The Empty Pampas: epitome of a biogeographical mystery, part 4
...continued from https://www.inaturalist.org/journal/milewski/55195-the-empty-pampas-epitome-of-a-biogeographical-mystery-part-3#
In order to understand the ecosystem of the pampas, one must appreciate just how numerous and diverse rodents are in this well-watered grassland. So much so that, in some sense, the rodents seem to have replaced ungulates as the main grazers.
The capybara (Hydrochoerus hydrochaeris, about 50 kg) occurred in the wettest parts of the pampas, together with the coypu (Myocastor coypus, about 6 kg, https://en.wikipedia.org/wiki/Coypu).
These can be seen as diminutive ecological counterparts of semi-aquatic ungulates such as Asian buffaloes (Bubalus arnee and B. bubalis) and African lechwes (Kobus leche and K. megaceros).
In the well-drained parts of the pampas, the plains viscacha (Lagostomus maximus, about 5 kg, https://en.wikipedia.org/wiki/Plains_viscacha) and tuco-tucos (Ctenomys spp., 0.1-1.0 kg, https://en.wikipedia.org/wiki/Tuco-tuco) were the main grazers.
These may seem to be little more than counterparts for North American prairie dogs and gophers. However, they differ significantly in being specialised for grazing.
Equally dependent on greens is the Brazilian guinea pig (Cavia aperea, about 0.6 kg, https://en.wikipedia.org/wiki/Brazilian_guinea_pig), a close relative of which was domesticated for the pot elsewhere in South America.
It is easy to assume that the most productive environments favour large organisms. However, the opposite is closer to the truth, for both the photosynthesisers and the consumers.
Think of intense cultivation by means of fertilisers and irrigation: repeated crops of small plants, turning over rapidly rather than growing large and woody.
It is no coincidence that the Serengeti is more similar to a grassland than to a forest, because tall woody vegetation tends actually to be something of a desert for large animals.
This raises a counterintuitive possibility:
that rodents were such efficient consumers of the treeless grassland of the pampas during the Holocene that they actually 'outcompeted', i.e. excluded, all ungulates other than the pampas deer.
The 'compensation' process after megafaunal extermination consisted not of an immigration of nearby species of deer, but rather of an increase in the populations of certain rodents.
And, if so, the aboriginal population followed the ecological flow, because their most productive foods were the rodents.
There would have been little incentive for bothering with domestic camelids, or even for bringing in the domestic guinea pig (Cavia porcellus). After all, wood was so scarce on the pampas that - far from being enough to make corrals - there was not even the stuff of spears.
The equestrian indigenes repelled would-be gauchos from most of the pampas by resourcefully converting Phragmites australis into flimsy but fearsome reed-spears.
To be continued...
Comments
After reading the first 3 journal instalments about the Pampas lack of large mammals wild and domestic I was thinking along these lines but wanted to wait to comment before reading this latest. My thought was, domestication and husbandry are pretty hard work and the great majority of humans aren't inclined to take on hard work when there is no pressing need. So why go through the rigors of the domestication process in an area where the food source is extremely profligate, easy to hunt/trap, and yields more than enough meat per carcass to feed a person for 5 days? And with no mammalian predators that food source wouldn't require the protection that is part of the domestication process either.
A haven for large rodents would be a heaven for a human culture.
@marshall20 Many thanks for your thoughts on this.
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