How can the savannah elephant afford to produce feces richer than its food? part 3
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Why does Loxodonta africana not eat its own feces, given that they are about as rich as its food?
Although infants of L. africana do eat the feces of adults in limited quantities (see https://herd.org.za/elephant-dung-a-daily-snack-for-khanyisa/ and https://en.wikipedia.org/wiki/Coprophagia), this behaviour ceases later in life.
Mammals with a caecotrophic mode of digestion, such as Castor (beavers), routinely eat their own feces throughout their lives (see https://www.naturebob.com/eats-its-poop and https://cdnsciencepub.com/doi/10.1139/z95-113). This is an alternative to the cud-chewing of the ruminant mode, achieving similarly thorough digestion by means of a different approach.
Caecotrophic mammals have appropriately adapted guts; no mammal with a simple, short gastrointestinal system routinely eats its own feces. And as we know from our own, human, psycho-sensory system, we are 'hardwired' to feel disgust at the prospect, regardless of the rational possibility that under certain circumstances the eating of our own feces might be harmless and economical.
At a deeper level, I suggest that L. africana rejects its own feces because it is adapted to a niche in which it is economically sound to act wastefully.
The argument here has two bases, as follows:
- continual gross damaging of large plants boosts the growth-rates of the vegetation in the height-zone within reach of the proboscis, and
- the depletion of certain crucial micronutrients in feces makes it more profitable to eat fresh food than to recycle already partially digested material (please see part 4).
It is typical of foraging by L. africana that certain plants are damaged to what seems to be a wanton extent. For example, trees are pushed over with little being eaten (see https://www.youtube.com/watch?v=-ki7mkAIWS8 and https://www.youtube.com/watch?v=tHzHec7mLC0 and https://onlinelibrary.wiley.com/doi/abs/10.1002/9781119081111.ch17 and https://journals.co.za/doi/abs/10.10520/EJC96413).
A reasonable explanation is that L. africana manages vegetation quasi-horticulturally, following the principles of pruning, hedging and composting. This would be consistent with a niche in which maintaining access to quantity takes priority.
Wanton damage to plants cannot be assumed for proboscideans generally. For example, certain species of Mammuthus (mammoths, https://en.wikipedia.org/wiki/Mammoth) relied on short, nutrient-rich grass, and were adapted to winters so cold that all growth of plants ceased.
Assuming that the quantity of food was limited, it is likely that the niches of these species of Mammuthus differed from those of L. africana (e.g. see https://www.nature.com/articles/srep09791#:~:text=A%20dietary%20niche%20implies%20that,of%20dung%20that%20fertilized%20the). In particular, I hypothesise that their intestines were relatively long and complex and that feces were routinely eaten during times of shortage.
And no sooner have I hypothesised this than I see that there is indeed evidence: https://www.researchgate.net/publication/222824797_Mycological_evidence_of_coprophagy_from_the_feces_of_an_Alaskan_Late_Glacial_mammoth and https://core.ac.uk/download/pdf/232416985.pdf.
The teeth have far fewer corrugations in L. africana (https://www.elephants.com/news/elenotes/posts/dental-health-for-aging-elephants and https://boneclones.com/product/african-elephant-tooth-KO-045) than in Mammuthus primigenius (https://rentadinosaur.com/fr/products/mammoth-woolly-mammoth-tooth-cast-replica-item-t17 and https://www.fossilera.com/pages/about-mammoth-molars and https://news.artnet.com/art-world/boy-finds-woolly-mammoth-tooth-1625770 and https://faopalfossils.com/Mammuthus-primigenius-tooth-2776-gram). This is consistent with far less thorough chewing in the savannah elephant than in the most extremely-adapted mammoths, with implications for digestive thoroughness - and the seasonal eating of feces.
The teeth of Elephas maximus (Asian elephant, https://en.wikipedia.org/wiki/Asian_elephant)
are intermediate (https://www.skeletonsandskullssuperstore.com/product/asian-elephant-tooth-replica/ and http://en.upali.ch/teeth/).
Elephas is more closely related to Mammuthus than to Loxodonta, and depends on grasses more than does L. africana. Its teeth have narrower ridges and its intestines are accordingly longer than those of L. africana, giving it a digestibility quotient of 25% instead of 20% (https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.565.4763&rep=rep1&type=pdf).
Elephas maximus is certainly destructive in plantations (https://asesg.org/PDFfiles/Gajah/08-19-Andau.pdf and https://indianexpress.com/article/trending/viral-videos-trending/elephants-destroy-over-300-banana-tress-leave-one-with-a-birds-nest-untouched-watch-viral-video-7305788/#:~:text=The%20incident%20happened%20in%20Sathyamangala,more%20than%20300%20banana%20trees.). However, is less renowned than L. africana for wanton damage to indigenous trees and large shrubs in natural vegetation.
to be continued...
Σχόλια
https://www.sciencedirect.com/science/article/abs/pii/S003101821930851X
https://markgelbart.wordpress.com/2016/02/23/the-eurasian-steppe-mammoth-mammuthus-trogontherii-may-be-the-same-species-as-the-north-american-mammoth-mammuthus-columbi/
https://animals.fandom.com/wiki/Columbian_Mammoth
Hystrix is not caecotrophic: https://www.tandfonline.com/doi/pdf/10.1080/02541858.1984.11447867 and http://www.jafs.com.pl/Digestive-physiology-resting-metabolism-and-methane-production-of-captive-Indian,102741,0,2.html.
Erethizon is not caecotrophic. See page 47 in: https://books.google.com.au/books?id=A3HuW_DMglQC&pg=PA52&lpg=PA52&dq=Coprophagy+in+porcupine&source=bl&ots=6LmXvy_nO9&sig=ACfU3U3PlKy5YPIPCcJNnSAMZbq0UKdpkQ&hl=en&sa=X&ved=2ahUKEwiGwt7Fg971AhUVheYKHccGAhUQ6AF6BAgbEAM#v=onepage&q=Coprophagy%20in%20porcupine&f=false
Interesting. I've never seen young elephants eating faeces - but have seen young hippos do it underwater. I guess as a result of them being 'pseudo ruminants' and being born with sterile guts that need to be charged with microorganisms for efficient digestion.
An odd fact is that the hook-lipped rhino (Diceros bicornis) in Ngorongoro Caldera sometimes eats the feces of the western white-bearded wildebeest (Connochaetes taurinus). Ref.: Klingel & Klingel (1966)
Here is an observation on pp. 625ff in a chapter, by Potter and Yeates, in the book ‘The Horse’ (1977), edited by Evans et al., and published by W H Freeman & Co, San Francisco.
“In pastures where stocking rate is high and in pastures that are not routinely harrowed, horses will graze portions of the pasture very close and will leave defecation areas to grow tall...Horses are likely to establish an elimination area in the pasture or paddocks and will not graze that area until there is no other source of feed...Horses will generally walk some distance to the elimination area to urinate or defecate...Adult horses will generally reject feces of their own kind, but foals will repeatedly eat feces of mares, especially when kept in dry lots. Coprophagy in adult horses is not believed to be a normal phenomenon.”
The caption of an accompanying photo reads: “Horses will establish an elimination area in a paddock or pasture. In this area the grass grows tall, and horses will not readily graze it.”
My comments:
I am not surprised that the domestic horse, as an adult, avoids feces of its own species. This is because feces can contain pathogens and parasites. The tendency of the male in particular to defecate on one small area makes sense in terms of both hygiene and social/sexual marking.
However, it is interesting that there is a limited incidence of coprophagy by juveniles.
Furthermore, there are consequences for the grasses. The domestic horse has to defecate somewhere in the grassland it inhabits. A corollary of the habit of defecating in certain spots, and then avoiding those spots while foraging, is that there is an inadvertent system of pasture management by the horse itself. There are patches of grass that are both fertilised and allowed to grow tall, presumably setting seed before being grazed again.
This spontaneous system might achieve the following two things: a) protection of the pasture from overgrazing, and b) allowance of the grasses to set seed (bearing in mind that the domestic horse is even fonder of grass seeds than it is of grass foliage). Were it not for the protective role of defecation, it is easy to imagine that the sward might be uniformly grazed to the point where it loses biological power, and to the point where it either fails to set seed or has all or most of its seeds predated by the horse.
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