Eco-evolutionary feedback between size and strategy; alternative migratory tactics in salmonid.

     In salmonids, some juveniles migrate to the ocean and come back to their natal river (migrant tactic), whereas others mature in the river without migration (resident tactic). There is a trend that larger one becomes a resident. This trend is explained by the status-dependent-strategy model(SDS), in which fitness functions of both tactics are functions of status, and the status where both fitness functions intersect is a threshold at which tactic changes. A density dependence of growth is documented. We incorporate the growth suppression of juveniles into the SDS, and explore how it affects the dynamics of alternative tactics. In this talk, we demonstrate that the negative feedback between resident density and juvenile body size can cause an instability of size distribution of juvenile, resulting in a fluctuation of the population density of migrant type as well as stream population. We also consider the effect of climate change on the average body size of juvenile, and investigate the ecological and evolutionary response to it. As a result, change in the average size can cause phase transition from stable to unstable and vice versa. Evolutionary response to the change can recover the state of population to the same state before environmental change, but various type of dynamics emerged during evolutionary response.