The reptile fauna of the southwestern tip of Africa, part 2: differences from the Stanford-Agulhas area

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...continued from https://www.inaturalist.org/journal/milewski/86215-the-reptile-fauna-of-the-southwestern-tip-of-africa-part-1-checklist-of-families-and-species-in-the-cape-point-area#

Cape Point is of biogeographical interest because it is at the southwestern tip of the African continent.

However, it is ecologically similar to a nearby section of the coast, viz. the strip between the southernmost tip of the African continent, at Cape Agulhas (https://en.wikipedia.org/wiki/Cape_Agulhas), and the town of Stanford (https://en.wikipedia.org/wiki/Stanford,_South_Africa). The main town within this strip is Gansbaai (https://en.wikipedia.org/wiki/Gansbaai).

The area in question has been called 'Strandveld' (https://en.wikipedia.org/wiki/Strandveld). However, I will instead call it 'the Stanford-Agulhas area', because 'strandveld' is ambiguous in several ways.

The Cape Point area and the Stanford-Agulhas area are separated by False Bay (https://en.wikipedia.org/wiki/False_Bay) and the Hottentots Holland mountains (https://en.wikipedia.org/wiki/Hottentots_Holland_Mountains).

However, either area might qualify for the description 'southwestern tip of Africa'.

Importantly, the Cape Point area and the Stanford-Agulhas area share

• a mediterranean-type climate,
• hills of sandstone, with fynbos vegetation (https://en.wikipedia.org/wiki/Fynbos),
• sandplains of nutrient-poor acidic sand, covered in fynbos of different composition,
• calcareous sands, derived from the beaches but now largely vegetated with strandveld (https://en.wikipedia.org/wiki/Cape_Flats_Dune_Strandveld), and,
• scattered marshes.

Furthermore, the two areas were connected, as a contiguous coastal strip, for most of the Pleistocene (https://www.semanticscholar.org/paper/Pleistocene-sea-level-fluctuations-and-human-on-the-Compton/fcc0e6f0da4a6785815a71d6ca7b69d2619c93a2/figure/2 and https://www.semanticscholar.org/paper/Pleistocene-sea-level-fluctuations-and-human-on-the-Compton/fcc0e6f0da4a6785815a71d6ca7b69d2619c93a2/figure/3 and https://www.sciencedirect.com/science/article/abs/pii/S0277379119309199 and https://www.sciencedirect.com/science/article/abs/pii/S0277379119301179 and https://en.wikipedia.org/wiki/Agulhas_Bank and https://www.sciencedirect.com/journal/quaternary-science-reviews/vol/235/suppl/C).

Based on this similarity, we might expect the reptile faunas of these two areas to be similar.

So, it surprised me to find the following differences.

PSEUDOXYRHOPHIIDAE

Amplorhinus multimaculatus (https://www.inaturalist.org/observations/118826654 and https://www.inaturalist.org/observations/118825697) is associated with marshes.

It occurs in the Stanford-Agulhas area (https://www.inaturalist.org/observations/10890965 and https://www.inaturalist.org/observations/65422587). However, it has not yet been recorded in the Cape Point area, in iNaturalist.

This may possibly be corrected in future, because an unpublished report by Andre Mader (Cadet Nature Conservation Officer), written on 16 July 1996, lists the species as having been recorded in the former Cape of Good Hope Nature Reserve.

PSAMMOPHIIDAE

Psammophis notostictus (https://reptile-database.reptarium.cz/species?genus=Psammophis&species=notostictus and https://www.tyroneping.co.za/snakes-southern-africa/psammophis-notostictus-karoo-sand-snake/) has been observed in the Cape Point area, in iNaturalist, An unpublished report by Andre Mader (Cadet Nature Conservation Officer), written on 16 July 1996, also lists the species as having been recorded in the former Cape of Good Hope Nature Reserve.

Also see https://www.inaturalist.org/observations/21049715 and https://www.inaturalist.org/observations/20996653.

However, it has not been observed in the Stanford-Agulhas area, in iNaturalist. This is despite a record at one locality near Agulhas, in the distribution map in Fitzsimons (https://www.amazon.com/Snakes-southern-Africa-Vivian-FitzSimons/dp/B0006CG1MS).

ELAPIDAE

Hemachatus haemachatus (https://www.inaturalist.org/taxa/30652-Hemachatus-haemachatus) occurs in the Stanford-Agulhas area (https://www.inaturalist.org/observations/95017386 and https://www.inaturalist.org/observations/99011820 and https://www.inaturalist.org/observations/139420078 and https://www.inaturalist.org/observations/129426683), but not in the Cape Point area.

VIPERIDAE

In both areas, a large-bodied adder, viz. Bitis arietans, is abundant, with a smaller congener also occurring.

However, what is odd is that Bitis atropos occurs on the Cape Peninsula, whereas Bitis armata occurs in the Stanford-Agulhas area (https://www.inaturalist.org/taxa/95801-Bitis-armata).

CORDYLIDAE

The two areas have different species of the rupicolous lizard, Cordylus.

Furthermore, these species differ significantly in adaptive colouration (https://zslpublications.onlinelibrary.wiley.com/doi/abs/10.1111/j.1469-7998.2009.00581.x). That on the Cape Peninsula is dark, whereas that in the Stanford-Agulhas area is pale (https://www.inaturalist.org/observations/149945283 and https://www.inaturalist.org/observations/70188286 and https://www.inaturalist.org/observations/141877806 and https://www.inaturalist.org/observations/46368002 and https://www.inaturalist.org/observations/66781529).

Pseudocordylus microlepidotus (https://www.inaturalist.org/observations/104286079) has been recorded in the Stanford-Agulhas area, but not in the Cape Point area.

These differences are consistent with a general pattern among Cordylidae, in which many species occur across eastern and southern Africa, each one restricted to a relatively small area of distribution. This contrasts with African Agamidae, in which A. atra spans a wide variety of ecosystems from fynbos through karoo, thicket, and highveld, to subtropical and even tropical savanna, and from sea level to an altitude of 2,200 m.

GEKKONIDAE

Chondrodactylus bibronii has been observed adjacent to the Cape Point area, in iNaruralist. However, it has not been recorded in the Stanford-Agulhas area.

Lygodactylus capensis has expanded its range, over the last few decades, into the southwestern Cape (https://www.researchgate.net/figure/Quarter-Degree-Grid-Cells-QDGCs-timescale-map-of-Lygodactylus-capensis-distribution-in_fig1_333968582).

It is now common on the Cape Peninsula, but has yet to be observed in the Stanford-Agulhas area. Since it reached Hermanus (https://en.wikipedia.org/wiki/Hermanus) this year (https://www.inaturalist.org/observations/170452071), it will probably reach Stanford within the next decade.

Pachydactylus geitjie (https://www.inaturalist.org/taxa/34148-Pachydactylus-geitje), is widespread in the southwestern Cape. However, for some reason it has not been recorded in the Cape Point area.

LACERTIIDAE

Meroles knoxii has frequently been observed in the Cape Point area, in iNaturalist. Its absence from the Stanford-Agulhas area is perhaps the single most striking difference in the reptile faunas of the two areas.

Tropidosaura gularis has been observed in the Cape Point area, in iNaturalist. However, it is absent from the Stanford-Agulhas area.

Also see 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#

Posted on October 26, 2023 07:20 PM by milewski