The adult squirrel population is affected by several factors. Foremost among these are yearlings which mature into adult squirrels and adult squirrels that die a natural death. These are affected by the food level; the less food, the less yearling survive and the more adults die.

Separate from the natural deaths category is the number of squirrels that are run over (roadkill). This is based on Additional factors that affect the adult squirrel population are immigration and emigration. When there is an abundance of food and at least enough area (0.4 acres per squirrel) for the existing population, more squirrels will come into the area. On the other hand, if there is too little food or space, squirrels will leave, facing the possibility of becoming roadkill.

Some additional variables were introduced to simplify expressions and make them more readable; in some cases, the names had to be shortened due to Stella's 255-character limit on expression length. Flev is a ratio of the food per squirrel to the adequate food per squirrel; in other words, when flev is 1, each squirrel has exactly enough food to survive comfortably (the adequate food level), and no food is left over. A_sq is the area (number of acres) per squirrel (total area / squirrel population). Total is simply the total number of squirrels.