How did pastoralism represent a change in hunter-gatherers?
Food became more available.
From Internet:
Pastoralism is a form of animal husbandry where domesticated animals known as livestock are released onto large vegetated outdoor lands (pastures) for grazing, historically by nomadic people who moved around with their herds. The species involved include cattle, camels, goats, yaks, llamas, reindeer, horse and sheep. Wikipedia