twovultures
Donor
Llama pastoralism probably spreads over the Mexican altiplano, which is well suited for llamas and marginal for agriculture. It certainly spreads as far north as the Pueblo peoples of the American Southwest, where people had trading relations deep into Mesoamerica and IOTL proved quite adept at adopting sheep pastoralism from Europeans. How fast this happens, I don't know. At least one paper I read has estimated that the maximum 'front speed' of the adoption of pastoralism in southern Africa was 3.3 km/year (Fort, Joaqim. Biased dispersal can explain fast human range expansions. Nature, June 3rd, 2020). I suppose it could conceivably spread even faster, as Native Americans as far as Canada had adopted horses within 250 years of Cortes' invasion of Mexico, but that was adding a domestic animal to an existing hunter-gatherer-farmer lifestyle, not changing one's lifestyle from hunting animals to raising stock, which is a much more drastic change.What would happen next?
The form llama pastoralism takes is not like the Old World, with nomadic pastoralists driving herds across the Serengeti or the Steppe. IOTL, llama pastoralist communities in the Andes seem to have been part of larger agriculturalist communities, instead of independent. IMO, it's because llamas don't produce enough milk to spare for human consumption, so pastoralists are denied renewable, storable calories in the form of dairy. So, llama pastoralism will be agropastoralism among the Pueblo, and maybe gatherer-pastoralism among other peoples in the mountain west absent other changes (it seems likely that potatoes come with llamas, and that might tip the balance in favor of agriculture over hunting and gathering in the region, but that's another thread).