Red blue and green: Dyeing population dynamics

Numbers or densities of a natural population typically change over time. These fluctuations result from density-dependence mechanisms in the populations or external environmental variations. According to modern ecological research, time series describing population sizes and physical environments tend to be dominated by low-frequency fluctuations, whereas, contrary to this, simple population dynamic models are mostly dominated by short-term fluctuations. We review the recent theoretical advances in this ecological research theme, referred to as the ecological colour problem. Here population dynamics are analysed in the frequency domain, and named, in analogy of the light wave length, red, white or blue. We emphasise the modern tendency of deriving population ecological insight from dynamic, non-equilibrium analyses. We first deal with deterministic and stochastic single-species population dynamics. We then study how simple communities may respond to environmental noise. We finish by raising the important problem of how the colour of the environmental noise may affect the risk of population extinction.