The hyperfecal-hypofecal continuum in consumers of plant matter

(writing in progress)

Faeces exist, almost as surely as eating exists.

The basic principles behind the production of faeces are of costs/benefits, and diminishing returns.

Various components of food have various digestibilities. The least digestible components are - depending on the species of consumer and its particular digestive system - discarded, as the biological equivalent of rubbish.

This occurs despite

• the investment of time and energy made in acquiring the food, and
• the risks taken as part of this foraging.

It would be naive to expect members of the 'food-chain' to be thorough processors, simply converting all of the matter and energy they consume.

However, what are remarkable are

• the degree to which various animals differ in the thoroughness of their digestive process,
• the quantity of faeces produced relative to food consumed, and
• the finding that it is not necessarily the most fibrous diets that produce the most faeces.

Some animals 'overproduce' faeces in the sense that they seem to extract little of what they eat, whereas others 'underproduce' faeces in the sense that they extract virtually all of what enters the digestive process. Most animals are intermediate.

It is the range in this continuum - which I dub the 'hyperfecal/hypofecal continuum' - that is greater than appreciated by many or most naturalists.

In this Post, I illustrate the hyperfecal/hypofecal continuum by examining its extremes, in the form of

• the giant panda (Ailuropoda melanoleuca, https://www.inaturalist.org/taxa/41659-Ailuropoda-melanoleuca), and
• fungus-culturing termites in genus Macrotermes (https://www.inaturalist.org/observations?place_id=any&taxon_id=346639&view=species).

Both the giant panda and Macrotermes forage on extremely fibrous matter, composed largely of cellulose (https://en.wikipedia.org/wiki/Cellulose) and lignin (https://en.wikipedia.org/wiki/Lignin).

However,

• the former acts as a 'fecal factory', whereas the latter recycles the fibre repeatedly within the system, until virtually nothing emerges; and
• the former seems to defecate for a living, whereas the latter - at least at the scale of the whole colony in this eusocial insect - hardly produces anything that can be called faeces.

Indeed, the digestive process of Macrotermes is such that it treats the faeces of various herbivores as part of the diet.

Crucial for understanding the hyperfecal/hypofecal continuum are

• the role of microbes, particularly fungi (https://en.wikipedia.org/wiki/Fungus#:~:text=Fungi%20include%20symbionts%20of%20plants,and%20exchange%20in%20the%20environment.), and particularly aerobic fungi (https://en.wikipedia.org/wiki/Termitomyces), and
• the repeated reingestion of food, slowing incremental breakdown of every particle of fibre.

In the giant panda, the gut is short and simple. There is minimal development of gut-chambers in which food is delayed for breakdown by bacteria and other microbes.

The result is that

• virtually all of the fibre emerges as faeces, and
• even the digestible proteins, such as chlorophyll, are only partly digested (https://www.pdxwildlife.com/does-panda-poop-stink/).

In other words, the hyperfecality of the giant panda is such that even the greenness of the plant matter consumed seems not to be converted to brown.

(writing in progress)

Publicado el 14 de septiembre de 2023 a las 11:25 PM por milewski