The center of the food submodel is the food stock - how much food is available to the squirrels each year. The food production is based on a weather graph, indicating how "good" the overall weather was during any given year (in terms of acorn production), and the area (number of acres) of trees that can produce food. Food consumption is based on the amount of food an average squirrel will eat if it is available (adequate_food) and the total squirrel population. Rotting is simply the amount of food produced but not eaten by squirrels.
Since the amount of food produced one year is entirely removed the next year, I had given thought to making food a simple converter, but decided against it, since a stock is more flexible.
The "food_squirrel_ratio" converter is the ratio of food available to
squirrel population, and is used in determining survival rates and litter
sizes of squirrels.