Starvation and Predation as Factors Limiting Population Size

We consider a simple model in which an animal can control both its probability of starvation and its probability of predation. Probability of starvation is decreased by increasing the mean amount of food obtained in the day, but this increases the probability of predation. The optimal mean gain minimizes that total mortality. It is shown that as the amount of food that is required per day increases, the probability of starvation does not necessarily increase, and may actually decrease. This result arises because as the food requirement increases, the animal increases its predation risk in order to avoid starvation. The results suggest that it is inappropriate to argue that food alone or predation alone limits the size of a population when there is a strong interaction between them. Furthermore, the number of animals that die from starvation may not provide a reliable indication of the importance of food.