Population dynamics in a noisy world: Lessons from a mite experimental system

Both density dependence and variability in the environment are ubiquitous for biological systems. Theory has repeatedly indicated that environmental noise and density dependence interact, sometimes in unpredictable ways. Phenomenological models may capture the dynamical processes, but often give little insight into the way organisms may "filter" an environmental signal into dynamical response. Laboratory models provide ideal systems in which to explore the effects of the current environment on future population size, as well as being proving grounds for time series analysis, because they can experimentally be used to concurrently explore the biology and the population dynamics. Here we give an overview of ongoing studies of the soil mite Sancassania berlesei living in a stochastic environment generated by random supplies of food. We show: (1) how environmental noise affects the mean, variance, and temporal pattern of the population dynamics, (2) how much biological knowledge can be extracted by time series analysis, in the presence or absence of knowledge of the stochastic forcing, and (3) how the stochastic forcing interacts with the population density and age structure to affect per capita food, and how this, in turn, changes growth rates and influences life history decisions, such as age and size at maturity, reproductive allocation, and so on. The biological mechanisms indicate that a given sequence of environmental states may lead to quite different population dynamics depending on subtleties of the initial age structures and density. Ultimately, understanding (or predicting) population dynamics, becomes a question of understanding the inter-relationship of the environment and the life history.