For more than a year Robin and the Honey Badger have felt inspired to compare the giant panda (Carnivora: Ursidae: Ailuropoda melanoleuca) of China with the capybara (Rodentia: Caviidae: Hydrochoerus) of South America. What has lagged, however, is a creative way to combine the relevant biological principle with the right expository form. Without both, this comparison may seem far-fetched, its subjects too disparate.
This morning it struck us that the central concept here may be a biological interpretation of ‘thrift’. This word has always risked misunderstanding but its true meaning is particularly forgotten today. There is a potential allegory in the distinction between thrift in the negative sense of austerity and thrift in the positive sense of prosperity. An apt injunction may be: ‘Waste not, want not – be provident if your family is to prosper, for thriving is borne from thrift’. We don’t doubt that both animals are appropriately adapted to their respective environments – the mountains of central China versus the floodplains of South America. However, the capybara seems thrifty in the same sense as the giant panda seems unthrifty, and this may have made all the difference to their prospects for survival.
What do the giant panda and capybara have in common? Both have a staple diet of grass[1] and both are unusual among large grazers in being drawn from lineages other than the ungulates[2] . Both compete so successfully with the naturally coexisting deer[3] that they monopolise their main foods. The giant panda belongs to a carnivorous order, but is oddly obsessed with grazing the very grasses shunned as food by ungulates. The capybara is essentially a human-size guinea pig, the largest living rodent on Earth – as if the grazing niche in the Neotropics has been so vacant that it has taken a bulge of gigantism from an unlikely source to fill this niche. Their compelling similarity is that both species have a staple diet of cellulose. And their compelling difference is that the giant panda wastes almost all the cellulose it consumes, whereas the capybara instead digests, absorbs and metabolises its cellulose with even more thoroughness than that of deer. This has divergent consequences for the ability of giant panda and capybara to withstand mounting pressures from people.
What needs to be explained is that, although both the giant panda and the capybara are specialised to eat a staple diet of grass, one species is so slow-breeding that it barely survives today – despite the devoted protection it receives – whereas the other is so fast-breeding[4] that it continues to defy an encroaching humanity that feels no protective urge towards it. Here we have mammals with comparable niches but incomparable prospects. The giant panda wanes even as it is adored and coddled: no matter how intensive the breeding programs, this poster child for endangered species seems reluctant to increase its numbers.
Conversely, the capybara is so lacking in common appeal that its public image is ‘capy-what?’, yet this rodent remains perhaps the most widespread and common of all the larger wild mammals of its continent. In fact, this oversize guinea pig has increased with livestock ranching and is expanding into new agricultural habitats in a few places[5] .
One way to explain this anomaly is to show that the capybara is thrifty – in the true sense of the word – in contrast to the giant panda. Thrift may seem synonymous with austerity, frugality and stinginess. But these would mislabel the capybara, which is characterised by rapid – perhaps profligate – reproduction. The critical difference, and this is indeed the basis of capitalism and the affluence we attribute to that system, is that the verb of thrift is to thrive. None of the superficially synonymous words are linked to a verb with similar meaning. Thrift is more than a way of making ends meet; it’s an economy of success.
Here, then, is a way to focus our prospective e-book chapter. The environment and niche of the capybara are such that this species thrives on neglect; whereas the environment and niche of the giant panda are such that this species is a stranger to thrift – and to thriving. And along the way we’ll learn a lot about the biology of these two species, of grazers and grasses, and of ecology and evolution.
We give readers the following preview of what we plan to write.
The giant panda wastes virtually all of the cellulose that it eats, chewing it only superficially and then defecating it as quickly as possible. By contrast, the capybara chews and digests its cellulose so thoroughly that, of all grazing mammals, it has the most elaborate system of processing and reprocessing its food. The giant panda spends most of its time eating: manipulating bamboo by means of a special wrist bone, stuffing the green culms into its mouth, and chewing. But after all this work its gut merely skims off the easily-digestible sugars and proteins, leaving the cellulose so unaffected that the resulting faeces are still a dull green. The capybara spends a similar time foraging, but makes the most of every gram it swallows. It chews more thoroughly than the giant panda the first time around and regurgitates[6] its food to give it another chew. Digesting what it can, it then forms a soft, tasty type of faecal pellet that it re-eats straight from the anus. Now that really is making ends meet. The material is chewed once again, for the third time, and the internal recycling process is then repeated to produce a tasteless type of faecal pellet, exhausted of all energy and nutrients, which is at last discarded.
These evolutionary divergences can ultimately be explained by a basic difference in the types of grasses that the two mammals eat. For it is characteristic of bamboos that they grow in cohorts; each generation culminates in flowering and senescence – a life-strategy that depends on herbivory being kept to a minimum. Whereas the characteristic life-strategy of the floodplain grasses of South America is to encourage repeated cropping and mowing, which the grasses compensate by continual vegetative regeneration. As a result, bamboos – including the relatively small ones preferred by the giant panda – defend themselves so heavily with lignin, cyanide precursors and goitrogens[7] that any grazer specialising on them must settle for real austerity and frugality in its reproductive life. By contrast, floodplain grasses – including the relatively fibrous ones characteristic of llanos, pantanal, and pampas – put up so little defence that they are worth digesting thoroughly.
With this allegory greening our minds, we continue to explore the Bio-edge. And we look forward to seeing you in our next blog-post.
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1 Poaceae, a family that includes both the low bamboos (e.g. Fargesia) eaten by the giant panda and the marsh grasses eaten by the capybara
2 hoofed mammals, i.e. Perissodactyla and Artiodactyla
3 Artiodactyla: Cervidae
4 Whereas the giant panda carries a maximum of three foetuses in each pregnancy, bears a maximum of two newborns, and usually raises only one of these because the other perishes from neglect, the capybara bears a maximum of seven and usually raises four offspring at a time. The giant panda breeds only once every two years whereas the capybara can breed twice per year. The single newborn of the giant panda is proportionally one of the smallest among non-marsupial mammals; by contrast each large newborn of the capybara outweighs the infant giant panda by an order of magnitude and the whole litter combines several of these extremely well-developed newborns. Offspring of the giant panda do not attempt to eat grass until six months old, whereas offspring of the capybara, which are born with a full set of permanent teeth, eat grass immediately. The giant panda reaches sexual maturity only after four years, whereas the capybara reaches sexual maturity at 1.5 years old. There is no contest: the capybara is by far the more fecund of the two mammals.
5 e.g. in the chaco of Paraguay, where semi-arid forest has recently been converted to irrigated cropland
6 i.e. merycism, not rumination
7 i.e. substances that induce further deficiency of iodine, a nutrient already in short supply at the high altitudes typical of the habitat of the giant panda