ABSTRACT
An important question in metapopulation dynamics is the influence of external perturbations on the population's long term dynamic behaviour. In this paper we address the question of how spatio-temporal variations in demographic parameters affect the dynamics of measles populations in England and Wales. Specifically we use nonparametric statistical methods to analyse how birth rate and population size modulate the negative density dependence between successive epidemics as well as their periodicity. For the observed spatio-temporal data from 60 cities and for simulated model data, the demographic variables act as bifurcation parameters on the joint density of the trade-off between successive epidemics. For increasing population size a transition occurs from an irregular unpredictable pattern in small communities towards a regular predictable endemic pattern in large places. Variations in the birth rate parameter lead to a bifurcation from annual towards biennial cyclicity in both observed data and model data.