Exponential growth of unstructured populations

Abstract The number of reproductive units is expected to grow exponentially in the absence of regulating feedbacks. The lack of feedbacks is a definitive assumption of any model predicting exponential growth, be it individual- or population-based, discrete or continuous, deterministic or stochastic. The exponential growth of a population can be characterised by its long-term per capita rate of increase (population growth rate, pgr) in any actual representation. Exponential growth with a constant pgr will occur whenever the stochastic changes in the environmental conditions—including modifying and regulating ones—affecting births and deaths are stationary in the long run. Case studies indicate that temporary periods of exponential population increase or decline must be regular in nature, and pgrs may show remarkable temporal and spatial invariance.