with Henrik G. Smith, and Niclas Jonzn

One of the most striking ecological responses to recent climate change is the shift in the timing of seasonal events (phenology)
documented in a wide range of organisms. The adaptive value and the demographic consequences of these changes are often
poorly known, however. We develop a game theory model to study adaptation of timing of reproduction in birds with social
dominance hierarchies. Specifically, we consider resident birds with winter flocks where early-fledged juveniles obtain higher
ranking because of prior residency advantages when flocks are formed. In the absence of competition birds should time their
reproduction to maximize the availability of food suitable for rearing the offspring in the form insect larvae available only
during a short period during spring. However, owing to the competitive advantages of early fledging, the evolutionarily stable
strategy (ESS) is to let offspring hatch before the date that maximizes the availability of their food. We study the effects of
environmental change on breeding population densities, ensuing selection pressures and long-term evolutionary equilibria in
this system. We show that the ESS hatching date will advance with increasing winter survival and habitat productivity since
these factors increases the pressure of the post-fledging competition. While much previous literature mainly links selection on
reproductive phenology to changes in food peak dates, our model offers a conceptually new set of explanations for understanding
phenological and demographic trends in a changing climate. Moreover these findings emphasize that treating phenology as an
evolutionary game rather than an optimization problem fundamentally changes what is to be considered as an adaptive response to climate change.