Thought-provoking observations from a brief visit to the Karoo Desert National Botanical Garden and Paarl Mountain Botanic Garden, October 2001
@tonyrebelo @jeremygilmore @hamishrobertson
On 20 October 2001, I visited the Karoo Desert Botanical Garden (https://en.wikipedia.org/wiki/Karoo_Desert_National_Botanical_Garden) and Paarl Mountain Botanic Garden (https://www.youtube.com/watch?v=h5rTCSop3-g), and also stopped at the head of Bainskloof Pass (https://en.wikipedia.org/wiki/Bainskloof_Pass) on the way. I had three companions.
The following are selected observations on plants and animals, which I still find noteworthy after two decades.
KAROO DESERT BOTANICAL GARDEN
I was struck with the sheer size of Albuca canadensis (https://www.inaturalist.org/taxa/522608-Albuca-canadensis and
https://www.pacificbulbsociety.org/pbswiki/index.php/Albuca_canadensis).
This was large-bodied for a geophyte, robust-looking, and common in karoid vegetation on stony slopes, and in transitional vegetation between karoo and renosterveld. The plants of A. canadensis were about 1 m high, the stalks and leaves still green, and the capsules ripe.
I found Septulina glauca (https://www.inaturalist.org/taxa/119511-Septulina-glauca) to be abundant on Euclea undulata, Searsia undulata (https://www.inaturalist.org/observations/18689587), and particularly Searsia incisa (https://www.inaturalist.org/observations/11049753). It was also present on Carissa haematocarpa (https://www.inaturalist.org/taxa/528768-Carissa-haematocarpa).
This mistletoe was conspicuous. Its foliage was green, except for 'autumn-yellow' leaves, and the stems were brittle.
What I found significant about this mistletoe was its large body-size and the greenness of its foliage, considering that it is a parasitic plant.
I observed a Viscum on Dodonaea and S. undulata. This mistletoe was leafless, and dark, dull green. It shared the host-plant, S. undulata, with S. glauca.
'Bushclumps' were present, about 2.5 m high and about 10 m in diameter. These consisted of intertwined Euclea undulata, Searsia undulata, Septulina glauca, Asparagus retrofractus? (https://www.inaturalist.org/taxa/495846-Asparagus-retrofractus), and others.
Searsia incisa formed 'hedge-hummocks', 2 m high and 5 m wide, each large and dense enough to hide a whole group of humans.
Searsia undulata was not spinescent. However, its rigid configuration of stems can obviously function to block the stripping of foliage by large folivores (https://www.inaturalist.org/observations/145088817 and https://www.inaturalist.org/observations/96698984 and https://www.inaturalist.org/observations/93584409).
I ate the fruits of S. incisa, which were abundant at the time. These fruits are technically fleshy, according to the syndrome of endozoochory. However, the surface of the fruits was brownish-felty (https://www.inaturalist.org/observations/140039365 and https://www.inaturalist.org/observations/141243223 and https://www.inaturalist.org/observations/140223421), and the taste was 'resinous'. I found the same puzzle as I have found with Searsia generally, which is that the fruits never seem to ripen in a conventional sense, and they are not necessarily conspicuous even when 'ripe'.
Small heuweltjies (https://en.wikipedia.org/wiki/Heuweltjie) were present in the slopes. These were so small that one might doubt that they qualify as heuweltjies. However, they were clearly marked by the associated plants. These were the grey-green Pteronja incana, plus clumps of the taller shrub Euclea undulata, different from the matrix of indifferently dull-green karoid shrublets.
Pteronia incana (https://www.inaturalist.org/taxa/524304-Pteronia-incana) is associated with heuweltjies, here.
At the picnic site, I observed a bumble/carpenter bee (black and yellow), attending flowers of Grewia occidentalis (https://www.inaturalist.org/taxa/334567-Grewia-occidentalis).
I observed Messor capensis (https://www.inaturalist.org/taxa/426213-Messor-capensis), as follows.
A hole in the ground had fruits of S. undulata littered at entrance, plus the burr-fruits of clover. The workers were carrying whitish nymphs (as large-bodied as the workers), and perching 20 cm above the ground on a mesemb plant. I formed the impression that this was to expose the nymphs to sunlight. These ants seemed oddly confident and fearless, because I and a companion approached them closely to examine their behaviour, kneeling at the hole and speaking at normal volume, and they did not react.
I observed an individual of Chersina angulata (https://www.inaturalist.org/taxa/40021-Chersina-angulata) at midday, on a mown and irrigated lawn of Pennisetum clandestinum. It was eating the leaflets of a clover, with prostrate growth-form. This indicated that this tortoise preferred a herbaceous legume over green grass-blades.
BAINSKLOOF PASS
I observed an individual of Duberria lutrix (https://www.inaturalist.org/taxa/30326-Duberria-lutrix), at 15h00 in sunny, calm weather. It was basking on a dirt road among the weekend-cottages at the head of Bainskoof Pass. I.e. the environment was anthropogenic, rather than natural.
Three individuals of Canis familiaris (small-bodied breeds) were present in full view nearby, on a verandah/porch. They seemed oblivious to the presence of this snake, either because they had not seen it, or because they had already investigated it but associated it with the well-known deterrent odour. A failure of the dogs to observe this snake seemed to be ruled out by the fact that we, several human individuals, attended the snake, in plain view nearby. I inferred that the dogs simply chose to ignore our flagging of the presence of the snake.
This individual of D. lutrix was so calm and confident that it allowed us to step right over it, without fleeing or reacting.
PAARL MOUNTAIN BOTANIC GARDEN
I observed Microhodotermes viator (https://www.inaturalist.org/taxa/568761-Microhodotermes-viator), active on the surface at 17h00 in warm, sunny, calm weather. The vegetation was fully mature fynbos (overdue for wildfire), with e.g. Protea and Watsonia, on granite-derived loam.
I observed a hive of M. viator, bisected by excavation for the construction of a footpath. In its intact state, this hive had been buried shallowly on this granite-derived loamy slope. I estimated the original volume if the intact hive to have been more than 20 litres.
I watched a mini-swarm at work, scurrying around and cutting material from green shrubs. I observed a hole on the footpath. The workers were collecting twigs about 2.5 cm long, green shoots, green fallen leaves, and dry (dry) fallen leaves. They were making little piles of this litter and freshly-cut material, including the shoot-tips, cut by the insects in the green state, of Aspalathus. Two small samples of the collected material, that I observed, comprised >50% and about 40% green material.
Present at the same site was Trinervitermes trinervoides (https://www.inaturalist.org/taxa/567385-Trinervitermes-trinervoides) and its mounds.
DISCUSSION
A companion on this excursion, Anne Gray (a contributor to 'Kite', the journal of the Tygerberg Bird Club, https://www.tygerbergbirdclub.org/), told me the following about what was identified as Microhodotermes viator.
The location was the coastal road near Yzerfontein/Darling Road intersection (https://en.wikipedia.org/wiki/R315_(South_Africa)), about 80 km north of Cape Town, in September 2001. The vegetation was strandveld (intact, as opposed to usurped by introduced Acacia).
Anne observed the swarming of termite alates. About 25 individuals of Milvus migrans (https://www.inaturalist.org/taxa/5268-Milvus-migrans) were swirling around on the wing, catching slates in their talons. They ate the insects while flying, by passing the items from foot to mouth.
The timing suggests that M. migrans had recently arrived from Europe.
Also present, higher in the air, were Apus melba (https://www.inaturalist.org/taxa/144634-Apus-melba), Apus caffer (https://www.inaturalist.org/taxa/6619-Apus-caffer), and Apus affinis (https://www.inaturalist.org/taxa/6612-Apus-affinis). These swifts were also presumably eating the slates.
Anne observed a rain of the insects' wings, descending to the ground.
What do all these observations, made on a day's excursion from Cape Town in spring, add up to?
The southwestern Cape of South Africa is generally regarded as nutrient-poor. This is true, but within the Fynbos Biome are enclaves of nutrient-richer ecosystems, in which there is remarkable evidence of biological productivity.
In the enclave of karoo vegetation that I visited, I formed the impression that herbivory by large mammals was a normal function in this ecosystem.
The abundance of mistletoes seemed to reflect the lack of herbivory by Taurotragus oryx (https://www.inaturalist.org/observations/157165364). Would Diceros bicornis, formerly present here, also have persecuted these mistletoes?
The slow-moving snake Duberria lutrix, which is widespread in the southwestern Cape, is remarkably specialised for a diet of molluscs (https://animalia.bio/duberria-lutrix), and for effective deterrence of carnivores.
Paarl Mountain is an example of fynbos on granite, slightly nutrient-richer than similar vegetation on the more widespread substrates, sandstone and quartzite. I find it remarkable that a partly herbivorous (as opposed to detritivorous) termite operates in this ecosystem.
In the case of strandveld on the sandy coastal plain to the west, it seems that this same termite is productive enough to attract congregations of Milvus migrans, a bird usually associated with productive ecosystems.
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