Why are rock-dwelling agamas absent from Kruger National Park, South Africa?
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Rock-dwelling spp. of Agama are widespread and common in Africa, from the Mediterranean coast in the north to Cape Agulhas at the southern tip of the continent.
In the African tropics, several spp. of rock-dwelling Agama may be sympatric. For example, in the Serengeti ecosystem of Tanzania and Kenya, Agama mwanzae (https://www.inaturalist.org/taxa/31132-Agama-mwanzae), Agama lionotus (https://www.inaturalist.org/taxa/31155-Agama-lionotus) and Agama dodomae (https://www.inaturalist.org/taxa/1439535-Agama-dodomae) all occur.
Kruger National Park (https://en.wikipedia.org/wiki/Kruger_National_Park) in South Africa contains various forms of rocky terrain, particularly
- the Lebombo range (https://en.wikipedia.org/wiki/Lebombo_Mountains), bearing Lebombo Mountain Bushveld (https://www.nhongosafaris.com/post/amazing-eco-zones-within-kruger-national-park),
- Malelane Mountain Bushveld (https://www.alamy.com/white-rhinoceros-ceratotherium-simum-below-a-koppie-on-the-malelane-image69795270.html?imageid=0BF0AE2B-321A-4707-B536-5D75CFE24A8B&p=174074&pn=1&searchId=0baf801e00220f275e418e2f49817dd2&searchtype=0 and https://www.krugerpark.co.za/Kruger_Park_Game_Viewing_Routes-travel/malelane-gate-game-viewing-routes.html and https://www.alamy.com/stock-photo-rocks-and-lichen-next-to-the-malelane-skukuza-road-in-the-kruger-national-57017763.html?imageid=1D7054F8-F13E-4884-9E24-F17423431DB1&p=89162&pn=1&searchId=0baf801e00220f275e418e2f49817dd2&searchtype=0 and http://www.thekruger.com/gertenbach/gertenbach2.htm and https://en.wikipedia.org/wiki/List_of_vegetation_types_of_South_Africa#/media/File:Savanna.svg and https://upload.wikimedia.org/wikipedia/commons/f/fb/Savanna_legend.svg and https://www.alamy.com/stock-photo-landscape-from-the-road-between-skukuza-and-malelane-with-fallen-tree-73018810.html?imageid=D9E4D49C-7483-42C9-A64C-14E415A17D6E&p=178601&pn=1&searchId=0baf801e00220f275e418e2f49817dd2&searchtype=0), and
- scattered inselbergs (https://en.wikipedia.org/wiki/Inselberg and https://www.shutterstock.com/image-photo/mountain-koppie-kruger-national-park-1102772459 and https://www.alamy.com/stock-photo-a-typical-granite-koppie-in-the-lowveld-of-south-africa-kruger-national-40133692.html and https://www.bigstockphoto.com/image-329771932/stock-photo-rhyolitic-rocky-outcrop-or-koppie-in-kruger-national-park-south-africa and https://www.naturepl.com/stock-photo-koppie-rhyolite-hill-dominating-the-landscape-kruger-np-south-africa-image01171880.html).
Kruger National Park is the best-known part of a larger area, namely the Great Limpopo Transfrontier Park (https://en.wikipedia.org/wiki/Great_Limpopo_Transfrontier_Park). This includes an additional category of rocky terrain, namely the Chilojo Cliffs (https://www.scottramsay.africa/journey-to-gonarezhou-national-park/ and https://www.facebook.com/watch/?v=3963643490363660 and https://www.facebook.com/watch/?v=2761797520730725) in Gonarhezou National Park (https://en.wikipedia.org/wiki/Gonarezhou_National_Park) in southeastern Zimbabwe (https://en.wikipedia.org/wiki/Zimbabwe).
Elsewhere in southern Africa, rocky terrain is inhabited by various spp. of Agama, namely
- Agama atra (https://www.inaturalist.org/taxa/31150-Agama-atra),
- Agama anchietae (https://www.inaturalist.org/taxa/31154-Agama-anchietae),
- Agama knobeli (https://www.inaturalist.org/taxa/539228-Agama-knobeli),
- Agama kirkii (https://www.inaturalist.org/taxa/31136-Agama-kirkii), and
- Agama planiceps (https://www.inaturalist.org/taxa/31127-Agama-planiceps).
These spp. represent three distinct clades within the large and diverse genus (https://ars.els-cdn.com/content/image/1-s2.0-S1055790314002267-fx1_lrg.jpg).
Some of the above spp. occur sympatrically in Namibia and Northern Cape province of South Africa, so that a given rocky outcrop can be inhabited by two congeners.
Therefore, I find it remarkable that no rock-dwelling agamid occurs in Kruger National Park or elsewhere in Great Limpopo Transfrontier Park.
Extending the puzzle:
An agamid similar to Agama, namely Acanthocercus atricollis (https://www.inaturalist.org/taxa/872122-Acanthocercus-atricollis), is abundant in Kruger National Park. This species inhabits trees and fallen logs, rather than rocks.
It is odd that A. atricollis does not extend its habitat on to rocky surfaces in Great Limpopo Transfrontier Park, because
- most rocky landforms in this area support at least scattered trees, and
- certain other spp. of Acanthocercus, elsewhere in Africa, do occur in rocky terrain, devoid of trees (https://www.inaturalist.org/taxa/558840-Acanthocercus-annectans and https://www.inaturalist.org/taxa/31437-Acanthocercus-cyanogaster and https://www.inaturalist.org/taxa/93047-Acanthocercus-guentherpetersi and https://www.inaturalist.org/taxa/31436-Acanthocercus-phillipsii).
What emerges is a biogeographical and ecological anomaly: what seems to be a gap in Nature, and an 'empty niche'.
Compounding this puzzle are other, ecologically-related lizards.
I refer to genus Cordylus (https://www.inaturalist.org/observations?place_id=any&subview=table&taxon_id=33024&view=species), which belongs to a different family, viz. Cordylidae.
Elsewhere in South Africa, rocky terrain is co-inhabited by Agama and Cordylus (https://www.inaturalist.org/journal/milewski/86270-a-comparison-of-life-history-strategies-between-two-rock-dependent-lizards-coexisting-in-the-cape-point-area-of-south-africa#).
This raises the possibility that Cordylus might have usurped the habitat and niche of Agama in Great Limpopo Transfrontier Park.
However this seems not to be the case.
One species of Cordylus (https://www.inaturalist.org/taxa/33034-Cordylus-jonesii) has been recorded in Kruger National Park. However, as in the case of A. atricollis, it is restricted to trees, not extending to rocks.
A species in a closely-related genus (https://www.inaturalist.org/taxa/33046-Smaug-warreni) is associated with the southern part of the Lebombo range (which extends to Mkuze in Zululand), and is rock-dwelling. However, it seems to be scarce, and has not been recorded in most of Kruger National Park.
Two rock-dwelling spp. of another, mainly tropical, genus in the same family occur in the relevant ecosystems. I refer to
- Platysaurus intermedius (https://www.inaturalist.org/taxa/33102-Platysaurus-intermedius) in the Great Limpopo Transfrontier Park, and
- Platysaurus lebomboensis (https://www.inaturalist.org/taxa/33098-Platysaurus-lebomboensis) in the southern Lebombo range.
However, their occurrence hardly explains the absence of rock-dwelling agamids. This is because
- elsewhere in southern Africa, Platysaurus is known to be sympatric with rock-dwelling Agama (https://www.inaturalist.org/taxa/540115-Platysaurus-attenboroughi and https://www.inaturalist.org/taxa/33099-Platysaurus-capensis),
- most spp. of Platysaurus are smaller-bodied than rock-dwelling spp. of Agama, and
- the two genera differ considerably in diet.
Can any reader explain why rock-dwelling agamids, despite being so widespread, common, and phylogenetically diverse in Africa, have failed to utilise what seems to be suitable terrain in and around Kruger National Park?
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Shift
MYRMECOPHAGY
https://www.tandfonline.com/doi/abs/10.1080/15627020.2023.2231974
Rocks are not just all rocks. Crucial to rocky terrain is either suitable and large-enough cracks to crawl safely into, or to hide underneath. Dolerite gives quite a different crack profile to sandstone, with granites intermediate and shales finer cracks. Similarly, hilly terrain has far more habitat than open plains for rock-dwellers, and some geologies (e.g. sandstone) are almost invariably rocky (although not always cracky).
Do any of the Agamas or Cordylus show any documented geological preferences? - presumably Geckos do?
I dont empathize enough with lizards, but I would imagine that a rocky habitat would be totally different lizard habitat with or without trees, both with regard to predators (esp sit-and-wait birds) and temperature profiles. May the Lowveld not just be too tree-ey for rock dwellers even with some emergent inselbergs and torrs?
It is indeed possible that the rocky terrain in Kruger National Park is not complex enough to provide refuge-crevices for agamas.
However, a) the Serengeti ecosystem has similarly 'smooth' inselbergs (https://www.amusingplanet.com/2014/09/the-kopjes-of-serengeti.html), yet Agama mwanzae is abundant there, b) Agama kirkii occupies similar inselbergs in Zimbabwe** (excluding Gonarhezou National Park), which are additionally relatively wooded because some fall within the miombo biome, and c) Agama atra extends to minimally rocky locations such as West Coast National Park (https://www.inaturalist.org/observations/84005550), De Hoop Nature Reserve, and Agulhas National Park.
** In and near Matobo National Park (https://en.wikipedia.org/wiki/Matobo_National_Park) alone, in southwestern Zimbabwe, there are 18 observations of Agama kirkii (https://www.inaturalist.org/observations?place_id=48794&subview=table&taxon_id=31136).
West Coast national park has both limestone and granite domes and slabs.
Both Agulhas National Park and De Hoop have huge areas of limestone and sandstone rocks filled with cracks, crevices, faults and holes, as well as boulders and slabs.
Matobo or Matopos Hills " ... has eroded to produce smooth "whaleback dwalas" and broken kopjes, strewn with boulders and interspersed with thickets of vegetation " - i.e. the boulder areas are often devoid of trees and account for a sizeable proportion of the area.
Observations of rock-dwelling Agama in ecosystems similar to Kruger National Park (all refer to Agama kirkii):
near Save Valley, Zimbabwe:
https://www.inaturalist.org/observations/180912091
north of Tuli Block, Zimbabwe:
https://www.inaturalist.org/observations/68292179
Hwange, Zimbabwe:
https://www.inaturalist.org/observations/10005132
near Mana Pools, Zimbabwe:
https://www.inaturalist.org/observations/161375852
Luangwa, Zambia:
https://www.inaturalist.org/observations/97602267
Majete, Malawi:
https://www.inaturalist.org/observations/83823994
Liwonde, Malawi:
https://www.inaturalist.org/observations/51719848
https://www.herpconbio.org/Volume_17/Issue_1/Telford_etal_2022.pdf
The relevance of the last to Kruger?
No particular relevance, just a reference of interest on the general topic of the biogeography of lizards in South Africa...
Rockhares (Leporidae: Pronolagus, https://www.inaturalist.org/observations?place_id=any&subview=table&taxon_id=43156&view=species) constitute another rupicolous lineage that is oddly scarce and undocumented in Great Limpopo Transfrontier Park.
Rockhares (4 spp.) coexist with rock-dwelling Agama spp. over most of southern Africa.
Pronolagus randensis occurs on rocky outcrops in the extreme north of Kruger National Park (https://koedoe.co.za/index.php/koedoe/article/view/467/477 and file:///C:/Users/Antoni%20Milewski/Downloads/795-3552-1-PB.pdf).
Pronolagus has also been recorded a) at Legogote (https://af.wikipedia.org/wiki/Legogote and https://www.sahistory.org.za/place/legogote-mountain-region-mpumalanga), near White River (https://en.wikipedia.org/wiki/White_River,_Mpumalanga), and b) in the form of bones excavated at an archaeological site in the central part of Kruger National Park (https://koedoe.co.za/index.php/koedoe/article/view/467/477).
Pronolagus crassicaudatus occurs in the Lebombo range in Eswatini (Roberts 1951).
However, no species of rockhare has been recorded in most of the rocky terrain in Kruger National Park, particularly a) the part of the Lebombo range that falls within the Park, and b) the Malelane Mountain Bushveld.
What this means is that rockhares are oddly limited in the same ecosystem as I have circumscribed in this Post for rock-dwelling agamas. These mammals are not categorically absent as in the case of the lizards, but the tendency seems analogous.
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