In a continually changing environment populations fluctuate in size and composition, deviating from a stable age-distribution. Making predictions about future behaviour of population dynamics should not, therefore, rely solely on asymptotic assumptions, as is often the case. These transient dynamics may arise as exceptional cohorts, e.g. baby-boomers, progress through their population’s age-structure or from a mismatch between the age-distribution of residents and migrants. Here, we examine the impact of transients on annual population growth across 31 European countries between 2002 and 2008.
Results/Conclusions
We find that observed population growth is larger than what we would expect from asymptotic growth alone in all but two countries, Latvia and Lithuania. Using perturbation analysis of spatial (mega)matrix population models, we show furthermore how continental asymptotic growth is driven by local demographic rates and continental transient growth is driven by within Europe migration. Our results emphasise the necessity to incorporate transients into population projection studies and the need for global-level fine resolution migration data to better our understanding of the processes through which migration and exceptional cohorts drive transient dynamics.