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 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 phasianoid birds (https://www.agefotostock.com/age/en/details-photo/helmeted-guineafowl-foraging-on-elephant-dung-numida-meleagris-reichenowi-maasai-mara-national-reserve-kenya-feb-2008/AAM-AAES39152).

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 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 https://www.shutterstock.com/nb/image-photo/giraffe-excrement-364864475 and https://www.flickr.com/photos/godutchbaby/3824446671 and https://www.shutterstock.com/nb/image-photo/giraffe-faecal-pellets-on-ground-1451382803).

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 https://www.zooklinik.uzh.ch/dam/jcr:b1c19dd5-e5bc-4f72-b642-593c68886add/Clauss_ElephantFeeding_181101_handout.pdf and https://nagonline.net/wp-content/uploads/2014/01/NAG-FS004-97-Elephants-JONI-FEB-24-2002-MODIFIED-2.pdf and https://www.jstor.org/stable/4214917#:~:text=On%20day%2014%20the%20mean,were%2071.4%25%20and%2069.3%25.&text=values%20are%20shown%20in%20Fig,1%20A.&text=of%20water%20loss%20from%20the%20dung and https://www.researchgate.net/publication/328007252_Assessing_the_nutrient_status_of_elephant_dung_in_the_Aberdare_National_Park_Kenya).

However, I have not seen a clear explanation, understandable to the lay person, of how this makes nutritional sense (e.g. https://www.zooklinik.uzh.ch/dam/jcr:0f7c3da0-58a2-4a80-937f-700d7fccc15f/8_Clauss_2005.pdf).

Clauss et al. (2003, https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.565.4763&rep=rep1&type=pdf) 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: https://africanelefund.weebly.com/comparative-anatomy.html. By contrast, the following shows the complexity and length of the intestines of giraffes: https://etc.usf.edu/clipart/26700/26710/int_giraffe_26710.htm. 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 (https://d-nb.info/111001418X/34).

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...

Posted on January 22, 2022 05:15 AM by milewski milewski

Comments

A study was 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 protein and nine elemental nutrients: phosphorus, potassium, calcium, magnesium, copper, manganese, zinc, molybdenum and boron. The results: in the case of protein and six of the nutrients, the feces of L. africana 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.

https://journals.co.za/doi/abs/10.10520/AJA03794369_3674

https://journals.co.za/doi/abs/10.10520/AJA03794369_3485

Posted by milewski about 2 years ago

In the domestic goat (Capra hircus), digestibility is about 84% (https://www.sciencedirect.com/science/article/pii/S0022030266880037), compared to about 20% in L. africana. This means that the domestic goat digests its food so thoroughly that for every 100 grams of food eaten only about 16 grams emerge as feces. Loxodonta africana digests its food so partially that for every 100 grams eaten about 80 grams emerge as feces (assuming similar wetness in food and feces).

Posted by milewski about 2 years ago

My current information is that the average adult female of Loxodonta africana, with body mass about 3000 kilograms, eats about 125 kilograms of food per day, and produces about 107 kilograms of feces. After correcting for the likelihood that the feces are wetter than the food, and subtracting about 7 kilograms of mass from the feces accordingly, this would be consistent with digestibility of 20%.

Posted by milewski about 2 years ago

Very interesting! Thank you for tagging me along.

Posted by wasinitourguide about 2 years ago

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