Why was Angola the Empty Quarter for African large mammals?

Please see https://journals.co.za/doi/pdf/10.10520/AJA03794369_2870.

Angola (https://upload.wikimedia.org/wikipedia/commons/8/89/Angola_%28orthographic_projection%29.svg) is a vast, well-watered country in south-central Africa.

Its human population is about as sparse as that of Tanzania (https://en.wikipedia.org/wiki/Tanzania).

However, the natural abundance of large wild mammals is surprisingly different between these two ecologically comparable countries.

This seems true even if the effects of a decades-long war of attrition (https://en.wikipedia.org/wiki/Angolan_Civil_War) in Angola are taken into account.

At the time when European explorers arrived, most of the country had only sparse populations of ungulates.

The human population densities of Angola and Tanzania can be compared in https://databasin.org/maps/698e24d966b74684a7634ba2851f15b5/.

The following shows the particular sparsity of human populations in most of eastern Angola: http://www.geo-ref.net/ph/ago.htm.

The best reference for the biogeography of mammals in Angola is https://www.researchgate.net/publication/331238719_The_Mammals_of_Angola .

The paucity and scarcity of large mammals was particular to the extensive mesic savannas of the central and eastern plateau: miombo woodland (https://en.wikipedia.org/wiki/Miombo) with dambos (grassy openings along drainage lines, https://en.wikipedia.org/wiki/Dambo).

Here, the only species of ruminants generally present in these savannas during the period of Portuguese colonisation were:

Possible additions to this list are:

Most of these are unusually widespread species in subSaharan Africa generally, and their populations were naturally sparser or more local in Angola than elsewhere.

By contrast, species common in Tanzania, in comparable 'moist-dystrophic' savannas, include all of the above, plus:

These spp. were, in central and east-central Angola, absent, or at best marginal/localised.

One exception:
The only species more reliably present in Angola than in southern Tanzania was the roan antelope.

The puku (https://www.inaturalist.org/taxa/42326-Kobus-vardonii) is an ambivalent case. This is because it was present in the miombo biome in both Angola and Tanzania, but in Angola it was restricted to the northern regions, while in Tanzania it was restricted to large patches of non-miombo vegetation.

(Also relevant is the lechwe (https://www.inaturalist.org/taxa/42329-Kobus-leche), a marshland-specialist which occurred marginally to central and east-central Angola, while being absent from Tanzania.)

This makes east-central and eastern Angola the part of Africa most similar, in the near-emptiness of its verdant savannas for large mammals, to South America.

In which environmental factors might the central and eastern plateau of Angola resemble the South American rather than the Tanzanian savannas?

One important factor in common is the homogeneous nutrient-poverty of the soils (https://link.springer.com/chapter/10.1007/978-3-031-18923-4_14).

The Angolan plateau is partly covered by deep Kalahari sand (https://www.researchgate.net/figure/Area-covered-by-Kalahari-Sands-in-Africa-after-Main-1987_fig4_260135414 and https://www.researchgate.net/figure/The-Kalahari-sands-and-sampling-locations-of-the-soil-profiles-The-Kalahari-sand-sheet_fig3_229428856).

Under this rainy climate, leaching of nutrients has produced the most extensively depleted soils in Africa, particularly for phosphorus (https://www.researchgate.net/profile/Emmanuel-Chidumayo/publication/254672165_Effects_of_deforestation_on_grass_biomass_and_soil_nutrient_status_in_Miombo_woodland_Zambia/links/5d6e2b10299bf1808d61d348/Effects-of-deforestation-on-grass-biomass-and-soil-nutrient-status-in-Miombo-woodland-Zambia.pdf) and zinc (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7693821/#:~:text=Zn%20deficiency%20negatively%20affects%20plant,for%20crop%20yield%20and%20quality.).

For explanations of dystrophy in terrestrial ecosystems, please see:

The result - as in the cerrado (https://en.wikipedia.org/wiki/Cerrado) of Brazil - is a 'green hell' for large animals, in which the vegetation grows copiously but is fibrous and unpalatable.

What may make the miombo biome (https://en.wikipedia.org/wiki/Miombo) of Tanzania more productive for large mammals is the influence of the nearby East African Rift (https://en.wikipedia.org/wiki/East_African_Rift). This geological disturbance is likely to have produced some degree of uplift, thus supplying fresh sources of nutrients to nearby landscapes.

Nutritious plants, such as acacias (https://www.inaturalist.org/observations?place_id=7144&taxon_id=72418&view=species and https://www.inaturalist.org/observations?place_id=7144&taxon_id=72356&view=species), grow here and there in the mosaic-like miombo savannas of southern and western Tanzania.

This contrasts with Angola, where the dystrophic woodland seems to be the most monotonous anywhere in Africa, despite the existence of a catenary pattern in which the grassy drainage lines tend to be treeless.

Posted on 18 de julho de 2021, 07:49 AM by milewski milewski

Comentários

Thanks ! The Botswana iBotanists may be interested in this post @grant_reed_botswana @murphy_tladi @rianafourie @robert_taylor @troos.

Publicado por botswanabugs mais de 2 anos antes

Thanks ! The Botswana iBotanists may be interested in this post @grant_reed_botswana @murphy_tladi @rianafourie @robert_taylor @troos.

Publicado por botswanabugs mais de 2 anos antes

Very interesting!

Publicado por troos mais de 2 anos antes

@milewski what other soil deficiencies are there apart from phosphate and zinc. Im not a biologist but have been trained in chemistry. Do the soil ion deficiencies affect the distribution of insects as well as mammals ?- like termites ?

Publicado por botswanabugs mais de 2 anos antes

@botswanabugs Many thanks for your question. Widespread nutrient-poverty affects all aspects of the ecosystems, so it can indeed be assumed to affect the invertebrate faunas. The situation with termites, though, is particularly interesting.

As one goes from dry-eutrophic savanna (dominated by nutritious acacias) through moderately nutrient-poor savanna (dominated by e.g. Terminalia or Baikiaea) to moist-dystrophic savanna (dominated by Brachystegia), fungus-culturing termites (Macrotermitimae) go from important but inconspicuous (mainly Microtermes) to extremely important and conspicuous (mainly Macrotermes, which in e.g. the Caprivi forms mounds so large that each mound has a little forest-patch on it). The colonies of Macrotermes are crucial for these 'mesotrophic' savannas because the insects go tens of metres deep to mine elements such as selenium, which are crucial for large mammals and thus the whole regime of herbivory vs fire. Most of the miombo lands in Zimbabwe, Zambia, Katanga and Tanzania are dotted with the islands of fertility created by Macrotermes mounds, and it is these that allow kudu, impala, etc. to penetrate the otherwise nutrient-poor landscapes. But what happens in the very poorest landscapes, i.e. those of the Angolan plateau? I do not know, but I suspect that Macrotermes cannot get the wherewithal to build its mounds there, because even at depth the crucial trace elements are unavailable. So I suspect that the lush-looking miombo of east-central Angola is a desert for large animals because it is also a desert for certain crucial kinds of insects. I would be fascinated to visit this area not despite the monotonous vegetation and lack of animals, but because of them.

Publicado por milewski mais de 2 anos antes

https://en.m.wikipedia.org/wiki/List_of_mammals_of_Angola
You stand corrected, there exists a diverse array of mammalian megafauna in Angola, however by citing historical accounts, the natural population densities weren’t on par with comparable areas elsewhere, even before colonial european entrance.

Publicado por paradoxornithidae mais de 1 ano antes

@paradoxornithidae

Many thanks for your comment. You are right to point out the potential confusion between two aspects, namely a) the checklist of species nominally present in Angola, and b) the densities of the populations.

This confusion may help to explain why the 'Empty Quarter' anomaly has not previously been discussed much.

However, even when one takes a parsimonious view, it is clear that several species associated with miombo ecosystems in Zambia and Tanzania are absent, or nearly so, in the miombo 'heartland' in east-central Angola.

Perhaps the best examples are Alcelaphus and Ourebia (see https://www.researchgate.net/publication/331238719_The_Mammals_of_Angola).

Both genera are typical of miombo ecosystems in Zambia and Tanzania, and widespread also in similar ecosystems in the Northern Hemisphere in Africa, from north-central Africa to far-West Africa.

So their absence over most of Angola seems odd, not so?

Publicado por milewski mais de 1 ano antes

@milewski
Indeed, it is anomalous. Also, the Macrotermes correlation to this puzzle is an explanation that matches with the apparent circumstances.

Publicado por paradoxornithidae mais de 1 ano antes
Publicado por milewski mais de 1 ano antes

@paradoxornithidae @tonyrebelo

Please see https://earthwise.bgs.ac.uk/index.php?title=File:Angola_LandCover.png&filetimestamp=20150514122636&.

It is the extensive area of green in east-central Angola, occupying perhaps a quarter of the country, that seems to be an 'Empty Quarter' for large mammals.

Publicado por milewski mais de 1 ano antes

@paradoxornithidae @tonyrebelo

Please see https://www.cia.gov/the-world-factbook/static/cdd4d2bb0cc5f37be72cd83a8f90a5e9/ANGOLA_Population_density.jpg.

This shows that the human population of southeast-central Angola is as sparse as in the Pro-Namib, despite the ample rainfall on the Angolan plateau. The 'Empty Quarter' is poor for both people and large wild animals (and, I suspect, large termites).

Publicado por milewski mais de 1 ano antes

Thank you @milewski for such thought-provoking articles and links.

Publicado por botswanabugs mais de 1 ano antes

@botswanabugs Once again, you're most welcome.

Publicado por milewski mais de 1 ano antes
Publicado por milewski 4 meses antes
Publicado por milewski 4 meses antes

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