Behavioral responses to variations in population size: a stochastic evolutionary game

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Abstract
The effects of variations in population size may be important in the evolution of individual behavior. We use simulation models to study the stochastic evolutionary contest between two behavioral strategies affecting individual survival and reproduction, one conservative (low fecundity and low mortality risk), the other risky (high fecundity and high mortality risk). Trade-offs of this kind are involved in many types of behavior, including foraging under risk of predation, parental care, size versus number of offspring, and so on. We treat the combined effects of demographic and environmental variance, demographic variance being important for small populations and environmental variance being important at all population levels. With high environmental variance, population numbers fluctuate sharply, so that demographic variance becomes intermittently important. As a consequence, either behavioral morph may become fixed in the population, depending on initial conditions and on chance events. We treat both phenotypic and genetic models. In a genetic model with the heterozygote employing the risky strategy, both behavioral morphs may coexist as a randomly fluctuating polymorphism.

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