Effects of territory competition and climate change on timing of arrival to breeding grounds: a game-theory approach

Phenology is an important part of life history that is gaining increased attention because of recent climate change. We use game theory to model phenological adaptation in migratory birds that compete for territories at their breeding grounds. We investigate how the evolutionarily stable strategy (ESS) for the timing of arrival is affected by changes in the onset of spring, the timing of the resource peak, and the season length. We compare the ESS mean arrival date with the environmental optimum, that is, the mean arrival date that maximizes fitness in the absence of competition. When competition is strong, the ESS mean arrival date responds less than the environmental optimum to shifts in the resource peak but more to changes in the onset of spring. Increased season length may not necessarily affect the environmental optimum but can still advance the ESS mean arrival date. Conversely, shifting a narrow resource distribution may change the environmental optimum without affecting the ESS mean arrival date. The ESS mean arrival date and the environmental optimum may even shift in different directions. Hence, treating phenology as an evolutionary game rather than an optimization problem fundamentally changes what we predict to be an adaptive response to environmental changes.