Strategy games; on survival and reproduction

Abstract: Classical evolutionary life history concerns questions such as optimal timing of maturation, life span and number of offspring. These questions have mostly been studied theoretically under the assumption that the environment is stable and without taking into account frequency and density dependence. Life history theory is the basis for my thesis, in which I have studied the evolution of different life history strategies with a game theoretical approach incorporating both stochasticity and frequency and density dependence. The evolution of sexual reproduction has been considered enigmatic, but by incorporating competition, mating system and survival I show that sexual reproduction does not necessarily suffer from a twofold cost in terms of net population growth rate. This makes it easier to explain why sexual reproduction is such a successful and widespread reproductive strategy. I have also studied bet-hedging, i.e., risk-spreading. In a stochastic environment, where it is impossible to predict how large eggs or seeds need to be in order to survive and reproduce optimally, a female has to hedge her bets in order to make sure that some of her offspring survive. My result shows that the optimal strategy is to have variation in offspring size both within and between clutches. For some organisms, stochastic changes in weather can mean that the environment changes from livable to impossible to sustain an active life. Depending on the autocorrelation in the environment, I show that dormancy can evolve in both juveniles and adults or in just one of the stages. Changes in the environment does not necessarily have to be so detrimental that the bad periods can not sustain life. Individuals then have the two options to survive, they can either migrate or stay and adjust to the ''bad'' season. The choice that individuals make is frequency and density dependent were each individual migrates with a certain probability. Depending on parameter values, the evolutionary stable strategy ranges from obligate residency to obligate migration. When separating juvenile and adult migration probabilities, an optimal strategy is for juveniles to migrate and adults to stay as residents (depending on parameter values). This way of modeling evolutionary and ecological problems are found in frameworks such as adaptive dynamics and evolutionary game theory. The combination of evolution and ecology that adaptive dynamics uses appears to be a useful tool that can be used to solve many evolutionary questions.