A diffusion-based approach to stochastic individual growth andenergy budget, with consequences to life-history optimizationand population dynamics

摘要

Using diffusion processes, I model stochastic individual growth, givenexogenous hazards and starvation risk. By maximizing survival to final size,optimal life histories (e.g. switching size for habitat/dietary shift) aredetermined by two ratios: mean growth rate over growth variance (diffusioncoefficient) and mortality rate over mean growth rate; all are size dependent.For example, switching size decreases with either ratio, if both are positive. Iprovide examples and compare with previous work on risk-sensitive foragingand the energy—predation trade-off. I then decompose individual size intoreversibly and irreversibly growing components, e.g. reserves and structure. Iprovide a general expression for optimal structural growth, when reservesgrow stochastically. I conclude that increased growth variance of reservesdelays structural growth (raises threshold size for its commencement) but mayeventually lead to larger structures. The effect depends on whether thestructural trait is related to foraging or defence. Implications for populationdynamics are discussed.