Archivos de diario de enero 2022

07 de enero de 2022

Dwarf ebonies, part 1: white milkwood as symbolically but not biogeographically South African

This Post is the first in a series about the peculiar occurrence of dwarf ebonies (Sideroxylon, Euclea and Diospyros) in South Africa.

Although the wood of the white milkwood (Sideroxylon inerme, and is pale, it can be considered a form of ebony because the family Sapotaceae is closely related to the family Ebenaceae (

And although the white milkwood can reach 15 metres high, its ability to persist for centuries as a knee-high shrub (e.g. see on the windswept coast near Cape Point ( and Cape Agulhas ( means that in some sense it can be described as a dwarf ebony.

South Africans have a special symbolic regard for the white milkwood (

The reasons are that this species is:

  • the only indigenous tree persisting to the southernmost tip of Africa,
  • capable of producing an 'arborescent thicket' in windswept littoral vegetation that is otherwise merely shrubby,
  • remarkably hardy in association with dense wood, which allows it to survive urbanisation (
  • non-flammable in a region generally subject to wildfires, and
  • proclaimed an historical monument where its durability as a natural landmark has been utilised by various explorers over the last half-millennium (e.g.

However, the local appropriation of the white milkwood is at odds with its actual affinities on a global basis. Whether geographically or ecologically, Sideroxylon hardly belongs in South Africa.

This genus originated in central America ( and is today associated mainly with North America rather than Africa.

Even in the African region, the genus - and indeed the white milkwood itself - is associated as much with tropical islands in the Indian Ocean as with the temperate zone in South Africa ( and

The occurrence of Sideroxylon in South Africa is an outlier in the sense that this genus is far more speciose in the southern United States of America and the Caribbean.

For example, there are 11 indigenous species of Sideroxylon in Florida alone (e.g., the natural companions of which include Pinus ( and

The North American species are tardily deciduous (e.g., and differ ecologically in this way from the white milkwood, which is fully evergreen.

Unlike the white milkwood (, the North American species of Sideroxylon do not have particularly dense wood ( The specific gravities of the dry wood, measured in kilograms per cubic meter, are more than 1.0 in the former vs only about 0.75 in the latter.

Particularly surprising to South African naturalists may be the fact that most or all of the North American species have a capacity for spinescence (e.g. and and This contrasts categorically with the white milkwood, which is completely devoid of spines despite occurring in floras with so many spinescent species of plants that it would be hard to list them all.

The contrast is best exemplified by Sideroxylon tenax, which grows as a shrub on coastal dunes in Florida. This species parallels the white milkwood in habitat and the size of the plants, but looks so different that no South African would find it familiar ( and and

Instead, any South African naturalist first encountering Sideroxylon in North America (e.g. might be reminded of Gymnosporia (Celastraceae). Gymnosporia buxifolia ( naturally occurs side-by-side with the white milkwood at the southern tip of South Africa (e.g., making the situation all the more confusing.

The southerly extension in Africa is to some degree paralleled in South America, where Sideroxylon obtusifolium reaches the coast of Uruguay at similar latitudes to the southwestern Cape of South Africa (e.g. and

However, as far as I know the South American species does not grow in stunted form, and thus does not qualify as a dwarf ebony (Uruguayan iNaturalists please correct me if I am wrong). Nor does it extend into a mediterranean-type (winter-rainfall) climate. The growth-form of S. obtusifolium ( remains in line with Mexican species rather than converging with the white milkwood.

Given this broadened view, will South African naturalists find their appreciation of one of the botanical symbols of this country to be boosted, or deflated?

to be continued in

Publicado el enero 7, 2022 01:46 MAÑANA por milewski milewski | 20 comentarios | Deja un comentario

Dwarf ebonies, part 2: Euclea tomentosa as a substitute for the ericas missing from the Cape Flora

...continued from

A major ecological pattern in southern Africa is reduction in the height of the natural vegetation (e.g. see and,partly%20because%20of%20entanglement%20between%20cause%20and%20effect.).

Over the southwestern and central parts of South Africa, the land - whether flat or steep - seems covered by a blanket of small plants conforming to a height of 0.5-1 meters. And this applies over a range of climates and floras, from fynbos ( and strandveld ( through succulent karoo ( and Nama karoo ( to various types of treeless grassland (

This phenomenon is difficult to describe, because 'stunting' and 'dwarfing' imply a suppression in the sense of a failure of phenotypes to reach a genotypic potential.

Suppression may apply, at least in part, to e.g. the white milkwood (see my last Post), which seems limited by wind on the littoral. However, many of the species common in fynbos, karoo and highveld seem to reach their full expression as plants of waist-height or less.

The phenomenon applies to both woody and herbaceous growth-forms.

Much of the short stature of fynbos and highveld reflects a predominance of graminoids (particularly Restionaceae and Poaceae). However, there are many kinds of low shrubs as well, epitomised by genera such as Erica (Ericaceae), Phylica (Rhamnaceae) and Pteronia (Asteraceae). Furthermore, although shrubs are typically multi-stemmed, many species in southern Africa are single-stemmed, thus resembling miniaturised trees.

The relationship between the ecological pattern described above and the floristic composition of southern Africa is complex. However, a particular surprise is that certain mainly arborescent clades, which elsewhere avoid winter-rainfall or semi-arid climates, have been recruited to the Cape Flora ( in 'dwarfed' form.

One clade showing this kind of aberrance is ebonies (Ericales: Sapotaceae and Ebenaceae).

Not only have ebonies been recruited to climates avoided by them on other continents, but their typical arborescence has been reduced to shrubbiness - in some cases to the point of genotypic 'hardwiring' - in southern Africa.

The result is a category of plants peculiar to southern Africa but not yet fully investigated by botanists: dwarf ebonies. (I realise that 'dwarf' is unsatisfactory but I lack a better word.)

A typical example is the multi-stemmed shrub Euclea tomentosa ( and

This species is closely related to Euclea acutifolia ( and Euclea polyandra ( and, which show the syndrome of dwarf ebonies less clearly.

Euclea tomentosa has such lignified leaves that it is possibly the most sclerophyllous ( of all of the 768 species of Ebenaceae worldwide. Not only has it converged in leaf texture with proteas (, a family typical of mediterranean-type climates in South Africa and Australia, but it exceeds most South African members of that family in degree of sclerophylly.

At the same time, Euclea tomentosa retains the fleshy fruits typical of ebonies ( and At first sight its fruits seem incongruous with its leaves and to some degree with the vegetation types into which its clade has been recruited.

Fleshy fruits, attractive when ripe to birds and certain mammals, tend worldwide to be associated with non-sclerophyllous foliage. This trend remains clear in southern Africa (e.g. see

However, it is in Ericales that the exceptions - in which sclerophyllous plants bear fleshy fruits - tend to occur (e.g. and

This leads to a possible explanation for the recruitment of Euclea into the Cape Flora.

The family Ericaceae ( is exceptionally speciose in fynbos, leading to an impression that the southwestern Cape of South Africa is in some sense particularly representative of this family.

However, southern Africa differs from climatically similar southwestern Australia, the southwestern USA, southwestern South America, and the Mediterranean Basin in that its ericaceous flora excludes species with fleshy fruits.

Southern Africa has 753 species of Ericaeae, but all except one belong to the tribe Ericeae of the subfamily Ericoideae (,are%20cultivated%20in%20the%20region.).

So it seems that Ericaceae in the Cape Flora - however species-rich - are unusually specialised to mesic-climate, small-leafed, heathy shrubs lacking fleshy fruits, and are thus far from representative of the family as a whole.

Accordingly, one way to view Euclea - the flowers of which reveal its relatedness to heathers - is as an erica-related clade which substitutes, in southern Africa, for niches occupied elsewhere in the world by Ericaceae.

Thus, a Californian naturalist might see Euclea as a southern African version of a manzanita (Arctostaphylos, For an Australian, it might seem like a large-leafed version of various genera of Epacridoideae (

However, this does not stand up to closer scrutiny, because:

  • chaparral in California is exceptional for shrubland under winter-rainfall climates globally, in having many fire-prone, sclerophyllous shrubs with fleshy fruits (not only Arctostaphylos but also Xylococcus, Prunus, Rhamnus, Frangula, Heteromeles, Cneoridium and Rhus),
  • most of these shrubs in California are taller than dwarf ebonies,
  • the fleshy-fruited epacridoids of temperate-climate Australia occur mainly along the eastern coast, those occurring in the winter-rainfall area tending to have small, dull-hued fruits and to be restricted to the understory of woodlands with no counterparts in southern Africa, and
  • Gaultheria, one of the few relevant genera in Chile, is restricted to climates rainier than any in South Africa (located well south of the area of sbrubland called matorral).

to be continued in

Publicado el enero 7, 2022 10:16 TARDE por milewski milewski | 25 comentarios | Deja un comentario

09 de enero de 2022

Dwarf ebonies, part 3: adaptation of Diospyros to winter-rainfall and adjacent climates is unique to South Africa

...continued from

The most obvious 'dwarfing' of ebonies in southern Africa belong to the genus Euclea (see my last Post).

This is because Euclea:

  • is, unlike its cosmopolitan relative Diospyros, restricted to Africa and Arabia,
  • tends to be shrubby even in its most arborescent forms,
  • is nowhere species-richer than in southern Africa, and
  • penetrates the winter-rainfall climates of South Africa in the cases of at least nine species, four of which are completely restricted to these climates.

However, confamilial Diospyros - an exceptionally widespread and speciose genus globally ( - also participates in the syndrome of dwarf ebonies to a surprising degree. This is partly because Diospyros is incomparably more widespread and ecologically differentiated in southern Africa than on climatically analogous landmasses.

Three forms of Diospyros in South Africa qualify as dwarf ebonies:

  • Diospyros glabra in mesic fynbos throughout the southwestern Cape,
  • Diospyros austro-africana in various vegetation types from the southwestern Cape through the Great Karoo to the Highveld, and
  • Diospyros scabrida var. cordata in certain types of scrubby vegetation (other than fynbos and succulent thicket) in the Eastern Cape.

In all three cases the plants tend to be low shrubs associated with rocky substrates (see for an extreme example).

None of these species is genotypically dwarfed to the degree seen in e.g. Euclea tomentosa, E. acutifolia and E. polyandra, because all can grow several meters high where protected from wildfire.

Nor can any species of Diospyros be called sclerophyllous. Euclea becomes sclerophyllous rather than small-leafed where the whole plant is diminutive. Although the foliage is also adapted in the case of Diospyros, the leaves of dwarf ebonies of this genus are reduced in size rather than being lignified.

Diospyros glabra ( is restricted to the acidic soils of the heartland of the Cape Floristic Region (, part of which is in a winter-rainfall climate. It has penetrated fynbos (e.g. and more deeply than has any species of Euclea, and it seems to be more adapted to a regime of frequent wildfires than is any other species of dwarf ebony (e.g. see

What this means is that Diospyros glabra is the prime example of an ebony exclusive to the Cape Flora. There is no similar plant in any analogous flora of nutrient-poor, fire-prone environments elsewhere on Earth (e.g.

The only feature of D. glabra that remains incongruous with fynbos is its fleshy fruit, attractive to seed-dispersing birds ( and and and and and and and and and and

More illustrations of Diospyros glabra:

It occurred to me that Diospyros glabra might be regarded as the biogeographical and ecological equivalent of Vaccinioideae, a tribe of Ericaceae notably absent from the Cape Flora and most of Africa. However, this idea did not stand up to scrutiny.

The following illustrate Diospyros austro-africana (, which has possibly the smallest leaves of any member of this genus worldwide:

The following illustrate Diospyros scabrida var. cordata (

It is easy for South African naturalists to take for granted the floristic integration of Diospyros into various types of low vegetation. However, the oddness of this emerges from comparison with other landmasses having similar latitudes and climates.

South America is extremely different from Africa in the incidence of Diospyros. Not only is there no counterpart for dwarf ebonies, but most of South America at the latitudes of South Africa lacks Diospyros completely.

North America has a few species (e.g. see of Diospyros at the latitudes of South Africa, but none is comparable with dwarf ebonies.

In Australia there are 12 indigenous species of Diospyros, the most southerly of which ( reaches as far south as the southern tip of South Africa. However, this species is restricted to the east coast, and all but the eastern and northern 5% of Australia is naturally devoid of this genus (

Despite the many floristic links among southern continents, no species of Ebenaceae occurs in any Australian (or South American) biome comparable with those described above in South Africa.

In partial summary, all continents and subcontinents ecologically comparable with the southwestern parts of South Africa have a negligible indigenous incidence of Diospyros.

Therefore the exceptional nature of southern Africa with reference to dwarf ebonies applies to Diospyros as much as to Euclea. The intercontinental difference is categorical in the sense that dwarf ebonies are exclusively southern African.

to be continued in

Publicado el enero 9, 2022 09:36 MAÑANA por milewski milewski | 21 comentarios | Deja un comentario

12 de enero de 2022

Dwarf ebonies, part 4: tough-wooded versions of ericas, resilient from megaherbivory?

...continued from

We have seen that various species show the syndrome of dwarf ebonies to various degrees.

The following list is in decreasing order, based on degree of diminution of the whole plant and the leaves, degree of sclerophylly, degree of resilience from wildfires, degree of tolerance to nutrient-poverty, and degree of restriction to winter-rainfall climates:

Diospyros glabra (the most extreme example of a dwarf ebony)

Euclea tomentosa

Euclea acutifolia

Diospyros austro-africana

Euclea racemosa racemosa

Euclea polyandra

Euclea coriacea

Euclea scabrida var. cordata

Euclea crispa var. ovata

Sideroxylon inerme

Diospyros lycioides (if qualifying as a dwarf ebony then only at the southwestern extreme of its distribution)

Diospyros dichrophylla

We have also seen that southern Africa is globally odd in the extension of ebonies (Ericales: Ebenaceae-Sapotaceae), in evergreen and non-spinescent form, to temperate latitudes and winter-rainfall climates.

In order to understand this pattern, one should first realise that southern Africa is equally odd in its lack of most other clades of Ericales.

Any claim that southern Africa lacks Ericales may at first sound ignorant of the unrivalled number of species of Erica ( in the Cape Flora. This number, about 700, happens to be similar to the number of species of Diospyros worldwide (

However, Ericales contains many families besides Ericaceae, and there are six subfamilies of Ericaceae besides Ericoideae. All of these are absent from southern Africa except for one isolated species. I refer to Vaccinium exul (, which itself occurs in the subtropics of South Africa, nowhere near the southwestern Cape.

More particularly, what is missing from the otherwise diverse floras of fynbos, karoo, and grassland in southern Africa is any member of Ericales combining lignified or diminutive leaves with fleshy fruits attractive to seed-dispersing birds.

This allows us to reframe the dwarf ebonies as uniquely African 'erica-substitutes'.

From an adaptive viewpoint, why would such floristic substitutions have occurred in Africa?

One possible reason is that Africa has been unusual in the intensity of its regime of damage to woody plants by large mammals.

Within the African context, the Cape Floristic Region (containing mainly fynbos vegetation) is regarded as being unsuitable for large ungulates with their mainly tropical associations. However, relative to comparable ecosystems on other continents the southwestern Cape of South Africa was surprisingly rich in large mammals (

The fauna of fynbos included the largest-bodied extant land mammal (Loxodonta africana) and the largest-bodied antelope (Taurotragus oryx oryx).

This raises the possibility that exceptionally tough wood helped to make Ebenaceae-Sapotaceae better-adapted than ericas - particularly Vaccinioideae, Arbutoideae and Epacridoideae - to a regime of physical breakage.

The available information is insufficient to test this idea, partly because the mechanical properties of wood are a complicated, technical subject. However, it is intriguing that Coates Palgrave mentions the following for Diospyros lycioides: "the tough black roots rapidly blunt ploughs and other farming implements".

Publicado el enero 12, 2022 06:18 MAÑANA por milewski milewski | 5 comentarios | Deja un comentario

14 de enero de 2022

Plants eaten by the savannah elephant in the Cape Floristic Region, part 1

One of the remarkable biogeographical features of southern Africa is the incidence, until recently, of up to four species of megaherbivores (elephants, rhinos and hippos) under temperate climates - in vegetation quite different from that usually associated with Africa.

What is particularly surprising is that the largest-bodied of all, the African bush elephant (Loxodonta africana), has survived to this day near the southern tip of the continent ( and, at the latitude of Buenos Aires, Los Angeles, Sydney and Casablanca.

The diet of the African bush elephant near its southernmost limit is of interest because the location of the last survivors:

Because the remaining population has dwindled to just one individual (, no further data are likely to be collected on the diet of Loxodonta africana at this edge of its habitat.

So now seems a good time to review the various mainly anecdotal/inferential strands of information (e.g. and Milewski, A. V. (2002) Elephant diet at the edge of the Fynbos Biome, South Africa. Pachyderm 32: 29-38).

The following refers to a combination of:

  • Koen J H (1983) Seed dispersal by the Knysna elephants, South African Forestry Journal 124: 56-58,
  • my own study of 2002, based on the observations of forest guards Wilfred Oraai and Karel Maswati, and
  • Patterson G, The Knysna elephants - observations on diet, with particular focus on the eating of the medicinal mushroom Ganoderma applanatum.

FOLIAGE (and bark*)

Trees of afromontane forest (

Shrubs of thicket and/or the edges/understorey of afromontane forest:

Herbaceous plants (including lianes and tree-ferns) in afromontane forest/thicket:

Shrubs of fynbos (

Herbaceous plants of fynbos:

to be continued in

Publicado el enero 14, 2022 01:40 MAÑANA por milewski milewski | 9 comentarios | Deja un comentario

15 de enero de 2022

Plants eaten by the savannah elephant in the Cape Floristic Region, part 2

...continued from



Herbaceous plants:

NON-INDIGENOUS PLANTS (*boles broken and bark stripped and eaten, in addition to the foliage and fruits being eaten)

RIPE/MATURE FLESHY FRUITS (*found germinating in faeces of L. africana)


  • Solanum linnaeanum*
  • Rapanea melanophloeos*
  • Celastraceae: Pterocelastrus tricuspidatus (mainly those fallen to the ground), Maytenus acuminata and Elaeodendron croceum*
  • Ilex mitis
  • Searsia chirindensis and possibly S. lucida
  • Burchellia bubalina





  • Acacia melanoxylon (ripe pods with arils, the latter in some cases still bright-hued when seen in faeces)
  • Acacia mearnsii (ripe pods with arils, the latter in some cases still bright-hued when seen in faeces)

Koen (1983) also recorded seeds of Acacia melanoxylon and Acacia mearnsi occasionally germinating in feces of L. africana.

Defensive adaptations in the above species:

Searsia chirindensis has spines not among the foliage but along the branches, which would hinder the gross damage of the shrub by L. africana.( and and

Scutia myrtina and and

Canthium inerme

Passerina: the 'bark' is so flexible and resistant to breakage that it was used as cordage (rope) (e.g. see This can be interpreted as a defence against L. africana.

to be continued in

Publicado el enero 15, 2022 03:35 MAÑANA por milewski milewski | 1 comentario | Deja un comentario

Plants eaten by the savannah elephant in the Cape Floristic Region, part 3

...continued from

Phillips (1925) found evidence of the following species, particularly their fruits: Trichocladus crinitus, Secamone alpini, Scutia myrtina, Maytenus acuminata, Maytenus peduncularis, Clematis brachyata, Physalis sp. (non-indigenous), and Quercus sp. (non-indigenous; recorded also by Carter 1970).

The following is my commentary on a study (von Gadow 1973) done a quarter of a century before my own, from a forester's viewpoint:

Before von Gadow began his study, it had already been noted that "observations within the whole Knysna forest area confirmed the high utilisation rate of Ilex mitis, Canthium ventosum (now Canthium inerme), Cassine peragua, Maytenus acuminata and Rhus macowanii (now Searsia rehmanniana)...High preference for Scolopia mundii and Kiggelaria africana".

(Here is information for the species, among the above, not already covered in parts 1 and 2 of this series of Posts: and and

Von Gadow found the following indigenous species of trees to be broken by L. africana in afromontane forest. The list is in decreasing order of preference by L. africana.

Non-indigenous species of trees:

  • Acacia melanoxylon (saplings were victimised by L. africana)

My commentary:

Zanthoxylum davyi ( and Ilex mitis were much preferred, the trees being avidly pushed over by L. africana.

Kiggelaria africana was eaten by L. africana despite being cyanogenic (and possibly goitrogenic), which may help to explain its ability to regenerate vegetatively from the base. Searsia and Pterocelastrus likewise regenerate from the base.

Canthium spp. were somewhat preferred by both L. africana and Philantomba monticola (

Maytenus spp. were preferred by both L. africana (M. acuminata) and Tragelaphus sylvaticus (M. peduncularis)(

The following were not pushed over, or their branches damaged; L. africana seems to exclude them from its diet:

Von Gadow stated:
"Maytenus peduncularis, Nuxia floribunda, Halleria lucida and especially Ocotea bullata are major feeding plants of other forest herbivores. It therefore seems remarkable that these species have not been taken by elephant."

Halleria lucida was not preferred by L. africana, although it seems preferred by Tragelaphus sylvaticus.

The foliage of Ocotea bullata was eaten by Tragelaphus sylvaticus but not L. africana.

Diospyros spp. (which occur in the understorey) were apparently ignored by L. africana.

The foliage of Afrocarpus falcatus and Podocarpus latifolius was apparently largely ignored by both L. africana and Tragelaphus sylvaticus.

The following show spinescence in Zanthoxylum davyi:

Spinescence in Zanthoxylum is difficult to interpret. Members of this genus have extremely spinescent boles, which look particularly adaptive as a defence against L. africana. However, this genus of about 250 species is remarkably widespread on Earth in the tropical and subtropical zones, and the spines occur on the boles of most species regardless of the megafauna - including Australia where the marsupial fauna has never contained any animal resembling elephants.

to be continued in

Publicado el enero 15, 2022 10:47 MAÑANA por milewski milewski | 1 comentario | Deja un comentario

Plants eaten by the savannah elephant in the Cape Floristic Region, part 4

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...continued from

Loxodonta africana has been recorded eating such a wide variety of plants in the Knysna area (see parts 1-3) that it may be more meaningful to focus on the species rejected than on those accepted.

So, in afromontane forest and fynbos in the Cape Floristic Region, which foliage is rejected as food by L. africana?

I have arranged the rejected species by categories as follows.

Dominant trees, the foliage of which is rejected by ruminants as well: Podocarpaceae, namely Afrocarpus falcatus and Podocarpus latifolius. Olea capensis shows a similar pattern although trees are occasionally damaged by, and Koen (1983) found a single seedling germinating in feces of, L. africana.

Other common trees in afromontane forest, the foliage of which is largely rejected by L. africana despite being accepted by ruminants: Nuxia floribunda, Ocotea bullata and Elaeodendron croceum.

Tall shrubs/small trees of forest edges: Diospyros whyteana and Diospyros dichrophylla.

Shrubs of forest edges/understorey, the foliage of which is rejected by L. africana despite being accepted by ruminants: Halleria lucida.

Legumes in fynbos and at forest edges: Aspalathus and most other species in most genera.

All geophytes and Iridaceae (although rhizomes, corms and non-green bases are accepted).


The rejection of podocarp conifers (and Olea) is unsurprising, because these constitute the tallest indigenous trees in the Cape Floristic Region. The foliage of geophytes tends to be toxic to folivores generally.

It is noteworthy that L. africana, when foraging in fynbos, accepts the foliage of nutrient-poor Ericaceae, Bruniaceae and certain Proteaceae.

The rejection of Nuxia and Fabaceae may be owing to certain toxins that are harmful to L. africana despite being neutralised by the digestive system of certain ruminants. Toxicity is particularly likely for Elaeodendron croceum, based on its tropical congener Elaeodendron buchananii (

The general rejection of Fabaceae is surprising in view of:

  • the relative richness in protein of these nitrogen-fixing plants,
  • the acceptance of non-indigenous, nitrogen-fixing legumes in the form of Australian species of Mimosaceae, and
  • the acceptance of both phyllodes (Acacia melanoxylon) and bipinnately compound leaves (Acacia mearnsi) in the latter cases.

It is particularly noteworthy that the indigenous Virgilia tends to be rejected by L. africana whereas the non-indigenous A. melanoxylon is a favourite. Acacia melanoxylon was deliberately planted for its valuable wood, but has been so persecuted by L. africana that foresters have abandoned the project in the Knysna area. Furthermore, the bark of the Australian spp. of Acacia seems palatable to L. africana despite being so astringent that these plants have commercial value as a source of tannins.

The rejection of Diospyros is surprising given that Diospyros mespiliformis is damaged by L. africana in tropical Africa (

It is noteworthy that Rhodocoma gigantea is eaten by L. africana. This is an exceptionally tall member of the Restionaceae, a family characteristic of fynbos.

Until Gareth Patterson recorded this species and other restios in 20% of his fecal samples of L. africana in the Knysna area, it had been assumed by scientists and naturalists that restios are too fibrous and nutrient-poor to qualify as food for megaherbivores. This had long been at odds with the simultaneous assumption that restios are a staple food of the vole-like rodent Otomys irroratus (

We now realise that L. africana does indeed eat restios. Furthermore, vernacular names for R. gigantea and species in at least four other genera (thanks to @tonyrebelo for pointing this out) hint that the consumption of restios by L. africana was known to the indigenous pastoralists of the southwestern Cape centuries ago. All these species are called 'olifantsriet'.

Finally, returning to the topic of spinescence:

In general, spinescence occurs in plants palatable, not unpalatable, to folivores. This principle seems largely to hold good for L. africana in the Knysna area, because the most spinescent species in the flora (e.g. Scolopia spp,, Gymnosporia buxifolia and Zanthoxylum davyi) are part of the diet. The principle extends to Aloe spp., which are leaf-spinescent but in a way configured to protect the pithy stems to some degree. However, it seems not to hold for Diospyros dichrophylla, which grows deterrent-looking struts on the boles (see comment in but seems to be ignored by L. africana.

Reviewing these findings overall, which are the biggest surprises?

For me, the answer is:

  • the routine acceptance by L. africana of the foliage of 'ericoid' (small-leafed, heath-like) shrubs in fynbos, despite the nutrient-poverty of these plants and their tendency to be consumed by wildfires rather than animals, and
  • the targeting of Australian spp. in both afromontane forest (Acacia melanoxylon) and fynbos (Acacia mearnsi and Hakea sericea) despite the general avoidance of other legumes and despite the failure of these acacias to support folivores in their natural habitats in Australia.
Publicado el enero 15, 2022 10:03 TARDE por milewski milewski | 11 comentarios | Deja un comentario

22 de enero de 2022

How can the savannah elephant afford to produce feces richer than its food? part 1

Loxodonta africana (the savannah elephant) chews and digests its food only partially.

The result is feces so rich that they form food for large beetles, e.g. see

They also contain plenty of intact seeds, attractive to e.g. baboons ( and phasianoid birds (

Feces-eating insects in turn attract insect-eaters such as starlings (e.g., hornbills (e.g. and mongooses (e.g.

It is not simply that all feces are rich food-sources for other animals. For example, giraffes (Giraffa) contrast with elephants in digesting their food thoroughly. Their feces are unattractive to the above insects, birds and mammals, because they are depleted of food-value (as well as being relatively dry, see and and

Loxodonta africana has such rich feces that It almost seems to eat on behalf of others more than itself.

The wasteful processing of food by elephants has been investigated technically (e.g. see and and,were%2071.4%25%20and%2069.3%25.&text=values%20are%20shown%20in%20Fig,1%20A.&text=of%20water%20loss%20from%20the%20dung and

However, I have not seen a clear explanation, understandable to the lay person, of how this makes nutritional sense (e.g.

Clauss et al. (2003, acknowledge the puzzle by stating: "elephants have surprisingly fast ingesta passage rates for their body size...Presently, no answer is given to why elephants apparently do not make use of the digestive potential theoretically provided by their body size".

I offer the following explanation to my fellow naturalists:

In L. africana, digestion and absorption reduce by about the same degree the fibre and the more valuable components (particularly protein and mineral nutrients). Digestion and absorption in this species are a mechanism for subtraction of quantity rather than depletion in quality. The result is that the feces are somewhat lesser in amount than the food, but not poorer in composition.

In giraffes, by contrast, digestion and absorption greatly reduce both the quantity and the quality. These ruminants digest fibre more thoroughly than do elephants, but they digest protein particularly thoroughly, absorbing the breakdown products plus the mineral nutrients to a point of such depletion that their feces hardly qualify as food for insects.

The crucial differences are that giraffes chew more finely, chew the same particles repeatedly (in the process of rumination), and ferment the fibre in specialised gut-compartments.

The gut of L. africana is remarkably simple and - relative to the size of the animal - short: By contrast, the following shows the complexity and length of the intestines of giraffes: In addition the stomach is so complex that it consists of four chambers - in contrast to the simple, single, proportionately small stomach of L. africana.

Loxodonta africana digests and absorbs only about 20% of its food, whereas giraffes of comparable body size - which eat some of the same foods, such as acacias - digest and absorb about 72% of their food (

Once it is realised that L. africana has a foraging strategy and digestive system capitalising on quantity rather than quality, several obvious questions arise. For example:

  • why has L. africana not evolved to digest its food thoroughly?
  • why does L. africana not eat its own feces, given that they are about as rich as its food? and
  • in which ways can the digestive system of L. africana be seen as efficient?

to be continued...

Publicado el enero 22, 2022 05:15 MAÑANA por milewski milewski | 14 comentarios | Deja un comentario

28 de enero de 2022

How can the savannah elephant afford to produce feces richer than its food? part 2

Why has Loxodonta africana not evolved to digest its food thoroughly?

I suggest that the basic answer is: because large plants regenerate so rapidly, particularly when subjected to gross damage, that a niche exists for a gross forager that capitalises on quantity rather than depending on quality.

This answer may be hard to grasp initially. However, let us continue to improve our understanding by comparing L. africana to other mammals, before adding further layers of explanation. We may as well choose humans as our next example.

Homo sapiens has a similar gastrointestinal tract to Loxodonta africana. However, our species digests food far more thoroughly, partly because cooking promotes digestion (

Despite our simple gut, digestive thoroughness in humans rivals that in ruminants such as giraffes ( and,NDFD%2C%20and%20StarchD%2C%20respectively.). The average adult human eats about 2 kg of food per day and defecates at most a quarter of this mass (0.5 kg or less).

Human feces are certainly rich enough to attract large dung beetles, and under some circumstances are eaten by the domestic dog (Canis familiaris). However, this is partly because human feces:

  • contain more water than those of giraffes, and
  • can be protein-rich after animal matter is eaten beyond the point of satiety.

The digestibility coefficient (,(intake%20%2D%20excreted)%2Fintake.) is more than 75% in Homo sapiens compared with only about 20% in L. africana. This means that digestion in humans is nearly fourfold more thorough than that in the savannah elephant, a difference unexplained by body sizes.

To understand the apparent wastefulness of digestion in L. africana, let us review the range of nutritional strategies in a broad spectrum of mammals. Some species make the least of what they eat, others make the most of what they eat, and many lie somewhere in between.

Plant-eating mammals vary greatly in thoroughness of digestion, elephants being at one extreme of the range. At the opposite extreme: the ruminant mode ( is one of the two most thorough modes of digestion in mammals - the other being the caecotrophic mode (

In both ruminant ungulates and caecotrophic lagomorphs, rodents and marsupials, the guts are long and complicated and food is repeatedly chewed and repeatedly fermented. The result is feces so depleted of nutrients that they can be nearly useless to feces-eating insects and other animals.

Bovines and hares, for example, process their food so extractively that the feces consist merely of finely mashed fibre in small quantity. Such matter resembles papier-mache ( regardless of whether it is defecated wet (bovines) or dry (hares).

Mammals with thorough digestion have an advantage of being able to make the most of a limited quantity of food. Grazers maintaining natural lawns are an example. Relatively little is available each day, but this is made to suffice without necessarily slowing down metabolism, growth or reproduction.

At the other end of the spectrum are mammals with relatively short, simple guts that chew their food only once and only cursorily.

An extreme example of partial digestion, besides L. africana, is the giant panda (Ailuropoda melanoleuca, which, like L. africana, digests and absorbs only 20% of the amount eaten. In some. cases, the feces remain greenish (e.g. and

The main advantage of partial digestion is that minimal time and energy are spent in processing a given particle of food. This can make economic sense where food is reliably abundant, and plentiful quantity compensates for indifferent quality.

to be continued...

Publicado el enero 28, 2022 04:40 MAÑANA por milewski milewski | 11 comentarios | Deja un comentario