22 de enero de 2022

How can elephants afford to produce feces richer than their food? part 1

Elephants (Proboscidea: Elephantidae) chew and digest their food only partially.

The result is feces so nutrient-rich that they form food for large beetles, e.g. see https://fineartamerica.com/featured/dung-beetle-on-elephant-dung-ivan-kuzmin.html). They also contain plenty of intact seeds, attractive to e.g. baboons (https://www.alamy.com/stock-photo-yellow-baboon-papio-cynocephalus-adult-foraging-in-african-elephant-47752810.html) and phasianid birds. Feces-eating insects in turn attract insect-eaters such as starlings (e.g. https://ms-my.facebook.com/110169597399002/videos/1079632775853826/?so=watchlist&rv=video_home_www_playlist_video_list), hornbills (e.g. https://www.dreamstime.com/ground-hornbill-feeding-elephant-dung-southern-ground-hornbill-feeding-elephant-dung-wilderness-africa-video186996764) and mongooses (e.g. http://www.shahrogersphotography.com/detail/8832.html).

It is not true that all feces are rich food-sources for these kinds of animals. For example, the feces of giraffes (Giraffa) are unattractive to the above animals, even allowing for the fact that they are pelletised and relatively dry.

The wasteful processing of food by elephants has been studied by experts (e.g. see https://www.zooklinik.uzh.ch/dam/jcr:b1c19dd5-e5bc-4f72-b642-593c68886add/Clauss_ElephantFeeding_181101_handout.pdf). However, I have not seen a clear explanation of how it makes nutritional sense.

One place to start is a study performed in afromontane forest and fynbos near the southern tip of South Africa (by J H Koen et al.). In this habitat, both foliage and feces were analysed, in order to compare the concentrations of nine elemental nutrients: phosphorus, potassium, calcium, magnesium, copper, manganese, zinc, molybdenum and boron.

The results: in the case of six of these nutrients, the feces of elephants were about equivalent in the concentrations to foliage in afromontane forest. In the case of calcium and manganese, the feces were richer than the foliage. The only nutrient for which the feces were the poorer was magnesium, and not by much.

In the case of comparison with fynbos: all the nutrients were richer in feces than in foliage, albeit only slightly in some cases.

The obvious question arises: in elephants, how is it adaptive for feces to exceed food in nutrient-richness? Where is the digestive profit? Surely the point of eating is to extract and absorb nutrients as food becomes feces?

To understand this, let us review the range of nutritional strategies in animals. Please bear in mind that plant-eating animals vary greatly in thoroughness of digestion, elephants being at one extreme of the range.

The two most thorough modes of digestion in mammals are the ruminant (https://en.wikipedia.org/wiki/Ruminant) and caecotrophic (https://en.wikipedia.org/wiki/Cecotrope) modes.

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

The feces of, for example, bovines and hares are so extractively processed that they retain little more than finely mashed fibre. Such feces are essentially papier-mache (https://en.wikipedia.org/wiki/Papier-m%C3%A2ch%C3%A9). The conversion of food to feces seems categorical.

The main advantage of thorough digestion is that mammals can live where there is a limited quantity of food available. Grazers maintaining lawns are an example. Relatively little can be eaten, but so much nutritional value is extracted that this suffices.

At the other end of the spectrum are mammals with relatively short, simple guts that chew their food only once and only cursorily. Mammalian examples are elephants and the giant panda (Ailuropoda melanoleuca, https://en.wikipedia.org/wiki/Giant_panda). In some cases, the feces remain greenish (e.g. https://es.123rf.com/photo_117579939_close-up-of-fresh-elephant-dung-excrement-on-ground-in-a-forest.html and https://www.gawker.com/5859434/worlds-most-expensive-tea-panda-poop).

The main advantage of partial digestion is that minimal time and energy are invested in processing food, which can make economic sense where food is abundant and quantity makes up for quantity.

An aspect of partial digestion that certain food-component will, by virtue of their chemical properties, be extracted more thoroughly than others. Nutrients vary from extremely easy to absorb (e.g. potassium, which is extremely soluble, and iodine, which is extremely volatile) to relatively hard to absorb (e.g. metals such as zinc and iron).

By the same token, the agaries of composition mean that a given diet can be sufficient in almost all nutrients yet deficient in a few odd nutrients such as iodine (https://en.wikipedia.org/wiki/Iodine#Deficiency) and selenium (https://en.wikipedia.org/wiki/Selenium#Deficiency) - which happen not to be essential for plants in the ways they are for animals (https://www.researchgate.net/publication/229774801_Why_are_very_large_herbivores_absent_from_Australia_A_new_theory_of_micronutrients).

The above ideas may help to explain the wastefulness of digestion in elephants, given their extreme body size and their exceptional braininess among land mammals besides primates.

to be continued...

Ingresado el 22 de enero de 2022 por milewski milewski | 3 comentarios | Deja un comentario

15 de enero de 2022

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

@dianastuder @botaneek @troos @ehbidault @craigpeter @alastairpotts @adriaan_grobler @dhoare @outramps-tanniedi @petrabroddle @vynbos @richardadcock @steve_cousins @chris_whitehouse @graham_g @cpvoget @sedgesrock @magdastlucia @lucstrydom @strandloper @abdullateefismail @drmckenzie @sp_bester @wynandc @yvettevanwijk1941 @rcswart @felix_riegel @wolfachim @annsymons @sandraf @lindaloffler @outrampsjenny @zaniekk @ludwig_muller @tonyrebelo @jeremygilmore @emmspaul @venturefoth @robertarcher397 @jan_hendrik @douglaseustonbrown @pieterwinter @benjamin_walton @andrew_hankey @francoisdurandt @warrenmcc @richardgill @tania_morkel @lukegallant @karooicus @s_k_johnsgard @joshua_tx @lanechaffin @jayhorn @frank_arroyo @aavankampen @qgroom @entwisle @nyoni-pete @jimmy_finsbury @rudivs @dereksilberblatt

continued from part 3:

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 rejected by L. africana despite being accepted by ruminants: Nuxia floribunda, Ocotea bullata and Elaeodendron croceum

Tall shrubs/small trees of forest edges: Cunonia capensis, 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: most species in most genera, including Virgilia and Aspalathus.

Graminoids in fynbos: all Restionaceae (although seed-heads may be accepted).

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


The rejection of the following is unsurprising:

  • podocarp conifers (and Olea), which constitute the tallest indigenous trees in the Cape Floristic Region,
  • Restionaceae, which are the most sclerophyllous (leafless with lignified green stems) of the graminoids in fynbos, and
  • geophytes, the foliage of which 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, Ocotea and all 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 (https://pdf.sciencedirectassets.com/273500/1-s2.0-S0254629998X42006/1-s2.0-S0254629915308425/main.pdf?X-Amz-Security-Token=IQoJb3JpZ2luX2VjEDIaCXVzLWVhc3QtMSJGMEQCIGmu3pJb%2FisBLfJOCeLoBzuZ0WhxOjzFTa9mujcqKbQBAiBJhGTK4IbC4bn9CTS3Lto5%2FyCfINJYtsCQTb%2FUIp6TmSr6AwhaEAQaDDA1OTAwMzU0Njg2NSIMvW2GYuQFIM%2BVMJcsKtcD4%2FxCvZIskYstV0%2BwgKUP63rmHW%2FXfz87UIAkTE5ExydeBOKT0Cc18C8CEy802yaSqmdt0IEENSnIMskod%2BUXIcxvdWGEXEFqIxUfWXyAIusNwCmKjxD%2FYcQAeKx7i819PGy9YkUqU34Pbl7OYkgrBt4PXszkVY3xfkVEk%2BZlQjmuyaV9qx4QT1vynO1n1vry7Ee0mkF16kdsg29viUOAxVMaul5rZR9rlZ3yM1P2%2BDduQ%2BaRsLH6e31iGDyjnRsfPEXVXX%2F0kSWBsZi2yJndXbrwC6d66OQvdB%2BaG8ZbEg%2BlAJIAXnMW%2BswuHSEkWe3JE2SVl9jxaSBxO6y6x7mhKkaIo7rra8nzLBnJ88%2Bjjl49JQrT%2FCr8n1ro8SBnexASEQZcOFclxe0CbyuVvVe0XpDhnEy1lcBfBT0V%2FwiVEVQ8lM26ZpwRL8VeJX8t%2FbSWFy2WfFj3F8mUBic%2BFiuaPCpqUs%2FJ4ZabamnsE0GqwdJ%2Bc8puSpNcvlhYzQLXyC8snBtVUNfZ%2BUNfgW%2B8CvW4lMZmkiPHe2xquiAmp852hwZdzOttPiF9Xa6bl7LyE5HssThavScxCQprZ6tqj8XHuTwMM%2BpJo9kbXnvob9DcmGjE3c8vDn%2F4MI22tI8GOqYBedHuwTWS5EEQUnCA1G8%2FQKqZVdiferCgpTcnilJ0ncv1rZcKI8omAIs%2BhHxP3lTssacUfhpS1hLdoM296992RXSRPFdhuCiMuJfAQtokf4darLMVnMKX6cjlHRIyYcFNJLxiz8j1e2yWrcs9EIWCRKp1USYgmw536zKD%2Bw0mf18pVJx3eRYoShYV%2FxWOZdbNqZo%2BflyS8riy3otz9RAyQTOywZ190w%3D%3D&X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Date=20220123T104503Z&X-Amz-SignedHeaders=host&X-Amz-Expires=300&X-Amz-Credential=ASIAQ3PHCVTYTRW2CXMO%2F20220123%2Fus-east-1%2Fs3%2Faws4_request&X-Amz-Signature=99148af27ce9251fbde27126587fed3436a729abb4d0f39f71a4ab2f8f099e18&hash=c2234326fde0e78bcc28cfafa3e8fd0b8c7fc4e6bce74e779320310dc945325f&host=68042c943591013ac2b2430a89b270f6af2c76d8dfd086a07176afe7c76c2c61&pii=S0254629915308425&tid=spdf-64759978-abcd-4fb1-8f34-8cad4cf285ef&sid=7ba1a56014d1844b70786665b7b44e4f12e6gxrqa&type=client).

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 seems 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 rich in tannins 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 (https://www.walshmedicalmedia.com/open-access/is-elephant-damage-to-woody-vegetation-selective-of-species-plant-parts-and-what-could-be-plausible-factors-influencing-.pdf).

In general, spinescence occurs in plants palatable to folivores, not those 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) remain palatable to L. africana. 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 https://www.inaturalist.org/journal/milewski/61009-dwarf-ebonies-part-1-white-milkwood-as-symbolically-but-not-biogeographically-south-african#new_comment) 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.

Ingresado el 15 de enero de 2022 por milewski milewski | 9 comentarios | Deja un comentario

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

continued from part 2:

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: https://www.researchgate.net/publication/269396526_Observations_on_the_utilization_of_indigenous_trees_by_the_Knysna_Elephants.

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: https://www.inaturalist.org/taxa/527633-Cassine-peragua and https://www.inaturalist.org/taxa/593914-Searsia-rehmanniana and https://www.inaturalist.org/taxa/593861-Scolopia-mundii).

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 (https://www.inaturalist.org/taxa/469304-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 (https://en.wikipedia.org/wiki/Blue_duiker).

Maytenus spp. were preferred by both L. africana (M. acuminata) and Tragelaphus sylvaticus (M. peduncularis)(https://en.wikipedia.org/wiki/Cape_bushbuck)

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...

Ingresado el 15 de enero de 2022 por milewski milewski | 0 comentarios | Deja un comentario

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

continued from part 1:



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* https://www.inaturalist.org/taxa/557692-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.(https://www.inaturalist.org/observations/67388304 and https://www.inaturalist.org/observations/62178427 and https://www.inaturalist.org/observations/96341485).

Scutia myrtina https://www.inaturalist.org/observations/102906771 and https://www.inaturalist.org/observations/92336274 and https://www.inaturalist.org/observations/98495378

Canthium inerme https://en.wikipedia.org/wiki/Canthium_inerme#/media/File:Canthium_inerme_-_Cape_Town_2.JPG

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

to be continued...

Ingresado el 15 de enero de 2022 por milewski milewski | 1 comentario | Deja un comentario

14 de enero de 2022

Plants eaten by the African bush 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 (https://en.wikipedia.org/wiki/Knysna_elephants and https://digitalcommons.wayne.edu/elephant/vol2/iss1/6/), 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 (http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532019000200016), 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. https://journals.co.za/doi/pdf/10.10520/AJA00423203_2578 and Milewski, A. V. (2002) Elephant diet at the edge of the Fynbos Biome, South Africa. Pachyderm 32: 29-38).

The following refers to my own study based on the observations of forest guards Wilfred Oraai and Karel Maswati. However, I have added information previously recorded by Koen J H (1983) Seed dispersal by the Knysna elephants, South African Forestry Journal 124: 56-58.

FOLIAGE (and bark*)

Trees of afromontane forest (https://en.wikipedia.org/wiki/Afromontane):

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 (https://en.wikipedia.org/wiki/Fynbos):

Herbaceous plants of fynbos:

to be continued...

Ingresado el 14 de enero de 2022 por milewski milewski | 9 comentarios | Deja un comentario

12 de enero de 2022

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

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 (https://en.wikipedia.org/wiki/Erica_(plant)) in the Cape Flora. This number, about 700, happens to be similar to the number of species of Diospyros worldwide (https://en.wikipedia.org/wiki/List_of_Diospyros_species).

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 (https://www.inaturalist.org/taxa/595940-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 (https://cdn.24.co.za/files/Cms/General/d/2276/69b122dacb504e22826fa5c7da943188.pdf).

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".

Ingresado el 12 de enero de 2022 por milewski milewski | 3 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

@cesarmassi @martinserrano @santiagomailhos @juanmacostero @dianastuder @botaneek @troos @ehbidault @craigpeter @alastairpotts @adriaan_grobler @dhoare @outramps-tanniedi @petrabroddle @alexiz @demianlescano @vynbos @richardadcock @waltermedina @steve_cousins @chris_whitehouse @graham_g @cpvoget @sedgesrock @magdastlucia @lucstrydom @strandloper @abdullateefismail @drmckenzie @sp_bester @wynandc @yvettevanwijk1941 @rcswart @felix_riegel @wolfachim @annsymons @sandraf @lindaloffler @outrampsjenny @zaniekk @ludwig_muller @tonyrebelo @jeremygilmore @emmspaul @venturefoth @robertarcher397 @jan_hendrik @douglaseustonbrown @pieterwinter @benjamin_walton @andrew_hankey @francoisdurandt @warrenmcc @richardgill @tania_morkel @lukegallant @karooicus @s_k_johnsgard @joshua_tx @lanechaffin @jayhorn @frank_arroyo @aavankampen @qgroom @entwisle @nyoni-pete @jimmy_finsbury @rudivs

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

This is because Euclea:

  • is restricted to Africa and Arabia, unlike its cosmopolitan relative Diospyros,
  • tends to be shrubby even in its most arborescent forms,
  • is species-richest 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 (https://en.wikipedia.org/wiki/Diospyros) - 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 karoo and 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 https://www.inaturalist.org/observations/67144217 for an extreme example).

None of these species is genotypically dwarfed to the degree seen in e.g. Euclea tomentosa, 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 particularly small rather than being lignified.

Diospyros glabra (https://www.inaturalist.org/taxa/569146-Diospyros-glabra) is restricted to the acidic soils of the heartland of the Cape Floristic Region (https://en.wikipedia.org/wiki/Cape_Floristic_Region), part of which is in a winter-rainfall climate. It has penetrated fynbos (e.g. https://www.inaturalist.org/observations/67105857 and https://www.inaturalist.org/observations/91888971) 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 https://www.inaturalist.org/observations/20952415).

What this means is that Diospyros glabra is the only ebony that is exclusive to the Cape Flora - or any analogous flora of nutrient-poor, fire-prone environments elsewhere on Earth (e.g. https://en.wikipedia.org/wiki/Kwongan).

The only feature of D. glabra that remains incongruous with fynbos is its fleshy fruit, attractive to seed-dispersing birds (https://www.inaturalist.org/observations/10084476 and https://www.inaturalist.org/observations/70307544 and https://www.inaturalist.org/observations/11278386 and https://www.inaturalist.org/observations/68855126 and https://www.inaturalist.org/observations/77290881 and https://www.inaturalist.org/observations/75933818 and https://www.inaturalist.org/observations/71651195 and https://www.inaturalist.org/observations/71303126 and https://www.inaturalist.org/observations/71057924 and https://www.inaturalist.org/observations/70489280 and https://scholar.ufs.ac.za/handle/11660/4322).

More illustrations of Diospyros glabra:


One way to look at Diospyros glabra is as the biogeographical and ecological equivalent of Vaccinioideae, a tribe of Ericaceae notably absent from the Cape Flora and most of Africa.

The following illustrate Diospyros austro-africana (https://www.inaturalist.org/taxa/583880-Diospyros-austro-africana), which has possibly the smallest leaves of any member of this genus worldwide:


The following illustrate Diospyros scabrida var. cordata (https://www.inaturalist.org/taxa/598746-Diospyros-scabrida-cordata):


It is easy for South African naturalists to take for granted the floristic integration of Diospyros into various types of low vegetation. However, a surprise comes when this is compared with other landmasses with similar latitudes and climates.

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

North America has a few species (e.g. see https://en.wikipedia.org/wiki/Diospyros_virginiana) 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 (https://www.inaturalist.org/taxa/538020-Diospyros-australis) 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 (https://www.jstor.org/stable/43869000).

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...

Ingresado el 09 de enero de 2022 por milewski milewski | 18 comentarios | Deja un comentario

07 de enero de 2022

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

@tonyrebelo @botaneek @troos @chris_whitehouse @adriaan_grobler @jeremygilmore @craigpeter @emmspaul @steve_cousins @richardadcock @vynbos @petrabroddle @outramps-tanniedi @dhoare @alastairpotts @jeremygilmore @venturefoth @robertarcher397 @jan_hendrik @douglaseustonbrown @pieterwinter @benjamin_walton @andrew_hankey @francoisdurandt @warrenmcc @richardgill @tania_morkel @lukegallant @dereksilberblatt

A major ecological pattern in southern Africa is reduction in the height of the natural vegetation (e.g. see https://www.jstor.org/stable/2844553 and https://www.researchgate.net/publication/282619832_Why_was_the_Highveld_treeless_Looking_laterally_to_the_Pampas_for_global_edaphic_principles_beyond_biogeographical_accidents#:~:text=The%20ultimate%20reasons%20for%20treelessness%20in%20the%20natural,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 (https://en.wikipedia.org/wiki/Fynbos) and strandveld (https://en.wikipedia.org/wiki/Cape_Flats_Dune_Strandveld) through succulent karoo (https://en.wikipedia.org/wiki/Succulent_Karoo) and Nama karoo (https://en.wikipedia.org/wiki/Nama_Karoo) to various types of treeless grassland (https://en.wikipedia.org/wiki/Highveld).

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 (https://en.wikipedia.org/wiki/Cape_Floristic_Region) 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 (https://www.inaturalist.org/taxa/585519-Euclea-tomentosa and https://plants.jstor.org/search?filter=name&so=ps_group_by_genus_species+asc&Query=Euclea+tomentosa).

This species is closely related to Euclea acutifolia (https://www.inaturalist.org/taxa/585511-Euclea-acutifolia) and Euclea polyandra (https://www.inaturalist.org/taxa/568323-Euclea-polyandra and https://plants.jstor.org/stable/10.5555/al.ap.flora.flosa003090369900018), which show the syndrome of dwarf ebonies less clearly.

Euclea tomentosa has such lignified leaves that it is possibly the most sclerophyllous (https://en.wikipedia.org/wiki/Sclerophyll) of all of the 768 species of Ebenaceae worldwide. Not only has it converged in leaf texture with proteas (https://en.wikipedia.org/wiki/Proteaceae), 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 (https://www.inaturalist.org/photos/24232778 and https://www.inaturalist.org/observations/16163420). 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 https://www.jstor.org/stable/2844617).

However, it is in Ericales that the exceptions - in which sclerophyllous plants bear fleshy fruits - tend to occur (e.g. https://www.inaturalist.org/observations/101827824 and https://www.fs.fed.us/database/feis/plants/shrub/arcvis/all.html).

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

The family Ericaceae (https://en.wikipedia.org/wiki/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 (http://biodiversityexplorer.info/plants/ericaceae/index.htm#:~:text=Ericaceae%20(erica%20and%20rhododendron%20family)&text=About%20126%20genera%20and%203995,are%20cultivated%20in%20the%20region.).

So an alternative view is 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.

According to this rationale, 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, https://en.wikipedia.org/wiki/Arctostaphylos). For an Australian, it might seem like a large-leafed version of various genera of Epacridoideae (http://anpsa.org.au/epacris1.html).

to be continued...

Ingresado el 07 de enero de 2022 por milewski milewski | 25 comentarios | Deja un comentario

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

@cesarmassi @martinserrano @santiagomailhos @juanmacostero @dianastuder @botaneek @troos @tonyrebelo @jeremygilmore @ehbidault @craigpeter @alastairpotts @adriaan_grobler @dhoare @outramps-tanniedi @petrabroddle @alexiz @demianlescano @vynbos @richardadcock @waltermedina @emmspaul @steve_cousins @chris_whitehouse @graham_g @cpvoget @sedgesrock @magdastlucia @lucstrydom @strandloper @abdullateefismail @drmckenzie @sp_bester @wynandc @yvettevanwijk1941 @rcswart @felix_riegel @wolfachim @annsymons @sandraf @lindaloffler @outrampsjenny @zaniekk @ludwig_muller

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, https://en.wikipedia.org/wiki/Sideroxylon_inerme and https://www.kariega.co.za/blog/in-bad-odour) is pale, it can be considered a form of ebony because the family Sapotaceae is closely related to the family Ebenaceae (https://en.wikipedia.org/wiki/Ericales#/media/File:EricalesRose2018.png).

And although the white milkwood can reach 15 metres high, its ability to persist for centuries as a knee-high shrub (e.g. see https://www.inaturalist.org/observations/83814910) on the windswept coast near Cape Point (https://en.wikipedia.org/wiki/Cape_Point) and Cape Agulhas (https://en.wikipedia.org/wiki/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 (https://www.inaturalist.org/taxa/362175-Sideroxylon-inerme).

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 (http://tropical.theferns.info/viewtropical.php?id=Sideroxylon+inerme)
  • 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. https://en.wikipedia.org/wiki/Treaty_Tree).

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 (https://www.researchgate.net/publication/266396476_Revisiting_the_biogeography_of_Sideroxylon_Sapotaceae_and_an_evaluation_of_the_taxonomic_status_of_Argania_and_Spiniluma) 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 (https://www.jstor.org/stable/2417064 and https://www.inaturalist.org/observations/36099669).

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. https://www.inaturalist.org/taxa/168950-Sideroxylon-lycioides), the natural companions of which include Pinus (https://en.wikipedia.org/wiki/Sideroxylon_tenax and https://www.fdacs.gov/content/download/82393/file/CIRCULAR_Buckthorns_SIderoxylon.pdf).

The North American species are tardily deciduous (e.g. https://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?kempercode=m830), and differ ecologically in this way from the white milkwood, which is fully evergreen.

Unlike the white milkwood (https://prota4u.org/database/protav8.asp?g=pe&p=Sideroxylon+inerme+L.), the North American species of Sideroxylon do not have particularly dense wood (https://www.fpl.fs.fed.us/documnts/fplrp/fplrp325.pdf). 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. https://www.inaturalist.org/photos/7045078 and https://www.inaturalist.org/observations/36812876 and https://www.inaturalist.org/observations/24496215). 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 (https://www.thesurvivalgardener.com/an-unknown-eleagnus/ and https://www.eattheweeds.com/tag/sideroxylon-tenax/ and https://plants.jstor.org/compilation/Sideroxylon.tenax).

Instead, any South African naturalist first encountering Sideroxylon in North America (e.g. https://www.inaturalist.org/observations/3521873) might be reminded of Gymnosporia (Celastraceae). Gymnosporia buxifolia (https://en.wikipedia.org/wiki/Gymnosporia_buxifolia) naturally occurs side-by-side with the white milkwood at the southern tip of South Africa (e.g. https://www.inaturalist.org/observations/30029230), 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. https://www.inaturalist.org/observations/69115540 and https://www.inaturalist.org/taxa/273914-Sideroxylon-obtusifolium).

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 (https://www.inaturalist.org/observations/61197783) 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...

Ingresado el 07 de enero de 2022 por milewski milewski | 17 comentarios | Deja un comentario

31 de diciembre de 2021

How brainy are ground parrots relative to Australian birds in general?

In my last Post, I showed that certain species of terrestrial parrots in Australia are the least brainy parrots on Earth, helping to explain why they are threatened with extermination by introduced predators.

However, Psittaciformes are the brainiest of all the orders of birds, reminding us that everything is relative. The obvious question thus arises: 'are even ground parrots brainier than comparable birds in orders other than Psittaciformes?'

The answer can be found by reading between the lines in Tables 1 and 2 in https://www.researchgate.net/publication/262565451_Relative_brain_size_in_Australian_birds, which provides average values for braininess for most orders of birds and many of the families of passerine birds (https://en.wikipedia.org/wiki/Passerine) in Australia.

If zero represents average braininess for Australian birds in general, then some orders (or passerine families) have averages in the negative range and others have averages in the positive range. For example, the least brainy orders of Australian birds are Galliformes (https://en.wikipedia.org/wiki/Galliformes), Casuariformes (https://en.wikipedia.org/wiki/Casuariiformes) and Podicipediformes (https://en.wikipedia.org/wiki/Grebe), all of which have averages of -0.27 or less.

At the opposite end of the spectrum are Psittaciformes and Strigiformes (https://en.wikipedia.org/wiki/Owl), which are by far the brainiest Australian birds with average values of +0.2 or more.

The least brainy parrots have values of +0.035, which remains on the positive side. In other words, even ground parrots (e.g. Pezoporus wallicus and P. flaviventris, see https://en.wikipedia.org/wiki/Pezoporus) are brainer than the average bird in Australia, brainier than most orders of birds in Australia, and brainier than most families of passerine birds in Australia.

We can narrow down the comparisons by focussing on other seed-eating birds.

Estrildidae (https://en.wikipedia.org/wiki/Estrildidae) are a mainly seed-eating family of passerines, and they average -0.03. This makes them slightly less brainy than the average Australian bird, compared to ground parrots which are slightly more brainy than the average Australian bird.

The comparison widens when applied to Columbiformes (https://en.wikipedia.org/wiki/Columbidae), which average -0.24. Pigeons and doves are brainier than Galliformes (Australian average -0.31), but they are the fourth least brainy order of Australian birds. This means that ground parrots are much brainier than doves with comparable habitats and diets.

Passerine birds include several brainy families, but the only ones in Australia with average values beating the value for ground parrots are (in order of increasing braininess):

The family Corvidae (https://en.wikipedia.org/wiki/Corvidae) is renowned for its braininess, but the Australian species average only +0.03, slightly less than the value for ground parrots.

So, what these data show is that parrots are so extremely brainy that even their most decephalised members - with their inconspicuous colouration, minimal sociality, crepuscular activity and secretive habits - remain among the brainiest birds in Australia.

Given this perspective, how can we explain the particular vulnerability of ground parrots to predation?

One answer is that ground parrots have particularly slow reproduction and growth. This is related to their specialisation for some of the nutrient-poorest environments on Earth, particularly heathland (kwongan https://en.wikipedia.org/wiki/Kwongan in Western Australia and wallum https://en.wikipedia.org/wiki/Wallum in eastern Australia) and hummock grassland (https://www.anbg.gov.au/photo/vegetation/hummock-grasslands.html).

The result may allow us to reframe the plight of ground parrots in a way. True, they are among the most threatened of Australian birds, but given their slow reproduction they might have been extinct already were they not as brainy as they are.

Ingresado el 31 de diciembre de 2021 por milewski milewski | 6 comentarios | Deja un comentario
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