https://www.tandfonline.com/doi/abs/10.1080/00359198609520116?journalCode=ttrs20

https://www.jstor.org/stable/1382468

The springbok, like the blesbok, the red hartebeest, and the black wildebeest, prefers grass. However, it is more versatile than those three spp. of grazers, and is able to subsist on the foliage of dwarf shrubs (e.g. https://www.inaturalist.org/observations?place_id=any&taxon_id=156634&view=species) for most of the year.

(In degree of specialisation on grass, as opposed to woody plants, blesbok > black wildebeest > red hartebeest > springbok)

Ken Tinley has a hypothesis that the irruptions of the springbok arose in seasons when a particular genus of small grasses, namely Enneapogon (https://www.inaturalist.org/observations?place_id=6986&taxon_id=72116&view=species), was abundant.

The extinct Antidorcas bondi differed from A. marsupialis not in its hypsodonty (https://en.wikipedia.org/wiki/Hypsodont), but also in its lesser body size.

Please see:

https://www.sciencedirect.com/science/article/abs/pii/S1040618217315896

https://www.researchgate.net/figure/Specimens-attributed-to-the-genus-Antidorcas-Sundevall-1847-from-Coopers-D-in-occlusal_fig2_360746108

http://eprints.bournemouth.ac.uk/30451/3/Sewell%20et%20al.%20Dietary%20Palaeoecology%20of%20PlioPleistocene%20%20Antidorcas.pdf

Hypsodonty is taken to indicate specialisation for grazing, although grittiness (such as that coating even shrubby foliage under semi-arid, windy conditions) might also play a part.

Αναρτήθηκε από milewski 3 μήνες πριν (Αναφορά)

Speaking of Enneapogon, the biogeography of grasses is remarkable. Enneapogon desvauxii (https://www.inaturalist.org/taxa/76820-Enneapogon-desvauxii), probably important in the diet of the springbok, is indigenous also to the southwestern parts of North America (and also Mongolia).

Please see https://swbiodiversity.org/seinet/taxa/index.php?taxon=535&clid=3#:~:text=Enneapogon%20desvauxii%20grows%20in%20open,Arabia%20and%20India%20to%20China.

Αναρτήθηκε από milewski 3 μήνες πριν (Αναφορά)

Please see https://www.researchgate.net/figure/The-extent-of-late-Quaternary-fossil-localities-with-Bonds-springbok-Antidorcas_fig3_312785048

In envisaging a South Africa in which Antidorcas bondi lived as a small, grazing gazelle (similar ecologically to Gazella thomsoni), it is remarkable to realise that even Kobus leche (https://www.inaturalist.org/taxa/42329-Kobus-leche) once lived in what is now the Karoo (https://en.wikipedia.org/wiki/Karoo). What are today 'pans' (dry, barren salinas, https://www.dreamstime.com/large-dry-salt-pan-karoo-wide-featureless-nama-northern-cape-south-africa-image215553662) were, in pluvial times in the Pleistocene, the habitat of the lechwe.

I retain a suspicion that Antidorcas bondi was actually a species of true gazelle, in which case its name would be Gazella bondi.

Αναρτήθηκε από milewski 3 μήνες πριν (Αναφορά)
Αναρτήθηκε από milewski 3 μήνες πριν (Αναφορά)

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