Risk-taking behaviour and the timing of life history events: consequences of body size and season

When faced with behavioural options differing in energetic gain and mortali ty risk due to predation. an individual's best compromise to the conflictin g demands of growth and survival will depend upon both its current energeti c state and the future opportunity for growth. Such state- and rime-depende nt tradeoffs are often investigated using dynamic programming. By specifyin g the relationship between fitness and the stale variable of interest at th e time of some relevant life history event, fitness-maximizing solutions fo r all state acid time combinations can be found. To date. however, no dynam ic programming modal has considered the possibility that animals may be cap able of delaying life history events beyond the time period modelled. In su ch cases, in addition to being influenced by future life history events, sh ort term behavioural responses to foraging-predation risk tradeoffs may als o indirectly affect the timing of those events. I use dynamic programming ( 1) to investigate the effects of body size and rime of year on patterns of risk-taking behaviour in animals capable of postponing life history events, and (2) to explore the outcome of such individual decisions on the subsequ ent timing of life history events and the states of individuals undergoing those events. In doing so, I relax the basic dynamic programming assumption of a finite time horizon and allow individuals to postpone initiating the life history event until some future favourable period of time. Such delays are frequently observed in anadromous fishes, including coho salmon, Oncor hynchus kisutch; hence, I use the relevant features of their biology to dev elop the model and illustrate the general problem of interest.