Journal archives for July 2022

July 01, 2022

Searsia (Anacardiaceae) in perspective, part 1

The genus Searsia of the Anacardiaceae is extremely important in the vegetation of the part of South Africa corresponding climatically to the southwest of Western Australia.

This genus

  • straddles the divide between vegetation dominated by pyrophiles and vegetation dominated by pyrofuges,
  • tends not to dominate any particular stand of vegetation (although tending to be common where it occurs),
  • has complex patterns w.r.t. fruit type and spinescence,
  • has no counterparts in eastern or northern Australia, and
  • has previously been confused taxonomically, in Asia and even in northern Australia, with Rhus, which is actually quite different.

So, the absence of Searsia from southwestern Australia is a minor question relative to the major question of the absence of this genus from Australasia generally. But the latter question is salient simply because Searsia is overall such an important genus in South Africa, across such a wide spectrum of vegetation types.
It is odd that Searsia disappears so abruptly once one leaves southern Africa. However, the genus persists into Mediterranean North Africa and the Middle East in the form of at least one species, namely S. pentaphylla, see . And there is at least one species in India, namely S. mysorensis.
Searsia in the southwestern Cape of South Africa is always recognisable by its trifoliate leaves, but otherwise varies greatly in life-form. It ranges from small shrubs to trees large enough to form forests, from non-spinescent to grossly stem-spinescent, from fleshy-fruited (most spp.) to non fleshy-fruited (e.g. S. tomentosa, S. incisa and S. angustifolia, common on the Cape Peninsula in scrub intermediate between pyrophilic and pyrofugic), and from fully evergreen (never really sclerophyllous) to semi-deciduous. One species (S. pyroides) even has toxin-laden spines.
In pyrofugic scrub/thicket near the littoral in the vicinity of Cape Town, the main spp. are S. glauca, S. crenata and S. laevigata. Two of these spp. have rigid branchwork representing a kind of semi-spinescence.
In fynbos, including the borders of pyrofugic forest patches, a main species is S. lucida. This is fully evergreen and completely non-spinescent, and has fruits that never quite seem to ripen to anything clearly describable as zoochorous.

However, there are also various minor spp. such as S. rosmarinifolia, S. dentata and S. longispina, again tending to hug the less fire-prone sites in fynbos such as boulderfields. Searsia longispina is more stem-spinescent than any common shrub in southwestern Australia.
In the semi-arid Karoo, Searsia undulata is a conspicuous shrub, because it tends to be larger than the predominant cover of small shrubs of Asteraceae. It is semi-spinescent in the sense of having rigid branchwork, and is evergreen but non-sclerophyllous. It is typically bird-dispersed for the genus, with small rather dull fruits that certainly have fruit-pulp and certainly ripen, but tend to dry out and become hollow as they ripen.
In the pyrofugic forest in the Knysna area, an important species is S. chirindensis, which can have long, stout stem-spines at least where broken by megaherbivores.
In drainage lines in the Karoo, immediately adjacent to the area of mediterranean climate, S. lancea is a prominent large shrub or small tree, and is evergreen.
The relationship between Searsia and pyrofugic vegetation is rather nebulous. However, what remains true is that in ‘pure’ fynbos, i.e. the most pyrophilic vegetation in southwestern South Africa, Searsia tends to be either absent or present only as occasional plants of non-spinescent, evergreen, non-zoochorous spp.

The genus Searsia does not really lend itself to features such as serotiny, bradyspory, or sclerophylly. It is never leaf-spinescent; and, even though it is ‘resinous’, I know of no species that is particularly flammable – the function of the ‘resin’ being defence against folivores.
Any biologist thoroughly familiar with the vegetation of the southwestern Cape of South Africa, if told that there is analogous vegetation in southwestern Australia, would surely assume that there must be some lookalike for Searsia in the Australian area, whether phylogenetically related or evolutionarily convergent. But they would be wrong.

This failure of southwestern Australia – and indeed the rest of Australia – to produce anything that I could call a counterpart to the various searsias (which are in many ways so diverse that they make for a remarkably plastic genus) is for me one of the most surprising aspects of the intercontinental comparison. It was among the first anomalies I noticed when I came to Australia in 1977.
In summary:
Searsia is a nebulous genus in various ways, tending to defy generalisation in its ecological role. It seems to play the part of a ‘filler-in’ in the vegetation, in many ways. Furthermore, one can never really call it a dominant in any vegetation type – although it approaches this in the case of

  • S. glauca near the littoral, where it tolerates wind-shearing well, or
  • S. undulata or S. lancea in moister microsites in Karoo, which are the tallest plants in the community.

Searsia is certainly shaped by large ungulates. However, it does not becomes downright spinescent without its branches being actually broken.

Searsia can best be thought of as a genus of ‘transitional scrub’. It is easy to imagine this or a lookalike shrub being common in places in southwestern Australia, including the relatively nutrient-rich microsites, protected from intense wildfires, in the Geraldton area, or some of the protected swales along the coast and on coastal islands.
At a biogeographical level, it is true to say that Searsia is a kind of ‘balancer’. On one hand it is true that there is a remarkable overlap between Australia and southern Africa in the sense that both landmasses contain Canthium, Carissa, Diospyros, Grewia, Flueggia, Solanum, Dioscorea, etc. etc. However, on the other hand the two landmasses are worlds apart when it comes to Searsia.

Searsia does occur in ‘rainforest’ (e.g. in the form of S. chirindensis) and it also occurs in pyrofugic vegetation of drier sorts in the form of the glauca-undulata group, plus the phreatophytic S. lancea.

No species of Searsia has fruit that remains succulent until separation from the plant by fruit-eaters, as seen in confamilials such as Sclerocarya caffra. In the Rhus/Malosma/Searsia complex, the fruits vary, according to genus and species, in the adherence of endo- and mesocarp, and resinousness vs waxiness,

Generally speaking, the spherical drupes of certain spp., e.g. Searsia dentata, Searsia crenata, Searsia chirindensis, and Searsia pyroides, are eaten by birds and monkeys while still fleshy. By contrast, the non-spherical, discoid fruits of e.g. Searsia undulata, Searsia burchellii, and Searsia lancea, are eaten by these animals also when 'post-ripe, i.e. when the exocarp of has dried without wrinkling (Rodney Moffett, who has taxonomically revised Rhus sensu lato, and is an author of, in email).

In Searsia incisa, the exocarp tends to crack. There is no suture as such, and some drupes simply crack spontaneously (owing to weathering or physical pressure) due to the fruit being relatively large, the stone small, and the exocarp thin. In his species one also finds some infructescences with the drupes so tightly packed that, when the individual fruits separate, it may give the impression of dehiscence.

Also see

to be continued in

Posted on July 01, 2022 02:39 AM by milewski milewski | 1 comment | Leave a comment

An anecdote of successful fighting against a predator by Grant's gazelle

(writing in progress)
In the book “Nature’s Paradise” by Jen and Des Bartlett (1967), most of a page (p. 139) is devoted to an anecdote which I have no reason to doubt but which I find hard to understand.
The location was Serengeti, early afternoon 17 Jan. 1958. A colour film (movie) was made of the entire sequence of actions (which I presume no longer exists, 64 years later).
A mature male anubis baboon was spotted starting to eat infant Grant’s gazelle (Nanger granti).
Suddenly the mother gazelle charged it, chasing it to a tree of Vachellia xanthophloea, one of just three in this open area, which the baboon climbed.
For some time the baboon was kept in the tree by the loitering gazelle, despite several attempts by the baboon to descend.
When the gazelle lost interest enough to wander a short distance, the baboon descended quickly and dashed for another tree nearby, being chased by the gazelle so rapidly that she seemed within inches of stabbing him.
This conflict continued for three hours, from one tree to another among the three trees. Meanwhile the rest of the group of baboons moved out of sight. The interaction was such that the baboon was clearly scared of the gazelle and the gazelle seems to hold back from actually stabbing the baboon although it seemed close enough to do so on occasion. I infer that the two adversaries never actually touched each other.
When by chance her movements brought the mother gazelle back to the carcase of its infant, she looked at without moving for perhaps 30 seconds, as if seeing for the first time that it was dead.
She then seemed to lose her anger and walked off slowly towards conspecifics without a backward glance, while the baboon ran rapidly in the opposite direction (note that he did not proceed back to the carcase to resume his meal).
From this I learn that the horns of the female Grant’s gazelle, although rather spindly and irregular-looking, are taken seriously by even an adversary as powerful as a male anubis baboon. Females of Grant’s gazelle weighs about 35 kg, compared with about 30 kg for males of the anubis baboon, so the adversaries were well-matched in body mass and both had dangerous weapons.

It is easy to imagine the baboon killing the gazelle despite the weapons of the latter, along the same lines that baboons often kill dogs (perhaps including individual dogs of about 35 kg). The fact that the mother gazelle tried to defend her infant does not surprise me, but the fact that the baboon took her so seriously does surprise me because it implies that his assessment was that she was more formidable than a dog. This assessment surprises me because females of Grant’s gazelle seldom use their horns and are not practised fighters; as far as I know they never spar intraspecifically, and it’s easy to imagine an individual female of Grant’s gazelle living its whole life without ever harming another animal with its horns or even touching a conspecific with its horns.

I do regard the horns of both male and female Grant’s gazelle as ‘idle weapons’ although those of the female are sometimes – as here – used to intimidate predators in situations where infants are threatened. Nobody would expect the male Grant’s gazelle to defend any infant and I doubt that any male gazelle uses its horns in anger on any predator. So I cannot really envisage a female gazelle deliberately stabbing a predator, least of all determinedly and repeatedly as would an animal that had evolved weapons for more than idle purposes. A male bushbuck yes, but a female Grant’s gazelle no.
Since males of baboons practise frequently in their macho ‘canine-fencing’, they are surely adept at dodging blows and thrusting and parrying, something that I can’t envisage the gazelle being a match for.
So the main puzzles in this anecdote are that

  • the male baboon viewed a mere gazelle, about its own size, as a match for its own strength and teeth, and
  • other members of the group of the anubis baboon did not join the fray, even if only to rob the prey; if they had joined the fray, it seems likely that the gazelle would have retired in fear from the collective threat of several individuals of baboons, potentially several males.

If this anecdote has involved a male bushbuck defending itself, I could accept the confidence of the antelope although I would not expect the conflict to last longer than the time taken to tree the baboon once.
Nanger sp.:

The following video clip and photo may help to explain why I find Des Bartlett’s anecdote so puzzling.

They show that adult male individual of the anubis baboon hardly takes the threat seriously from an adult female individual of Thomson’s gazelle (Eudorcas thomsoni), despite the fact that this gazelle does possess short sharp horns. The baboon does take evasive action, but it by no means abandons the infant it is eating. Adult females of Thomson’s gazelle weigh about 18 kg, compared with about 35 kg in the case of Grant’s gazelle, so there is a two-fold difference in body mass involved.
See video at
Papio anubis & Eudorcas sp.:

(writing in progress)

Posted on July 01, 2022 08:06 AM by milewski milewski | 0 comments | Leave a comment

How do baboons use their eyes in social communication?

(writing in progress)
I have chosen the photos below, to illustrate the patterns in one species, the olive baboon (Papio anubis, and The chacma baboon (P. ursinus), not shown here, is similar.
Baboons differ from humans in that they generally hide their eye movements.

Humans reveal our direction of gaze, and we can read these movements by virtue of the shifting proportions of dark and pale in an eyeball exposing the whitish sclera. The system is different in baboons, which do use their eyes to communicate, but in a crude way and mainly by means of the closed eyelids, something missing in the repertoire of humans.

Humans read another’s intentions with great subtlety by means of eye movements. Baboons are morphologically adapted not to do so. Humans share information by means of their eyes; baboons withhold information by means of their eyes.
Baboons differ from macaques (Macaca spp.), which do accentuate the gaze by means of scleral tone, albeit in a simper way than in humans and only for restricted messages.

Although baboons and macaques are convergent in that both include the most terrestrial of monkeys on their continents, they are not convergent in the use of their eyes for social communication. Baboons have specialised on eye-hiding while macaques have specialised on eye-display (with more variation within the genus Macaca than within Papio/Theropithecus/Mandrillus.
From a human point of view, the eyes of baboons seem inscrutable/obscure/beady/shadowed. In another Post, I show photos of Papio hamadryas (which has flesh-coloured facial skin) and Theropithecus gelada (which has an extraordinary lip-flipping display). Although the various genera and species of baboons differ greatly in various ways, they all seem to have the same approach to the display of the eyes: all hide their eye movements as much as possible, presumably to avoid divulging their intentions.
Please follow the captions below, which use selected photos to convey the limited complexity in the appearance of the eyes in adults and juveniles (but not infants) of the olive baboon.
The following photo is unusual in showing the irides brightly against the dark facial skin. Usually the eyes are harder to see than this. And even in this view, please note the lack of any visible sclera, the part of the eyeball that is so conspicuously whitish in all humans, including black-skinned human races.

The following close-up of the eyes shows that the sclera of the olive baboon is actually dark-pigmented, more or less matching the darkness of the facial skin. This effectively hides eye movements by reducing tonal contrast. The same is true for chimpanzees and gorillas.

The following again shows that the sclera is dark in the olive baboon, where it would be pale in all humans. Although the direction in which this individual is looking is clear in such close-up, well-illuminated view, in normal views it would be hard for one baboon to see exactly where another is looking.
The following photo shows that, although the irides are somewhat brighter-hued than the facial skin, the tone (in terms of dark vs pale) is similar to the facial skin, and in the absence of exposure of a white sclera the whole eye is rather hidden.
The following photo shows that, although the upper eyelids are pale (grey) in the olive baboon, this is not obvious when this surface is shaded, which it tends to be owing to the brow-ridges.
The following photo shows that the upper eyelids are rather pale in the olive baboon, but this is not normally conspicuous (in contrast to e.g. the long-tailed macaque Macaca fascicularis).

The following photo shows that in intraspecific confrontation the olive baboon does not stare, but instead partly closes the eyes, signalling by means of its pale upper eyelids. Although this is common among monkey spp., baboons have reduced the repertoire of eye displays to this display alone, which is a crude system of signalling.

The following photo is revealing because it shows that the olive baboon can do something with its brows beyond what humans can do: it can contract the brows far back above the eyes, stretching the pale upper eyelids to the point that they actually cover the brow-ridges, greatly expanding the pale flash. This was even more spectacularly illustrated in my email on the gelada Theropithecus, which really goes in for this ‘pale eyebrow’ display in conjunction with lip-flipping. Spectacular but still a relatively crude signal.

The following photo shows that the pale of the upper eyelids is not normally displayed when the animal raises its eyes to survey the sky or the treetops.

The following photo shows that the passive-aggressive fang-baring display by males of the olive baboon involves shutting the eyes to show the pale upper eyelids. This is, in a sense, a ‘false-stare’, but the meaning it conveys is simple and crude.
The following photo shows that the pale upper eyelids in the olive baboon are found in all age/sex classes beyond infancy. and and

The following photo of the olive baboon in Uganda shows unusually extensive pale upper eyelids. This is perhaps a geographical variation? However, once again the shading by the brow-ridges ensures that the pale is not conspicuous unless the eyes are closed.

The following photo shows once again that the visible part of the sclera, in a sideways glance, is dark enough in its pigmentation to hide the direction of gaze. This is not true in various spp. of Macaca, in which there is a panel of whitish that accentuates a sideways glance/gaze.
The following photo, and its enlargement, show how even an extreme sideways glance is hidden in the olive baboon where it would be obvious in humans and certain species of macaques. This is because of the pigmentation of the sclera adjacent to the iris. Chimpanzees and gorillas show the same pattern. At any distance, an observer cannot easily see the direction of movement of the eyes.,_2009).jpg
The following photo shows that, in some individuals of the olive baboon, there is a macaque-like exposure of a pale surface of the sclera. This is exceptional in the olive baboon although normal in some spp. of macaques.

The following ‘toddler’ of the olive baboon still has its unpigmented sclera (as at birth), because the scleral pigmentation sets in only when the distinctively infantile black-and-pink colouration of the face is lost.

The eyelid/brow is also used in courtship – in chacmas at least - where males and females use rapid blinking in the direction of a potential mate.

(writing in progress)

Posted on July 01, 2022 10:19 AM by milewski milewski | 9 comments | Leave a comment

Juniperus communis, a widespread example of foliar spinescence in the Northern Hemisphere

(writing in progress)
Several genera of coniferous plants are foliar-spinescent, such as

In most of the foliar-spinescent spp., only the ‘juvenile’ (including recrudescent) foliage is spinescent.
Juniperus communis ( and is a particularly strong example of foliar spinescence in conifers because

  • it is extremely widespread, being described as the most widespread sp. of woody plant on Earth,
  • it never attains adult/mature foliage even when it reaches its maximum height of up to 16 m, and
  • the spinescent leaves can be conspicuous in a way that suggests aposematic colouration (warning colouration) directed at large herbivores.

Please see .
In North America and Eurasia alike, J. communis inhabits mainly the boreal ecosystem (, which is the biome of coniferous forest on permafrost. It ranges right up to the Arctic Circle (, where trees give way to tundra ( and J. communis itself adopts a nearly prostrate growth-form contrasting with the nearly cypress-like shape adopted in milder climates.

In Europe it extends into the mediterranean climate (reaching as far south as Greece, Sicily, and southern Spain) to a degree not seen in North America. Juniperus communis does occur in California, but only in small areas of the Sierra Nevada (, a mountain range too high to conform strictly with the mediterranean-type climate.
In several photos of J. communis, the leaves appear conspicuously pale, which has puzzled me. The pale surface seems to be on the underside (ventral surface) of the leaf, which is flanked by the rolled-under, green margins of the leaf (

It is not odd for semi-sclerophyllous small-leafed plants in mediterranean-type climates to have leaves with rolled edges, or pale-coloured undersides, features which are usually explained in terms of drought-tolerance and protection of the stomata in the interests of conserving water in transpiration.

However, what is odd is that in several photos the pale surface seems to be uppermost on many of the leaves, indicating that the leaves have been twisted somewhat at the petiole, turning them in a sense ‘upside down’ ( and

Since the leaves are prickly ( and, it is tempting to think that this sort of display of dark/pale contrast (in which the leaves look like pale needles against a dark background) is a form of warning colouration to browsing herbivores, such as deer, which would forage on the plants.
The following ( illustrates the distribution of J. communis. The species spans Eurasia and North America above certain latitudes and altitudes.

Nowhere does this species reach the latitudes of kwongan ( in Australia, which (except possibly for Tasmania, is warmer in winter than any habitat of J. communis.
The following shows that J. communis can attain a growth-form similar to that of a typical cypress ( and However, as I understand it the species retains its ‘juvenile’, spinescent foliage even when its crown attains this mature form, above the height of even the moose (Alces alces,

The following shows the nearly prostrate growth-form of J. communis in cold and windy climates, at high latitudes and/or altitudes. I do not know if the leaves are more spinescent in this growth-form than in that shown above.

The following shows J. communis in vegetation otherwise dominated by the erica Calluna vulgaris ( This sort of vegetation is a ‘heathland’ comparable with kwongan although growing in a colder climate and being far simpler floristically.
The following again shows the coexistence of J. communis with a heathy stratum, the conifer adopting a cypress-like growth-form but apparently retaining ‘pungent’-tipped leaves right to the top of its crown, which in this instance I estimate to be perhaps 5 m high.
The following two photos show J. communis in a shrubby growth-form: and

The following three photos show the conspicuous paleness of the ‘ventral’ surfaces of the spinescent leaves, which are here for some reason turned upwards instead of being invisible in ventral orientation as expected. I suggest that this functions as warning colouration.

(writing in progress)

Posted on July 01, 2022 09:04 PM by milewski milewski | 14 comments | Leave a comment

July 02, 2022

Why do baboons have long muzzles?

@tonyrebelo @dejong @jeremygilmore @ludwig_muller @alexanderr @beartracker

When one thinks of baboons in even the most cursory or superficial way, something that stands out is their long muzzles ( and and

Baboons (in the loose sense, including Mandrillus, and are the only 'higher primates' with long muzzles.
What is the adaptive value of long muzzles in baboons?
One possible answer is the deployment of the extremely-developed canines, for self-defence against predators. This hardly makes sense, because

Another possible answer is for foraging.

Canids have long muzzles to facilitate biting prey, and ungulates have long muzzles to reach into foliage and to compensate for the length of the limbs, which tends to distance the mouth from the herbaceous stratum. Bears have long muzzles for both reasons.

However, there is nothing about the foraging methods of baboons that makes it adaptive to use the muzzle to reach into anything. Instead it is the hands that are used to bring food to the mouth.
A third possible answer is for chewing.

It is noteworthy that, unlike most other mammals with long muzzles, baboons lack a diastema ( and, the toothrows instead being continuous from front to back. So, it is possible that baboons eat food so hard or fibrous that a particularly long row of cheek-teeth is needed to chew this food sufficiently.

Baboons do indeed eat grass - a fibrous and abrasive food - to a greater extent than any other primates, and their dentition is also tough and massive enough rapidly to crack hard objects such as acacia seeds.

Perhaps a fairly satisfactory explanation emerges if one combines the chewing by both sexes with the deployment of canines by males.

However, detracting from this is the fact that the gelada (Theropithecus, – which is the species most specialised for grazing – has a shorter, not longer, muzzle than those of baboons (including Mandrillus). Also, grazing and seed-cracking would hardly explain why the muzzle is sexually dimorphic, being noticeably longer in males than in females in baboons and Mandrillus. The two sexes, after all, have similar diets.
To summarise the explanation so far:
Baboons (including Mandrillus and Theropithecus) have long muzzles mainly because they rely on tough, fibrous foods, and this length is further extended in males because of the use of the canines - which is mainly intraspecific, for masculine rivalry, and includes ‘fencing’ with the canines as a mode of fighting.
I have pointed out, in previous Posts (, that baboons have hidden eyes, particularly compared with humans.

Whereas humans display the eyes in various ways (eyebrow hair, extensive exposure of the sclera, paleness of the sclera in contrast to either iris colour or skin colour, or both), baboons obscure the gaze by means of pigmentation of the sclera and shading of the orbits by superciliary ridges. Instead of displaying the eyeballs themselves, baboons display the pale upper eyelids by blinking (this can be either friendly or antagonistic depending on context).
The crucial observation is that, the hiding of the eyes notwithstanding, the direction of gaze is a powerful factor in social interactions in baboons.

See Fagot and Deruelle (2002, and and

Baboons are extremely sensitive to being gazed at directly, and take this as a sign of aggression. The eyes seem to be adapted to be inconspicuous (apart from the displaying of the closed eyelids). And a feature of baboons is that they remain extremely observant of each other as individuals, without looking at each other directly; they have extremely attentive peripheral vision and manage to observe each other directly by means of furtive and fleeting glances rather than outright staring.

For baboons it is crucial to keep an eye on each other socially while not looking at each other directly as we humans normally do. Baboons want the information but direct gazing is taken as offensive.
Hans Kummer ( relates his own experience, which is fascinating in the insight it gives into the psychology of baboons.

Kummer was studying the hamadryas baboon (Papio hamadryas, in remote Ethiopia, by sitting right in among the habituated animals. He was sometimes at risk of being attacked by mature males as the result of some misunderstanding in which he became accidentally implicated in some social faux pas. What he observed was that if one pretended not to notice the angry stare of the mature male individual in question, and its fang-baring, eyelid-flashing yawns, and just looked somewhere else in a relaxed way while busying oneself normally, this would invariably ‘switch off’ the aggression. The masculine anger of the hamadryas baboon would be thus appeased.

The psychology of baboons seems odd to us, because honesty is punished. The fact that Kummer’s ignorance/naivety was completely a pretence was obviously far less provocative to the angry baboon that it would have been for Kummer simply to look back in a questioning and friendly way in a peacemaking attempt - which would have provoked attack. Baboons value feigned innocence more than they value honest and empathetic interaction, and the biology of the eyes reflects this amoral value-system (see
This is where the long muzzle may matter.

It occurs to me that the sheer length of the muzzle gives this part of the face considerable value as a pointer to the direction of gaze. All that one individual has to do to see where the other is looking is to glance quickly sideways at how its whole face is oriented, something that is so obvious from its long muzzle that the information can be gleaned even by peripheral vision. So, in a sense we can see that the long muzzle of baboons goes with, i.e. is consistent with, the hiding of the eyeballs by means of dark sclera and shading by the ridge between forehead and orbits.

No baboon wants to look much at the eyes of its kind, because this is usually a fearful experience. However, every baboon wants to know where important individuals are looking, because the mind of baboons is acutely and continually tuned in to keeping track of everyone’s status, via watching and analysing the interactions of every individual in its group.
So, is it possible that, in a strange way, the social complexity of baboons goes with their facial shape in profile? The muzzles are, at least in part and at least as a corollary function, pointers to gaze. This is part of the sly indirectness with which baboons juggle/balance the use of gaze as a clue to attention, and the use of gaze as a ‘weapon’.
It may be hard for a human to consider this, because our minds work differently.

We do have an element of ‘what are you staring at, asshole’ about us when it comes to strangers. However, by and large – at least among those we know and more or less trust - we value and respect an honest and direct gaze according to our basic value of exchange of technical information, explanation, and emotional candour as part of an empathetic mindset in which honesty is rewarded rather than punished. In us, the ambivalence of the direct gaze is heavily weighted towards valuing this as ‘honest’, ‘good’, and ‘moral’, with the aggressive aspect as a minor part, whereas it is the other way around in baboons.

Hence, I suggest that the extremely projecting muzzle of baboons and flatter-than-flat face of the modern human go together with the differences in the eyes (as well as the specialisation of the dentition, explained above).
Supporting the idea presented above is the dual difference between macaques (Macaca, and baboons.

Macaques have showier eyeballs than do baboons ( and and and and and, depending on the species.

Furthermore, the eyes are not as shaded by the superciliary ridges as is the case in baboons.

Accordingly, no macaque has a muzzle as long as that of any baboon. Even the superficially baboon-like macaques of Sulawesi have ventrally elongated faces rather than horizontally elongated faces ( and and

So, if one looks at the whole group of baboons and macaques, it does seem that long horizontally-oriented muzzles correlate with ‘hidden eyes’ (except for the pale upper eyelids, which occur in both baboons and macaques

Posted on July 02, 2022 03:44 AM by milewski milewski | 3 comments | Leave a comment

Ontogenetic change in scleral pigmentation in the bonnet macaque

In a previous Post, we have seen that baboons, in general have eyes that are inconspicuous owing to their colouration.

This generalisation does not apply to macaques (Macaca spp.), which are the closest counterparts to baboons in Eurasia. The eyes of macaques tend to be somewhat conspicuous, owing to various features of small-scale colouration on the sclera, the eyelids, and the adjacent parts of the face.

The species I examine here is the bonnet macaque (Macaca radiata, of southern India.

Two facts emerge in this species of monkey.

Firstly, scleral pigmentation is absent at birth despite being characteristic of the species.

Secondly, despite the tightness of the eyelids, the scleral pigmentation is so dark that it confers the most salient feature of the face of all ages and sexes (except the infant): dark-accentuated eyes that appear to stare. 

The following shows clearly that the sclera adjacent to the iris in infants of the bonnet macaque is unpigmented. 
Ditto but with a hint of pigmentation starting on the lateral (as opposed to medial) side of the iris: 

Pigmentation appears in the sclera of the bonnet macaque in young juveniles, as shown by the following.

In young juveniles of the bonnet macaque, the eyes already assume a staring aspect accentuated by the dark sclera immediately adjacent to the iris, as shown in the following. Please note that the iris in the bonnet macaque is not particularly dark, and not dark enough to confer a stark appearance to the eyes in the absence of its dark scleral definition.

The following of a juvenile of the bonnet macaque shows the pigmented sclera. 

In adults of the bonnet macaque, there is a hint of pale eyelids, further accentuating the dark-rimmed stare. However, this is not as well-developed as in e.g. Macaca fascicularis.

In adults of the bonnet macaque, the facial skin remains pale enough that the dark sclera gives the eyes a dark-rimmed stare. However, the eyelids encompass the eyeballs too tightly to show as much of the sclera as in humans.

The following, of an adult female of the bonnet macaque, glancing sideways, shows clearly that the sclera is dark-pigmented, with no incidence of pale scleral exposure as seen in the infants above. Most of the sclera is presumably white (as in all mammals), but none of the white surface seems ever to be exposed in this species in adulthood, partly owing to the breadth of the pigmented ring adjacent to the iris and partly owing to the tightness of the eyelids.

Mature females of the bonnet macaque sometimes have a blush on the flesh-coloured bare skin of the face. However, this is not dark enough to cancel the effect of the dark sclera in accentuating the stare. 

The following shows a warning expression in mature females of the bonnet macaque. Although the face is as dark in this blushed mother as in any member of the species, the eyes still tend to stand out as dark-rimmed items in an accentuated stare, in which any paleness of the upper eyelids plays a negligible role (in contrast to M. fascicularis, in which the pale eyelids greatly accentuate the stare in conjunction with the dark sclera). 

The following shows an adult male of the bonnet macaque, proving that the dark sclera occurs likewise in the male, and that the male like the female has an essentially dark-rimmed accentuation of the stare on a pale face.

The following again shows an adult male of the bonnet macaque. Please note the tightness of the eyelids, showing little of the sclera. What little is evident of the sclera is all dark-pigmented. In this view there is no noticeable pale display of the upper eyelids.

In the following self-asserting expression, an adult male of the bonnet macaque does seem to be showing pale eyelids, but the main impression remains of dark-rimmed eyes on an overall pale face.

The following confirms the difference between mother and infant, w.r.t. the pigmentation of the sclera.,1243282988,4/stock-photo-bonnet-macaque-nursing-in-bandipur-national-park-30886564.jpg

The following (which states bonnet macaque but could possibly be closely related toque macaque in Sri Lanka, in view of the dark ear pinnae) confirms the overall aspect of the face in the bonnet macaque: dark-rimmed eyes staring from an essentially pale face. What this photo-series does is to establish beyond doubt that in this species the pigmentation of the sclera is absent at birth, but develops early in life, remaining as the most conspicuous feature of the face, overall.

A pattern possibly overlooked by all primatologists in the past is as follows.

The eyelids themselves, immediately adjacent to the eyeball, develop dark pigmentation at the same time (early in life), when the dark scleral pigmentation appears. If one looks closely at this photo-series, one can see this clearly in several photos. In the infant, the eyelids are flesh-coloured. However, in juveniles and adults, the lower eyelid in particular, between the eyelash line and the eyeball, shows a dark pigmentation, possibly no broader than 1 mm – but sufficient to accentuate the stare in conjunction with the dark sclera.

This is a noteworthy observation because

  • I have never previously read of any mammal with a pale (flesh-coloured) face but dark-pigmentation on the edge of the eyelids, and
  • in the normal stare, the eyelids marginally overlap the cornea.

The latter point means that, in the normal stare, the sclera is only visible laterally and medially to the iris, and the dorsal and ventral edges of the iris would lack accentuation were it not for the narrow dark rim provided by the eyelids themselves.

This eyelid darkening is extremely narrow but quite discernible. It is a case of natural ‘make-up’, adding to the already known paleness of the upper eyelid in various spp. of macaques.

Posted on July 02, 2022 10:29 AM by milewski milewski | 3 comments | Leave a comment

Towards a comparison of North and South American aboriginals w.r.t. riding the feral horse on treeless grassland

(writing in progress) 
There is a remarkable parallel between North and South America in the introduction of the domestic horse, its subsequent population explosion as a feral species on treeless grassland, and the adoption of the horse by the aboriginal people.
The best counterparts in North America, for the indigenous peoples who waged guerilla warfare on the gauchos in Buenos Aires Province, were the Comanche. Other tribes were also involved, but the Comanches epitomised the way the horse transformed the lives of native Americans in the Northern Hemisphere, and delayed their subjugation by European invaders.
Please see below for a map showing the area inhabited by the Comanche. This area comprises about half of Texas plus parts of adjoining states to the northwest. I estimate the range of the Comanche to be about 600,000 square km. In this area, at their heyday in the 1700’s or early 1800’s, the Comanche numbered about 45 thousand persons, living partly on the bison (Bison bison), and doing so to an unprecedented degree among native Americans.
Buenos Aires Province is only about 300,000 square km, so is a smaller area. But both areas contain hundreds of thousands of square km of treeless grassland, on which the domestic horse bred rapidly between about 1500 (when introduced by the Spanish) and about 1650. It is estimated that the total population of the domestic horse, in feral form, in Comanche territory reached a maximum of about two million, i.e. more than all the migratory ungulates in the whole Serengeti ecosystem today.
The Comanche tribe in fact only came into existence because of this advent of the domestic horse. Before 1550, the ancestors of the Comanche were Shoshone, living farther north near the Rocky Mountains in Wyoming. I don’t know which tribe lived in the treeless grassland of northwestern Texas and adjoining states, but I suspect that they were sparse and poor, being unable to hunt the bison systematically although I’m sure they scavenged the bison whenever possible. Whoever they were, these aboriginal Americans probably lived not much more complicated lives than those of the Pampas aboriginals of the time. One difference was that the North American aboriginals of the treeless grassland used the domestic dog as a beast of burden (I’ll find out more but I think they had wheel-less sleds used to drag possessions across the ground, particularly in winter when there was snow). I don’t know if the original inhabitants of the Pampas even kept the domestic dog – and possibly nobody ever will know this.
Both original, primitive tribes were to be swept into oblivion by the increase in the horse and the advent of other tribes, originating on mountain ranges to the northwest (North America) or southwest (South America) which could rapidly adapt to the new opportunities presented by the horse.
By virtue of the horse, the Comanches came into existence in 1650-1700, and came to utilize the bison in a way never previously possible. The whole culture was revolutionised, leading to the invention of e.g. the tepee (made from buffalo hides).
Although other tribes also came to utilise the horse in North America, it was the Comanche who did so first, pioneering the whole enterprise for themselves and gaining such power that it was only in the late 1800’s that they were finally overcome by ‘civilisation’ – actually in the form of contagious diseases rather than direct outgunning by the Europeans. During their period of control of their range the Comanche took many captives from the Mexicans, ‘Americans’ and surrounding indigenous tribes, whom they sold into slavery. They actually systematically enslaved white people, i.e. the pioneers who passed through or tried to settle in Comanche land.
Please see below for a map of Comanche lands, which were about as extensive as Texas although only partly in Texas. Also see various other maps putting the size of Texas, and thus the size of Comanche lands, in context geographically in various parts of the world, including West Africa whence you’ve just returned. As you can see, Niger is more extensive than Texas (and former Comanche lands) but the sizes are comparable.
The bottom line is that I see the Comanche as the Northern Hemisphere counterparts for the Mapuche of South America. Both groups moved into the areas of interest (Texas in the USA and the Pampas in Argentina) about the same time, and both held sway for remarkably long, terrorising Europeans who dared to enter their lands. Both owed their new-found power to the feral horse, which transformed lands once occupied by poor hunter-gatherers to lands occupied by warlike people who actually matched the firepower of European guns and ammunition by means of their great mobility as equestrians. The main difference is that the main food of the Comanche – namely Bison bison – was a native bovine, whereas the main food of the Mapuche was a feral bost. So the Argentinian situation is the more extreme and remarkable in that the Pampas was not as remote as the lands northwest of Texas, and the whole way of life of the Mapuche was owing to European introductions of livestock – not only the horse but also a feral ecological counterpart for the wild bison of North America.

(writing in progress)

Posted on July 02, 2022 08:57 PM by milewski milewski | 0 comments | Leave a comment

Ecology of the pappusgrasses Schmidtia and Enneapogon in southern Africa and Australia

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Mokala National Park ( in South Africa is ecologically interesting because it occurs at the junction of three major vegetation types, viz. treeless grassland, savanna, and low shrubland. In other words, this small national park straddles the Highveld (, the Kalahari (, and the Karoo (

A particularly abundant grass in Mokala National Park, particularly on sandy substrates, is Schmidtia pappophoroides (

See and and

This is puzzling, because S. pappophoroides is not particularly typical of any of the three biomes referred to above.

How, then, can this abundance be interpreted in ecological terms?

Schmidtia is a pappusgrass ( As such, it is related to Enneapogon - which occurs in Mokala National Park but also has a cosmopolitan distribution (

We can best find clues to the ecology of pappusgrasses in Australia, because Enneapogon

  • is fully indigenous to Australia, and diverse here in number of species, and
  • has been particularly well-studied on this continent.

Beadle (1981, and gives information on Enneapogon in Australia, on pp. 540-541. This suggests that this genus can best be thought of as successional, and suited to times/places where only limited biomass can be supported.
Enneapogon occurs in ‘ephemeral grasslands’ on sandy soils in Australia. The vegetation is always woodlands or shrublands, not treeless grasslands. The grasses are called ephemeral because, even if they are technically perennials, they tend to be killed by drought after only a few years.
Here are further facts that I gleaned from Beadle (1981):
In dry parts of tropical Australia, woodlands of Eucalyptus terminalis and E. argillacea occur on slopes, with mean rainfall 300-600mm per year. Here, the grasses restricted to annuals, leaving much bare ground. The soils are not particularly sandy. Enneapogon is patchily common in these woodlands, the spp. being E. pallidus, E. avenaceus, and E. polyphyllus. Sporobolus is always co-dominant. Other genera of grasses occurring in these communities are Tragus, Chloris, Dactyloctenium, Aristida, and Brachyachne.
Over large areas of the arid zone of Australia (formerly dominated by Acacia or Atriplex/Maireana), the vegetation has been degraded by pastoralism. As a result Enneapogon avenaceus has become common, functioning effectively as an annual. It now commonly covers large areas as monospecific stands, only 20 cm high. Beadle shows this in a photo, Fig. 20.19, which is obviously a form of treeless grassland, although not fully natural. “Even if the tussocks of Enneapogon do not grow during the second year, the dead tussocks remain and, in these, either new plants of E. avenaceus or another annual species become established.”
Furthermore, Beadle (1981) informs us that:

  • In the mulga lands, Enneapogon (e.g. summer-growing E. avenaceus) are restricted to hills with rock exposures. Sandy patches of mulga have hummock grasses (Triodia, instead.
  • Enneapogon avenaceus also occurs in eucalypt woodlands in the arid zone, on loams, where it is just one of various grasses (Aristida, Danthonia, Eragrostis, Neurachne, Paspalidium, Stipa).
  • Enneapogon avenaceus also penetrates areas characterised by the saltbush Atriplex vesicaria on gilgaied clay soil, although it is not dominant here. Ditto for saline/sodic sands bearing the shrub Maireana pyramidata (which vaguely resembles 'ganna' in southern Africa,
  • On some claypans, the dominant grass is the tall Eragrostis australasica, with E. avenaceus forming a peripheral zone, in this case mildly sodic rather than saline.
  • Right across the arid zone of Australia, one finds narrow belts of clay, bearing the grass Eragrostis xerophila. Sometimes Enneapogon planifolius is one of the associated grasses, along with Chloris, Dicanthium, Eragrostis (other spp.), Panicum, Sporobolus and Triraphis.

What emerges is that Enneapogon

  • occurs widely, here and there, in semi-arid Australia,
  • tolerates sodicity and even perhaps salinity, and ranges from sand to clay and stony shallow soils,
  • is always naturally associated with shrubs or trees, but is capable of achieving a rather unnatural commonness on degraded surfaces where the woody plants have largely died off, and
  • does not grow with hummock grasses, being mutually exclusive with them.

The edaphic and climatic distinctions between hummock grasses (which are fire-prone) and Enneapogon are rather subtle within Australia.

Enneapogon obviously prefers somewhat nutrient-richer soil than that typically associated with hummock grasses, with a corresponding difference in soil texture. However, the main point about Enneapogon is that it is essentially a grass of somewhat degraded sites, i.e. it is only competitive where larger plants have been removed.

It would be simplistic to describe Enneapogon as an annual. Instead, it is best thought of as a small, short-lived, insubstantial grass which cannot compete with more substantial plants. It is one of various smallish tussocks forming an ‘understorey’ to woody vegetation (typically Acacia but also halophytic amaranths) in semi-arid Australia.

It is only where the competitors have been removed that Enneapogon can approach dominance, and this is not strictly natural.
This may help us to understand the abundance of a related pappusgrass, in South Africa. The implication is that part of the reason for the dominance of Schmidtia pappophoroides in Mokala National Park is disturbance - originally by livestock, and now by dense populations of wild grazers.

Australia is the continent of wildfire. Fire is unlikely in mulga ( and saltbush vegetation, except on sandy patches suited to Triodia = hummock grasses. Although many grasses in Australia benefit from fire, nothing in Beadle’s description hints at any role of fire w.r.t. Enneapogon.

Beadle does not state this as such, but I infer that fire-prone vegetation is mutually exclusive with Enneapogon in Australia, as I think it is on other continents. I see this as more important than any distinction in substrate-preference between hummock grasses on the one hand and Enneapogon on the other.

The main aspects that I have learned about Enneapogon are as follows:

  • These are small, annual-like grasses, superficially looking as if they might spring up after fire, in a kind of successional stage as the main fire-prone plants recover. However, I doubt this.
  • As effectively an 'annual', Enneapogon is not a post-fire successional grass. Instead it characterises categories of disturbance other than fire, i.e. usually overgrazing.
  • Some of the features of Enneapogon are somewhat specialised for herbivory (in a positive sense, i.e. supportive to grazers instead of being inimical). This is because it manages to regenerate from seed within the previous small tussock. That is to say, it regenerates in its own infrastructure, and thus achieves some of the continuity and reliability of a lawn grass, without having to produce the same mat-form and rhizomes as a lawn - which would be impractical in such a dry climate and where woody competition is so strong.

Enneapogon, Schmidtia, and other pappusgrasses are not fire-weeds, not lawn-formers, and not unpalatable ‘scab-plants’ that keep herbivores off until cover has been restored. Instead, they are adapted to a regime of herbivory where the following conditions apply:

  • no grass can be really vigorous because the dominant plants are woody plants, and
  • there is enough grazing to ensure that the biomass of grass is kept sparse.

In conclusion for now:

The inference is that it is the herbivores in Mokala National Park that are responsible for keeping pappusgrasses dominant. Were the herbivores to be removed or drastically reduced, I suspect that S. pappophoroides would become scarce. I am unsure what would replace it in savanna of Vachellia erioloba ( on Kalahari sand. Perhaps a coarse species of Stipagrostis?

Posted on July 02, 2022 09:15 PM by milewski milewski | 1 comment | Leave a comment

July 03, 2022

Introducing pappusgrasses

In the subfamily Chloridoideae ( of the family Poaceae, there is a tribe called Pappophoreae. The common name of this tribe is pappusgrasses. There is nothing weedy- or vulgar-looking about these grasses, yet they are widespread.

Pappusgrasses are insubstantial-looking. However, when one gets an eye for them, they turn out to be important grasses in semi-arid ecosystems on at least four continents – that is, functionally, if not in terms of sheer biomass.
In the strict sense, pappusgrasses consist of just three genera: Schmidtia, Cottea and Enneapogon.

Pappophorum (American and also called pappusgrass, is similar, but probably not particularly closely related.
Pappusgrasses, at the level of tribe, genus and species, are remarkably widespread.

Cottea ( is monospecific and restricted to the semi-arid USA.

Schmidtia occurs in Africa and Pakistan, and the two species common in South Africa, viz. the annual S. kalahariensis and the perennial S. pappophoroides, both occur also in the Sahel. They are not naturally restricted to southern Africa. So, there are situations north of the equator in which Schmidtia - which South Africans tend to associate with Kalahari sands - occurs with presumably equivalent commonness.

The largest genus of pappusgrasses in the strict sense is Enneapogon. Its species present as local grasses, but the genus and some of its species are actually widespread.

For example, Enneapogon desvauxii (formerly called E. brachystachyus or brachystachys in South Africa) occurs commonly in the Karoo, where it is regarded as exologically typical and an important part of the diet of the springbok (Antidorcas marsupialis, However, the same species occurs naturally also in America, as far south as Chile and Argentina.

For some reason, pappusgrasses seem absent from Patagonia, which surprises me because that might seem to be idea habitat for them. Perhaps they are restricted to warm climates?

About 16 spp. of Enneapogon occur in Australia, where they are an important part of the diet of the red kangaroo just as their congeners are important to gazelles in Africa and presumably Asia.

If I recall correctly, Ken Tinley’s explanation of the former treks of the springbok has to do with Enneapogon and the periodic usurping of this resource by irruptive locusts in the Karoo. Discussing Enneapogon over the years with Ken, I always had the sense that this was a genus of grasses which, if not restricted to southern Africa, was closely associated with indigenous grazers here. I now see this differently, i.e. with a wider perspective.
Summarising so far, for emphasis:
What passes off as a typical Karoo grass, associated with the springbok, is actually a cosmopolitan grass (putting aside the details of which species is which), abundant and widespread also in Australia.

All pappusgrasses seem similar in growth-form: perennial or annual, too flimsy to be called tussocks, but on the other hand only weakly able to spread vegetatively. I would not call them lawn-forming. The seeding culms are fairly short (< 50cm and usually < 30cm). All seem to dry off in the dry season. These grasses are unsuitable for bulk-and-roughage grazers, but are particularly suitable for gazelles (and hartebeest/tsessebe) and kangaroos, and presumably guanaco in South America and pronghorn/hare in North America.

As far as I know, all pappusgrasses are palatable and easily digestible. However, that they are not substantial enough to form a staple for most grazers.

Some species have a peculiar mode of regeneration, in which the small ‘tussock’ appears to be perennial because greens re-emerge from the dry plant. On closer examination, what has happened is that the plant has died (i.e. it is actually annual) but the seed-heads have a special design in which they remain lodged at ground level within the plant, and then germinate in-situ instead of being dispersed.

Some qualify as cleistogamous (, somewhat like the peanut (Arachis hypogaea, However, the fruit is not actually borne underground, as far as I know.

I am unsure if this self-pollination and 'anti-dispersal' is, at least in part, an adaptation to grazing, i.e. some kind of alternative to lawn-formation. However, it does seem to mean that herbivores can keep the sward short (eating whatever seed-heads emerge above the leaves) without destroying the regenerative capacity of these apparently flimsy plants.
In a sense, what this hints at is that pappusgrasses tend to be something analogous with a lawn - but suited to semi-arid conditions, and never achieving the kind of conspicuousness that most ecologists notice. They seem to be a mere tissue (low, sparse, and usually dried-out looking), but may actually be quite productive for grazers overall.
It seems obvious that pappusgrasses have little to do with fire. Not only do they tend to be eaten/decomposed before becoming flammable, but they grow with limited biomass, unable to carry fire even in drought.
The important inference of all this is as follows:

Australia is the only continent on which both pappusgrasses and hummock grasses are locally dominant (in separate areas). Therefore, it is to Australia that we should look for the environmental distinctions (particularly edaphic differences) between hummock grasslands (which accumulate biomass and are adapted to wildfire) and pappusgrasslands (which support herbivores and do not benefit from fire).

Australia may show that the main difference is based on soil texture (hummock grasses more on sands). However, the vegetation on loams in e.g. the Pilbara is complex, so this needs further investigation.

Enneapogon desvauxii:

Distribution of Enneapogon desvauxii in southern Africa:

Distribution of Enneapogon desvauxii in North America:

Examples of the distribution of Enneapogon spp. in Australia, showing about a dozen of the ?16 spp.:

Global distribution of genus Enneapogon:

Cottea pappophoroides, southwestern USA:

Posted on July 03, 2022 01:35 AM by milewski milewski | 0 comments | Leave a comment

Why do grasses become seasonally dormant in winter despite the continued availability of water and sunlight?

(writing in progress)

The Highveld clearly turns brown in winter, with the dormancy, and above-ground drying-out, of the grasses. However, this phenological pattern cannot be ultimately explained by either desiccation or frost.

Throughout the dry season in the Highveld, soils remained wet in bottomlands. The dry season is in winter, but temperatures are not extreme, and then days remain sunny. Ambient temperatures in the Highveld during winter remain above those of the peak growing season in the tundra (Bonan and Shugart, 1989),

This indicates that the winter dormancy of the dominant grasses is a phenological tactic rather than a reflection of absolute physiological constraints imposed by air temperature.

suggesting that interrupted photosynthesis is part of a life-history strategy of grasses as opposed to being an inevitable consequence of the seasonal drought and cold in the Highveld.

In seasonal marshes in the Highveld, the topsoil in vleis remained moist in the middle of winter, when all the grasses are dry and brown. What can be seen repeatedly, in the treeless grasslands of southern Africa, are situations in which winter dormancy in grasses cannot be explained by the seasonal drought of the winter season.

just because no rain falls in winter; the dormancy of grasses at vlei edges proves this because the topsoils remain moist there.
So what could cause the dormancy? Another possible cause is the seasonal cold. However, this too makes little sense, because grasses actually grow in the Arctic summer at temperatures lower than those prevailing in the Highveld winter. With appropriate adaptation, grasses should be able to grow all winter long in the Highveld because there is plenty of moisture in the soils in that season, and grasses elsewhere on Earth are known to grow despite the cold.
One example taxon: Arctic cottongrasses (Cyperaceae: Eriophorum spp.) are known to be able to maintain growth and positive photosynthesis at temperatures as low as –4 degrees Celsius, i.e. 4 degrees below freezing!
Perhaps fire is involved, but perhaps there is a World War 1 trench warfare ‘mentality’ or ‘tactic’ at play here. The grasses/sedges are perhaps resting to save their reserves for the intense battle that plays out in spring and summer when conditions are optimal for growth (and war against competing entities). I am suggesting here that the battle between grasses and trees is not necessarily a continual one; there are peaks and troughs in the battle; and the plants need to have sufficient energy available for the peaks. I am suggesting further that grasses/sedges would lose condition, so to speak, if they grew in winter, relative to grasses/sedges that ‘choose’ not to.
When grasses in the Highveld go dormant in winter, what they are doing could either be

  • suffering an environmental limitation, or
  • exhibiting a strategic choice.

Most naturalists in South Africa, if asked to explain the seasonal behaviour of the vegetation, would assume that environmental limitation is the correct answer.

However, ifnstrategic choice is the right answer, what are the costs and benefits of the choice to enter seasonal dormancy despite the possibility of continuing growth? Why do grasses not just grow throughout the year in the Highveld (obviously, more slowly in winter than in summer, but growing nonetheless in the dry and cold season, which is far warmer than the growing season of Arctic grasses)?
This is where it gets conceptually interesting. Just as the dominance of herbaceous plants means that the tree niche is empty here, so the dominance of winter-dormant herbaceous plants means that the ‘Arctic grass’ niche is empty here.
Put a different way: the fact that Highveld does not support native trees, despite their being ample soil, water, and nutrients for trees here, means that what prevails is a plant community that chooses to fall short of its maximum potential biomass/woodiness/height. Something else is instead maximised, possibly overall rate of catabolism, or biological energy intensity. And the fact that Highveld does not support winter-growing grasses, despite their being more than enough sunshine, ample water (at least in bottomlands), and adequate temperatures (cold but not prohibitively so for grasses as a life-form), means that what prevails is a plant community that chooses to fall short of its maximum potential period of activity. In the niche hyperspace, evolutionary/adaptive decisions have been taken to ‘switch off’ or ‘decline’ certain opportunities despite the resources being available for exploiting those opportunities. The option of growing into tall, woody plants has been declined, and this growth-form has been ‘switched off’; and the option of growing all year long has been declined, and the phenological behaviour of growth during winter has been ‘switched off’ as well.
My point: by this thinking the Highveld is doubly ‘self-restrained’: it has opted to forgo a whole ‘spatial stratum’ of plants, namely trees and tall shrubs (which are elsewhere deemed to be the superior competitors for light), and it has opted to forgo a whole ‘temporal stratum’ of plants, namely winter-growing herbaceous plants (or even trees for that matter).
Now, the theoretical juice in this is as follows.
If opting for treelessness means that the grassland achieves greater power without trees than with trees, and if this is because the most powerful way of using the available resources is expressed by small plants as opposed to big ones, then could it be that the winter dormancy of the grassland also somehow achieves greater power than a theoretical grassland that grows all year long? If so, how exactly does a winter-dormant grass ‘overpower’ a theoretical competitor in the form of an ‘Arctic grass’? What exactly is the payoff in desisting from growth in winter, such that this payoff is more profitable than the alternative payoff of continuing to photosynthesise and grow? And what is the resource parameter in which this payoff should be measured?
One possible line of thought: by choosing winter dormancy, the grasses promote seasonal fire, which pays off by .....?

(writing in progress)

Posted on July 03, 2022 03:40 AM by milewski milewski | 1 comment | Leave a comment