Sustentation means the act of providing support or nourishment to something or someone.
Sustentation is about giving help or food to keep something or someone alive and well.
Examples:
The sustentation of the baby bird is the job of its mother.
The sustentation of the plants is important for the garden to grow.
We need to think about the sustentation of the animals in the zoo.
The sustentation of the big tree is the job of the earth and the sun.
The sustentation of the whole town is the job of the farmers.
The sustentation of the baby is the job of its parents.