Can nonlinear dynamics elucidate mechanisms in ecology and epidemiology?

Using recently developed methods in nonlinear dynamics, two hypotheses often advanced to account for recurrent outbreaks of childhood diseases such as measles are investigated. The first, maintenance of otherwise damped oscillations by noise, appears incapable of reproducing essential features of the data. The second, cycles and chaos sustained by seasonal variation in contact rates gives qualitative and quantitative agreement between model and observation. It is concluded that nonlinear dynamics offers a methodology which may allow students of ecology and epidemiology to distinguish between competing mechanistic hypotheses.