Final answer:
Crop circles are not a form of subsistence agriculture as they do not involve the cultivation of crops for sustenance.
Step-by-step explanation:
Pastoral nomadism, shifting cultivation, and the Mediterranean are all forms of subsistence agriculture. However, crop circles are not a form of subsistence agriculture. Crop circles are geometric patterns that appear in fields, often created by humans as a form of art or hoax. They do not involve the cultivation of crops for sustenance.