Final answer:
The expansion of open woodlands and savanna habitats influenced austral piths to vary their diet, potentially including more grassland resources like seeds and tubers, in addition to their usual foraging.
Step-by-step explanation:
The expansion of open woodland and savanna habitats caused austral piths to adapt their diets according to the varying availability of food resources in their environments. These changes in habitat likely led to shifts in the types of plants and animals they consumed. With the spread of open woodlands and savannas, austral piths may have incorporated more grassland resources such as seeds, tubers, and possibly grazing animals into their diet, alongside the diverse plants and smaller game they typically foraged for in more wooded or forest-like settings.