The Empty Pampas: epitome of a biogeographical mystery, part 1

When Spanish adventurers, on a misguided quest for silver, stumbled on the Pampas of Buenos Aires Province in 1516, they found something so unexpected that it has taken centuries for us to realise the full mystery of it. The most fertile plain on Earth, virtually empty of large animals.

There is nowhere on any continent to match this well-watered, deep, nutrient-rich soil under a mild climate (see https://reader.elsevier.com/reader/sd/pii/S0254629915003051?token=148F2A14B66B88352DA774E299F629491B477C6039911361AD6A91D3ACE255E055AE04170E951A11E08E0884D5D3C13C&originRegion=us-east-1&originCreation=20210812033236 and https://en.wikipedia.org/wiki/Pampas). And yet the indigenous fauna at the time of European arrival contained no ungulate larger than the pampas deer (Ozotoceros bezoarticus celer, about 30 kg, https://en.wikipedia.org/wiki/Pampas_deer).

The fertility of the pampas seems to have been fully expressed during the Pleistocene, with the term 'megafauna' being understatement rather than exaggeration (see file:///C:/Users/Antoni%20Milewski/Downloads/Vizcanoetal.2012.Chap.5.Evolutionlargesizeherbivores.pdf). And it has been fully expressed for the last two centuries, in the form of the most productive farmland on Earth (see https://en.wikipedia.org/wiki/Buenos_Aires_Province). So why does it seem not to have been expressed for the ten thousand years between the megafaunal extinction and the arrival of the gauchos?

The easy answer for palaeontologists is that the megafaunal extermination - whatever its ultimate cause - simply left the pampas empty. Most agree that here we have a gross artefact of human destructiveness: the fate of a naive fauna exposed for the first time to the technical predation brought by sudden human colonisation of the American supercontinent from the north about 14 thousand years ago (see https://en.wikipedia.org/wiki/Quaternary_extinction#Hunting_hypothesis and https://en.wikipedia.org/wiki/Settlement_of_the_Americas).

The trouble with this 'hunting hypothesis' is that it raises more questions than it answers. These include 'why was there so little faunal compensation?' and 'why was there no domestication?'

All that was needed for the pampas to be restored to some semblance of a 'big game' ecosystem in the Holocene was adjustments of body size, habitat, diet, gregariousness and anti-predator behaviour in a considerable surviving fauna of South American herbivores and carnivores. And all that was needed for the aboriginal people to herd livestock in the pampas was a lateral transfer of practices already established in the nearby Andes (see https://link.springer.com/chapter/10.1007%2F978-0-387-74907-5_8).

Yet for some strange reason neither process actually occurred - and this is why the Empty Pampas deserves a deeper explanation.

To be continued...

Publicado por milewski milewski, 12 de agosto de 2021

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