Survival and production in variable resource environments

A dynamic energy budget (DEB) model describes the rates at which organisms assimilate and utilize energy from food for maintenance, growth, reproducti on and development. We study the dynamic behavior of one particular DEB mod el, Kooijman's kappa -rule model, whose key assumption is that somatic and reproductive tissues are competing for energy. We assume an environment in which the food density fluctuates either periodically or stochastically (pi nk noise). Both types of fluctuations stimulate growth; the magnitude of th e (average) increase in size depends on both the strength and duration of t he fluctuations. In a stochastic environment, the risk of mortality due to starvation increases with increasing fluctuation intensity. The mean lifesp an is also a function of the model parameter kappa characterizing the parti tioning of energy between somatic and reproductive tissues. Organisms commi tting a large fraction of resources to reproduction endure periods of food shortage relatively well. The effects of food fluctuations on reproduction are complex. With stochastic food, reproduction in survivors increases with increasing fluctuation intensities, but lifetime reproduction decreases. P eriodic fluctuations may enhance reproduction, depending on the value of ka ppa. Thus, a variable food supply stimulates growth, increases mortality an d may enhance reproduction, depending on life history. (C) 2000 Society for Mathematical Biology.