What factor can lead to high population densities of these macaques when resources are plentiful?

Answer

Their highly social nature

Because they are highly social and adaptable, their population density can become quite high when the resources available to them are plentiful, which in turn increases demand for accessible food.

What factor can lead to high population densities of these macaques when resources are plentiful?
dietanimalCrabPrimateMacaque