The level of food shortage you're talking about is extreme and very unlikely, excepting an extremely unlikely series of major disasters. It would take a lot to

The level of food shortage you're talking about is extreme and very unlikely, excepting an extremely unlikely series of major disasters. It would take a lot to overcome people's inertia to action and by that stage of your theoretical disaster they will be too focused on immediate needs of food, energy & safety for them and their family to consider wider actions.