Answer:
Food availability affects positively in every society. In Mesopotamia, as society they had a efficient system of irrigations and farms, which guaranteed food, even they storage the excess, to prepare hard seasons.
So, this food wealth allow population to grow, because they're having a good standard life. Also, this positive situation allow them to trade.
On the other hand, if they are lacking of food, soon or later, people are going to die, or emigrate to other regions.